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Sample records for se te optical

  1. Optical properties of n-CdSe sub 1-x Te sub x polycrystalline thin films

    Energy Technology Data Exchange (ETDEWEB)

    Gutierrez, M T [Centro de Investigaciones Energeticas, Medioambientales y Tecnologicas, Madrid (Spain). Inst. de Energias Renovables

    1991-01-01

    Absorption coefficient, {alpha}({lambda}), and energy gap, E{sub g}, of CdSe{sub 1-x}Te{sub x} thin films were determined from the measured transmittance and reflectance at normal incidence of light in the wavelength range 450-2500 nm. The thin film were electrochemically prepared on glass plates coated with conducting thin films of SnO{sub 2}. A combined method from Goodman and Lubberts was used to determine the absorption coefficient and its dependence on the wavelength. The evolution of the optical gap versus the composition of Te in CdSe{sub 1-x}Te{sub x} was made and a value of 1.4 eV of the optical gap was obtained for the composition of CdSe{sub 0.65}Te{sub 0.35}. (orig.).

  2. Structural and optical properties of alloyed quaternary CdSeTeS core and CdSeTeS/ZnS core–shell quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Adegoke, Oluwasesan, E-mail: adegoke.sesan@mailbox.co.za [Department of Chemistry, Faculty of Natural and Agricultural Sciences, University of Pretoria, Lynnwood Road, Pretoria 0002 (South Africa); Nyokong, Tebello, E-mail: t.nyokong@ru.ac.za [Department of Chemistry, Rhodes University, Grahamstown 6140 (South Africa); Forbes, Patricia B.C., E-mail: patricia.forbes@up.ac.za [Department of Chemistry, Faculty of Natural and Agricultural Sciences, University of Pretoria, Lynnwood Road, Pretoria 0002 (South Africa)

    2015-10-05

    Highlights: • Alloyed quaternary CdSeTeS core quantum dots (QDs) were synthesized. • Passivation was carried out using a ZnS shell. • Quaternary CdSeTeS core exhibited unique optical properties over CdSeTe/ZnS. • CdSeTeS can be employed as a useful alternative to core/shell QDs. - Abstract: Synthesis of fluorescent alloyed quantum dots (QDs) with unique optical properties suitable for a wide array of chemical, physical and biological applications is of research interest. In this work, highly luminescent and photostable alloyed quaternary CdSeTeS core QDs of two different sizes were fabricated via the organometallic hot-injection synthetic route. Characterization of the nanocrystals were performed using TEM, XRD, UV/vis and fluorescence spectrophotometric techniques. We have demonstrated in this work that the well fabricated alloyed quaternary CdSeTeS core QDs possess unique optical properties that are advantageous over conventional core/shell systems. Formation of the CdSeTeS/ZnS core/shell with the desired optical properties comes with a number of challenges, hence the advantages of the quaternary alloyed core over the core/shell QDs are (i) avoidance of the challenging process of determining the proper shell thickness which can provide the desired optical properties in the core/shell system and (ii) avoidance of the lattice-induced mismatch between the core and the shell material which can either lead to incomplete exciton confinement or dislocation at the core/shell interface.

  3. Optical characterization of CdSe/ZnTe type-II interfaces for photovoltaics

    Energy Technology Data Exchange (ETDEWEB)

    Richters, Jan-Peter; Bleuse, Joel [CEA-CNRS group ' ' Nanophysique et semiconducteurs' ' , CEA-Grenoble, INAC, SP2M, 17 rue des Martyrs, 38042 Grenoble (France); Gerard, Lionel; Andre, Regis [CEA-CNRS group ' ' Nanophysique et semiconducteurs' ' , Institut Neel, CNRS, BP 166, 38042 Grenoble Cedex 9 (France)

    2012-07-01

    Solar cells based on direct bandgap semiconductors (GaAs,CdTe,CdSe..) show an efficient light absorption compared to silicon solar cells. This is an advantage for material savings due to thinner absorbers, but it also comes with the drawback of higher losses due to efficient radiative electron-hole recombination. Such losses could be prevented through the use of type-II interfaces which separate electrons and holes within the active area, similar to a p-n junction. We report a study of CdSe/ZnTe samples showing such an interface. The CdSe bandgap (1.7 eV) is well adapted to the solar spectrum and its lattice parameter mismatch with ZnTe is exceptionally low. We have grown, by MBE, different kinds of samples like CdSe/ZnTe 2D interfaces and superlattices and present time-resolved spectroscopy results which specify the efficiency of the electron-hole separation in these type-II structures. The measured decay time can be above 100 ns for the interface optical transition, i.e. 3 orders of magnitude slower than the typical PL decay time for the constitutive materials taken separately.

  4. Elaboration and optical properties of type-II ZnTe on ZnSe heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Najjar, Rita, E-mail: rita.najjar@cea.f [CEA-CNRS group ' Nanophysique et semiconducteurs' , Institut NEEL-CNRS, BP166, 25 rue des martyrs, 38042 Grenoble Cedex 9 (France); Andre, Regis; Besombes, Lucien; Bougerol, Catherine; Tatarenko, Serge; Mariette, Henri [CEA-CNRS group ' Nanophysique et semiconducteurs' , Institut NEEL-CNRS, BP166, 25 rue des martyrs, 38042 Grenoble Cedex 9 (France)

    2009-11-25

    Special growth conditions are presented in this work, in order to produce ZnTe/ZnSe type-II quantum dots and preserve them during the capping stage. A detailed study emphasizes the high sensitivity of the sample structure to Se/Zn ratio as opposed to other growth parameters. It is shown that nominally identical samples can evolve into two-dimensional quantum well or quantum dot plane, depending on which element is in excess. Transmission electron microscopy, atomic force microscopy and optical characterizations evidence this phenomenon.

  5. Optical properties of Sb(Se,Te)I and photovoltaic applications

    Energy Technology Data Exchange (ETDEWEB)

    Tablero, C., E-mail: ctablero@etsit.upm.es

    2016-09-05

    SbXI (X = Se, Te) are ferroelectric semiconductors that allow a variety of applications including optoelectronic and photovoltaic applications. An analysis of the optical properties is carried out starting from first-principles density-functional theory with orbital-dependent one-electron potentials. To go into the contributions to the optical properties more deeply, the absorption coefficients have been split into inter- and intra-species contributions and into atomic angular momentum contributions. The optical results are used to evaluate the efficiencies when this material is used to absorb sunlight at several sunlight concentrations and the usual radiative and the ferroelectric photovoltaic mechanisms. The results indicate their applicability in photovoltaic devices as absorbent of the solar spectrum with high conversion efficiency. - Highlights: • The SbXI (X = Se, Te) are ferroelectric semiconductors with a high optical absorption. • The absorption coefficients have been split into different contributions to understand the cause of the high absorption. • Using the first-principles results the maximum efficiency of this photovoltaic absorber material has been estimated. • The efficiency of this compound is near the maximum efficiency for single-gap solar cells even using small-width devices. • The coexistence of the R-PV and R-PV effects has been evaluated.

  6. Optical properties change in Te diffused As{sub 50}Se{sub 50} chalcogenide thin film

    Energy Technology Data Exchange (ETDEWEB)

    Naik, Ramakanta; Behera, M.; Panda, R.; Mishra, N. C. [Department of Physics, Utkal University, Bhubaneswar, 751004, Odisha (India)

    2016-05-23

    In the present report, we present the effect of Te diffusion into As{sub 50}Se{sub 50} thin film which changes the optical properties. The Te/As{sub 50}Se{sub 50} film was irradiated by a laser beam of 532 nm to study the diffusion mechanism due to photo induced effect. The As{sub 50}Se{sub 50}, Te/As{sub 50}Se{sub 50} films show a completely amorphous nature from X-ray diffraction study. A non direct transition was found for these films on the basis of optical transmission data carried out by Fourier Transform infrared Spectroscopy. The optical bandgap is found to be decreased with Te deposition and photo darkening phenomena is observed for the diffused film. The change in the optical constants are well supported by the corresponding change in different types of bonds which are being studied by X-ray photoelectron spectroscopy.

  7. Photo- and Thermo-Induced Changes in Optical Constants and Structure of Thin Films from GeSe2-GeTe-ZnTe System

    Science.gov (United States)

    Petkov, Kiril; Todorov, Rossen; Vassilev, Venceslav; Aljihmani, Lilia

    We examined the condition of preparation of thin films from GeSe2-GeTe-ZnTe system by thermal evaporation and changes in their optical properties after exposure to light and thermal annealing. The results for composition analysis of thin films showed absence of Zn independently of the composition of the bulk glass. By X-ray diffraction (XRD) analysis it was found that a reduction of ZnTe in ZnSe in bulk materials takes of place during the film deposition. A residual from ZnSe was observed in the boat after thin film deposition. Optical constants (refractive index, n and absorption coefficient, α) and thickness, d as well as the optical band gap, Eg, depending of the content of Te in ternary Ge-Se-Te system are determined from specrophotometric measurements in the spectral range 400-2500 nm applying the Swanepoel's envelope method and Tauc's procedure. With the increase of Te content in the layers the absorption edge is shifted to the longer wavelengths, refractive index increases while the optical band gap decreases from 2.02 eV for GeSe2 to 1.26 eV for Ge34Se42Te24. The values of the refractive index decrease after annealing of all composition and Eg increase, respectively. Thin films with composition of Ge27Se47Te9Zn17 and Ge28Se49Te10Zn13 were prepared by co-evaporation of (GeSe2)78(GeTe)22 and Zn from a boat and a crucible and their optical properties, surface morphology and structure were investigated. The existence of a correlation between the optical band gap and the copostion of thin films from the system studied was demonstrated.

  8. Study of optical properties of vacuum evaporated carbon nanotube containing Se80Te16Cu4 thin films

    Science.gov (United States)

    Upadhyay, A. N.; Tiwari, R. S.; Singh, Kedar

    2016-08-01

    Thin films of Se80Te16Cu4 glassy alloy and 3 wt.% of carbon nanotubes (CNTs) containing Se80Te16Cu4 glassy composite were deposited on clean glass substrate by thermal evaporation technique. The scanning electron microscope and energy dispersive x-ray analysis were performed to investigate the surface morphology and elemental composition of as synthesised samples. The reflectance and transmittance spectra of as-deposited thin films were recorded (200-1100 nm) by using UV/VIS/NIR spectrophotometer. The optical band gap and optical constants such as absorption coefficient (α), refractive index (n) and extinction coefficient (k) of Se80Te16Cu4 and 3 wt.% CNTs-Se80Te16Cu4 glassy composite thin films were calculated. It is observed that optical properties alter due to CNTs incorporation in Se80Te16Cu4 glassy alloy. Effect on optical properties due to CNTs incorporation can be explained in terms of concentration of unsaturated bonds/defects in the localised states.

  9. Optical properties change in laser-induced Te/As{sub 2}Se{sub 3} chalcogenide thin films

    Energy Technology Data Exchange (ETDEWEB)

    Behera, Mukta; Naik, Ramakanta [Utkal University, Department of Physics, Bhubaneswar (India)

    2016-10-15

    In the present work, we report the change in optical parameters due to the deposition and photo-induced diffusion of Te layer into the chalcogenide As{sub 2}Se{sub 3} film. The photo-diffusion creates a solid solution of As-Se-Te which has potential application in optical devices. The Te/As{sub 2}Se{sub 3} bilayer films prepared by thermal evaporation technique were studied by various experimental techniques. The photo-diffusion of Te into As{sub 2}Se{sub 3} matrix was done by 532-nm laser irradiation. The structure of the As{sub 2}Se{sub 3}, as-prepared and irradiated Te/As{sub 2}Se{sub 3} films was studied by X-ray diffraction which were amorphous in nature. The presence of all the elements was checked by energy-dispersive X-ray analysis, and the optical transmission spectra were recorded by Fourier transform infrared spectrometer. The optical band gap is reduced by the deposition and diffusion of Te into As{sub 2}Se{sub 3} film which is due to the increase in density of defect states in the gap region. The transmission is decreased, whereas the absorption efficiency is increased with the increase in disorderness. The X-ray photoelectron spectroscopy carried out on these films gives information about the bonding change due to the photo-diffusion process. Therefore, this is an important result which will open up new directions for the application of this material in semiconducting devices. (orig.)

  10. MSM optical detector on the basis of II-type ZnSe/ZnTe superlattice

    Energy Technology Data Exchange (ETDEWEB)

    Kuznetzov, P. I., E-mail: pik218@ire216.msk.su; Averin, S. V., E-mail: sva278@ire216.msk.su; Zhitov, V. A.; Zakharov, L. Yu.; Kotov, V. M. [Russian Academy of Sciences, Kotel’nikov Institute of Radioengineering and Electronics (Fryazino Branch) (Russian Federation)

    2017-02-15

    On the basis of a type-II ZnSe/ZnTe superlattice, a MSM (metal—semiconductor–metal) photodetector is fabricated and investigated. The detector features low dark currents and a high sensitivity. The spectral characteristic of the detector provides the possibility of the selective detection of three separate spectral portions of visible and near-infrared radiation.

  11. To study the linear and nonlinear optical properties of Se-Te-Bi-Sn/PVP (polyvinylpyrrolidone) nanocomposites

    Science.gov (United States)

    Tyagi, Chetna; Yadav, Preeti; Sharma, Ambika

    2018-05-01

    The present work reveals the optical study of Se82Te15Bi1.0Sn2.0/polyvinylpyrrolidone (PVP) nanocomposites. Bulk glasses of chalcogenide was prepared by well-known melt quenching technique. Wet chemical technique is proposed for making the composite of Se82Te15Bi1.0Sn2.0 and PVP polymer as it is easy to handle and cost effective. The composites films were made on glass slide from the solution of Se-Te-Bi-Sn and PVP polymer using spin coating technique. The transmission as well as absorbance is recorded by using UV-Vis-NIR spectrophotometer in the spectral range 350-700 nm. The linear refractive index (n) of polymer nanocomposites are calculated by Swanepoel approach. The linear refractive index (n) PVP doped Se82Te15Bi1.0Sn2.0 chalcogenide is found to be 1.7. The optical band gap has been evaluated by means of Tauc extrapolation method. Tichy and Ticha model was utilized for the characterization of nonlinear refractive index (n2).

  12. Effect of substrate temperature on the optical parameters of thermally evaporated Ge-Se-Te thin films

    Energy Technology Data Exchange (ETDEWEB)

    Sharma, Pankaj, E-mail: pks_phy@yahoo.co.i [Department of Physics, Jaypee University of Information Technology, Waknaghat, Solan, H.P. 173215 India (India); Katyal, S.C. [Department of Physics, Jaypee University of Information Technology, Waknaghat, Solan, H.P. 173215 India (India)

    2009-05-01

    Thin films of Ge{sub 10}Se{sub 90-x}Te{sub x} (x = 0, 10, 20, 30, 40, 50) glassy alloys were deposited at three substrate temperatures (303 K, 363 K and 423 K) using conventional thermal evaporation technique at base pressure of {approx} 10{sup -4} Pa. X-ray diffraction results show that films deposited at 303 K are of amorphous nature while films deposited at 363 K and 423 K are of polycrystalline nature. The optical parameters, refractive index and optical gap have been derived from the transmission spectra (using UV-Vis-NIR spectrophotometer) of the thin films in the spectral region 400-1500 nm. This has been observed that refractive index values remain almost constant while the optical gap is found to decrease considerably with the increase of substrate temperature. The decrease in optical gap is explained on the basis of change in nature of films, from amorphous to polycrystalline state, with the increase of substrate temperature. The optical gap has also been observed to decrease with the increase of Te content.

  13. Nonlinear optical diagnostic of semimagnetic semiconductors Pb1-xYb xX (X = S, Se, Te)

    International Nuclear Information System (INIS)

    Nouneh, K.; Kityk, I.V.; Viennois, R.; Benet, S.; Charar, S.; Plucinski, K.J.

    2007-01-01

    Nonlinear optical measurements were performed to elucidate the influence of magnetic ions on the behavior of charge carriers in magnetic semiconductors-Pb 1-x Yb x X (X = S, Se, Te at x = 1-3%). It was shown that nonlinear optical methods could be used as sensitive tools for investigations of electron-phonon anharmonicity near low-temperature semiconductor-insulator phase transitions. There exists a difference between surface and bulk-like contributions to the nonlinear optical effects. It was shown that only low-temperature Two Photon Absorption (TPA) oscillator may be related to the number of the electron-phonon anharmonic modes responsible for the observed phase transformation. The explanation of the anomalous temperature dependences is given in accordance with dipole momentum's behaviors determined by low-temperature spin-spin interactions and by electron-phonon anharmonic interactions. We have discovered that low-temperature dependence of specific heat of Pb 1-x R x Te (R = Yb, Pr with x = 3% and 1.6%, respectively) exhibits a non-magnetic order caused by large electron-phonon contributions and structural disorder effects

  14. Syntheses and characterization of thin films of Te94Se6 nanoparticles for semiconducting and optical devices

    International Nuclear Information System (INIS)

    Salah, Numan; Habib, Sami S.; Memic, Adnan; Alharbi, Najlaa D.; Babkair, Saeed S.; Khan, Zishan H.

    2013-01-01

    Thin films of Te 94 Se 6 nanoparticles were synthesized using the physical vapor condensation technique at different argon (Ar) pressures. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy, absorption spectrum, photoluminescence (PL) and Raman spectroscopy. XRD results show that the as-grown films have a polycrystalline structure. SEM images display uniform nanoparticles in these films where the size increases from ∼ 12 to about 60 nm by decreasing Ar pressure from 667 to 267 Pa. These as-grown thin films were found to have direct band gaps, whose value decreases with increasing particle size. The absorption and extinction coefficients for these films were also investigated. PL emission spectra exhibit three bands peaking at 666, 718 and 760 nm, while Raman spectra displayed three bands located at 123, 143 and 169 cm −1 . No significant changes are observed in positions or intensities of these bands by decreasing the Ar pressure, except that of the last band of PL; where the intensity increases. The obtained results on this Te 94 Se 6 nanomaterial especially its controlled direct bandgap might be useful for development of optical disks and other semiconducting devices. - Highlights: ► Thin films of Te 94 Se 6 nanoparticles were grown at different argon (Ar) pressures. ► Size of the nanoparticles increased by decreasing Ar pressure. ► They have direct band gap, whose value decreases by increasing the particle size. ► These nanomaterials might be useful for development of semiconducting devices

  15. Selenium Se and tellurium Te

    International Nuclear Information System (INIS)

    Busev, A.I.; Tiptsova, V.G.; Ivanov, V.M.

    1978-01-01

    The basic methods for determining selenium and tellurium in various objects are presented. The bichromatometric determination of Te in cadmium, zinc and mercury tellurides is based on oxidation of Te(4) to (6) in H 2 SO 4 with potassium bichromate. In steels, Te is determined photometrically with the aid of KI. The determination is hindered by Fe(3), Cu(2), Bi(3) and Se(4) ions, which must be separated. The extraction-photometric determination of Te in native sulfur is carried out with the aid of 5-mercapto-3-(naphthyl-2)-1,3,4-thiadiazolthione-2 (pH=4.8-5.0). The dyed complex is readily extracted with chloroform and benzene. The spectrophotometric determination of Te in selenium is performed with the aid of 3,5-diphenylpyrazoline-1-dithiocarbamate of sodium. Te is determined in commercial indium, arsenic and their semiconductor compounds photometrically with the aid of copper diethyldithiocarbamate. The method permits determining 5x10 -5 % Te in a weighed amount of 0.5 g. The chloride complex of Te(4) with diantipyriodolpropylmethane is quantitatively extracted with dichloroethane from hydrochloric acid solutions. Thus, any amounts of Te can be separated from Se and determined photometrically. The extraction-photometric determination of Te in commercial lead and bismuth is carried out with the aid of pyrazolone derivatives, in commercial copper with the aid of diantipyridolpropylmethane, and in ores (more than 0.01% Te) with the aid of bismuthol 2. Also described is the extraction-polarographic determination of Te in sulfide ores

  16. Optical characterization of a-Se85−xTe15Znx thin films

    Indian Academy of Sciences (India)

    analysis of transmission spectra, measured at normal incidence, in the spectral ... Optical band gap (Eg) has also been calculated and found to decrease ... Chalcogenide glasses have recently gained much importance as, unlike conventional.

  17. X = S, Se, Te) heterostructures

    KAUST Repository

    Zhang, Qingyun; Schwingenschlö gl, Udo

    2018-01-01

    Using first-principles calculations, we investigate the electronic properties of the two-dimensional GaX/MX2 (M = Mo, W; X = S, Se, Te) heterostructures. Orbital hybridization between GaX and MX2 is found to result in Rashba splitting at the valence

  18. Structural, electronic and optical properties of AgXY{sub 2}(X = Al, Ga, In and Y = S, Se, Te)

    Energy Technology Data Exchange (ETDEWEB)

    Ullah, Saeed; Din, Haleem Ud [Materials Modeling Lab, Department of Physics, Islamia College University, Peshawar (Pakistan); Murtaza, G., E-mail: murtaza@icp.edu.pk [Materials Modeling Lab, Department of Physics, Islamia College University, Peshawar (Pakistan); Ouahrani, T. [Laboratoire de Physique Théorique, B.P. 119, Université de Tlemcen, Tlemcen 13000 (Algeria); Khenata, R., E-mail: khenata_rabah@yahoo.fr [Laboratoire de Physique Quantique et de Modélisation Mathématique, Université de Mascara, Mascara 29000 (Algeria); Naeemullah [Department of Physics, G.D.C. Darra Adam Khel, F.R. Kohat, KPK (Pakistan); Bin Omran, S. [Department of Physics and Astronomy, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia)

    2014-12-25

    Highlights: • The compounds are studied by FP-LAPW method within mBJ approximation. • All of the studied materials show isotropic behavior. • All the compounds show direct band gap nature. • Bonding nature is mostly covalent among the studied compounds. • High absorption peaks and reflectivity ensures there utility in optoelectronic devices. - Abstract: The structural, electronic and optical properties of the ternary semiconducting compounds AgXY{sub 2} (X = Al, Ga, In and Y = S, Se, Te) in Heusler and chalcopyrite crystal phases have been investigated using the density functional theory (DFT) based on the full potential linear augmented plane wave (FP-LAPW) method. The calculated lattice constant and band gap values for AgXY{sub 2} in chalcopyrite phase are in good agreement with the available experimental data. Band structure calculations are performed using modified Becke–Johnson (mBJ) method which match closely with experimental data and yield better band gaps rather than those obtained by using generalized gradient approximation (GGA) and Engel–Vosko generalized gradient approximation (EV–GGA). Decrease in band gap is observed by changing cations X and Y from the top to bottom of periodic table. Chemical bonding trends are predicted through charge density plots and quantified by Bader’s analysis. Optical properties reveal that these compounds are suitable candidates for optoelectronic devices in the visible and ultraviolet (UV) regions.

  19. ZnSe/ZnSeTe Superlattice Nanotips

    Directory of Open Access Journals (Sweden)

    Young SJ

    2010-01-01

    Full Text Available Abstract The authors report the growth of ZnSe/ZnSeTe superlattice nanotips on oxidized Si(100 substrate. It was found the nanotips exhibit mixture of cubic zinc-blende and hexagonal wurtzite structures. It was also found that photoluminescence intensities observed from the ZnSe/ZnSeTe superlattice nanotips were much larger than that observed from the homogeneous ZnSeTe nanotips. Furthermore, it was found that activation energies for the ZnSe/ZnSeTe superlattice nanotips with well widths of 16, 20, and 24 nm were 76, 46, and 19 meV, respectively.

  20. First-principles study on electronic and optical properties of Cu2ZnSiV I4 (VI=S, Se, and Te quaternary semiconductors

    Directory of Open Access Journals (Sweden)

    Xuebiao Zhang

    2015-05-01

    Full Text Available The electronic and optical properties of Cu2ZnSiS4, Cu2ZnSiSe4 and Cu2ZnSiTe4 in kesterite and stannite structures are systematically studied using first-principles calculations. Crystal field splitting, optical transitions, p-d bonding, and anti-bonding overlapping are analyzed. The physical and chemical trends in these properties are investigated with respect to the crystal structure and anion atomic number. The optical spectra, such as dielectric function, refractive index, reflectivity and absorption coefficient are explored in a broad range of energy. A good agreement between the calculated results and experimental data is obtained.

  1. Effect of compositional dependence on physical and optical parameters of Te{sub 17}Se{sub 83−x}Bi{sub x} glassy system

    Energy Technology Data Exchange (ETDEWEB)

    Sharma, Pankaj, E-mail: pks_phy@yahoo.co.in [Department of Physics and Materials Science, Jaypee University of Information Technology, Waknaghat, Solan, HP 173234 (India); El-Bana, M.S.; Fouad, S.S. [Nano-Science and Semiconductor Laboratories, Department of Physics, Faculty of Education, Ain Shams University, Cairo (Egypt); Sharma, Vineet [Department of Physics and Materials Science, Jaypee University of Information Technology, Waknaghat, Solan, HP 173234 (India)

    2016-05-15

    In the present paper we have studied the effect of Bi addition on the physical and optical properties of thermally evaporated Te{sub 17}Se{sub 83−x}Bi{sub x} thin films. With Bi addition the density, mean coordination number, mechanical constraints, glass transition temperature increases. The other parameters theoretical energy gap, lone pair electron, deviation from stoichiometry decreases. Transmission spectra have been taken in the spectral range 400 nm–2500 nm using ultraviolet–visible–near infrared spectrophotometer. The fundamental absorption edge shifts towards longer wavelength with Bi incorporation. Optical energy gap and linear refractive index have been determined using transmission spectra. A good correlation has been drawn between the optical and theoretical parameters. Using linear optical parameters, the nonlinear optical susceptibility and nonlinear refractive index have been estimated. - Highlights: • Physical and optical parameters have been analyzed for Te{sub 17}Se{sub 83−x}Bi{sub x} glassy alloys. • The addition of Bi leads to decrease of average heat of atomization and cohesive energy. • The optical band gap decreases with increasing Bi content. • The third order susceptibility and nonlinear refractive index show an increase with increase in the Bi content.

  2. Forming Glasses from Se and Te

    Directory of Open Access Journals (Sweden)

    Pierre Lucas

    2009-10-01

    Full Text Available Despite being close neighbors on the Periodic Table, selenium and tellurium present a totally different abilities to form glasses. Se is a very good glass former, and gives rise to numerous glass compositions which are popular for their transparency in the infrared range and their stability against crystallization. These glasses can be shaped into sophisticated optical devices such as optical fibers, planar guides or lenses. Nevertheless, their transparencies are limited at about 12 μm (depending on the thickness of the optical systems due to the relatively small mass of the Se element. On the other hand, tellurium is heavier and its use in substitution for Se permits to shift the IR cutoff beyond 20 μm. However, the semimetallic nature of Te limits its glass formation ability and this glass family is known to be unstable and consequently has found application as phase change material in the Digital Versatile Disk (DVD technology. In this paper, after a review of selenide glasses and their applications, it will be shown how, in a recent past, it has been possible to stabilize tellurium glasses by introducing new elements like Ga or I in their compositions.

  3. Ab initio studies of structural, electronic, optical, elastic and thermal properties of silver gallium dichalcogenides (AgGaX2: X = S, Se, Te)

    International Nuclear Information System (INIS)

    Sharma, Sheetal; Verma, A.S.; Jindal, V.K.

    2014-01-01

    Graphical abstract: - Highlights: • FP-LAPW method has been used to compute the solid state properties of AgGaX 2 (X = S, Se, Te). • Electronic and optical properties reported with recently developed mBJ potential. • Thermal expansion, heat capacity, Debye temperature, entropy and Grüneisen parameter were evaluated. • Hardness was calculated for the first time at different temperature and pressure. - Abstract: We have performed ab initio calculations for the structural, electronic, optical, elastic and thermal properties of the silver gallium dichalcogenides (AgGaX 2 : X = S, Se, Te). In this study, we have used the accurate full potential linearized augmented plane wave (FP-LAPW) method to find the equilibrium structural parameters and to compute the six elastic constants (C 11 , C 12 , C 13 , C 33 , C 44 and C 66 ). We have reported electronic and optical properties with the recently developed density functional theory of Tran and Blaha, and this theory is used along with the Wu-Cohen generalized gradient approximation (WC-GGA) for the exchange-correlation potential. Furthermore, optical features such as dielectric functions, refractive indices, extinction coefficient, optical reflectivity, absorption coefficients and optical conductivities were calculated for photon energies up to 40 eV. The thermodynamical properties such as thermal expansion, heat capacity, debye temperature, entropy, Grüneisen parameter and bulk modulus were calculated employing the quasi-harmonic Debye model at different temperatures (0–900 K) and pressures (0–8 GPa) and the silent results were interpreted. Hardness of the materials was calculated for the first time at different temperatures and pressures

  4. Structural phase change and optical band gap bowing in hot wall deposited CdSe{sub x}Te{sub 1-x} thin films

    Energy Technology Data Exchange (ETDEWEB)

    Muthukumarasamy, N. [Department of Physics, Coimbatore Institute of Technology, Coimbatore, Tamilnadu (India); Jayakumar, S.; Kannan, M.D.; Balasundaraprabhu, R. [Thin Film Center, PSG College of Technology, Coimbatore, Tamilnadu (India)

    2009-04-15

    CdSe{sub x}Te{sub 1-x} thin films of different compositions have been deposited on glass substrates by hot wall deposition method under conditions very close to thermodynamical equilibrium with minimum loss of material. The structural studies carried out on the deposited films revealed that they are crystalline in nature and exhibit either cubic zinc blende or hexagonal phase or both depending on the composition of the material. The lattice parameter values for both cubic and hexagonal phases have been determined and are observed to vary with composition according to Vegard's law. The optical properties of the deposited CdSe{sub x}Te{sub 1-x} thin films have been studied using transmittance spectra. The spectra shows a sharp fall in transmittance at wavelength corresponding to the band gap of the material. The optical band gap has been determined and found to be direct allowed. The band gap has been observed to strongly depend on film composition. The variation of band gap with composition has been observed to be quadratic in nature exhibiting a bowing behaviour. (author)

  5. Syntheses and characterization of thin films of Te{sub 94}Se{sub 6} nanoparticles for semiconducting and optical devices

    Energy Technology Data Exchange (ETDEWEB)

    Salah, Numan, E-mail: nsalah@kau.edu.sa [Center of Nanotechnology, King Abdulaziz University, Jeddah-21589 (Saudi Arabia); Habib, Sami S.; Memic, Adnan [Center of Nanotechnology, King Abdulaziz University, Jeddah-21589 (Saudi Arabia); Alharbi, Najlaa D. [Center of Nanotechnology, King Abdulaziz University, Jeddah-21589 (Saudi Arabia); Sciences Faculty for Girls, King Abdulaziz University, Jeddah-21589 (Saudi Arabia); Babkair, Saeed S. [Center of Nanotechnology, Department of Physics, Faculty of Science, King Abdulaziz University, Jeddah-21589 (Saudi Arabia); Khan, Zishan H. [Department of Applied Sciences and Humanities, Jamia Millia Islamia (Central University), New Delhi-110025 (India)

    2013-03-01

    Thin films of Te{sub 94}Se{sub 6} nanoparticles were synthesized using the physical vapor condensation technique at different argon (Ar) pressures. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy, absorption spectrum, photoluminescence (PL) and Raman spectroscopy. XRD results show that the as-grown films have a polycrystalline structure. SEM images display uniform nanoparticles in these films where the size increases from ∼ 12 to about 60 nm by decreasing Ar pressure from 667 to 267 Pa. These as-grown thin films were found to have direct band gaps, whose value decreases with increasing particle size. The absorption and extinction coefficients for these films were also investigated. PL emission spectra exhibit three bands peaking at 666, 718 and 760 nm, while Raman spectra displayed three bands located at 123, 143 and 169 cm{sup −1}. No significant changes are observed in positions or intensities of these bands by decreasing the Ar pressure, except that of the last band of PL; where the intensity increases. The obtained results on this Te{sub 94}Se{sub 6} nanomaterial especially its controlled direct bandgap might be useful for development of optical disks and other semiconducting devices. - Highlights: ► Thin films of Te{sub 94}Se{sub 6} nanoparticles were grown at different argon (Ar) pressures. ► Size of the nanoparticles increased by decreasing Ar pressure. ► They have direct band gap, whose value decreases by increasing the particle size. ► These nanomaterials might be useful for development of semiconducting devices.

  6. The system SnTe-InSe

    International Nuclear Information System (INIS)

    Gurshumov, A.P.; Alidzhanov, M.A.; Aliev, A.S.; Gadzhiev, T.G.; Mamedov, N.A.

    1986-01-01

    This paper discusses the nature of the interaction and physicochemical properties of the alloys of the system SnTe-InSe. The DTA was performed on an NTR-74 pyrometer, XPA on a Dron-2.0 diffractometer and MSA on an MIM-7 metallographic microscope. The microhardness of the samples was determined on a PMT-3 microhardness tester. The congruently melting compound SnInTeSe and solid solutions based on the starting components are formed in the system

  7. Optical and electrical properties of heterostructures Zn{sub 1-x}Mg{sub x}Se crystallized on ZnTe and GaAs crystals by MBE method; Wlasnosci optyczne i elektryczne heterostruktur Zn{sub 1-x}Mg{sub x}Se krystalizowanych metoda MBE w krysztalach ZnTe i GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Gapinski, A; Glowacki, G; Bala, W [Uniwersytet Mikolaja Kopernika, Torun (Poland). Inst. Fizyki

    1997-12-01

    Triple component mixing crystals Zn{sub 1-x}Mg{sub x}Se have been crystallized on ZnTe and GaAs monocrystals by means of molecular beam epitaxy method. The optical and electrical properties of such structures with different magnesium content have been studied. The applicability for optoelectronial and light-pipe use have been discussed as well. 6 refs, 4 figs.

  8. Atomistic tight-binding computations of the structural and optical properties of CdTe/CdX (X=S and Se)/ZnS core/shell/shell nanocrystals

    Science.gov (United States)

    Sukkabot, Worasak

    2018-05-01

    A study of CdTe/CdX (X=S and Se)/ZnS core/shell/shell nanocrystals is carried out using atomistic tight-binding theory and the configuration interaction method to provide information for applications in bioimaging, biolabeling, display devices and near-infrared electronic instruments. The calculations yield the dependences of the internal and external passivated shells on the natural behaviours of CdTe/CdX (X=S and Se)/ZnS core/shell/shell nanocrystals. The reduction of the optical band gaps is observed with increasing numbers of monolayers in the external ZnS shell due to quantum confinement. Interestingly, the optical band gaps of CdTe/CdS/ZnS core/shell/shell nanocrystals are greater than those of CdTe/CdSe/ZnS core/shell/shell nanocrystals. In the presence of an external ZnS-coated shell, electron-hole wave function overlaps, oscillation strengths, ground-state exchange energies and Stokes shift are improved, whereas ground-state coulomb energies and fine-structure splitting are reduced. The oscillation strengths, Stokes shift and fine-structure splitting are reduced with the increase in external ZnS shell thickness. The oscillation strengths, Stokes shift and fine-structure splitting of CdTe/CdS/ZnS core/shell/shell nanocrystals are larger than those of CdTe/CdSe/ZnS core/shell/shell nanocrystals. Reduction of the atomistic electron-hole interactions is observed with increasing external ZnS shell size. The strong electron-hole interactions are more probed in CdTe/CdS/ZnS core/shell/shell nanocrystals than in CdTe/CdSe/ZnS core/shell/shell nanocrystals.

  9. Optical properties and photoinduced phenomena in glasses and thin films of system As2Se3-As2Te3-SnTe

    Czech Academy of Sciences Publication Activity Database

    Parchanski, V.; Frumarová, Božena; Frumar, M.; Hrdlička, M.; Vlček, Milan

    2012-01-01

    Roč. 14, 1-2 (2012), 150-156 ISSN 1454-4164 R&D Projects: GA ČR GA203/09/0827 Institutional research plan: CEZ:AV0Z40500505 Keywords : chalcogenides * thin films * optical properties Subject RIV: CA - Inorganic Chemistry Impact factor: 0.516, year: 2012 http://joam.inoe.ro/index.php?option=magazine&op=view&idu=2997&catid=69

  10. Phase diagram of SnTe-CdSe cross-section of SnTe+CdSe reversible SnSe+CdTe ternary reciprocal system

    International Nuclear Information System (INIS)

    Dubrovin, I.V.; Budennaya, L.D.; Mizetskaya, I.B.; Sharkina, Eh.V.

    1986-01-01

    Phase equilibrium diagram of SnTe-CdSe cross-section of Sn, Cd long Te, Se ternary reciprocal system is investigated using the methods of differential thermal, X-ray phase, and microstructural analyses. Maximum length of solid solutions on the base of SnTe corresponds to approximately 14 mol.% at 1050 K and approximately 3 mol.% of CdSe at 670 K. Region of solid solutions on the base of CdSe corresponds to less than 1 mol.% of SnTe at room temperature. SnTe-CdSe cross-section is not a quasibinar one. Equilibrium is shifted to the left in the SnTe+CdSe reversible SnSe+CdTe reciprocal system

  11. Effect of increasing tellurium content on the electronic and optical properties of cadmium selenide telluride alloys CdSe{sub 1-x}Te{sub x}: An ab initio study

    Energy Technology Data Exchange (ETDEWEB)

    Reshak, Ali Hussain, E-mail: maalidph@yahoo.co.uk [Institute of Physical Biology-South Bohemia University, Nove Hrady 37333 (Czech Republic); School of Material Engineering, Malaysia University of Perlis, P.O Box 77, d/a Pejabat Pos Besar, 01007 Kangar, Perlis (Malaysia); Kityk, I.V. [Electrical Engineering Department, Technical University of Czestochowa, Al. Armii Krajowej 17/19, Czestochowa (Poland); Khenata, R. [Laboratoire de Physique Quantique et de Modelisation Mathematique de la Matiere (LPQ3 M), universite de Mascara, Mascara 29000 (Algeria); Department of Physics and Astronomy, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia); Auluck, S. [National Physical Laboratory Dr. K S Krishnan Marg, New Delhi 110012 (India)

    2011-06-16

    Highlights: > Theoretical study of effect of vary Te content on band structure, density of states, linear and nonlinear optical susceptibilities of CdSe{sub 1-x}Te{sub x}. > Increasing Te content leads to a decrease in the energy band gap. > Significant enhancement of the electronic properties as a function of tellurium concentration - Abstract: An all electron full potential linearized augmented plane wave method, within a framework of GGA (EV-GGA) approach, has been used for an ab initio theoretical study of the effect of increasing tellurium content on the band structure, density of states, and the spectral features of the linear and nonlinear optical susceptibilities of the cadmium-selenide-telluride ternary alloys CdSe{sub 1-x}Te{sub x} (x = 0.0, 0.25, 0.5, 0.75 and 1.0). Our calculations show that increasing Te content leads to a decrease in the energy band gap. We find that the band gaps are 0.95 (1.76), 0.89 (1.65), 0.83 (1.56), 0.79 (1.44) and 0.76 (1.31) eV for x = 0.0, 0.25, 0.5, 0.75 and 1.0 in the cubic structure. As these alloys are known to have a wurtzite structure for x less than 0.25, the energy gaps are 0.8 (1.6) eV and 0.7 (1.55) eV for the wurtzite structure (x = 0.0, 0.25) for the GGA (EV-GGA) exchange correlation potentials. This reduction in the energy gaps enhances the functionality of the CdSe{sub 1-x}Te{sub x} alloys, at least for these concentrations, leading to an increase in the effective second-order susceptibility coefficients from 16.75 pm/V (CdSe) to 18.85 pm/V (CdSe{sub 0.75}Te{sub 0.25}), 27.23 pm/V (CdSe{sub 0.5}Te{sub 0.5}), 32.25 pm/V (CdSe{sub 0.25}Te{sub 0.75}), and 37.70 pm/V (CdTe) for the cubic structure and from 12.65 pm/V (CdSe) to 21.11 pm/V (CdSe{sub 0.75}Te{sub 0.25}) in the wurtzite structure. We find a nonlinear relationship between the absorption/emission energies and composition, and a significant enhancement of the electronic properties as a function of tellurium concentration. This variation will help in

  12. Determination of K shell fluorescence cross-section and Kβ/Kα intensity ratios for Fe, Se, Te, FeSe, FeTe and TeSe

    International Nuclear Information System (INIS)

    Saydam, M.; Aksoy, C.; Cengiz, E.; Alaşalvar, C.; Tıraşoğlu, E.; Apaydın, G.

    2012-01-01

    The fluorescence cross-sections (σ Ki ) and the intensity ratios K β /K α for pure Fe, Se, Te elements and FeSe, FeTe, TeSe complexes have been investigated. The samples were excited by 59.5 keV γ-rays from 241 Am annular radioactive source and emitted X-rays. They were counted by an Ultra-LEGe detector with resolution of 150 eV at 5.9 keV. For pure elements results have been compared with the theoretical calculated values. According to our results band length and mutual interaction of atoms affected the results. We claimed that these effects would help researchers who study on superconductors, especially determining which compound can be show the superconductor properties. - Highlights: ► TeSe, FeSe and FeTe complexes have affected each other in terms of charge transfer. ► Fe excitement and enhancement have been made by Se and Te. ► Attractive interactions between electrons can help to becoming superconductivity.

  13. A comparison investigation of optical, structural and luminescence properties of CdOxTe1-x and CdTexSe1-x nanoparticles prepared by a simple one pot method

    Science.gov (United States)

    Kiprotich, Sharon; Onani, Martin O.; Dejene, Francis B.

    2018-04-01

    We present L-cysteine capped CdOXTe1-X and CdTeXSe1-X nanoparticles (NPs) prepared in one pot. The as-prepared CdOXTe1-X NPs were found to have a hexagonal crystal structure of CdTe with a cubic phase of CdO. There was, however, change in phase to cubic type when 2 mM of Se was introduced into the CdTe at 60 min of reaction time. The average crystallite sizes obtained from X-ray diffraction analysis for CdOXTe1-X and CdTeXSe1-X NPs were in the range of 10-36 nm. The diffraction peaks shifted to higher diffraction angle with longer growth time. Scanning electron microscope images display change in shape and size as reaction progress. Photoluminescence (PL) emission was observed to shift from 510-566 nm and 620-653 nm for CdOXTe1-X and CdTeXSe1-X NPs respectively followed by variation in the peak intensities. The emission spectra displayed a good symmetry and a narrow full width at half maximum ranging from 41 to 100 nm in both cases. The absorbance analysis of the as-prepared NPs displayed well-resolved absorption bands. The optical band gaps of the as-prepared NPs were found to decrease with increase in reaction time. Reaction parameters such as pH, reaction time, reaction temperature and the molar concentration could have major effects on the optical properties of the as-prepared nanoparticles hence their need to control them.

  14. Solution Grown Se/Te Nanowires: Nucleation, Evolution, and The Role of Triganol Te seeds

    Directory of Open Access Journals (Sweden)

    Shan Xudong

    2009-01-01

    Full Text Available Abstract We have studied the nucleation and growth of Se–Te nanowires (NWs, with different morphologies, grown by a chemical solution process. Through systematic characterization of the Se–Te NW morphology as a function of the Te nanocrystallines (NCs precursor, the relative ratio between Se and Te, and the growth time, a number of significant insights into Se–Te NW growth by chemical solution processes have been developed. Specifically, we have found that: (i the growth of Se–Te NWs can be initiated from either long or short triganol Te nanorods, (ii the frequency of proximal interactions between nanorod tips and the competition between Se and Te at the end of short Te nanorods results in V-shaped structures of Se–Te NWs, the ratio between Se and Te having great effect on the morphology of Se–Te NWs, (iii by using long Te nanorods as seeds, Se–Te NWs with straight morphology were obtained. Many of these findings on Se–Te NW growth can be further generalized and provide very useful information for the rational synthesis of group VI based semiconductor NW compounds.

  15. HgSe(Te)-HgHal2 systems

    International Nuclear Information System (INIS)

    Pan'ko, V.V.; Khudolij, V.A.; Voroshilov, Yu.V.

    1989-01-01

    Using the methods of differential thermal and X-ray phase analyses the character of chemical interaction in the systems HgTe(Se)-HgHal 2 , where Hal is Cl, Br, I, is investigated. Formation of compounds Hg 3 Se 2 Hal 2 , Hg 3 Te 2 Hal 2 , Hg 3 TeCl 4 and Hg 3 TeBr 4 in these systems is established. The phase diagrams of the studied systems are presented. The parameters of elementary cells of the compounds with the unknown structure, as well as their unknown physicochemical properties, are determined

  16. A Neutron Scattering Study of Lattice Dynamics of HgTe and HgSe

    DEFF Research Database (Denmark)

    Kepa, H.; Giebultowicz, T.; Buras, B.

    1982-01-01

    The dispersion relations for the acoustic and optic phonons in HgTe and for the acoustic phonons in HgSe were determined by neutron inelastic scattering in three high symmetry directions. The effect of the free-carrier screening of the long-range electric field of LO phonons in HgTe was observed....... The formalism of the rigid ion model is used for numerical calculations of the phonon dispersion relations and the phonon densities of states in HgTe and HgSe....

  17. Thermal characterization of Se-Te thin films

    Czech Academy of Sciences Publication Activity Database

    Svoboda, R.; Kincl, Miloslav; Málek, J.

    2015-01-01

    Roč. 644, 25 September (2015), s. 40-46 ISSN 0925-8388 Institutional support: RVO:61389013 Keywords : krystallization kinetics * DSC * Se-Te glass Subject RIV: CA - Inorganic Chemistry Impact factor: 3.014, year: 2015

  18. Nonlinear Absorptions of CdSeTe Quantum Dots under Ultrafast Laser Radiation

    Directory of Open Access Journals (Sweden)

    Zhijun Chai

    2016-01-01

    Full Text Available The oil-soluble alloyed CdSeTe quantum dots (QDs are prepared by the electrostatic method. The basic properties of synthesized CdSeTe QDs are characterized by UV-Vis absorption spectroscopy, photoluminescence spectroscopy, inductively coupled plasma mass spectrometry, and transmission electron microscope. The off-resonant nonlinear optical properties of CdSeTe QDs are studied by femtosecond Z-scan at 1 kHz (low-repetition rate and 84 MHz (high-repetition rate. Nonlinear absorption coefficients are calculated under different femtosecond laser excitations. Due to the long luminescent lifetime of CdSeTe QDs, under the conditions of high-repetition rate, for open-aperture curve, heat accumulation and bleaching of ground state are responsible for the decrease of two-photon absorption (TPA coefficient.

  19. Stokes shift and fine-structure splitting in CdSe / CdTe invert type-II ...

    Indian Academy of Sciences (India)

    Worasak Sukkabot

    2018-01-09

    Jan 9, 2018 ... optical properties can be easily manipulated. The entan- ... and shape on the Stokes shift and FSS in core/shell .... Figure 4. Ground-state wave function overlaps of. CdSe/CdTe and CdTe/CdSe core/shell nanocrystals as.

  20. Resonance tunneling of charge carriers in photoexcited type-II ZnSe/BeTe heterostructures

    International Nuclear Information System (INIS)

    Zaitsev, S. V.; Maksimov, A. A.; Tartakovskii, I. I.; Yakovlev, D. R.; Waag, A.

    2008-01-01

    In is shown that, at high densities of spatially separated electrons and holes in type-II ZnSe/BeTe heterostructures, the conditions for resonance tunneling of photoexcited holes from the ZnSe layer to the BeTe layer are attainable. Nonlinear behavior of the intensity of the photoluminescence band corresponding to spatially direct optical transitions with photoexcitation intensity is observed. Numerical calculations are carried out, and the results are in good agreement with the experimental data in a wide region of variation of the optical pumping intensity

  1. Characterization of single crystalline ZnTe and ZnSe grown by vapor phase transport

    Energy Technology Data Exchange (ETDEWEB)

    Trigubo, A B; Di Stefano, M C [FRBA-UTN, (1179) Buenos Aires (Argentina); Aguirre, M H [Dpto de Quim Inorg, Fac de Cs Quim, Univ Complutense, (28040) Madrid (Spain); Martinez, A M; D' Elia, R; Canepa, H; Heredia, E, E-mail: atrigubo@citefa.gov.a [CINSO-CITEFA: (1603) Villa Martelli, Pcia de Buenos Aires (Argentina)

    2009-05-01

    Tubular furnaces were designed and built to obtain single crystalline ZnTe and ZnSe ingots using respectively physical and chemical transport methods. Different temperature profiles and growth rates were analyzed in order to optimize the necessary crystalline quality for device development. Optical and scanning electron micrographs of the corrosion figures produced by chemical etching were used to obtain the dislocation density and the misorientation between adjacent subgrains in ZnTe and ZnSe wafers. Structural quality of the single crystalline material was determined by transmission electronic microscopy. Optical transmittance was measured by infrared transmission spectrometry and the resulting values were compared to commercial samples.

  2. CdSe/ZnSe quantum dot structures grown by molecular beam epitaxy with a CdTe submonolayer stressor

    International Nuclear Information System (INIS)

    Sedova, I. V.; Lyublinskaya, O. G.; Sorokin, S. V.; Sitnikova, A. A.; Toropov, A. A.; Donatini, F.; Dang, Si Le; Ivanov, S. V.

    2007-01-01

    A procedure for formation of CdSe quantum dots (QDs) in a ZnSe matrix is suggested. The procedure is based on the introduction of a CdTe submonolayer stressor deposited on the matrix surface just before deposition of the material of the QDs. (For CdTe/ZnSe structure, the relative lattice mismatch is Δa/a ∼ 14%.) The stressor forms small strained islands at the ZnSe surface, thus producing local fields of high elastic stresses controlling the process of the self-assembling of the QDs. According to the data of transmission electron microscopy, this procedure allows a considerable increase in the surface density of QDs, with a certain decrease in their lateral dimensions (down to 4.5 ± 1.5 nm). In the photoluminescence spectra, a noticeable (∼150 meV) shift of the peak to longer wavelengths from the position of the reference CdSe/ZnSe QD structure is observed. The shift is due to some transformation of the morphology of the QDs and an increase in the Cd content in the QDs. Comprehensive studies of the nanostructures by recording and analyzing the excitation spectra of photoluminescence, the time-resolved photoluminescence spectra, and the cathodoluminescence spectra show that the emission spectra involve two types of optical transitions, namely, the type-I transitions in the CdSeTe/ZnSe QDs and the type-II transitions caused mainly by the low cadmium content (Zn,Cd)(Se,Te)/ZnSe layer formed between the QDs

  3. Se-Se isoelectronic centers in high purity CdTe

    Energy Technology Data Exchange (ETDEWEB)

    Najjar, Rita; Andre, Regis; Mariette, Henri [CEA-CNRS, Nanophysique et Semiconducteurs, Institut Neel, 25 rue des martyrs, 38042 Grenoble (France); Golnik, Andrzej; Kossacki, Piotr; Gaj, Jan A. [Institute of Experimental Physics, University of Warsaw, Hoza 69, 00-681 Warsaw (Poland)

    2010-06-15

    We evidence zero-dimensional exciton states trapped on isoelectronic Se centers in CdTe quantum wells, {delta}-doped with Se. Thanks to special precautions taken to have very high purity CdTe heterostructures, it is possible to observe, in photoluminescence spectra, sharp discrete lines arising from individual centers related to the Se doping. These emission lines appear at about 40 meV below the CdTe band gap energy. The most prominent lines are attributed to the recombination of excitons bound to nearest-neighbor selenium pairs in a tetrahedral CdTe environment. This assignment is confirmed by a common linear polarization direction of the emitted light, parallel to <110>. These excitons localized on individual isoelectronic traps are good candidates as single photon emitters (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  4. Optical phonons in PbTe/CdTe multilayer heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Novikova, N. N.; Yakovlev, V. A. [Russian Academy of Sciences, Institute for Spectroscopy (Russian Federation); Kucherenko, I. V., E-mail: kucheren@sci.lebedev.ru [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation); Karczewski, G. [Polish Academy of Sciences, Institute of Physics (Poland); Aleshchenko, Yu. A.; Muratov, A. V.; Zavaritskaya, T. N.; Melnik, N. N. [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation)

    2015-05-15

    The infrared reflection spectra of PbTe/CdTe multilayer nanostructures grown by molecular-beam epitaxy are measured in the frequency range of 20–5000 cm{sup −1} at room temperature. The thicknesses and high-frequency dielectric constants of the PbTe and CdTe layers and the frequencies of the transverse optical (TO) phonons in these structures are determined from dispersion analysis of the spectra. It is found that the samples under study are characterized by two TO phonon frequencies, equal to 28 and 47 cm{sup −1}. The first frequency is close to that of TO phonons in bulk PbTe, and the second is assigned to the optical mode in structurally distorted interface layers. The Raman-scattering spectra upon excitation with the radiation of an Ar{sup +} laser at 514.5 nm are measured at room and liquid-nitrogen temperatures. The weak line at 106 cm{sup −1} observed in these spectra is attributed to longitudinal optical phonons in the interface layers.

  5. Distributed Bragg reflectors obtained by combining Se and Te compounds: Influence on the luminescence from CdTe quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Rousset, J.-G., E-mail: j-g.rousset@fuw.edu.pl; Kobak, J.; Janik, E.; Slupinski, T.; Golnik, A.; Kossacki, P.; Nawrocki, M.; Pacuski, W. [Faculty of Physics, Institute of Experimental Physics, University of Warsaw, ul. Pasteura 5, PL-02-093 Warszawa (Poland); Parlinska-Wojtan, M. [Institute of Nuclear Physics, Polish Academy of Sciences, PL-31342 Krakow (Poland)

    2016-05-14

    We report on the optical properties of structures containing self assembled CdTe quantum dots (QDs) combined with Te and Se based distributed Bragg reflectors either in a half cavity geometry with a relatively broad cavity mode or in a full cavity geometry where the cavity mode is much narrower. We show that for both structures the extraction coefficient of the light emitted from the QDs ensemble is enhanced by more than one order of magnitude with respect to the QDs grown on a ZnTe buffer. However, a single QD line broadening is observed and attributed to an unintentional incorporation of Se in the vicinity of the CdTe QDs. We show that postponing the QDs growth for 24 h after the distributed Bragg reflector deposition allows recovering sharp emission lines from individual QDs. This two step growth method is proven to be efficient also for the structures with CdTe QDs containing a single Mn{sup 2+} ion.

  6. Stimulated transformation in nano-layered composites with Se0.6Te0.4

    International Nuclear Information System (INIS)

    Malyovanik, M.; Shipljak, M.; Cheresnya, V.; Ivan, I.; Csik, A.; Kokenyesi, S.; Debrecen Univ.

    2005-01-01

    Complete text of publication follows. The main types of the photo-induced structural transformations (PST) in chalcogenide glasses and amorphous layers can be systematized as i) structural transformations within amorphous phase, ii) photo-induced crystallization or amorphyzation, iii) photo-induced mass transport. These main known types of PST can be further detailed, for example concerning photo-induced anisotropy, photo- bleaching, etc., and are widely investigated. But the fundamentals of these effects even in the most known compositions like AsSe, As 2 S 3 are not clear, especially for the nanostructures, where the possible cluster formation, size restrictions and interface conditions may essentially influence the parameters of the material. Furthermore, the basic applied problem related to the PST consists of the possibility of digital or analog optical information storage, phase change memory, fabrication of elements for optics and photonics. These applications require determined spectral and temperature range of functioning, increased sensitivity, transformation rates and stability of the memory at the same time. The realization of such requirements can be expected in nanosized objects made of chalcogenides due to the suitable change of thermodynamical parameters, conductivity, optical and other characteristics. The establishment of correlations between the compositional modulation at nanoscale-dimensions (3-10 nm) in Se 0.6 Te 0.4 and the changes of the optical and electrical parameters as well as the possible improvement of optical recording process in comparison with homogeneous Se 0.6 Te 0.4 films were the aims of the present work. Two types of nano-multilayers, namely Se 0.6 Te 0.4 /SiO x and Se 0.6 Te 0.4 /As 2 S 3 were investigated with respect to the thermo- or light-stimulated structural transformations, since they strongly di r by the possibility of intermixing or crystallization in a steady-state process of heating or laser illumination. Photo

  7. Atomic structures of Cd Te and Cd Se (110) surfaces

    International Nuclear Information System (INIS)

    Watari, K.; Ferraz, A.C.

    1996-01-01

    Results are reported based on the self-consistent density-functional theory, within the local-density approximation using ab-initio pseudopotentials of clean Cd Te and Cd Se (110) surfaces. We analyzed the trends for the equilibrium atomic structures, and the variations of the bond angles at the II-VI (110). The calculations are sensitive to the ionicity of the materials and the results are in agreement with the arguments which predict that the relaxed zinc-blend (110) surfaces should depend on ionicity. (author). 17 refs., 1 figs., 3 tabs

  8. Excitation states in type-II ZnSe/BeTe quantum wells

    International Nuclear Information System (INIS)

    Platonov, A.V.; Kochereshko, V.P.; Yakovlev, D.R.; Zehnder, U.; Ossau, W.; Fisher, F.; Litz, Th.; Waag, A.; Landwehr, G.

    1997-01-01

    We present an optical investigation of novel heterostructures based on beryllium chalcogenides with a type-I and type-II band alignment. In the type-II quantum well structures (ZnSe/BeTe) we observed a strong exciton transition involving an electron confined in the conduction band well and a hole localized in the valence band barrier (both in ZnSe layer). This transition is drastically broadened by the temperature increase due to enhanced exciton-acoustic phonon interaction. (author)

  9. Electronic structure of ZrX2 (X = Se, Te)

    Science.gov (United States)

    Shkvarin, A. S.; Merentsov, A. I.; Shkvarina, E. G.; Yarmoshenko, Yu. M.; Píš, I.; Nappini, S.; Titov, A. N.

    2018-03-01

    The electronic structure of the ZrX2 (X = Se, Te) compounds has been studied using photoelectron, resonant photoelectron and X-ray absorption spectroscopy, theoretical calculations of the X-ray absorption spectra, and density of electronic states. It was found that the absorption spectra and valence band spectra are influenced by the chalcogen type. The results of the multiplet calculation of the Zr4+ atom show that the change in the splitting in the crystal field, which is described by the 10Dq parameter, is due to the change in the ratio of covalent and ionic contributions to the chemical bond. The resonance band near the Fermi level in the valence band spectra is observed for ZrTe2 in the Zr 3p-4d resonant excitation mode. The extent of photon energy indicates the charge localization on the Zr atom. Similar resonance band for ZrSe2 is absent; it indicates the presence of a gap at the Fermi level.

  10. Two new ternary chalcogenides Ba{sub 2}ZnQ{sub 3} (Q = Se, Te) with chains of ZnQ{sub 4} tetrahedra. Syntheses, crystal structure, and optical and electronic properties

    Energy Technology Data Exchange (ETDEWEB)

    Prakash, Jai; Beard, Jessica; Malliakas, Christos D.; Ibers, James A. [Northwestern Univ., Evanston, IL (United States). Dept. of Chemistry; Mesbah, Adel [Northwestern Univ., Evanston, IL (United States). Dept. of Chemistry; ICSM, UMR 5257 CEA/CNRS/UM2/ENSCM, Bagnols-sur-Ceze (France); Rocca, Dario; Lebegue, Sebastien [Univ. de Lorraine, Vandoeuvre-les-Nancy (France). Lab. de Cristallographie, Resonance Magnetique et Modelisations (CRM2, UMR CNRS 7036)

    2016-08-01

    Single crystals of Ba{sub 2}ZnQ{sub 3} (Q = Se, Te) were obtained by solid-state reactions at 1173 K. These isostructural compounds crystallize in the K{sub 2}AgI{sub 3} structure type. The Zn atoms in this structure are coordinated to four Q atoms (2 Q1, 1 Q2, 1 Q3) and these form a distorted tetrahedron around each Zn atom. Each ZnQ{sub 4} tetrahedron shares two corners with neighboring ZnQ{sub 4} tetrahedra resulting in the formation of infinite chains of [ZnQ{sub 4}{sup 4-}] units. The absorption spectrum of a single crystal of Ba{sub 2}ZnTe{sub 3} shows an absorption edge at 2.10(2) eV, consistent with the dark-red color of the crystals. From DFT calculations Ba{sub 2}ZnSe{sub 3} and Ba{sub 2}ZnTe{sub 3} are found to be semiconductors with electronic band gaps of 2.6 and 1.9 eV, respectively.

  11. Impact of Antibody Bioconjugation on Emission and Energy Band Profile of CdSeTe/ZnS Quantum Dots

    Science.gov (United States)

    Torchynska, T. V.; Gomez, J. A. Jaramillo; Polupan, G.; Macotela, L. G. Vega

    2018-03-01

    The variation of the photoluminescence (PL) and Raman scattering spectra of CdSeTe/ZnS quantum dots (QDs) on conjugation to an antibody has been investigated. Two types of CdSeTe/ZnS QD with different emission wavelength (705 nm and 800 nm) were studied comparatively before and after conjugation to anti-pseudorabies virus antibody (AB). Nonconjugated QDs were characterized by Gaussian-type PL bands. PL shifts to higher energy and asymmetric shape of PL bands was detected in PL spectra of bioconjugated QDs. The surface-enhanced Raman scattering effect was exhibited by the bioconjugated CdSeTe/ZnS QDs, indicating that the excitation light used in the Raman study generated electric dipoles in the AB molecules. The optical bandgap of the CdSeTe core was calculated numerically as a function of its radius based on an effective mass approximation model. The energy band diagrams for non- and bioconjugated CdSeTe/ZnS QDs were obtained, revealing a type II quantum well in the CdSeTe core. The calculations show that AB dipoles, excited in the bioconjugated QDs, stimulate a change in the energy band diagram of the QDs that alters the PL spectrum. These results could be useful for improving the sensitivity of QD biosensors.

  12. Optical absorption, piezoelectric effect and second harmonic generation studies of single crystal AgGaGe{sub 3}Se{sub 7.6}Te{sub 0.4} solid solution

    Energy Technology Data Exchange (ETDEWEB)

    Myronchuk, G.L.; Krymus, A.S.; Piasecki, M. [Institute of Physics, J. Dlugosz University, Czestochowa (Poland); Eastern European National University, Physics Department, Lutsk (Ukraine); Lakshminarayana, G. [Universiti Putra Malaysia, Wireless and Photonic Networks Research Centre, Faculty of Engineering, Serdang, Selangor (Malaysia); Kityk, I.V. [Czestochowa University of Technology, Faculty of Electrical Engineering, Czestochowa (Poland); Eastern European National University, Physics Department, Lutsk (Ukraine); Parasyuk, O.V. [Eastern European National University, Department of Chemistry, Lutsk (Ukraine); Rudysh, M.Ya.; Shchepanskyi, P.A. [Institute of Physics, J. Dlugosz University, Czestochowa (Poland); Ivan Franko National University of Lviv, Physics Department, Lviv (Ukraine)

    2017-03-15

    Spectral features of absorption were studied for novel AgGaGe{sub 3}Se{sub 7.6}Te{sub 0.4} solid-state alloys at different temperatures. The synthesized crystals structure parameters are obtained by the X-ray Rietveld refinement method. During increasing temperature from 100 up to 300 K, the energy gap of AgGaGe{sub 3}Se{sub 7.6}Te{sub 0.4} decreases linearly from 2.05 up to 1.94 eV at a rate 5.7 x 10{sup -4} eV/K. The magnitudes of piezoelectric coefficients are significantly changed and demonstrate substantial anisotropy. At room temperature, these values are equal to 5.2 pm/V (d{sub 11}), 31.5 pm/V (d{sub 22}) and 35.5 pm/V (d{sub 33}). It is crucial that with an increasing temperature the piezoelectric efficiencies are increased. We have explored temperature and laser-induced changes of piezoelectric coefficients. (orig.)

  13. A first-principles study of II-VI (II = Zn; VI = O{,} S{,} Se{,} Te) semiconductor nanostructures

    NARCIS (Netherlands)

    Azpiroz, Jon M.; Infante, Ivan; Lopez, Xabier; Ugalde, Jesus M.; De Angelis, Filippo

    2012-01-01

    We present a systematic investigation of the structural{,} electronic and optical properties of wurtzite-like ZnX (X = O{,} S{,} Se{,} Te) nanostructures at the DFT/TDDFT level of theory. To provide a direct comparison with the experiment{,} realistic 1.0-1.5 nm quantum dots have been built up from

  14. Molecular beam epitaxy of CdSe epilayers and quantum wells on ZnTe substrate

    International Nuclear Information System (INIS)

    Park, Y.M.; Andre, R.; Kasprzak, J.; Dang, Le Si; Bellet-Amalric, E.

    2007-01-01

    We have grown zinc-blende cadmium selenide (CdSe) epilayers on ZnTe-(0 0 1) substrate by molecular beam epitaxy (MBE). By controlling the substrate temperature and beam-equivalent pressure (BEP) ratio, of Se to Cd, we determined the most suitable growth condition based on reflection high-energy electron diffraction (RHEED) pattern. At a substrate temperature of 280 deg. C and a BEP ratio of 3.6, the RHEED pattern showed a V-like feature, indicating a rough surface with facets. As the substrate temperature was increased to 360 deg. C at the same BEP ratio, a V-like RHEED pattern moved to a clear streaky pattern. Moreover when the BEP ratio was increased to 4.8 at 360 deg. C of substrate temperature, a clear (2 x 1) reconstruction of the CdSe layer was observed. A CdSe/CdMgSe single quantum well structure was also grown on ZnTe-(0 0 1) substrate by MBE. The RHEED pattern showed a clear (2 x 1) surface reconstruction during the growth. By photoluminescence measurement, a good optical property of the structure was obtained

  15. Differential thermal analysis of the glassy system AsSe-AsTe

    International Nuclear Information System (INIS)

    El Den, M.B.; El Mously, M.K.

    1986-11-01

    Thermal induced phase transformation for the system AsSe-AsTe has been studied using DTA. The dependence of the characteristic temperature Tg, Tc and Tm on the ratio of Se/Tc has been determined. The increase of Te content leads to the decrease of both Tg and Tc, i.e. tellurium enhances the crystallization process in these glasses exactly as in the case of AsSe 3/2-x Te x and AsSe 5/2-x Te x . The kinetic calculations have also been tried. Reasonable results have been obtained for two compositions only AsSe 0.5 Te 0.5 and AsSe 0.1 Te 0.9 with E cryst equal to 31.0 kcal/mole for the first and 45 and 65 kcal/mole for the second. The other compositions either do not crystallize completely or have complicated and overlapped peaks. (author)

  16. Quarternair CuGaSeTe and CuGa0.5In 0.5Te2 Thin Films Fabrication Using Flash Evaporation

    Directory of Open Access Journals (Sweden)

    A Harsono Soepardjo

    2010-10-01

    Full Text Available Quarternair materials CuGaSeTe and CuGa0.5In 0.5Te2 are the basic materials to solar cell fabrication. These materials have high absorption coefficients around 103 - 105 cm-1 and band gap energy in the range of 1-5 eV. In this research, the films were made by flash evaporation method using quarternair powder materials of CuGaSeTe and CuGa0.5In 0.5Te2 to adhere in a glass substrate. After the films were obtained, the properties of these films will be characterized optically and electrically. The lattice parameter of the films and the crystalline film structure were obtained using X-Ray Diffraction (XRD spectroscopy. The XRD results show that the quarternair CuGaSeTe and CuGa0.5In 0.5Te2 films have a chalcopyrite structure. The absorption coefficient and the  band gap energy of the films were calculated using transmittance and reflectance patterns that measured using UV-VIS Difractometer. The films composition can be detected by using the Energy Dispersive Spectroscopy (EDS, while the films resistivity, mobility and the majority carrier of the films were obtained from Hall Effect experiments.

  17. M = Mo, W; X = S, Se, Te) heterostructures

    KAUST Repository

    Zhang, Qingyun

    2018-04-16

    Using first-principles calculations, we investigate the electronic properties of the two-dimensional GaX/MX2 (M = Mo, W; X = S, Se, Te) heterostructures. Orbital hybridization between GaX and MX2 is found to result in Rashba splitting at the valence-band edge around the Γ point, which grows for increasing strength of the spin-orbit coupling in the p orbitals of the chalcogenide atoms. The location of the valence-band maximum in the Brillouin zone can be tuned by strain and application of an out-of-plane electric field. The coexistence of Rashba splitting (in-plane spin direction) and band splitting at the K and K′ valleys (out-of-plane spin direction) makes GaX/MX2 heterostructures interesting for spintronics and valleytronics. They are promising candidates for two-dimensional spin-field-effect transistors and spin-valley Hall effect devices. Our findings shed light on the spin-valley coupling in van der Waals heterostructures.

  18. Properties of the ZnSe/ZnTe heterojunction prepared by a multi-source evaporation of ZnTe:Sb on ZnSe single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Romeo, N [Parma Univ. (Italy). Ist. di Fisica; First, F [Uniwersytet Mikolaja Kopernika, Torun (Poland). Inst. Fizyki; Seuret, D [Universidad de La Habana, (Cuba). Facultad de Fisica-Matematica

    1979-07-16

    A new method of preparation is described of a ZnSe/ZnTe heterojunction in which Sb-doped ZnTe is deposited by a multi-source apparatus on ZnSe monocrystals. The properties of the heterojunction was studied, esp. the I-U characteristic, the 1/C/sup 2/ plot as a function of applied voltage, the photocurrent spectrum, and the electroluminescence spectrum.

  19. Explorations of new phases in the Ga(III)/In(III)-Mo(VI)-Se(IV)/Te(IV)-O systems.

    Science.gov (United States)

    Kong, Fang; Hu, Chun-Li; Hu, Ting; Zhou, Yong; Mao, Jiang-Gao

    2009-07-07

    Systematic explorations of new phases in the Ga(III)/In(III)-Mo(VI)-Se(IV)/Te(IV)-O systems by hydrothermal syntheses or solid-state reactions at high-temperature led to four new quaternary compounds, namely, Ga(2)MoQ(2)O(10) (Q = Se, Te), In(2)Mo(2)Se(2)O(13)(H(2)O) and In(2)MoTe(2)O(10). Ga(2)MoQ(2)O(10) (Q = Se, Te) are isostructural and their structures feature a 3D network of gallium selenite/tellurite with 12-member ring tunnels along b-axis, the distorted MoO(6) octahedra are attached on the wall of the above tunnels. The structure of In(2)Mo(2)Se(2)O(13)(H(2)O) features a new pillared-layered architecture composed of 2D indium(III) selenite layers that are interconnected by Mo(2)O(10) dimers, forming 8-membered ring tunnels along the b-axis. The structure of In(2)MoTe(2)O(10) features a 2D indium oxide layer formed by corner- and edge-sharing InO(6) and InO(7) polyhedra with MoO(4) tetrahedra and TeO(n) (n = 4, 5) polyhedra hanging on both sides of the layer, there are weak interlayer Te-O bonds of 2.512 A. Results of optical diffuse reflectance spectrum measurements indicate that all four compounds are insulators, which are in agreement with results of band structure calculations based on DFT methods.

  20. Highest-order optical phonon-mediated relaxation in CdTe/ZnTe quantum dots

    International Nuclear Information System (INIS)

    Masumoto, Yasuaki; Nomura, Mitsuhiro; Okuno, Tsuyoshi; Terai, Yoshikazu; Kuroda, Shinji; Takita, K.

    2003-01-01

    The highest 19th-order longitudinal optical (LO) phonon-mediated relaxation was observed in photoluminescence excitation spectra of CdTe self-assembled quantum dots grown in ZnTe. Hot excitons photoexcited highly in the ZnTe barrier layer are relaxed into the wetting-layer state by emitting multiple LO phonons of the barrier layer successively. Below the wetting-layer state, the LO phonons involved in the relaxation are transformed to those of interfacial Zn x Cd 1-x Te surrounding CdTe quantum dots. The ZnTe-like and CdTe-like LO phonons of Zn x Cd 1-x Te and lastly acoustic phonons are emitted in the relaxation into the CdTe dots. The observed main relaxation is the fast relaxation directly into CdTe quantum dots and is not the relaxation through either the wetting-layer quantum well or the band bottom of the ZnTe barrier layer. This observation shows very efficient optical phonon-mediated relaxation of hot excitons excited highly in the ZnTe conduction band through not only the ZnTe extended state but also localized state in the CdTe quantum dots reflecting strong exciton-LO phonon interaction of telluride compounds

  1. Defect complexes formed with Ag atoms in CDTE, ZnTe, and ZnSe

    CERN Document Server

    Wolf, H; Ostheimer, V; Hamann, J; Lany, S; Wichert, T

    2000-01-01

    Using the radioactive acceptor $^{111}\\!$Ag for perturbed $\\gamma$-$\\gamma$-angular correlation (PAC) spectroscopy for the first time, defect complexes formed with Ag are investigated in the II-VI semiconductors CdTe, ZnTe and ZnSe. The donors In, Br and the Te-vacancy were found to passivate Ag acceptors in CdTe via pair formation, which was also observed in In-doped ZnTe. In undoped or Sb-doped CdTe and in undoped ZnSe, the PAC experiments indicate the compensation of Ag acceptors by the formation of double broken bond centres, which are characterised by an electric field gradient with an asymmetry parameter close to h = 1. Additionally, a very large electric field gradient was observed in CdTe, which is possibly connected with residual impurities.

  2. Syntheses, crystal structures and characterizations of BaZn(SeO3)2 and BaZn(TeO3)Cl2

    International Nuclear Information System (INIS)

    Jiang Hailong; Feng Meiling; Mao Jianggao

    2006-01-01

    Two new barium zinc selenite and tellurite, namely, BaZn(SeO 3 ) 2 and BaZn(TeO 3 )Cl 2 , have been synthesized by the solid state reaction. The structure of BaZn(SeO 3 ) 2 features double chains of [Zn(SeO 3 ) 2 ] 2- anions composed of four- and eight-member rings which are alternatively along a-axis. The double chains of [Zn 2 (TeO 3 ) 2 Cl 3 ] 3- anions in BaZn(TeO 3 )Cl 2 are formed by Zn 3 Te 3 rings in which each tellurite group connects with three ZnO 3 Cl tetrahedra. BaZn(SeO 3 ) 2 and BaZn(TeO 3 )Cl 2 are wide bandgap semiconductors based on optical diffuse reflectance spectrum measurements. -- Graphical abstract: Two new barium zinc selenite and tellurite, namely, BaZn(SeO 3 ) 2 and BaZn(TeO 3 )Cl 2 , have been synthesized by solid state reaction. The structure of BaZn(SeO 3 ) 2 features 1D double chains of [Zn(SeO 3 ) 2 ] 2- anions composed of four- and eight-member rings which are alternatively along a-axis. The 1D double chains of [Zn 2 (TeO 3 ) 2 Cl 3 ] 3- anions in BaZn(TeO 3 )Cl 2 are formed by Zn 3 Te 3 rings in which each tellurite group connects with one ZnO 3 Cl and two ZnO 2 Cl 2 tetrahedra. BaZn(SeO 3 ) 2 and BaZn(TeO 3 )Cl 2 are wide bandgap semiconductors based on optical diffuse reflectance spectrum measurements

  3. CdTe and CdSe quantum dots: synthesis, characterizations and applications in agriculture

    International Nuclear Information System (INIS)

    Ung, Thi Dieu Thuy; Tran, Thi Kim Chi; Pham, Thu Nga; Nguyen, Quang Liem; Nguyen, Duc Nghia; Dinh, Duy Khang

    2012-01-01

    This paper highlights the results of the whole work including the synthesis of highly luminescent quantum dots (QDs), characterizations and testing applications of them in different kinds of sensors. Concretely, it presents: (i) the successful synthesis of colloidal CdTe and CdSe QDs, their core/shell structures with single- and/or double-shell made by CdS, ZnS or ZnSe/ZnS; (ii) morphology, structural and optical characterizations of the synthesized QDs; and (iii) testing examples of QDs as the fluorescence labels for agricultural-bio-medical objects (for tracing residual pesticide in agricultural products, residual clenbuterol in meat/milk and for detection of H5N1 avian influenza virus in breeding farms). Overall, the results show that the synthesized QDs have very good crystallinity, spherical shape and strongly emit at the desired wavelengths between ∼500 and 700 nm with the luminescence quantum yield (LQY) of 30–85%. These synthesized QDs were used in fabrication of the three testing fluorescence QD-based sensors for the detection of residual pesticides, clenbuterol and H5N1 avian influenza virus. The specific detection of parathion methyl (PM) pesticide at a content as low as 0.05 ppm has been realized with the biosensors made from CdTe/CdS and CdSe/ZnSe/ZnS QDs and the acetylcholinesterase (AChE) enzymes. Fluorescence resonance energy transfer (FRET)-based nanosensors using CdTe/CdS QDs conjugated with 2-amino-8-naphthol-6-sulfonic acid were fabricated that enable detection of diazotized clenbuterol at a content as low as 10 pg ml −1 . For detection of H5N1 avian influenza virus, fluorescence biosensors using CdTe/CdS QDs bound on the surface of chromatophores extracted and purified from bacteria Rhodospirillum rubrum were prepared and characterized. The specific detection of H5N1 avian influenza virus in the range of 3–50 ng μl −1 with a detection limit of 3 ng μL −1 has been performed based on the antibody-antigen recognition. (review)

  4. Emission variation in infrared (CdSeTe)/ZnS quantum dots conjugated to antibodies

    Energy Technology Data Exchange (ETDEWEB)

    Jaramillo Gómez, J.A. [UPIITA – Instituto Politécnico Nacional, México D. F. 07320, México (Mexico); Casas Espinola, J.L., E-mail: jlcasas@esfm.ipn.mx [ESFM – Instituto Politécnico Nacional, México D. F. 07738, México (Mexico); Douda, J. [UPIITA – Instituto Politécnico Nacional, México D. F. 07320, México (Mexico)

    2014-11-15

    The paper presents the photoluminescence (PL) and Raman scattering investigations of infrared CdSeTe/ZnS quantum dots (QDs) with emission at 800 nm (1.60 eV) in nonconjugated states and after the conjugation to the anti-papilloma virus antibodies (Ab). The Raman scattering study has shown that the CdSeTe core includes two layers with different material compositions such as: CdSe{sub 0.5}Te{sub 0.5} and CdSe{sub 0.7}Te{sub 0.3}. PL spectra of nonconjugated CdSeTe/ZnS QDs are characterized by two Gaussian shape PL bands related to exciton emission in the CdSeTe core and in intermediate layer at the core/shell interface. PL spectra of bioconjugated QDs have changed essentially: the main PL band related to the core emission shifts into high energy and become asymmetric. The energy diagram of double core/shell CdSeTe/ZnS QDs has been analyzed to explain the PL spectrum of nonconjugated QDs and its transformation at the bioconjugation to the papiloma virus antibodies. It is shown that the PL spectrum transformation in bioconjugated QDs can be a powerful technique for biology and medicine.

  5. Use of INAA to study the interaction between Se and Te in cells of Saccharomyces cerevisiae

    International Nuclear Information System (INIS)

    Czauderna, M.; Turska, M.; Sierokowska, S.; Smolinski, S.

    1996-01-01

    The differences in the effects of inorganic Se (IV and VI) compounds and seleno-cystine [(CySe) 2 ] on the Te (as Na 2 TeO 3 ) uptake by the yeast, Saccharomyces cerevisiae, has been studied. Se, Te, Ag, Zn, Fe and Co contents of the cells were measured by instrumental neutron activation analysis. For the determination of the Ag content, the monostandard method was applied as the analytical method. The contents of other elements were determined by comparison with standards having similar amounts of the determined element as the sample. Results obtained show that an antagonist interaction occurs between SeO 2 and Te. There was a significant increase in the concentration of Se and Te when the yeast was incubated in the medium containing (CySe) 2 and Te. (CySe) 2 markedly increased the Ag content of cells, especially within the first 8 h of incubation. The low level of SeO 2 in the medium are the exterior factor which produce an observable increase of the Ag concentration in the cells. The higher level of SeO 2 in the medium causes a long-term marked increase in the Ag content of the cells. The uptake yield of Ag also increased in the presence of (NH 4 ) 2 SeO 4 in the medium. The Te supply produced a significant enhancement in the Ag content of the cells during the initial 8 h of incubation. The presence of Se and/or Te in the medium causes change in the intracellular Zn, Fe and Co levels. (author)

  6. Electrical and optical properties of SnEuTe and SnSrTe films

    Science.gov (United States)

    Ishida, Akihiro; Tsuchiya, Takuro; Yamada, Tomohiro; Cao, Daoshe; Takaoka, Sadao; Rahim, Mohamed; Felder, Ferdinand; Zogg, Hans

    2010-06-01

    The SnTe, Sn1-xEuxTe and Sn1-xSrxTe (x<0.06) films were prepared by hot wall epitaxy. The ternary alloy films prepared in cation rich condition had hole concentration around 1×1019 cm-3 with high mobility exceeding 2000 cm2/V s at room temperature. Optical transmission spectra were also measured in the temperature range from 100 to 400 K and compared with theoretical calculations. Optical transmission spectra of the SnTe were simulated successfully assuming bumped band edge structures. A band inversion model was proposed for the Sn1-xEuxTe and Sn1-xSrxTe systems, and the optical transmission spectra were also simulated successfully assuming the band inversion model.

  7. Scanning tunneling microscopy on iron-chalcogenide superconductor Fe(Se, Te) single crystal

    International Nuclear Information System (INIS)

    Ukita, R.; Sugimoto, A.; Ekino, T.

    2011-01-01

    We show scanning tunneling microscopy/spectroscopy (STM/STS) results of Fe(Se, Te). STM topography shows square arrangements of spots with the lattice spacing 0.37 nm. Te and Se atoms are randomly distributed in the STM topography. The STM topography of FeTe exhibits clusters of separated iron atoms. We have investigated the iron-chalcogenide superconductor Fe(Se, Te) using a low-temperature scanning tunneling microscopy/spectroscopy (STM/STS) technique. STM topography at 4.9 K shows clear regular square arrangements of spots with the lattice spacing ∼0.37 nm, from which what we observe are attributed to Se or Te atomic plane. In the topography, brighter and darker atomic spots are randomly distributed, which are most probably due to Te and Se atoms, respectively. For the FeTe compound, the topography exhibits clusters of the bright spots probably arising from separated iron atoms distributing over several Te lattice sites. The STS measurements clarify the existence of the large-size gap with 2Δ = 0.4-0.6 eV.

  8. Observation of interface carrier states in no-common-atom heterostructures ZnSe/BeTe

    Science.gov (United States)

    Gurevich, A. S.; Kochereshko, V. P.; Bleuse, J.; Mariette, H.; Waag, A.; Akimoto, R.

    2011-09-01

    The existence of intrinsic carrier interface states in heterostructures with no common atom at the interface (such as ZnSe/BeTe) is shown experimentally by ellipsometry and photoluminescence spectroscopy. These states are located on interfaces and lie inside the effective bandgap of the structure; they are characterized by a high density and a long lifetime. A tight binding model confirms theoretically the existence of these states in ZnSe/BeTe heterostructures for a ZnTe-type interface, in contrast to the case of the BeSe-type interface for which they do not exist.

  9. Observation of interface carrier states in no-common-atom heterostructures ZnSe/BeTe

    Energy Technology Data Exchange (ETDEWEB)

    Gurevich, A S; Kochereshko, V P [A F Ioffe Physical-Technical Institute, St Petersburg 194021 (Russian Federation); Bleuse, J; Mariette, H [CEA-CNRS Group ' Nanophysique et Semiconducteurs' , CEA, INAC/SP2M, and Institut Neel, 17 rue des Martyrs, F-38054 Grenoble (France); Waag, A [Braunschweig Technical University, Hans-Sommer-Strasse 66, D-38106 Braunschweig (Germany); Akimoto, R, E-mail: vladimir.kochereshko@mail.ioffe.ru [National Institute of Advanced Industrial Science and Technology (AIST), AIST Tsukuba Central 2-1, Tsukuba 305-8568 (Japan)

    2011-09-07

    The existence of intrinsic carrier interface states in heterostructures with no common atom at the interface (such as ZnSe/BeTe) is shown experimentally by ellipsometry and photoluminescence spectroscopy. These states are located on interfaces and lie inside the effective bandgap of the structure; they are characterized by a high density and a long lifetime. A tight binding model confirms theoretically the existence of these states in ZnSe/BeTe heterostructures for a ZnTe-type interface, in contrast to the case of the BeSe-type interface for which they do not exist.

  10. Fiber sensor on the basis of Ge26As17Se25Te32 glass for FEWS analysis

    Science.gov (United States)

    Velmuzhov, A. P.; Shiryaev, V. S.; Sukhanov, M. V.; Kotereva, T. V.; Churbanov, M. F.; Zernova, N. S.; Plekhovich, A. D.

    2018-01-01

    The high-purity Ge26As17Se25Te32 glass sample was prepared by chemical distillation purification method. This glass is characterized by high value of glass transition temperature (263°С), high optical transparency in the spectral range of 2-10 μm, and low content of residual impurities. The Ge26As17Se25Te32 glass rods were drawn into single-index fibers using the "rod" method and the single crucible technique. The optical losses in the 400 μm diameter fiber, fabricated by the "rod" method, were within 0.3-1 dB/m in the spectral range 5.2-9.3 μm. The minimum optical losses in the 320 μm diameter fiber, fabricated by the "crucible" technique, were 1.6-1.7 dB/m in the spectral range 6-8.5 μm. Using these Ge26As17Se25Te32 glass fibers as a sensor, the aqueous solutions of acetone (0-20 mol.%) and ethanol (0-90 mol.%) were analyzed by fiber evanescent wave spectroscopy. Peculiarities in the change of the integrated intensity and spectral position of absorption bands of these organic substances in dependence on the analyte composition and the length of the sensitive zone were established.

  11. Composite detector for mixed radiations based on CsI(Tl) and dispersions of small ZnSe(Te) crystals

    International Nuclear Information System (INIS)

    Ryzhikov, V.; Gal'chinetskii, L.; Katrunov, K.; Lisetskaya, E.; Gavriluk, V.; Zelenskaya, O.; Starzhynskiy, N.; Chernikov, V.

    2005-01-01

    A new large area detector of high-energy X-ray and β-radiation has been designed and studied. A composite material based on small-crystalline ZnSe(Te) was applied onto the wide surface of a light guide. An experimental specimen has been prepared, which showed β-sensitivity C β =5.5cm 2 . The spectrograms of a 90 Sr+ 90 Y β-source obtained with the specimen under study make it possible to evaluate the age of the source by the ratio of low- and high-energy regions of the spectrum. The combined detector (CD) comprises a single crystalline plate of ZnSe(Te) placed onto the output window of a scintillating transparent light guide made of CsI(Tl) in the shape of a truncated pyramid. The CsI(Tl) light guide is used to create an additional channel for detection of γ-radiation, as well as for protecting the photodiode from the penetrating radiation. It is shown that introduction of the light guide does not worsen the energy resolution characteristics of ZnSe(Te). Separate detection of α- and γ-radiation has been achieved under simultaneous excitation by 239 Pu (ZnSe(Te), R α =6%) and 241 Am (CsI(Tl), R γ =20%). The use of selective optical filters allows separation of the peaks of total absorption (p.t.a.) in the case of their superposition

  12. Inversion symmetry breaking induced triply degenerate points in orderly arranged PtSeTe family materials

    Science.gov (United States)

    Xiao, R. C.; Cheung, C. H.; Gong, P. L.; Lu, W. J.; Si, J. G.; Sun, Y. P.

    2018-06-01

    k paths exactly with symmetry allow to find triply degenerate points (TDPs) in band structures. The paths that host the type-II Dirac points in PtSe2 family materials also have the spatial symmetry. However, due to Kramers degeneracy (the systems have both inversion symmetry and time reversal symmetry), the crossing points in them are Dirac ones. In this work, based on symmetry analysis, first-principles calculations, and method, we predict that PtSe2 family materials should undergo topological transitions if the inversion symmetry is broken, i.e. the Dirac fermions in PtSe2 family materials split into TDPs in PtSeTe family materials (PtSSe, PtSeTe, and PdSeTe) with orderly arranged S/Se (Se/Te). It is different from the case in high-energy physics that breaking inversion symmetry I leads to the splitting of Dirac fermion into Weyl fermions. We also address a possible method to achieve the orderly arranged in PtSeTe family materials in experiments. Our study provides a real example that Dirac points transform into TDPs, and is helpful to investigate the topological transition between Dirac fermions and TDP fermions.

  13. Electronic properties of mixed molybdenum dichalcogenide MoTeSe: LCAO calculations and Compton spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Ahuja, Ushma [Department of Electrical Engineering, Veermata Jijabai Technological Institute, H. R. Mahajani Marg, Matunga (East), Mumbai 400019, Maharashtra (India); Kumar, Kishor; Joshi, Ritu [Department of Physics, University College of Science, M.L. Sukhadia University, Udaipur 313001, Rajasthan (India); Bhavsar, D.N. [Department of Physics, Bhavan' s Seth R.A. College of Science, Khanpur, Ahmedabad 380001, Gujarat (India); Heda, N.L., E-mail: nlheda@yahoo.co.in [Department of Pure and Applied Physics, University of Kota, Kota 324007, Rajasthan (India)

    2016-07-01

    We have employed linear combination of atomic orbitals (LCAO) method to compute the Mulliken’s population (MP), energy bands, density of states (DOS) and Compton profiles for hexagonal MoTeSe. The density functional theory (DFT) and hybridization of Hartree-Fock with DFT (B3LYP) have been used within the LCAO approximation. Performance of theoretical models has been tested by comparing the theoretical momentum densities with the experimental Compton profile of MoTeSe measured using {sup 137}Cs Compton spectrometer. It is seen that the B3LYP prescription gives a better agreement with the experimental data than other DFT based approximations. The energy bands and DOS depict an indirect band gap character in MoTeSe. In addition, a relative nature of bonding in MoTeSe and its isovalent MoTe{sub 2} is discussed in terms of equal-valence-electron-density (EVED) profiles. On the basis of EVED profiles it is seen that MoTeSe is more covalent than MoTe{sub 2}.

  14. Structure of Se-Te glasses studied using neutron, X-ray diffraction and reverse Monte Carlo modelling

    Energy Technology Data Exchange (ETDEWEB)

    Itoh, Keiji, E-mail: itoh@okayama-u.ac.jp [Graduate School of Education, Okayama University, Tsushima-naka, Okayama 700-8530 (Japan); Research Reactor Institute, Kyoto University, Kumatori, Osaka 590-0494 (Japan)

    2017-02-15

    Pulsed neutron diffraction and synchrotron X-ray diffraction measurements were performed on Se{sub 100-x}Te{sub x} bulk glasses with x=10, 20, 30 and 40. The coordination numbers obtained from the diffraction results demonstrate that Se and Te atoms are twofold coordinated and the glass structure is formed by the chain network. The three-dimensional structure model for Se{sub 60}Te{sub 40} glass obtained by using reverse Monte Carlo modelling shows that the alternating arrangements of Se and Te atoms compose the major part of the chain clusters but several other fragments such as Se{sub n} chains and Te-Te dimers are also present in large numbers. The chain clusters have geometrically disordered forms and the interchain atomic order is different from those in the crystal structures of trigonal Se and trigonal Te. - Graphical abstract: Coordination environment in Se{sub 60}Te{sub 40} glass.

  15. Superconductivity with twofold symmetry in Bi2Te3/FeTe0.55Se0.45 heterostructures

    Science.gov (United States)

    Du, Zengyi

    2018-01-01

    Topological superconductors are an interesting and frontier topic in condensed matter physics. In the superconducting state, an order parameter will be established with the basic or subsidiary symmetry of the crystalline lattice. In doped Bi2Se3 or Bi2Te3 with a basic threefold symmetry, it was predicted, however, that bulk superconductivity with order parameters of twofold symmetry may exist because of the presence of odd parity. We report the proximity effect–induced superconductivity in the Bi2Te3 thin film on top of the iron-based superconductor FeTe0.55Se0.45. By using the quasiparticle interference technique, we demonstrate clear evidence of twofold symmetry of the superconducting gap. The gap minimum is along one of the main crystalline axes following the so-called Δ4y notation. This is also accompanied by the elongated vortex shape mapped out by the density of states within the superconducting gap. Our results provide an easily accessible platform for investigating possible topological superconductivity in Bi2Te3/FeTe0.55Se0.45 heterostructures. PMID:29888330

  16. Optical studies of CdSe/HgSe and CdSe/Ag2Se core/shell nanoparticles embedded in gelatin

    International Nuclear Information System (INIS)

    Azhniuk, Yu M; Dzhagan, V M; Valakh, M Ya; Raevskaya, A E; Stroyuk, A L; Kuchmiy, S Ya; Zahn, D R T

    2008-01-01

    CdSe/HgSe and CdSe/Ag 2 Se core-shell nanoparticles are obtained by colloidal synthesis from aqueous solutions in the presence of gelatin. Optical absorption, luminescence, and Raman spectra of the nanoparticles obtained are measured. The variation of the optical spectra of CdSe/HgSe and CdSe/Ag 2 Se core-shell nanoparticles with the shell thickness is discussed. Sharp non-monotonous variation of the photoluminescence spectra at low shell coverage is observed.

  17. Photoemission investigation of the ZnSe/CdTe heterojunction band discontinuity

    International Nuclear Information System (INIS)

    Nelson, A.J.

    1995-01-01

    Synchrotron radiation soft x-ray photoemission spectroscopy and reflection high-energy electron diffraction were used to investigate the structural and electronic properties at the ZnSe/CdTe(100) heterojunction interface. ZnSe overlayers were sequentially grown in steps on p-type CdTe(100) single crystals at 200 degree C. In situ photoemission measurements were acquired after each growth in order to observe changes in the valence band electronic structure as well as changes in the Cd 4d, Zn 3d, and Te 4d core lines. The results were used to correlate the interfacial chemistry with the electronic structure and to directly determine the ZnSe/CdTe heterojunction valence band discontinuity and the consequent heterojunction band diagram. Results of these measurements reveal that the valence band offset is ΔE v =0.20 eV. copyright 1995 American Institute of Physics

  18. Intensification of electroluminescence of ZnSe(Te,O) crystals after gamma-irradiation

    International Nuclear Information System (INIS)

    Elmurotova, D.B.; Ibragimova, E. M.

    2006-01-01

    Full text: Wide-gap A 2 B 6 semiconductors are of special interest within eyeshot of energy-saving, on the base of which light sources are produced. Excitation voltage for injection electro luminescence (EL) corresponds to a transition potential barrier height, and wavelength determines the radiative transition energy and a recombination level position. The problem is in increasing the EL excitation efficiency, in particular the way of lowering the working voltage. The aim of the present work is experimental researches of possible amendment of EL characteristics of wide-gap ZnSe(Te,O) single crystals by influence of ionizing gamma-radiation on the electrical and optical active centers, and also exposure of possibility for creation of light emitting structures. We studied ZnSe crystals grown with Bridgman method at the Research Institute for Single Crystals (Kharkov, Ukraine). Diffusion doping with Te was used for creation of p-n transition in ZnSe crystals, that resulted in additional generation of Zn vacancies, treatment in oxidizing environment caused formation of extra Zn interstitials. Dominating evaporation of Zn, which is stipulated by a higher mobility of Zn i , leads to the increase of defect concentration of V Zn type, this process is vividly expressed in the crystals doped with Te that may be explained by the formation of stable V Zn Te Se Zn i associates. A few samples of each series were irradiated with≅ 1.25 MeV gamma-rays of 60 Co radioisotope source at the dose power of 10 Gy/s to the dose of 10 6 Gy at 300 K and compared with the non-irradiated reference samples. Spectra of EL were measured in the wave range of 200-900 nm at 300 K. A constant voltage in the range of 7-80 V was applied in straight and inverse direction for exposing hysteresis in the EL voltage-brightness dependences. The EL spectra include a wide band with the maximum at 600 nm. For the untreated samples the threshold voltage was 70-80 V, when the EL intensity began growing sharply

  19. The effect of substrate temperature upon the compositions of Mg and Se in Zn{sub 1-x}Mg{sub x}Se{sub y}Te{sub 1-y} layer grown by MOVPE

    Energy Technology Data Exchange (ETDEWEB)

    Nishio, M.; Ito, R.; Tanaka, K.; Urata, K.; Nakamura, Y.; Tanaka, T. [Department of Electrical and Electronic Engineering, Graduate School of Science and Engineering, Saga University, 1 Honjo, Saga 840-8502 (Japan); Saito, K.; Guo, Q.X. [Synchrotron Light Application Center, Saga University, 1 Honjo, Saga 840-8502 (Japan)

    2014-07-15

    The growth of Zn{sub 1-x}Mg{sub x}Se{sub y}Te{sub 1-y} layers was performed on (100) ZnTe substrate by metalorganic vapour phase epitaxy using dimethylzinc, bis-methylcyclopentadienyl-magnesium, diethyltelluride and diethylselenide. The effects of substrate temperature upon the compositions of Mg and Se have been investigated. The Mg composition in Zn{sub 1-x}Mg{sub x}Se{sub y}Te{sub 1-y} layer is significantly enhanced at low substrate temperature. Although the Se composition decreases with decreasing the substrate temperature, Zn{sub 1-x}Mg{sub x}Se{sub y}Te{sub 1-y} layer with a relatively high Se composition of 0.3 is obtainable at a low substrate temperature as low as 380 C. For all the layers, a two-mode behaviour with ZnTe- and MgTe-like longitudinal optical phonon modes is confirmed by Raman scattering. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  20. The geological and microbiological controls on the enrichment of Se and Te in sedimentary rocks

    Science.gov (United States)

    Bullock, Liam; Parnell, John; Armstrong, Joseph; Boyce, Adrian; Perez, Magali

    2017-04-01

    Selenium (Se) and tellurium (Te) have become elements of high interest, mainly due to their photovoltaic and photoconductive properties, and can contaminate local soils and groundwater systems during mobilisation. Due to their economic and environmental significance, it is important to understand the processes that lead to Se- and Te-enrichment in sediments. The distribution of Se and Te in sedimentary environments is primarily a function of redox conditions, and may be transported and concentrated by the movement of reduced fluids through oxidised strata. Se and Te concentrations have been measured in a suite of late Neoproterozoic Gwna Group black shales (UK) and uranium red bed (roll-front) samples (USA). Due to the chemical affinity of Se and sulphur (S), variations in the S isotopic composition of pyrite have also been measured in order to provide insights into their origin. Scanning electron microscopy of pyrite in the black shales shows abundant inclusions of the lead selenide mineral clausthalite. The data for the black shale samples show marked enrichment in Te and Se relative to crustal mean and several hundreds of other samples processed through our laboratory. While Se levels in sulphidic black shales are typically below 5 ppm, the measured values of up to 116 ppm are remarkable. The Se enrichment in roll-fronts (up to 168 ppm) is restricted to a narrow band of alteration at the interface between the barren oxidised core, and the highly mineralised reduced nose of the front. Te is depleted in roll-fronts with respect to the continental crust and other geological settings and deposits. S isotope compositions for pyrite in both the black shales and roll-fronts are very light and indicate precipitation by microbial sulphate reduction, suggesting that Se was microbially sequestered. Results show that Gwna Group black shales and U.S roll-front deposits contain marked elemental enrichments (particularly Se content). In Gwna Group black shales, Se and Te were

  1. Fabrication Process and Thermoelectric Properties of CNT/Bi2(Se,Te3 Composites

    Directory of Open Access Journals (Sweden)

    Kyung Tae Kim

    2015-01-01

    Full Text Available Carbon nanotube/bismuth-selenium-tellurium composites were fabricated by consolidating CNT/Bi2(Se,Te3 composite powders prepared from a polyol-reduction process. The synthesized composite powders exhibit CNTs homogeneously dispersed among Bi2(Se,Te3 matrix nanopowders of 300 nm in size. The powders were densified into a CNT/Bi2(Se,Te3 composite in which CNTs were randomly dispersed in the matrix through spark plasma sintering process. The effect of an addition of Se on the dimensionless figure-of-merit (ZT of the composite was clearly shown in 3 vol.% CNT/Bi2(Se,Te3 composite as compared to CNT/Bi2Te3 composite throughout the temperature range of 298 to 473 K. These results imply that matrix modifications such as an addition of Se as well as the incorporation of CNTs into bismuth telluride thermoelectric materials is a promising means of achieving synergistic enhancement of the thermoelectric performance levels of these materials.

  2. Band alignment of type I at (100ZnTe/PbSe interface

    Directory of Open Access Journals (Sweden)

    Igor Konovalov

    2016-06-01

    Full Text Available A junction of lattice-matched cubic semiconductors ZnTe and PbSe results in a band alignment of type I so that the narrow band gap of PbSe is completely within the wider band gap of ZnTe. The valence band offset of 0.27 eV was found, representing a minor barrier during injection of holes from PbSe into ZnTe. Simple linear extrapolation of the valence band edge results in a smaller calculated band offset, but a more elaborate square root approximation was used instead, which accounts for parabolic bands. PbSe was electrodeposited at room temperature with and without Cd2+ ions in the electrolyte. Although Cd adsorbs at the surface, the presence of Cd in the electrolyte does not influence the band offset.

  3. Thermoelectric properties of quaternary (Bi,Sb){sub 2}(Te,Se){sub 3} compound

    Energy Technology Data Exchange (ETDEWEB)

    Lu, Pengfei, E-mail: photon.bupt@gmail.com [State Key Laboratory of Information Photonics and Optical Communications, Ministry of Education, Beijing University of Posts and Telecommunications, P.O. Box 72, Beijing 100876 (China); Li, Yiluan; Wu, Chengjie; Yu, Zhongyuan; Cao, Huawei; Zhang, Xianlong; Cai, Ningning; Zhong, Xuxia [State Key Laboratory of Information Photonics and Optical Communications, Ministry of Education, Beijing University of Posts and Telecommunications, P.O. Box 72, Beijing 100876 (China); Wang, Shumin [State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050 (China); Photonics Laboratory, Department of Microtechnology and Nanoscience, Chalmers University of Technology, 41296 Gothenburg (Sweden)

    2014-01-25

    Highlights: • Sb and Se spin–orbit coupling play a key role in the band structure. • Substituted Bi/Sb and Te/Se have a limited impact on the transport coefficients. • n-Type doping will be preferred for quaternary (Bi,Sb){sub 2}(Te,Se){sub 3} compound. -- Abstract: The quaternary (Bi,Sb){sub 2}(Te,Se){sub 3} compounds are investigated using first-principles study and Boltzmann transport theory. The energy band structure and density of states are studied in detail. The electronic transport coefficients are then calculated as a function of chemical potential. The figure of merit ZT is obtained assuming a constant relaxation time and an averaged thermal conductivity. Our theoretical result agrees well with previous experimental data.

  4. Thermoelectric properties of quaternary (Bi,Sb)2(Te,Se)3 compound

    International Nuclear Information System (INIS)

    Lu, Pengfei; Li, Yiluan; Wu, Chengjie; Yu, Zhongyuan; Cao, Huawei; Zhang, Xianlong; Cai, Ningning; Zhong, Xuxia; Wang, Shumin

    2014-01-01

    Highlights: • Sb and Se spin–orbit coupling play a key role in the band structure. • Substituted Bi/Sb and Te/Se have a limited impact on the transport coefficients. • n-Type doping will be preferred for quaternary (Bi,Sb) 2 (Te,Se) 3 compound. -- Abstract: The quaternary (Bi,Sb) 2 (Te,Se) 3 compounds are investigated using first-principles study and Boltzmann transport theory. The energy band structure and density of states are studied in detail. The electronic transport coefficients are then calculated as a function of chemical potential. The figure of merit ZT is obtained assuming a constant relaxation time and an averaged thermal conductivity. Our theoretical result agrees well with previous experimental data

  5. Growth and optical properties of CdTe quantum dots in ZnTe nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Wojnar, Piotr; Janik, Elzbieta; Baczewski, Lech T.; Kret, Slawomir; Karczewski, G.; Wojtowicz, Tomasz [Institute of Physics, Polish Academy of Sciences, Al Lotnikow 32/46, 02-668 Warsaw (Poland); Goryca, Mateusz; Kazimierczuk, Tomasz; Kossacki, Piotr [Institute of Experimental Physics, Faculty of Physics, University of Warsaw, ul Hoza 69, 00-681 Warsaw (Poland)

    2011-09-12

    We report on the formation of optically active CdTe quantum dots in ZnTe nanowires. The CdTe/ZnTe nanostructures have been grown by a gold nanocatalyst assisted molecular beam epitaxy in a vapor-liquid solid growth process. The presence of CdTe insertions in ZnTe nanowire results in the appearance of a strong photoluminescence band in the 2.0 eV-2.25 eV energy range. Spatially resolved photoluminescence measurements reveal that this broad emission consists of several sharp lines with the spectral width of about 2 meV. The large degree of linear polarization of these individual emission lines confirms their nanowire origin, whereas the zero-dimensional confinement is proved by photon correlation spectroscopy.

  6. Wide emission-tunable CdTeSe/ZnSe/ZnS core–shell quantum dots and their conjugation with E. coli O-157

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Haifeng [State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100 (China); Zhou, Guangjun, E-mail: gjzhou@sdu.edu.cn [State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100 (China); Zhou, Juan [Center for Disease Control and Prevention of Jinan Military Command, Jinan 250014 (China); Xu, Dong; Zhang, Xingshuang; Kong, Peng; Yang, Zhongsen [State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100 (China)

    2015-05-15

    Highlights: • QDs with variety morphology were obtained via an injection controlled process. • 3-D PL spectra of core–shell QDs show different excitation wavelength dependence. • The PL intensity of QDs with ZnSe transition layer increases dramatically. • Core–shell QDs were processed into aqueous phase and conjugated with E. coli O-157. - Abstract: Wide emission-tunable and different morphological alloyed CdTeSe quantum dots (QDs), CdTeSe/ZnS and CdTeSe/ZnSe/ZnS core–shell QDs were successfully synthesized via an injection controlled process. The effect of injection procedure and reaction temperature were systematically discussed and the growth mechanism was proposed. Most efficient PL wavelength was correlated with reaction time and temperature. The 3-D PL spectra of spherical bare CdTeSe and core–shell QDs with different passivation showed different excitation wavelength dependency. The PL intensity of CdTeSe/ZnSe/ZnS core–shell QDs increased greatly in comparison with that of CdTeSe and CdTeSe/ZnSe QDs. ZnSe transition layer played an important role in improving the PL intensity by providing a smoothened interface and gradient band offsets. The core–shell QDs were transferred into aqueous phase and successfully conjugated with Escherichia coli O-157. The proposed phase-transfer and bio-labeling strategy may be applicable to various QDs with different compositions.

  7. Influence of Te and Se doping on ZnO films growth by SILAR method

    Science.gov (United States)

    Güney, Harun; Duman, Ćaǧlar

    2016-04-01

    The AIP Successive ionic layer adsorption and reaction (SILAR) is an economic and simple method to growth thin films. In this study, SILAR method is used to growth Selenium (Se) and Tellurium (Te) doped zinc oxide (ZnO) thin films with different doping rates. For characterization of the films X-ray diffraction (XRD), absorbance and scanning electron microscopy (SEM) are used. XRD results are showed well-defined strongly (002) oriented crystal structure for all samples. Also, absorbance measurements show, Te and Se concentration are proportional and inversely proportional with band gap energy, respectively. SEM measurements show that the surface morphology and thickness of the material varied with Se and/or Te and varying concentrations.

  8. Influence of Te and Se doping on ZnO films growth by SILAR method

    International Nuclear Information System (INIS)

    Güney, Harun; Duman, Çağlar

    2016-01-01

    The AIP Successive ionic layer adsorption and reaction (SILAR) is an economic and simple method to growth thin films. In this study, SILAR method is used to growth Selenium (Se) and Tellurium (Te) doped zinc oxide (ZnO) thin films with different doping rates. For characterization of the films X-ray diffraction (XRD), absorbance and scanning electron microscopy (SEM) are used. XRD results are showed well-defined strongly (002) oriented crystal structure for all samples. Also, absorbance measurements show, Te and Se concentration are proportional and inversely proportional with band gap energy, respectively. SEM measurements show that the surface morphology and thickness of the material varied with Se and/or Te and varying concentrations.

  9. Influence of Te and Se doping on ZnO films growth by SILAR method

    Energy Technology Data Exchange (ETDEWEB)

    Güney, Harun, E-mail: harunguney25@hotmail.com [Department of Electric and Energy, Vocation High School, Ağrı İbrahim Çeçen University (Turkey); Duman, Çağlar, E-mail: caglarduman@erzurum.edu.tr [Department of Electrical and Electronic Engineering, Faculty of Engineering, Erzurum Technical University (Turkey)

    2016-04-18

    The AIP Successive ionic layer adsorption and reaction (SILAR) is an economic and simple method to growth thin films. In this study, SILAR method is used to growth Selenium (Se) and Tellurium (Te) doped zinc oxide (ZnO) thin films with different doping rates. For characterization of the films X-ray diffraction (XRD), absorbance and scanning electron microscopy (SEM) are used. XRD results are showed well-defined strongly (002) oriented crystal structure for all samples. Also, absorbance measurements show, Te and Se concentration are proportional and inversely proportional with band gap energy, respectively. SEM measurements show that the surface morphology and thickness of the material varied with Se and/or Te and varying concentrations.

  10. Superconductivity in Pd-Intercalated Ternary Rare-Earth Polychalcogenide NdSeTe_2

    International Nuclear Information System (INIS)

    Wang Pei-Pei; Xue Mian-Qi; Long Yu-Jia; Zhao Ling-Xiao; Cai Yao; Yang Huai-Xin; Li Jian-Qi; Ren Zhi-An; Chen Gen-Fu

    2015-01-01

    We synthesize a set of Pd-doped polycrystalline samples Pd_xNdSeTe_2 and measure their physical properties. Compared with pure NdSeTe_2, the charge density wave (CDW) order is continuously suppressed with the Pd-intercalation. Bulk superconductivity first appears at x = 0.06 with T_c nearly 2.5K, coexisting with a CDW transition at 176K. Further Pd-doping enhances T_c, until it reaches the maximum value 2.84K at x=0.1, meanwhile the CDW transition vanishes. The upper critical field for the optimal doping sample Pd_0_._1NdSeTe_2 is determined from the R-H measurement, which is estimated to be 0.6 T. These results provide another kind of ideal compound for studying the interplay between CDW and superconductivity systematically. (paper)

  11. Investigation of omnidirectional reflection band in ZnTe/ZnSe distributed Bragg reflector

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Ying-Shin [Department of Electrical Engineering, National Taiwan Ocean University, Keelung 20224, Taiwan (China); Hu, Sheng-Yao [Department of Digital Technology Design, Tungfang Design University, Kaohsiung 82941, Taiwan (China); Lee, Yueh-Chien, E-mail: jacklee@mail.tnu.edu.tw [Department of Electronic Engineering, Tungnan University, New Taipei City 22202, Taiwan (China); Chang, Chung-Cheng; Tiong, Kwong-Kau [Department of Electrical Engineering, National Taiwan Ocean University, Keelung 20224, Taiwan (China); Shen, Ji-Lin [Department of Physics, Chung Yuan Christian University, Chung-Li 32023, Taiwan (China); Chou, Wu-Ching [Department of Electrophysics, National Chiao Tung University, Hsinchu 30010, Taiwan (China)

    2015-11-15

    We report the characteristics of reflectance spectra of the 15- and 20-period ZnTe/ZnSe distributed Bragg reflector grown on GaAs (001) substrates by molecular beam epitaxy. The reflectance spectra measured at various incident angles and polarizations were investigated by the theoretical curves simulated using transfer matrix method. The wavelength variation of the refractive indices described by Sellmeier equation and random thickness model were also considered for the interpretation of the experimentally observed curves. An omnidirectional reflection range defined from the edge of incident-angle-dependent reflection band with TE and TM polarizations is about 15 nm, and is consistent with the observed experimental curves. The results showed that the selected ZnTe and ZnSe materials are suitable for constructing multilayer structures having omnidirectional reflection band. - Highlights: • ZnTe/ZnSe distributed Bragg reflector grown by molecular beam epitaxy. • The reflectance spectra are measured at various incidence angles and polarizations. • The theoretical curves are considered by Sellmeier and random thickness models. • An observed omnidirectional reflection range in ZnTe/ZnSe DBR is about 15 nm.

  12. Phase equilibria in TlX-Cd(Zn)X (X-S, Se, Te) systems

    International Nuclear Information System (INIS)

    Gusejnov, F.Kh.; Babanly, M.B.; Kuliev, A.A.

    1982-01-01

    The methods of DTA, RPA and measurement of the alloys microhardness have been used to investigate the phase equilibria in the TlX-Zn(Cd)X systems. It is established that the TlZn(Cd)X 2 compounds, the presence of which is mentioned in the literature earlier, do not form in these systems. The TlSe-Zn(Cd)Se systems apply to the simple eutectic type and characterized by digenerated eutectic near the TlSe. Thermodynamical analysis of the liquidus of the TlSe-CdSe and TlTe-Zn(Cd)Te systems in approximation of the regular solutions, taking into account the dissociation of tallium chalcogenides in liquid phase, is made

  13. Dual-bath electrodeposition of n-type Bi–Te/Bi–Se multilayer thin films

    Energy Technology Data Exchange (ETDEWEB)

    Matsuoka, Ken; Okuhata, Mitsuaki; Takashiri, Masayuki, E-mail: takashiri@tokai-u.jp

    2015-11-15

    N-type Bi–Te/Bi–Se multilayer thin films were prepared by dual-bath electrodeposition. We varied the number of layers from 2 to 10 while the total film thickness was maintained at approximately 1 μm. All the multilayer films displayed the X-ray diffraction peaks normally observed from individual Bi{sub 2}Te{sub 3} and Bi{sub 2}Se{sub 3} crystal structures, indicating that both phases coexist in the multilayer. The cross-section of the 10-layer Bi–Te/Bi–Se film was composed of stacked layers with nano-sized grains but the boundaries between the layers were not planar. The Seebeck coefficient was almost constant throughout the entire range of our experiment, but the electrical conductivity of the multilayer thin films increased significantly as the number of layers was increased. This may be because the electron mobility increases as the thickness of each layer is decreased. As a result of the increased electrical conductivity, the power factor also increased with the number of layers. The maximum power factor was 1.44 μW/(cm K{sup 2}) for the 10-layer Bi–Te/Bi–Se film, this was approximately 3 times higher than that of the 2-layer sample. - Highlights: • N-type Bi–Te/Bi–Se multilayer thin films were deposited by electrodeposition. • We employed a dual-bath electrodeposition process for preparing the multilayers. • The Bi–Te/Bi–Se film was composed of stacked layers with nano-sized grains. • The electrical conductivity increased as the number of layers was increased. • The power factor improved by 3 times as the number of layers was increased.

  14. Demonstration of surface transport in a hybrid Bi2Se3/Bi2Te3 heterostructure

    OpenAIRE

    Zhao, Yanfei; Chang, Cui-Zu; Jiang, Ying; DaSilva, Ashley; Sun, Yi; Wang, Huichao; Xing, Ying; Wang, Yong; He, Ke; Ma, Xucun; Xue, Qi-Kun; Wang, Jian

    2013-01-01

    In spite of much work on topological insulators (TIs), systematic experiments for TI/TI heterostructures remain absent. We grow a high quality heterostructure containing single quintuple layer (QL) of Bi2Se3 on 19 QLs of Bi2Te3 and compare its transport properties with 20 QLs Bi2Se3 and 20 QLs Bi2Te3. All three films are grown on insulating sapphire (0001) substrates by molecular beam epitaxy (MBE). In situ angle-resolved photoemission spectroscopy (ARPES) provides direct evidence that the su...

  15. Andreev spectroscopy of FeSe{sub x}Te{sub 1−x}

    Energy Technology Data Exchange (ETDEWEB)

    Fujioka, Naoya, E-mail: f-naoya@moegi.waseda.jp; Shirai, Yoshiki; Miyamoto, Yukihiro; Tachibana, Hironori; Matsuda, Azusa

    2015-11-15

    Highlights: • We fabricated FeSe{sub 0.2}Te{sub 0.8}/oxide/Pb and FeSe{sub 0.2}Te{sub 0.8}/Al/Al{sub 2}O{sub 3}/Pb junctions. • These junctions show anomalous conductance spectra and no Josephson current. • These spectra are explained by S/N interface model with extraordinarily gaps. • Except for anomalous gap values, the result is consistent with s+− symmetry. - Abstract: We fabricated two types of junctions on the c-axis plane of FeSe{sub 0.2}Te{sub 0.8} (Fe[Se,Te], T{sub c} ∼ 13 K) crystals. In the superconductor/oxide/superconductor heterojunctions with a Pb film as a counter electrode, we found a large conductance peak centered at 0 V, and a gap-like feature, which has a much higher energy scale than those reported as a gap energy of Fe[Se,Te]. In spite of a large energy scale, their temperature dependence approximately follows a BCS curve, indicating they come from superconductivity of Fe[Se,Te]. Since these structures can be understood as the results of Andreev bound state at the S/N boundary and the interference effect in the normal metal [1], we tried to identify the effect of a normal layer by fabricating Fe[Se,Te]/Al/Al{sub 2}O{sub 3}/Pb junction. Here, we could realize a clean controlled S/N interface and the tunnel junction to investigate electronic properties of the Al slab. We found similar conductance spectra as those junctions without Al layer, giving a support that the anomalous conductance spectra come from the effect of the S/N interface. As expected, the energy scale of the observed features was reduced when the thickness of the normal metal was increased. The absence of Josephson current and the existence of an Andreev bound state may be a signature of the sign-reversal paring in Fe[Se,Te].

  16. Optical Properties of Multilayer CdSe/POLYMER Structures

    Science.gov (United States)

    Red'Ko, V. P.; Voitenkov, A. I.; Kovalenko, O. E.

    The effects of preparation condition, concentration and size of particles upon optical and photoelectrical characteristics of multilayer structures CdSe/polyethylene terephthalate obtained by electron-beam evaporation were investigated.

  17. Different effect of quenching temperature on Fe1+σTe0.5Se0.5 and β-FeSe

    Directory of Open Access Journals (Sweden)

    Zhongnan Guo

    2015-02-01

    Full Text Available In this work, we have demonstrated a different effect on Fe1+σTe0.5Se0.5 and β-FeSe by changing the quenching temperature. Tc is clearly reduced in Fe1+σTe0.5Se0.5 after increasing the quenching temperature from 300 °C to 500 °C, while that of β-FeSe is almost unchanged. Structure refinement indicates that after quenched at 500 °C, FeTe4 tetrahedron exhibits an expansion with the stretched Fe-Te bond, together with the increased amount of interstitial iron. These particular changes on structure are believed to be responsible for the suppression of superconductivity in Fe1+σTe0.5Se0.5.

  18. Structural and optical properties of CdSe nanosheets

    Science.gov (United States)

    Solanki, Rekha Garg; Rajaram, P.; Arora, Aman

    2018-04-01

    Nanosheets of CdSe have been synthesized using a solvothermal route using citric acid as an additive. It is found that the citric acid effectively controls the structural and optical properties of CdSe nanostructures. XRD studies confirm the formation of hexagonal wurtzite phase of CdSe. The FESEM micrographs show that the obtained CdSe nanocrystals are in the form of very thin sheets (nanosheets). Optical absorption studies as well as Photoluminescence spectra show that the optical gap is around 1.76 eV which is close to the reported bulk value of 1.74 eV. The prepared CdSe nanosheets because of large surface area may be useful for catalytic activities in medicine, biotechnology and environmental chemistry and in biomedical imaging for in vitro detection of a breast cancer cells.

  19. In Situ X-ray Diffraction Study of the Formation of Fe(Se,Te) from Various Precursors

    DEFF Research Database (Denmark)

    Grivel, Jean-Claude; Yue, Zhao; Wulff, Anders Christian

    2012-01-01

    The formation of the FeSe0.5Te0.5 phase was studied by means of high energy synchrotron x-ray diffraction. The precursors consisted of Fe, Se and Te or Se0.5Te0.5 powder mixtures and were encased in a metal (Cu/Nb) composite sheath to prevent evaporation of Se and Te during high temperature...... equilibria of the SeTe system. The grain size of the starting Fe powder has no influence on the reaction path for the grain sizes used in the present study. However, the reaction rate for Fe(Se,Te) formation is clearly sensitive to this parameter....

  20. Electrochemical preparation and characterization of n-CdSe sub 0. 65 Te sub 0. 35 polycrystalline thin films: Influence of annealing

    Energy Technology Data Exchange (ETDEWEB)

    Gutierrez, M T; Ortega, J [Centro de Investigaciones Energeticas, Medioambientales y Tecnologicas, Madrid (Spain). Inst. de Energias Renovables

    1989-12-01

    CdSe{sub 0.65}Te{sub 0.35} thin films have been prepared by electrodeposition. The films were characterized by X-ray diffraction, optical and photoelectrochemical methods. The influence of annealing treatments on the physical parameters (grain size, d, donor concentration, N{sub D}, and hole diffusion length, L{sub P}) determining the photoelectrochemical behaviour of electrodeposited CdSe{sub 0.65}Te{sub 0.35} thin films in contact with sulfide/polysulfide electrolytes have been systematically studied. (orig.).

  1. Effect of Se substitution on the phase change properties of Ge2Sb2Te5

    Science.gov (United States)

    Shekhawat, Roopali; Rangappa, Ramanna; Gopal, E. S. R.; Ramesh, K.

    2018-05-01

    Ge2Sb2Te5 popularly known as GST is being explored for non-volatile phase change random access memory(PCRAM) applications. Under high electric field, thin films of amorphous GST undergo a phase change from amorphous to crystalline with a high contrast in electrical resistivity (about 103). The phase change is between amorphous and metastable NaCl structure occurs at about 150°C and not to the stable hexagonal phase which occurs at a high temperature (> 250 °C). In GST, about 50 % of Te substituted by Se (Ge2Sb2Te2.5Se2.5) is found to increase the contrast in electrical resistivity by 7 orders of magnitude (about 4 orders of magnitude higher than GST). The phase transition in Se added GST also found to be between amorphous and the stable hexagonal structure. The threshold voltage at which the Ge2Sb2Te2.5Se2.5 switches to the high conducting state increases to 9V as compared to 2V in GST. Interestingly, the threshold current decrease to 1mA as compared to 1.8mA in GST indicating the Se substitution reduces the power needed for switching between the low and high conducting states. The reduction in power needed for phase change, high contrast in electrical resistivity with high thermal stability makes Ge2Sb2Te2.5Se2.5 as a better candidate for PCRAM.

  2. Optical band gap study of a-Se and Se-Sb thin films

    International Nuclear Information System (INIS)

    Kaur, Ramandeep; Singh, Palwinder; Thakur, Anup

    2016-01-01

    Amorphous selenium (a-Se) and a-Se_9_5Sb_5 alloy were prepared using melt quenching technique. X-ray diffraction (XRD) pattern confirmed the amorphous nature of the prepared samples. Composition of the prepared samples has been determined using Energy dispersive X-ray fluorescence (EDXRF) technique. Differential thermal analysis (DTA) confirmed the glassy nature of the prepared samples. Thin films of the prepared samples were deposited on glass substrate using thermal evaporation method. Amorphous nature of the deposited films was confirmed using XRD. Optical properties of these films were obtained from the UV-VIS transmission spectra, at normal incidence, over 200-1100 nm spectral range. The optical absorption edge was described by using the model given by the Tauc. Optical band gap of the deposited films was calculated using Tauc plot. Optical characterization showed that average transmission and optical band gap decreased with the addition of antinomy.

  3. Few-Layer Nanoplates of Bi 2 Se 3 and Bi 2 Te 3 with Highly Tunable Chemical Potential

    KAUST Repository

    Kong, Desheng

    2010-06-09

    A topological insulator (TI) represents an unconventional quantum phase of matter with insulating bulk band gap and metallic surface states. Recent theoretical calculations and photoemission spectroscopy measurements show that group V-VI materials Bi2Se3, Bi2Te3, and Sb2Te3 are TIs with a single Dirac cone on the surface. These materials have anisotropic, layered structures, in which five atomic layers are covalently bonded to form a quintuple layer, and quintuple layers interact weakly through van der Waals interaction to form the crystal. A few quintuple layers of these materials are predicted to exhibit interesting surface properties. Different from our previous nanoribbon study, here we report the synthesis and characterizations of ultrathin Bi2Te3 and Bi2Se3 nanoplates with thickness down to 3 nm (3 quintuple layers), via catalyst-free vapor-solid (VS) growth mechanism. Optical images reveal thickness-dependent color and contrast for nanoplates grown on oxidized silicon (300 nm SiO2/Si). As a new member of TI nanomaterials, ultrathin TI nanoplates have an extremely large surface-to-volume ratio and can be electrically gated more effectively than the bulk form, potentially enhancing surface state effects in transport measurements. Low-temperature transport measurements of a single nanoplate device, with a high-k dielectric top gate, show decrease in carrier concentration by several times and large tuning of chemical potential. © 2010 American Chemical Society.

  4. Ultrafast quasiparticle dynamics of FeTe0.75Se0.25 superconductor

    Directory of Open Access Journals (Sweden)

    Katagiri T.

    2013-03-01

    Full Text Available The electron-phonon coupling constant (λ≈0.45 obtained from femtosecond pump-probe reflection measurements suggests that a phonon-mediated process cannot be the dominant mechanism for superconductivity of FeTe0.75Se0.25.

  5. A{sup I}B{sup III}C{sup VI}{sub 2} (A = Cu, Ag; B = Ga, In; C = S, Se, Te) based photonic crystal superlattices: Optical properties

    Energy Technology Data Exchange (ETDEWEB)

    Simsek, Sevket [Faculty of Engineering, Department of Material Science and Engineering, Hakkari University, 3000, Hakkari (Turkey); Palaz, Selami [Faculty of Science and Letters, Department of Physics, Harran University, 63000, Sanliurfa (Turkey); Akhundov, Chingiz [International Scientific Center, Baku State University, Baku (Azerbaijan); Mamedov, Amirullah M. [International Scientific Center, Baku State University, Baku (Azerbaijan); Nanotechnology Research Center, Bilkent University, 06800, Ankara (Turkey); Ozbay, Ekmel [Nanotechnology Research Center, Bilkent University, 06800, Ankara (Turkey)

    2017-06-15

    In this study, we present an investigation of the optical properties and band structures for the photonic structures based on A{sup I}B{sup III}C{sup VI}{sub 2} with a Fibonacci sequence that can act as a multi-wavelength birefringent filter. The filtering wavelengths are analyzed by the indices concerning the quasi-periodicity of a Fibonacci sequence and the average lattice parameter. The transmittances of filtering wavelengths can be tuned by varying structure parameters such as the lengths of poled domains, filling factor, and dispersion relation. In our simulation, we employed the finite-difference time domain (FDTD) technique, which implies a solution from Maxwell equation. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  6. OSPF-TE Extensions for Green Routing in Optical Networks

    DEFF Research Database (Denmark)

    Wang, Jiayuan; Ricciardi, S.; Fagertun, Anna Manolova

    2012-01-01

    This paper proposes extensions to the OSPF-TE protocol to enable green routing in GMPLS-controlled optical networks. Simulation results show a remarkable reduction in CO2 emissions by preferring network elements powered by green energy sources in the connection routing.......This paper proposes extensions to the OSPF-TE protocol to enable green routing in GMPLS-controlled optical networks. Simulation results show a remarkable reduction in CO2 emissions by preferring network elements powered by green energy sources in the connection routing....

  7. Quasi-optical millimeter wave rotating TE62 mode generator

    International Nuclear Information System (INIS)

    Li Shaopu; Zhang Conghui; Wang Zhong; Guo Feng; Chen Hongbin; Hu Linlin; Pan Wenwu

    2011-01-01

    The design,measurement technique and experimental results of rotating TE 6 2 mode generator are presented. The source includes millimeter wave optical system and open coaxial wave guide system. The millimeter wave optical system consists of pyramid antenna, hyperbolical reflector, parabolic reflector and quasi parabolic reflector. The open coaxial wave guide system contains open coaxial wave guide cavity, cylinder wave guide and output antenna. It is tested by network analyser and millimeter wave near field pattern auto-test system, and the purity of rotating TE 6 2 mode at 96.4 GHz is about 97%. (authors)

  8. Influence of CdTe sub-monolayer stressor on CdSe quantum dot self-assembling in ZnSe

    International Nuclear Information System (INIS)

    Sedova, I.V.; Lyublinskaya, O.G.; Sorokin, S.V.; Sitnikova, A.A.; Solnyshkov, D.D.; Rykhova, O.V.; Toropov, A.A.; Ivanov, S.V.

    2006-01-01

    This paper reports on the attempt to apply the stressor-controlled quantum dot (QD) fabrication technique to the conventional CdSe/ZnSe nanostructures. Super-strained CdTe fractional monolayer (Δa/a∝14% for CdTe/ZnSe) grown on top of the Te-stabilized ZnSe surface prior to deposition of the QD material (CdSe) has been used as a stressor which is expected to affect size, composition and density of CdSe QDs. The grown structures are studied by X-ray diffraction, transmission-electron microscopy, photoluminescence (PL) and PL excitation in comparison with conventional CdSe/ZnSe QDs obtained by a modified migration enhanced epitaxy technique. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  9. Ab initio calculations of half-metallic ferromagnetism in Cr-doped MgSe and MgTe semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Noor, N.A. [Department of Physics, University of the Punjab, Quaid-e-Azam Campus, 54590 Lahore (Pakistan); Alay-e-Abbas, S.M. [Department of Physics, University of Sargodha, Sargodha 40100 (Pakistan); Department of Physics, GC University Faisalabad, Allama Iqbal Road, Faisalabad 38000 (Pakistan); Sohaib, M.U. [Lahore Development Authority, 54590 Lahore (Pakistan); Ghulam Abbas, S.M. [Department of Chemistry, University of Agriculture, Faisalabad 38040 (Pakistan); Shaukat, A., E-mail: schaukat@gmail.com [Department of Physics, University of Sargodha, Sargodha 40100 (Pakistan)

    2015-01-15

    The full-potential linear-augmented-plane-waves plus local-orbitals (FP-LAPW+lo) method has been employed for investigation of half-metallic ferromagnetism in Cr-doped ordered zinc-blende MgSe and MgTe semiconductors. Calculations of exchange and correlation (XC) effects have been carried out using generalized gradient approximation (GGA) and orbital independent modified Becke–Johnson potential coupled with local (spin) density approximation (mBJLDA). The thermodynamic stability of the compounds and their preferred magnetic orders have been analyzed in terms of the heat of formation and minimum total energy difference in ferromagnetic (FM) and anti-ferromagnetic (AFM) ordering, respectively. Calculated electronic properties reveal that the Cr-doping induces ferromagnetism in MgSe and MgTe which gives rise to a half-metallic (HM) gap at Fermi level (E{sub F}). Further, the electronic band structure is discussed in terms of s (p)–d exchange constants that are consistent with typical magneto-optical experiment and the behavior of charge spin densities is presented for understanding the bonding nature. Our results demonstrate that the higher effective potential for the spin-down case is responsible for p–d exchange splitting. Total magnetic moment (mainly due to Cr-d states) of these compounds is 4µ{sub B}. Importantly, the electronic properties and HM gap obtained using mBJLDA show remarkable improvement as compared to the results obtained using standard GGA functional. - Highlights: • Spin effect theoretical study on Cr-doped MgSe and MgTe is performed. • Half-metallic ferromagnetism in Cr{sub x}Mg{sub 1−x}Se and Cr{sub x}Mg{sub 1−x}Te is established. • Results of WC-GGA and mBJLDA are compared for performance. • HM gaps for Cr{sub x}Mg{sub 1−x}Se and Cr{sub x}Mg{sub 1−x}Te show nonlinear variation with x. • Important values of exchange splitting/constants and moments are reported.

  10. Study of the CdX-B2X3-X (X=S, Se), CdTe-B-Te systems

    International Nuclear Information System (INIS)

    Odin, I.N.; Grin'ko, V.V.; Safronov, E.V.; Kozlovskij, V.F.

    2001-01-01

    Liquidus surfaces of the CdX-B 2 X 3 -X (X=S, Se), CdTe-B-Te systems are plotted for the first time. It is shown that in equilibrium solid solutions on the basis of ternary Cd 2 B 2 X 5 compounds and binary B 2 X 3 , CdX, BS 2 compounds take part with liquid phases. p gen -T and T-x projects of p-T-x phase diagram of B-S (59-100 at. % S), B-Se (59-100 at. % Se), B-Te systems are plotted . B 2 X 3 , BS 2 compounds are formed in that regions of compositions of B-X systems . In the B-Te system compounds are not formed. Ternary compounds are not formed in the CdTe-B-Te system [ru

  11. Ab initio study of lattice instabilities of zinc chalcogenides ZnX (X=O, S, Se, Te induced by ultrafast intense laser irradiation

    Directory of Open Access Journals (Sweden)

    Dahua Ren

    2017-09-01

    Full Text Available Ab initio calculations of lattice constants, lattice stabilities of ZnX (X=O, S, Se, Te at different electronic temperatures (Te have been performed using generalized gradient approximation (GGA pseudopotential method within the density functional theory (DFT. The calculated phonon frequencies of ZnX at Te = 0 eV accord well with the experimental and other theoretical values. Firstly, it is indicated that the lattice constants of ZnX increase and all the phonon frequencies reduce as Te increases. Additionally, the transverse-acoustic phonon frequencies of ZnX are imaginary with the elevation of Te, namely the lattices of ZnX become unstable under ultrafast intense laser irradiation. Moreover, the transverse optical mode-longitudinal optical mode (LO-TO splitting degree of ZnX (X=S, Se, Te gradually decreases as the electronic temperature increases, mainly due to the reason that the electronic excitation weakens the strength ionicity of ionic crystal ZnX under intense laser irradiation. However, the LO-TO splitting degree of ZnO firstly increases and then decreases with the increase of electronic temperature. After that, it can be helpful for understanding the mechanism of ultrafast intense laser induced semiconductors damage.

  12. Thermoelectric properties of Bi2Te3-Bi2Se3 solid solutions prepared by attrition milling and hot pressing

    International Nuclear Information System (INIS)

    Lee, Go-Eun; Kim, Il-Ho; Choi, Soon-Mok; Lim, Young-Soo; Seo, Won-Seon; Park, Jae-Soung; Yang, Seung-Ho

    2014-01-01

    Bi 2 Te 3-y Se y (y = 0.15 - 0.6) solid solutions were prepared by attrition milling and hot pressing. The lattice constants decreased with increasing Se content, indicating that the Se atoms were successfully substituted into the Te sites. All specimens exhibited n-type conduction, and their electrical resistivities increased slightly with increasing temperature. With increasing Se content, the Seebeck coefficients increased while the thermal conductivity decreased due to the increase in phonon scattering. The maximum figure of merit obtained was 0.63 at 440 K for the undoped Bi 2 Te 2.4 Se 0.6 solid solution.

  13. Reassignment of oxygen-related defects in CdTe and CdSe

    Energy Technology Data Exchange (ETDEWEB)

    Bastin, Dirk

    2015-05-22

    This thesis reassigns the O{sub Te}-V{sub Cd} complex in CdTe and the O{sub Se}-V{sub Cd} complex in CdSe to a sulfur-dioxygen complex SO{sub 2}*, and the O{sub Cd} defect in CdSe to a V{sub Cd}H{sub 2} complex using Fourier transformed infrared absorption spectroscopy. The publications of the previous complexes were investigated by theoreticians who performed first-principle calculations of theses complexes. The theoreticians ruled out the assignments and proposed alternative defects, instead. The discrepancy between the experimentally obtained and theoretically proposed defects was the motivation of this work. Two local vibrational modes located at 1096.8 (ν{sub 1}) and 1108.3 cm{sup -1} (ν{sub 2}) previously assigned to an O{sub Te}-V{sub Cd} complex are detected in CdTe single crystals doped with CdSO{sub 4} powder. Five weaker additional absorption lines accompanying ν{sub 1} and ν{sub 2} could be detected. The relative intensities of the absorption lines match a sulfur-dioxygen complex SO{sub 2}* having two configurations labeled ν{sub 1} and ν{sub 2}. A binding energy difference of 0.5±0.1 meV between the two configurations and an energy barrier of 53±4 meV separating the two configurations are determined. Uniaxial stress applied to the crystal leads to a splitting of the absorption lines which corresponds to an orthorhombic and monoclinic symmetry for ν{sub 1} and ν{sub 2}, respectively. In virgin and oxygen-doped CdSe single crystals, three local vibrational modes located at 1094.1 (γ{sub 1}), 1107.5 (γ{sub 2}), and 1126.3 cm{sup -1} (γ{sub 3}) previously attributed to an O{sub Se}-V{sub Cd} complex could be observed. The signals are accompanied by five weaker additional absorption features in their vicinity. The additional absorption lines are identified as isotope satellites of a sulfur-dioxygen complex SO{sub 2}* having three configurations γ{sub 1}, γ{sub 2}, and γ{sub 3}. IR absorption measurements with uniaxial stress applied to the

  14. The Structural, Dielectric, Lattice Dynamical and Thermodynamic Properties of Zinc-Blende CdX (X=S, Se, Te) from First-Principles Analysis

    International Nuclear Information System (INIS)

    Feng Shi-Quan; Li Jun-Yu; Cheng Xin-Lu

    2015-01-01

    The structural, dielectric, lattice dynamical and thermodynamic properties of zinc-blende CdX (X=S, Se, Te) are studied by using a plane-wave pseudopotential method within the density-functional theory. Our calculated lattice constants and bulk modulus are compared with the published experimental and theoretical data. In addition, the Born effective charges, electronic dielectric tensors, phonon frequencies, and longitudinal optical-transverse optical splitting are calculated by the linear-response approach. Some of the characteristics of the phonon-dispersion curves for zinc-blende CdX (X=S, Se, Te) are summarized. What is more, based on the lattice dynamical properties, we investigate the thermodynamic properties of CdX (X=S, Se, Te) and analyze the temperature dependences of the Helmholtz free energy F, the internal energy E, the entropy S and the constant-volume specific heat C_v. The results show that the heat capacities for CdTe, CdSe, and CdS approach approximately to the Petit-Dulong limit 6R. (paper)

  15. Physical reasons of emission transformation in infrared CdSeTe/ZnS quantum dots at bioconjugation

    Science.gov (United States)

    Torchynska, T. V.

    2015-04-01

    The core/shell CdSeTe/ZnS quantum dots (QDs) with emission at 780-800 nm (1.55-1.60 eV) have been studied by means of photoluminescence (PL) and Raman scattering methods in the nonconjugated state and after conjugation to different antibodies (Ab): (i) mouse monoclonal [8C9] human papilloma virus Ab, anti-HPV 16-E7 Ab, (ii) mouse monoclonal [C1P5] human papilloma virus HPV16 E6+HPV18 E6 Ab, and (iii) pseudo rabies virus (PRV) Ab. The transformations of PL and Raman scattering spectra of QDs, stimulated by conjugated antibodies, have been revealed and discussed. The energy band diagram of core/shell CdSeTe/ZnS QDs has been designed that helps to analyze the PL spectra and their transformations at the bioconjugation. It is shown that the core in CdSeTe/ZnS QDs is complex and including the type II quantum well. The last fact permits to explain the nature of infrared (IR) optical transitions (1.55-1.60 eV) and the high energy PL band (1.88-1.94 eV) in the nonconjugated and bioconjugated QDs. A set of physical reasons has been analyzed with the aim to explain the transformation of PL spectra in bioconjugated QDs. Finally it is shown that two factors are responsible for the PL spectrum transformation at bioconjugation to charged antibodies: (i) the change of energy band profile in QDs and (ii) the shift of QD energy levels in the strong quantum confinement case. The effect of PL spectrum transformation is useful for the study of QD bioconjugation to specific antibodies and can be a powerful technique for early medical diagnostics.

  16. Electrodeposition and characterization of CdSe x-Te 1- x semiconducting thin films

    Science.gov (United States)

    Benamar, E.; Rami, M.; Fahoume, M.; Chraibi, F.; Ennaoui, A.

    1999-07-01

    Thin polycrystalline films of cadmium chalcogenides CdSe xTe 1-x ( 0 ≤ x ≤ 1) have been prepared by electrochemical plating on ITO (indium tin oxide) coated glass substrates from an acid sulfate solution at 90 °C. Structural, morphological and compositional studies of the deposited films are reported as a function of the x coefficient. XRD analysis shows that all deposits have a cubic structure with a preferred orientation along the (111) direction. The composition in the films is found to vary linearly with the composition in the solution. The increase in the selenium content x in the CdSe xTe 1-x films decreases the lattice constant and increases the band gap. Nevertheless this latter presents a minimum for x = 0.27.

  17. Influence of gamma-irradiation on the electroluminescence of ZnSe:Zn,Te crystals

    International Nuclear Information System (INIS)

    Elmuratova, D.B.; Ibragimova, E.M.

    2007-01-01

    Effect of 60 Co gamma-radiation at the dose rate of 10 Gy/s on electroluminescence (El)Zn Se crystals with 0.5 weight % Te treated in zinc vapor was studied for possible manufacturing of light emitting structures. Broad El band with the maximum at 610 nm is excited in the origin samples at a voltage above 15 V. After irradiation to the high dose of 10 6 Gy the El intensity grows by ∼2.5 times in the direct polarity at 24 V. The observed El of Zn Se:Zn,Te single crystals is assumed to be caused by the charge carrier recombination at the interstitial zinc centers by the excitation mechanism of a barrier sub breakdown type (authors)

  18. Weak Antilocalization in Bi 2 (Se x Te 1– x ) 3 Nanoribbons and Nanoplates

    KAUST Repository

    Cha, Judy J.; Kong, Desheng; Hong, Seung-Sae; Analytis, James G.; Lai, Keji; Cui, Yi

    2012-01-01

    Studying the surface states of Bi 2Se 3 and Bi 2Te 3 topological insulators has proven challenging due to the high bulk carrier density that masks the surface states. Ternary compound Bi 2(Se xTe 1-x) 3 may present a solution to the current materials challenge by lowering the bulk carrier mobility significantly. Here, we synthesized Bi 2(Se xTe 1-x) 3 nanoribbons and nanoplates via vapor-liquid-solid and vapor-solid growth methods where the atomic ratio x was controlled by the molecular ratio of Bi 2Se 3 to Bi 2Te 3 in the source mixture and ranged between 0 and 1. For the whole range of x, the ternary nanostructures are single crystalline without phase segregation, and their carrier densities decrease with x. However, the lowest electron density is still high (∼10 19 cm -3) and the mobility low, suggesting that the majority of these carriers may come from impurity states. Despite the high carrier density, weak antilocalization (WAL) is clearly observed. Angle-dependent magnetoconductance study shows that an appropriate magnetic field range is critical to capture a true, two-dimensional (2D) WAL effect, and a fit to the 2D localization theory gives α of -0.97, suggesting its origin may be the topological surface states. The power law dependence of the dephasing length on temperature is ∼T -0.49 within the appropriate field range (∼0.3 T), again reflecting the 2D nature of the WAL. Careful analysis on WAL shows how the surface states and the bulk/impurity states may interact with each other. © 2012 American Chemical Society.

  19. Weak Antilocalization in Bi 2 (Se x Te 1– x ) 3 Nanoribbons and Nanoplates

    KAUST Repository

    Cha, Judy J.

    2012-02-08

    Studying the surface states of Bi 2Se 3 and Bi 2Te 3 topological insulators has proven challenging due to the high bulk carrier density that masks the surface states. Ternary compound Bi 2(Se xTe 1-x) 3 may present a solution to the current materials challenge by lowering the bulk carrier mobility significantly. Here, we synthesized Bi 2(Se xTe 1-x) 3 nanoribbons and nanoplates via vapor-liquid-solid and vapor-solid growth methods where the atomic ratio x was controlled by the molecular ratio of Bi 2Se 3 to Bi 2Te 3 in the source mixture and ranged between 0 and 1. For the whole range of x, the ternary nanostructures are single crystalline without phase segregation, and their carrier densities decrease with x. However, the lowest electron density is still high (∼10 19 cm -3) and the mobility low, suggesting that the majority of these carriers may come from impurity states. Despite the high carrier density, weak antilocalization (WAL) is clearly observed. Angle-dependent magnetoconductance study shows that an appropriate magnetic field range is critical to capture a true, two-dimensional (2D) WAL effect, and a fit to the 2D localization theory gives α of -0.97, suggesting its origin may be the topological surface states. The power law dependence of the dephasing length on temperature is ∼T -0.49 within the appropriate field range (∼0.3 T), again reflecting the 2D nature of the WAL. Careful analysis on WAL shows how the surface states and the bulk/impurity states may interact with each other. © 2012 American Chemical Society.

  20. Electrochemical synthesis of photosensitive nano-nest like CdSe{sub 0.6}Te{sub 0.4} thin films

    Energy Technology Data Exchange (ETDEWEB)

    Shinde, Surendra K., E-mail: surendrashinde.phy@gmail.com [Holography and Material Research Laboratory, Department of Physics, Shivaji University, Kolhapur 416004, M.S (India); Thombare, Jagannath V. [Holography and Material Research Laboratory, Department of Physics, Shivaji University, Kolhapur 416004, M.S (India); Dubal, Deepak P. [Department of Electrochemistry, Technische Universität Chemnitz Institut für Chemie, Straße der Nationen 62, D-09111 Chemnitz (Germany); Fulari, Vijay J., E-mail: vijayfulari@gmail.com [Holography and Material Research Laboratory, Department of Physics, Shivaji University, Kolhapur 416004, M.S (India)

    2013-10-01

    Polycrystalline CdSe{sub 0.6}Te{sub 0.4} thin films were deposited on stainless steel and ITO coated glass (ITO) substrates by using simple and inexpensive electrodeposition method. CdSe{sub 0.6} Te{sub 0.4} films are characterized by different characterization techniques such as X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FTIR) and contact angle measurement. The X-ray diffraction analysis shows that the films are polycrystalline with hexagonal crystal structure. FE-SEM studies reveal that the entire substrate surface is covered with CdSe{sub 0.6} Te{sub 0.4} nano-nest. Formation of CdSe{sub 0.6}Te{sub 0.4} compound was confirmed from the FTIR studies. Optical absorption study shows the presence of direct transition and a considerable band gap, E{sub g} = 1.7 eV. Surface wettability with solid–liquid interface showed hydrophilic nature with water contact angle 57° (<90°). Further photovoltaic activity of CdSe{sub 0.6}Te{sub 0.4} films were studied by forming the photoelectrochemical cell having CdSe{sub 0.6}Te{sub 0.4}/1 M (Na{sub 2}S + S + NaOH)/C cell configuration. The efficiency and fill factor of these PEC cells are found to be 0.64% and 0.49 respectively.

  1. The lunar core can be a major reservoir for volatile elements S, Se, Te and Sb.

    Science.gov (United States)

    Steenstra, Edgar S; Lin, Yanhao; Dankers, Dian; Rai, Nachiketa; Berndt, Jasper; Matveev, Sergei; van Westrenen, Wim

    2017-11-06

    The Moon bears a striking compositional and isotopic resemblance to the bulk silicate Earth (BSE) for many elements, but is considered highly depleted in many volatile elements compared to BSE due to high-temperature volatile loss from Moon-forming materials in the Moon-forming giant impact and/or due to evaporative loss during subsequent magmatism on the Moon. Here, we use high-pressure metal-silicate partitioning experiments to show that the observed low concentrations of volatile elements sulfur (S), selenium (Se), tellurium (Te), and antimony (Sb) in the silicate Moon can instead reflect core-mantle equilibration in a largely to fully molten Moon. When incorporating the core as a reservoir for these elements, their bulk Moon concentrations are similar to those in the present-day bulk silicate Earth. This suggests that Moon formation was not accompanied by major loss of S, Se, Te, Sb from Moon-forming materials, consistent with recent indications from lunar carbon and S isotopic compositions of primitive lunar materials. This is in marked contrast with the losses of other volatile elements (e.g., K, Zn) during the Moon-forming event. This discrepancy may be related to distinctly different cosmochemical behavior of S, Se, Te and Sb within the proto-lunar disk, which is as of yet virtually unconstrained.

  2. Morphological and luminescent evolution of near-infrared-emitting CdTe{sub x}Se{sub 1-x} nanocrystals

    Energy Technology Data Exchange (ETDEWEB)

    Zhang Ruili; Yang Ping, E-mail: mse_yangp@ujn.edu.cn [University of Jinan, School of Material Science and Engineering (China)

    2012-08-15

    A facile organic route has been developed to synthesize CdTe{sub x}Se{sub 1-x} nanocrystals (NCs) using stearic acid as a capping agent. Because of growth kinetics of CdTe and CdSe, the molar ratio of Te/Se enables CdTe{sub x}Se{sub 1-x} NCs with various morphologies. By increasing the Te/Se ratio, the morphology of the NCs can be adjusted from tetrahedron to tetrapod. This is ascribed to the energy difference between wurtzite and the zinc-blende structures, which determines the nucleation and growth processes of the NCs. The diameters of the branches of tetrapod were 4-6 nm and their lengths were 7-20 nm. The CdTe{sub x}Se{sub 1-x} NCs revealed near-infrared (NIR) range (700-800 nm) photoluminescence (PL). The PL properties of the resulting NCs are strongly dependent on preparation conditions such as the molar ratio of Te/Se as well as the reaction temperature and time. In the cases of various reaction temperature (120-260 Degree-Sign C), the NCs revealed adjusted PL peak wavelength from visible to NIR range and narrow PL spectra. In addition, even though a high Te/Se molar ratio (0.67) was used, the CdTe{sub x}Se{sub 1-x} NCs revealed improved stability compared with CdTe NCs. Being coated with a composite Cd{sub y}Zn{sub 1-y}S shell, the PL intensity was drastically enhanced. The approach described here is utilizable to the fabrication of other semiconductor NCs with various morphologies. Because of the adjusted morphologies, tunable NIR range emission, and high stability of these composite NCs, we will focus on their applications such as solar cell and biolabeling.

  3. Nonlinear optical characteristics of monolayer MoSe{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Le, Chinh Tam; Ullah, Farman; Senthilkumar, Velusamy; Kim, Yong Soo [Department of Physics and Energy Harvest Storage Research Center, University of Ulsan (Korea, Republic of); Clark, Daniel J.; Jang, Joon I. [Department of Physics, Applied Physics and Astronomy, Binghamton University, Binghamton, NY (United States); Sim, Yumin; Seong, Maeng-Je [Department of Physics, Chung-Ang University, Seoul (Korea, Republic of); Chung, Koo-Hyun [School of Mechanical Engineering, University of Ulsan (Korea, Republic of); Park, Hyoyeol [Electronics, Communication and Semiconductor Applications Department, Ulsan College (Korea, Republic of)

    2016-08-15

    In this study, we utilized picosecond pulses from an Nd:YAG laser to investigate the nonlinear optical characteristics of monolayer MoSe{sub 2}. Two-step growth involving the selenization of pulsed-laser-deposited MoO{sub 3} film was employed to yield the MoSe{sub 2} monolayer on a SiO{sub 2}/Si substrate. Raman scattering, photoluminescence (PL) spectroscopy, and atomic force microscopy verified the high optical quality of the monolayer. The second-order susceptibility χ{sup (2)} was calculated to be ∝50 pm V{sup -1} at the second harmonic wavelength λ{sub SHG} ∝810 nm, which is near the optical gap of the monolayer. Interestingly, our wavelength-dependent second harmonic scan can identify the bound excitonic states including negatively charged excitons much more efficiently, compared with the PL method at room temperature. Additionally, the MoSe{sub 2} monolayer exhibits a strong laser-induced damage threshold ∝16 GW cm{sup -2} under picosecond-pulse excitation{sub .} Our findings suggest that monolayer MoSe{sub 2} can be considered as a promising candidate for high-power, thin-film-based nonlinear optical devices and applications. (copyright 2016 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  4. Band structure and optical properties of sinusoidal superlattices: ZnSe1-xTex

    International Nuclear Information System (INIS)

    Yang, G.; Lee, S.; Furdyna, J. K.

    2000-01-01

    This paper examines the band structure and optical selection rules in superlattices with a sinusoidal potential profile. The analysis is motivated by the recent successful fabrication of high quality ZnSe 1-x Te x superlattices in which the composition x varies sinusoidally along the growth direction. Although the band alignment in the ZnSe 1-x Te x sinusoidal superlattices is staggered (type II), they exhibit unexpectedly strong photoluminescence, thus suggesting interesting optical behavior. The band structure of such sinusoidal superlattices is formulated in terms of the nearly-free-electron (NFE) approximation, in which the superlattice potential is treated as a perturbation. The resulting band structure is unique, characterized by a single minigap separating two wide, free-electron-like subbands for both electrons and holes. Interband selection rules are derived for optical transitions involving conduction and valence-band states at the superlattice Brillouin-zone center, and at the zone edge. A number of transitions are predicted due to wave-function mixing of different subband states. It should be noted that the zone-center and zone-edge transitions are especially easy to distinguish in these superlattices because of the large width of the respective subbands. The results of the NFE approximation are shown to hold surprisingly well over a wide range of parameters, particularly when the period of the superlattice is short. (c) 2000 The American Physical Society

  5. Optical nonlinear absorption characteristics of Sb2Se3 nanoparticles

    Science.gov (United States)

    Muralikrishna, Molli; Kiran, Aditha Sai; Ravikanth, B.; Sowmendran, P.; Muthukumar, V. Sai; Venkataramaniah, Kamisetti

    2014-04-01

    In this work, we report for the first time, the nonlinear optical absorption properties of antimony selenide (Sb2Se3) nanoparticles synthesized through solvothermal route. X-ray diffraction results revealed the crystalline nature of the nanoparticles. Electron microscopy studies revealed that the nanoparticles are in the range of 10 - 40 nm. Elemental analysis was performed using EDAX. By employing open aperture z-scan technique, we have evaluated the effective two-photon absorption coefficient of Sb2Se3 nanoparticles to be 5e-10 m/W at 532 nm. These nanoparticles exhibit strong intensity dependent nonlinear optical absorption and hence could be considered to have optical power limiting applications in the visible range.

  6. Optics of colloidal quantum-confined CdSe nanoscrolls

    Energy Technology Data Exchange (ETDEWEB)

    Vasiliev, R B; Sokolikova, M S [M. V. Lomonosov Moscow State University, Moscow (Russian Federation); Vitukhnovskii, A G; Ambrozevich, S A; Selyukov, A S; Lebedev, V S [P N Lebedev Physics Institute, Russian Academy of Sciences, Moscow (Russian Federation)

    2015-09-30

    Nanostructures in the form of 1.2-nm-thick colloidal CdSe nanoplatelets rolled into scrolls are investigated. The morphology of these scrolls is analysed and their basic geometric parameters are determined (diameter 29 nm, longitudinal size 100 – 150 nm) by TEM microscopy. Absorption and photoluminescence spectra of these objects are recorded, and the luminescence decay kinetics is studied. It is shown that the optical properties of CdSe nanoscrolls differ significantly from the properties of CdSe quantum dots and that these nanoscrolls are attractive for nanophotonic devices due to large oscillator strengths of the transition, small widths of excitonic peaks and short luminescence decay times. Nanoscrolls can be used to design hybrid organic–inorganic pure-color LEDs with a high luminescence quantum yield and low operating voltages. (optics and technology of nanostructures)

  7. Reactively sputtered TeOx optical recording media

    International Nuclear Information System (INIS)

    Di Giulio, M.; Manno, D.; Micocci, G.; Rella, R.; Rizzo, A.; Tepore, A.

    1987-01-01

    Telluriom suboxide (TeO x ) thin films have been obtained by R.F. reactive sputtering deposition by using a Te target and an Ar-O 2 gas mixture. This technique of preparation has been shown to be a valid method because it is possible to easily obtain films with desired characteristics by an appropriate selection of the deposition conditions. Different samples were prepared by changing both the R.F. power (80-300 Watt) and the oxygen concentration in the sputtering gas. The films were analyzed in order to study their optical characteristics and the morphology before and after heat treatment. In particular, transmissivity and reflectivity have been found to change markedly by thermal treatment and critical temperatures in the range 120-150 grades centigrade. This property makes these films suitable for optical recording with a low output power laser diode

  8. Inhomogeneities and superconductivity in poly-phase Fe-Se-Te systems

    Science.gov (United States)

    Hartwig, S.; Schäfer, N.; Schulze, M.; Landsgesell, S.; Abou-Ras, D.; Blum, Ch. G. F.; Wurmehl, S.; Sokolowski, A.; Büchner, B.; Prokeš, K.

    2018-02-01

    The impact of synthesis conditions, post-preparation heating procedure, aging and influence of pressure on the superconducting properties of FeSe0.4Te0.6 crystals is reported. Two FeSe0.4Te0.6 single crystals were used in the study, prepared from stoichiometric melt but cooled down with very different cooling rates, and investigated using magnetic bulk and electrical-resistivity methods. The fast-cooled crystal contains large inclusions of Fe3Se2.1Te1.8 and exhibits bulk superconductivity in its as-prepared state, while the other is homogeneous and shows only traces of superconductivity. AC susceptibility measurements under hydrostatic pressure show that the superconducting transition temperature of the inhomogeneous crystal increases from 12.3 K at ambient pressure to Tsc = 17.9 K at 9 kbar. On the other hand, neither pressure nor mechanically-induced stress is sufficient to induce superconductivity in the homogeneous crystal. However, an additional heat treatment at 673 K followed by fast cooling down and/or long-term aging at ambient conditions leads to the appearance of bulk superconductivity also in the latter sample. This sample remains homogeneous on a scale down to few μm but shows an additional magnetic phase transition around 130 K suggesting that it must be inhomogeneous. For comparison also Fe3Se2.1Te1.8 polycrystals have been prepared and their magnetic properties have been studied. It appears that this phase is not superconducting by itself. It is concluded that nano-scale inhomogeneities that appear in the FeSexTe1-x system due to a spinodal decomposition in the solid state are necessary for bulk superconductivity, possibly due to minor changes in the crystal structure and microstructure. Macroscopic inclusions quenched by fast cooling from high temperatures lead obviously to strain and hence variations in the lattice constants, an effect that is further supported by application of pressure/stress.

  9. Optical studies of CdSe/PVA nanocomposite films

    Science.gov (United States)

    Kushwaha, Kamal Kumar; Ramrakhaini, Meera

    2018-05-01

    The nanocomposite films of CdSe nanocrystals in polyvinyl alcohol (PVA) matrix were synthesized by environmental friendly chemical method. These composites were characterized by X-ray diffraction which indicates the hexagonal crystalline structure of CdSe with crystal size up to a few nm. The crystal size is found to decrease by increasing PVA Concentration. The photoluminescence (PL) characteristics of these composite films with varying concentration of PVA as well as Cd2+ content have been investigated. The PL peak of CdSe was observed at 510 nm and higher intensity is observed by increasing PVA concentration without any change in position of PL peak. Due to proper passivation of surface states non-radiative transition are reduced which enhance the PL intensity. By increasing concentration of Cd2+ content in the CdSe/PVA nanocomposite films, smaller CdSe nanocrystals were obtained giving higher intensity and blue shift in the PL peak due to enhanced oscillator strength and quantum confinement effect. The PL peak in green and blue region makes these composite films promising materials for optical display devices. The Refractive index of these composites was also measured at sodium line with the help of Abee's refractometer and was found in the range of 2.20-2.45. It is seen that refractive index varies with polymer concentration. This may be useful for their potential application in anti-reflection coating, display devices and optical sensors.

  10. Effect of adding Te to layered GaSe crystals to increase the van der Waals bonding force

    Science.gov (United States)

    Tanabe, Tadao; Zhao, Shu; Sato, Yohei; Oyama, Yutaka

    2017-10-01

    The interplanar binding strength of layered GaSe1-xTex crystals was directly measured using a tensile testing machine. The GaSe1-xTex crystals were grown by a low temperature liquid phase solution method under a controlled Se vapor pressure. The stoichiometry-controlled GaSe1-xTex crystal has the ɛ-polytype structure of GaSe, where the Te atoms are substituted for some of the Se atoms in the GaSe crystal. The effect of adding Te on the bonding strength between the GaSe layers was determined from direct measurements of the van der Waals bonding energy. The bonding energy was increased from 0.023 × 106 N/m2 for GaSe to 0.16 × 106 N/m2 for GaSe1-xTex (x = 0.106).

  11. Reassignment of oxygen-related defects in CdTe and CdSe

    International Nuclear Information System (INIS)

    Bastin, Dirk

    2015-01-01

    This thesis reassigns the O_T_e-V_C_d complex in CdTe and the O_S_e-V_C_d complex in CdSe to a sulfur-dioxygen complex SO_2*, and the O_C_d defect in CdSe to a V_C_dH_2 complex using Fourier transformed infrared absorption spectroscopy. The publications of the previous complexes were investigated by theoreticians who performed first-principle calculations of theses complexes. The theoreticians ruled out the assignments and proposed alternative defects, instead. The discrepancy between the experimentally obtained and theoretically proposed defects was the motivation of this work. Two local vibrational modes located at 1096.8 (ν_1) and 1108.3 cm"-"1 (ν_2) previously assigned to an O_T_e-V_C_d complex are detected in CdTe single crystals doped with CdSO_4 powder. Five weaker additional absorption lines accompanying ν_1 and ν_2 could be detected. The relative intensities of the absorption lines match a sulfur-dioxygen complex SO_2* having two configurations labeled ν_1 and ν_2. A binding energy difference of 0.5±0.1 meV between the two configurations and an energy barrier of 53±4 meV separating the two configurations are determined. Uniaxial stress applied to the crystal leads to a splitting of the absorption lines which corresponds to an orthorhombic and monoclinic symmetry for ν_1 and ν_2, respectively. In virgin and oxygen-doped CdSe single crystals, three local vibrational modes located at 1094.1 (γ_1), 1107.5 (γ_2), and 1126.3 cm"-"1 (γ_3) previously attributed to an O_S_e-V_C_d complex could be observed. The signals are accompanied by five weaker additional absorption features in their vicinity. The additional absorption lines are identified as isotope satellites of a sulfur-dioxygen complex SO_2* having three configurations γ_1, γ_2, and γ_3. IR absorption measurements with uniaxial stress applied to the CdSe crystal yield a monoclinic C_1_h symmetry for γ_1 and γ_2. The SO_2* complex is stable up to 600 C. This thesis assigns the ν-lines in

  12. Studies on Cd1Se0.6Te0.4 Thin Films by Spectroscopic and Diffractometer Characterization

    Directory of Open Access Journals (Sweden)

    Cliff Orori Mosiori

    2017-09-01

    Full Text Available Cadmium selenide tellurium is a compound containing cadmium, tellurium and selenium elements forming a combined solid. Hall measurements suggest that it is an n-type semiconductor. Related optical studies indicate that is transparent to infra-red radiation. Structural studies clearly show that it has a wurtzite, sphalerite crystalline forms. Cadmium is a toxic heavy metal, and selenium is only toxic in large amounts or doses. By this toxicity, cadmium selenide is a known to be carcinogen to humans; however, this does not stop investigating it for optoelectronic applications. Current research has narrowed down to investigating cadmium selenide when in the form of nanoparticles. Cadmium selenide finds applications has found applications in opto-electronic devices like laser diodes, biomedical imaging, nano-sensing, high-efficiency solar cells and thin-film transistors. By chemical bath deposition, Cd1Se0.6Te0.4 thin films were grown onto glass. Tellurium was gradually introduced as an impurity and its crystalline structure and optical properties were investigated by XRD and UV-VIS spectroscopy. The main Cd1Se0.6Te0.4/glass characteristics were correlated with the conditions of growing and post-growth treatment and it was found out that films were homogeneous films with controllable thickness onto the glass substrate and suitable for n-type “sandwich” heterostructures applications. Comparison of the intensities of equivalent reflexions provided a test for the internal consistency of the measurements. Equivalent reflexions in two specimens differed on average by 1.4 % and 0.6% from the mean measured intensity, attesting to the high internal consistency of measurements from extended-face crystals. By comparison from data obtained from all samples showed their average deviation from the mean to be 0.9 %.

  13. Symmetry and optical anisotropy in CdSe/ZnSe quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Kiessling, Tobias

    2009-10-29

    The material system of choice for the investigations performed in the frame of this Thesis were self-assembled CdSe/ZnSe QDs. The reason for this choice is twofold. First, CdSe/ZnSe QDs can be grown with excellent optical quality, which is a prerequiste for optical studies. Second, due to the polar nature of II-VI compound semiconductors, optical anisotropies induced by various asymmetries are more pronounced than in their IIIV or element IV counterparts. Unlike in the III-V materials, where the self-organization of QDs is well described by the Stranski-Krastanow growth mode, the peculiarities of the QD formation are not entirely clear in II-VI alloys. For the purposes of the current work QDs emerging from two variants of Molecular Beam Epitaxy (MBE) growth were studied. In order to establish a clear connection between the optically observed anisotropies and the growth induced asymmetries in the QDs we start out by summarizing all available structural and morphological studies that were performed on the resultant QDs, including x-ray diffraction, atomic force microscopy, high resolution transmission electron microscopy and resonant Raman scattering. Extensive investigations by Photoluminescence (PL) and Photoluminescence Excitation (PLE) spectroscopy hence detail the resultant electronic structure of excitons confined to the above QDs as well as their energy relaxation across the latter. We find that for these small-sized strongly confining QDs k-vector conservation is entirely relaxed, which enables interaction of the excitons with a continuum of phonons and explains fast and efficient exciton capture by the QDs, even for excitation conditions far above the ground state. We demonstrate how this provides an alternative fast relaxation channel to Auger-like electron-hole scattering, that may also explain fast hole relaxation and adds to the understanding of the absence of a phonon bottleneck in the energy relaxation in these type of QDs. With the above analysis as a

  14. Symmetry and optical anisotropy in CdSe/ZnSe quantum dots

    International Nuclear Information System (INIS)

    Kiessling, Tobias

    2009-01-01

    The material system of choice for the investigations performed in the frame of this Thesis were self-assembled CdSe/ZnSe QDs. The reason for this choice is twofold. First, CdSe/ZnSe QDs can be grown with excellent optical quality, which is a prerequiste for optical studies. Second, due to the polar nature of II-VI compound semiconductors, optical anisotropies induced by various asymmetries are more pronounced than in their IIIV or element IV counterparts. Unlike in the III-V materials, where the self-organization of QDs is well described by the Stranski-Krastanow growth mode, the peculiarities of the QD formation are not entirely clear in II-VI alloys. For the purposes of the current work QDs emerging from two variants of Molecular Beam Epitaxy (MBE) growth were studied. In order to establish a clear connection between the optically observed anisotropies and the growth induced asymmetries in the QDs we start out by summarizing all available structural and morphological studies that were performed on the resultant QDs, including x-ray diffraction, atomic force microscopy, high resolution transmission electron microscopy and resonant Raman scattering. Extensive investigations by Photoluminescence (PL) and Photoluminescence Excitation (PLE) spectroscopy hence detail the resultant electronic structure of excitons confined to the above QDs as well as their energy relaxation across the latter. We find that for these small-sized strongly confining QDs k-vector conservation is entirely relaxed, which enables interaction of the excitons with a continuum of phonons and explains fast and efficient exciton capture by the QDs, even for excitation conditions far above the ground state. We demonstrate how this provides an alternative fast relaxation channel to Auger-like electron-hole scattering, that may also explain fast hole relaxation and adds to the understanding of the absence of a phonon bottleneck in the energy relaxation in these type of QDs. With the above analysis as a

  15. Short-range order parameters in amorphous YBaS4X7(X-S, SE, TE) films

    International Nuclear Information System (INIS)

    Hajiyev, E.S.

    2005-01-01

    Full text : Electron scattering intensity curves from amorphous YbAs 4 X 7 (X-S, SE, TE) films have ben obtained by the transmission electron diffraction (TED) method with rotation sector before screen up. The energy of electrons was 100 keV. Amorphous samples were crystallized and the composition of the products were measured by TED. The atomic radial distribution function has been calculated by the Fourier synthesis of intensities in the TED of amorphous YbAs 4 X 7 (X-S, SE, TE) films. The interatomic average distances of As - S (Se, Te) and As-Yb + 2 and partial coordination numbers have been estimated in these thilms. Based on these numbers, chemical orders in these films differ. This difference is due to differing topological order in the amorphous YbAs 4 X 7 (X-S, SE, TE) films

  16. Magneto-optical imaging of polycrystalline FeTe1-xSex prepared at various conditions

    International Nuclear Information System (INIS)

    Ding, Q.; Taen, T.; Mohan, S.; Nakajima, Y.; Tamegai, T.

    2011-01-01

    High-quality FeTe 1-x Se x polycrystals with T c ∼ 14 K were prepared by sintering at different temperatures. Intragranular critical current density of FeTe 1-x Se x polycrystals estimated from M-H curve is 5 x 10 4 A/cm 2 at 5 K under zero field. The observed intragranular J c value was confirmed by the magneto-optical images in the remanent state. The weak-link feature of FeTe 1-x Se x polycrystals is also revealed through magneto-optical imaging. We have prepared high-quality polycrystalline FeTe 1-x Se x by sintering at different temperatures and characterized their structural and magnetic properties with X-ray diffraction, magnetization measurements, and magneto-optical imaging. The intragranular J c was estimated to be 5 x 10 4 A/cm 2 , which is smaller than the single crystal, but still in the range for practical applications.

  17. Signatures of charge inhomogeneities in the infrared spectra of topological insulators Bi2Se3, Bi2Te3 and Sb2Te3

    International Nuclear Information System (INIS)

    Dordevic, S V; Wolf, M S; Stojilovic, N; Lei Hechang; Petrovic, C

    2013-01-01

    We present the results of an infrared spectroscopy study of topological insulators Bi 2 Se 3 , Bi 2 Te 3 and Sb 2 Te 3 . Reflectance spectra of all three materials look similar, with a well defined plasma edge. However, there are some important differences. Most notably, as temperature decreases the plasma edge shifts to lower frequencies in Bi 2 Se 3 , whereas in Bi 2 Te 3 and Sb 2 Te 3 it shifts to higher frequencies. In the loss function spectra we identify asymmetric broadening of the plasmon, and assign it to the presence of charge inhomogeneities. It remains to be seen if charge inhomogeneities are characteristic of all topological insulators, and whether they are of intrinsic or extrinsic nature.

  18. Neutron Activation Resonance Integrals of 74Se, 78Se, 80Se, 81Br, 127I, 130Te, 138Ba, 140Ce, and 142Ce

    International Nuclear Information System (INIS)

    Ricabarra, M. D.; Turjanskl, R.; Ricabarra, G. H.; Bigham, C.B.

    1968-01-01

    A lithium-drift germanium γ-ray spectrometer has been used to make accurate intercomparisons of the ratio of resonance-integral to thermal-activation cross section by measuring cadmium ratios or relative activation rates in two different neutron spectra. The standard, gold, or secondary standard, indium, was mixed uniformly in the samples and the activities resolved with the spectrometer. Expressed as Westcott S 0 values, the results relative to S 0 = 17.7 for gold were as follows: 74 Se = 10.3 +± 0.1, 78 Se = 12.3 ± 0.3, 80 Sc = 2.65 ± 0.02, 81 Br = 24.3 ± 0.5, 127 I = 27.8 ± 0.5, 130 Te = 2.10 ± 0.07, 138 Ba = 0.649 ± 0.004, 140 Ce = 0.476 ± 0.003, 142 Ce = 0.865 ± 0.005. (author)

  19. Optical properties of thermally annealed CdZnSe/ZnSe quantum dots

    International Nuclear Information System (INIS)

    Margapoti, Emanuela

    2010-01-01

    To analyse the diffusion characteristics, photoluminescence (PL) spectroscopy has been carried out in extensive detail on single, as well as, ensembles of thermally annealed (TA) CdSe/ZnSe QDs. For a series of QD-ensembles, each annealed for t A = 30 s at temperatures from T A = 300-550 C, the change in the QD-composition has been calculated from the blue-shift of the exciton ground-state PL-emission, using a concentration function based on Fick's laws of diffusion. The diffusion length (L D ) and the activation energy (E A ) have been determined thereof. For the studied QDs, E A has been evaluated to be 2.2 eV. Additionally, TA results also in an enhancement of the PL-intensity and reduction of the full-width-at-half maximum (FWHM) of the spectra. This point towards an increased homogeneity of the QD-size and composition, and decrease in the concentration of defects around the QDs. For single CdSe/ZnSe QDs, TA has been varied from 100-240 C, in steps for 20 C, with t A kept fixed at 30 s. Finally, the evolution of the magneto-optic response with post-growth thermal annealing has been studied for both individual QDs and QD-ensembles. An external magnetic field, applied perpendicular to the plane of the QDs (Faraday configuration), results in Zeeman spin splitting of the ground exciton state. The emissions from the Zeeman-split states are left and right circularly polarized and from the degree of circular polarization (DCP), as well as, the spectral separation of the PL-peaks, the g-factor can be estimated. For CdSe/ZnSe QD-ensembles, the g-factor has been observed to change sign with TA. (orig.).

  20. Optical properties of thermally annealed CdZnSe/ZnSe quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Margapoti, Emanuela

    2010-07-01

    To analyse the diffusion characteristics, photoluminescence (PL) spectroscopy has been carried out in extensive detail on single, as well as, ensembles of thermally annealed (TA) CdSe/ZnSe QDs. For a series of QD-ensembles, each annealed for t{sub A} = 30 s at temperatures from T{sub A} = 300-550 C, the change in the QD-composition has been calculated from the blue-shift of the exciton ground-state PL-emission, using a concentration function based on Fick's laws of diffusion. The diffusion length (L{sub D}) and the activation energy (E{sub A}) have been determined thereof. For the studied QDs, E{sub A} has been evaluated to be 2.2 eV. Additionally, TA results also in an enhancement of the PL-intensity and reduction of the full-width-at-half maximum (FWHM) of the spectra. This point towards an increased homogeneity of the QD-size and composition, and decrease in the concentration of defects around the QDs. For single CdSe/ZnSe QDs, TA has been varied from 100-240 C, in steps for 20 C, with t{sub A} kept fixed at 30 s. Finally, the evolution of the magneto-optic response with post-growth thermal annealing has been studied for both individual QDs and QD-ensembles. An external magnetic field, applied perpendicular to the plane of the QDs (Faraday configuration), results in Zeeman spin splitting of the ground exciton state. The emissions from the Zeeman-split states are left and right circularly polarized and from the degree of circular polarization (DCP), as well as, the spectral separation of the PL-peaks, the g-factor can be estimated. For CdSe/ZnSe QD-ensembles, the g-factor has been observed to change sign with TA. (orig.).

  1. Large magnetoresistance and Fermi surface study of Sb2Se2Te single crystal

    Science.gov (United States)

    Shrestha, K.; Marinova, V.; Graf, D.; Lorenz, B.; Chu, C. W.

    2017-09-01

    We have studied the magnetotransport properties of a Sb2Se2Te single crystal. Magnetoresistance (MR) is maximum when the magnetic field is perpendicular to the sample surface and reaches a value of 1100% at B = 31 T with no sign of saturation. MR shows Shubnikov de Haas (SdH) oscillations above B = 15 T. The frequency spectrum of SdH oscillations consists of three distinct peaks at α = 32 T, β = 80 T, and γ = 117 T indicating the presence of three Fermi surface pockets. Among these frequencies, β is the prominent peak in the frequency spectrum of SdH oscillations measured at different tilt angles of the sample with respect to the magnetic field. From the angle dependence β and Berry phase calculations, we have confirmed the trivial topology of the β-pocket. The cyclotron masses of charge carriers, obtained by using the Lifshitz-Kosevich formula, are found to be mβ*=0.16mo and m γ*=0.63 mo for the β and γ bands, respectively. The Large MR of Sb2Se2Te is suitable for utilization in electronic instruments such as computer hard discs, high field magnetic sensors, and memory devices.

  2. Density functional study of BiSbTeSe{sub 2} topological insulator thin films

    Energy Technology Data Exchange (ETDEWEB)

    Mohammadpourrad, Zahra; Abolhassani, Mohammadreza [Department of Physics, Science and Research Branch, Islamic Azad University, Tehran (Iran, Islamic Republic of)

    2017-08-15

    In this work, using density functional theory calculations, we have investigated the band topology of bulk BiSbTeSe{sub 2} and its thin film electronic properties in several thicknesses. It is one member of the quaternary compounds Bi{sub 2-x}Sb{sub x}Te{sub 3-y}Se{sub y} (BSTS) with the best intrinsic bulk insulating behavior. Based on our calculations we have found that a band inversion at Γ-point is induced when spin-orbit coupling is turned on, with an energy gap of about 0.318 eV. The film thickness has an effect on the surface states such that a gap opens at Dirac point in 6 quintuple-layers film and with decrease in thickness, the magnitude of the gap increases. The atomic contributions have been mapped out for the first few layers of thin films to demonstrate the surface states. The relative charge density has been calculated layer-wise and the penetration depth of the surface states into the bulk region is found to be about 2.5-3.5 quintuple layers, depending on the termination species of thin films. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  3. NIR-Emitting Alloyed CdTeSe QDs and Organic Dye Assemblies: A Nontoxic, Stable, and Efficient FRET System

    Directory of Open Access Journals (Sweden)

    Doris E. Ramírez-Herrera

    2018-04-01

    Full Text Available In the present work, we synthesize Near Infrared (NIR-emitting alloyed mercaptopropionic acid (MPA-capped CdTeSe quantum dots (QDs in a single-step one-hour process, without the use of an inert atmosphere or any pyrophoric ligands. The quantum dots are water soluble, non-toxic, and highly photostable and have high quantum yields (QYs up to 84%. The alloyed MPA-capped CdTeSe QDs exhibit a red-shifted emission, whose color can be tuned between visible and NIR regions (608–750 nm by controlling the Te:Se molar ratio in the precursor mixtures and/or changing the time reaction. The MPA-capped QDs were characterized by UV-visible absorption spectroscopy, fluorescence spectroscopy, transmission electron microscopy (TEM, energy dispersive X-ray spectroscopy (EDS, and zeta potential measurements. Photostability studies were performed by irradiating the QDs with a high-power xenon lamp. The ternary MPA-CdTeSe QDs showed greater photostability than the corresponding binary MPA-CdTe QDs. We report the Förster resonance energy transfer (FRET from the MPA-capped CdTeSe QDs as energy donors and Cyanine5 NHS-ester (Cy5 dye as an energy acceptor with efficiency (E up to 95%. The distance between the QDs and dye (r, the Förster distance (R0, and the binding constant (K are reported. Additionally, cytocompatibility and cell internalization experiments conducted on human cancer cells (HeLa cells revealed that alloyed MPA-capped CdTeSe QDs are more cytocompatible than MPA-capped CdTe QDs and are capable of ordering homogeneously all over the cytoplasm, which allows their use as potential safe, green donors for biological FRET applications.

  4. Optically detected SdH oscillations in CdTe/(CdMg)Te and CdTe/(CdMnMg)Te modulation doped quantum wells

    International Nuclear Information System (INIS)

    Shen, J.X.; Ossau, W.; Fischer, F.; Waag, A.; Landwehr, G.

    1995-01-01

    Oscillations of photoluminescence properties in external magnetic fields are investigated in CdTe modulation doped quantum wells. The oscillatory behaviour of the luminescence intensity, the line width and the g factor is due to many-body effects in the 2-dimensional electron gas. The oscillation of photoluminescence intensity can be easily used as optically detected Shubnikov de Haas effect to determine the electron concentration in quantum wells without contacts. (author)

  5. Optically detected SdH oscillations in CdTe/(CdMg)Te and CdTe/(CdMnMg)Te modulation doped quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Shen, J.X.; Ossau, W.; Fischer, F.; Waag, A.; Landwehr, G. [Physikalisches Institut der Uniwersitaet Wuerzburg, Wuerzburg (Germany)

    1995-12-31

    Oscillations of photoluminescence properties in external magnetic fields are investigated in CdTe modulation doped quantum wells. The oscillatory behaviour of the luminescence intensity, the line width and the g factor is due to many-body effects in the 2-dimensional electron gas. The oscillation of photoluminescence intensity can be easily used as optically detected Shubnikov de Haas effect to determine the electron concentration in quantum wells without contacts. (author). 5 refs, 3 figs, 1 tab.

  6. Peculiarity of electron optical orientation in Hg1-xMnxTe and Hg1-xCdxTe alloys

    International Nuclear Information System (INIS)

    Georgitseh, E.I.; Ivanov-Omskij, V.I.; Pogorletskij, V.M.

    1991-01-01

    To clarify the effect of exchange interaction of electrons with manganese ions on electron spin relaxation, a study was made on optical orientation in Hg 1-x Mn x Te alloy and Hg 1-x Cd x Te alloys with similar parameters of energy spectrum at 4.2 K. It is shown that exchange interaction in semimagnetic Hg 1-x Mn x Te solutions, caused by the presence of manganese ions, reduced the time of spin relaxation. However, this reduction is not sufficient make optical orientation of electrons not observable

  7. Annealing effect on thermal conductivity and microhardness of carbon nanotube containing Se80Te16Cu4 glassy composites

    Science.gov (United States)

    Upadhyay, A. N.; Tiwari, R. S.; Singh, Kedar

    2018-02-01

    This study deals with the effect of thermal annealing on structural/microstructural, thermal and mechanical behavior of pristine Se80Te16Cu4 and carbon nanotubes (CNTs) containing Se80Te16Cu4 glassy composites. Pristine Se80Te16Cu4, 3 and 5 wt%CNTs-Se80Te16Cu4 glassy composites are annealed in the vicinity of glass transition temperature to onset crystallization temperature (340-380 K). X-ray diffraction (XRD) pattern revealed formation of polycrystalline phases of hexagonal CuSe and trigonal selenium. The indexed d-values in XRD patterns are in well conformity with the d-values obtained after the indexing of the ring pattern of selected area electron diffraction pattern of TEM images. The SEM investigation exhibited that the grain size of the CNTs containing Se80Te16Cu4 glassy composites increased with increasing annealing temperature and decreased at further higher annealing temperature. Thermal conductivity, microhardness exhibited a substantial increase with increasing annealing temperature of 340-360 K and slightly decreases for 380 K. The variation of thermal conductivity and microhardness can be explained by cross-linking formation and voids reduction.

  8. Crystalline structure and XMCD studies of Co40Fe40B20 grown on Bi2Te3, BiTeI and Bi2Se3

    OpenAIRE

    Kaveev, A. K.; Sokolov, N. S.; Suturin, S. M.; Zhiltsov, N. S.; Golyashov, V. A.; Tereshchenko, O. E.; Prosvirin, I. P.; Kokh, K. A.; Sawada, M.

    2018-01-01

    Epitaxial films of Co40Fe40B20 (further - CoFeB) were grown on Bi2Te3(001) and Bi2Se3(001) substrates by laser molecular beam epitaxy (LMBE) technique at 200-400C. Bcc-type crystalline structure of CoFeB with (111) plane parallel to (001) plane of Bi2Te3 was observed, in contrast to polycrystalline CoFeB film formed on Bi2Se3(001) at RT using high-temperature seeding layer. Therefore, structurally ordered ferromagnetic thin films were obtained on the topological insulator surface for the firs...

  9. Topological insulators in Bi2Se3, Bi2Te3 and Sb2Te3 with a single Dirac cone on the surface

    Science.gov (United States)

    Zhang, Haijun; Liu, Chao-Xing; Qi, Xiao-Liang; Dai, Xi; Fang, Zhong; Zhang, Shou-Cheng

    2009-06-01

    Topological insulators are new states of quantum matter in which surface states residing in the bulk insulating gap of such systems are protected by time-reversal symmetry. The study of such states was originally inspired by the robustness to scattering of conducting edge states in quantum Hall systems. Recently, such analogies have resulted in the discovery of topologically protected states in two-dimensional and three-dimensional band insulators with large spin-orbit coupling. So far, the only known three-dimensional topological insulator is BixSb1-x, which is an alloy with complex surface states. Here, we present the results of first-principles electronic structure calculations of the layered, stoichiometric crystals Sb2Te3, Sb2Se3, Bi2Te3 and Bi2Se3. Our calculations predict that Sb2Te3, Bi2Te3 and Bi2Se3 are topological insulators, whereas Sb2Se3 is not. These topological insulators have robust and simple surface states consisting of a single Dirac cone at the Γ point. In addition, we predict that Bi2Se3 has a topologically non-trivial energy gap of 0.3eV, which is larger than the energy scale of room temperature. We further present a simple and unified continuum model that captures the salient topological features of this class of materials.

  10. Secondary overprinting of S-Se-Te signatures in the Earth's mantle: Implications for the Late Veneer

    Science.gov (United States)

    Koenig, S.; Luguet, A.; Lorand, J.; Pearson, D.

    2013-12-01

    Sulphur, Selenium and Tellurium are both chalcophile and highly siderophile elements (HSE) with near-chondritic ratios and absolute abundances in the terrestrial mantle that exceed those predicted by core-mantle differentiation[1]. These 'excess' HSE abundances have been attributed to addition of ca. 0.5% of chondrite-like material that hit the Earth in its accretionary stage between 4 to 3.8 billion years ago after core-mantle differentiation (Late Veneer[2]). Therefore, like other HSE, S, Se and Te are considered potential tracers for the composition of the Late Veneer, provided that their bulk silicate Earth abundances are properly constrained. In contrast to ca. 250 ppm S, Se and Te are ultra-trace elements in the terrestrial mantle. Like all HSE, they are furthermore controlled by base metal sulphides (BMS) and micrometric platinum group minerals (PGMs)[3]. This strong control exerted by the host mineralogy and petrology on the S-Se-Te systematics at both the micro-scale and the whole-rock scale makes detailed mineralogical and petrological studies of BMS and PGM a pre-requisite to fully understand and accurately interpret the whole-rock signatures. Here we combine in-situ sulphide data and detailed mineralogical observations with whole-rock S-Se-Te-HSE signatures of both lherzolites and harburgites from different geodynamic settings. We demonstrate that the near-chondritic Se and Te signature of 'fertile' mantle rocks (Se/Te ≈9×5) is not a primitive signature of the Earth's mantle, but rather reflects strong enrichment in metasomatic HSE host phases, which erased previous pristine signatures. Consequently, current attempts to identify a potential Late Veneer composition are seriously flawed because, neither refertilisation/metasomatism nor true melt depletion (e.g. harzburgitic residues) have been taken into account for the Primitive Upper Mantle composition estimate[4]. Our combined whole rock and in-situ sulphide data indicate a refertilisation trend

  11. Thermal analysis studies of Ge additive of Se-Te glasses

    International Nuclear Information System (INIS)

    Mohamed, M.; Abdel-Rahim, M.A.

    2016-01-01

    Ge x Se 50 Te 50-x (x= 5, 15, 20, 35 at.%) bulk glasses were synthesized by the melt quenching method. The amorphous nature of the investigated glasses was determined by X-ray diffraction. Results of differential scanning calorimetry (DSC) of the studied compositions under non-isothermal conditions were reported and discussed. The glass transition temperature (T g ), onset crystallization temperature (T c ), and crystallization peak temperature (T p ) were determined from DSC traces at different heating rates. It was found that the values of T g , T c , and T p rely on both composition and heating rate. A double crystallization stages were observed in the DSC results. Various kinetics parameters such as the glass transition energy (E g ), crystallization activation energy (E c ), and rate constant (K p ) were calculated. The glass-forming ability of the studied compositions was discussed as function of the determined kinetics parameters. (orig.)

  12. Polytypism in ZnS, ZnSe, and ZnTe: First-principles study

    KAUST Repository

    Boutaiba, F.; Belabbes, Abderrezak; Ferhat, M.; Bechstedt, F.

    2014-01-01

    We report results of first-principles calculations based on the projector augmented wave (PAW) method to explore the structural, thermodynamic, and electronic properties of cubic (3C) and hexagonal (6H, 4H, and 2H) polytypes of II-VI compounds: ZnS, ZnSe, and ZnTe. We find that the different bond stacking in II-VI polytypes remarkably influences the resulting physical properties. Furthermore, the degree of hexagonality is found to be useful to understand both the ground-state properties and the electronic structure of these compounds. The resulting lattice parameters, energetic stability, and characteristic band energies are in good agreement with available experimental data. Trends with hexagonality of the polytype are investigated.

  13. Polytypism in ZnS, ZnSe, and ZnTe: First-principles study

    KAUST Repository

    Boutaiba, F.

    2014-06-23

    We report results of first-principles calculations based on the projector augmented wave (PAW) method to explore the structural, thermodynamic, and electronic properties of cubic (3C) and hexagonal (6H, 4H, and 2H) polytypes of II-VI compounds: ZnS, ZnSe, and ZnTe. We find that the different bond stacking in II-VI polytypes remarkably influences the resulting physical properties. Furthermore, the degree of hexagonality is found to be useful to understand both the ground-state properties and the electronic structure of these compounds. The resulting lattice parameters, energetic stability, and characteristic band energies are in good agreement with available experimental data. Trends with hexagonality of the polytype are investigated.

  14. Photoconductivity of Se85-xTe15Hgx thin films

    International Nuclear Information System (INIS)

    Chaudhary, Neetu; Bahishti, Adam A.; Zulfequar, M.

    2012-01-01

    The photoconductive properties such as dark conductivity, steady state and transient characteristics of a-Se 85-x Te 15 Hg x thin films, prepared by thermal vacuum evaporation technique have been studied in the temperature range 312-380 K. Analysis of data shows that the activation energy of dark current is greater as compared to the activation energy of photocurrent. The activation energy increases at higher concentration of Hg which shows that the defect density of states decreases. Analysis of intensity dependent photoconductivity shows that the bimolecular recombination is predominant. The transient photoconductivity shows that the carrier lifetime decreases with the increase in Hg concentration and increases at higher concentration of Hg. This decrease is due to the transition trapping process. Further the photosensitivity and carrier lifetime increases at higher concentration of Hg which also confirms that the density of defect states decreases.

  15. Chalcogenidosilicates: Ba/sub 2/SiTe/sub 4/ and Ba/sub 2/SiSe/sub 4/

    Energy Technology Data Exchange (ETDEWEB)

    Brinkmann, C; Eisenmann, B; Schaefer, H [Technische Hochschule Darmstadt (Germany, F.R.). Fachbereich Anorganische Chemie und Kernchemie

    1985-05-01

    The new compounds Ba/sub 2/SiSe/sub 4/ and Ba/sub 2/SiTe/sub 4/ crystallize in the monoclinic system, space group: P2/sub 1//m (No. 11) with the lattice constants Ba/sub 2/SiSe/sub 4/: a = 918.4(5) pm, b = 703.3(3) pm, c = 687.2(3) pm, ..beta.. = 109.2(1)/sup 0/, Ba/sub 2/SiTe/sub 4/: a = 965.0(5) pm, b = 762.6(3) pm, c = 746.6(3) pm, ..beta.. = 108.9(1)/sup 0/. Both compounds are isotypic to the Sr/sub 2/GeS/sub 4/ structure. Ba/sub 2/SiTe/sub 4/ is the first o-telluridosilicate with discrete SiTe/sub 4//sup 4 -/ anions.

  16. Third-order nonlinear optical properties of GeSe2-Ga2Se3-PbI2 glasses

    International Nuclear Information System (INIS)

    Tang Gao; Liu Cunming; Luo Lan; Chen Wei

    2010-01-01

    The third-order nonlinear optical (NLO) properties of new selenium-based GeSe 2 -Ga 2 Se 3 -PbI 2 glasses have been measured using the optical Kerr effect (OKE) technique, with picosecond and femtosecond laser pulses. The 0.70GeSe 2 -0.15Ga 2 Se 3 -0.15PbI 2 glass has the largest third-order optical nonlinear susceptibility in GeSe 2 -Ga 2 Se 3 -PbI 2 glass system with χ (3) of 5.28x10 12 esu. In addition, the response time of glasses is sub-picosecond, which is predominantly associated with electron cloud. Local structure of the glasses has been identified by using Raman studies, while the origins of the observed nonlinear optical response are discussed. The [Ge(Ga)Se 4 ] tetrahedral and lone-pair electrons from highly polarizable Pb atom in glasses play an important role in enhanced NLO response. These results as well as their good chemical stability indicate that GeSe 2 -Ga 2 Se 3 -PbI 2 glasses are promising materials for photonic applications of third-order nonlinear optical signal processing.

  17. Isotopic equilibrium constants of the deuterium exchange between HDO and H2S, H2Se and H2Te

    International Nuclear Information System (INIS)

    Marx, D.

    1959-11-01

    We have determined experimentally the equilibrium constant K of each of the following isotope exchanges: SH 2 + OHD ↔ SHD + OH 2 ; SeH 2 + OHD ↔ SeHD + OH 2 ; TeH 2 + OHD ↔ TeHD + OH 2 . In gaseous phase, statistical thermodynamics leads to the expression: K (Z OHD x Z RH 2 )/(Z OH 2 x Z RHD ) x e W/T (R being the elements S, Se or Te). Z, the partition functions, have been calculated and, through our experimental results, the constant W has been determined. Having obtained W, the equilibrium constant K has been calculated for a series of temperatures. (author) [fr

  18. Structural and optical investigation of Te-based chalcogenide thin films

    Energy Technology Data Exchange (ETDEWEB)

    Sharma, Rita, E-mail: reetasharma2012@gmail.com; Sharma, Shaveta; Thangaraj, R.; Mian, M. [Semiconductors Laboratory, Department of Physics, GND University, Amritsar (India); Chander, Ravi [Applied Science Deptt. Govt. Polytechnic College Amritsar (India); Kumar, Praveen [Department of Physics, DAV University, Sarmastipur, Jalandhar-144012 (India)

    2015-05-15

    We report the structural and optical properties of thermally evaporated Bi{sub 2}Te{sub 3}, In{sub 2}Te{sub 3} and InBiTe{sub 3} films by using X-ray diffraction, optical and Raman Spectroscopy techniques. The as-prepared thin films were found to be Semi-crystalline by X-ray diffraction. Particle Size and Strain has been calculated from XRD data. The optical constants, film thickness, refractive index and optical band gap (E{sub g}) has been reported for In{sub 2}Te{sub 3}, InBiTe{sub 3} films. Raman Spectroscopy was performed to investigate the effect of Bi, In, on lattice vibration and chemical bonding in Te based chalcogenide glassy alloys.

  19. Phonons of single quintuple Bi 2 Te 3 and Bi 2 Se 3 films and bulk materials

    KAUST Repository

    Cheng, Wei; Ren, Shang-Fen

    2011-01-01

    Phonons of single quintuple films of Bi2Te3 and Bi2Se3 and corresponding bulk materials are calculated in detail by MedeA (a trademark of Materials Design) and Vienna ab initio simulation package (VASP). The calculated results with and without spin-orbit couplings are compared, and the important roles that the spin-orbit coupling plays in these materials are discussed. A symmetry breaking caused by the anharmonic potentials around Bi atoms in the single quintuple films is identified and discussed. The observed Raman intensity features in Bi 2Te3 and Bi2Se3 quintuple films are explained. © 2011 American Physical Society.

  20. Physicochemical properties of new As2Se3–Ag4SSe–CdTe glasses

    International Nuclear Information System (INIS)

    Aljihmani, Lilia; Vassilev, Venceslav; Hristova-Vasileva, Temenuga; Fidancevska, Emilija

    2009-01-01

    Chalcogenide glasses from the As 2 Se 3 –Ag 4 SSe–CdTe system were synthesized. The basic physicochemical parameters such as density (d), microhardness (HV) and the temperatures glass transition Tg were measured. Compactness (C) and some thermomechanical characteristics such as volume (Vh) and formation energy (Eh) of micro-voids in the glassy network, as well as the module of elasticity (E) were calculated. A correlation between the composition and properties of the As 2 Se 3 –Ag 4 SSe–CdTe glasses was established and comprehensively discussed. Keywords: chalcogenide glasses, density, microhardness, compactness, elasticity modulus, thermomechanical characteristics

  1. Millimeter wave absorption by confined acoustic modes in CdSe/CdTe core-shell quantum dots

    International Nuclear Information System (INIS)

    Liu, T-M; Lu, J-Y; Kuo, C-C; Wen, Y-C; Lai, C-W; Yang, M-J; Chou, P-T; Murray, D B; Saviot, L; Sun, C-Kuang

    2007-01-01

    Taking advantage of the specific core-shell charge separation structure in the CdSe/CdTe core-shell Type-II quantum dots (QDs), we experimentally observed the resonant-enhanced dipolar interaction between millimeter-wave (MMW) photons and their corresponding (l = 1) confined acoustic phonons. With proper choice of size, the absorption band can be tuned to desired frequency of MMW imaging. Exploiting this characteristic absorption, in a fiber-scanned MMW imaging system, we demonstrated the feasibility of CdSe/CdTe QDs as the contrast agents of MMW imaging

  2. Detection of current-induced spin polarization in BiSbTeSe{sub 2} toplogical insulator

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Fan; Ghatak, Subhamoy; Taskin, Alexey; Ando, Yoichi [Institute of Physics II, University of Cologne (Germany); Ando, Yuichiro [Department of Electronic Science and Engineering, Kyoto University (Japan)

    2016-07-01

    Topological insulators (TIs) are a class of quantum matter which possess spin-momentum-locked Dirac Fermions on the surfaces. Due to the spin-momentum locking, spin polarization will be induced when a charge current flows through the surface of a TI. Such spin polarization can be detected by using a ferromagnetic tunneling contact as a detector. In this talk, we present our results measured in devices fabricated from BiSbTeSe{sub 2} flakes. Spin signals were observed in both n-type and p-type BiSbTeSe{sub 2} samples.

  3. Phonons of single quintuple Bi 2 Te 3 and Bi 2 Se 3 films and bulk materials

    KAUST Repository

    Cheng, Wei

    2011-03-10

    Phonons of single quintuple films of Bi2Te3 and Bi2Se3 and corresponding bulk materials are calculated in detail by MedeA (a trademark of Materials Design) and Vienna ab initio simulation package (VASP). The calculated results with and without spin-orbit couplings are compared, and the important roles that the spin-orbit coupling plays in these materials are discussed. A symmetry breaking caused by the anharmonic potentials around Bi atoms in the single quintuple films is identified and discussed. The observed Raman intensity features in Bi 2Te3 and Bi2Se3 quintuple films are explained. © 2011 American Physical Society.

  4. A Micro-Raman Study of Exfoliated Few-Layered n-Type Bi2Te2.7Se0.3 (Postprint)

    Science.gov (United States)

    2017-11-28

    is feasible because the Bi-Te1 bond strength is the strongest bond in the quintuple20. In addition, the Te2 atom is known to lie at the inversion ...ii) mitigation of the bipolar effect in thermopower, and iii) a simultaneous reduction in the thermal conductivity, that led to the broadening of the...or Se-dopant at the Te sites (Te1 and Te2), where Te2 is the inversion center of the crystal symmetry (see Supplementary Fig. S1)33. As Se is

  5. High absorption coefficients of the CuSb(Se,Te2 and CuBi(S,Se2 alloys enable high-efficient 100 nm thin-film photovoltaics

    Directory of Open Access Journals (Sweden)

    Chen Rongzhen

    2017-01-01

    Full Text Available We demonstrate that the band-gap energies Eg of CuSb(Se,Te2 and CuBi(S,Se2 can be optimized for high energy conversion in very thin photovoltaic devices, and that the alloys then exhibit excellent optical properties, especially for tellurium rich CuSb(Se1−xTex2. This is explained by multi-valley band structure with flat energy dispersions, mainly due to the localized character of the Sb/Bi p-like conduction band states. Still the effective electron mass is reasonable small: mc ≈ 0.25m0 for CuSbTe2. The absorption coefficient α(ω for CuSb(Se1−xTex2 is at ħω = Eg + 1 eV as much as 5–7 times larger than α(ω for traditional thin-film absorber materials. Auger recombination does limit the efficiency if the carrier concentration becomes too high, and this effect needs to be suppressed. However with high absorptivity, the alloys can be utilized for extremely thin inorganic solar cells with the maximum efficiency ηmax ≈ 25% even for film thicknesses d ≈ 50 − 150 nm, and the efficiency increases to ∼30% if the Auger effect is diminished.

  6. High absorption coefficients of the CuSb(Se,Te)2 and CuBi(S,Se)2 alloys enable high-efficient 100 nm thin-film photovoltaics

    Science.gov (United States)

    Chen, Rongzhen; Persson, Clas

    2017-06-01

    We demonstrate that the band-gap energies Eg of CuSb(Se,Te)2 and CuBi(S,Se)2 can be optimized for high energy conversion in very thin photovoltaic devices, and that the alloys then exhibit excellent optical properties, especially for tellurium rich CuSb(Se1-xTex)2. This is explained by multi-valley band structure with flat energy dispersions, mainly due to the localized character of the Sb/Bi p-like conduction band states. Still the effective electron mass is reasonable small: mc ≈ 0.25m0 for CuSbTe2. The absorption coefficient α(ω) for CuSb(Se1-xTex)2 is at ħω = Eg + 1 eV as much as 5-7 times larger than α(ω) for traditional thin-film absorber materials. Auger recombination does limit the efficiency if the carrier concentration becomes too high, and this effect needs to be suppressed. However with high absorptivity, the alloys can be utilized for extremely thin inorganic solar cells with the maximum efficiency ηmax ≈ 25% even for film thicknesses d ≈ 50 - 150 nm, and the efficiency increases to ˜30% if the Auger effect is diminished.

  7. Highly Enhanced Fluorescence of CdSeTe Quantum Dots Coated with Polyanilines via In-Situ Polymerization and Cell Imaging Application.

    Science.gov (United States)

    Xue, Jingjing; Chen, Xinyi; Liu, Shanglin; Zheng, Fenfen; He, Li; Li, Lingling; Zhu, Jun-Jie

    2015-09-02

    The polyaniline (PAN)-coated CdSeTe quantum dots (QDs) were prepared by in situ polymerization of aniline on the surface of CdSeTe QDs. The PAN-coated CdSeTe QDs has a tremendously enhanced fluorescence (∼40 times) and improved biocompatibility compared to the uncoated CdSeTe QDs. The fluorescence intensity of the PAN-coated CdSeTe QDs can be adjusted by controlling the construction parameters of the PAN shell. The kinetics of the in situ controllable polymerization process was studied by varying the temperature, and the apparent activation energy of polymerization was estimated. With the same method, a series of the PAN derivatives were also tested to coat the CdSeTe QDs in this study. All the QDs showed a significant enhancement of the fluorescence intensity and better biocompatibility. The significantly enhanced fluorescence can provide highly amplified signal for luminescence-based cell imaging.

  8. Stellar laboratories . IX. New Se v, Sr iv-vii, Te vi, and I vi oscillator strengths and the Se, Sr, Te, and I abundances in the hot white dwarfs G191-B2B and RE 0503-289

    Science.gov (United States)

    Rauch, T.; Quinet, P.; Knörzer, M.; Hoyer, D.; Werner, K.; Kruk, J. W.; Demleitner, M.

    2017-10-01

    Context. To analyze spectra of hot stars, advanced non-local thermodynamic equilibrium (NLTE) model-atmosphere techniques are mandatory. Reliable atomic data is crucial for the calculation of such model atmospheres. Aims: We aim to calculate new Sr iv-vii oscillator strengths to identify for the first time Sr spectral lines in hot white dwarf (WD) stars and to determine the photospheric Sr abundances. To measure the abundances of Se, Te, and I in hot WDs, we aim to compute new Se v, Te vi, and I vi oscillator strengths. Methods: To consider radiative and collisional bound-bound transitions of Se v, Sr iv - vii, Te vi, and I vi in our NLTE atmosphere models, we calculated oscillator strengths for these ions. Results: We newly identified four Se v, 23 Sr v, 1 Te vi, and three I vi lines in the ultraviolet (UV) spectrum of RE 0503-289. We measured a photospheric Sr abundance of 6.5+ 3.8-2.4× 10-4 (mass fraction, 9500-23 800 times solar). We determined the abundances of Se (1.6+ 0.9-0.6× 10-3, 8000-20 000), Te (2.5+ 1.5-0.9× 10-4, 11 000-28 000), and I (1.4+ 0.8-0.5× 10-5, 2700-6700). No Se, Sr, Te, and I line was found in the UV spectra of G191-B2B and we could determine only upper abundance limits of approximately 100 times solar. Conclusions: All identified Se v, Sr v, Te vi, and I vi lines in the UV spectrum of RE 0503-289 were simultaneously well reproduced with our newly calculated oscillator strengths. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26666. Based on observations made with the NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer. Full Tables A.15 to A.21 are only available via the German Astrophysical Virtual Observatory (GAVO) service TOSS (http://dc.g-vo.org/TOSS).

  9. Charge separation and transfer in hybrid type II tunneling structures of CdTe and CdSe nanocrystals

    International Nuclear Information System (INIS)

    Gross, Dieter Konrad Michael

    2013-01-01

    Closely packed nanocrystal systems have been investigated in this thesis with respect to charge separation by charge carrier tunneling. Clustered and layered samples have been analyzed using PL-measurements and SPV-methods. The most important findings are reviewed in the following. A short outlook is also provided for potential further aspects and application of the presented results. The main purpose of this thesis was to find and quantify electronic tunneling transfer in closely packed self-assembled nanocrystal structures presenting quantum mechanical barriers of about 1 nm width. We successfully used hybrid assemblies of CdTe and CdSe nanocrystals where the expected type II alignment between CdTe and CdSe typically leads to a concentration of electrons in CdSe and holes in CdTe nanocrystals. We were able to prove the charge selectivity of the CdTe-CdSe nanocrystal interface which induces charge separation. We mainly investigated the effects related to the electron transfer from CdTe to CdSe nanocrystals. Closely packing was achieved by two independent methods: the disordered colloidal clustering in solution and the layered assembly on dry glass substrates. Both methods lead to an inter-particle distance of about 1 nm of mainly organic material which acts as a tunneling barrier. PL-spectroscopy was applied. The PL-quenching of the CdTe nanocrystals in hybrid assemblies indicates charge separation by electron transfer from CdTe to CdSe nanocrystals. A maximum quenching rate of up to 1/100 ps was measured leading to a significant global PL-quenching of up to about 70 % for the CdTe nanocrystals. It was shown that charge separation dynamics compete with energy transfer dynamics and that charge separation typically dominates. The quantum confinement effect was used to tune the energetic offset between the CdTe and CdSe nanocrystals. We thus observe a correlation of PL-quenching and offset of the energy states for the electron transfer. The investigated PL

  10. Charge separation and transfer in hybrid type II tunneling structures of CdTe and CdSe nanocrystals

    Energy Technology Data Exchange (ETDEWEB)

    Gross, Dieter Konrad Michael

    2013-11-08

    Closely packed nanocrystal systems have been investigated in this thesis with respect to charge separation by charge carrier tunneling. Clustered and layered samples have been analyzed using PL-measurements and SPV-methods. The most important findings are reviewed in the following. A short outlook is also provided for potential further aspects and application of the presented results. The main purpose of this thesis was to find and quantify electronic tunneling transfer in closely packed self-assembled nanocrystal structures presenting quantum mechanical barriers of about 1 nm width. We successfully used hybrid assemblies of CdTe and CdSe nanocrystals where the expected type II alignment between CdTe and CdSe typically leads to a concentration of electrons in CdSe and holes in CdTe nanocrystals. We were able to prove the charge selectivity of the CdTe-CdSe nanocrystal interface which induces charge separation. We mainly investigated the effects related to the electron transfer from CdTe to CdSe nanocrystals. Closely packing was achieved by two independent methods: the disordered colloidal clustering in solution and the layered assembly on dry glass substrates. Both methods lead to an inter-particle distance of about 1 nm of mainly organic material which acts as a tunneling barrier. PL-spectroscopy was applied. The PL-quenching of the CdTe nanocrystals in hybrid assemblies indicates charge separation by electron transfer from CdTe to CdSe nanocrystals. A maximum quenching rate of up to 1/100 ps was measured leading to a significant global PL-quenching of up to about 70 % for the CdTe nanocrystals. It was shown that charge separation dynamics compete with energy transfer dynamics and that charge separation typically dominates. The quantum confinement effect was used to tune the energetic offset between the CdTe and CdSe nanocrystals. We thus observe a correlation of PL-quenching and offset of the energy states for the electron transfer. The investigated PL

  11. Charge separation and transfer in hybrid type II tunneling structures of CdTe and CdSe nanocrystals

    Energy Technology Data Exchange (ETDEWEB)

    Gross, Dieter Konrad Michael

    2013-11-08

    Closely packed nanocrystal systems have been investigated in this thesis with respect to charge separation by charge carrier tunneling. Clustered and layered samples have been analyzed using PL-measurements and SPV-methods. The most important findings are reviewed in the following. A short outlook is also provided for potential further aspects and application of the presented results. The main purpose of this thesis was to find and quantify electronic tunneling transfer in closely packed self-assembled nanocrystal structures presenting quantum mechanical barriers of about 1 nm width. We successfully used hybrid assemblies of CdTe and CdSe nanocrystals where the expected type II alignment between CdTe and CdSe typically leads to a concentration of electrons in CdSe and holes in CdTe nanocrystals. We were able to prove the charge selectivity of the CdTe-CdSe nanocrystal interface which induces charge separation. We mainly investigated the effects related to the electron transfer from CdTe to CdSe nanocrystals. Closely packing was achieved by two independent methods: the disordered colloidal clustering in solution and the layered assembly on dry glass substrates. Both methods lead to an inter-particle distance of about 1 nm of mainly organic material which acts as a tunneling barrier. PL-spectroscopy was applied. The PL-quenching of the CdTe nanocrystals in hybrid assemblies indicates charge separation by electron transfer from CdTe to CdSe nanocrystals. A maximum quenching rate of up to 1/100 ps was measured leading to a significant global PL-quenching of up to about 70 % for the CdTe nanocrystals. It was shown that charge separation dynamics compete with energy transfer dynamics and that charge separation typically dominates. The quantum confinement effect was used to tune the energetic offset between the CdTe and CdSe nanocrystals. We thus observe a correlation of PL-quenching and offset of the energy states for the electron transfer. The investigated PL

  12. Homologous series of layered structures in binary and ternary Bi-Sb-Te-Se systems : Ab initio study

    NARCIS (Netherlands)

    Govaerts, K.; Sluiter, M.H.F.; Partoens, B.; Lamoen, D.

    2014-01-01

    In order to account explicitly for the existence of long-periodic layered structures and the strong structural relaxations in the most common binary and ternary alloys of the Bi-Sb-Te-Se system, we have developed a one-dimensional cluster expansion (CE) based on first-principles electronic structure

  13. Influence of Bi, Se and Te additions on the formation temperature of MgB2

    DEFF Research Database (Denmark)

    Grivel, Jean-Claude; Andersen, Niels Hessel; Pallewatta, P. G. Asanka Pramod

    2012-01-01

    The formation of the MgB2 superconducting compound from a mixture of Mg and amorphous B powders with various low melting point metals (Bi, Se and Te) was studied in situ by means of high-energy (synchrotron) x-ray diffraction in wires with a composite Cu/Nb sheath. In comparison with an undoped s...

  14. Dispersion of the second-order nonlinear susceptibility in ZnTe, ZnSe, and ZnS

    DEFF Research Database (Denmark)

    Wagner, Hans Peter; Kühnelt, M.; Langbein, Wolfgang Werner

    1998-01-01

    We have measured the absolute values of the second-harmonic generation (SHG) coefficient \\d\\ for the zinc-blende II-VI semiconductors ZnTe, ZnSe, and ZnS at room temperature. The investigated spectral region of the fundamental radiation lambda(F) ranges from 520 to 1321 nm using various pulsed...

  15. Biogenic SeNPs from Bacillus mycoides SelTE01 and Stenotrophomonas maltophilia SelTE02: Characterization with reference to their associated organic coating

    Science.gov (United States)

    Piacenza, Elena; Bulgarini, Alessandra; Lampis, Silvia; Vallini, Giovanni; Turner, Raymond J.

    2017-08-01

    The exploitation of biological systems (i.e. plants, fungi and bacteria) for the production of nanomaterials relies on their ability to bioconvert toxic metal(loid) ions into their less toxic and bioavailable elemental states forming mainly nanoparticles (NPs) or nanorods (NRs). Further, these methods of nanomaterial production are nowadays recognized as eco-friendly alternatives to the chemical synthesis processes. A common feature among the so-called biogenic nanomaterials is the presence of an organic layer surrounding them. However, we are just learning the existing relation between biogenic nanostructures and their organic material. Our work is focused on the study of bacterial strains for the production of selenium nanoparticles (SeNPs) as end product of selenite (SeO32 -) bioconversion. In this context, our previous reports described the ability of two bacteria, namely Bacillus mycoides SelTE01 and Stenotrophomonas maltophilia SelTE02, to generate SeNPs, which were surrounded by organic material. Here, the potential role of this organic material as stabilizing agent of SeNPs was investigated altering both the bacteria cells culturing and the SeNPs extraction procedure, in order to understand the interaction between these two elements in suspension. As a result, SeNPs produced by both bacterial strains showed the tendency to aggregate when subjected to the treatments tested, suggesting an involvement of the surrounding organic material in their stabilization in suspension.

  16. Effect of surface treatment of thermoelectric materials on the properties of thermoelements made from solid solutions of Bi2Te3-Bi2Se3 and Bi2Te3-Sb2Te3 systems

    International Nuclear Information System (INIS)

    Alieva, T.D.; Abdinov, D.Sh.; Salaev, Eh.Yu.

    1981-01-01

    Effect of surface treatment technology of samples of solid solutions of Ei 2 Te 3 -Bi 2 Se 3 and Bi 2 Te 3 -Sb 2 Te 3 systems on their thermoelectric efficiency is studied. Branches of thermoelements have been produced with the help of electroerosion or mechanical cutting of monocrystal ingots of semiconducting solid Bi 2 Te 3 -base solutions. It is shown that in case of the treatment of side surfaces of branches of thermoelements produced of monocrystals of Bi 2 Te 3 base solid solutions their thermoelectrical efficiency grows considerably. Maximum growth of efficiency (approximately 20%) is observed during mechanical grinding of branches surfaces with diamond paste with the following chemical or electrochemical etching [ru

  17. Generalized stacking fault energies, cleavage energies, ionicity and brittleness of Cu(Al/Ga/In)Se2 and CuGa(S/Se/Te)2

    Science.gov (United States)

    Xue, H. T.; Tang, F. L.; Gruhn, T.; Lu, W. J.; Wan, F. C.; Rui, Z. Y.; Feng, Y. D.

    2014-04-01

    We calculate the generalized stacking fault (GSF) energies and cleavage energies γcl of the chalcopyrite compounds CuAlSe2, CuGaSe2, CuInSe2, CuGaS2 and CuGaTe2 using first principles. From the GSF energies, we obtain the unstable stacking fault energies γus and intrinsic stacking fault energies γisf. By analyzing γus and γisf, we find that the \\langle \\bar{{1}}\\,1\\,0\\rangle (1 1 2) direction is the easiest slip direction for these five compounds. Also, for CuInSe2, it is most possible to undergo a dislocation-nucleation-induced plastic deformation along the \\langle \\bar{{1}}\\,1\\,0\\rangle (1 1 2) slip direction. We show that the (1 1 2) plane is the preferable plane for fracture in the five compounds by comparing γcl of the (0 0 1) and (1 1 2) planes. It is also found that both γus and γcl decrease as the cationic or anionic radius increases in these chalcopyrites, i.e. along the sequences CuAlSe2 → CuGaSe2 → CuInSe2 and CuGaS2 → CuGaSe2 → CuGaTe2. Based on the values of the ratio γcl/γus, we discuss the brittle-ductile properties of these compounds. All of the compounds can be considered as brittle materials. In addition, a strong relationship between γcl/γus and the total proportion of ionic bonding in these compounds is found.

  18. Investigation on lattice parameters and superconducting properties in Fe(Te, Se, S) ternary-chalcogen system

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Zhongnan; Zhang, Huanhuan; Han, Bingling; Yuan, Wenxia, E-mail: wxyuanwz@163.com

    2015-02-15

    Highlights: • A series sample of Fe{sub 1.02}Te{sub 0.85}Se{sub 0.15−x}S{sub x} has been synthesised. • The lattice parameters is basically unchanged with the S doping. • The superconductivity is clearly suppressed with the S substitution of Se. • The solid solubility region of the tetragonal phase in this system is discussed. - Abstract: A series of samples with the nominal compositions Fe{sub 1.02}Te{sub 0.85}Se{sub 0.15−x}S{sub x} (x = 0, 0.0375, 0.075, 0.1125 and 0.15) have been synthesized to study the influence of the S substitution of Se on the lattice parameters and superconducting properties. It has been found that the S substitution basically has no effect on the lattice parameters a and c of the tetragonal phase. However, T{sub c} of Fe{sub 1.02}(Te{sub 0.85}Se{sub 0.15−x}S{sub x}) superconductors clearly decreases with S doping.

  19. Microstructure and optical studies of electron beam evaporated ZnSe1−xTex nanocrystalline thin films

    International Nuclear Information System (INIS)

    Emam-Ismail, M.; El-Hagary, M.; Shaaban, E.R.; Al-Hedeib, A.M.

    2012-01-01

    Highlights: ► The structural and optical properties of ZnSeTe thin films were studied. ► The micro structural parameters of the films have been determined. ► The room temperature reflectance and transmittance data are analyzed. ► The refractive index and energy gap are determined. ► The single oscillator parameters were calculated. - Abstract: Nanocrystalline thin films of ZnSe 1−x Te x (0.0 ≤ x ≤ 1.0) were deposited on glass substrate using electron beam deposition technique. The structure of the prepared films was examined using X-ray diffraction technique and revealed that the deposited films have polycrystalline zinc blend structure with lattice constant, a, increasing linearly from 0.55816 to 0.59989 nm as x varies from 0 to 1. The optical studies of the nanocrystalline ZnSe 1−x Te x films showed that the refractive index increases and fundamental band gap E g decreases from 2.58 to 2.21 eV as the tellurium concentration increases from 0 to 1. Furthermore, it was also found that the variation of E g with composition shows quadratic behavior with bowing parameter equal to 0.105. In addition, the thickness and annealing effects on the structure and optical properties of the deposited films were also investigated. The refractive index dispersion and its dependence on composition were discussed in terms of single oscillator model proposed by Wemple–DiDomenico.

  20. RGDS-conjugated CdSeTe/CdS quantum dots as near-infrared fluorescent probe: preparation, characterization and bioapplication

    Energy Technology Data Exchange (ETDEWEB)

    Li, Zhenzhen; Zhang, Qiyi; Huang, Huaying; Ren, Changjing; Pan, Yujin; Wang, Qing; Zhao, Qiang, E-mail: Zhaoqiang@scu.edu.cn [Sichuan University, School of Chemical Engineering (China)

    2016-12-15

    In the experiments, high-quality, water-soluble and near-infrared (NIR)-emitting CdSeTe and CdSeTe/CdS quantum dots (QDs) were successfully prepared. The average size of CdSeTe⁄CdS QDs was 7.68 nm and CdSeTe QDs was 4.33 nm. Arginine-glycine-aspartic-serine acid (RGDS) peptides were linked to CdSeTe/CdS QDs by N-(3-(dimethylamino)propyl)-N′-ehtylcarbodiimide hydrochloride (EDC) and N′-hydroxysuccinimide (NHS). The prepared RGDS-tagged NIR CdSeTe/CdS QDs (denoted as RGDS-CdSeTe/CdS) had an average diameter of 24.83 nm and were used for cancer cell immunofluorescence imaging. The characteristics of RGDS-conjugated CdSeTe/CdS such as morphology, structure, spectra, stability, cytotoxicity, and near-infrared microscopic imaging were investigated in detail. HepG2 cells were incubated with the novel fluorescent probe (RGDS-CdSeTe/CdS), which realized immunofluorescence targeting and imaging. The results reported here open up new perspectives for integrin-targeted near-infrared imaging and may aid in tumor detection including imaging-guided surgery.

  1. Chemical states and optical properties of thermally evaporated Ge-Te and Ge-Sb-Te amorphous thin films

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, S.; Singh, D.; Shandhu, S. [Semiconductor Laboratory, Department of Physics, Guru Nanak Dev University Amritsar (India); Thangaraj, R., E-mail: rthangaraj@rediffmail.com [Semiconductor Laboratory, Department of Physics, Guru Nanak Dev University Amritsar (India)

    2012-07-15

    Thin amorphous films of Ge{sub 22}Sb{sub 22}Te{sub 56} and Ge{sub 50}Te{sub 50} have been prepared from their respective polycrystalline bulk on glass substrates by thermal evaporation technique. The amorphous nature of the films was checked with X-ray diffraction studies. Amorphous-to-crystalline transition of the films has been induced by thermal annealing and the structural phases have been identified by X-ray diffraction. The phase transformation temperature of the films was evaluated by temperature dependent sheet resistance measurement. The chemical structure of the amorphous films has been investigated using X-ray photoelectron spectroscopy and the role of Sb in phase change Ge{sub 22}Sb{sub 22}Te{sub 56} film is discussed. Survey and core level (Ge 3d, Te 3d, Te 4d, Sb 3p, Sb 3d, O 1s, C 1s) band spectra has been recorded and analyzed. For optical studies, the transmittance and the reflectance spectra were measured over the wavelength ranges 400-2500 nm using UV-vis-NIR spectroscopy. The optical band gap, refractive index and extinction coefficient are also presented for thermally evaporated amorphous thin films.

  2. Using CdTe/ZnSe core/shell quantum dots to detect DNA and damage to DNA

    Directory of Open Access Journals (Sweden)

    Moulick A

    2017-02-01

    Full Text Available Amitava Moulick,1,2 Vedran Milosavljevic,1,2 Jana Vlachova,1,2 Robert Podgajny,3 David Hynek,1,2 Pavel Kopel,1,2 Vojtech Adam1,2 1Department of Chemistry and Biochemistry, Mendel University, 2Central European Institute of Technology, Brno University of Technology, Brno, Czech Republic; 3Faculty of Chemistry, Jagiellonian University, Krakow, Poland Abstract: CdTe/ZnSe core/shell quantum dot (QD, one of the strongest and most highly luminescent nanoparticles, was directly synthesized in an aqueous medium to study its individual interactions with important nucleobases (adenine, guanine, cytosine, and thymine in detail. The results obtained from the optical analyses indicated that the interactions of the QDs with different nucleobases were different, which reflected in different fluorescent emission maxima and intensities. The difference in the interaction was found due to the different chemical behavior and different sizes of the formed nanoconjugates. An electrochemical study also confirmed that the purines and pyrimidines show different interactions with the core/shell QDs. Based on these phenomena, a novel QD-based method is developed to detect the presence of the DNA, damage to DNA, and mutation. The QDs were successfully applied very easily to detect any change in the sequence (mutation of DNA. The QDs also showed their ability to detect DNAs directly from the extracts of human cancer (PC3 and normal (PNT1A cells (detection limit of 500 pM of DNA, which indicates the possibilities to use this easy assay technique to confirm the presence of living organisms in extreme environments. Keywords: nanoparticles, nucleobases, biosensor, fluorescence, mutation

  3. The effect of Se/Te ratio on transient absorption behavior and nonlinear absorption properties of CuIn0.7Ga0.3(Se1-xTex)2 (0 ≤ x ≤ 1) amorphous semiconductor thin films

    Science.gov (United States)

    Karatay, Ahmet; Küçüköz, Betül; Çankaya, Güven; Ates, Aytunc; Elmali, Ayhan

    2017-11-01

    The characterization of the CuInSe2 (CIS), CuInGaSe (CIGS) and CuGaSe2 (CGS) based semiconductor thin films are very important role for solar cell and various nonlinear optical applications. In this paper, the amorphous CuIn0.7Ga0.3(Se1-xTex)2 semiconductor thin films (0 ≤ x ≤ 1) were prepared with 60 nm thicknesses by using vacuum evaporation technique. The nonlinear absorption properties and ultrafast transient characteristics were investigated by using open aperture Z-scan and ultrafast pump-probe techniques. The energy bandgap values were calculated by using linear absorption spectra. The bandgap values are found to be varying from 0.67 eV to 1.25 eV for CuIn0.7Ga0.3Te2, CuIn0.7Ga0.3Se1.6Te0.4, CuIn0.7Ga0.3Se0.4Te1.6 and CuIn0.7Ga0.3Se2 thin films. The energy bandgap values decrease with increasing telluride (Te) doping ratio in mixed CuIn0.7Ga0.3(Se1-xTex)2 films. This affects nonlinear characteristics and ultrafast dynamics of amorphous thin films. Ultrafast pump-probe experiments indicated that decreasing of bandgap values with increasing the Te amount switches from the excited state absorption signals to ultrafast bleaching signals. Open aperture Z-scan experiments show that nonlinear absorption properties enhance with decreasing bandgaps values for 65 ps pulse duration at 1064 nm. Highest nonlinear absorption coefficient was found for CuIn0.7Ga0.3Te2 thin film due to having the smallest energy bandgap.

  4. Atomistic tight-binding theory of excitonic splitting energies in CdX(X = Se, S and Te)/ZnS core/shell nanocrystals

    Science.gov (United States)

    Sukkabot, Worasak; Pinsook, Udomsilp

    2017-01-01

    Using the atomistic tight-binding theory (TB) and a configuration interaction description (CI), we numerically compute the excitonic splitting of CdX(X = Se, S and Te)/ZnS core/shell nanocrystals with the objective to explain how types of the core materials and growth shell thickness can provide the detailed manipulation of the dark-dark (DD), dark-bright (DB) and bright-bright (BB) excitonic splitting, beneficial for the active application of quantum information. To analyze the splitting of the excitonic states, the optical band gaps, ground-state wave function overlaps and atomistic electron-hole interactions tend to be numerically demonstrated. Based on the atomistic computations, the single-particle and excitonic gaps are mainly reduced with the increasing ZnS shell thickness owing to the quantum confinement. In the range of the higher to lower energies, the order of the single-particle gaps is CdSe/ZnS, CdS/ZnS and CdTe/ZnS core/shell nanocrystals, while one of the excitonic gaps is CdS/ZnS, CdSe/ZnS and CdTe/ZnS core/shell nanocrystals because of the atomistic electron-hole interaction. The strongest electron-hole interactions are mainly observed in CdSe/ZnS core/shell nanocrystals. In addition, the computational results underline that the energies of the dark-dark (DD), dark-bright (DB) and bright-bright (BB) excitonic splitting are generally reduced with the increasing ZnS growth shell thickness as described by the trend of the electron-hole exchange interaction. The high-to-low splitting of the excitonic states is demonstrated in CdSe/ZnS, CdTe/ZnS and CdS/ZnS core/shell nanocrystals because of the fashion in the electron-hole exchange interaction and overlaps of the electron-hole wave functions. As the resulting calculations, it is expected that CdS/ZnS core/shell nanocrystals are the best candidates to be the source of entangled photons. Finally, the comprehensive information on the excitonic splitting can enable the use of suitable core

  5. The optical properties of TeO2-Based Glasses

    International Nuclear Information System (INIS)

    Sahar, M.R.; Isahak, R.

    1994-01-01

    A series of binary glasses based on TeO2-PbCl2 has been prepared and their spectroscopy in the UV-Visible and IR regions has been investigated. It was found that the IR cut-off edge can go beyond 7μm and are largely influenced by the absorption due to Te-O-Te stretching vibrations around 638-644 cmsup -1 peaks

  6. The optical properties of TeO2-Based Glasses

    Energy Technology Data Exchange (ETDEWEB)

    Sahar, M R; Isahak, R [University Technology of Malaysia, Skudai Johor (Malaysia)

    1994-03-01

    A series of binary glasses based on TeO2-PbCl2 has been prepared and their spectroscopy in the UV-Visible and IR regions has been investigated. It was found that the IR cut-off edge can go beyond 7{mu}m and are largely influenced by the absorption due to Te-O-Te stretching vibrations around 638-644 cmsup -1 peaks.

  7. Structure and optical properties of GaSe-CdSe composites driven by Cd intercalation in GaSe lamellar crystals

    International Nuclear Information System (INIS)

    Caraman, Iuliana; Kantser, Valeriu; Evtodiev, Igor; Untila, Dumitru; Dmitroglo, Liliana; Leontie, Liviu; Arzumanyan, Grigory

    2015-01-01

    A new composite material composed of GaSe and CdSe has been obtained by treatment of GaSe single-crystal lamellas in Cd vapors at temperatures of 773-853 K and intercalation of Cd interlayers. The structure and optical properties of the GaSe-CdSe composite material have been studied. The content of CdSe crystallites was found to grow with increasing treatment temperature or with increasing duration of treatment at a constant temperature. Analysis of XRD, PL, XPS, AFM, and Raman patterns has shown that the heterogeneous composite composed of micro and nanocrystallites of CdSe in GaSe can be obtained by Cd intercalation in a temperature range of 753-853 K. On the basis of Raman spectrum, the vibrational modes of the composite have been identified. The PL of these materials contains emission bands of free and bound excitons, donor-acceptor bands, and bands of recombination via impurity levels. The PL emission spectra measured at a temperature of 78 and 300 K for the composites result from the overlapping of the emission bands of the components of GaSe doped with Cd and the CdSe crystallites. (authors)

  8. A study of Sn addition on bonding arrangement of Se-Te alloys using far infrared transmission spectroscopy

    International Nuclear Information System (INIS)

    Kumar, Rajneesh; Rangra, V. S.; Sharma, Parikshit; Katyal, S. C.; Sharma, Pankaj

    2011-01-01

    Far infrared transmission spectra of Se 92 Te 8-x Sn x (x = 0, 1, 2, 3, 4, 5) glassy alloys are obtained in the spectral range 50-600 cm -1 at room temperature. The results are interpreted in terms of the vibrations of the isolated molecular units in such a way so as to preserve fourfold and twofold coordination for Sn and chalcogen atoms (Se,Te), respectively. With the addition of Sn, Far-IR spectra shift toward high frequency side and some new bands start appearing. Sn atoms appear to substitute for the selenium atoms in the outrigger sites due to large bond formation probability. Theoretical calculations of bond energy, relative probability of bond formation, force constant, and wave number were also made to justify the result.

  9. Thermal studies of Se85-xTe15Inx (x = 3,6,9,12) glasses

    International Nuclear Information System (INIS)

    Sushama, D.; George, Achamma; Asokan, S.

    2011-01-01

    Bulk glasses of compositions Se 85-x Te 15 In x (x = 3,6,9,12) are prepared by melt quenching technique and Differential scanning calorimetry (DSC) is employed to study the thermal stability, crystallization mechanism as well as specific heat of these glasses. It is found that the addition of indium increases the glass transition temperature. From the heating rate dependence of the glass transition temperature the activation energy of glass transition is determined using Kissinger's equation for non-isothermal crystallization of materials. An attempt has been made to explain the variation in the value of T c , T p and ΔC p for the composition Se 73 Te 15 In 12 using rigidity percolation threshold (RPT). From the values of (T c -T g ) the stable glass system is determined.

  10. Electrodeposition and characterization of CdSe{sub x}Te{sub 1-x} semiconducting thin films

    Energy Technology Data Exchange (ETDEWEB)

    Benamar, E.; Rami, M.; Fahoume, M.; Chraibi, F.; Ennaoui, A. [Faculty of Sciences, Laboratory of Materials Physics, Dept. of Physics, Rabat (Morocco)

    1999-07-01

    Thin polycrystalline films of cadmium chalcogenides CdSe{sub x}Te{sub 1-x} (0{<=}x{<=}1) can be used for various technical applications in particular for the conversion of solar energy in photoelectrochemical devices. They have been prepared by electrochemical plating on ITO (indium tin oxide) coated glass substrates from an acid sulfate solution at 90 deg. C. Structural, morphological and compositional studies of the deposited films are reported as a function of the x coefficient. XRD analysis shows that all deposits have a cubic structure with a preferred orientation along the (111) direction. The composition in the films is found to vary linearly with the composition in the solution. The increase in the selenium content x in the CdSe{sub x}Te{sub 1-x} films decreases the lattice constant and increases the band gap. Nevertheless this latter presents a minimum for x = 0.27.

  11. Single-mode molecular beam epitaxy grown PbEuSeTe/PbTe buried-heterostructure diode lasers for CO2 high-resolution spectroscopy

    International Nuclear Information System (INIS)

    Feit, Z.; Kostyk, D.; Woods, R.J.; Mak, P.

    1991-01-01

    Buried-heterostructure tunable PbEuSeTe/PbTe lasers were fabricated using a two-stage molecular beam epitaxy growth procedure. Improvements in the processing technique yielded lasers that show performance characteristics significantly better than those reported previously. A continuous wave (cw) operating temperature of 203 K was realized, which is the highest cw operating temperature ever reported for lead-chalcogenides diode lasers. This laser exhibited exceptionally low-threshold currents of 1.4 mA at 90 K and 43 mA at 160 K with single-mode operation for injection currents up to 30I th and 0.18 mW power at 100 K. The usefulness of the laser, when operating cw at 200 K, was demonstrated by the ability to perform high-resolution spectroscopy of a low-pressure CO 2 gas sample

  12. Structural and optical properties of nanocrystalline CdSe and Al:CdSe thin films for photoelectrochemical application

    Energy Technology Data Exchange (ETDEWEB)

    Gawali, Sanjay A. [Electrochemical Materials Laboratory, Department of Physics, Shivaji University, Kolhapur - 416 004 (India); Bhosale, C.H., E-mail: bhosale_ch@yahoo.com [Electrochemical Materials Laboratory, Department of Physics, Shivaji University, Kolhapur - 416 004 (India)

    2011-10-03

    Highlights: {yields} The CdSe and Al:CdSe thin films have been successfully deposited by SPT. {yields} Hexagonal cubic structured CdSe and Al: CdSe thin films are observed. {yields} Large number of fine grains, Uniform and compact growth morphology. {yields} Hydrophilic surface nature. {yields} Al:CdSe have better PEC performance than CdSe. - Abstract: Nanocrystalline CdSe and Al:CdSe semiconductor thin films have been successfully synthesized onto amorphous and FTO glass substrates by spray pyrolysis technique. Aqueous solutions containing precursors of Cd and Se have been used to obtain good quality films. The optimized films have been characterized for their structural, morphological, wettability and optical properties. X-ray diffraction (XRD) studies show that the films are polycrystalline in nature with hexagonal crystal structure. Scanning electron microscopy (SEM) studies show that the film surface is smooth, uniform and compact in nature. Water wettability study reveals that the films are hydrophilic behavior. The formation of CdSe and Al:CdSe thin film were confirmed with the help of FTIR spectroscopy. UV-vis spectrophotometric measurement showed a direct allowed band gap lying in the range 1.673-1.87 eV. Output characteristics were studied by using cell configuration n- CdSe/Al:CdSe |1 M (NaOH + Na{sub 2} + S)|C. An efficient solar cell having a power conversion efficiency of 0.38% at illumination 25 mW cm{sup -2} was fabricated.

  13. Anomalous X-ray diffraction from self-assembled PbSe/PbEuTe quantum dots

    International Nuclear Information System (INIS)

    Holy, V.; Schuelli, T.U.; Lechner, R.T.; Springholz, G.; Bauer, G.

    2005-01-01

    Anomalous X-ray scattering from self-assembled PbSe quantum dots embedded in Pb 1-x Eu x Te was used for the study of their structure. The measured reciprocal-space distributions of diffracted intensity were compared with simulations based on kinematical scattering theory and continuum elasticity. From the comparison, the mean chemical composition of the dots and their aspect ratio (height/width) were estimated

  14. Effects of annealing, acid and alcoholic beverages on Fe1+yTe0.6Se0.4

    International Nuclear Information System (INIS)

    Sun, Y; Taen, T; Tsuchiya, Y; Tamegai, T; Shi, Z X

    2013-01-01

    We have systematically investigated and compared different methods to induce superconductivity in the iron chalcogenide Fe 1+y Te 0.6 Se 0.4 , including annealing in a vacuum, N 2 , O 2 and I 2 atmospheres and immersing samples into acid and alcoholic beverages. Vacuum and N 2 annealing are proved to be ineffective in inducing superconductivity in a Fe 1+y Te 0.6 Se 0.4 single crystal. Annealing in O 2 and I 2 and immersion in acid and alcoholic beverages can induce superconductivity by oxidizing the excess Fe in the sample. Superconductivity in O 2 annealed samples is of a bulk nature, while I 2 , acid and alcoholic beverages can only induce superconductivity near the surface. By comparing the different effects of O 2 , I 2 , acid and alcoholic beverages we propose a scenario to explain how the superconductivity is induced in the non-superconducting as-grown Fe 1+y Te 0.6 Se 0.4 . (paper)

  15. Solar-energy conversion by combined photovoltaic converters with CdTe and CuInSe2 base layers

    International Nuclear Information System (INIS)

    Khrypunov, G. S.; Sokol, E. I.; Yakimenko, Yu. I.; Meriuts, A. V.; Ivashuk, A. V.; Shelest, T. N.

    2014-01-01

    The possibility of the combined use of bifacial thin-film solar cells based on CdTe and frontal solar cells with a CuInSe 2 base layer in tandem structures is experimentally confirmed. It is found that, for the use of bifacial solar cells based on cadmium telluride in a tandem structure, the optimal thickness of their base layer should be 1 μm. The gain in the efficiency of the tandem structure, compared with an individual CuInSe 2 -based solar cell, is 1.8% in the case of series-connected solar cells and 1.3%, for parallel-connected

  16. Photoluminescence of double core/shell infrared (CdSeTe)/ZnS quantum dots conjugated to Pseudo rabies virus antibodies

    Science.gov (United States)

    Torchynska, T. V.; Casas Espinola, J. L.; Jaramillo Gómez, J. A.; Douda, J.; Gazarian, K.

    2013-06-01

    Double core CdSeTe/ZnS quantum dots (QDs) with emission at 800 nm (1.60 eV) have been studied by photoluminescence (PL) and Raman scattering methods in the non-conjugated state and after the conjugation to the Pseudo rabies virus (PRV) antibodies. The transformation of PL spectra, stimulated by the electric charge of antibodies, has been detected for the bioconjugated QDs. Raman scattering spectra are investigated with the aim to reveal the CdSeTe core compositions. The double core QD energy diagrams were designed that help to analyze the PL spectra and their transformation at the bioconjugation. It is revealed that the interface in double core QDs has the type II quantum well character that permits to explain the near IR optical transition (1.60 eV) in the double core QDs. It is shown that the essential transformation of PL spectra is useful for the study of QD bioconjugation with specific antibodies and can be a powerful technique in early medical diagnostics.

  17. Theoretical optoelectronic analysis of intermediate-band photovoltaic material based on ZnY1−xOx (Y = S, Se, Te) semiconductors by first-principles calculations

    International Nuclear Information System (INIS)

    Wu Kong-Ping; Zhou Meng-Ran; Huang You-Rui; Gu Shu-Lin; Ye Jian-Dong; Zhu Shun-Ming; Zhang Rong; Zheng You-Dou; Tang Kun

    2013-01-01

    The structural, energetic, and electronic properties of lattice highly mismatched ZnY 1−x O x (Y = S, Se, Te) ternary alloys with dilute O concentrations are calculated from first principles within the density functional theory. We demonstrate the formation of an isolated intermediate electronic band structure through diluted O-substitute in zinc-blende ZnY (Y = S, Se, Te) at octahedral sites in a semiconductor by the calculations of density of states (DOS), leading to a significant absorption below the band gap of the parent semiconductor and an enhancement of the optical absorption in the whole energy range of the solar spectrum. It is found that the intermediate band states should be described as a result of the coupling between impurity O 2p states with the conduction band states. Moreover, the intermediate bands (IBs) in ZnTeO show high stabilization with the change of O concentration resulting from the largest electronegativity difference between O and Te compared with in the other ZnSO and ZnSeO. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  18. Synthesis, structure, and characterization of two new bismuth(III) selenite/tellurite nitrates: [(Bi3O2)(SeO3)2](NO3) and [Bi(TeO3)](NO3)

    Science.gov (United States)

    Meng, Chang-Yu; Wei, Ming-Fang; Geng, Lei; Hu, Pei-Qing; Yu, Meng-Xia; Cheng, Wen-Dan

    2016-07-01

    Two new bismuth(III) selenite/tellurite nitrates, [(Bi3O2)(SeO3)2](NO3) and [Bi(TeO3)](NO3), have been synthesized by conventional facile hydrothermal method at middle temperature 200 °C and characterized by single-crystal X-ray diffraction, powder diffraction, UV-vis-NIR optical absorption spectrum, infrared spectrum and thermal analylsis. Both [(Bi3O2)(SeO3)2](NO3) and [Bi(TeO3)](NO3) crystallize in the monoclinic centronsymmetric space group P21/c with a=9.9403(4) Å, b=9.6857(4) Å, c=10.6864(5) Å, β=93.1150(10)° for [(Bi3O2)(SeO3)2](NO3) and a=8.1489(3) Å, b=9.0663(4) Å, c=7.4729(3) Å, β=114.899(2)° for Bi(TeO3)(NO3), respectively. The two compounds, whose structures are composed of three different asymmetric building units, exhibit two different types of structures. The structure of [(Bi3O2)(SeO3)2](NO3) features a three-dimensional (3D) bismuth(III) selenite cationic tunnel structure [(Bi3O2)(SeO3)2] 3∞ with NO3- anion group filling in the 1D tunnel along b axis. The structure of [Bi(TeO3)](NO3) features 2D bismuth(III) tellurite [Bi(TeO3)2]2∞ layers separated by NO3- anion groups. The results of optical diffuse-reflectance spectrum measurements and electronic structure calculations based on density functional theory methods show that the two compounds are wide band-gap semiconductors.

  19. Exploration work function and optical properties of monolayer SnSe allotropes

    Science.gov (United States)

    Cui, Zhen; Wang, Xia; Ding, Yingchun; Li, Meiqin

    2018-02-01

    The work function and optical properties are investigated with density functional theory for three monolayer SnSe allotropes. The calculated results indicate that the α-SnSe, δ-SnSe, ε-SnSe are semiconductor with the band gaps of 0.90, 1.25, and 1.50 eV, respectively. Meanwhile, the work function of δ-SnSe is lower than α-SnSe and ε-SnSe, which indicates that the δ-SnSe can be prepared of photoemission and field emission nanodevices. More importantly, the α-SnSe, δ-SnSe, ε-SnSe with the large static dielectric constants are 4.22, 5.48, and 3.61, which demonstrate that the three monolayer SnSe allotropes can be fabricated the capacitor. In addition, the static refractive index of δ-SnSe is larger than α-SnSe and ε-SnSe. The different optical properties with three monolayer SnSe allotropes reveal that the allotropes can regulate the properties of the materials. Moreover, our researched results show that the three monolayer SnSe allotropes are sufficient for fabrication of optoelectronic nanodevices.

  20. New semiconductor scintillators ZnSe(Te,O) and integrated radiation detectors based thereon

    NARCIS (Netherlands)

    Ryzhikov, [No Value; Starzhinskiy, N; Gal'chinetskii, L; Gashin, P; Kozin, D; Danshin, E

    Data are presented on properties of a new type of scintillator based on isovalently doped crystals of zinc selenide. Depending upon concentration of activating dopants Te and O, the wavelength of the luminescence maximum is 590-640 nm, response time is 1-50 mus, and afterglow level after 5 ms is not

  1. Strain tuning of optical properties in Bi2Se3

    DEFF Research Database (Denmark)

    Jensen, Mathias Rosdahl; Mørk, Jesper; Willatzen, Morten

    2017-01-01

    Based on symmetry principles we determine the most general Hamiltonian for the low energy physics of Bi2Se3, including contributions due to a static electric field and strain. The full three-dimensional model is projected into the surface states at k= 0, giving an effective two-dimensional Hamilt...

  2. Tuning optical properties of water-soluble CdTe quantum dots for biological applications

    Energy Technology Data Exchange (ETDEWEB)

    Schulze, Anne S.; Tavernaro, Isabella; Machka, Friederike [Justus-Liebig-University Giessen, Institute of Inorganic and Analytical Chemistry (Germany); Dakischew, Olga; Lips, Katrin S. [Justus-Liebig-University Giessen, Laboratory of Experimental Trauma Surgery (Germany); Wickleder, Mathias S., E-mail: mathias.wickleder@anorg.chemie.uni-giessen.de [Justus-Liebig-University Giessen, Institute of Inorganic and Analytical Chemistry (Germany)

    2017-02-15

    In this study, two different synthetic methods in aqueous solution are presented to tune the optical properties of CdTe and CdSe semiconductor nanoparticles. Additionally, the influence of different temperatures, pressures, precursor ratios, surface ligands, bases, and core components in the synthesis was investigated with regard to the particle sizes and optical properties. As a result, a red shift of the emission and absorption maxima with increasing reaction temperature (100 to 220°C), pressure (1 to 25 bar), and different ratios of core components of alloyed semiconductor nanoparticles could be observed without a change of the particle size. An increase in particle size from 2.5 to 5 nm was only achieved by variation of the mercaptocarboxylic acid ligands in combination with the reaction time and used base. To get a first hint on the cytotoxic effects and cell uptake of the synthesized quantum dots, in vitro tests mesenchymal stem cells (MSCs) were carried out.

  3. Covalency effects of Te substitution on the antiferromagnetic stability of Cr3Se4-yTey

    International Nuclear Information System (INIS)

    Ohta, S.; Adachi, Y.

    1996-01-01

    Measurements of the magnetic susceptibility χ as a function of temperature T for Te-substituted Cr 3 Se 4-y Te y (0≤y≤1) with the NiAs-like crystal structure (space group I2/m) have been carried out. As y increases, the Neel temperature T N shifts to the lower temperature side. The magnetic transition temperature T A , where a sharp peak is observed in χ versus T plots, decreases with increasing y, in a similar fashion to the concentration dependence of T N . The effective number of Bohr magnetons per Cr takes an intermediate value which is expected in Cr 2+ and Cr 3+ states. Characteristic features of a spin-glass-like phase are observed in the sample with y=1. The results obtained are discussed qualitatively from the viewpoint of antiferromagnetic stability through d-p covalent mixing between Cr 3d and chalcogen p orbitals. (orig.)

  4. Tunable (δπ, δπ)-Type Antiferromagnetic Order in α-Fe(Te,Se) Superconductors

    Science.gov (United States)

    Bao, Wei; Qiu, Y.; Huang, Q.; Green, M. A.; Zajdel, P.; Fitzsimmons, M. R.; Zhernenkov, M.; Chang, S.; Fang, Minghu; Qian, B.; Vehstedt, E. K.; Yang, Jinhu; Pham, H. M.; Spinu, L.; Mao, Z. Q.

    2009-06-01

    The new α-Fe(Te,Se) superconductors share the common iron building block and ferminology with the LaFeAsO and BaFe2As2 families of superconductors. In contrast with the predicted commensurate spin-density-wave order at the nesting wave vector (π, 0), a completely different magnetic order with a composition tunable propagation vector (δπ, δπ) was determined for the parent compound Fe1+yTe in this powder and single-crystal neutron diffraction study. The new antiferromagnetic order survives as a short-range one even in the highest TC sample. An alternative to the prevailing nesting Fermi surface mechanism is required to understand the latest family of ferrous superconductors.

  5. Optical properties of Cd Se thin films obtained by pyrolytic dew

    International Nuclear Information System (INIS)

    Perez G, A.M.; Tepantlan, C.S.; Renero C, F.

    2006-01-01

    In this paper the optical properties of Cd Se thin films obtained by spray pyrolysis are presented. The films are prepared by Sodium Seleno sulphate (Na 2 SSeO 3 ) and Cadmium Chloride (CdC 12 ) mixing in aqueous environment. Optical parameters of the films (refractive index, absorption coefficient and optical ban gap) were calculated from transmittance spectra. The obtained values of the optical ban gap are compared with the result obtained by other deposition method. (Author)

  6. Composition-controlled optical properties of colloidal CdSe quantum dots

    International Nuclear Information System (INIS)

    Ayele, Delele Worku; Su, Wei-Nien; Chou, Hung-Lung; Pan, Chun-Jern; Hwang, Bing-Joe

    2014-01-01

    Graphical abstract: - Highlights: • The surface of CdSe QDs are modified with cadmium followed by selenium. • The optical properties of CdSe QDs can be controlled by manipulating the composition. • Surface compositional change affects the surface defects or traps and recombination. • The surface trapping state can be controlled by tuning the surface composition. • A change in composition shows a change in the carrier life time. - Abstract: A strategy with respect to band gap engineering by controlling the composition of CdSe quantum dots (QDs) is reported. After the CdSe QDs are prepared, their compositions can be effectively manipulated from 1:1 (Cd:Se) CdSe QDs to Cd-rich and then to Se-rich QDs. To obtain Cd-rich CdSe QDs, Cd was deposited on equimolar CdSe QDs. Further deposition of Se on Cd-rich CdSe QDs produced Se-rich CdSe QDs. The compositions (Cd:Se) of the as-prepared CdSe quantum dots were acquired by Energy-dispersive X-ray spectroscopy (EDX). By changing the composition, the overall optical properties of the CdSe QDs can be manipulated. It was found that as the composition of the QDs changes from 1:1 (Cd:Se) CdSe to Cd-rich and then Se-rich CdSe, the band gap decreases along with a red shift of UV–vis absorption edges and photoluminescence (PL) peaks. The quantum yield also decreases with surface composition from 1:1 (Cd:Se) CdSe QDs to Cd-rich and then to Se-rich, largely due to the changes in the surface state. Because of the involvement of the surface defect or trapping state, the carrier life time increased from the 1:1 (Cd:Se) CdSe QDs to the Cd-rich to the Se-rich CdSe QDs. We have shown that the optical properties of CdSe QDs can be controlled by manipulating the composition of the surface atoms. This strategy can potentially be extended to other semiconductor nanocrystals to modify their properties

  7. Composition-controlled optical properties of colloidal CdSe quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Ayele, Delele Worku [Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan (China); Department of Chemistry, Bahir Dar University, Bahir Dar (Ethiopia); Su, Wei-Nien, E-mail: wsu@mail.ntust.edu.tw [Graduate Institute of Applied Science and Technology, National Taiwan University of Science and Technology, Taipei 106, Taiwan (China); Chou, Hung-Lung [Graduate Institute of Applied Science and Technology, National Taiwan University of Science and Technology, Taipei 106, Taiwan (China); Pan, Chun-Jern [Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan (China); Hwang, Bing-Joe, E-mail: bjh@mail.ntust.edu.tw [Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan (China); National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan (China)

    2014-12-15

    Graphical abstract: - Highlights: • The surface of CdSe QDs are modified with cadmium followed by selenium. • The optical properties of CdSe QDs can be controlled by manipulating the composition. • Surface compositional change affects the surface defects or traps and recombination. • The surface trapping state can be controlled by tuning the surface composition. • A change in composition shows a change in the carrier life time. - Abstract: A strategy with respect to band gap engineering by controlling the composition of CdSe quantum dots (QDs) is reported. After the CdSe QDs are prepared, their compositions can be effectively manipulated from 1:1 (Cd:Se) CdSe QDs to Cd-rich and then to Se-rich QDs. To obtain Cd-rich CdSe QDs, Cd was deposited on equimolar CdSe QDs. Further deposition of Se on Cd-rich CdSe QDs produced Se-rich CdSe QDs. The compositions (Cd:Se) of the as-prepared CdSe quantum dots were acquired by Energy-dispersive X-ray spectroscopy (EDX). By changing the composition, the overall optical properties of the CdSe QDs can be manipulated. It was found that as the composition of the QDs changes from 1:1 (Cd:Se) CdSe to Cd-rich and then Se-rich CdSe, the band gap decreases along with a red shift of UV–vis absorption edges and photoluminescence (PL) peaks. The quantum yield also decreases with surface composition from 1:1 (Cd:Se) CdSe QDs to Cd-rich and then to Se-rich, largely due to the changes in the surface state. Because of the involvement of the surface defect or trapping state, the carrier life time increased from the 1:1 (Cd:Se) CdSe QDs to the Cd-rich to the Se-rich CdSe QDs. We have shown that the optical properties of CdSe QDs can be controlled by manipulating the composition of the surface atoms. This strategy can potentially be extended to other semiconductor nanocrystals to modify their properties.

  8. Beam splitter coupled CdSe optical parametric oscillator

    International Nuclear Information System (INIS)

    Levinos, N.J.; Arnold, G.P.

    1980-01-01

    An optical parametric oscillator is disclosed in which the resonant radiation is separated from the pump and output radiation so that it can be manipulated without interfering with them. Thus, for example, very narrow band output may readily be achieved by passing the resonant radiation through a line narrowing device which does not in itself interfere with either the pump radiation or the output radiation

  9. Optical sensing of triethylamine using CdSe aerogels

    International Nuclear Information System (INIS)

    Yao Qinghong; Brock, Stephanie L

    2010-01-01

    The photoluminescence (PL) response of highly porous CdSe aerogels to triethylamine (TEA) is investigated and compared to results from prior studies on single crystals and nanoparticle-polymer composites. As-prepared CdSe aerogels show significant and reversible enhancement of luminescence intensity upon exposure to TEA relative to the intensity in pure argon carrier gas. The enhancement in the PL response is dependent on the concentration and linear over the range of TEA concentration studied (4.7 x 10 3 -75 x 10 3 ppm). The sensing response of previously tested samples exhibits saturation behavior that is modeled using Langmuir adsorption isotherms, yielding adsorption equilibrium constants in the range 300-380 atm -1 . The response is sensitively affected by the surface characteristics of the aerogel; when the wet gels are treated with pyridine prior to aerogel formation, the response to TEA is diminished, and when as-prepared aerogels are heated in a vacuum, no subsequent response is observed. Deactivation is attributed to an increase in surface oxide (SeO 2 ) and decrease in surface Cd 2+ Lewis acid sites. Sensing runs of approximately one hour have little impact on the morphology or crystallinity of the aerogels, but do result in partial removal of residual thiolate ligands left over from the gelation process.

  10. Optical spectroscopy and Fermi surface studies of BiTeCl and BiTeBr

    Science.gov (United States)

    Martin, Catalin; Suslov, A. V.; Buvaev, S.; Hebard, A. F.; Bugnon, Philippe; Berger, Helmuth; Magrez, Arnaud; Tanner, D. B.

    2014-03-01

    The observation of a large bulk Rashba effect in the non-centrosymmetric semiconductors BiTeX(X=Cl, Br, I) has stimulated the interest in these sys- tems, as promising candidates for studying spin related phenomena and for the realization of spin devices. Here we present a comparative study of the electronic properties of BiTeCl and BiTeBr, determined from temperature dependent infrared spectroscopy and Shubnikov-de Haas oscillations. In par- ticular, we compare the angle dependence of quantum oscillations between the two compounds and discuss possible differences between the topology of their Fermi surfaces. Supported by NSF Cooperative Agreement DMR-1157490 to the National High Magnetic Field Laboratory.

  11. Fabrication of fluorescence-based biosensors from functionalized CdSe and CdTe quantum dots for pesticide detection

    International Nuclear Information System (INIS)

    Chi Tran, Thi Kim; Vu, Duc Chinh; Thuy Ung, Thi Dieu; Nguyen, Hai Yen; Nguyen, Ngoc Hai; Dao, Tran Cao; Pham, Thu Nga; Nguyen, Quang Liem

    2012-01-01

    This paper presents the results on the fabrication of highly sensitive fluorescence biosensors for pesticide detection. The biosensors are actually constructed from the complex of quantum dots (QDs), acetylcholinesterase (AChE) and acetylthiocholine (ATCh). The biosensor activity is based on the change of luminescence from CdSe and CdTe QDs with pH, while the pH is changed with the hydrolysis rate of ATCh catalyzed by the enzyme AChE, whose activity is specifically inhibited by pesticides. Two kinds of QDs were used to fabricate our biosensors: (i) CdSe QDs synthesized in high-boiling non-polar organic solvent and then functionalized by shelling with two monolayers (2-ML) of ZnSe and eight monolayers (8-ML) of ZnS and finally capped with 3-mercaptopropionic acid (MPA) to become water soluble; and (ii) CdTe QDs synthesized in aqueous phase then shelled with CdS. For normal checks the fabricated biosensors could detect parathion methyl (PM) pesticide at very low contents of ppm with the threshold as low as 0.05 ppm. The dynamic range from 0.05 ppm to 1 ppm for the pesticide detection could be expandable by increasing the AChE amount in the biosensor. (paper)

  12. Lattice parameters of the Hg1-xFexSe and Cd1-xFexTe semimagnetic semiconductors

    International Nuclear Information System (INIS)

    Sarem, A.; Soulayman, S.

    2004-01-01

    Full text.Hg 1-x Fe x Se and Cd 1-x Fe x Te are members of a family of semiconducting alloys referred to as diluted magnetic semiconductors (DMS), i.e., ternary alloys whose lattice is made up in part of substitutional magnetic ions (in the present case, fe 2+ ). These materials are of considerable interest because, apart from the opportunities provided by the ternary nature of these compounds (e.g., tunability of the energy gap or the lattice constant), they display interesting magnetic properties as well as exchange interaction between the localized Fe 2+ moments and band electrons, resulting in a host of novel effects. In this paper we investigate the behavior of the crystal lattice of Hg 1-x Fe x Se and Cd 1-x Fe x Te, grown using modified Bridgman method. The purpose of the study is providing precise quantitative data for the lattice parameter as a function of x, which can then be used as a means of determining composition. The results of lattice parameter measurements on the ternary semiconductor alloys Hg 1-x Fe x Se over the range (0≤x≤0.15) and Cd 1-x Fe x Te in the range (0≤x≤0.03) are reports. Each sample was subjected to chemical analysis for determining the real concentration of iron. Here it was found that the differences between the nominal compositions and the real ones for all investigated samples are negligible. The powdered samples of Hg 1-x Fe x Se and Cd 1-x Fe x Te with different nominal compositions were studied using a DRON diffractometer with filtered Cο radiation (λ kα1 =1.78892A; λ kα2 =1.79278A). The diffraction patterns with a scan rate of 1 degree 2θ/min were taken. Precise measurements of the line position diffracted and extrapolation method to determine a to value θ=90 degree were made by Least Square Method. This method allowed determining cell parameters foe each sample with accuracy ±0.0001A. The crystal structure of these compounds was determined as a cubic one of the zinc blede type. The structural homogeneity of

  13. Synthesis and nonlinear optical property of polycrystalline MnTeMoO{sub 6}

    Energy Technology Data Exchange (ETDEWEB)

    Jin, Chengguo [Yibin University, Key Laboratory of Computational Physics of Sichuan Province, Yibin (China); Yibin University, School of Physics and Electronic Engineering, Yibin (China)

    2017-04-15

    Polycrystalline MnTeMoO{sub 6} powder has been synthesized by a new approach that MnO{sub 2} is used as the manganese source. The transformation mechanism of manganese ions in the new approach has been discussed. The nonlinear optical property of polycrystalline MnTeMoO{sub 6} has been investigated, and compared with single-crystalline samples. The transformation Mn{sup 4+} → Mn{sup 2+} may be formed directly without stable intermediates, and TeO{sub 2} may serve as catalyst. The SHG response of polycrystalline MnTeMoO{sub 6} powder is worse than that of single-crystalline powder in the same particle size distribution as its pseudo-size. The results indicate that it should pay special attention with the pseudo-size of polycrystalline powder when the potential nonlinear optical materials are screened by powder second harmonic generation measurements. (orig.)

  14. Microstructural, optical and electrical properties of Cl-doped CdTe single crystals

    Directory of Open Access Journals (Sweden)

    Choi Hyojeong

    2016-09-01

    Full Text Available Microstructural, optical and electrical properties of Cl-doped CdTe crystals grown by the low pressure Bridgman (LPB method were investigated for four different doping concentrations (unintentionally doped, 4.97 × 1019 cm−3, 9.94 × 1019 cm−3 and 1.99 × 1020 cm−3 and three different locations within the ingots (namely, samples from top, middle and bottom positions in the order of the distance from the tip of the ingot. It was shown that Cl dopant suppressed the unwanted secondary (5 1 1 crystalline orientation. Also, the average size and surface coverage of Te inclusions decreased with an increase in Cl doping concentration. Spectroscopic ellipsometry measurements showed that the optical quality of the Cl-doped CdTe single crystals was enhanced. The resistivity of the CdTe sample doped with Cl at the 1.99 × 1020 cm−3 was above 1010 Ω.cm.

  15. CdTe Quantum Dots Embedded in Multidentate Biopolymer Based on Salep: Characterization and Optical Properties

    Directory of Open Access Journals (Sweden)

    Ghasem Rezanejade Bardajee

    2013-01-01

    Full Text Available This paper describes a novel method for surface modification of water soluble CdTe quantum dots (QDs by using poly(acrylic acid grafted onto salep (salep-g-PAA as a biopolymer. As-prepared CdTe-salep-g-PAA QDs were characterized by Fourier transform infrared (FT-IR spectrum, thermogravimetric (TG analysis, and transmission electron microscopy (TEM. The absorption and fluorescence emission spectra were measured to investigate the effect of salep-g-PAA biopolymer on the optical properties of CdTe QDs. The results showed that the optical properties of CdTe QDs were significantly enhanced by using salep-g-PAA-based biopolymer.

  16. Synthesis and nonlinear optical property of polycrystalline MnTeMoO_6

    International Nuclear Information System (INIS)

    Jin, Chengguo

    2017-01-01

    Polycrystalline MnTeMoO_6 powder has been synthesized by a new approach that MnO_2 is used as the manganese source. The transformation mechanism of manganese ions in the new approach has been discussed. The nonlinear optical property of polycrystalline MnTeMoO_6 has been investigated, and compared with single-crystalline samples. The transformation Mn"4"+ → Mn"2"+ may be formed directly without stable intermediates, and TeO_2 may serve as catalyst. The SHG response of polycrystalline MnTeMoO_6 powder is worse than that of single-crystalline powder in the same particle size distribution as its pseudo-size. The results indicate that it should pay special attention with the pseudo-size of polycrystalline powder when the potential nonlinear optical materials are screened by powder second harmonic generation measurements. (orig.)

  17. Unprecedented Integral-Free Debye Temperature Formulas: Sample Applications to Heat Capacities of ZnSe and ZnTe

    Directory of Open Access Journals (Sweden)

    R. Pässler

    2017-01-01

    Full Text Available Detailed analytical and numerical analyses are performed for combinations of several complementary sets of measured heat capacities, for ZnSe and ZnTe, from the liquid-helium region up to 600 K. The isochoric (harmonic parts of heat capacities, CVh(T, are described within the frame of a properly devised four-oscillator hybrid model. Additional anharmonicity-related terms are included for comprehensive numerical fittings of the isobaric heat capacities, Cp(T. The contributions of Debye and non-Debye type due to the low-energy acoustical phonon sections are represented here for the first time by unprecedented, integral-free formulas. Indications for weak electronic contributions to the cryogenic heat capacities are found for both materials. A novel analytical framework has been constructed for high-accuracy evaluations of Debye function integrals via a couple of integral-free formulas, consisting of Debye’s conventional low-temperature series expansion in combination with an unprecedented high-temperature series representation for reciprocal values of the Debye function. The zero-temperature limits of Debye temperatures have been detected from published low-temperature Cp(T data sets to be significantly lower than previously estimated, namely, 270 (±3 K for ZnSe and 220 (±2 K for ZnTe. The high-temperature limits of the “true” (harmonic lattice Debye temperatures are found to be 317 K for ZnSe and 262 K for ZnTe.

  18. Fabrication of Fe1.1Se0.5Te0.5 bulk by a high energy ball milling technique

    Science.gov (United States)

    Liu, Jixing; Li, Chengshan; Zhang, Shengnan; Feng, Jianqing; Zhang, Pingxiang; Zhou, Lian

    2017-11-01

    Fe1.1Se0.5Te0.5 superconducting bulks were successfully synthesized by a high energy ball milling (HEBM) aided sintering technique. Two advantages of this new technique have been revealed compared with traditional solid state sintering method. One is greatly increased the density of sintered bulks. It is because the precursor powders with β-Fe(Se, Te) and δ-Fe(Se, Te) were obtained directly by the HEBM process and without formation of liquid Se (and Te), which could avoid the huge volume expansion. The other is the obvious decrease of sintering temperature and dwell time due to the effective shortened length of diffusion paths. The superconducting critical temperature Tc of 14.2 K in our sample is comparable with those in previous reports, and further optimization of chemical composition is on the way.

  19. Structural and superconducting properties of epitaxial Fe{sub 1+y}Se{sub 1-x}Te{sub x} thin films

    Energy Technology Data Exchange (ETDEWEB)

    Richter, Stefan; Yuan, Feifei; Grinenko, Vadim; Huehne, Ruben [Institute for Metallic Materials, IFW Dresden (Germany); Sala, Alberto; Putti, Marina [Dipartimento di Fisica, Universita di Genova (Italy)

    2015-07-01

    The iron based superconductor Fe(Se,Te) is in the center of much ongoing research. The reason for this is on the one hand its simple crystal structure, that consists only of stacked Fe(Se,Te) layers so that structural and superconducting properties can be connected more easily, on the other hand FeSe itself shows a high sensibility for strain and changes in stoichiometry and can have potentially very high critical temperatures under hydrostatic pressure or in monolayers. We investigate epitaxial thin films of Fe{sub 1+y}Se{sub 1-x}Te{sub x} grown by pulsed laser deposition on different single crystalline substrates. A high crystalline quality and a superconducting transition of up to about 20 K can be achieved using optimized deposition parameters. The influence of growth conditions, Te-doping, film thickness and post growth oxygen treatment on the structural and superconducting properties on these films will be presented in detail.

  20. Magneto-transport studies on Bi2Te2+xSe1–x (x = 0.05 and 0.10 topological insulators

    Directory of Open Access Journals (Sweden)

    Bushra Irfan

    2016-09-01

    Full Text Available Bi2Te2Se is one of the most promising three dimensional topological insulators, for the study of surface states. In this work, we report the results of transport and magneto-transport behavior of Bi2Te2+xSe1–x (x=0.05 and 0.10 single crystals grown using modified Bridgeman technique. Resistance versus temperature measurements show semiconducting behavior for x = 0.05 and 0.10 crystals. Linear magnetoresistance is observed for Bi2Te2.05Se0.95 (i.e. x=0.05 whereas, Bi2Te2.10Se0.90 (x=0.10 single crystal shows a conductance fluctuations at low magnetic field.

  1. Nonlinear optical properties of TeO$_2$ crystalline phases from first principles

    OpenAIRE

    Berkaine, Nabil; Orhan, Emmanuelle; Masson, Olivier; Thomas, Philippe; Junquera, Javier

    2010-01-01

    We have computed second and third nonlinear optical susceptibilities of two crystalline bulk tellurium oxide polymorphs: $\\alpha$-TeO$_{2}$ (the most stable crystalline bulk phase) and $\\gamma$-TeO$_{2}$ (the crystalline phase that ressembles the more to the glass phase. Third order nonlinear susceptibilities of the crystalline phases are two orders of magnitude larger than $\\alpha$-SiO$_{2}$ cristoballite, thus extending the experimental observations on glasses to the case of crystalline com...

  2. Band alignment of two-dimensional metal monochalcogenides MXs (M=Ga,In; X=S,Se,Te

    Directory of Open Access Journals (Sweden)

    Huazheng Sun

    2017-09-01

    Full Text Available Monolayer metal monochalcogenides MXs (M=Ga,In; X=S,Se,Te form a new class of two-dimensional semiconductors with indirect band gaps, and their band alignment information is investigated via first principles calculations. The dependence of band gap, valence-band maximum, conduction band minimum, and charge transfer on the M or X element has been obtained and can be understood from the orbital analysis of the band edges. Potential applications of metal monochalcogenides to design van der Waals heterostructures and catalyse the photo-splitting reaction of water have been discussed.

  3. Large-area and highly crystalline MoSe2 for optical modulator

    Science.gov (United States)

    Yin, Jinde; Chen, Hao; Lu, Wei; Liu, Mengli; Li, Irene Ling; Zhang, Min; Zhang, Wenfei; Wang, Jinzhang; Xu, Zihan; Yan, Peiguang; Liu, Wenjun; Ruan, Shuangchen

    2017-12-01

    Transition metal dichalcogenides (TMDs) have been successfully used as broadband optical modulator materials for pulsed fiber laser systems. However, the nonlinear optical absorptions of exfoliated TMDs are strongly limited by their nanoflakes morphology with uncontrollable lateral size and thickness. In this work, we provide an effective method to fully explore the nonlinear optical properties of MoSe2. Large-area and high quality lattice MoSe2 grown by chemical vapor deposition method was adopted as an optical modulator for the first time. The large-area MoSe2 shows excellent nonlinear optical absorption with a large modulation depth of 21.7% and small saturable intensity of 9.4 MW cm-2. After incorporating the MoSe2 optical modulator into fiber laser cavity as a saturable absorber, a highly stable Q-switching operation with single pulse energy of 224 nJ is achieved. The large-area MoSe2 possessing superior nonlinear optical properties compared to exfoliated nanoflakes affords possibility for the larger-area two-dimensional materials family as high performance optical devices.

  4. Structural properties and spatial ordering in multilayered ZnMgTe/ZnSe type-II quantum dot structures

    International Nuclear Information System (INIS)

    Manna, U.; Noyan, I. C.; Neumark, G. F.; Zhang, Q.; Moug, R.; Salakhutdinov, I. F.; Dunn, K. A.; Novak, S. W.; Tamargo, M. C.; Kuskovsky, I. L.

    2012-01-01

    We report the structural properties and spatial ordering of multilayer ZnMgTe quantum dots (QDs) embedded in ZnSe, where sub-monolayer quantities of Mg were introduced periodically during growth in order to reduce the valence band offset of ZnTe QDs. The periodicity, period dispersion, individual layer thickness, and the composition of the multilayer structures were determined by comparing the experimental high resolution x-ray diffraction (HRXRD) spectra to simulated ones for the allowed (004) and quasi-forbidden (002) reflections in combination with transmission electron microscopy (TEM) results. Secondary ion mass spectroscopy (SIMS) profiles confirmed the incorporation of Mg inside the QD layers, and the HRXRD analysis revealed that there is approximately 32% Mg in the ZnMgTe QDs. The presence of Mg contributes to higher scattering intensity of the HRXRD, leading to the observation of higher order superlattice peaks in both the (004) and (002) reflections. The distribution of scattered intensity in the reciprocal space map (RSM) shows that the diffuse scattered intensity is elongated along the q x axis, indicating a vertical correlation of the dots, which is found to be less defined for the sample with larger periodicity. The diffuse scattered intensity is also found to be weakly correlated along the q z direction indicating a weak lateral correlation of the dots.

  5. Langmuir-Blodgett films of alkane chalcogenice (S, Se, Te) stabilized gold nanoparticles

    DEFF Research Database (Denmark)

    Brust, M.; Stuhr-Hansen, N.; Norgaard, K.

    2001-01-01

    Gold nanoparticles stabilized by alkanethiolates, alkaneselenides, and alkanetellurides have been prepared by analogous methods. Chloroform solutions of thiolate and selenide stabilized particles were spread and evaporated on the water/air interface where the particles formed well-defined Langmuir...... films. The films were transferred to solid supports of freshly cleaved mica and were studied by atomic force microscopy (AFM). The particles were found to have an average core diameter of 2 nm. The stability of the particles under ambient conditions increased in the order Te

  6. Optical properties and electronic band structure of AgInSe2

    International Nuclear Information System (INIS)

    Ozaki, Shunji; Adachi, Sadao

    2006-01-01

    Optical properties of a chalcopyrite semiconductor AgInSe 2 have been studied by optical absorption, spectroscopic ellipsometry (SE), and thermoreflectance (TR) measurements. The measurements reveal distinct structures at energies of the critical points in the Brillouin zone. By performing the band-structure calculation, these critical points have been successfully assigned to specific points in the Brillouin zone. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (Abstract Copyright [2006], Wiley Periodicals, Inc.)

  7. Structural and optical properties of electrodeposited culnSe2 thin films for photovoltaic solar cells

    International Nuclear Information System (INIS)

    Guillen, C.; Herrero, J.; Galiano, F.

    1990-01-01

    Optical an structural properties of electrodeposited copper indium diselenide, CulnSe2, thin films were studied for its application in photovoltaic devices. X-ray diffraction patterns showed that thin films were grown in chalcopyrite phase after suitable treatments. Values of Eg for the CulnSe2 thin films showed a dependence on the deposition potential as determined by optical measurements. (Author) 47 refs

  8. Thermoelectric Properties of Cu-Doped n-Type Bi2Te2.85Se0.15 Prepared by Liquid Phase Growth Using a Sliding Boat

    Science.gov (United States)

    Kitagawa, Hiroyuki; Matsuura, Tsukasa; Kato, Toshihito; Kamata, Kin-ya

    2015-06-01

    N-type Bi2Te2.85Se0.15 thermoelectric materials were prepared by liquid phase growth (LPG) using a sliding boat, a simple and short fabrication process for Bi2Te3-related materials. Cu was selected as a donor dopant, and its effect on thermoelectric properties was investigated. Thick sheets and bars of Cu x Bi2 Te2.85Se0.15 ( x=0-0.25) of 1-2mm in thickness were obtained using the process. X-ray diffraction patterns and scanning electron micrographs showed that the in-plane direction tended to correspond to the hexagonal c-plane, which is the preferred direction for thermoelectric conversion. Cu-doping was effective in controlling conduction type and carrier (electron) concentration. The conduction type was p-type for undoped Bi2Te2.85Se0.15 and became n-type after Cu-doping. The Hall carrier concentration was increased by Cu-doping. Small resistivity was achieved in Cu0.02Bi2Te2.85Se0.15 owing to an optimized amount of Cu-doping and high crystal orientation. As a result, the maximum power factor near 310K for Cu0.02Bi2Te2.85Se0.15 was approximately 4×10-3W/K2m and had good reproducibility. Furthermore, the thermal stability of Cu0.02Bi2Te2.85Se0.15 was also confirmed by thermal cycling measurements of electrical resistivity. Thus, n-type Bi2Te2.85Se0.15 with a large power factor was prepared using the present LPG process.

  9. Band engineering in core/shell ZnTe/CdSe for photovoltage and efficiency enhancement in exciplex quantum dot sensitized solar cells.

    Science.gov (United States)

    Jiao, Shuang; Shen, Qing; Mora-Seró, Iván; Wang, Jin; Pan, Zhenxiao; Zhao, Ke; Kuga, Yuki; Zhong, Xinhua; Bisquert, Juan

    2015-01-27

    Even though previously reported CdTe/CdSe type-II core/shell QD sensitizers possess intrinsic superior optoelectronic properties (such as wide absorption range, fast charge separation, and slow charge recombination) in serving as light absorbers, the efficiency of the resultant solar cell is still limited by the relatively low photovoltage. To further enhance photovoltage and cell efficiency accordingly, ZnTe/CdSe type-II core/shell QDs with much larger conduction band (CB) offset in comparison with that of CdTe/CdSe (1.22 eV vs 0.27 eV) are adopted as sensitizers in the construction of quantum dot sensitized solar cells (QDSCs). The augment of band offset produces an increase of the charge accumulation across the QD/TiO2 interface under illumination and induces stronger dipole effects, therefore bringing forward an upward shift of the TiO2 CB edge after sensitization and resulting in enhancement of the photovoltage of the resultant cell devices. The variation of relative chemical capacitance, Cμ, between ZnTe/CdSe and reference CdTe/CdSe cells extracted from impedance spectroscopy (IS) characterization under dark and illumination conditions clearly demonstrates that, under light irradiation conditions, the sensitization of ZnTe/CdSe QDs upshifts the CB edge of TiO2 by the level of ∼ 50 mV related to that in the reference cell and results in the enhancement of V(oc) of the corresponding cell devices. In addition, charge extraction measurements have also confirmed the photovoltage enhancement in the ZnTe/CdSe cell related to reference CdTe/CdSe cell. Furthermore, transient grating (TG) measurements have revealed a faster electron injection rate for the ZnTe/CdSe-based QDSCs in comparison with the CdSe cells. The resultant ZnTe/CdSe QD-based QDSCs exhibit a champion power conversion efficiency of 7.17% and a certified efficiency of 6.82% under AM 1.5 G full one sun illumination, which is, as far as we know, one of the highest efficiencies for liquid-junction QDSCs.

  10. Ab initio study of point defects in PbSe and PbTe: Bulk and nanowire

    Energy Technology Data Exchange (ETDEWEB)

    Wrasse, E. O. [Instituto de Física, Universidade Federal de Uberlândia, 38408-100, Uberlândia, MG, Brazil and Departamento de Física, Universidade Federal de Santa Maria, 97105-900, Santa Maria, RS (Brazil); Venezuela, P. [Instituto de Física, Universidade Federal Fluminense, 24210-346, Niteroi, RJ (Brazil); Baierle, R. J., E-mail: rbaierle@smail.ufsm.br [Departamento de Física, Universidade Federal de Santa Maria, 97105-900, Santa Maria, RS (Brazil)

    2014-11-14

    First principles investigations, within the spin-polarized density functional theory, are performed to study energetic stability and electronic properties of point defects (vacancies and antisites) in PbSe and PbTe: bulk and nanowire (NW). Our results show that the energetic stability of these defects is ruled by relaxation process. These defects have lower formation energies in the nanowire structures as compared to the bulk, being more stable in the surface of the NWs. We also show that in the bulk system only one charge state is stable, otherwise, due to the larger band gaps, more than one charge state may be stable in the NWs. In addition, we have investigated how the presence of intrinsic defects affects the electronic properties of bulk and NW systems. Vacancies give rise to new electronic states near to the edges of the valence and conduction bands while the energetic position of the electronic states from antisites depends on the charge state, being localized inside the band gap or near the edges of the valence or conduction bands. We discuss how these changes in the electronic properties due to intrinsic defects may affect the thermoelectric properties of PbSe and PbTe NWs.

  11. Weak antilocalization effect due to topological surface states in Bi2Se2.1Te0.9

    Science.gov (United States)

    Shrestha, K.; Graf, D.; Marinova, V.; Lorenz, B.; Chu, C. W.

    2017-10-01

    We have investigated the weak antilocalization (WAL) effect in the p-type Bi2Se2.1Te0.9 topological system. The magnetoconductance shows a cusp-like feature at low magnetic fields, indicating the presence of the WAL effect. The WAL curves measured at different tilt angles merge together when they are plotted as a function of the normal field components, showing that surface states dominate the magnetoconductance in the Bi2Se2.1Te0.9 crystal. We have calculated magnetoconductance per conduction channel and applied the Hikami-Larkin-Nagaoka formula to determine the physical parameters that characterize the WAL effect. The number of conduction channels and the phase coherence length do not change with temperature up to T = 5 K. In addition, the sample shows a large positive magnetoresistance that reaches 1900% under a magnetic field of 35 T at T = 0.33 K with no sign of saturation. The magnetoresistance value decreases with both increasing temperature and tilt angle of the sample surface with respect to the magnetic field. The large magnetoresistance of topological insulators can be utilized in future technology such as sensors and memory devices.

  12. Effect of temperature and pressure on non-linear conduction in GeTeSe chalcogenide glass

    International Nuclear Information System (INIS)

    El-Mansy, M.K.

    1998-01-01

    The I-V characteristic curves were studied in the temperature range 301-359 K and pressure range up to 7.15 x 10 9 Pa which illustrate a non-linear behaviour below (high-resistance region) and beyond (negative-resistance region) a breakdown point characterising Ge 27 Te 62 Se 11 chalcogenide glasses. The general behaviour is shifted towards lower voltage and higher current when the ambient temperature and/or the applied pressure were increased. The non-linear behaviour in the pre breakdown region is discussed according to the Poole-Frenkel field emission of electrons from deep traps located at a depth equal to 0.372eV. The analysis of the effect of field on the non-linear conduction in Ge 27 Te 62 Se 11 chalcogenide glass suggests a modification of the energy difference between filled and empty sites, where the effect of pressure suggests a reduction of the energy gap width. The analysis based on simple thermal effects in the region closer to the breakdown point implies the electrothermal process initiating the negative resistance region. The results of post breakdown region (negative-resistance region) imply the electron hopping between filled and empty localised states at Fermi level. The density of localised states is estimated which lies in the range 5.7 x 10 16 -1.84 x 10 18 cm -3 /eV

  13. Effect of Te doping on superconductivity and charge-density wave in dichalcogenides 2H-NbSe2-χTeχ(χ=0,0.1,0.2)

    Institute of Scientific and Technical Information of China (English)

    Wang Hong-Tao; Li Lin-Jun; Ye De-shu; Cheng Xin-Hong; Xu Zhu-An

    2007-01-01

    Single crystals of Te-doped dichalcogenides 2H-NbSe2-χTeχ(χ=0,0.10,0.20)were grown by vapour transport method.The effect of Te doping on the superconducting and charge-density wave(CDW)transitions has been investigated.The sharp decrease of residual resistance ratio,RRR=R(300K)/R(8K),with increasing Te content was observed,indicating that the disorder in the conducting plane is induced by Te doping.Meanwhile the superconducting transition temperature,Tc,decreases monotonically with Te content.However,the CDW transition temperature,TCDW,shown by a small jump in the temperature dependence of the resistivity near 30 K,increases slightly.The results show that the suppression of superconductivity might be caused by the enhancement of CDW ordering.The disorder has little influence on the CDW ordering.

  14. Analysis of optical transitions in Zn1-x Cdx Se quantum wells

    International Nuclear Information System (INIS)

    Diaz A, P.; Melo P, Osvaldo de; Hernandez C, I.; Martin A, J.

    1998-01-01

    In this work we will address our attention to three different but actual aspects concerning the physics of Zn 1-x Cd x Se/ Zn Se quantum wells (Q Ws). After a brief introduction where the main interest of these structures in the fabrication of blue-green laser and light emitting diodes will be discussed, we will touch first the problem of the band-offsets in Zn 1-x Cd x Se/Zn Se heterostructure. Then we will illustrate how the shape of a Zn 1-x Cd x Se/Zn Se Q W can be found from two measured transition energies in optical experiment. Finally, the main features of the optical transitions in these Q Ws are demonstrated. (Author)

  15. Structural, morphological and optical properties of pulsed laser deposited ZnSe/ZnSeO3 thin films

    Science.gov (United States)

    Hassan, Syed Ali; Bashir, Shazia; Zehra, Khushboo; Salman Ahmed, Qazi

    2018-04-01

    The effect of varying laser pulses on structural, morphological and optical behavior of Pulsed Laser Deposited (PLD) ZnSe/ZnSeO3 thin films has been investigated. The films were grown by employing Excimer laser (100 mJ, 248 nm, 18 ns, 30 Hz) at various number of laser pulses i.e. 3000, 4000, 5000 and 6000 with elevated substrate temperature of 300 °C. One film was grown at Room Temperature (RT) by employing 3000 number of laser pulses. In order to investigate the structural analysis of deposited films, XRD analysis was performed. It was observed that the room temperature is not favorable for the growth of crystalline film. However, elevated substrate temperature to 300°C, two phases with preferred orientation of ZnSeO3 (2 1 2) and ZnSe (3 3 1) were identified. AFM and SEM analysis were performed to explore the surface morphology of grown films. Morphological analysis also confirmed the non-uniform film growth at room temperature. At elevated substrate temperature (300 °C), the growth of dendritic rods and cubical crystalline structures are observed for lower number of laser pulses i.e. 3000 and 4000 respectively. With increased number of pulses i.e. 5000 and 6000, the films surface morphology becomes smooth which is confirmed by measurement of surface RMS roughness. Number of grains, skewness, kurtosis and other parameters have been evaluated by statistical analysis. In order to investigate the thickness, and optical properties of deposited films, ellipsometery and UV–Vis spectroscopy techniques were employed. The estimated band gap energy is 2.67 eV for the film grown at RT, whereas band gap values varies from 2.80 eV to 3.01 eV for the films grown at 300 °C with increasing number of laser pulses.

  16. Improvement of thermoelectric properties induced by uniquely ordered lattice field in Bi2Se0.5Te2.5 pillar array

    International Nuclear Information System (INIS)

    Tan, Ming; Hao, Yanming; Wang, Gangzhi

    2014-01-01

    In this study, it was found that uniquely ordered lattice field favors transport of carriers but hinder that of phonons. The n-Bi 2 Se 0.5 Te 2.5 pillar array film was successfully achieved by a simple ion beam assisted deposition technique. This oriented pillar array structure is clear with pillar diameter of about 30 nm, exhibiting a uniquely ordered lattice field. The properties of the ordered Bi 2 Se 0.5 Te 2.5 pillar array were greatly enhanced in comparison with those of the ordinary film. The Bi 2 Se 0.5 Te 2.5 pillar array with a thermoelectric dimensionless figure-of-merit ZT=1.28 was obtained at room temperature. The in-plane transport mechanisms of the ordered pillar array and the ordinary structures, lattice field model, are proposed and investigated. The specially ordered lattice field is the main reason for the properties enhancement observed in the Bi 2 Se 0.5 Te 2.5 film. Introduction of such ordered lattice field into TE films is therefore a very promising approach. - Graphical abstract: In this study, it was found that uniquely ordered lattice field favors transport of carriers but hinder that of phonons. The Bi 2 Se 0.5 Te 2.5 pillar array film with a thermoelectric dimensionless figure-of-merit ZT=1.28 was obtained at room temperature. The in-plane transport mechanisms of the ordered pillar array and the ordinary structures, the lattice field model, are proposed and investigated. The specially ordered lattice field is the main reason for the properties enhancement observed in the Bi 2 Se 0.5 Te 2.5 pillar array. Introduction of such uniquely ordered lattice field into TE films is therefore a very promising approach. In (a) TEM and (b) HRTEM images of the ordered Bi 2 Se 0.5 Te 2.5 column array. - Highlights: • Uniquely ordered Bi 2 Se 0.5 Te 2.5 pillar array was achieved by an IBAD method. • The pillar array with an ordered lattice field exhibits attractive TE property. • The transport mechanism of such ordered pillar array is proposed and

  17. Composition determination of CdSxSe1-x mixed crystals by optical dispersion

    International Nuclear Information System (INIS)

    Iliev, I.; Dimov, T.; Ribarov, D.; Lange, H.

    1989-01-01

    An optical dispersion method has been developed determining the CdS/CdSe ratio in CdS x Se 1-x mixed crystals from the relationship between position of the isotropic point (birefrigence becomes zero for a definite wavelength at the absorption edge) and chemical composition x. Birefrigence spectra and piezo-optic spectra of samples with x = 0.2, 0.6, and 0.875 give the spectral position of the isotropic point (ip). A curve of wavelength of ip versus x of CdS x Se 1-x is evaluated by the least-squares procedure and tested by X-ray fluorescence analysis

  18. Linear and nonlinear optical characteristics of Te nanoparticles-doped germanate glasses

    Science.gov (United States)

    Xu, Zhousu; Guo, Qiangbing; Liu, Chang; Ma, Zhijun; Liu, Xiaofeng; Qiu, Jianrong

    2016-10-01

    Te nanoparticles (NPs)-doped GeO2-MgO-B2O3-Al2O3-TeO2 glasses were prepared by the conventional melt-quenching method. Based on X-ray photoelectron spectroscopy, Raman spectroscopy and transmission electron microscope observation, the coloration of the glass at high TeO2 concentration is ascribed to the precipitation of elemental Te NPs with a size of 5-10 nm in the germanate glass. Optical absorption spectra and nonlinear optical (NLO) properties of the glass samples were analyzed by UV-3600 spectrophotometry and Z-scan technique, respectively. The nonlinear absorption coefficient ( β) and the imaginary part of the third-order NLO susceptibility (Im χ (3)) were estimated to be 1.74 cm/GW and 1.142 × 10-12 esu for laser power of 95 μW, respectively. Due to the excellent NLO properties, the Te NPs-doped germanate glasses may have potential applications for ultrafast optical switch and photonics.

  19. Synthesis, structural, optical and Raman studies of pure and lanthanum doped ZnSe nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Pushpendra, E-mail: push.nac@gmail.com [Department of Physics, Faculty of Science, Banaras Hindu University, Varanasi 221005 (India); Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 11529, Taiwan (China); Singh, Jai [Department of Physics, Faculty of Science, Banaras Hindu University, Varanasi 221005 (India); Department of Materials Science and Engineering, Pusan National University, 30 Jangjeon-dong, Geumjeong-gu, Busan 609-735 (Korea, Republic of); Pandey, Mukesh Kumar [Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 11529, Taiwan (China); Jeyanthi, C.E. [Research and Development Centre, Bharathiar University, Coimbatore 641 046 (India); Siddheswaran, R. [Department of Materials Science and Engineering, University of Concepcion, Concepcion (Chile); Paulraj, M. [Department of Physics, Faculty of Physical sciences and Mathematics, University of Concepcion, Casilla 160, Concepcion (Chile); Hui, K.N. [Department of Materials Science and Engineering, Pusan National University, 30 Jangjeon-dong, Geumjeong-gu, Busan 609-735 (Korea, Republic of); Hui, K.S., E-mail: kshui@hanyang.ac.kr [Department of Mechanical Engineering, Hanyang University, 17 Haengdang-dong, Seongdong-gu, Seoul 133-791 (Korea, Republic of)

    2014-01-01

    Graphical abstract: - Highlights: • Template-free synthesis of ZnSe and ZnSe:La nanoparticles was developed at low temperature 100 °C. • Cubic ZnSe and ZnSe:La nanoparticles were obtained by chemical route. • As-synthesized ZnSe:La nanoparticles showed higher emission intensity than ZnSe nanoparticles. • Band gap (E{sub g}) of ZnSe nanoparticles was bigger than ZnSe nanoparticles due to nanosized effect. - Abstract: In this work, a simple, effective and reproducible chemical synthetic route for the production of high-quality, pure ZnSe nanoparticles (NPs), and lanthanum-doped ZnSe (ZnSe:La) NPs is presented. The wide bandgap, luminescent pure ZnSe and ZnSe:La NPs has been synthesized at a low temperature (100 °C) in a single template-free step. The size and optical bandgap of the NPs was analyzed from powder X-ray diffraction (XRD), UV–visible (UV–vis) spectroscopy, transmission electron microscopy (TEM), and high resolution transmission electron microscopy (HRTEM). A broad photoluminescence (PL) emission across the visible spectrum has been demonstrated by a systematic blue-shift in emission due to the formation of small nanoparticles. Here, contribution to emission intensity from surface states of NPs increases with La doping. TEM data revealed that the average size of ZnSe and ZnSe:La NPs is 14 and 8 nm, respectively. On the other hand, band gap energy E{sub g} of ZnSe and ZnSe:La NPs were found to be 3.59 eV and 3.65 eV, respectively. Results showed that hydrazine hydrate played multiple roles in the formation of ZnSe and ZnSe:La NPs. A possible reaction mechanism for the growth of NPs is also discussed.

  20. The radioluminescence and optical behaviour of nanocomposites with CdSeS quantum dot

    Energy Technology Data Exchange (ETDEWEB)

    Keskin, İ.Ç., E-mail: ilkercetinkeskin@hotmail.com [Department of Physics, Faculty of Art and Science, Celal Bayar University, Manisa-Turkey (Turkey); Türemiş, M. [Department of Physics, Faculty of Art and Science, Celal Bayar University, Manisa-Turkey (Turkey); Katı, M.İ. [Experimental Science Applications and Research Center, Celal Bayar University, Manisa (Turkey); Kibar, R. [Department of Physics, Faculty of Art and Science, Celal Bayar University, Manisa-Turkey (Turkey); Şirin, K. [Department of Chemistry, Faculty of Art and Science, Celal Bayar University, Manisa-Turkey (Turkey); Çipiloğlu, M.A. [Department of Physics, Faculty of Art and Science, Celal Bayar University, Manisa-Turkey (Turkey); Kuş, M.; Büyükçelebi, S. [Advanced Technology Research and Application, Center Selcuk University, Konya (Turkey); Çetin, A. [Department of Physics, Faculty of Art and Science, Celal Bayar University, Manisa-Turkey (Turkey)

    2017-05-15

    In this work, highly luminescent alloyed CdSeS QDs are successfully synthesized by two phase route method by using oleic acid (OA) as a surfactant. OA capped CdSeS QDs prepared in two different synthesis duration were compared in terms of luminescence and optical properties. The nanocomposites blended with CdSeS QDs which have highly luminescent efficiency in different ratios by Low Density Polyethylene (LDPE) and these nanocomposites were mainly investigated radioluminescence (RL) and optical properties (UV/VIS absorption). Structural, morphological, thermal properties of the nanocrystal and nanocomposites were examined using; XRD, FT-IR, TEM, SEM, TG-DTA techniques. OA capped CdSeS and also nanocomposites were showed two RL spectrum peaks in green and red region at around 528 nm and 710 nm respectively. Also, it is seen that the radioluminescence intensity changes linearly with the particle size of the QDs and about 12% size change of quantum dot led to a threefold increase in RL intensity. The luminescence glow curves are in compliance with absorption and fluorescence spectra. The absorption bands showed a significant blue shift for the nanocomposites as compare to powder CdSeS. The optical band gap of the OA capped CdSeS calculated as 1.77 eV. It was observed that the optical band gap of LDPE was decreased by the adding ratio of CdSeS from 3.71 eV to 2.25 eV.

  1. The radioluminescence and optical behaviour of nanocomposites with CdSeS quantum dot

    International Nuclear Information System (INIS)

    Keskin, İ.Ç.; Türemiş, M.; Katı, M.İ.; Kibar, R.; Şirin, K.; Çipiloğlu, M.A.; Kuş, M.; Büyükçelebi, S.; Çetin, A.

    2017-01-01

    In this work, highly luminescent alloyed CdSeS QDs are successfully synthesized by two phase route method by using oleic acid (OA) as a surfactant. OA capped CdSeS QDs prepared in two different synthesis duration were compared in terms of luminescence and optical properties. The nanocomposites blended with CdSeS QDs which have highly luminescent efficiency in different ratios by Low Density Polyethylene (LDPE) and these nanocomposites were mainly investigated radioluminescence (RL) and optical properties (UV/VIS absorption). Structural, morphological, thermal properties of the nanocrystal and nanocomposites were examined using; XRD, FT-IR, TEM, SEM, TG-DTA techniques. OA capped CdSeS and also nanocomposites were showed two RL spectrum peaks in green and red region at around 528 nm and 710 nm respectively. Also, it is seen that the radioluminescence intensity changes linearly with the particle size of the QDs and about 12% size change of quantum dot led to a threefold increase in RL intensity. The luminescence glow curves are in compliance with absorption and fluorescence spectra. The absorption bands showed a significant blue shift for the nanocomposites as compare to powder CdSeS. The optical band gap of the OA capped CdSeS calculated as 1.77 eV. It was observed that the optical band gap of LDPE was decreased by the adding ratio of CdSeS from 3.71 eV to 2.25 eV.

  2. Structural and electronic properties of Cu2Q and CuQ (Q = O, S, Se, and Te) studied by first-principles calculations

    Science.gov (United States)

    Zhao, Ting; Wang, Yu-An; Zhao, Zong-Yan; Liu, Qiang; Liu, Qing-Ju

    2018-01-01

    In order to explore the similarity, difference, and tendency of binary copper-based chalcogenides, the crystal structure, electronic structure, and optical properties of eight compounds of Cu2Q and CuQ (Q = O, S, Se, and Te) have been calculated by density functional theory with HSE06 method. According to the calculated results, the electronic structure and optical properties of Cu2Q and CuQ present certain similarities and tendencies, with the increase of atomic number of Q elements: the interactions between Cu-Q, Cu-Cu, and Q-Q are gradually enhancing; the value of band gap is gradually decreasing, due to the down-shifting of Cu-4p states; the covalent feature of Cu atoms is gradually strengthening, while their ionic feature is gradually weakening; the absorption coefficient in the visible-light region is also increasing. On the other hand, some differences can be found, owing to the different crystal structure and component, for example: CuO presents the characteristics of multi-band gap, which is very favorable to absorb infrared-light; the electron transfer in CuQ is stronger than that in Cu2Q; the absorption peaks and intensity are very strong in the ultraviolet-light region and infrared-light region. The findings in the present work will help to understand the underlying physical mechanism of binary copper-based chalcogenides, and available to design novel copper-based chalcogenides photo-electronics materials and devices.

  3. Evidence for surface-generated photocurrent in (Bi,Sb)2Se3and(Bi,Sb)2Te3 thin films

    Science.gov (United States)

    Pan, Yu; Richardella, Anthony; Yao, Bing; Lee, Joon Sue; Flanagan, Thomas; Kandala, Abhinav; Samarth, Nitin; Yeats, Andrew; Mintun, Peter; Awschalom, David

    2015-03-01

    Illumination with circularly polarized light is known produce a helicity-dependent photocurrent in topological insulators such as Bi2Se3 [e.g. Nature Nanotech. 7, 96 (2012)]. However, the exact origin of this effect is still unclear since it is observed with photons well above the bulk band gap. We report measurements of the polarization-dependent photocurrent in a series of (Bi,Sb)2Se3 thin films with different carrier concentrations and find that the photocurrent is enhanced as we increase the population of the surface states. This finding is supported by a study of helicity-dependent photocurrents in back-gated (Bi,Sb)2Te3 thin films, where the chemical potential is varied electrostatically. By illuminating our samples at different wavelengths, we show that the helicity-dependent photocurrent is enhanced when the photon energy approaches the energy difference between the lowest and first excited (unoccupied) topological surface states. This leads us to attribute the helicity-dependent photocurrent in topological insulators to optical excitations between these two spin-textured surface states. We will also discuss experiments imaging the spatial variation of these helicity-dependent photocurrents. This work is supported by ONR.

  4. Structural study of (CdS/ZnSe)/BeTe superlattices for λ=1.55 μm intersubband transition

    International Nuclear Information System (INIS)

    Li, B.S.; Akimoto, R.; Akita, K.; Hasama, H.

    2004-01-01

    A (CdS/ZnSe)/BeTe superlattice (SL), based on wide band gap II-VI compounds, with a large band offset of 3.1 eV was grown on a GaAs (001) substrate using molecular-beam epitaxy and an intersubband transition (ISB-T) of 0.78 eV (λ=1.58 μm) with a full width at half maximum (FWHM) of 96 meV observed. We studied structural properties using high-resolution x-ray diffraction combined with dynamic simulation and found through the strain state in samples that a ZnSe/BeTe interface having a quaternary interface layer (ZnTe) 0.45 (BeSe) 0.55 is preferentially formed despite the promotion of one molecular layer (ML) ZnTe interface formation. Be-Se bonds thus replace the Zn-Te bond in the transition region. For the CdS/ZnSe interface, an approximately 1 ML Zn 0.75 Cd 0.25 S ternary layer accompanied by ∼1 ML Zn 0.85 Cd 0.15 Se forms at the transition region due to Cd diffusion. X-ray (002) ω/2θ scan curves for (CdS/ZnSe)/BeTe SLs show sharp, intense satellite peaks exceeding ten orders, indicating high structure quality. We obtained excellent agreement between experimental diffraction patterns and the calculated curve via dynamic simulation for (CdS/ZnSe)/BeTe SLs. The good fits allows us to identify structure parameters in (CdS/ZnSe)/BeTe SLs, which are consistent with results of high-resolution transmission electron microscopy measurement. Based on dynamic simulated results, we obtained a structure of (CdS/ZnSe)/Be 1-x Mg x Te (x=1.2%) with an average lattice constant a SL matching the GaAs substrate. An ISB-T located at wavelength λ=1.55 μm with a narrow FWHM of 90 meV was thus realized at room temperature

  5. Cuidado que el medicamento no se te salga por la nariz

    Directory of Open Access Journals (Sweden)

    Feijoo Calles D

    2017-12-01

    Full Text Available La enfermedad pulmonar obstructiva crónica (EPOC es una patología caracterizada por una reducción persistente del flujo de aire. Esta enfermedad pulmonar es progresiva y potencialmente mortal. Suele causar disnea y las exacerbaciones y comorbilidades asociadas hacen que el pronóstico sea peor. Se presenta un caso de seguimiento farmacoterapéutico realizado siguiendo la metodología del Foro de Atención Farmacéutica en Farmacia Comunitaria en el Aula de Práctica Farmacéutica “Paco Martínez” de la Universidad CEU Cardenal Herrera a un paciente real con EPOC y polimedicado, utilizando como método el “aprendizaje basado en problemas”. Como apoyo para la evaluación de la situación se realiza un análisis de las diferentes teorías publicadas sobre la ineficacia del tratamiento. Además, se expone el nuevo enfoque que se le quiere dar al tratamiento de los pacientes con EPOC, valorando la heterogeneidad de la enfermedad y la variabilidad clínica de cada paciente mediante la revisión bibliográfica en bases de datos científicas Pubmed/Medline y Google Académico, junto con la búsqueda de información en las diferentes páginas web de organismos oficiales, Organización Mundial de la Salud y Agencia Española de Medicamentos y Productos Sanitarios.

  6. Fundamental optical absorption edge in MnGa2Te4 single crystals

    International Nuclear Information System (INIS)

    Medvedkin, G.A.; Rud, Yu.V.; Tairov, M.A.

    1988-01-01

    A study is made of the optical properties of oriented MnGa 2 Te 4 crystals in the region of the fundamental absorption edge. The energy gap width for the temperatures 77, 300, and 370 K is determined to be E G = 1.635, 1.52, and 1.50 eV. The spectral response α(ℎω/2π) is found to follow Urbach's rule thoughout the temperature range studied, the slope of the absorption edge remaining constant (α = 10 2 cm -1 ). Crystal annealing with subsequent rapid cooling results in a shift of the absorption edge longward by 25 meV with the exponential form of α(ℎω/2π) prevailing over the range T = 77 to 370 K. An analysis shows the optical absorption in the region of the fundamental edge to be a sum of the effects coming from the density-of-states tails, local scattering centers associated with a high vacancy concentration, and electron-phonon interaction. Optical linear dichroism of the absorption edge of MnGa 2 Te 4 single crystals with pseudotetragonal structure is revealed and studied. The single crystals are established to be optically uniaxial, their optical transmission dichroism being negative. It is shown that the minimal direct optical transitions in MnGa 2 Te 4 are allowed in the E parallel c polarization in the temperature range 77 to 370 K, the crystal-field splitting of the valence band increasing with temperature. (author)

  7. Arsenic complexes optical signatures in As-doped HgCdTe

    Energy Technology Data Exchange (ETDEWEB)

    Gemain, F.; Robin, I. C.; Brochen, S.; Ballet, P.; Gravrand, O.; Feuillet, G. [CEA-LETI Minatec Campus, 17 rue des Martyrs, 38000 Grenoble (France)

    2013-04-08

    In this paper, the optical signatures of arsenic complexes in As-doped HgCdTe samples grown by molecular beam epitaxy are clearly identified using comparison between photoluminescence spectra, Extended X-Ray Absorption Fine Structure, and Hall measurements. The ionization energies of the different complexes are measured both by photoluminescence and Hall measurements.

  8. Arsenic complexes optical signatures in As-doped HgCdTe

    International Nuclear Information System (INIS)

    Gemain, F.; Robin, I. C.; Brochen, S.; Ballet, P.; Gravrand, O.; Feuillet, G.

    2013-01-01

    In this paper, the optical signatures of arsenic complexes in As-doped HgCdTe samples grown by molecular beam epitaxy are clearly identified using comparison between photoluminescence spectra, Extended X-Ray Absorption Fine Structure, and Hall measurements. The ionization energies of the different complexes are measured both by photoluminescence and Hall measurements.

  9. Synthesis, structure, optical property, and electronic structure of Ba7AgGa5Se15

    International Nuclear Information System (INIS)

    Yin, Wenlong; He, Ran; Feng, Kai; Hao, Wenyu; Yao, Jiyong; Wu, Yicheng

    2013-01-01

    Graphical abstract: -- Highlights: •A new quaternary chalcogenide Ba 7 AgGa 5 Se 15 was synthesized. •It adopts a new structure type in the space group P31c of the trigonal system. •The structure contains a three-dimensional framework built from GaSe 4 and AgSe 4 tetrahedra. •Ba 7 AgGa 5 Se 15 is a direct semiconductor with the band gap of 2.60 (2) eV. •The electronic structure was calculated to explain the optical properties. -- Abstract: A new quaternary chalcogenide Ba 7 AgGa 5 Se 15 was synthesized by solid state reaction. It crystallizes in a new structure type in the noncentrosymmetric space group P31c of the trigonal system. In the structure, three Ga2Se 4 tetrahedra and one Ga1Se 4 tetrahedron are connected to each other by corner-sharing to form [Ga 4 Se 10 ] 8− anion clusters, which are further connected to AgSe 4 tetrahedra by corner-sharing to form a three-dimensional framework with Ba, Se7, and isolated Ga3Se 4 tetrahedra residing in the cavities. The optical band gap of 2.60 (2) eV for Ba 7 AgGa 5 Se 15 was deduced from the diffuse reflectance spectrum. From a band structure calculation, Ba 7 AgGa 5 Se 15 is a direct semiconductor and the transition between Se and Ba plays an important role in the band gap

  10. Cuidado que el medicamento no se te salga por la nariz

    OpenAIRE

    Feijoo Calles, Daniela; Moreno Royo, Lucrecia; Salar Ibáñez, Luis

    2017-01-01

    La enfermedad pulmonar obstructiva crónica (EPOC) es una patología caracterizada por una reducción persistente del flujo de aire. Esta enfermedad pulmonar es progresiva y potencialmente mortal. Suele causar disnea y las exacerbaciones y comorbilidades asociadas hacen que el pronóstico sea peor. Se presenta un caso de seguimiento farmacoterapéutico realizado siguiendo la metodología del Foro de Atención Farmacéutica en Farmacia Comunitaria en el Aula de Práctica Farmacéutica “Paco Martínez...

  11. Electrochemical lithium and sodium intercalation into the tantalum-rich layered chalcogenides Ta2Se and Ta2Te3

    International Nuclear Information System (INIS)

    Lavela, P.; Tirado, J.L.

    1999-01-01

    Two-layered tantalum chalcogenides are evaluated as alkali metal intercalation hosts in lithium and sodium electrochemical cells. The metal-rich pseudo-two-dimensional solid Ta 2 Se shows a poor intercalation behaviour. Lithium reacts with the selenide by deintercalating selenium from the blocks of Ta-related b.c.c. structure leading to a collapse of the structure and the formation of tantalum metal. Sodium is reversibly intercalated to a limited extent leading to complex structural changes in the selenide, as revealed by electron diffraction. The two-dimensional telluride Ta 2 Te 3 allows a topotactic intercalation of lithium below 1 F/mol, while a more extended reaction leads to sample amorphization. The better intercalation behaviour of this solid can be related with the one-atom thick metal layer and the van der Waals gap separating tellurium atoms of successive layers. Sodium can be reversibly intercalated into Ta 2 Te 3 in sodium cells which show a good cycling behaviour. Exposure of the intercalated solid to water vapour allows the preparation of hydrated products with a monolayer or a bilayer of water molecules solvating sodium in the interlayer space. (orig.)

  12. Optically Active CdSe-Dot/CdS-Rod Nanocrystals with Induced Chirality and Circularly Polarized Luminescence.

    Science.gov (United States)

    Cheng, Jiaji; Hao, Junjie; Liu, Haochen; Li, Jiagen; Li, Junzi; Zhu, Xi; Lin, Xiaodong; Wang, Kai; He, Tingchao

    2018-05-30

    Ligand-induced chirality in semiconductor nanocrystals (NCs) has attracted attention because of the tunable optical properties of the NCs. Induced circular dichroism (CD) has been observed in CdX (X = S, Se, Te) NCs and their hybrids, but circularly polarized luminescence (CPL) in these fluorescent nanomaterials has been seldom reported. Herein, we describe the successful preparation of l- and d-cysteine-capped CdSe-dot/CdS-rods (DRs) with tunable CD and CPL behaviors and a maximum anisotropic factor ( g lum ) of 4.66 × 10 -4 . The observed CD and CPL activities are sensitive to the relative absorption ratio of the CdS shell to the CdSe core, suggesting that the anisotropic g-factors in both CD and CPL increase to some extent for a smaller shell-to-core absorption ratio. In addition, the molar ratio of chiral cysteine to the DRs is investigated. Instead of enhancing the chiral interactions between the chiral molecules and DRs, an excess of cysteine molecules in aqueous solution inhibits both the CD and CPL activities. Such chiral and emissive NCs provide an ideal platform for the rational design of semiconductor nanomaterials with chiroptical properties.

  13. Fabrication and thermoelectric performance of textured n-type Bi2(Te,Se)3 by spark plasma sintering

    International Nuclear Information System (INIS)

    Jiang Jun; Chen Lidong; Bai Shengqiang; Yao Qin; Wang Qun

    2005-01-01

    The n-type Bi 2 (Te,Se) 3 thermoelectric materials with preferred grain orientation have been fabricated through the spark plasma sintering (SPS) technique. The c-axis of the grains in the sintered samples were preferentially oriented parallel to the pressing direction, the orientation factor of the (0 0 l) planes changed from 0.4 to 0.85 with the sintering conditions. The anisotropy was investigated by measuring the electrical conductivities in the two directions perpendicular and parallel to the pressing direction. The optimal figure of merit ZT (ZT = α 2 σT/κ) of the sintered materials in the direction perpendicular to the pressing direction was comparative to that of the zone-melted materials in the same crystallographic direction, while the bending strength reached about 80 MPa, which is 7-8 times of that of the zone-melted materials

  14. Extension of Mediema's Macroscopic Atom Model to the Elements of Group 16 (O, S, Se, Te ,Po)

    CERN Document Server

    Neuhausen, J

    2003-01-01

    A consistent set of Miedema-parameters has been developed for the elements of the chalcogen group (Group 16 of the periodic table of the elements: 0, S, Se, Te, Po) from ab-initio quantum-mechanical calculations as weIl as empirical correlations. Using this parameter set thermochemical properties such as enthalpies of formation of solid metal chalcogenides, partial molar enthalpies of solution of chalcogens in liquid and solid metaIs, partial molar enthalpies of evaporation of the chalcogens from liquid metal solution into the monoatomic gaseous state, partial molar enthalpies of adsorption of chalcogenides on metal surfaces at zero coverage and partial molar enthalpies of segregation of the chalcogens in trace amounts within solid metal matrices have been calculated. These properties are compared with available experimental data and discussed with an emphasis on the periodic behaviour of the elements. The model calculations show that a description of the thermochemical properties of the chalcogens using the ...

  15. Dynamical control of Mn spin-system cooling by photogenerated carriers in a (Zn,Mn)Se/BeTe heterostructure

    Science.gov (United States)

    Debus, J.; Maksimov, A. A.; Dunker, D.; Yakovlev, D. R.; Tartakovskii, I. I.; Waag, A.; Bayer, M.

    2010-08-01

    The magnetization dynamics of the Mn spin system in an undoped (Zn,Mn)Se/BeTe type-II quantum well was studied by a time-resolved pump-probe photoluminescence technique. The Mn spin temperature was evaluated from the giant Zeeman shift of the exciton line in an external magnetic field of 3 T. The relaxation dynamics of the Mn spin temperature to the equilibrium temperature of the phonon bath after the pump-laser-pulse heating can be accelerated by the presence of free electrons. These electrons, generated by a control laser pulse, mediate the spin and energy transfer from the Mn spin system to the lattice and bypass the relatively slow direct spin-lattice relaxation of the Mn ions.

  16. Thermoelectric Transport Properties of Cu Nanoprecipitates Embedded Bi2Te2.7Se0.3

    Directory of Open Access Journals (Sweden)

    Eunsil Lee

    2015-01-01

    Full Text Available We suggest a simple and scalable synthesis to prepare Cu-Bi2Te2.7Se0.3 (Cu-BTS nanocomposites. By precipitating Cu nanoparticle (NP in colloidal suspension of as-exfoliated BTS, homogeneous mixtures of Cu NP and BTS nanosheet were readily achieved, and then the sintered nanocomposites were fabricated by spark plasma sintering technique using the mixed powder as a raw material. The precipitated Cu NPs in the BTS matrix effectively generated nanograin (BTS and heterointerface (Cu/BTS structures. The maximum ZT of 0.90 at 400 K, which is 15% higher compared to that of pristine BTS, was obtained in 3 vol% Cu-BTS nanocomposite. The enhancement of ZT resulted from improved power factor by carrier filtering effect due to the Cu nanoprecipitates in the BTS matrix.

  17. Visible-active photocatalytic behaviors observed in nanostructured lead chalcogenides PbX (X = S, Se, Te)

    International Nuclear Information System (INIS)

    Qiao, Li-Na; Wang, H.C.; Shen, Y.; Lin, Yuan-Hua; Nan, Ce-Wen

    2016-01-01

    Nanostructured lead chalcogenides (PbX, X = Te, Se, S) were prepared via a simple hydrothermal method. The powder samples were characterized by XRD, SEM, SAED and DRS. Phase composition and microstructure analysis indicate that these samples are pure lead chalcogenides phases and have similar morphologies. These lead chalcogenides display efficient absorption in the UV-visible light range. The photocatalytic properties of lead chalcogenides nanoparticles were evaluated by the photodegradation of Congo red under UV-visible light irradiation in air atmosphere. The Congo red solution can be efficiently degraded under visible light in the presence of lead chalcogenides nanoparticles. The photocatalytic activities of lead chalcogenides generally increase with increasing their band gaps and shows no appreciable loss after repeated cycles. Our results may be useful for developing new photocatalyst systems responsive to visible light among narrow band gap semiconductors

  18. Optical spectroscopy, optical conductivity, dielectric properties and new methods for determining the gap states of CuSe thin films

    International Nuclear Information System (INIS)

    Sakr, G.B.; Yahia, I.S.; Fadel, M.; Fouad, S.S.; Romcevic, N.

    2010-01-01

    Research highlights: → The structural, optical dispersion parameters and the Raman spectroscopy have been studied for CuSe thin films. → X-ray diffraction results indicate the amorphous nature of the thermally evaporated CuSe thin films. → The refractive index shows an anomalous dispersion at the lower wavelength (absorption region) and a normal dispersion at the higher wavelengths (transparent region). → The refractive index dispersion obeys the single oscillator model proposed by Wemple and DiDomenico WDD model and the single oscillator parameters were determined. → The band gap of CuSe thin films was determined by three novel methods i.e. (relaxation time, real and imaginary dielectric constant and real and imaginary optical conductivity) which in a good agreement with the Tauc band gap value. - Abstract: The paper describes the structural and optical properties of CuSe thin films. X-ray diffraction pattern indicates that CuSe thin film has an amorphous structure. Transmittance T(λ) and reflectance R(λ) measurements in the wavelength range (300-1700 nm) were used to calculate the refractive index n(λ), the absorption index and the optical dispersion parameters according to Wemple and Didomenico WDD model. The dispersion curve of the refractive index shows an anomalous dispersion in the absorption region and a normal dispersion in the transparent region. The optical bandgap has been estimated and confirmed by four different methods. The value for the direct bandgap for the as-deposited CuSe thin film approximately equals 2.7 eV. The Raman spectroscopy was used to identify and quantify the individual phases presented in the CuSe films.

  19. Effects of high-energy proton irradiation on the superconducting properties of Fe(Se,Te) thin films

    Science.gov (United States)

    Sylva, G.; Bellingeri, E.; Ferdeghini, C.; Martinelli, A.; Pallecchi, I.; Pellegrino, L.; Putti, M.; Ghigo, G.; Gozzelino, L.; Torsello, D.; Grimaldi, G.; Leo, A.; Nigro, A.; Braccini, V.

    2018-05-01

    In this paper we explore the effects of 3.5 MeV proton irradiation on Fe(Se,Te) thin films grown on CaF2. In particular, we carry out an experimental investigation with different irradiation fluences up to 7.30 · 1016 cm‑2 and different proton implantation depths, in order to clarify whether and to what extent the critical current is enhanced or suppressed, what are the effects of irradiation on the critical temperature, resistivity, and critical magnetic fields, and finally what is the role played by the substrate in this context. We find that the effect of irradiation on superconducting properties is generally small compared to the case of other iron-based superconductors. The irradiation effect is more evident on the critical current density Jc, while it is minor on the transition temperature Tc, normal state resistivity ρ, and on the upper critical field Hc2 up to the highest fluences explored in this work. In more detail, our analysis shows that when protons implant in the substrate far from the superconducting film, the critical current can be enhanced up to 50% of the pristine value at 7 T and 12 K; meanwhile, there is no appreciable effect on critical temperature and critical fields together with a slight decrease in resistivity. On the contrary, when the implantation layer is closer to the film–substrate interface, both critical current and temperature show a decrease accompanied by an enhancement of the resistivity and lattice strain. This result evidences that possible modifications induced by irradiation in the substrate may affect the superconducting properties of the film via lattice strain. The robustness of the Fe(Se,Te) system to irradiation-induced damage makes it a promising compound for the fabrication of magnets in high-energy accelerators.

  20. Thermophysical and Optical Properties of Semiconducting Ga2Te3 Melt

    Science.gov (United States)

    Li, Chao; Su, Ching-Hua; Lehoczky, Sandor L.; Scripa, Rosalie N.; Ban, Heng

    2005-01-01

    The majority of bulk semiconductor single crystals are presently grown from their melts. The thermophysical and optical properties of the melts provide a fundamental understanding of the melt structure and can be used to optimize the growth conditions to obtain higher quality crystals. In this paper, we report several thermophysical and optical properties for Ga2Te3 melts, such as electrical conductivity, viscosity, and optical transmission for temperatures ranging from the melting point up to approximately 990 C. The conductivity and viscosity of the melts are determined using the transient torque technique. The optical transmission of the melts is measured between the wavelengths of 300 and 2000 nm by an dual beam reversed-optics spectrophotometer. The measured properties are in good agreement with the published data. The conductivities indicate that the Ga2Te3 melt is semiconductor-like. The anomalous behavior in the measured properties are used as an indication of a structural transformation in the Ga2Te3 melt and discussed in terms of Eyring's and Bachinskii's predicted behaviors for homogeneous melts.

  1. Optical Properties of Al- and Sb-Doped CdTe Thin Films

    Directory of Open Access Journals (Sweden)

    A. A. J. Al-Douri

    2010-01-01

    Full Text Available Nondoped and (Al, Sb-doped CdTe thin films with 0.5, 1.5, and 2.5  wt.%, respectively, were deposited by thermal evaporation technique under vacuum onto Corning 7059 glass at substrate temperatures ( of room temperature (RT and 423 K. The optical properties of deposited CdTe films such as band gap, refractive index (n, extinction coefficient (, and dielectric coefficients were investigated as function of Al and Sb wt.% doping, respectively. The results showed that films have direct optical transition. Increasing and the wt.% of both types of dopant, the band gap decrease but the optical is constant as n, and real and imaginary parts of the dielectric coefficient increase.

  2. Optical properties of Cd Se thin films obtained by pyrolytic dew; Propiedades opticas de peliculas delgadas de CdSe obtenidas por rocio pirolitico

    Energy Technology Data Exchange (ETDEWEB)

    Perez G, A.M. [UPAEP, 72160 Puebla (Mexico); Tepantlan, C.S. [UPT, 43626 Tulancingo, Hidalgo (Mexico); Renero C, F. [INAOE, 72840 Puebla (Mexico)

    2006-07-01

    In this paper the optical properties of Cd Se thin films obtained by spray pyrolysis are presented. The films are prepared by Sodium Seleno sulphate (Na{sub 2}SSeO{sub 3}) and Cadmium Chloride (CdC{sub 12}) mixing in aqueous environment. Optical parameters of the films (refractive index, absorption coefficient and optical ban gap) were calculated from transmittance spectra. The obtained values of the optical ban gap are compared with the result obtained by other deposition method. (Author)

  3. Crystallization behavior of Ge-doped eutectic Sb70Te30 films in optical disks

    International Nuclear Information System (INIS)

    Khulbe, Pramod K.; Hurst, Terril; Mansuripur, Masud; Horie, Michikazu

    2002-01-01

    We report laser-induced crystallization behavior of binary Sb-Te and ternary Ge-doped eutectic Sb70Te30 thin film samples in a typical quadrilayer stack as used in phase-change optical disk data storage. Several experiments have been conducted on a two-laser static tester in which one laser operating in pulse mode writes crystalline marks on amorphous film or amorphous marks on crystalline film, while the second laser operating at low-power cw mode simultaneously monitors the progress of the crystalline or amorphous mark formation in real time in terms of the reflectivity variation. The results of this study show that the crystallization kinetics of this class of film is strongly growth dominant, which is significantly different from the crystallization kinetics of stochiometric Ge-Sb-Te compositions. In Sb-Te and Ge-doped eutectic Sb70Te30 thin-film samples, the crystallization behavior of the two forms of amorphous states, namely, as-deposited amorphous state and melt-quenched amorphous state, remains approximately same. We have also presented experiments showing the effect of the variation of the Sb/Te ratio and Ge doping on the crystallization behavior of these films

  4. Reactively sputtered TeO/sub x/ thin films for optical recording systems

    International Nuclear Information System (INIS)

    Di Giulio, M.; Micocci, G.; Rella, R.; Tepore, A.

    1988-01-01

    Tellurium suboxide (TeO/sub x/ ) thin films have been obtained by rf reactive sputtering deposition by using a Te target and an Ar--O 2 gas mixture. Different samples were prepared by changing both the rf power (80--200 W) and the oxygen concentration in the sputtering gas. The transmissivity and the reflectivity of these films change markedly by thermal treatment at critical temperatures in the range 120--150 0 C. This property makes these films suitable for optical disk recording with a low-output power laser diode

  5. Temperature dependence of Raman scattering by optical phonons in ZnTe

    International Nuclear Information System (INIS)

    Simmonds, P.E.; Martin, A.D.

    1987-01-01

    Measurements of the temperature dependence of Raman scattering by optical phonons between temperatures 5 K and 293 K in the II-VI semiconductor ZnTe are reported. Typical Raman spectra for ZnTe at different temperatures are shown and values of the measured LO and TO phonon Raman shifts and linewidths are given for T = 5, 77, and 293 K. The measured linewidth of the LO Raman line as a function of temperature is plotted and compared with model predictions based on various three- and four-phonon processes

  6. Chevrel-phase solid solution Mo 6Se 8- xTe x. Study of its superconducting, magnetic and NMR properties

    Science.gov (United States)

    Hamard1a, C.; Auffret, V.; Peña, O.; Le Floch, M.; Nowak, B.; Wojakowski, A.

    2000-09-01

    The Chevrel-phase solid solution Mo 6Se 8-Mo 6Te 8 was studied by X-ray diffraction, AC and DC magnetic susceptibility and 77Se and 125Te NMR spectroscopy. From the smooth evolution of the lattice parameters and superconducting critical temperatures, a progressive substitution of selenium atoms by tellurium is shown, on the whole range of composition 0⩽ x⩽8, in the formulation Mo 6Se 8- xTe x: the unit-cell volume increases linearly because of the larger ionic size of tellurium, while Tc decreases rapidly (from 6.45 down to 0 K) because of the different formal oxidation states of the anions and a probable evolution of the Fermi level in the density of states. Results of magnetic susceptibility support this model and suggest the inhibition of the intrinsic metallic behavior with increasing x. The NMR spectra of the binaries Mo 6Se 8 and Mo 6Te 8 reveal two significant features, attributed to two different chalcogen positions in the R 3¯ symmetry. At low Se contents in Mo 6Se 8- xTe x ( x=7.5, 7 and 6), selenium first fills the two X(2) sites along the three-fold axis (2c positions), and then it becomes statistically distributed over the general 6f positions, leading to broad 77Se NMR lines. On the other hand, substitution of Te atoms in Mo 6Se 8 seems to occur in a random way, creating large perturbations on the 125Te NMR spectra, over the whole range of x. Theoretical analysis based on the presence of two anisotropic lines (of axial and non-axial symmetries, respectively) allowed us to estimate their anisotropy factors and to perfectly simulate the frequency response of both Mo 6Se 8 and Mo 6Te 8 binaries. Analysis of the Knight shift anisotropy leads us to conclude about the importance of the molybdenum z 2 molecular orbital contribution which controls the Mo-X dipolar interactions.

  7. Structural and optical properties of Sb65Se35-xGex thin films

    Science.gov (United States)

    Saleh, S. A.; Al-Hajry, A.; Ali, H. M.

    2011-07-01

    Sb65Se35-xGex (x=0-20 at.%) thin films, prepared by the electron beam evaporation technique on ultrasonically cleaned glass substrates at 300 K, were investigated. The amorphous structure of the thin films was confirmed by x-ray diffraction analysis. The structure was deduced from the Raman spectra measured for all germanium contents in the Sb-Se-Ge matrix. The absorption coefficient (α) of the films was determined by optical transmission measurements. The compositional dependence of the optical band gap is discussed in light of topological and chemical ordered network models.

  8. Optical studies of 2DEGs in ZnSe quantum wells in high magnetic fields.

    Energy Technology Data Exchange (ETDEWEB)

    Ossau, Wolfgang J.; Astakhov, G. V.; Yakovlev, D. R.; Crooker, S. A. (Scott A.); Waag, A.

    2002-01-01

    Optical properties of a two-dimensional electron gas in ZnSe/(Zn,Be,Mg)Se quantum well structures have been examined by means of photoluminescence and reflectivity techniques in external magnetic fields up to 50 T. For these structures the Fermi energy of the two-dimensional electron gas is falling in the range between the trion binding energy and the exciton binding energy, which keeps the dominating role of Coulombic interaction between electrons and photoexcited holes. Characteristic peculiarities of optical spectra are discussed.

  9. Enhanced superconductivity and anisotropy of FeTe0.6Se0.4 single crystals with Li -NH3 intercalation

    Science.gov (United States)

    Li, Chenghe; Sun, Shanshan; Wang, Shaohua; Lei, Hechang

    2017-10-01

    We report a systematic study of anisotropy resistivity, magnetoresistance, and Hall effect of Li0.32(NH3)yFe2Te1.2Se0.8 single crystals. When compared to the parent compound FeTe0.6Se0.4 , the Li-NH3 intercalation not only increases the superconducting transition temperature but also enhances the electronic anisotropy in both normal and superconducting states. Moreover, in contrast to the parent compound, the Hall coefficient RH becomes negative at low temperature, indicating electron-type carriers are dominant due to Li doping. On the other hand, the sign reverse of RH at high temperature and the failure of scaling behavior of magnetoresistance imply that hole pockets may be still crossing or just below the Fermi energy level, leading to the multiband behavior in Li0.32(NH3)yFe2Te1.2Se0.8 .

  10. Effect of the external electric field on the kinetics of recombination of photoexcited carriers in a ZnSe/BeTe type II heterostructure

    Science.gov (United States)

    Filatov, E. V.; Maksimov, A. A.; Tartakovskii, I. I.; Yakovlev, D. R.; Waag, A.

    2012-02-01

    The kinetics of the radiative recombination of photoexcited electrons and holes for a spatially direct transition in a ZnSe/BeTe type II heterostructure in an external electric field has been analyzed. A strong decrease (more than two orders of magnitude) in the photoluminescence intensity, as well as a decrease in the duration of the relaxation of the direct transition, is observed when the electric field is applied. The energy levels and wavefunctions of electrons and holes in the ZnSe/BeTe heterostructure subjected to the electric field have been numerically calculated. It has been shown that the observed decrease in the photoluminescence intensity and duration of the relaxation of the direct transition is due to both an increase in the radiative recombination time and an increase in the rate of escape of photoexcited holes from the above-barrier level in the ZnSe layer to the BeTe layer.

  11. Ab-initio study of pure sup 7 sup 7 Se and sup 1 sup 2 sup 5 Te systems and of the sup 7 sup 7 Se nuclear quadrupole interaction in tellurium

    CERN Document Server

    Oh, Y K; Cho, H S

    1999-01-01

    Using the Hartree-Fock cluster procedure, we have studied the electric-field gradient tensors at the nuclear sites of sup 7 sup 7 Se and sup 1 sup 2 sup 5 Te in pure sup 1 sup 2 sup 5 Te systems and in tellurium crystalline system's with a sup 7 sup 7 Se impurity. From the results for the pure systems, sup 7 sup 7 Se in selenium and sup 1 sup 2 sup 5 Te in tellurium, using the observed quadrupole moments: Q( sup 7 sup 7 Se) 0.75 +- 0.07 barns and Q( sup 1 sup 2 sup 5 Te) = 0.35 +- 0.04 barns. Comparison is made with earlier values obtained by different methods. Using our calculated values of Q and the results of a study of the field-gradient tensors for sup 7 sup 7 Se in tellurium, the theoretical values of the quadrupole coupling constants are found to agree, within about 7 percent, with experiment. The calculated asymmetry parameters are also found to be in reasonable agreement with the experiment values, although the agreement not as close as in the case of the quadrupole -coupling constants. Directions fo...

  12. The relationship between structural and optical properties of Se-Ge-As glasses

    Science.gov (United States)

    Ghayebloo, M.; Rezvani, M.; Tavoosi, M.

    2018-05-01

    In this study, the structural and optical characterization of bulk Se-Ge-As glasses has been investigated. In this regards, six different Se60Ge40-xAsx (0 ≤ x ≤ 25) glasses were prepared by conventional melt quenching technique in quartz ampoule. The produced samples were characterized using X-ray diffraction (XRD), Raman spectroscopy, differential thermal analysis (DTA), ultraviolet-visible (UV-Vis) and Fourier transform infrared (FTIR) spectroscopy. The fundamental absorption edge for all the glasses was analyzed in terms of the theory proposed by Davis and Mott. According to achieved results, fully amorphous phase can easily form in different Se-Ge-As systems. The thermal and optical characteristic of Se60Ge40-xAsx glasses shows anomalous behavior at 5 mol% of As for the glass transition temperature, transmittance, absorption edge, optical energy gap and Urbach energy. The highest glass transition temperature, transmittance, optical energy gap and Urbach energy properties were achieved in Se60Ge35As5 glass as a result of the highest connectivity of cations and anions in glass network.

  13. Aqueous-Processed Inorganic Thin-Film Solar Cells Based on CdSe(x)Te(1-x) Nanocrystals: The Impact of Composition on Photovoltaic Performance.

    Science.gov (United States)

    Zeng, Qingsen; Chen, Zhaolai; Zhao, Yue; Du, Xiaohang; Liu, Fangyuan; Jin, Gan; Dong, Fengxia; Zhang, Hao; Yang, Bai

    2015-10-21

    Aqueous processed nanocrystal (NC) solar cells are attractive due to their environmental friendliness and cost effectiveness. Controlling the bandgap of absorbing layers is critical for achieving high efficiency for single and multijunction solar cells. Herein, we tune the bandgap of CdTe through the incorporation of Se via aqueous process. The photovoltaic performance of aqueous CdSexTe1-x NCs is systematically investigated, and the impacts of charge generation, transport, and injection on device performance for different compositions are deeply discussed. We discover that the performance degrades with the increasing Se content from CdTe to CdSe. This is mainly ascribed to the lower conduction band (CB) of CdSexTe1-x with higher Se content, which reduces the driving force for electron injection into TiO2. Finally, the performance is improved by mixing CdSexTe1-x NCs with conjugated polymer poly(p-phenylenevinylene) (PPV), and power conversion efficiency (PCE) of 3.35% is achieved based on ternary NCs. This work may provide some information to further optimize the aqueous-processed NC and hybrid solar cells.

  14. Third-order nonlinear optical response of Ag-CdSe/PVA hybrid nanocomposite

    Energy Technology Data Exchange (ETDEWEB)

    Tripathi, S.K.; Kaur, Ramneek; Kaur, Jaspreet; Sharma, Mamta [Panjab University, Department of Physics, Center of Advanced Study in Physics, Chandigarh (India)

    2015-09-15

    Hybrid nanocomposites of II-VI semiconductor nanoparticles are gaining great interest in nonlinear optoelectronic devices. Present work includes the characterization of CdSe polymer nanocomposite prepared by chemical in situ technique. From X-ray diffraction, the hexagonal wurtzite structure of nanoparticles has been confirmed with spherical morphology from transmission electron microscopy. Ag-CdSe hybrid polymer nanocomposite has been prepared chemically at different Ag concentrations. The presence of Ag in hybrid nanocomposite has been confirmed with energy-dispersive X-ray spectroscopy. The effect of varying Ag concentration on the linear and nonlinear optical properties of the nanocomposites has been studied. In linear optical parameters, the linear absorption coefficient, refractive index, extinction coefficient and optical conductivity have been calculated. The third-order nonlinear optical properties have been observed with open- and closed-aperture Z-scan technique. The large nonlinear refractive index ∝10{sup -5} cm{sup 2}/W with self-focusing behaviour is due to the combined effect of quantum confinement and thermo-optical effects. The enhanced nonlinearity with increasing Ag content is due to the surface plasmon resonance, which enhances the local electric field near the nanoparticle surface. Thus, Ag-CdSe hybrid polymer nanocomposite has favourable nonlinear optical properties for various optoelectronic applications. (orig.)

  15. Third-order nonlinear optical response of Ag-CdSe/PVA hybrid nanocomposite

    International Nuclear Information System (INIS)

    Tripathi, S.K.; Kaur, Ramneek; Kaur, Jaspreet; Sharma, Mamta

    2015-01-01

    Hybrid nanocomposites of II-VI semiconductor nanoparticles are gaining great interest in nonlinear optoelectronic devices. Present work includes the characterization of CdSe polymer nanocomposite prepared by chemical in situ technique. From X-ray diffraction, the hexagonal wurtzite structure of nanoparticles has been confirmed with spherical morphology from transmission electron microscopy. Ag-CdSe hybrid polymer nanocomposite has been prepared chemically at different Ag concentrations. The presence of Ag in hybrid nanocomposite has been confirmed with energy-dispersive X-ray spectroscopy. The effect of varying Ag concentration on the linear and nonlinear optical properties of the nanocomposites has been studied. In linear optical parameters, the linear absorption coefficient, refractive index, extinction coefficient and optical conductivity have been calculated. The third-order nonlinear optical properties have been observed with open- and closed-aperture Z-scan technique. The large nonlinear refractive index ∝10 -5 cm 2 /W with self-focusing behaviour is due to the combined effect of quantum confinement and thermo-optical effects. The enhanced nonlinearity with increasing Ag content is due to the surface plasmon resonance, which enhances the local electric field near the nanoparticle surface. Thus, Ag-CdSe hybrid polymer nanocomposite has favourable nonlinear optical properties for various optoelectronic applications. (orig.)

  16. Effect of vacancies on the structure and properties of Ga{sub 2}(Se{sub 0.33}Te{sub 0.67}){sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Abdul-Jabbar, N. M. [Department of Nuclear Engineering, University of California, Berkeley, California 94720 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Materials Department, University of California, Santa Barbara, California 93106 (United States); Forrest, T. R. [European Synchrotron Radiation Facility, BP 220, F-38043 Grenoble Cedex (France); Department of Physics, University of California, Berkeley, California 94720 (United States); Gronsky, R. [Department of Materials Science and Engineering, University of California, Berkeley, California 94720 (United States); Bourret-Courchesne, E. D. [Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Wirth, B. D. [Department of Nuclear Engineering, University of California, Berkeley, California 94720 (United States); Department of Nuclear Engineering, University of Tennessee, Knoxville, Tennessee 37996 (United States)

    2015-08-28

    Ga{sub 2}(Se{sub 0.33}Te{sub 0.67}){sub 3} belongs to a family of materials with large intrinsic vacancy concentrations that are being actively studied due to their potential for diverse applications that include thermoelectrics and phase-change memory. In this article, the Ga{sub 2}(Se{sub 0.33}Te{sub 0.67}){sub 3} structure is investigated via synchrotron x-ray diffraction, electron microscopy, and x-ray absorption experiments. Diffraction and microscopy measurements showed that the extent of vacancy ordering in Ga{sub 2}(Se{sub 0.33}Te{sub 0.67}){sub 3} is highly dependent on thermal annealing. It is posited that stoichiometric vacancies play a role in local atomic distortions in Ga{sub 2}(Se{sub 0.33}Te{sub 0.67}){sub 3} (based on the fine structure signals in the collected x-ray absorption spectra). The effect of vacancy ordering on Ga{sub 2}(Se{sub 0.33}Te{sub 0.67}){sub 3} material properties is also examined through band gap and Hall effect measurements, which reveal that the Ga{sub 2}(Se{sub 0.33}Te{sub 0.67}){sub 3} band gap redshifts by ≈0.05 eV as the vacancies order and accompanied by gains in charge carrier mobility. The results serve as an encouraging example of altering material properties via intrinsic structural rearrangement as opposed to extrinsic means, such as doping.

  17. Batch and column adsorption behaviors of Se(IV) and Te(IV) on organic and inorganic ion exchangers from HCl solutions

    Energy Technology Data Exchange (ETDEWEB)

    El-Sweify, Fatma H.; Abdel-Fattah, Alaa El-Din A.; Aly, Shorouk M.; Ghamry, Mohamed A. [Atomic Energy Authority, Cairo (Egypt). Hot Laboratories Center; El-Sheikh, Ragaa [Zagazig Univ. (Egypt). Chemistry Dept.

    2017-07-01

    Adsorption behaviors of Se(IV) and Te(IV) on the inorganic ion exchanger ceric tungstate (CeW) was studied under static and dynamic conditions and compared with the adsorption on the organic cation and anion exchangers Dowex-50X8 and AG-2X8, respectively. The radioactive isotopes {sup 75}Se and {sup 123m}Te were used to trace the respective elements. Some parameters affecting the adsorption were investigated under static conditions. In the case of batch technique the adsorption was studied from slightly acidic HCl as well as slightly alkaline media, i.e. at two pH-ranges. Se(IV) and Te(IV) were adsorbed on both the inorganic ion exchanger (CeW) and on AG-2X8, from slightly alkaline solutions. From the similarity of adsorption on both ion exchangers it was clear that (CeW) acts as an anion exchanger. Moreover, the obtained K{sub d}-values for the adsorption on (CeW) were much higher than those for the adsorption on the organic anion exchanger AG-2X8. Se(IV) was not adsorbed on Dowex-50X8 all over the studied pH-range whereas Te(IV) was slightly adsorbed. Loading and elution behaviors of Se(IV) and Te(IV) on columns of AG-2X8 and (CeW) were studied using solutions of HCl of different concentrations. Some good separation alternatives of Se(IV) and Te(IV) under certain conditions were achieved.

  18. Theoretical Determination of Optimal Material Parameters for ZnCdTe/ZnCdSe Quantum Dot Intermediate Band Solar Cells

    Science.gov (United States)

    Imperato, C. M.; Ranepura, G. A.; Deych, L. I.; Kuskovsky, I. L.

    2018-03-01

    Intermediate band solar cells (IBSCs) are designed to enhance the photovoltaic efficiency significantly over that of a single-junction solar cell as determined by the Shockley-Queisser limit. In this work we present calculations to determine parameters of type-II Zn1-xCdxTe/Zn1-yCdySe quantum dots (QDs) grown on the InP substrate suitable for IBSCs. The calculations are done via the self-consistent variational method, accounting for the disk form of the QDs, presence of the strained ZnSe interfacial layer, and under conditions of a strain-free device structure. We show that to achieve the required parameters relatively thick QDs are required. Barriers must contain Cd concentration in the range of 35-44%, while Cd concentration in QD can vary widely from 0% to 70%, depending on their thickness to achieve the intermediate band energies in the range of 0.50-0.73 eV. It is also shown that the results are weakly dependent on the barrier thickness.

  19. Synthesis, field emission properties and optical properties of ZnSe nanoflowers

    Energy Technology Data Exchange (ETDEWEB)

    Xue, S.L., E-mail: slxue@dhu.edu.cn [Department of Applied Physics, College of Science, Donghua University, Shanghai 201620 (China); Wu, S.X.; Zeng, Q.Z.; Xie, P.; Gan, K.X.; Wei, J.; Bu, S.Y.; Ye, X.N.; Xie, L. [Department of Applied Physics, College of Science, Donghua University, Shanghai 201620 (China); Zou, R.J. [State Key Laboratory for Modification and Chemical Fibers and Polymer Materials, Donghua University, Shanghai 201620 (China); Zhang, C.M.; Zhu, P.F. [Department of Physics, School of Fundamental Studies, Shanghai University of Engineering Science, Shanghai 201620 (China)

    2016-03-01

    Graphical abstract: Unique ZnSe nanoflowers have been successfully synthesized by reaction of Se powder with Zn substrates. They are characterized by XRD, SEM, TEM, XPS, EDS and Raman spectroscopy and were single crystals with cubic zinc blende (ZB) structure. They also have excellent field emission properties and optical properties. - Highlights: • Novel ZnSe nanoflowers are grown on Zn foils. • ZnSe nanoflowers are characterized by XRD, SEM, TEM, XPS and Raman spectra. • ZnSe nanoflowers on Zn foils as cathodes possess good FE properties. - Abstract: ZnSe nanoflowers have been synthesized by reaction of Se powder with Zn substrates at low temperature. The as-prepared ZnSe nanoflowers were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), X-ray energy dispersive spectroscope (EDS) and Raman spectroscopy measurements. It was found that the morphologies of the as-prepared samples highly depended on reaction time. ZnSe nanoclusters and nanoflowers formed at 573 K when the reaction time was 20 and 60 min, respectively. The as-prepared ZnSe nanoflowers were composed of radically aligned ZnSe nanorods with smooth surfaces. The results of XRD, XPS, EDS, TEM and Raman showed that the as-prepared ZnSe nanocrystals were single crystals with cubic zinc blende (ZB) structure. The formation mechanism of the as-prepared ZnSe nanoflowers was also discussed. In addition, the as-prepared ZnSe nanoflowers had excellent electron emission properties. The turn-on field of the as-prepared ZnSe nanoflowers was 3.5 V/μm and the enhancement factor was 3499. The optical properties of the as-prepared ZnSe nanoflowers were also investigated. The results demonstrated that the as-prepared ZnSe nanoflowers were potential candidates for optoelectronic devices.

  20. Probing the Optical Properties and Strain-Tuning of Ultrathin Mo1- xW xTe2.

    Science.gov (United States)

    Aslan, Ozgur Burak; Datye, Isha M; Mleczko, Michal J; Sze Cheung, Karen; Krylyuk, Sergiy; Bruma, Alina; Kalish, Irina; Davydov, Albert V; Pop, Eric; Heinz, Tony F

    2018-04-11

    Ultrathin transition metal dichalcogenides (TMDCs) have recently been extensively investigated to understand their electronic and optical properties. Here we study ultrathin Mo 0.91 W 0.09 Te 2 , a semiconducting alloy of MoTe 2 , using Raman, photoluminescence (PL), and optical absorption spectroscopy. Mo 0.91 W 0.09 Te 2 transitions from an indirect to a direct optical band gap in the limit of monolayer thickness, exhibiting an optical gap of 1.10 eV, very close to its MoTe 2 counterpart. We apply tensile strain, for the first time, to monolayer MoTe 2 and Mo 0.91 W 0.09 Te 2 to tune the band structure of these materials; we observe that their optical band gaps decrease by 70 meV at 2.3% uniaxial strain. The spectral widths of the PL peaks decrease with increasing strain, which we attribute to weaker exciton-phonon intervalley scattering. Strained MoTe 2 and Mo 0.91 W 0.09 Te 2 extend the range of band gaps of TMDC monolayers further into the near-infrared, an important attribute for potential applications in optoelectronics.

  1. Nonlinear optical behaviour of absorbing CdSxSe1-x interference filters

    International Nuclear Information System (INIS)

    Ferencz, K.; Szipoecs, R.

    1988-01-01

    First experimental results of nonlinear, thin film interference filter wedges with mixed CdS x Se 1-x as spacer material at the 633 nm wavelength of He-Ne laser are reported. Optical bistability is observed with less than 7.5 mW of optical power in single-cavity structures. The change in refractive index is found to be positive which is in accordance with the thermal mechanism of nonlinearity. Producing a double-cavity structure a device is obtained which works as an optical astable multivibrator having periodical change of transmission as the function of time. (author)

  2. Physical and optical properties of size-selective CdTe nanocrystals

    Energy Technology Data Exchange (ETDEWEB)

    Fok, Alice [Department of Chemistry, The City College of New York, CUNY New York, NY 10031 (United States); Morales, Jorge [Department of Biology, City College of New York, CUNY New York, NY 10031 (United States); Sohel, Mohammad [Natural Sciences Department, Hostos College, CUNY Bronx, NY 10451 (United States)

    2010-06-15

    Physical and optical properties of colloidal cadmium telluride nanocrystals (CdTe NCs) were investigated. The CdTe NCs were synthesized by reacting elemental tellurium dissolved in tributylphosphine with a mixture of cadmium oxide, octadecene, and oleic acid. These NCs, which were characterized by transmission electron microscopy (TEM) are spherical and ranged from 5 to 7 nm in diameter. The identity of the compound post-synthesis was confirmed by X-Ray diffraction (XRD) patterns. UV-Vis and photoluminescence (PL) properties as grown and pure CdTe samples were investigated. Bright excitonic photoluminescence emission was observed (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  3. Substrate-Dependent Differences in the Crystal Structures and Optical Properties of ZnSe Nanowires

    Directory of Open Access Journals (Sweden)

    Keumyoung Seo

    2015-01-01

    Full Text Available The optical and structural properties of ZnSe nanowires directly grown on three different substrates, SiO2, ITO, and graphene, were investigated. ZnSe nanowires grown on graphene and SiO2 were found to have cubic structures, while ZnSe nanowires grown on ITO had a mixed cubic and hexagonal structure. The main peaks in the photoluminescence spectra of ZnSe nanowires grown on SiO2, ITO, and graphene were located at 459, 627, and 627/460 nm, respectively. In addition, a field-emission light-emitting device was fabricated using ZnSe nanowires as a phosphor and graphene as an electrode. The device showed a red emission peak with Commission Internationale de L’Eclairage coordinates of (0.621, 0.315.

  4. Ferromagnetism regulated by edged cutting and optical identification in monolayer PtSe2 nanoribbons

    Science.gov (United States)

    Meng, Ming; Zhang, QiZhen; Wang, Lifen; Shan, Yun; Du, Yuandong; Qin, Nan; Liu, Lizhe

    2018-06-01

    Regulation of ferromagnetism and electronic structure in PtSe2 nanostructures has attracted much attention because of its potential in spintronics. The magnetic and optical properties of PtSe2 nanoribbons with different edge reconstruction and external deformations are calculated by density function theory. In 1 T phase PtSe2 nanoribbons, the ferromagnetism induced by spin polarization of exposed Pt or Se atoms is decreased with the reducing nanoribbon width. For smaller nanoribbon, the magnetism can be regulated by external strain more easily. However, the magnetism cannot occur in 1 H phase PtSe2 nanoribbon. The absorption spectra are suggested to identify the nanoribbon structural changes in detail. Our results suggest the use of edge reconstruction and strain engineering in spintronics applications.

  5. Optical and electrical properties of ZrSe3 single crystals grown by ...

    Indian Academy of Sciences (India)

    Unknown

    The optical band gap ... The indirect as well as direct band gap of ZrSe3 were found to be 1⋅1 eV and 1⋅47 eV, respec- ... solar cell studies have attracted attention of crystal grow- ers. .... shown in figures 1 and 2, it is possible to determine the.

  6. Optical absorption and Faraday rotation in spin doped Cd1-xHgxSe : Mn crystals

    NARCIS (Netherlands)

    Savchuk, AI; Paranchich, SY; Paranchich, LD; Romanyuk, OS; Andriychuk, MD; Nikitin, PI; Tomlinson, RD; Hill, AE; Pilkington, RD

    1998-01-01

    Optical absorption spectra and the Faraday effect in crystals of Cd1-xHgxSe : Mn have been studied. The studied samples have been characterized abrupt absorption edge and transparency region with high transmission coefficient. The measured values of Verdet constant were considerably larger than in

  7. Surface composition of Cd{sub 1–x}Fe(Mn){sub x}Te{sub 1–y}Se{sub y} systems exposed to air

    Energy Technology Data Exchange (ETDEWEB)

    Bundaleski, Nenad [University of Belgrade–Vinča Institute of Nuclear Sciences, P.O. Box 522, 11001 Belgrade (Serbia); Universidade Nova de Lisboa–Faculdade de Ciências e Tecnologia, Quinta da Torre, 2829–516 Caparica (Portugal); Radisavljević, Ivana, E-mail: iva@vin.bg.ac.rs [University of Belgrade–Vinča Institute of Nuclear Sciences, P.O. Box 522, 11001 Belgrade (Serbia); Trigueiro, João [Universidade Nova de Lisboa–Faculdade de Ciências e Tecnologia, Quinta da Torre, 2829–516 Caparica (Portugal); Tolstogouzov, Alexander [Universidade Nova de Lisboa–Faculdade de Ciências e Tecnologia, Quinta da Torre, 2829–516 Caparica (Portugal); Ryazan State Radio Engineering University, Gagarin 59/1, 390005 Ryazan (Russian Federation); Rakočević, Zlatko; Medić, Mirjana [University of Belgrade–Vinča Institute of Nuclear Sciences, P.O. Box 522, 11001 Belgrade (Serbia); Teodoro, Orlando M.N.D. [Universidade Nova de Lisboa–Faculdade de Ciências e Tecnologia, Quinta da Torre, 2829–516 Caparica (Portugal); Romčević, Nebojša [University of Belgrade–Institute of Physics, Pregrevica 118, 11000 Belgrade (Serbia); Ivanović, Nenad [University of Belgrade–Vinča Institute of Nuclear Sciences, P.O. Box 522, 11001 Belgrade (Serbia)

    2017-03-01

    Using X–ray induced Photoelectron Spectroscopy, Time–of–Flight Secondary Ion Mass Spectrometry and Atomic Force Microscopy we have investigated elemental composition, structure and oxidation process taking place at the surfaces of polycrystalline Cd{sub 0.99}Fe{sub 0.01}Te{sub 0.97}Se{sub 0.03} and Cd{sub 0.95}Mn{sub 0.05}Te{sub 0.97}Se{sub 0.03} systems stored in ambient conditions. The surface oxidation destroys the native CdTe matrix and provokes substantial atomic rearrangement in the first few atomic layers. The near–surface region of both systems is enriched in Cd and to some extent Te–deficient, but the surface structure, morphology and the native oxide composition are all found to be considerably different. In Cd{sub 0.99}Fe{sub 0.01}Te{sub 0.97}Se{sub 0.03} system both Fe and Se dopants diffuse into the bulk and oxidation of its surface results in formation of a thin CdTeO{sub 3} layer which covers the CdTe matrix. In Cd{sub 0.95}Mn{sub 0.05}Te{sub 0.97}Se{sub 0.03} system oxygen–rich atmosphere triggers Mn and Se out–diffusion and the nonuniform oxide layer predominantly consists of MnO and a small amount of Te–oxide which both lay underneath a thin layer of metallic Cd segregated at the top of the surface. - Highlights: • Nature of the CdFe(Mn)TeSe surfaces exposed to air is substantially different. • Near–surface region is enriched in Cd and to some extent Te–deficient. • Presence of Mn drastically changes the surface oxidation conditions. • The surface oxidation in ambient conditions undergoes different mechanisms. • Oxygen triggers Mn out–diffusion, while Fe diffuses into the bulk.

  8. Fabrication of CdSe nanocrystals using porous anodic alumina and their optical properties

    Energy Technology Data Exchange (ETDEWEB)

    Laatar, Fakher, E-mail: fakher8laatar@gmail.com [Laboratory of Semiconductors, Nanostructures and Advanced Technology (LSNTA), Center for Research and Technology Energy, Tourist Route Soliman, BP 95, 2050 Hammam-Lif (Tunisia); Science faculty of Bizerte–Carthage University (Tunisia); Hassen, Mohamed [Laboratory of Semiconductors, Nanostructures and Advanced Technology (LSNTA), Center for Research and Technology Energy, Tourist Route Soliman, BP 95, 2050 Hammam-Lif (Tunisia); Higher Institute of Applied Science and Technology of Sousse, City Taffala (Ibn Khaldun), 4003 Sousse (Tunisia); Amri, Chohdi [Laboratory of Semiconductors, Nanostructures and Advanced Technology (LSNTA), Center for Research and Technology Energy, Tourist Route Soliman, BP 95, 2050 Hammam-Lif (Tunisia); Laatar, Fekri [Laboratory of Physical Chemistry of Minerals and Materials Applications, National Research Center for Materials Science, Technopole Borj Cedria (Tunisia); Smida, Alia; Ezzaouia, Hatem [Laboratory of Semiconductors, Nanostructures and Advanced Technology (LSNTA), Center for Research and Technology Energy, Tourist Route Soliman, BP 95, 2050 Hammam-Lif (Tunisia)

    2016-10-15

    In this paper, Porous anodic alumina (PAA) template with highly ordered nanopores structure was synthesized on aluminum foils by two step anodization process. PAA template has hexagonal pores with average size between 30 and 180 nm. L-cysteine (L-Cys) functionalized cadmium selenide nanocrystals (CdSe NCs) were successfully embedded inside PAA layers by simple immersion in aqueous solution. The effect of pore diameter enlargement on the microstructure of CdSe NCs/PAA films was systematically studied by FE-SEM, XRD, EDX, Raman, UV–VIS absorbance and PL analysis. FE-SEM microscopy was used to investigate the surface morphology of PAA templates before and after CdSe NCs deposition. XRD investigation demonstrates that CdSe NCs into PAA templates were cubic in nature with zinc-blende structure. Raman measurements exhibit the characteristic modes of CdSe on the PAA layers as well as the films crystallinity as function of widening pores diameter. Optical properties of deposited CdSe NCs on PAA templates have been investigated using optical absorption and PL techniques. Photoluminescence spectroscopy has been used to determine the bandgap energy and the average size of CdSe NCs deposited on PAA layer. This method involves fitting the experimental spectra, using a model based on quantum confinement of electrons in CdSe nanocrystals having spherical and cylindrical forms (Quantum Dots (QDs) and Quantum Wires (QWs)). This model allows correlation between the PL spectra and the microstructure of the CdSe/PAA. Both photoluminescence and optical absorption show that the PL peak energy and the optical absorption edge of CdSe NCs/PAA exhibit similar behavior with changes in nanostructure size. The spectral behaviors of optical absorption and PL are consistent with a quantum confinement model throughout the sizes and shapes of the CdSe nanocrystals of the luminescent films. The effective bandgap energies determined from the PL peaks position are in good agreement with those

  9. Fabrication of CdSe nanocrystals using porous anodic alumina and their optical properties

    International Nuclear Information System (INIS)

    Laatar, Fakher; Hassen, Mohamed; Amri, Chohdi; Laatar, Fekri; Smida, Alia; Ezzaouia, Hatem

    2016-01-01

    In this paper, Porous anodic alumina (PAA) template with highly ordered nanopores structure was synthesized on aluminum foils by two step anodization process. PAA template has hexagonal pores with average size between 30 and 180 nm. L-cysteine (L-Cys) functionalized cadmium selenide nanocrystals (CdSe NCs) were successfully embedded inside PAA layers by simple immersion in aqueous solution. The effect of pore diameter enlargement on the microstructure of CdSe NCs/PAA films was systematically studied by FE-SEM, XRD, EDX, Raman, UV–VIS absorbance and PL analysis. FE-SEM microscopy was used to investigate the surface morphology of PAA templates before and after CdSe NCs deposition. XRD investigation demonstrates that CdSe NCs into PAA templates were cubic in nature with zinc-blende structure. Raman measurements exhibit the characteristic modes of CdSe on the PAA layers as well as the films crystallinity as function of widening pores diameter. Optical properties of deposited CdSe NCs on PAA templates have been investigated using optical absorption and PL techniques. Photoluminescence spectroscopy has been used to determine the bandgap energy and the average size of CdSe NCs deposited on PAA layer. This method involves fitting the experimental spectra, using a model based on quantum confinement of electrons in CdSe nanocrystals having spherical and cylindrical forms (Quantum Dots (QDs) and Quantum Wires (QWs)). This model allows correlation between the PL spectra and the microstructure of the CdSe/PAA. Both photoluminescence and optical absorption show that the PL peak energy and the optical absorption edge of CdSe NCs/PAA exhibit similar behavior with changes in nanostructure size. The spectral behaviors of optical absorption and PL are consistent with a quantum confinement model throughout the sizes and shapes of the CdSe nanocrystals of the luminescent films. The effective bandgap energies determined from the PL peaks position are in good agreement with those

  10. Giant magneto-optical faraday effect in HgTe thin films in the terahertz spectral range.

    Science.gov (United States)

    Shuvaev, A M; Astakhov, G V; Pimenov, A; Brüne, C; Buhmann, H; Molenkamp, L W

    2011-03-11

    We report the observation of a giant Faraday effect, using terahertz (THz) spectroscopy on epitaxial HgTe thin films at room temperature. The effect is caused by the combination of the unique band structure and the very high electron mobility of HgTe. Our observations suggest that HgTe is a high-potential material for applications as optical isolator and modulator in the THz spectral range.

  11. Characterization of Electronic Materials HgZnSe and HgZnTe Using Innovative and Conventional Techniques

    Science.gov (United States)

    Tanton, George; Kesmodel, Roy; Burden, Judy; Su, Ching-Hua; Cobb, Sharon D.; Lehoczky, S. L.

    2000-01-01

    HgZnSe and HgZnTe are electronic materials of interest for potential IR detector and focal plane array applications due to their improved strength and compositional stability over HgCdTe, but they are difficult to grow on Earth and to fully characterize. Conventional contact methods of characterization, such as Hall and van der Paw, although adequate for many situations are typically labor intensive and not entirely suitable where only very small samples are available. To adequately characterize and compare properties of electronic materials grown in low earth orbit with those grown on Earth, innovative techniques are needed that complement existing methods. This paper describes the implementation and test results of a unique non-contact method of characterizing uniformity, mobility, and carrier concentration together with results from conventional methods applied to HgZnSe and HgZnTe. The innovative method has advantages over conventional contact methods since it circumvents problems of possible contamination from alloying electrical contacts to a sample and also has the capability to map a sample. Non- destructive mapping, the determination of the carrier concentration and mobility at each place on a sample, provides a means to quantitatively compare, at high spatial resolution, effects of microgravity on electronic properties and uniformity of electronic materials grown in low-Earth orbit with Earth grown materials. The mapping technique described here uses a 1mm diameter polarized beam of radiation to probe the sample. Activation of a magnetic field, in which the sample is placed, causes the plane of polarization of the probe beam to rotate. This Faraday rotation is a function of the free carrier concentration and the band parameters of the material. Maps of carrier concentration, mobility, and transmission generated from measurements of the Faraday rotation angles over the temperature range from 300K to 77K will be presented. New information on band parameters

  12. Elucidating the Impact of Chalcogen Content on the Photovoltaic Properties of Oxychalcogenide Perovkskites: NaMO3-x Qx (M=Nb, Ta; Q=S, Se, Te).

    Science.gov (United States)

    Park, Heesoo; Alharbi, Fahhad H; Sanvito, Stefano; Tabet, Nouar; El-Mellouhi, Fedwa

    2018-03-19

    In the quest for nontoxic and stable perovskites for solar cells, we have conducted a systematic study of the effect of chalcogen content in oxychalcogenide perovskite by using DFT and quasi-particle perturbation theory. We explored the changes in the electronic structure due to the substitution of O atoms in NaNbO 3 and NaTaO 3 perovskite structures with various chalcogens (S, Se, Te) at different concentrations. Interestingly, the introduction of the chalcogen atoms resulted in a drastic reduction in the electronic band gap, which made some of the compounds fall within the visible range of the solar spectrum. In addition, our analysis of the electronic structure shows that the optical transition becomes direct as a result of the strong hybridization between the orbitals of the transition metal and those of the chalcogen ion, in contrast to the indirect band feature of NaNbO 3 and NaTaO 3 . We identified candidates with a high theoretical solar conversion efficiency that approached the Shockley-Queisser limit, which makes them suitable for thin-film solar cell applications. The present work serves as a guideline for experimental efforts by identifying the chalcogen content that should be targeted during the synthetic route of thermodynamically stable and strongly photoactive absorbers for oxychalcogenide perovskites in thin-film solar cells. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Linear and nonlinear optical properties of Sb-doped GeSe2 thin films

    Science.gov (United States)

    Zhang, Zhen-Ying; Chen, Fen; Lu, Shun-Bin; Wang, Yong-Hui; Shen, Xiang; Dai, Shi-Xun; Nie, Qiu-Hua

    2015-06-01

    Sb-doped GeSe2 chalcogenide thin films are prepared by the magnetron co-sputtering method. The linear optical properties of as-deposited films are derived by analyzing transmission spectra. The refractive index rises and the optical band gap decreases from 2.08 eV to 1.41 eV with increasing the Sb content. X-ray photoelectron spectra further confirm the formation of a covalent Sb-Se bond. The third-order nonlinear optical properties of thin films are investigated under femtosecond laser excitation at 800 nm. The results show that the third-order nonlinear optical properties are enhanced with increasing the concentration of Sb. The nonlinear refraction indices of these thin films are measured to be on the order of 10-18 m2/W with a positive sign and the nonlinear absorption coefficients are obtained to be on the order of 10-10 m/W. These excellent properties indicate that Sb-doped Ge-Se films have a good prospect in the applications of nonlinear optical devices. Project supported by the National Key Basic Research Program of China (Grant No. 2012CB722703), the National Natural Science Foundation of China (Grant No. 61377061), the Young Leaders of Academic Climbing Project of the Education Department of Zhejiang Province, China (Grant No. pd2013092), the Program for Innovative Research Team of Ningbo City, China (Grant No. 2009B217), and the K. C. Wong Magna Fund in Ningbo University, China.

  14. Effect of Se addition on optical and electrical properties of chalcogenide CdSSe thin films

    Science.gov (United States)

    Hassanien, A. S.; Akl, Alaa A.

    2016-01-01

    Compositional dependence of optical and electrical properties of chalcogenide CdSxSe1-x (0.4 ≥ x ≥ 0.0 at. %) thin films was studied. Cadmium sulphoselenide films were deposited by thermal evaporation technique at vacuum (8.2 × 10-4 Pa) onto preheated glass substrates (523 K). The evaporation rate and film thickness were kept constant at 2.50 nm/s and 375 ± 5 nm, respectively. X-ray diffractograms showed that, the deposited films have the low crystalline nature. Energy dispersive analysis by X-ray (EDAX) was used to check the compositional elements of deposited films. The absorption coefficient was determined from transmission and reflection measurements at room temperature in the wavelength range 300-2500 nm. Optical density, skin depth, optical energy gap and Urbach's parameters of CdSSe thin films have also been estimated. The direct optical energy gap decreased from 2.248 eV to 1.749 eV when the ratio of Se-content was increased from 0.60 to 1.00 . Conduction band and valance band positions were evaluated. The temperature dependence of dc-electrical resistivity in the temperature range (293-450 K) has been reported. Three conduction regions due to different conduction mechanisms were detected. Electrical sheet resistance, activation energy and pre-exponential parameters were discussed. The estimated values of optical and electrical parameters were strongly dependent upon the Se-content in CdSSe matrix.

  15. First principles study of structural, electronic and optical properties of polymorphic forms of Rb 2Te

    Science.gov (United States)

    Alay-e-Abbas, S. M.; Shaukat, A.

    2011-05-01

    First-principles density functional theory calculations have been performed for structural, electronic and optical properties of three polymorphic forms of rubidium telluride. Our calculations show that the sequence of pressure induced phase transitions for Rb 2Te is Fm3¯m → Pnma → P6 3/mmc which is governed by the coordination numbers of the anions. From our calculated low transition pressure value for the Fm3¯m phase to the Pnma phase transition of Rb 2Te, the experimentally observed meta-stability of Fm3¯m phase at ambient conditions seems reasonable. The electronic band structure has been calculated for all the three phases and the change in the energy band gap is discussed for the transitioning phases. The energy band gaps obtained for the three phases of Rb 2Te decrease on going from the meta-stable phase to the high-pressure phases. Total and partial density of states for the polymorphs of Rb 2Te has been computed to elucidate the contribution of various atomic states on the electronic band structure. Furthermore, optical properties for all the polymorphic forms have been presented in form of the complex dielectric function.

  16. Epitaxial growth and optical investigations of ZnTeO alloys

    International Nuclear Information System (INIS)

    Nabetani, Y.; Okuno, T.; Aoki, K.; Kato, T.; Matsumoto, T.; Hirai, T.

    2006-01-01

    We have grown zincblende-structured ZnTeO alloy semiconductors on GaAs substrates by molecular beam epitaxy using RF-excited O. O concentrations measured by secondary ion mass spectroscopy were found to increase with the increase of O 2 flow rate supplied during the growth, while the change of lattice constant measured by X-ray diffraction does not follow Vegard's law. It is considered that the O atoms are incorporated not only into group-VI sites but also as interstitials. Formation of other compounds such as ZnTeO 3 , Zn 2 Te 3 O 8 , and TeO 2 was not detected. Optical reflectance spectroscopy revealed the increase of the band-gap energy with O concentration that can be interpreted as the repulsive interaction between the energy states originated in the localized states of O and the conduction-band edge of host ZnTe. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (Abstract Copyright [2006], Wiley Periodicals, Inc.)

  17. Synthesis, crystal structure, optical, and electronic study of the new ternary thorium selenide Ba{sub 3}ThSe{sub 3}(Se{sub 2}){sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Prakash, Jai [Department of Chemistry, Northwestern University, Evanston, IL 60208-3113 (United States); Mesbah, Adel [Department of Chemistry, Northwestern University, Evanston, IL 60208-3113 (United States); ICSM, UMR 5257 CEA/CNRS/UM2/ENSCM, Site de Marcoule-Bât. 426, BP 17171, 30207 Bagnols-sur-Cèze cedex (France); Beard, Jessica [Department of Chemistry, Northwestern University, Evanston, IL 60208-3113 (United States); Lebègue, Sébastien [Laboratoire de Cristallographie, Résonance Magnétique et Modélisations (CRM2, UMR CNRS 7036), Institut Jean Barriol, Université de Lorraine, BP 239, Boulevard des Aiguillettes, 54506 Vandoeuvre-lès-Nancy (France); Malliakas, Christos D. [Department of Chemistry, Northwestern University, Evanston, IL 60208-3113 (United States); Ibers, James A., E-mail: ibers@chem.northwestern.edu [Department of Chemistry, Northwestern University, Evanston, IL 60208-3113 (United States)

    2015-11-15

    The compound Ba{sub 3}ThSe{sub 3}(Se{sub 2}){sub 2} has been synthesized by solid-state methods at 1173 K. Its crystal structure features one-dimensional chains of {sup 1}{sub ∞}[Th(Se){sub 3}(Se{sub 2}){sub 2}{sup 6−}] separated by Ba{sup 2+} cations. Each Th atom in these chains is coordinated to two Se–Se single-bonded pairs and four Se atoms to give rise to a pseudooctahedral geometry around Th. The Th–Se distances are consistent with Th{sup 4+} and hence charge balance of Ba{sub 3}ThSe{sub 3}(Se{sub 2}){sub 2} is achieved as 3×Ba{sup 2+}, 1×Th{sup 4+}, 3×Se{sup 2−}, and 2×Se{sub 2}{sup 2−}. From optical measurements the band gap of Ba{sub 3}ThSe{sub 3}(Se{sub 2}){sub 2} is 1.96(2) eV. DFT calculations indicate that the compound is a semiconductor. - Graphical abstract: Local coordination environment of Th atoms in the Ba{sub 3}ThSe{sub 3}(Se{sub 2}){sub 2} structure. - Highlights: • Ba{sub 3}ThSe{sub 3}(Se{sub 2}){sub 2} has been synthesized by solid-state methods at 1173 K. • The structure features chains of {sup 1}{sub ∞}[Th(Se){sub 3}(Se{sub 2}){sub 2}{sup 6−}] separated by Ba{sup 2+} cations. • Ba{sub 3}ThSe{sub 3}(Se{sub 2}){sub 2} is a semiconductor with a band gap of 1.96(2) eV.

  18. Electrical and optical properties of spray - deposited CdSe thin films

    International Nuclear Information System (INIS)

    Bedir, M.; Oeztas, M.; Bakkaloglu, O. F.

    2002-01-01

    The CdSe thin films were developed by using spray-deposition technique at different substrate temperatures of 380C, 400C and, 420C on the glass substrate. All spraying processes involved CdCI 2 (0.05 moles/liter) and SeO 2 (0.05 moles/liter ) and were carried out in atmospheric condition. The CdSe thin film samples were characterized using x-ray diffractometer and optical absorption measurements. The electrical properties of the thin film samples were investigated via Wander Pauw method. XRD patterns indicated that the CdSe thin film samples have a hexagonal structure. The direct band gap of the CdSe thin film samples were determined from optical absorption and spectral response measurements of 1.76 eV. The resistivity of the CdSe thin film samples were found to vary in the range from 5.8x10''5 to 7.32x10''5 Ωcm depending to the substrate temperature

  19. Synthesis and optical study of green light emitting polymer coated CdSe/ZnSe core/shell nanocrystals

    Energy Technology Data Exchange (ETDEWEB)

    Tripathi, S.K., E-mail: surya@pu.ac.in [Department of Physics, Center of Advanced Study in Physics, Panjab University, Chandigarh 160 014 (India); Sharma, Mamta [Department of Physics, Center of Advanced Study in Physics, Panjab University, Chandigarh 160 014 (India)

    2013-05-15

    Highlights: ► Synthesis of Polymer coated core CdSe and CdSe/ZnSe core/shell NCs. ► From TEM image, the spherical nature of CdSe and CdSe/ZnSe is obtained. ► Exhibiting green band photoemission peak at 541 nm and 549 nm for CdSe core and CdSe/ZnSe core/shell NCs. ► The shell thickness has been calculated by using superposition of quantum confinement energy model. - Abstract: CdSe/ZnSe Core/Shell NCs dispersed in PVA are synthesized by chemical method at room temperature. This is characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), UV/Vis spectra and photoluminescence spectroscopy (PL). TEM image shows the spherical nature of CdSe/ZnSe core/shell NCs. The red shift of absorption and emission peak of CdSe/ZnSe core/shell NCs as compared to CdSe core confirmed the formation of core/shell. The superposition of quantum confinement energy model is used for calculation of thickness of ZnSe shell.

  20. Electric field manipulation in Al/CdTe/Pt detectors under optical perturbations

    Energy Technology Data Exchange (ETDEWEB)

    Turturici, A.A. [Dipartimento di Fisica e Chimica, Università di Palermo, Viale delle Scienze, Edificio 18, Palermo 90128 (Italy); Franc, J.; Grill, R.; Dědič, V. [Institute of Physics of Charles University, MFF, Ke Karlovu 5, Prague 2 (Czech Republic); Abbene, L., E-mail: leonardo.abbene@unipa.it [Dipartimento di Fisica e Chimica, Università di Palermo, Viale delle Scienze, Edificio 18, Palermo 90128 (Italy); Principato, F. [Dipartimento di Fisica e Chimica, Università di Palermo, Viale delle Scienze, Edificio 18, Palermo 90128 (Italy)

    2017-06-21

    Al/CdTe/Pt detectors are very attractive devices for high-resolution X-ray spectroscopy, even though they suffer from polarization phenomena, which cause a progressive time degradation of the spectroscopic performance. In this work we investigated on the time dependence of the electric field of an Al/CdTe/Pt detector under optical perturbation by means of Pockels effect measurements. A tunable laser with wavelengths ranging within 700−1000 nm and a 940 nm light emitting diode (LED) were used. The measurements of both the electric field profile and the total current were used to better understand the effects of the optical perturbation on polarization phenomena. The results point out as the above band-gap light, due to the trapping of photo-generated holes at the anode (the Al/CdTe blocking contact), brings to a reduction of the negative space charge caused by the bias voltage (bias induced polarization) and the LED irradiation (radiation induced polarization). The reduction of the negative space charge ensures a quite stable and uniform electric field distribution, typically termed depolarization. Conversely, optical perturbation with sub-band-gap light enhances the polarization with the formation of two oppositely charged regions within the detector.

  1. The half-metallic ferromagnetism character in Be1−xVxY (Y=Se and Te) alloys: An ab-initio study

    International Nuclear Information System (INIS)

    Sajjad, M.; Manzoor, Sadia; Zhang, H.X.; Noor, N.A.; Alay-e-Abbas, S.M.; Shaukat, A.; Khenata, R.

    2015-01-01

    Ab-initio calculations for V-doped BeSe and BeTe semiconductors are performed by means of all-electrons full-potential linearized augmented plane wave plus local orbital (FP-LAPW+lo) method. The structural properties are optimized using the Wu-Cohen generalized gradient approximation functional, whereas modified Becke and Jhonson local density approximation functional has been employed for evaluating the spin-polarized electronic and magnetic properties. Magnetic stability at various doping concentrations in ferromagnetic (FM) and anti-ferromagnetic (AFM) ordering is investigated by comparing the minimum total energies and enthalpies of formation (ΔH). Studied band structures, density of states, total energy, exchange interactions and magnetic moments manifest both alloys with half-metallic ferromagnetic behavior. Moreover, their valance bands are found to be paired ferromagnetically with V atoms. Furthermore, it was observed that the magnetic moment of vanadium atom reduces from free space charge value due to p–d hybridization which yields small magnetic moments on the Be, Se and Te sites. - Highlights: • Density functional calculations for V-doped BeSe and BeTe are performed. • V-doped BeSe and BeTe are found to be stable half-metallic ferromagnetism. • Improved electronic properties are achieved using mBJLDA which confirm HMF. • The half-metallic gaps show non-linear variation with increasing dopant concentration

  2. TeSeR – Technology for Self-Removal – First results of an H2020 Project to develop a Post-Mission-Disposal Module

    DEFF Research Database (Denmark)

    Voigt, p.; Vogt, C.; Schubert, R.

    2017-01-01

    The goal of TeSeR (Technology for Self-Removal) is to take the first step towards the development of a scalable, flexible, cost-efficient, but highly reliable Post-Mission-Disposal (PMD) module. This module is to be attached to the spacecraft (S/C) on ground and it shall ensure the PMD of the S/C...

  3. Determination of total Sb,Se Te, and Bi and evaluation of their inorganic species in garlic by hydride-generation-atomic-fluorescence spectrometry

    Energy Technology Data Exchange (ETDEWEB)

    Matos Reyes, M.N.; Cervera, M.L.; Guardia, M. de la [University of Valencia, Department of Analytical Chemistry, Burjassot, Valencia (Spain)

    2009-07-15

    A sensitive and simple analytical method has been developed for determination of Sb(III), Sb(V), Se(IV), Se(VI), Te(IV), Te(VI), and Bi(III) in garlic samples by using hydride-generation-atomic-fluorescence spectrometry (HG-AFS). The method is based on a single extraction of the inorganic species by sonication at room temperature with 1 mol L{sup -1} H{sub 2}SO{sub 4} and washing of the solid phase with 0.1% (w/v) EDTA, followed by measurement of the corresponding hydrides generated under two different experimental conditions directly and after a pre-reduction step. The limit of detection of the method was 0.7 ng g{sup -1} for Sb(III), 1.0 ng g{sup -1} for Sb(V), 1.3 ng g{sup -1} for Se(IV), 1.0 ng g{sup -1} for Se(VI), 1.1 ng g{sup -1} for Te(IV), 0.5 ng g{sup -1} for Te(VI), and 0.9 ng g{sup -1} for Bi(III), in all cases expressed in terms of sample dry weight. (orig.)

  4. Quasiparticle self-consistent GW calculations for PbS, PbSe, and PbTe: Band structure and pressure coefficients

    DEFF Research Database (Denmark)

    Svane, Axel; Christensen, Niels Egede; Cardona,, M.

    2010-01-01

    The electronic band structures of PbS, PbSe, and PbTe in the rocksalt structure are calculated with the quasiparticle self-consistent GW (QSGW) approach with spin-orbit coupling included. The semiconducting gaps and their deformation potentials as well as the effective masses are obtained. The GW...

  5. Benchmark assessment of density functional methods on group II-VI MX (M = Zn, Cd; X = S, Se, Te) quantum dots

    NARCIS (Netherlands)

    Azpiroz, Jon M.; Ugalde, Jesus M.; Infante, Ivan

    2014-01-01

    In this work, we build a benchmark data set of geometrical parameters, vibrational normal modes, and low-lying excitation energies for MX quantum dots, with M = Cd, Zn, and X = S, Se, Te. The reference database has been constructed by ab initio resolution-of-identity second-order approximate coupled

  6. Interaction between counter-propagating quantum Hall edge channels in the 3D topological insulator BiSbTeSe2

    NARCIS (Netherlands)

    Li, C.; De Ronde, B.; Nikitin, A.; Huang, Y.; Golden, M.S.; De Visser, A.; Brinkman, A.

    2017-01-01

    The quantum Hall effect is studied in the topological insulator BiSbTeSe2. By employing top- and back-gate electric fields at high magnetic field, the Landau levels of the Dirac cones in the top and bottom topological surface states can be tuned independently. When one surface is tuned to the

  7. Ab-initio calculations of Co-based diluted magnetic semiconductors Cd 1-xCoxX (X=S, Se, Te)

    KAUST Repository

    Saeed, Yasir; Nazir, Safdar; Shaukat, Ali; Reshak, A. H.

    2010-01-01

    Ab-initio calculations are performed to investigate the structural, electronic and magnetic properties of spin-polarized diluted magnetic semiconductors composed of IIVI compounds Cd1-xCoxX (X=S, Se, Te) at x=0.25. From the calculated results

  8. Efficient optical trapping of CdTe quantum dots by femtosecond laser pulses

    KAUST Repository

    Chiang, Weiyi

    2014-12-11

    The development in optical trapping and manipulation has been showing rapid progress, most of it is in the small particle sizes in nanometer scales, substituting the conventional continuous-wave lasers with high-repetition-rate ultrashort laser pulse train and nonlinear optical effects. Here, we evaluate two-photon absorption in optical trapping of 2.7 nm-sized CdTe quantum dots (QDs) with high-repetition-rate femtosecond pulse train by probing laser intensity dependence of both Rayleigh scattering image and the two-photon-induced luminescence spectrum of the optically trapped QDs. The Rayleigh scattering imaging indicates that the two-photon absorption (TPA) process enhances trapping ability of the QDs. Similarly, a nonlinear increase of the two-photon-induced luminescence with the incident laser intensity fairly indicates the existence of the TPA process.

  9. Controlling Lateral Fano Interference Optical Force with Au-Ge2Sb2Te5 Hybrid Nanostructure

    DEFF Research Database (Denmark)

    Cao, Tun; Bao, Jiaxin; Mao, Libang

    2016-01-01

    is revealed through optical singularity in the Poynting vector. A thermal-electric simulation is adopted to investigate the temporal change of the Ge2Sb2Te5 film's temperature, which demonstrates the possibility of transiting the Ge2Sb2Te5 state by electrical heating. Our mechanism by tailoring the DQ...... in flexible nanomechanical control and may provide a new means of biomedical sensing and nano -optical conveyor belts....

  10. Dynamic traffic grooming with Spectrum Engineering (TG-SE) in flexible grid optical networks

    Science.gov (United States)

    Yu, Xiaosong; Zhao, Yongli; Zhang, Jiawei; Wang, Jianping; Zhang, Guoying; Chen, Xue; Zhang, Jie

    2015-12-01

    Flexible grid has emerged as an evolutionary technology to satisfy the ever increasing demand for higher spectrum efficiency and operational flexibility. To optimize the spectrum resource utilization, this paper introduces the concept of Spectrum Engineering in flex-grid optical networks. The sliceable optical transponder has been proposed to offload IP traffic to the optical layer and reduce the number of IP router ports and transponders. We discuss the impact of sliceable transponder in traffic grooming and propose several traffic-grooming schemes with Spectrum Engineering (TG-SE). Our results show that there is a tradeoff among different traffic grooming policies, which should be adopted based on the network operator's objectives. The proposed traffic grooming with Spectrum Engineering schemes can reduce OPEX as well as increase spectrum efficiency by efficiently utilizing the bandwidth variability and capability of sliceable optical transponders.

  11. Theoretical investigation of lithium adsorption, diffusion and coverage on MX2 (M = Mo, W; X = O, S, Se, Te) monolayers

    Science.gov (United States)

    Ersan, F.; Ozaydin, H. D.; Gökoğlu, G.; Aktürk, E.

    2017-12-01

    It is important to improve the high-efficient anode materials for Li batteries, which require the large capacity, high stability and mobility. In this work, we present the adsorption and diffusion properties of lithium atom on MX2 (M = Mo, W; X = O, S, Se, Te) transition metal dichalcogenide structures using first principles calculations within density functional theory. All the MX2 systems considered are semiconductor in bare state with band gaps between 0.93 eV (MoO2) and 1.79 eV (WS2). They turn into metal upon single Li adsorption. Li atom is adsorbed on MoO2 and WO2 rather stronger than other systems. The energy barrier for diffusion of single Li on MX2 varies between 0.15 eV and 0.28 eV which are lower or comparable to that of graphene or silicene. Two Li atoms are preferably adsorbed on MX2 monolayer symmetrically at opposite sides with high adsorption energy. The increasing number of Li atoms does not remarkably affect the adsorption energy per Li atom. This can be attributed to that Li atoms do not accumulate on certain regions of the surface. The systems under investigation provide insights into exploring electronic properties which are rather adequate for possible applications in Li-ion batteries.

  12. Magnetic properties and crystal field effects in TlLnX2 compounds (X=S, Se, Te)

    International Nuclear Information System (INIS)

    Duczmal, M.; Pawlak, L.

    1997-01-01

    Ternary thallium lanthanide chalcogenides TlLnX 2 (X=S, Se or Te) crystallize in the α-NaFeO 2 type of structure (R anti 3m). Each kind of the metal ions, surrounded by the distorted chalcogenide octahedra, forms separate layers. The TlX 6 octahedra are strongly elongated and the LnX 6 octahedra slightly shrunk along the threefold axis. The deformations of the coordination polyhedra and the cell volumes change regularly with the lanthanide ionic radii. The difference between the experimental and the calculated M-X distances increases on going from sulphides to tellurides, as a result of the growing covalent character of the bonds. The crystal field parameters were estimated from the high field magnetization (0-14 T) assuming trigonal distortion of the octahedral symmetry of LnX 6 polyhedra. The second-order crystal field parameters were found to correlate with the deformation of the lanthanide ions' environments. No magnetic transition was observed down to 4.2 K. (orig.)

  13. Extension of Mediema's Macroscopic Atom Model to the Elements of Group 16 (O, S, Se, Te ,Po)

    Energy Technology Data Exchange (ETDEWEB)

    Neuhausen, J.; Eichler, B

    2003-09-01

    A consistent set of Miedema-parameters has been developed for the elements of the chalcogen group (Group 16 of the periodic table of the elements: 0, S, Se, Te, Po) from ab-initio quantum-mechanical calculations as weIl as empirical correlations. Using this parameter set thermochemical properties such as enthalpies of formation of solid metal chalcogenides, partial molar enthalpies of solution of chalcogens in liquid and solid metaIs, partial molar enthalpies of evaporation of the chalcogens from liquid metal solution into the monoatomic gaseous state, partial molar enthalpies of adsorption of chalcogenides on metal surfaces at zero coverage and partial molar enthalpies of segregation of the chalcogens in trace amounts within solid metal matrices have been calculated. These properties are compared with available experimental data and discussed with an emphasis on the periodic behaviour of the elements. The model calculations show that a description of the thermochemical properties of the chalcogens using the semi-empirical Miedema approach is possible. The calculated properties can serve as a basis for the prediction of the chemical interactions for metal-chalcogen combinations that have not been studied experimentally so far. (author)

  14. Extension of Mediema's Macroscopic Atom Model to the Elements of Group 16 (O, S, Se, Te ,Po)

    International Nuclear Information System (INIS)

    Neuhausen, J.; Eichler, B.

    2003-09-01

    A consistent set of Miedema-parameters has been developed for the elements of the chalcogen group (Group 16 of the periodic table of the elements: 0, S, Se, Te, Po) from ab-initio quantum-mechanical calculations as weIl as empirical correlations. Using this parameter set thermochemical properties such as enthalpies of formation of solid metal chalcogenides, partial molar enthalpies of solution of chalcogens in liquid and solid metaIs, partial molar enthalpies of evaporation of the chalcogens from liquid metal solution into the monoatomic gaseous state, partial molar enthalpies of adsorption of chalcogenides on metal surfaces at zero coverage and partial molar enthalpies of segregation of the chalcogens in trace amounts within solid metal matrices have been calculated. These properties are compared with available experimental data and discussed with an emphasis on the periodic behaviour of the elements. The model calculations show that a description of the thermochemical properties of the chalcogens using the semi-empirical Miedema approach is possible. The calculated properties can serve as a basis for the prediction of the chemical interactions for metal-chalcogen combinations that have not been studied experimentally so far. (author)

  15. ac conductivity and dielectric properties of amorphous Se80Te20-xGex chalcogenide glass film compositions

    International Nuclear Information System (INIS)

    Hegab, N.A.; Afifi, M.A.; Atyia, H.E.; Farid, A.S.

    2009-01-01

    Thin films of the prepared Se 80 Te 20-x Ge x (x = 5, 7 and 10 at.%) were prepared by thermal evaporation technique. X-ray diffraction patterns showed that the films were in amorphous state. The ac conductivity and dielectric properties of the investigated film compositions were studied in the frequency range 0.1-100 kHz and in temperature range (303-373 K). The experimental results indicated that the ac conductivity and the dielectric properties depended on the temperature and frequency. The ac conductivity is found to obey the ω s law, in accordance with the hopping model, s is found to be temperature dependent (s 1 and dielectric loss ε 2 were found to decrease with frequency and increase with temperature. The maximum barrier height W m , calculated from dielectric measurements according to Guintini equation, agrees with that proposed by the theory of hopping over potential barrier as suggested by Elliott in case of chalcogenide glasses. The density of localized states was estimated for the studied film compositions. The variation of the studied properties with Ge content was also investigated.

  16. Topological surface states of Bi{sub 2}Te{sub 2}Se are robust against surface chemical modification

    Energy Technology Data Exchange (ETDEWEB)

    Thomas, Conor R.; Sahasrabudhe, Girija; Kushwaha, Satya Kumar; Cava, Robert J.; Schwartz, Jeffrey [Department of Chemistry, Princeton University, Princeton, NJ (United States); Xiong, Jun [Department of Physics, Princeton University, Princeton, NJ (United States)

    2014-12-01

    The robustness of the Dirac-like electronic states on the surfaces of topological insulators (TIs) during materials process-ing is a prerequisite for their eventual device application. Here, the (001) cleavage surfaces of crystals of the topological insulator Bi{sub 2}Te{sub 2}Se (BTS) were subjected to several surface chemical modification procedures that are common for electronic materials. Through measurement of Shubnikov-de Hass (SdH) oscillations, which are the most sensitive measure of their quality, the surface states of the treated surfaces were compared to those of pristine BTS that had been exposed to ambient conditions. In each case - surface oxidation, deposition of thin layers of Ti or Zr oxides, or chemical modification of the surface oxides - the robustness of the topological surface electronic states was demonstrated by noting only very small changes in the frequency and amplitude of the SdH oscillations. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  17. High-energy ion treatments of amorphous As40Se60 thin films for optical applications

    Directory of Open Access Journals (Sweden)

    Rashmi Chauhan

    2014-06-01

    Full Text Available The treatment of 100 MeV Ag swift-heavy ion (SHI irradiation with five different fluences (3×1010, 1×1011, 3×1011, 1×1012, and 3×1012 ions/cm2 was used to design optical and structural properties of amorphous (a- As40Se60 chalcogenide thin films. Swanepoel method was applied on transmission measurements to determine the changes in optical bandgap, Tauc parameter and linear optical parameters, i.e., linear optical absorption, extinction coefficient and linear refractive index. Dispersion of the material was determined by Wemple–DiDomenico relation. Changes in nonlinear optical parameters of third-order optical susceptibility and nonlinear refractive index were determined using semi-empirical relations. Changes in surface morphology of the films were investigated using SEM observation, which indicated that fluence 3×1012 ions/cm2 was upper threshold limit for these films for ion treatment. It is observed that optical bandgap reduces from 1.76 eV to 1.64 eV, and nonlinear refractive index increases from 1.31×10−10 [esu] to 1.74×10−10 [esu]. Linear refractive index initially increases from 2.80 to 3.52 (for fluence 3×1010 ions/cm2 and then keeps decreasing. The observed changes in optical properties upon irradiation were explained in terms of structural rearrangements by Raman measurement. The study was compiled with the previous literature to propose SHI as an effective optical engineering technique to achieve desired changes according to the need of optical/photonic applications.

  18. Optical absorption of CdSe quantum dots on electrodes with different morphology

    Directory of Open Access Journals (Sweden)

    Witoon Yindeesuk

    2013-10-01

    Full Text Available We have studied the optical absorption of CdSe quantum dots (QDs adsorbed on inverse opal TiO2 (IO-TiO2 and nanoparticulate TiO2 (NP-TiO2 electrodes using photoacoustic (PA measurements. The CdSe QDs were grown directly on IO-TiO2 and NP-TiO2 electrodes by a successive ionic layer adsorption and reaction (SILAR method with different numbers of cycles. The average diameter of the QDs was estimated by applying an effective mass approximation to the PA spectra. The increasing size of the QDs with increasing number of cycles was confirmed by a redshift in the optical absorption spectrum. The average diameter of the CdSe QDs on the IO-TiO2 electrodes was similar to that on the NP-TiO2 ones, indicating that growth is independent of morphology. However, there were more CdSe QDs on the NP-TiO2 electrodes than on the IO-TiO2 ones, indicating that there were different amounts of active sites on each type of electrode. In addition, the Urbach parameter of the exponential optical absorption tail was also estimated from the PA spectrum. The Urbach parameter of CdSe QDs on IO-TiO2 electrodes was higher than that on NP-TiO2 ones, indicating that CdSe QDs on IO-TiO2 electrodes are more disordered states than those on NP-TiO2 electrodes. The Urbach parameter decreases in both cases with the increase of SILAR cycles, and it tended to move toward a constant value.

  19. Insights into the optical and anti-bacterial properties of biogenic PbSe quantum rods

    Directory of Open Access Journals (Sweden)

    Jaya Mary Jacob

    2016-07-01

    Full Text Available The detailed optical properties of lead selenide (PbSe quantum rods biosynthesized in marine Aspergillus terreus were apprehended theoretically using ab initio calculations based on the experimental absorption spectrum. These studies indicate that the absorption coefficient of the biosynthesized PbSe quantum rods increases linearly with incident photon energies. The variation of other optical constants like extinction coefficient, refractive index and reflectance was comparable to that of the chemically synthesized counterparts. Further, the high dielectric constant and remarkable fluorescence of the biogenic PbSe quantum rods pronounce their application in opto-electronic devices in the Near Infra-Red and Ultraviolet spectral regime. The biosynthesized PbSe quantum rods were also found to possess appreciable anti-bacterial activity against various gram positive and gram negative bacterial species thus enhancing the relevance of the same for practical utility. Based on these results it can be concluded that biogenic PbSe quantum rods can be envisaged as potential candidates for bio-imaging, bio-sensing and other photo-voltaic applications.

  20. Au36(SePh)24 nanomolecules: synthesis, optical spectroscopy and theoretical analysis.

    Science.gov (United States)

    Rambukwella, Milan; Chang, Le; Ravishanker, Anish; Fortunelli, Alessandro; Stener, Mauro; Dass, Amala

    2018-05-16

    Here, we report the synthesis of selenophenol (HSePh) protected Au36(SePh)24 nanomolecules via a ligand-exchange reaction of 4-tert-butylbenzenethiol (HSPh-tBu) protected Au36(SPh-tBu)24 with selenophenol, and its spectroscopic and theoretical analysis. Matrix assisted laser desorption ionization (MALDI) mass spectrometry, electrospray ionization (ESI) mass spectrometry and optical characterization confirm that the composition of the as synthesized product is predominantly Au36(SePh)24 nanomolecules. Size exclusion chromatography (SEC) was employed to isolate the Au36(SePh)24 and temperature dependent optical absorption studies and theoretical analysis were performed. Theoretically, an Independent Component Maps of Oscillator Strength (ICM-OS) analysis of simulated spectra shows that the enhancement in absorption intensity in Au36(SePh)24 with respect to Au36(SPh)24 can be ascribed to the absence of interference and/or increased long-range coupling between interband metal core and ligand excitations. This work demonstrates and helps to understand the effect of Au-Se bridging on the properties of gold nanomolecules.

  1. Manipulating the optical properties of CdSe/ZnSSe quantum dot based monolithic pillar microcavities

    Energy Technology Data Exchange (ETDEWEB)

    Seyfried, Moritz; Kalden, Joachim; Lohmeyer, Henning; Sebald, Kathrin; Gutowski, Juergen [Semiconductor Optics, Institute of Solid state Physics, University of Bremen (Germany); Kruse, Carsten; Hommel, Detlef, E-mail: Seyfried@ifp.uni-bremen.d [Semiconductor Epitaxy, Institute of Solid state Physics, University of Bremen (Germany)

    2010-02-01

    A customization of the optical properties of pillar microcavities on the desired applications is essential for their future use as quantum-optical devices. Therefore, all-epitaxial cavities with CdSe quantum dot embedded in pillar structures with different geometries have been realized by focused-ion-beam etching. The quality factors of circularly shaped pillar microcavities have been measured and their dependence on the excitation power is discussed. As a possibility to achieve polarized light emission, asymmetrically shaped microcavities are presented. Examples of an elliptically shaped pillar as well as of photonic molecules are investigated with respect to their photoluminescence characteristics and polarization.

  2. Study on the optical properties of CdSe QDs with different ligands in specific matrix

    International Nuclear Information System (INIS)

    Lin Wei; Zou Wei; Du Zhongjie; Li Hangquan; Zhang Chen

    2013-01-01

    Different ligand structures of CdSe quantum dots were designed and synthesized for the specific matrix and the effect of the ligands on the photoluminescence and optical properties were further investigated. Ligand exchange reaction was used to synthesize thioglycolic acid-capped CdSe QDs and the process was characterized by FT-IR and titration. The influence of environmental pH value and storing time on the properties of thioglycolic acid-capped CdSe QDs in aqueous solution were studied by absorption and photoluminescence spectra. It was found that alkaline environment was more beneficial for the application of CdSe QDs. Therefore, the amino ligands with different molecular weight were grafted onto CdSe QDs for improving the compatibility with epoxy matrix and then amino-capped CdSe QDs/epoxy nanocomposites were fabricated. The morphologies and properties of the nanocomposites were characterized by DLS, HR-TEM, UV–Vis spectra, and photoluminescence spectra. As a result, amino ligands with short-molecular chain-capped CdSe QDs/epoxy nanocomposites exhibited good dispersion, high transparency and photoluminescence, and would be suitable for potential application in light-emitting diode device.

  3. Structural, optical and electrical characterization of Ag doped lead chalcogenide (PbSe) thin films

    Energy Technology Data Exchange (ETDEWEB)

    Al-Ghamdi, A.A., E-mail: aghamdi90@hotmail.com [Department of Physics, Faculty of Science, King Abdulaziz University, Jeddah (Saudi Arabia); Al-Heniti, S. [Department of Physics, Faculty of Science, King Abdulaziz University, Jeddah (Saudi Arabia); Khan, Shamshad A. [Department of Physics, St. Andrew' s College, Gorakhpur, UP (India)

    2013-03-15

    Research and development efforts are currently underway to fabricate a variety of solid state devices. A good deal of information regarding the synthesis, structural, optical and electrical properties of Ag doped lead chalcogenides have been revealed. The bulk polycrystalline (PbSe){sub 100-x}Ag{sub x} ternary chalcogenides are prepared by diffusion technique. The XRD patterns recorded for the (PbSe){sub 100-x}Ag{sub x} thin films prepared by vacuum deposition technique, show that these films are polycrystalline in nature. The optical measurements reveal that the (PbSe){sub 100-x}Ag{sub x} thin films possess direct band gap and the band gap energy decreases with an increase of Ag concentration. The extinction coefficient (k) and refractive index (n) are found to be changing by increasing Ag concentration in PbSe. These results are interpreted in terms of the change in concentration of localized states due to the shift in Fermi level. The dc conductivities of (PbSe){sub 100-x}Ag{sub x} thin films are measured in temperature range 303-403 K. It is observed that the dc conductivity increases at all the temperatures with an increase of Ag content in PbSe system. The experimental data suggests that the conduction is due to thermally assisted tunneling of the charge carriers in the localized states near the band edges. The activation energy and optical band gap are found to decrease with increasing Ag concentration in lead chalcogenide and there are good agreements between these two values. - Highlights: Black-Right-Pointing-Pointer (PbSe){sub 100-x}Ag{sub x} thin films has been investigated. Black-Right-Pointing-Pointer Polycrystalline nature has been verified by X-ray diffraction. Black-Right-Pointing-Pointer Optical absorption data showed the rules of direct transitions predominate. Black-Right-Pointing-Pointer Dc conductivity increases with an increase of Ag content in PbSe system. Black-Right-Pointing-Pointer Increase of Ag concentration causes a decrease in E{sub g

  4. Thermoelectric PbTe thin film for superresolution optical data storage

    International Nuclear Information System (INIS)

    Lee, Hyun Seok; Cheong, Byung-ki; Lee, Taek Sung; Lee, Kyeong Seok; Kim, Won Mok; Lee, Jae Won; Cho, Sung Ho; Youl Huh, Joo

    2004-01-01

    To find its practical use in ultrahigh density optical data storage, superresolution (SR) technique needs a material that can render a high SR capability at no cost of durability against repeated readout and write. Thermoelectric materials appear to be promising candidates due to their capability of yielding phase-change-free thermo-optic changes. A feasibility study was carried out with PbTe for its large thermoelectric coefficient and high stability over a wide temperature range as a crystalline single phase. Under exposure to pulsed red light, the material was found to display positive, yet completely reversible changes of optical transmittance regardless of laser power, fulfilling basic requirements for SR readout and write. The material was also shown to have a high endurance against repeated static laser heating of up to 10 6 -10 7 cycles tested. A read only memory disk with a PbTe SR layer led to the carrier to noise ratio value of 47 dB at 3.5 mW for 0.25 μm pit; below the optical resolution limit (∼0.27 μm) of the tester

  5. CdSe/CdTe interface band gaps and band offsets calculated using spin-orbit and self-energy corrections

    Energy Technology Data Exchange (ETDEWEB)

    Ribeiro, M. [Centro de Pesquisas Avancadas Wernher von Braun, Av. Alice de Castro P.N. Mattosinho 301, CEP 13098-392 Campinas, SP (Brazil); Ferreira, L.G. [Departamento de Fisica dos Materiais e Mecanica, Instituto de Fisica, Universidade de Sao Paulo, 05315-970 Sao Paulo, SP (Brazil); Fonseca, L.R.C. [Center for Semiconductor Components, State University of Campinas, R. Pandia Calogeras 90, 13083-870 Campinas, SP (Brazil); Ramprasad, R. [Department of Chemical, Materials and Biomolecular Engineering, Institute of Materials Science, University of Connecticut, 97 North Eagleville Road, Storrs, CT 06269 (United States)

    2012-09-20

    We performed ab initio calculations of the electronic structures of bulk CdSe and CdTe, and their interface band alignments on the CdSe in-plane lattice parameters. For this, we employed the LDA-1/2 self-energy correction scheme to obtain corrected band gaps and band offsets. Our calculations include the spin-orbit effects for the bulk cases, which have shown to be of importance for the equilibrium systems and are possibly degraded in these strained semiconductors. Therefore, the SO showed reduced importance for the band alignment of this particular system. Moreover, the electronic structure calculated along the transition region across the CdSe/CdTe interface shows an interesting non-monotonic variation of the band gap in the range 0.8-1.8 eV, which may enhance the absorption of light for corresponding frequencies at the interface between these two materials in photovoltaic applications.

  6. Ultrafast optical control of the electronic properties of ZrTe5

    Energy Technology Data Exchange (ETDEWEB)

    Crepaldi, Alberto; Cilento, Federico [Elettra-Sincrotrone Trieste (Italy); Manzoni, Giulia; Sterzi, Andrea; Diego, Michele [Universita degli Studi di Trieste (Italy); Kuhn, Timo; Gragnaniello, Luca; Fonin, Mikhail [University of Konstanz (Germany); Autes, Gabriel; Bugnon, Philippe; Magrez, Arnaud; Berger, Helmuth; Yazyev, Oleg; Grioni, Marco [EPFL (Switzerland); Zacchigna, Michele [C.N.R.-I.O.M. (Italy); Parmigiani, Fulvio [Elettra-Sincrotrone Trieste (Italy); Universita degli Studi di Trieste (Italy)

    2016-07-01

    ZrTe5 has recently attracted considerable interest owing to some unique, albeit only partially understood, properties. The electrical resistivity exhibits a peak at a temperature where the nature of the charge carriers changes from holes to electrons. The observed negative magneto-resistance has been attributed to the presence of Dirac particles, either three-dimensional or two-dimensional and spin-polarized. Our time and angle-resolved photoelectron spectroscopy (tr-ARPES) study has addressed the origin of the anomalous transport behavior of ZrTe5, while showing the possibility to control the electronic properties of this material via sub-ps IR laser pulses. These observations open the way to the exploitation of ZrTe5 as a platform for magnetoelectric optical and thermoelectric transport applications. Finally, by combining ab initio calculations, ARPES and scanning tunneling microscopy (STM) we are contributing to shed light on the topological nature of ZrTe5, which is shown to be close to transition between strong and weak topological insulator phases.

  7. Optical and photoelectric properties of nanolamellar structures obtained by thermal annealing of InSe plates in Zn vapours

    Energy Technology Data Exchange (ETDEWEB)

    Untila, Dumitru; Evtodiev, Igor [Faculty of Physics and Engineering, Moldova State University, Chisinau (Moldova, Republic of); Ghitu Institute of Electronic Engineering and Nanotechnologies, Academy of Sciences of Moldova, Chisinau (Moldova, Republic of); Caraman, Iuliana [Engineering Department ' ' Vasile Alecsandri' ' , University of Bacau (Romania); Spalatu, Nicolae [Department of Materials Science, Tallinn University of Technology (Estonia); Dmitroglo, Liliana; Caraman, Mihail [Faculty of Physics and Engineering, Moldova State University, Chisinau (Moldova, Republic of)

    2018-02-15

    The structural, optical and photoelectric properties of InSe crystals grown by Bridgman-Stockbarger method and ZnSe/InSe structures obtained on InSe by thermal annealing in Zn vapours are studied in this paper. The study of structural properties confirms that ZnSe compound is formed. The analysis of photoelectric properties reveal that both the ZnSe-InSe composite layer and the composite/InSe heterojunction are photosensitive in the VIS-NIR spectral region. (copyright 2018 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  8. Core–shell interaction and its impact on the optical absorption of pure and doped core-shell CdSe/ZnSe nanoclusters

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Xinqin; Cui, Yingqi; Zeng, Qun; Yang, Mingli, E-mail: myang@scu.edu.cn [Institute of Atomic and Molecular Physics, Key Laboratory of High Energy Density Physics and Technology of Ministry of Education, Sichuan University, Chengdu 610065 (China); Yu, Shengping [College of Chemistry and Environment Protection Engineering, Southwest University for Nationalities, Chengdu 610041 (China)

    2016-04-07

    The structural, electronic, and optical properties of core-shell nanoclusters, (CdSe){sub x}@(CdSe){sub y} and their Zn-substituted complexes of x = 2–4 and y = 16–28, were studied with density functional theory calculations. The substitution was applied in the cores, the shells, and/or the whole clusters. All these clusters are characterized by their core-shell structures in which the core-shell interaction was found different from those in core or in shell, as reflected by their bondlengths, volumes, and binding energies. Moreover, the core and shell combine together to compose a new cluster with electronic and optical properties different from those of separated individuals, as reflected by their HOMO-LUMO gaps and optical absorptions. With the substitution of Cd by Zn, the structural, electronic, and optical properties of clusters change regularly. The binding energy increases with Zn content, attributed to the strong Zn–Se bonding. For the same core/shell, the structure with a CdSe shell/core has a narrower gap than that with a ZnSe shell/core. The optical absorption spectra also change accordingly with Zn substitution. The peaks blueshift with increasing Zn concentration, accompanying with shape variations in case large number of Cd atoms are substituted. Our calculations reveal the core-shell interaction and its influence on the electronic and optical properties of the core-shell clusters, suggesting a composition–structure–property relationship for the design of core-shell CdSe and ZnSe nanoclusters.

  9. Optical properties of P3HT:tributylphosphine oxide-capped CdSe nanocomposites

    Energy Technology Data Exchange (ETDEWEB)

    Benchaabane, A. [Faculte des Sciences d' Amiens, Laboratoire de Physique de la Matiere Condensee, Amiens (France); Universite Tunis El-Manar, Laboratoire de Materiaux avances et phenomenes quantiques, Faculte des Sciences de Tunis El Manar, Tunis (Tunisia); Universite Arabe des Sciences, Ecole Superieure d' Ingenieurs et des Etudes Technologiques, Tunis (Tunisia); Ben Hamed, Z.; Kouki, F.; Bouchriha, H. [Universite Tunis El-Manar, Laboratoire de Materiaux avances et phenomenes quantiques, Faculte des Sciences de Tunis El Manar, Tunis (Tunisia); Lahmar, A.; Zellama, K.; Zeinert, A. [Faculte des Sciences d' Amiens, Laboratoire de Physique de la Matiere Condensee, Amiens (France); Sanhoury, M.A. [Laboratoire de Chimie Organique Structurale, Synthese et Etudes Physicochimiques, Tunis (Tunisia)

    2016-08-15

    The optical properties of nanocomposite layers prepared by incorporation of tributylphosphine oxide (TBPO)-capped CdSe nanocrystals (NCs) in a P3HT polymer matrix are studied using different nanocrystal concentrations. Reflection spectra analyzed through Kim oscillator model lead to the determination of optical constants such as refractive index n, extinction coefficient k, dielectric permittivity ε and absorption coefficient α. Using the common Cauchy, Drude-Lorentz, Tauc and single-effective-oscillator theoretical models, we have determined the values of static refractive index n{sub s} and permittivity ε{sub s}, plasma frequency ω{sub p}, carrier density N, optical band gap E{sub g} and oscillator and dispersion energies E{sub 0} and E{sub d}, respectively. It is found that TBPO-capped CdSe NCs concentration affects the optoelectronic parameters of the nanocomposite thin films. Moreover, the disorder of this hybrid system is also studied by the determination of Urbach energy, which increases with TBPO-capped CdSe concentration. (orig.)

  10. TE-TM dynamics in a semiconductor laser subject to polarization-rotated optical feedback

    International Nuclear Information System (INIS)

    Heil, T.; Uchida, A.; Davis, P.; Aida, T.

    2003-01-01

    We present a comprehensive experimental characterization of the dynamics of semiconductor lasers subject to polarization-rotated optical feedback. We find oscillatory instabilities appearing for large feedback levels and disappearing at large injection currents, which we classify in contrast to the well-known conventional optical-feedback-induced dynamics. In addition, we compare our experiments to theoretical results of a single-mode model assuming incoherence of the optical feedback, and we identify differences concerning the average power of the laser. Hence, we develop an alternative model accounting for both polarizations, where the emission of the dominant TE mode is injected with delay into the TM mode of the laser. Numerical simulations using this model show good qualitative agreement with our experimental results, correctly reproducing the parameter dependences of the dynamics. Finally, we discuss the application of polarization-rotated-feedback induced instabilities in chaotic carrier communication systems

  11. Structural and optical properties of Ni doped ZnSe nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Yadav, Kanta; Dwivedi, Y.; Jaggi, Neena, E-mail: neena_jaggi@rediffmail.com

    2015-02-15

    In the present work synthesis of ZnSe:Ni nanoparticles using a simple solvothermal method has been discussed. The structural characterizations of as synthesized materials were done by powder X-ray diffraction (XRD), Transmission electron microscope (TEM) and High resolution transmission microscope (HRTEM) imaging techniques, which revealed formation of core–shell nanoparticles with crystallite size 2–4 nm. The structural parameters such as lattice constants, internal strain, dislocation density etc. of ZnSe and Ni doped ZnSe nanocrystals were estimated. Nickel doping in ZnSe host is verified by the Raman spectroscopy. Optical properties were diagnosed by UV–vis absorption and photoluminescence (PL) techniques. The observed blue-shift in UV–vis absorption edge of the prepared sample of ZnSe as compared to its value for the bulk counterpart indicates formation of nanosized particles. PL spectra of Ni{sup 2+} doped samples indicate red-shift and improved emission intensity. - Highlights: • Synthesis of core shell structures of the ZnSe by simple approach. • Enhancement of the photoluminescence emission with the increase in the concentration of Ni a transition metal into the host material. • Increase in the dislocation density and strain with decrease in grain size.

  12. Optical, electrical and the related parameters of amorphous Ge-Bi-Se thin films

    International Nuclear Information System (INIS)

    El-Korashy, A.; El-Kabany, N.; El-Zahed, H.

    2005-01-01

    The related optical and electrical parameters of amorphous Ge-Bi-Se thin films were studied. The dependence of optical and electrical properties on the Bi content was observed in most compositions. At Bi >10at% the behavior show a switch from p to n type conduction mechanism. The correlation between the optical band gap E g and the average heats of atomization H s were observed. The results indicated that both the number of topological constant N con and the radial and angular N α , N β valence force constants exhibit the same trend with increasing Bi content. On the other hand, the mean bond energy increases with increasing Bi content to x=15at%. It may be concluded that is a function of the mean coordination number N co , the type of bonds, the degree of cross-linking and the band energy forming the network

  13. The influence of Ge on optical and thermo- mechanical properties of S-Se chalcogenide glasses

    Science.gov (United States)

    Samudrala, Kavitha; Babu Devarasetty, Suresh

    2018-05-01

    S-Se-Ge glasses were prepared by melt quenching method to investigate the effect of Germanium on thermo-mechanical and optical properties of chalcogenide glasses. The glassy nature of the samples has been verified by x-ray diffraction and DSC studies that the samples are glassy in nature. The optical band gap of the samples was estimated by the absorption spectrum fitting method. The optical band gap increased from 1.61 ev for x = 0 sample to 1.90 ev for x = 40 sample and is explained in terms of cohesive energies. The basic thermo-mechanical parameters such as micro-hardness, Volume (Vh) and formation energy (Eh) of micro voids in the glassy network, as well as the modulus of Elasticity (E) have been calculated for prepared glasses.in present glasses. The variation in these parameters with Ge content correlated with heat of atomization of alloys.

  14. γ - irradiation induced effect on the optical parameters of Cu10 Se90 thin films

    International Nuclear Information System (INIS)

    Abu EL-Fadl, A.; Hafiz, M. M.; Aashour, A.S.; Wakaad, M.M.

    2007-01-01

    The optical constants of Cu 10 SE 90 Chalcogenide films successfully deposited by evaporation coating technique have been measured. The absorption coefficient (a) for the as-deposited or after being γ-irradiation at various doses have been computed in the spectral wavelength range 400-900 nm from the transmittance (T) and reflectance (R) measurements of normally-incident light. Both irradiated and as-prepared films showed direct transition. The direct optical band gaps of the films were found to decrease from 2.017 for as prepared to 1.941 eV for γ-irradiation at 190 kGy doses. The width of the tails of localized states E e were calculated and found to be increasing after γ-irradiation. The effects of the γ-irradiation on the refractive index n and extinction coefficient k were studied. Other optical parameters (ε I , ε 2 were calculated at different γ-irradiation doses the obtained values of both ε 1 and ε 2 were found to be incident light and γ-doses dependent. The effect of γ-irradiation on the high-frequency dielectric constant (ε ∞ ) and carrier concentration (N/m * ) is also studied. The change on the degree of disorder as will as the radiation-induced defect changes applied to explain the radiation effects on nature of optical properties Cu 10 SE 90 glasses

  15. Ultrafast optical manipulation of atomic motion in multilayer Ge-Sb-Te phase change materials

    Directory of Open Access Journals (Sweden)

    Fons P.

    2013-03-01

    Full Text Available Phase change random access memory devices have evolved dramatically with the recent development of superlattice structure of Ge-Sb-Te material (GST-SL in terms of its low power consumption. The phase change in GST-SL is mainly characterized by the displacement of Ge atoms. Here we examine a new phase change method, that is the manipulation of Ge-Te bonds using linearly-polarized femtosecond near-infrared optical pulses. As a result, we found that the p-polarized pump pulse is more effective in inducing the reversible and irreversible displacement of Ge atoms along [111] direction in the local structure. This structural change would be induced by the anisotropic carrier-phonon interaction along the [111] direction created by the p-polarized pulse.

  16. Optical and structural properties of natural MnSeO{sub 4} mineral thin film

    Energy Technology Data Exchange (ETDEWEB)

    Kariper, Ishak Afsin, E-mail: akariper@gmail.com [Erciyes University, Education Faculty, Kayseri (Turkey)

    2017-05-15

    Manganese selenite (MnSeO{sub 4}) crystalline thin film has been produced with chemical bath deposition on substrates (commercial glass). Properties of the thin film, such as transmittance, absorption, and optical band gap and refraction index have been investigated via UV/VIS Spectrum. The structural properties of orthorhombic form have been observed in XRD. The structural and optical properties of MnSeO{sub 4} thin films, deposited at different pH levels were analyzed. Some properties of the films have been changed with the change of pH level, which has been deeply investigated. The grain size of MnSeO{sub 4} thin film has reached its highest value at pH 9. The refraction index and extinction coefficient of MnSeO{sub 4} thin films were measured to be 1.53, 2.86, 2.07, 1.53 (refraction index) and 0.005, 0.029, 0.014, 0.005 (extinction coefficient) for grain sizes 21, 13, 26, and 5 nm respectively. The band gaps (Eg) of the films were measured to be 2.06, 2.57, 2.04, and 2.76 eV for the grain sizes mentioned above. The value of dielectric constant at pH 10 was calculated as 1.575. (author)

  17. Optical properties of single wurtzite/zinc-blende ZnSe nanowires grown at low temperature

    Energy Technology Data Exchange (ETDEWEB)

    Zannier, V. [IOM-CNR Laboratorio TASC, S. S. 14, Km. 163.5, I-34149 Trieste (Italy); Department of Physics, University of Trieste, Via Valerio 2, I-34127 Trieste (Italy); Cremel, T.; Kheng, K. [Univ. Grenoble Alpes, F-38000 Grenoble (France); CEA, INAC-SP2M, « Nanophysique et Semiconducteurs » Group, F-38000 Grenoble (France); Artioli, A.; Ferrand, D. [Univ. Grenoble Alpes, F-38000 Grenoble (France); CNRS, Institut Néel, « Nanophysique et Semiconducteurs » Group, F-38000 Grenoble (France); Grillo, V. [IMEM-CNR, Parco Area delle Scienze 37/A, I-43010 Parma (Italy); S3 NANO-CNR, Via Campi 213/A, I-41125 Modena (Italy); Rubini, S. [IOM-CNR Laboratorio TASC, S. S. 14, Km. 163.5, I-34149 Trieste (Italy)

    2015-09-07

    ZnSe nanowires with a dominant wurtzite structure have been grown at low temperature (300 °C) by molecular beam epitaxy assisted by solid Au nanoparticles. The nanowires emission is polarized perpendicularly to their axis in agreement with the wurtzite selection rules. Alternations of wurtzite and zinc-blende regions have been observed by transmission electron microscopy, and their impact on the nanowires optical properties has been studied by microphotoluminescence. The nanowires show a dominant intense near-band-edge emission as well as the ZnSe wurtzite free exciton line. A type II band alignment between zinc-blende and wurtzite ZnSe is evidenced by time-resolved photoluminescence. From this measurement, we deduce values for the conduction and valence band offsets of 98 and 50 meV, respectively.

  18. Effects of laser irradiation on optical properties of amorphous and annealed Ga15Se81In4 and Ga15Se79In6 chalcogenide thin films

    International Nuclear Information System (INIS)

    Al-Ghamdi, A.A.; Khan, Shamshad A.; Al-Heniti, S.; Al-Agel, F.A.; Al-Harbi, T.; Zulfequar, M.

    2010-01-01

    Amorphous thin films of Ga 15 Se 81 In 4 and Ga 15 Se 79 In 6 glassy alloys with thickness 3000 A were prepared by thermal evaporation onto chemically cleaned glass substrates. The changes in optical properties due to the influence of laser radiation on amorphous and thermally annealed thin films of Ga 15 Se 81 In 4 and Ga 15 Se 79 In 6 were calculated from absorbance and reflectance spectra as a function of photon energy in the wave length region 400-1000 nm. Analysis of the optical absorption data shows that the rule of non-direct transitions predominates. The optical band gaps observed to decrease with the increase of annealing temperatures. Furthermore, exposing thin films to laser irradiation leads to a decrease in optical band gap, absorption coefficient, refractive index and extinction coefficient for both as-prepared and annealed films. The decrease in the optical band gap is explained on the basis of change in nature of films, from amorphous to polycrystalline state, with the increase of annealing temperature and by laser irradiation for 10 min exposure time. Outcomes of our study confirm that this system may be used for photovoltaic devices.

  19. Optical and structural characterization of oleic acid-stabilized CdTe nanocrystals for solution thin film processing

    Directory of Open Access Journals (Sweden)

    Claudio Davet Gutiérrez-Lazos

    2014-06-01

    Full Text Available This work presents results of the optical and structural characterization of oleic acid-stabilized cadmium telluride nanocrystals (CdTe-NC synthesized by an organometallic route. After being cleaned, the CdTe-NC were dispersed in toluene to obtain an ink-like dispersion, which was drop-cast on glass substrate to deposit a thin film. The CdTe-NC colloidal dispersion as well as the CdTe drop-cast thin films were characterized with regard to the optical and structural properties. TEM analysis indicates that the CdTe-NC have a nearly spherical shape (3.5 nm as mean size. Electron diffraction and XRD diffraction analyses indicated the bulk-CdTe face-centered cubic structure for CdTe-NC. An additional diffraction line corresponding to the octahedral Cd3P2 was also detected as a secondary phase, which probably originates by reacting free cadmium ions with trioctylphosphine (the tellurium reducing agent. The Raman spectrum exhibits two broad bands centered at 141.6 and 162.3 cm−1, which could be associated to the TO and LO modes of cubic CdTe nanocrystals, respectively. Additional peaks located in the 222 to 324 cm−1 range, agree fairly well with the wavenumbers reported for TO modes of octahedral Cd3P2.

  20. Origin of localized states in zinc-blende ZnCdSe thin films and the influence on carrier relaxation of self-assembled ZnTe/ZnCdSe quantum dots

    International Nuclear Information System (INIS)

    Lee, Ling; Dai, Yue-Ru; Yang, Chu-Shou; Fan, Wen-Chung; Chou, Wu-Ching

    2015-01-01

    Highlights: • The localized emission in zinc-blende ZnCdSe is induced by excess selenium. • An optimized growth is demonstrated as the VI/II ratio approaches unity. • Size-independent lifetimes are observed in ZnTe/ZnCdSe quantum dots. • Localized electrons in the capping layer dominate size-independent lifetimes. - Abstract: This study discovered the origin of deep level emission in zinc-blende ZnCdSe thin films grown by molecular beam epitaxy, in which a localization behavior was noticed. Pronounced deep level emission observed in films grown under a VI/II ratio of 1.74 (Se-accumulated regime) could be suppressed by a lower VI/II ratio of 1.04 (intermediate regime) and 0.74 (metal-rich regime). Hence the localized states could be correlated to excess selenium accumulated at the growth surface. The localized states also influence the carrier relaxation process of self-assembled ZnTe quantum dots embedded in a ZnCdSe matrix. Once quantum dots surmount the wetting layer, localized electrons in the capping layer dominate the type-II transition and exhibit size-independent lifetimes

  1. About the use of photoacoustic spectroscopy for the optical characterization of semiconductor thin films: CdTe

    International Nuclear Information System (INIS)

    Marin, E.; Calderon, A.; Vigil G, O.; Sastre, J.; Contreras P, G.; Aguilar H, J.; Saucedo, E.; Ruiz, C.M.

    2006-01-01

    CdTe has been used satisfactorily in multiple and diverse technological applications such as detectors of X and gamma rays that operate at room temperature, for digital imagenology of X rays with medical and industrial applications and as active part in CdTe/CdS solar cells. In form of films, CdTe is generally grown with thicknesses ranging between 3 and 15 μm, for which it is difficult to measure, by means of optical techniques, absorption coefficients greater than 10 3 cm -1 because nearly full absorption of light should occur below 800 nm. The exact determination of the optical absorption coefficient in detectors on the basis of CdTe is very important since this parameter determines the absorption length at which 90% of the photons with energies over the forbidden zone of the CdTe will be absorbed by this. In CdS/CdTe polycrystalline solar cells the greater efficiency of conversion have been reported for film thicknesses of 10 mm, however, the optimal value of this parameter depends strongly on the method and the variables of growth. The optical absorption coefficient spectrum can be determined by several methods, often involving several approximations and the knowledge of some minority carrier related electronic parameters that reduce their application in general way. In this work we propose to determine the absorption coefficient in CdTe thin films by photoacoustic spectroscopy (PAS), because this technique allow us to obtain the optical absorption spectra in thicker layers and therefore the study of the influence of the several growth and post-growth processes in the optical properties of this thin films. We measure by PAS the optical-absorption coefficients of CdTe thin films in the spectral region near the fundamental absorption edge ranging from 1.0 to 2.4 eV using an open cell in the transmission configuration. The films were deposited on different substrates by the CSVT-HW (hot wall) technique. In order to study the influence of several growth

  2. About the use of photoacoustic spectroscopy for the optical characterization of semiconductor thin films: CdTe

    Energy Technology Data Exchange (ETDEWEB)

    Marin, E.; Calderon, A. [CICATA-IPN, Av. Legaria 694, 11500 Mexico D.F. (Mexico); Vigil G, O.; Sastre, J.; Contreras P, G.; Aguilar H, J. [ESFM-IPN, 07738 Mexico D.F. (Mexico); Saucedo, E.; Ruiz, C.M. [Departamento de Fisica de Materiales, Facultad de Ciencias, Universidad Autonoma de Madrid, 28049 Madrid (Spain)

    2006-07-01

    CdTe has been used satisfactorily in multiple and diverse technological applications such as detectors of X and gamma rays that operate at room temperature, for digital imagenology of X rays with medical and industrial applications and as active part in CdTe/CdS solar cells. In form of films, CdTe is generally grown with thicknesses ranging between 3 and 15 {mu}m, for which it is difficult to measure, by means of optical techniques, absorption coefficients greater than 10{sup 3} cm{sup -1} because nearly full absorption of light should occur below 800 nm. The exact determination of the optical absorption coefficient in detectors on the basis of CdTe is very important since this parameter determines the absorption length at which 90% of the photons with energies over the forbidden zone of the CdTe will be absorbed by this. In CdS/CdTe polycrystalline solar cells the greater efficiency of conversion have been reported for film thicknesses of 10 mm, however, the optimal value of this parameter depends strongly on the method and the variables of growth. The optical absorption coefficient spectrum can be determined by several methods, often involving several approximations and the knowledge of some minority carrier related electronic parameters that reduce their application in general way. In this work we propose to determine the absorption coefficient in CdTe thin films by photoacoustic spectroscopy (PAS), because this technique allow us to obtain the optical absorption spectra in thicker layers and therefore the study of the influence of the several growth and post-growth processes in the optical properties of this thin films. We measure by PAS the optical-absorption coefficients of CdTe thin films in the spectral region near the fundamental absorption edge ranging from 1.0 to 2.4 eV using an open cell in the transmission configuration. The films were deposited on different substrates by the CSVT-HW (hot wall) technique. In order to study the influence of several

  3. Electronic structure and optical properties of defect chalcopyrite HgGa2Se4

    Science.gov (United States)

    Gabrelian, B. V.; Lavrentyev, A. A.; Vu, Tuan V.; Parasyuk, O. V.; Khyzhun, O. Y.

    2018-01-01

    We report on studies from an experimental and theoretical viewpoint of the electronic structure of mercury digallium selenide, HgGa2Se4, a very promising optoelectronic material. In particular, the method of X-ray photoelectron spectroscopy (XPS) was used to evaluate binding energies of the constituent element core electrons and the shape of the valence band for pristine and Ar+-ion bombarded surfaces of HgGa2Se4 single crystal. First principles band-structure calculations were performed in the present work using the augmented plane wave + local orbitals (APW+lo). These calculations indicate that the Se 4p states are the main contributors at the top and in the upper portion of the valence band with slightly smaller contributions of the Ga 4p states in the upper portion of the band as well. Further, the central portion of the valence band is determined mainly by contributions of the Ga 4s states, and the Hg 5d states are the principal contributors to the bottom of the valence band. These theoretical data are in fair agreement when matching on a common energy scale of the X-ray emission bands giving information on the energy distribution of the Se 4p and Ga 4p states and the XPS valence-band spectrum of the HgGa2Se4 crystal. The principal optical constants are elucidated from the DFT calculations.

  4. The influence of capping thioalkyl acid on the growth and photoluminescence efficiency of CdTe and CdSe quantum dots

    International Nuclear Information System (INIS)

    Aldeek, Fadi; Lambert, Jacques; Balan, Lavinia; Schneider, Raphael

    2008-01-01

    The influence of thioalkyl acid ligand was evaluated during aqueous synthesis at 100 deg. C and under hydrothermal conditions (150 deg. C) of CdTe and CdSe quantum dots (QDs). Experiments performed with 3-mercaptopropionic acid (MPA), 6-mercaptohexanoic acid (MHA) and 11-mercaptoundecanoic acid (MUA) demonstrated that the use of MHA and MUA allowed for the preparation of very small nanoparticles (0.6-2.5 nm) in carrying out the reaction under atmospheric pressure or in an autoclave and that the photophysical properties of QDs were dependent on the ligand and on the synthesis conditions. The influence of various experimental conditions, including the Te-to-Cd ratio, temperature, and precursor concentration, on the growth rate of CdTe or CdSe QDs has been systematically investigated. The fluorescence intensities of CdTe QDs capped with MPA, MHA, or MUA versus pH were also found to be related to the surface coverage of the nanoparticles.

  5. Size-selective precipitation in colloidal semiconductor nanocrystals of CdTe and CdSe: a study by UV-VIS spectroscopy; Precipitacao seletiva de tamanhos em nanoparticulas semicondutoras coloidais de CdTe e CdSe: um estudo por espectroscopia UV-VIS

    Energy Technology Data Exchange (ETDEWEB)

    Viol, Livia Cristina de Souza; Silva, Fernanda Oliveira; Ferreira, Diego Lourenconi; Alves, Jose Luiz Aarestrup; Schiavon, Marco Antonio, E-mail: schiavon@ufsj.edu.b [Universidade Federal de Sao Joao del Rei, MG (Brazil). Dept. de Ciencias Naturais

    2011-07-01

    The post-preparative size-selective precipitation technique was applied in CdTe and CdSe semiconductor nanocrystals prepared via colloidal route in water. The synthesis of CdTe and CdSe nanoparticles and the effect of the post-preparative size-selective precipitation have been characterized mainly by mean of ultraviolet and visible absorption spectroscopy (UV-Vis). It was demonstrated that the size-selective precipitation are able to isolate particles of different sizes and purify the nanoparticles as well. (author)

  6. Resonant optical alignment and orientation of Mn2+ spins in CdMnTe crystals

    Science.gov (United States)

    Baryshnikov, K. A.; Langer, L.; Akimov, I. A.; Korenev, V. L.; Kusrayev, Yu. G.; Averkiev, N. S.; Yakovlev, D. R.; Bayer, M.

    2015-11-01

    We report on spin orientation and alignment of Mn2 + ions in (Cd,Mn)Te diluted magnetic semiconductor crystals using resonant intracenter excitation with circular- and linear-polarized light. The resulting polarized emission of the magnetic ions is observed at low temperatures when the spin relaxation time of the Mn2 + ions is in the order of 1 ms , which considerably exceeds the photoluminescence decay time of 23 μ s . We demonstrate that the experimental data on optical orientation and alignment of Mn2 + ions can be explained using a phenomenological model that is based on the approximation of isolated centers.

  7. Development of a computer model for polycrystalline thin-film CuInSe sub 2 and CdTe solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Gray, J.L.; Schwartz, R.J.; Lee, Y.J. (Purdue Univ., Lafayette, IN (United States))

    1992-09-01

    This report describes work to develop an accurate numerical model for CuInSe{sub 2} (CIS) and CdTe-based solar cells capable of running on a personal computer. Such a model will aid researchers in designing and analyzing CIS- and CdTe-based solar cells. ADEPT (A Device Emulation Pregrain and Tool) was used as the basis for this model. An additional objective of this research was to use the models developed to analyze the performance of existing and proposed CIS- and CdTe-based solar cells. The development of accurate numerical models for CIS- and CdTe-based solar cells required the compilation of cell performance data (for use in model verification) and the compilation of measurements of material parameters. The development of the numerical models involved implementing the various physical models appropriate to CIS and CdTe, as well as some common window. A version of the model capable of running on an IBM-comparable personal computer was developed (primary code development is on a SUN workstation). A user-friendly interface with pop-up menus is continuing to be developed for release with the IBM-compatible model.

  8. Terahertz conductivity measurement of FeSe0.5Te0.5 and Co-doped BaFe2As2 thin films

    International Nuclear Information System (INIS)

    Nakamura, D.; Akiike, T.; Takahashi, H.; Nabeshima, F.; Imai, Y.; Maeda, A.; Katase, T.; Hiramatsu, H.; Hosono, H.; Komiya, S.; Tsukada, I.

    2011-01-01

    We investigated the THz conductivity of FeSe 0.5 Te 0.5 and Ba (Fe 2-x Co x )As 2 thin films. We estimated the superconducting gap energy values. We found anomolous conductivity spectrum in the antiferromagnetic phase. The terahertz (THz) conductivity of FeSe 0.5 Te 0.5 ('11'-type) and Co-doped BaFe 2 As 2 ('122'-type) thin films are investigated. For '11'-type, the frequency dependence of the complex conductivity can be understood as that of BCS-type superconductor near the superconducting gap energy, and we estimated the superconducting gap energy to be 0.6 meV. For '122'-type, we estimated the superconducting gap energy to be 2.8 meV, which is considered to be the superconducting gap opened at the electron-type Fermi surface near the M point.

  9. Influence of Ga-doping on the thermoelectric properties of Bi(2−xGaxTe2.7Se0.3 alloy

    Directory of Open Access Journals (Sweden)

    Xingkai Duan

    2015-02-01

    Full Text Available Bi(2−xGaxTe2.7Se0.3 (x=0, 0.04, 0.08, 0.12 alloys were fabricated by vacuum melting and hot pressing technique. The structure of the samples was evaluated by means of X-ray diffraction. The peak shift toward higher angle can be observed by Ga-doping. The effects of Ga substitution for Bi on the electrical and thermal transport properties were investigated in the temperature range of 300–500 K. The power factor values of the Ga-doped samples are obviously improved in the temperature range of 300–440 K. Among all the samples, the Bi(2−xGaxTe2.7Se0.3 (x=0.04 sample showed the lowest thermal conductivity near room temperature and the maximum ZT value reached 0.82 at 400 K.

  10. Strong 3D and 1D magnetism in hexagonal Fe-chalcogenides FeS and FeSe vs. weak magnetism in hexagonal FeTe

    Energy Technology Data Exchange (ETDEWEB)

    Parker, David S. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

    2017-06-13

    We present a comparative theoretical study of the hexagonal forms of the Fe-chalcogenides FeS, FeSe and FeTe with their better known tetragonal forms. While the tetragonal forms exhibit only an incipient antiferromagnetism and experimentally show superconductivity when doped, the hexagonal forms of FeS and FeSe display a robust magnetism. We show that this strong magnetism arises from a van Hove singularity associated with the direct Fe-Fe c-axis chains in the generally more three-dimensional NiAs structure. We also find that hexagonal FeTe is much less magnetic than the other two hexagonal materials, so that unconventional magnetically-mediated superconductivity is possible, although a large Tc value is unlikely.

  11. Strong 3D and 1D magnetism in hexagonal Fe-chalcogenides FeS and FeSe vs. weak magnetism in hexagonal FeTe.

    Science.gov (United States)

    Parker, David S

    2017-06-13

    We present a comparative theoretical study of the hexagonal forms of the Fe-chalcogenides FeS, FeSe and FeTe with their better known tetragonal forms. While the tetragonal forms exhibit only an incipient antiferromagnetism and experimentally show superconductivity when doped, the hexagonal forms of FeS and FeSe display a robust magnetism. We show that this strong magnetism arises from a van Hove singularity associated with the direct Fe-Fe c-axis chains in the generally more three-dimensional NiAs structure. We also find that hexagonal FeTe is much less magnetic than the other two hexagonal materials, so that unconventional magnetically-mediated superconductivity is possible, although a large T c value is unlikely.

  12. Kinetics of crystal growth in amorphous solid and supercooled liquid TeSe20 using DTA and d.c. conductivity measurements

    International Nuclear Information System (INIS)

    Kotkata, M.F.; Mahmoud, E.A.; El-Mously, M.K.

    1979-07-01

    Curves of reaction rate versus temperature for constant heating rates (phi=1-10 0 C/min) constructed by analytical methods have been used to demonstrate the crystallization kinetics of amorphous solid TeSe 20 . The devitrification process takes place with predominance of random nucleation and one-dimensional growth, and is limited by combined switching and splitting of the chemical bonds. The mean value for the activation energy of the amorphous-crystal transformation, average E, is found to be 64 Kcal/mole. While, the quantity E calculated on the basis of d.c. conductivity changes during different isothermal crystallization (120-175 0 C) in supercooled liquid TeSe 20 , amounts to 11.5 Kcal/mole and suggests the existence of mixed chains in the liquid alloys. (author)

  13. Compositions of Mg and Se, surface morphology, roughness and Raman property of Zn1-xMgxSeyTe1-y layers grown at various substrate temperatures or dopant transport rates by MOVPE

    Science.gov (United States)

    Nishio, Mitsuhiro; Saito, Katsuhiko; Urata, Kensuke; Okamoto, Yasuhiro; Tanaka, Daichi; Araki, Yasuhiro; Abiru, Masakatsu; Mori, Eiichiro; Tanaka, Tooru; Guo, Qixin

    2015-03-01

    The growth of undoped and phosphorus (P)-doped Zn1-xMgxSeyTe1-y layers on (100) ZnTe substrates by metalorganic vapor phase epitaxy was carried out. The compositions of Mg and Se, surface morphology, roughness and Raman property were characterized as a function of substrate temperature. Not only the compositions of Mg and Se but also the crystal quality of undoped Zn1-xMgxSeyTe1-y layer strongly depended upon the substrate temperature. Furthermore, the growth of Zn1-xMgxSeyTe1-y layer nearly-lattice-matched to ZnTe substrate was achieved independent of the transport rate of trisdimethylaminophosphorus. Undoped Zn1-xMgxSeyTe1-y layer nearly-lattice-matched to ZnTe led to improvement of surface roughness. On the other hand, P doping brought about deterioration of crystalline quality.

  14. Changes in the shapes of self-organized PbSe quantum dots during PbEuTe overgrowth investigated by anomalous X-ray diffraction

    International Nuclear Information System (INIS)

    Holy, V.; Schuelli, T.U.; Lechner, R.T.; Springholz, G.; Bauer, G.

    2006-01-01

    Anomalous X-ray diffraction was used for the investigation of shape and chemical composition of self-organized PbSe quantum dots covered by PbEuTe capping layers. From reciprocal-space maps of diffracted intensities measured at two energies of the primary radiation, we discriminated the contributions of the dot volumes and the surrounding crystal lattice to the diffracted intensity. We have found that the presence of Eu atoms suppresses the flattening of the dots during their overgrowth

  15. Studies of scintillation light nonproportionality of ZnSe(Te), CsI(Tl) and YAP(Ce) crystals using heavy ions

    CERN Document Server

    Klamra, W; Kapusta, M; Kérek, A; Moszynski, M; Norlin, L O; Novák, D; Possnert, G

    2002-01-01

    The scintillation light yield for ZnSe(Te), CsI(Tl) and YAP(Ce) crystals have been studied with alpha particles, sup 1 sup 2 C and sup 8 sup 1 Br in the energy region 2.8-42.2 MeV. A nonproportional behavior was observed, mostly pronounced for alpha particles on YAP(Ce). The results are understood in terms of delta-rays effect.

  16. Study of the optical properties of TeO2-PbO-TiO2 glass system

    Directory of Open Access Journals (Sweden)

    Raul F. Cuevas

    1998-06-01

    Full Text Available We describe the preparation and some optical properties of high refractive index TeO2-PbO-TiO2 glass system. Highly homogeneous glasses were obtained by agitating the mixture during the melting process in an alumina crucible. The characterization was done by X-ray diffraction, Raman scattering, light absorption and linear refractive index measurements. The results show a change in the glass structure as the PbO content increases: the TeO4 trigonal bipyramids characteristics of TeO2 glasses transform into TeO3 trigonal pyramids. However, the measured refractive indices are almost independent of the glass composition. We show that third-order nonlinear optical susceptibilities calculated from the measured refractive indices using Lines' theoretical model are also independent of the glass composition.

  17. Electrical conduction studies of hot wall deposited CdSe{sub x}Te{sub 1-x} thin films

    Energy Technology Data Exchange (ETDEWEB)

    Muthukumarasamy, N. [Department of Physics, Coimbatore Institute of Technology, Coimbatore 641014 (India); Balasundaraprabhu, R.; Jayakumar, S.; Kannan, M.D. [Department of Physics, PSG College of Technology, Coimbatore (India)

    2008-08-15

    CdSe{sub x}Te{sub 1-x} thin films of different compositions have been deposited on cleaned glass substrates using the hot wall deposition technique under conditions very close to thermodynamical equilibrium with minimum loss of material. The electrical conductivity of the deposited films has been studied as a function of temperature. All the films showed a transition from phonon-assisted hopping conduction through the impurity band to grain-boundary-limited conduction in the conduction/valence band at temperature around 325 K. The conductivity has been found to vary with composition; it varied from 0.0027 to 0.0198 {omega}{sup -1} cm{sup -1} when x changed from 0 to 1. The activation energies of the films of different compositions determined at 225 and 400 K have been observed to lie in the range 0.0031-0.0098 and 0.0285-0.0750 eV, respectively. The Hall-effect studies carried out on the deposited films revealed that the nature of conductivity (p or n-type) was dependent on film composition; films with composition x=0 and 0.15 have been found to be p-type and the ones with composition x=0.4, 0.6, 0.7, 0.85 and 1 have been observed to exhibit n-type conductivity. The carrier concentration has been determined and is of the order of 10{sup 17} cm{sup -3}. The majority of carrier mobilities of the films have been observed to vary from 0.032 to 0.183 cm{sup 2} V{sup -1} s{sup -1} depending on film composition. The study of the mobility of the charge carriers with temperature in the range of 300-450 K showed that the mobility increased with 3/2 power of temperature indicating that the type of scattering mechanism in the studied temperature range is the ionized impurity scattering mechanism. (author)

  18. Influence of substrate type on transport properties of superconducting FeSe0.5Te0.5 thin films

    International Nuclear Information System (INIS)

    Yuan, Feifei; Shi, Zhixiang; Iida, Kazumasa; Langer, Marco; Hänisch, Jens; Hühne, Ruben; Schultz, Ludwig; Ichinose, Ataru; Tsukada, Ichiro; Sala, Alberto; Putti, Marina

    2015-01-01

    FeSe 0.5 Te 0.5 thin films were grown by pulsed laser deposition on CaF 2 , LaAlO 3 and MgO substrates and structurally and electro-magnetically characterized in order to study the influence of the substrate on their transport properties. The in-plane lattice mismatch between FeSe 0.5 Te 0.5 bulk and the substrate shows no influence on the lattice parameters of the films, whereas the type of substrate affects the crystalline quality of the films and, therefore, the superconducting properties. The film on MgO showed an extra peak in the angular dependence of critical current density J c (θ) at θ = 180° (H||c), which arises from c-axis defects as confirmed by transmission electron microscopy. In contrast, no J c (θ) peaks for H||c were observed in films on CaF 2 and LaAlO 3 . J c (θ) can be scaled successfully for both films without c-axis correlated defects by the anisotropic Ginzburg–Landau approach with appropriate anisotropy ratio γ J . The scaling parameter γ J is decreasing with decreasing temperature, which is different from what we observed in FeSe 0.5 Te 0.5 films on Fe-buffered MgO substrates. (paper)

  19. Effect of O- and Mn-doping on superconductivity in FeTe{sub 0.5}Se{sub 0.5} superconductor

    Energy Technology Data Exchange (ETDEWEB)

    Thakur, Gohil S.; Haque, Zeba; Ganguli, Ashok K. [Department of Chemistry, Indian Institute of Technology, New Delhi (India); Neha, Prakriti; Patnaik, Satyabrata [School of Physical Science, Jawaharlal Nehru University, New Delhi (India); Gupta, Laxmi C. [Department of Chemistry, Indian Institute of Technology, New Delhi (India); Visiting project scientist at the:Solid State and Nanomaterials Research Laboratory, Department of Chemistry, IIT Delhi (India)

    2014-05-15

    The effect of oxygen substitution at the selenium site and manganese substitution at the iron site in FeTe{sub 0.5}Se{sub 0.5} superconductor was investigated. It was found that upon partial O substitution, T{sub c} marginally decreases as seen in both resistivity and magnetization experiments. T{sub c} decreases even by a small amount of oxygen concentration (as low as 1 %). This observation is in contrast against an earlier work on Fe(Te/Se) samples,1 wherein T{sub c} as well as superconducting volume fraction were reported to increase in the samples annealed in air. Mn-doping leads to a decrease in T{sub c} in FeTe{sub 0.5}Se{sub 0.5}, which one would expect considering pair-breaking due to Mn{sup 2+}-ions. (Copyright copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  20. Luminescence of polyethylene glycol coated CdSeTe/ZnS and InP/ZnS nanoparticles in the presence of copper cations.

    Science.gov (United States)

    Beaune, Grégory; Tamang, Sudarsan; Bernardin, Aude; Bayle-Guillemaud, Pascale; Fenel, Daphna; Schoehn, Guy; Vinet, Françoise; Reiss, Peter; Texier, Isabelle

    2011-08-22

    The use of click chemistry for quantum dot (QD) functionalization could be very promising for the development of bioconjugates dedicated to in vivo applications. Alkyne-azide ligation usually requires copper(I) catalysis. The luminescence response of CdSeTe/ZnS nanoparticles coated with polyethylene glycol (PEG) is studied in the presence of copper cations, and compared to that of InP/ZnS QDs coated with mercaptoundecanoic acid (MUA). The quenching mechanisms appear different. Luminescence quenching occurs without any wavelength shift in the absorption and emission spectra for the CdSeTe/ZnS/PEG nanocrystals. In this case, the presence of copper in the ZnS shell is evidenced by energy-filtered transmission electron microscopy (EF-TEM). By contrast, in the case of InP/ZnS/MUA nanocrystals, a redshift of the excitation and emission spectra, accompanied by an increase in absorbance and a decrease in photoluminescence, is observed. For CdSeTe/ZnS/PEG nanocrystals, PL quenching is enhanced for QDs with 1) smaller inorganic-core diameter, 2) thinner PEG shell, and 3) hydroxyl terminal groups. Whereas copper-induced PL quenching can be interesting for the design of sensitive cation sensors, copper-free click reactions should be used for the efficient functionalization of nanocrystals dedicated to bioapplications, in order to achieve highly luminescent QD bioconjugates. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Ab-initio calculations of Co-based diluted magnetic semiconductors Cd 1-xCoxX (X=S, Se, Te)

    KAUST Repository

    Saeed, Yasir

    2010-10-01

    Ab-initio calculations are performed to investigate the structural, electronic and magnetic properties of spin-polarized diluted magnetic semiconductors composed of IIVI compounds Cd1-xCoxX (X=S, Se, Te) at x=0.25. From the calculated results of band structure and density of states, the half-metallic character and stability of ferromagnetic state for Cd1-xCoxS, Cd1-xCoxSe and Cd 1-xCoxTe alloys are determined. It is found that the tetrahedral crystal field gives rise to triple degeneracy t2g and double degeneracy eg. Furthermore, we predict the values of spin-exchange splitting energies Δx(d) and Δ x(p-d) and exchange constants N0α and N 0β produced by the Co 3d states. Calculated total magnetic moments and the robustness of half-metallicity of Cd1-xCo xX (X=S, Se, Te) with respect to the variation in lattice parameters are also discussed. We also extend our calculations to x=0.50, 0.75 for S compounds in order to observe the change due to increase in Co. © 2010 Elsevier B.V.

  2. Observation of an electron band above the Fermi level in FeTe0.55Se0.45 from in-situ surface doping

    International Nuclear Information System (INIS)

    Zhang, P.; Ma, J.; Qian, T.; Richard, P.; Ding, H.; Xu, N.; Xu, Y.-M.; Fedorov, A. V.; Denlinger, J. D.; Gu, G. D.

    2014-01-01

    We used in-situ potassium (K) evaporation to dope the surface of the iron-based superconductor FeTe 0.55 Se 0.45 . The systematic study of the bands near the Fermi level confirms that electrons are doped into the system, allowing us to tune the Fermi level of this material and to access otherwise unoccupied electronic states. In particular, we observe an electron band located above the Fermi level before doping that shares similarities with a small three-dimensional pocket observed in the cousin, heavily electron-doped KFe 2−x Se 2 compound.

  3. Investigation of fundamental physical properties of CdSiP{sub 2} and its application in solar cell devices by using (ZnX; X = Se, Te) buffer layers

    Energy Technology Data Exchange (ETDEWEB)

    Verma, A.S., E-mail: ajay_phy@rediffmail.com [Department of Physics, Banasthali Vidyapith, Rajasthan 304022 (India); Gautam, Ruchita; Singh, Pravesh [Department of Physics, Banasthali Vidyapith, Rajasthan 304022 (India); Department of Electronics and Communication, Krishna Institute of Engineering and Technology, Ghaziabad, Uttar Pradesh 201206 (India); Sharma, Sheetal [Department of Physics, Swami Premanand Mahavidyalaya, Mukerian, Punjab 144211 (India); Kumari, Sarita [Department of Physics, University of Rajasthan, Jaipur 302004 (India)

    2016-03-15

    Graphical abstract: - Highlights: • FP-LAPW method has been used to compute the solid state properties of CdSiP{sub 2}. • Electronic and optical properties reported by WIEN2K with recently developed mBJ potential. • The elastic and thermal properties were evaluated by first principles calculations. • Hardness was calculated for the first time at different temperature and pressure. • Solar cell devices with ZnSe/ZnTe buffer layers by simulated work. - Abstract: The first principles calculations were performed by the linearized augmented plane wave (LAPW) method as implemented in the WIEN2K code within the density functional theory to obtain the structural, electronic and optical properties of CdSiP{sub 2} in the body centered tetragonal (BCT) phase. The six elastic constants (C{sub 11}, C{sub 12}, C{sub 13}, C{sub 33}, C{sub 44} and C{sub 66}) and mechanical parameters were presented and compared with the available experimental data. The thermodynamic calculations within the quasi-harmonic approximation is used to give an accurate description of the pressure-temperature dependence of the thermal-expansion coefficient, bulk modulus, specific heat, Debye temperature, entropy Grüneisen parameters and hardness. Further, CdSiP{sub 2} solar cell devices have been modeled; device physics and performance parameters are analyzed for zinc chalcogenide (ZnX; X = Se, Te) buffer layers. Simulation results for CdSiP{sub 2} thin layer solar cell show the maximum efficiency (25.7%) with ZnSe as the buffer layer.

  4. Laser operated optical features in β-BaTeMo2O9:Cr3+ nanocrystallites

    International Nuclear Information System (INIS)

    Majchrowski, A.; Jaroszewicz, L.R.; Fedorchuk, A.O.; Kityk, I.V.

    2015-01-01

    An increase of second order nonlinear optical efficiency was established for Cr 3+ doped β-BaTeMo 2 O 9 (BTMO) nanocrystallites (with sizes varying within up to 150 nm range) under influence of two coherent beams of 532 nm nanosecond pulsed lasers at power densities up to 600 MW/cm 2 . It was found that maximal enhancement of optical second harmonic generation was achieved for BTMO:Cr 3+ nanocrystallites possessing sizes about 60–80 nm. Occurrence of some quasi-periodic space radial grating was observed as well. This is a consequence of competition between the photo-polarization and photo-thermal effects. Band structure simulations within a framework of the norm-conserving pseudopotential were performed. - Highlights: • BMTO nanocrystallites with the sizes 60 nm–120 nm were synthesized. • Photoinduced SHG is found. • The effect is caused by additional photopolarization

  5. Characterization of CdSe-nanocrystals used in semiconductors for aerospace applications: Production and optical properties

    Directory of Open Access Journals (Sweden)

    Maroof A. Hegazy

    2014-06-01

    Full Text Available Semiconductor nanocrystals (NC’s are the materials with dimensions less than 10 nm. When the dimensions of nanocrystals are reduced the bulk bohr diameter, the photo generated electron-hole pair becomes confined and nanocrystal exhibits size dependent upon optical properties. This work is focused on the studying of CdSe semiconductor nanocrystals. These nanocrystals are considered as one of the most widely studies semiconductors because of their size – tunable optical properties from the visible spectrum. CdSe-nanocrystals are produced and obtained throughout the experimental setup initiated at Nano-NRIAG Unit (NNU, which has been constructed and assembled at NRIAG institute. This unit has a specific characterization for preparing chemical compositions, which may be used for solar cell fabrications and space science technology. The materials prepared included cadmium oxide and selinid have sizes ranging between 2.27 nm and 3.75 nm. CdSe-nanocrystals are synthesized in “TOP/TOPO (tri–octyl phosphine/tri–octyl phosphine oxide. Diagnostic tools, include UV analysis, TEM microscope, and X-ray diffraction, which are considered for the analytical studies of the obtained materials. The results show that, in this size regime, the generated particles have unique optical properties, which is achieved from the UV analysis. Also, the TEM image analysis shows the size and shape of the produced particles. These studies are carried out to optimize the photoluminescent efficiency of these nanoparticles. Moreover, the data revealed that, the grain size of nanocrystals is dependent upon the growth time in turn, it leads to a change in the energy gap. Some applications of this class of materials are outlined.

  6. Optical properties of CuCdTeO thin films sputtered from CdTe-CuO composite targets

    Energy Technology Data Exchange (ETDEWEB)

    Mendoza-Galván, A., E-mail: amendoza@qro.cinvestav.mx [Cinvestav-IPN, Unidad Querétaro, Libramiento Norponiente 2000, 76230 Querétaro (Mexico); Laboratory of Applied Optics, Department of Physics, Chemistry and Biology, Linköping University, SE-581 83 Linköping (Sweden); Arreola-Jardón, G. [Cinvestav-IPN, Unidad Querétaro, Libramiento Norponiente 2000, 76230 Querétaro (Mexico); Karlsson, L.H.; Persson, P.O.Å. [Thin Film Physics Division, Department of Physics, Chemistry and Biology, Linköping University, SE-581 83 Linköping (Sweden); Jiménez-Sandoval, S. [Cinvestav-IPN, Unidad Querétaro, Libramiento Norponiente 2000, 76230 Querétaro (Mexico)

    2014-11-28

    The effective complex dielectric function (ε) of Cu and O containing CdTe thin films is reported in the spectral range of 0.05 to 6 eV. The films were fabricated by rf sputtering from targets comprised by a mixture of CdTe and CuO powders with nominal Cu and O concentrations in the range of 2–10 at.%. Low concentration levels improved the crystalline quality of the films. Spectroscopic ellipsometry and transmittance measurements were used to determine ε. The critical point energies E{sub 1}, E{sub 1} + Δ{sub 1}, and E{sub 2} of CdTe are red-shifted with the incorporation of Cu and O. Also, an absorption band is developed in the infrared range which is associated with a mixture of CdTe and low resistivity phases Cu{sub 2−x}Te according to an effective medium analysis. The elemental distribution of the films was mapped by energy dispersive X-ray spectroscopy using scanning transmission electron microscopy. - Highlights: • Incorporation of 2 to 10 at.% of Cu and O atoms in CdTe films • Improved crystalline quality with 2 and 3 at.% of Cu and O • Complex dielectric function of Cu and O containing CdTe thin films • Effective medium modeling of below band-gap absorption.

  7. Structural, optical and electrical properties of cadmium-doped lead chalcogenide (PbSe) thin films

    International Nuclear Information System (INIS)

    Khan, Shamshad A.; Khan, Zishan H.; El-Sebaii, A.A.; Al-Marzouki, F.M.; Al-Ghamdi, A.A.

    2010-01-01

    (PbSe) 100-x Cd x thin films of thickness 3000 A with variable concentrations of Cd (x=5, 10, 15 and 20) were prepared by thermal evaporation on glass substrates at room temperature at a base pressure of 10 -6 Torr. The structural, optical and electrical properties of these films were studied. X-ray diffraction patterns were used to determine the crystal structure of the films. Films were of polycrystalline texture over the whole range of study. Optical constants of all films were determined by absorbance and reflection measurements in a wavelength range 400-1200 nm. Analysis of the optical absorption data showed that the rule of direct transitions predominates. The values of the absorption coefficient (α), extinction coefficient (k) and imaginary part of the dielectric constant were found to increase with increasing Cd content in lead chalcogenides while the refractive index (n) and real part of dielectric constant were increased with increasing Cd concentration up to 15% and then they decreased with 20% of Cd content in PbSe. These results were interpreted in terms of the change in concentration of localized states due to the shift in Fermi level. The dc conductivities and activation energies of the films were measured in the temperature range 298-398 K. It was observed that the dc conductivity increases at all temperatures with the increase of Cd content in lead chalcogenide system. The experimental data suggests that the conduction is due to the thermally assisted tunneling of the carriers in the localized states near the band edges. The activation energy and optical band gap were found to decrease with increasing Cd concentration in lead chalcogenide.

  8. Structural, electronic, linear, and nonlinear optical properties of ZnCdTe{sub 2} chalcopyrite

    Energy Technology Data Exchange (ETDEWEB)

    Ouahrani, Tarik [Laboratoire de Physique Theorique, Universite de Tlemcen, B.P. 230, Tlemcen 13000 (Algeria); Reshak, Ali H. [Institute of Physical Biology, South Bohemia University, Nove Hrady 37333 (Czech Republic); School of Microelectronic Engineering, University of Malaysia Perlis (UniMAP), Block A, Kompleks Pusat Pengajian, 02600 Arau Jejawi, Perlis (Malaysia); Khenata, R. [Laboratoire de Physique Quantique et de Modelisation Mathematique, Universite de Mascara, Mascara 29000 (Algeria); Department of Physics and Astronomy, Faculty of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia); Baltache, H.; Amrani, B. [Laboratoire de Physique Quantique et de Modelisation Mathematique, Universite de Mascara, Mascara 29000 (Algeria); Bouhemadou, A. [Department of Physics and Astronomy, Faculty of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia); Faculty of Sciences, Department of Physics, University of Setif, Setif 19000 (Algeria)

    2011-03-15

    We report results of first-principles density functional calculations using the full-potential linearized augmented plane wave method. The generalized gradient approximation (GGA) and the Engel-Vosko-GGA (EV-GGA) formalism were used for the exchange-correlation energy to calculate the structural, electronic, linear, and nonlinear optical properties of the chalcopyrite ZnCdTe{sub 2} compound. The valence band maximum and the conduction band minimum are located at the {gamma}-point, resulting in a direct band gap of about 0.71 eV for GGA and 1.29 eV for EV-GGA. The results of bulk properties, such as lattice parameters (a, c, and u), bulk modulus B, and its pressure derivative B' are evaluated. The optical properties of this compound, namely the real and the imaginary parts of the dielectric function, reflectivity, and refractive index, show a considerable anisotropy as a consequence ZnCdTe{sub 2} posseses a strong birefringence. In addition, the extinction coefficient, the electron energy loss function, and the nonlinear susceptibility are calculated and their spectra are analyzed. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  9. Facile synthesis of red- to near-infrared-emitting CdTe{sub x}Se{sub 1-x} alloyed quantum dots via a noninjection one-pot route

    Energy Technology Data Exchange (ETDEWEB)

    Liao Lifang; Zhang Hua [Key Laboratory for Advanced Materials, Department of Chemistry, East China University of Science and Technology, Shanghai 200237 (China); Zhong Xinhua, E-mail: zhongxh@ecust.edu.c [Key Laboratory for Advanced Materials, Department of Chemistry, East China University of Science and Technology, Shanghai 200237 (China)

    2011-02-15

    High-quality CdTeSe colloidal nanocrystals with gradient distribution of components, consisting of Te-rich inner cores and Se-rich outer shells, were synthesized in a 'green' solvent paraffin via a noninjection one-pot approach with the use of cadmium oxide (CdO), elemental tellurium, and elemental selenium as Cd, Te, and Se sources, respectively. All of these reactants were loaded at room temperature. This features synthetic reproducibility and large-scale capability. The bandgap engineering of the obtained CdTeSe QDs can be conveniently realized through the variation of growth temperature. Red- to near-infrared-emitting (620-780 nm) QDs with nearly identical particle sizes can be obtained when the reaction temperature was changed from 180 to 280 {sup o}C with the fixation of precursor feed ratio at 5Cd-0.5Te-0.5Se. The as-prepared CdTeSe QDs exhibit PL QY as high as 53%. The resulting CdTeSe QDs were characterized by UV-vis and photoluminescence spectroscopy, powder X-ray diffraction, transmission electron microscopy, and inductively coupled plasma atomic emission spectroscopy.

  10. Effect of surface treatment of thermoelectric materials on the properties of thermoelements made from solid solutions of Bi/sub 2/Te/sub 3/-Bi/sub 2/Se/sub 3/ and Bi/sub 2/Te/sub 3/-Sb/sub 2/Te/sub 3/ systems

    Energy Technology Data Exchange (ETDEWEB)

    Alieva, T.D.; Abdinov, D.Sh.; Salaev, Eh.Yu.

    1981-10-01

    Effect of surface treatment technology of samples of solid solutions of Ei/sub 2/Te/sub 3/-Bi/sub 2/Se/sub 3/ and Bi/sub 2/Te/sub 3/-Sb/sub 2/Te/sub 3/ systems on their thermoelectric efficiency is studied. Branches of thermoelements have been produced with the help of electroerosion or mechanical cutting of monocrystal ingots of semiconducting solid Bi/sub 2/Te/sub 3/-base solutions. It is shown that in case of the treatment of side surfaces of branches of thermoelements produced of monocrystals of Bi/sub 2/Te/sub 3/ base solid solutions their thermoelectrical efficiency grows considerably. Maximum growth of efficiency (approximately 20%) is observed during mechanical grinding of branches surfaces with diamond paste with the following chemical or electrochemical etching.

  11. The role of ligands in the optical and electronic spectra of CdSe nanoclusters

    Energy Technology Data Exchange (ETDEWEB)

    Kilina, Svletana [Los Alamos National Laboratory; Sergei, Ivanov A [Los Alamos National Laboratory; Victor, Klimov I [Los Alamos National Laboratory; Sergei, Tretiak [Los Alamos National Laboratory

    2008-01-01

    We investigate the impact of ligands on morphology, electronic structure, and optical response of the Cd33Se33 cluster, which already overlapps in size with the smallest synthesized CdSe quantum dots (QDs). Our Density Functional Theory (DFT) calculations demonstrate significant surface reorganization both for the bare cluster and for the cluster capped by amine and phosphine oxide ligand models. We observe strong surface-ligand interactions leading to substantial charge redistribution and polarization effects on the surface. This effect results in the appearance of hybridized states, where the electronic density is spread over the cluster and the ligands. Neither the ligand's nor hybridized molecular orbitals appear as trap states inside or near the band gap of the QD. Instead, being optically dark, dense hybridized states from the edges of the valence and the conduction bands could open new relaxation channels for high energy photoexcitations. Comparing quantum dots passivated by different ligands, we found that hybridized states are denser in at the edge of the conduction band of the cluster ligated with phosphine oxide molecules than that with primary amines. Such a different manifestation of ligand binding may potentially lead to the faster electron relaxation in dots passivated by phosphine oxide than by amine ligands, which is in agreement with experimental data.

  12. Plutonium oxychalcogenides Pu2O2X (X=O, S, Se, Te) crystal chemistry, magnetic and electrical properties. 5f electrons delocalization

    International Nuclear Information System (INIS)

    Costantini, Jean-Marc.

    1980-05-01

    We have studied the influence of the chalcogen X on the bonding and on the magnetic and electrical properties of the oxychalcogenides Pu 2 O 2 X. These compounds are isostructural with hexagonal La 2 O 3 for X=O, S, Se and with tetragonal La 2 O 2 Te for X=Te. Comparison of Nd 2 O 2 X and Pu 2 O 2 X cell volumes showed that plutonium crystal radius decreases from Pu 2 O 3 through Pu 2 O 2 Te with increasing 5f electrons delocalization and 5f-np overlap. Superexchange interactions through O 2- and X 2- were thought to be responsible for the observed antiferromagnetic ordering. Neel temperatures increase from Pu 2 O 3 through Pu 2 O 2 Te showing that these interactions and subsequent 5f-np covalency are strengthened as chalcogen electronegativity decreases. Hexagonal Pu 2 O 3 is an insulator while the other compounds are semi-conductors with energy gaps around 0.6 eV which were interpreted as the separation between the 6d-7s conduction band and the np valence band. The localized 5f states were located just below the np band, partially overlapping it [fr

  13. Optical performance evolutions of reductive glutathione coated CdSe quantum dots in different environments

    International Nuclear Information System (INIS)

    Wang Lili; Jiang Jisen

    2011-01-01

    Optical performances of reductive glutathione coated CdSe quantum dots were studied under different ageing conditions. The enhancements of luminescence were obviously occurred for the samples ageing under illumination. The quantum yield of CdSe was enhanced continuously over 44 days at room temperature, and reached as high as 36.6%. O 2 was proved to make a certain contribute to the enhancement. The evolutions of the systems during the ageing time were deduced according to the variations of pH values with ageing time and the XRD results of the samples ageing in air with illumination. We conferred that the reduction of surface defects resulted from the photo-induced decomposition of CdSe quantum dots was the main reason for the enhancement of fluorescence. The production of CdO as a result of the surface reaction with O 2 made contributions to the enhancement for a certain extent. The curves of quantum yield versus ageing time were fitted with a stretched exponential function. It was found that the course of fluorescence enhancement accorded with the dynamics of system with strongly coupled hierarchical degrees of freedom.

  14. A study of the reactivity of elemental Cr/Se/Te thin multilayers using X-ray reflectometry, in situ X-ray diffraction and X-ray absorption spectroscopy

    International Nuclear Information System (INIS)

    Behrens, Malte; Tomforde, Jan; May, Enno; Kiebach, Ragnar; Bensch, Wolfgang; Haeussler, Dietrich; Jaeger, Wolfgang

    2006-01-01

    The reactivity of [Cr/Se/Te] multilayers under annealing was investigated using X-ray reflectometry, in situ X-ray diffraction, X-ray absorption fine structure (XAFS) measurements and transmission electron microscopy. For all samples, interdiffusion was complete at temperatures between 100 and 300 deg. C, depending on the repeating tri-layer thickness. A crystalline phase nucleated approximately 20 deg. C above the temperature where interdiffusion was finished. The first crystalline phase in a binary Cr/Te sample was layered CrTe 3 nucleating at 230 deg. C. In ternary samples (Se:Te=0.6-1.2), the low-temperature nucleation of such a layered CrQ 3 (Q=Se, Te) phase is suppressed and instead the phase Cr 2 Q 3 nucleates first. Interestingly, this phase decomposes around 500 deg. C into layered CrQ 3 . In contrast, binary Cr/Se samples form stable amorphous alloys after interdiffusion and Cr 3 Se 4 nucleates around 500 deg. C as the only crystalline phase. Evaluation of the XAFS data of annealed samples yield Se-Cr distances of 2.568(1) and 2.552(1) A for Cr 2 Q 3 and CrQ 3 , respectively. In the latter sample, higher coordination shells around Se are seen accounting for the Se-Te contacts in the structure. - Graphical abstract: The first step of the reaction of elemental Cr/Te/Se-multilayers is the interdiffusion of the elements as evidenced by the decay of the modulation peaks in the low-angle region of the X-ray diffraction patterns. The subsequent growth of Bragg peaks at higher scattering angles indicates crystallization of chromium chalcogenide Cr 2 Te 3- x Se x

  15. Metastable phases freezing from melts of reciprocal systems PbX + CdI2=CdX + PbI2 (X=S, Se, Te)

    International Nuclear Information System (INIS)

    Odin, I.N.; Chukichev, M.V.

    2001-01-01

    The transformations in the mutual PbX + CdI 2 =CdX + PbI 2 (X=S, Se, Te) systems leading to the crystallization of metastable polytypical modifications of lead iodide in metastable ternary compounds are studied for the first time. Microstructural and X-ray diffraction analyses were conducted. Their phase diagrams were constructed. The luminescence properties of the stable and metastable modifications of the lead iodide and the metastable compound Pb 4 SeI 6 were investigated. The lines 504 and 512 nm are noted in the 2H-PbI 2 cathodoluminescence spectra. The close lines - 508 and 516 nm provide for the 6R-PbI 2 modification. The metastable compound Pb 4 SeI 6 is characterized by the 769 and 868 nm lines [ru

  16. Effect of composition on optical properties of GeSe3–Sb2Se3–ZnSe ...

    Indian Academy of Sciences (India)

    Administrator

    to a scanning electron microscope (JEOL-JSM-5400) with an EDX detector of ... angle inverted 5° ≤ 2θ ≥ 90° with steps of size Δ(2θ) = 0⋅05°. Optical .... E h ν ν. = +. −. (12) where Eo is the oscillator energy and Ed the dispersion energy.

  17. First-principles study on the electronic, optical, and transport properties of monolayer α - and β -GeSe

    Science.gov (United States)

    Xu, Yuanfeng; Zhang, Hao; Shao, Hezhu; Ni, Gang; Li, Jing; Lu, Hongliang; Zhang, Rongjun; Peng, Bo; Zhu, Yongyuan; Zhu, Heyuan; Soukoulis, Costas M.

    2017-12-01

    The extraordinary properties and the novel applications of black phosphorene induce the research interest in the monolayer group-IV monochalcogenides. Here using first-principles calculations, we systematically investigate the electronic, transport, and optical properties of monolayer α - and β -GeSe, revealing a direct band gap of 1.61 eV for monolayer α -GeSe and an indirect band gap of 2.47 eV for monolayer β -GeSe. For monolayer β -GeSe, the electronic/hole transport is anisotropic, with an extremely high electron mobility of 2.93 ×104cm2/Vs along the armchair direction, comparable to that of black phosphorene. Furthermore, for β -GeSe, robust band gaps nearly independent of the applied tensile strain along the armchair direction are observed. Both monolayer α - and β -GeSe exhibit anisotropic optical absorption in the visible spectrum.

  18. Screened coulomb hybrid DFT study on electronic structure and optical properties of anionic and cationic Te-doped anatase TiO2

    KAUST Repository

    Harb, Moussab

    2013-06-27

    The origin of the enhanced visible-light optical absorption in Te-doped bulk anatase TiO2 is investigated in the framework of DFT and DFPT within HSE06 in order to ensure accurate electronic structure and optical transition predictions. Various oxidation states of Te species are considered based on their structural location in bulk TiO2. In fact, TiO (2-x)Tex (with isolated Te2- species at Te-Te distance of 8.28 Å), TiO2Tex (with isolated TeO 2- species at Te-Te distance of 8.28 Å), TiO2Te 2x (with two concomitant TeO2- species at Te-Te distance of 4.11 Å), and Ti(1-2x)O2Te2x (with two neighboring Te4+ species at nearest-neighbor Te-Te distance of 3.05 Å) show improved optical absorption responses in the visible range similarly as it is experimentally observed in Te-doped TiO2 powders. The optical absorption edges of TiO(2-x)Tex, TiO 2Tex, and TiO2Te2x are found to be red-shifted by 400 nm compared with undoped TiO2 whereas that of Ti(1-2x)O2Te2x is red-shifted by 150 nm. On the basis of calculated valence and conduction band edge positions of Te-doped TiO2, only TiO(2-x)Tex and Ti (1-2x)O2Te2x show suitable potentials for overall water splitting under visible-light irradiation. The electronic structure analysis revealed narrower band gaps of 1.12 and 1.17 eV with respect to undoped TiO2, respectively, resulting from the appearance of new occupied electronic states in the gap of TiO2. A delocalized nature of the gap states is found to be much more pronounced in TiO (2-x)Tex than that with Ti(1-2x)O 2Te2x due to the important contribution of numerous O 2p orbitals together with Te 5p orbitals. © 2013 American Chemical Society.

  19. Synthesis of metals chalcogenides nano-particles from H{sub 2}X (X=S, Se, Te) produced electrochemically; Synthese de nanoparticules de chalcogenures de metaux a partir de H{sub 2}X (X=S, Se, Te) produit electrochimiquement

    Energy Technology Data Exchange (ETDEWEB)

    Bastide, S.; Tena-Zaera, R.; Alleno, E.; Godart, C.; Levy-Clement, C. [Centre National de la Recherche Scientifique (CNRS), Lab. de Chimie Metallurgique des Terres Rares, 94 - Thiais (France); Hodes, G. [Weizmann Institute of Science, Rehovot (Israel)

    2006-07-01

    In this work, an electrochemical method to produce H{sub 2}X (X=S, Se, Te) hydrides in a controlled way (without being able to store them) and to transfer them directly in the synthesis reactor has been perfected. By this method, the use of H{sub 2}Te has been possible. The method uses the reduction of the elementary chalcogenide in acid medium. The Te being conductor, it can be directly used as electrode, on the other hand S and Se are insulators. Nevertheless, graphite-S or Se conducing composite electrodes can also be used. When the electrolyte composition (pH, salts presence) is well adjusted, the essential of the cathodic current is consumed by the chalcogenide reduction (low evolution of H{sub 2}) with faradic yields of about 100% for H{sub 2}S and H{sub 2}Se and 40% for HeTe. The use of H{sub 2}X allows the synthesis of nano-particles of metals chalcogenides directly by reaction with dissolved metallic salts in aqueous or organic medium and precipitation. Thus it has been possible to prepare all the CdX compounds under the form of nano-particles of diameter between 3 and 5 nm by bubbling of the gaseous hydrides in aqueous acetate solutions of Cd. In producing concomitantly H{sub 2}S and H{sub 2}Se, nano-particles of solid solutions CdS{sub x}Se{sub 1-x} have been synthesized too. (O.M.)

  20. The influence of CdSe and ZnSe nanoparticles on the optical properties of Sm"3"+ ions in lead borate glasses

    International Nuclear Information System (INIS)

    Mallur, Saisudha B.; Heidorn, William D.; Fatokun, Stephen O.; Joshi, Krishna D.; Bista, Sandip S.; Babu, Panakkattu K.

    2017-01-01

    The effect of glass composition and the presence of CdSe/ZnSe nanoparticles (NPs) on the optical absorption and fluorescence of Sm-doped lead borate glasses are studied. Three sets of glass samples xPbO:(99.5-x) B_2O_3:0.5Sm_2O_3, x = 29.5–69.5 mol%, xPbO:(96.5-x) B_2O_3:0.5Sm_2O_3: 3CdSe/ZnSe, x = 36.5, and 56.5 mol% are prepared. NPs are grown by annealing these glasses just below the glass transition temperature. Average size of both types of NPs increases with annealing time; however, CdSe NPs grew to a larger size range (2 to 20 nm) compared to ZnSe NPs (1 to 16 nm). We analyzed the hypersensitive transition, intensity parameters, radiative transition probability, stimulated emission cross section (σ_p), and the area ratio of the electric dipole/magnetic dipole transitions of Sm"3"+. The intensity parameters show a minimum at 11 h annealing for 36.5 mol% and a maximum for the same annealing duration in 56.5 mol% PbO containing CdSe NPs. The σ_p for 56.5 mol% of PbO with CdSe NPs is found to be a maximum when the average NP size is around 14 nm. ZnSe NPs containing glasses also show significant changes in σ_p when the average particle size is ~16 nm, for 36.5 mol% PbO. Our results suggest that the optical properties of Sm"3"+ in lead borate glasses are sensitive to its electronic environment which can be modified by varying the base glass composition and/or incorporating large NPs of CdSe/ZnSe. The large σ_p values that we observe for some of the glass compositions make them attractive materials for photonic devices and photovoltaic applications.

  1. The influence of CdSe and ZnSe nanoparticles on the optical properties of Sm{sup 3+} ions in lead borate glasses

    Energy Technology Data Exchange (ETDEWEB)

    Mallur, Saisudha B.; Heidorn, William D.; Fatokun, Stephen O.; Joshi, Krishna D.; Bista, Sandip S.; Babu, Panakkattu K., E-mail: PK-Babu@wiu.edu [Western Illinois University, Department of Physics (United States)

    2017-03-15

    The effect of glass composition and the presence of CdSe/ZnSe nanoparticles (NPs) on the optical absorption and fluorescence of Sm-doped lead borate glasses are studied. Three sets of glass samples xPbO:(99.5-x) B{sub 2}O{sub 3}:0.5Sm{sub 2}O{sub 3}, x = 29.5–69.5 mol%, xPbO:(96.5-x) B{sub 2}O{sub 3}:0.5Sm{sub 2}O{sub 3}: 3CdSe/ZnSe, x = 36.5, and 56.5 mol% are prepared. NPs are grown by annealing these glasses just below the glass transition temperature. Average size of both types of NPs increases with annealing time; however, CdSe NPs grew to a larger size range (2 to 20 nm) compared to ZnSe NPs (1 to 16 nm). We analyzed the hypersensitive transition, intensity parameters, radiative transition probability, stimulated emission cross section (σ{sub p}), and the area ratio of the electric dipole/magnetic dipole transitions of Sm{sup 3+}. The intensity parameters show a minimum at 11 h annealing for 36.5 mol% and a maximum for the same annealing duration in 56.5 mol% PbO containing CdSe NPs. The σ{sub p} for 56.5 mol% of PbO with CdSe NPs is found to be a maximum when the average NP size is around 14 nm. ZnSe NPs containing glasses also show significant changes in σ{sub p} when the average particle size is ~16 nm, for 36.5 mol% PbO. Our results suggest that the optical properties of Sm{sup 3+} in lead borate glasses are sensitive to its electronic environment which can be modified by varying the base glass composition and/or incorporating large NPs of CdSe/ZnSe. The large σ{sub p} values that we observe for some of the glass compositions make them attractive materials for photonic devices and photovoltaic applications.

  2. Structural phase transition and erasable optically memorized effect in layered γ-In2Se3 crystals

    International Nuclear Information System (INIS)

    Ho, Ching-Hwa; Chen, Ying-Cen; Pan, Chia-Chi

    2014-01-01

    We have grown In 2 Se 3 layered-type crystals using chemical vapor transport method with ICl 3 as the transport agent. The as-grown crystals show two different color groups of black shiny for α-phase In 2 Se 3 and red to yellow for γ-phase In 2 Se 3 . High-resolution transmission electron micro scopy verifies crystalline state and structural polytype of the as-grown In 2 Se 3 . The results indicate that the α-In 2 Se 3 crystals present more crystalline states than those of the other amorphous γ-In 2 Se 3 . The amorphous effect on the advancing of optoelectronic property of γ-In 2 Se 3 shows erasable optical-memorized effect in the disordered and polycrystalline γ-In 2 Se 3 layers. Laser-induced photodarkening and annealed-recovery test verified that a reversible structural-phase transition of γ↔α can occur inside the γ-In 2 Se 3 . Thermoreflectance and Raman scattering measurements are carried out to identify the inter-phase transformation of the γ-In 2 Se 3 polycrystals using different heat treatments. Direct band gaps and Raman vibration modes for the γ- and α-In 2 Se 3 crystalline phases are, respectively, characterized and identified. The character of γ↔α inter-phase transition promotes feasible optical and optoelectronic applications of the γ-In 2 Se 3 material in optical memory, optics, and solar-energy devices

  3. Structural phase transition and erasable optically memorized effect in layered γ-In2Se3 crystals

    Science.gov (United States)

    Ho, Ching-Hwa; Chen, Ying-Cen; Pan, Chia-Chi

    2014-01-01

    We have grown In2Se3 layered-type crystals using chemical vapor transport method with ICl3 as the transport agent. The as-grown crystals show two different color groups of black shiny for α-phase In2Se3 and red to yellow for γ-phase In2Se3. High-resolution transmission electron micro scopy verifies crystalline state and structural polytype of the as-grown In2Se3. The results indicate that the α-In2Se3 crystals present more crystalline states than those of the other amorphous γ-In2Se3. The amorphous effect on the advancing of optoelectronic property of γ-In2Se3 shows erasable optical-memorized effect in the disordered and polycrystalline γ-In2Se3 layers. Laser-induced photodarkening and annealed-recovery test verified that a reversible structural-phase transition of γ↔α can occur inside the γ-In2Se3. Thermoreflectance and Raman scattering measurements are carried out to identify the inter-phase transformation of the γ-In2Se3 polycrystals using different heat treatments. Direct band gaps and Raman vibration modes for the γ- and α-In2Se3 crystalline phases are, respectively, characterized and identified. The character of γ↔α inter-phase transition promotes feasible optical and optoelectronic applications of the γ-In2Se3 material in optical memory, optics, and solar-energy devices.

  4. Optical characterization of bulk Zn1-xBexTe crystals

    International Nuclear Information System (INIS)

    Shih, Y C; Huang, Y S; Firszt, F; Legowski, S; Meczynska, H; Tiong, K K

    2008-01-01

    This paper presents an optical characterization of three bulk sphalerite Zn 1-x Be x Te crystals grown by the modified high pressure Bridgman method. The study was conducted in the near-band-edge interband transition regime using low temperature photoluminescence (PL), temperature-dependent contactless electroreflectance (CER) and/or photoreflectance (PR) in the temperature range of 15-400 K, and surface photovoltage spectroscopy (SPS) at room temperature. PL spectra at low temperatures of the samples investigated consist of an excitonic line, a band due to recombination of free electrons with holes located at shallow acceptors and a broad band related to recombination through deeper level defects. The band-edge excitonic transitions have been observed in the CER/PR spectra. The fundamental transition energies E 0 are determined via lineshape fits to the CER/PR spectra. The values of E 0 at room temperature obtained from CER/PR spectra correspond well to that determined from SPS measurements, and the Be contents x of the samples are determined using a linear equation which describes the room temperature band gap dependence on composition for the Zn 1-x Be x Te alloy system. The parameters describing the temperature dependence of the band-edge excitonic transition energies are evaluated and discussed

  5. Large optical second-order nonlinearity of poled WO3-TeO2 glass.

    Science.gov (United States)

    Tanaka, K; Narazaki, A; Hirao, K

    2000-02-15

    Second-harmonic generation, one of the second-order nonlinear optical properties of thermally and electrically poled WO>(3)-TeO>(2) glasses, has been examined. We poled glass samples with two thicknesses (0.60 and 0.86 mm) at various temperatures to explore the effects of external electric field strength and poling temperature on second-order nonlinearity. The dependence of second-harmonic intensity on the poling temperature is maximum at a specific poling temperature. A second-order nonlinear susceptibility of 2.1 pm/V was attained for the 0.60-mm-thick glass poled at 250 degrees C. This value is fairly large compared with those for poled silica and tellurite glasses reported thus far. We speculate that the large third-order nonlinear susceptibility of WO>(3)- TeO>(2) glasses gives rise to the large second-order nonlinearity by means of a X((2)) = 3X((3)) E(dc) process.

  6. Synthesis and characterization of Cu{sub 3}TaIn{sub 3}Se{sub 7} and CuTa{sub 2}InTe{sub 4}

    Energy Technology Data Exchange (ETDEWEB)

    Calderon, E.; Munoz-Pinto, M.; Duran-Pina, S.; Quintero, M.; Quintero, E.; Morocoima, M. [Centro de Estudios de Semiconductores, Departamento de Fisica, Facultad de Ciencias, Universidad de Los Andes, Merida (Venezuela); Delgado, G.E. [Laboratorio de Cristalografia, Departamento de Quimica, Facultad de Ciencias, Universidad de Los Andes, Merida (Venezuela); Romero, H. [Laboratorio de Magnetismo, Departamento de Fisica, Facultad de Ciencias, Universidad de Los Andes, Merida (Venezuela); Briceno, J.M.; Fernandez, J. [Laboratorio de Analisis Quimico y Estructural (LAQUEM), Departamento de Fisica, Facultad de Ciencias, Merida (Venezuela); Grima-Gallardo, P.

    2008-07-15

    Polycrystalline samples of Cu{sub 3}TaIn{sub 3}Se{sub 7} and CuTa{sub 2}InTe{sub 4} were synthesized by the usual melt and anneal technique. X-ray powder diffraction showed a single phase behavior for both samples with tetragonal symmetry and unit cell parameter values a=5.794{+-}0.002 A, c=11.66{+-}0.01 A, c/a=2.01, V=391{+-}1 A{sup 3} and a=6.193{+-}0.001 A, c=12.400 {+-}0.002A, c/a=2.00, V=475{+-}1 A{sup 3}, respectively. Differential thermal analysis (DTA) measurements suggested a complicated behavior near the melting point with several thermal transitions observed in the heating and cooling runs. From the shape of the DTA peaks it was deduced that the melting is incongruent for both materials. Magnetic susceptibility measurements (zero-field cooling and field cooling) indicated an antiferromagnetic character with transition temperatures of T=70 K (Cu{sub 3}TaIn{sub 3}Se{sub 7}) and 42 K (CuTa{sub 2}InTe{sub 4}). A spin-glass transition was observed in Cu{sub 3}TaIn{sub 3}Se{sub 7} with T{sub f}{approx}50 K. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  7. Synthesis and characterization of Cu3TaIn3Se7 and CuTa2InTe4

    International Nuclear Information System (INIS)

    Calderon, E.; Munoz-Pinto, M.; Duran-Pina, S.; Quintero, M.; Quintero, E.; Morocoima, M.; Delgado, G.E.; Romero, H.; Briceno, J.M.; Fernandez, J.; Grima-Gallardo, P.

    2008-01-01

    Polycrystalline samples of Cu 3 TaIn 3 Se 7 and CuTa 2 InTe 4 were synthesized by the usual melt and anneal technique. X-ray powder diffraction showed a single phase behavior for both samples with tetragonal symmetry and unit cell parameter values a=5.794±0.002 A, c=11.66±0.01 A, c/a=2.01, V=391±1 A 3 and a=6.193±0.001 A, c=12.400 ±0.002A, c/a=2.00, V=475±1 A 3 , respectively. Differential thermal analysis (DTA) measurements suggested a complicated behavior near the melting point with several thermal transitions observed in the heating and cooling runs. From the shape of the DTA peaks it was deduced that the melting is incongruent for both materials. Magnetic susceptibility measurements (zero-field cooling and field cooling) indicated an antiferromagnetic character with transition temperatures of T=70 K (Cu 3 TaIn 3 Se 7 ) and 42 K (CuTa 2 InTe 4 ). A spin-glass transition was observed in Cu 3 TaIn 3 Se 7 with T f ∼50 K. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  8. Critical thickness and strain relaxation in high-misfit heteroepitaxial systems: PbTe1-xSex on PbSe (001)

    International Nuclear Information System (INIS)

    Wiesauer, Karin; Springholz, G.

    2004-01-01

    Strain relaxation and misfit dislocation formation is investigated for the high-misfit PbTe 1-x Se x /PbSe (001) heteroepitaxial system in which the lattice mismatch varies from 0% to 5.5%. Because a two-dimensional (2D) layer growth prevails for all PbTe 1-x Se x ternary compositions, the lattice mismatch is relaxed purely by misfit dislocations. In addition, it is found that strain relaxation is not hindered by dislocation kinetics. Therefore, this material combination is an ideal model system for testing the equilibrium Frank-van der Merwe and Matthews-Blakeslee strain relaxation models. In our experiments, we find significantly lower values of the critical layer thickness as compared to the model predictions. This discrepancy is caused by the inappropriate description of the dislocation self-energies when the layer thickness becomes comparable to the dislocation core radius. To resolve this problem, a modified expression for the dislocation self-energy is proposed. The resulting theoretical critical thicknesses are in excellent agreement with the experimental data. In addition, a remarkable universal scaling behavior is found for the strain relaxation data. This underlines the breakdown of the current strain relaxation models

  9. Bond-equilibrium theory of liquid Se-Te alloys. II. Effect of singly attached ring molecules

    Science.gov (United States)

    Cutler, Melvin; Bez, Wolfgang G.

    1981-06-01

    A statistical-mechanical theory for bond equilibrium of chain polymers containing threefold (3F) and onefold (1F) bond defects is extended to include the effects of free ring molecules and ring molecules attached to chains by a single 3F atom. Positively charged singly attached rings are shown to play a key role in bond equilibrium in liquid Sex Te1-x by permitting the formation of ion pairs in which both constituents are effectively chain terminators, thus decreasing the average polymer size. The theory is applied to explain the behavior of the paramagnetic susceptibility, χp, and electronic transport as affected by the Fermi energy EF. It is found that the increase in χp with the concentration of Te is primarily the result of the smaller energy for breaking Te bonds. In addition, attached rings play an important role in determining the effect of temperature on χp. At x<~0.5, the concentrations of both free and attached rings becomes small at high T because of the high concentration of bond defects.

  10. On the role of Pb0 atoms on the nucleation and growth of PbSe and PbTe nanoparticles

    International Nuclear Information System (INIS)

    Garcia-Gutierrez, Domingo I.; Leon-Covian, Lina M. De; Garcia-Gutierrez, Diana F.; Treviño-Gonzalez, M.; Garza-Navarro, M. A.; Sepulveda-Guzman, S.

    2013-01-01

    In this contribution, a nucleation and growth mechanism of PbSe and PbTe nanoparticles are proposed. The formation and growth of PbSe and PbTe nanoparticles during their reaction synthesis were studied and followed using transmission electron microscopy, and their related techniques. In the synthesis method, trioctylphosphine-selenide and telluride were used as the chalcogen precursors, while lead oleate was employed as the lead precursor. Different synthesis conditions were tested to assess the effect of varying the reaction time, lead to chalcogen ratio, reaction temperature, and lead oleate concentration. The synthesized nanoparticles were characterized by means of electron diffraction, energy dispersive X-ray spectroscopy, scanning transmission electron microscopy, and electron energy loss spectroscopy, to obtain information related to their morphology, crystal structure, and composition. The experimental results suggest that the growth of the lead chalcogenide nanoparticles greatly relies on the reduction of Pb 2+ ions to Pb 0 atoms at early reaction times; this reduction of the lead precursor is evidenced by the formation of Pb nanoparticles with sizes between 1 and 3 nm under certain synthesis conditions. These Pb nanoparticles gradually disappear as the reaction progresses, suggesting that the reduced Pb 0 atoms are able to contribute to the growth of the PbSe and PbTe nanoparticles, reaching sizes between 8 and 18 nm. The current results contribute to a better understanding of the nucleation and growth mechanisms of lead chalcogenide nanoparticles, which will enable the definition of more efficient synthesis routes of these types of nanostructures.

  11. On the role of Pb{sup 0} atoms on the nucleation and growth of PbSe and PbTe nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Garcia-Gutierrez, Domingo I., E-mail: domingo.garciagt@uanl.edu.mx; Leon-Covian, Lina M. De; Garcia-Gutierrez, Diana F. [Universidad Autonoma de Nuevo Leon, UANL, Facultad de Ingenieria Mecanica y Electrica, FIME (Mexico); Trevino-Gonzalez, M. [Centro de Innovacion, Investigacion y Desarrollo en Ingenieria y Tecnologia, CIIDIT, Universidad Autonoma de Nuevo Leon, UANL (Mexico); Garza-Navarro, M. A.; Sepulveda-Guzman, S. [Universidad Autonoma de Nuevo Leon, UANL, Facultad de Ingenieria Mecanica y Electrica, FIME (Mexico)

    2013-05-15

    In this contribution, a nucleation and growth mechanism of PbSe and PbTe nanoparticles are proposed. The formation and growth of PbSe and PbTe nanoparticles during their reaction synthesis were studied and followed using transmission electron microscopy, and their related techniques. In the synthesis method, trioctylphosphine-selenide and telluride were used as the chalcogen precursors, while lead oleate was employed as the lead precursor. Different synthesis conditions were tested to assess the effect of varying the reaction time, lead to chalcogen ratio, reaction temperature, and lead oleate concentration. The synthesized nanoparticles were characterized by means of electron diffraction, energy dispersive X-ray spectroscopy, scanning transmission electron microscopy, and electron energy loss spectroscopy, to obtain information related to their morphology, crystal structure, and composition. The experimental results suggest that the growth of the lead chalcogenide nanoparticles greatly relies on the reduction of Pb{sup 2+} ions to Pb{sup 0} atoms at early reaction times; this reduction of the lead precursor is evidenced by the formation of Pb nanoparticles with sizes between 1 and 3 nm under certain synthesis conditions. These Pb nanoparticles gradually disappear as the reaction progresses, suggesting that the reduced Pb{sup 0} atoms are able to contribute to the growth of the PbSe and PbTe nanoparticles, reaching sizes between 8 and 18 nm. The current results contribute to a better understanding of the nucleation and growth mechanisms of lead chalcogenide nanoparticles, which will enable the definition of more efficient synthesis routes of these types of nanostructures.

  12. Optical properties and the use of CdSe quantum dot for biolabeling applications

    International Nuclear Information System (INIS)

    Tran Hong Nhung; Nguyen Thi Van; Vu Xuan Hoa; Pham Minh Tan; Tong Kim Thuan; Tran Thi Thu Thuy; Jean Claude Brochon; Patrick Tauc

    2008-01-01

    The quantum dots CdSe type Qtracker 565 and 605 of Quantum Dot Company have been investigated by size, chemical structure and optical properties. The Qtracker 605 QDs were introduced into Lipomyces Starkeyi yeast cells. It was found that for the young cells (36 h of culture), the labeling QDs are mainly located in vacuoles, and the emission remains narrow with the maximum is clearly around 605 nm. For age cells (96 h of culture), the labeling QDs are concentrated in the cell cytoplasm, the emission is broaden with the maximum shifted to 580 nm. The live cell image was still observed after two months of introduction. The Qtracker 605 QDs were also successfully introduced into mouse blood cancerous cells. (author)

  13. Effects of Pb doping on the magneto-optical properties of EuPbTe epitaxial films

    Energy Technology Data Exchange (ETDEWEB)

    Heredia, E.; Motisuke, P. [Laboratório Associado de Sensores e Materiais, Instituto Nacional de Pesquisas Espaciais, São José dos Campos, 12227-010 SP (Brazil); Couto, O.D.D. Jr. [Instituto de Física “Gleb Wataghin” – Universidade Estadual de Campinas, Campinas, 13083-859 SP (Brazil); Lang, R. [Instituto de Física “Gleb Wataghin” – Universidade Estadual de Campinas, Campinas, 13083-859 SP (Brazil); Institute of Science and Technology, UNIFESP, São José dos Campos, 12231-280 SP (Brazil); Balanta, M.A.G.; Brasil, M.J.S.P. [Instituto de Física “Gleb Wataghin” – Universidade Estadual de Campinas, Campinas, 13083-859 SP (Brazil); Oliveira Rappl, P.H. de [Laboratório Associado de Sensores e Materiais, Instituto Nacional de Pesquisas Espaciais, São José dos Campos, 12227-010 SP (Brazil); Iikawa, F., E-mail: iikawa@ifi.unicamp.br [Laboratório Associado de Sensores e Materiais, Instituto Nacional de Pesquisas Espaciais, São José dos Campos, 12227-010 SP (Brazil); Instituto de Física “Gleb Wataghin” – Universidade Estadual de Campinas, Campinas, 13083-859 SP (Brazil)

    2015-11-15

    We investigate the magneto-optical properties of magnetic-semiconductor Eu{sub 1−x}Pb{sub x}Te epitaxial layers with Pb contents up to 5%. We show that the inclusion of a small amount of Pb atoms in EuTe affects the optical and magnetic properties of the resulting alloy. The incorporation of Pb gives rise to a reduction of the Néel temperature and of the slope of the giant magneto-red-shift of the magnetic polaron optical emission. All those effects can be understood in terms of the magnetic dilution effect due to the reduced Eu concentration. The introduction of Pb also reveals a splitting of the high emission energy side-band under applied magnetic field, presenting a more complex feature of the band structure of the alloys. Our results cannot be fully explained on the basis of the current theoretical knowledge of the EuTe band structure and, therefore, we expect that they can stimulate future theoretical investigations and encourage applied investigations of spintronic devices based on these materials. - Highlights: • Reduction of the Néel temperature when small amount of Pb is introduced into EuTe. • The saturation magnetic field needed to fully order the magnetic moments of Eu also reduces increasing Pb content. • Splitting of the high energy optical emission line under applied magnetic field, which is more evident for Pb doped samples.

  14. Crystal structure of mineral grechishchevite synthetic analogue and Hg-X (X=S, Se, Te) bonds topology in structures of mercury chalcogenhalides

    International Nuclear Information System (INIS)

    Pervukhina, N.V.; Borisov, S.V.; Magarill, S.A.; Naumov, D.Yu.; Vasil'ev, V.I.; Nenashev, B.G.

    2004-01-01

    Structural studies of synthetic analog of mineral grechishchevite Hg 3 S 2 Br 1.00 Cl 0.50 I 0.50 were conducted, the mineral crystal structure was refined, the results of the studies being analyzed. For chalcogenhalides Hg 3 X 2 Hal 2 (X=S, Se, Te; Hal=Cl, Br, I) inventory was taken of intergrowing isolated and infinite, i.e. continuous, layered and carcass, covalently bonded Hg-X-radicals into pseudocubical matrix from halide ions [ru

  15. Optical and electrical properties of thermally evaporated In49Se48Sn3 films

    International Nuclear Information System (INIS)

    Salem, A.M.; El-Gendy, Y.A.; El-Sayad, E.A.

    2009-01-01

    Nearly stoichiometric thin films of In 49 Se 48 Sn 3 were deposited at room temperature, by conventional thermal evaporation of the presynthesized materials, onto precleaned glass substrates. The microstructural studies on the as-deposited and annealed films, using transmission electron microscopy and diffraction (TEMD), revealed that the as-deposited films are amorphous in nature, while those annealed at 498 K are crystalline. The optical properties of the investigated films were determined from the transmittance and reflectance data, in the spectral range 650-2500 nm. An analysis of the optical absorption spectra revealed a non-direct energy gap characterizing the amorphous films, while both allowed and forbidden direct energy gaps characterized the crystalline films. The electrical resistance of the deposited films was carried out during heating and cooling cycles in the temperature range 300-600 K. The results show an irreproducible behavior, while after crystallization the results become reproducible. The analysis of the temperature dependence of the resistance (ln(R) vs. 1000/T) for crystalline films shows two straight lines corresponding to both extrinsic and intrinsic conduction. The room temperature I-V characteristics of the as-deposited films sandwiched between similar Ag metal electrodes shows an ohmic behavior, while non-ohmic behavior attributed to space charge limited conduction has been observed when the films are sandwiched between dissimilar Ag/Al metal electrodes.

  16. Influence of substitution, nonstoichiometry and annealing-conditions on superconductivity and normal conductivity of Fe1+δ (Te1‑x Xx ) (X=Se, S)

    Science.gov (United States)

    Lima, M. S. L.; ElMassalami, M.; Deguchi, K.; Takeya, H.; Takano, Y.

    2018-03-01

    Thermal evolution of resistivity, ρ(T, x), of as-prepared samples of Fe1+δ Te1‑x S x (δ ≈ 0, x ≤ 0.2 = solubility limit) demonstrate a granular log-in-T character within Ts < T <300K, a Kondo-like resistive contribution within Tc < T < Ts and granular superconductivity at low temperature (Ts = structural transition point of Fe1+δ Te, Tc =superconducting transition point). We attribute the log-in-T character as well as the nonbulk superconducting features of as-prepared samples to their granular superconductor nature. Annealing in oxygen removes Kondo-like contribution, annihilates pair-breaking centres and establishes bulk superconductivity but, in contrast, the high-temperature granular log-in-T character is hardly influenced. This analysis was successfully extended to the isomorphous Fe1+δ Te1‑x Se x as well as to other types of post-synthesis sample-treatment (e.g. annealing in different gas ambient or soaking in particular liquids).

  17. Cytotoxicity assessment of functionalized CdSe, CdTe and InP quantum dots in two human cancer cell models

    International Nuclear Information System (INIS)

    Liu, Jing; Hu, Rui; Liu, Jianwei; Zhang, Butian; Wang, Yucheng; Liu, Xin; Law, Wing-Cheung; Liu, Liwei; Ye, Ling; Yong, Ken-Tye

    2015-01-01

    The toxicity of quantum dots (QDs) has been extensively studied over the past decade. Some common factors that originate the QD toxicity include releasing of heavy metal ions from degraded QDs and the generation of reactive oxygen species on the QD surface. In addition to these factors, we should also carefully examine other potential QD toxicity causes that will play crucial roles in impacting the overall biological system. In this contribution, we have performed cytotoxicity assessment of four types of QD formulations in two different human cancer cell models. The four types of QD formulations, namely, mercaptopropionic acid modified CdSe/CdS/ZnS QDs (CdSe-MPA), PEGylated phospholipid encapsulated CdSe/CdS/ZnS QDs (CdSe-Phos), PEGylated phospholipid encapsulated InP/ZnS QDs (InP-Phos) and Pluronic F127 encapsulated CdTe/ZnS QDs (CdTe-F127), are representatives for the commonly used QD formulations in biomedical applications. Both the core materials and the surface modifications have been taken into consideration as the key factors for the cytotoxicity assessment. Through side-by-side comparison and careful evaluations, we have found that the toxicity of QDs does not solely depend on a single factor in initiating the toxicity in biological system but rather it depends on a combination of elements from the particle formulations. More importantly, our toxicity assessment shows different cytotoxicity trend for all the prepared formulations tested on gastric adenocarcinoma (BGC-823) and neuroblastoma (SH-SY5Y) cell lines. We have further proposed that the cellular uptake of these nanocrystals plays an important role in determining the final faith of the toxicity impact of the formulation. The result here suggests that the toxicity of QDs is rather complex and it cannot be generalized under a few assumptions reported previously. We suggest that one have to evaluate the QD toxicity on a case to case basis and this indicates that standard procedures and comprehensive

  18. Cytotoxicity assessment of functionalized CdSe, CdTe and InP quantum dots in two human cancer cell models

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Jing [Institute of Gerontology and Geriatrics & Beijing Key Lab of Aging and Geriatrics, Chinese PLA General Hospital, Beijing 100853 (China); Hu, Rui [School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore); Liu, Jianwei [Institute of Gerontology and Geriatrics & Beijing Key Lab of Aging and Geriatrics, Chinese PLA General Hospital, Beijing 100853 (China); Zhang, Butian; Wang, Yucheng [School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore); Liu, Xin [Lawrence Berkeley National Laboratory, Berkeley, CA (United States); Law, Wing-Cheung [Department of Industrial and System Engineering, The Hang Kong Polytechnic University, Hung Hom (Hong Kong); Liu, Liwei [School of Science, Changchun University of Science and Technology, Changchun 130022 (China); Ye, Ling, E-mail: lye_301@163.com [Institute of Gerontology and Geriatrics & Beijing Key Lab of Aging and Geriatrics, Chinese PLA General Hospital, Beijing 100853 (China); Yong, Ken-Tye, E-mail: ktyong@ntu.edu.sg [School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore)

    2015-12-01

    The toxicity of quantum dots (QDs) has been extensively studied over the past decade. Some common factors that originate the QD toxicity include releasing of heavy metal ions from degraded QDs and the generation of reactive oxygen species on the QD surface. In addition to these factors, we should also carefully examine other potential QD toxicity causes that will play crucial roles in impacting the overall biological system. In this contribution, we have performed cytotoxicity assessment of four types of QD formulations in two different human cancer cell models. The four types of QD formulations, namely, mercaptopropionic acid modified CdSe/CdS/ZnS QDs (CdSe-MPA), PEGylated phospholipid encapsulated CdSe/CdS/ZnS QDs (CdSe-Phos), PEGylated phospholipid encapsulated InP/ZnS QDs (InP-Phos) and Pluronic F127 encapsulated CdTe/ZnS QDs (CdTe-F127), are representatives for the commonly used QD formulations in biomedical applications. Both the core materials and the surface modifications have been taken into consideration as the key factors for the cytotoxicity assessment. Through side-by-side comparison and careful evaluations, we have found that the toxicity of QDs does not solely depend on a single factor in initiating the toxicity in biological system but rather it depends on a combination of elements from the particle formulations. More importantly, our toxicity assessment shows different cytotoxicity trend for all the prepared formulations tested on gastric adenocarcinoma (BGC-823) and neuroblastoma (SH-SY5Y) cell lines. We have further proposed that the cellular uptake of these nanocrystals plays an important role in determining the final faith of the toxicity impact of the formulation. The result here suggests that the toxicity of QDs is rather complex and it cannot be generalized under a few assumptions reported previously. We suggest that one have to evaluate the QD toxicity on a case to case basis and this indicates that standard procedures and comprehensive

  19. Optical properties and surface topography of CdCl2 activated CdTe thin films

    Science.gov (United States)

    Patel, S. L.; Purohit, A.; Chander, S.; Dhaka, M. S.

    2018-05-01

    The effect of post-CdCl2 heat treatment on optical properties and surface topography of evaporated CdTe thin films is investigated. The pristine and thermally annealed films were subjected to UV-Vis spectrophotometer and atomic force microscopy (AFM) to investigate the optical properties and surface topography, respectively. The absorbance is found to be maximum (˜90%) at 320°C temperature and transmittance found to be minimum and almost constant in ultraviolet and visible regions. The direct band gap is increased from 1.42 eV to 2.12 eV with post-CdCl2 annealing temperature. The surface topography revealed that the uniformity is improved with annealing temperature and average surface roughness is found in the range of 83.3-144.3 nm as well as grains have cylindrical hill-like shapes. The investigated results indicate that the post-CdCl2 treated films annealed at 320°C may be well-suitable for thin film solar cells as an absorber layer.

  20. The influence of oxygen and nitrogen doping on GeSbTe phase-change optical recording media properties

    Energy Technology Data Exchange (ETDEWEB)

    Dimitrov, D.; Shieh, H.-P.D

    2004-03-15

    Nitrogen and oxygen doped and co-doped GeSbTe (GST) films for phase-change optical recording are investigated. It is found that the crystallization temperature increased as well as the crystalline microstructure refined by doping. The carrier-to-noise ratio (CNR) and erasability of phase-change optical disks are improved being up to 52 and 35 dB, respectively, by using an appropriate nitrogen doping or co-doping concentration in the recording layer. Optical disks with co-doped recording layer are found to be superior in the recording characteristics then the single doped recording layer disks.

  1. Structural, optical and photoacoustic study of Sb{sub 2}Te{sub 3} prepared by mechanical alloying

    Energy Technology Data Exchange (ETDEWEB)

    Souza, S.M.; Triches, D.M. [Departamento de Engenharia Mecanica, Universidade Federal de Santa Catarina, Campus Universitario Trindade, S/N, C.P. 476, 88040-900 Florianopolis, Santa Catarina (Brazil); Lima, J.C. de, E-mail: fsc1jcd@fisica.ufsc.b [Departamento de Fisica, Universidade Federal de Santa Catarina, Campus Universitario Trindade, S/N, C.P. 476, 88040-900 Florianopolis, Santa Catarina (Brazil); Grandi, T.A. [Departamento de Fisica, Universidade Federal de Santa Catarina, Campus Universitario Trindade, S/N, C.P. 476, 88040-900 Florianopolis, Santa Catarina (Brazil); Biasi, R.S. de [Secao de Engenharia Mecanica e de Materiais, Instituto Militar de Engenharia, 22290-270 Rio de Janeiro, RJ (Brazil)

    2010-07-01

    Nanostructured Sb{sub 2}Te{sub 3} was produced from Sb and Te by mechanical alloying for 3 h. Volume fractions of crystalline and interfacial components of the milled powder were estimated from the X-ray diffraction (XRD) pattern corrected for polarization, re-absorption, and inelastic scattering and converted to electron units using the theoretical value of the mean square scattering factor of Sb{sub 2}Te{sub 3}. Annealing showed that the particles are stable up to at least 583 K. The influence of the interfacial component on optical and thermal properties of as-milled and annealed Sb{sub 2}Te{sub 3} was studied through Raman and photoacoustic absorption measurements. The contribution of the interfacial component to the thermal diffusivity of milled Sb{sub 2}Te{sub 3} was investigated assuming that the measured thermal diffusivity can be described as a random mixture of crystalline and interfacial components. The large volume fraction of interfacial component in the milled powder seems to be responsible for a significant increase in thermal diffusivity. After annealing at 583 K the value of thermal diffusivity is much smaller, close to the one reported for bulk Sb{sub 2}Te{sub 3}.

  2. The half-metallic ferromagnetism character in Be1-xVxY (Y=Se and Te) alloys: An ab-initio study

    Science.gov (United States)

    Sajjad, M.; Manzoor, Sadia; Zhang, H. X.; Noor, N. A.; Alay-e-Abbas, S. M.; Shaukat, A.; Khenata, R.

    2015-04-01

    Ab-initio calculations for V-doped BeSe and BeTe semiconductors are performed by means of all-electrons full-potential linearized augmented plane wave plus local orbital (FP-LAPW+lo) method. The structural properties are optimized using the Wu-Cohen generalized gradient approximation functional, whereas modified Becke and Jhonson local density approximation functional has been employed for evaluating the spin-polarized electronic and magnetic properties. Magnetic stability at various doping concentrations in ferromagnetic (FM) and anti-ferromagnetic (AFM) ordering is investigated by comparing the minimum total energies and enthalpies of formation (ΔH). Studied band structures, density of states, total energy, exchange interactions and magnetic moments manifest both alloys with half-metallic ferromagnetic behavior. Moreover, their valance bands are found to be paired ferromagnetically with V atoms. Furthermore, it was observed that the magnetic moment of vanadium atom reduces from free space charge value due to p-d hybridization which yields small magnetic moments on the Be, Se and Te sites.

  3. Heat treatment and thickness-dependent electrical study of Se{sub 50}Te{sub 20}S{sub 30} thin film

    Energy Technology Data Exchange (ETDEWEB)

    Abd-Elrahman, M.I.; Hafiz, M.M.; Qasem, Ammar; Abdel-Rahim, M.A. [Assiut University, Physics Department, Faculty of Science, Assiut (Egypt)

    2016-08-15

    Chalcogenide Se{sub 50}Te{sub 20}S{sub 30} thin film of different thickness was deposited using thermal evaporation technique. The thermogram of the chalcogenide bulk Se{sub 50}Te{sub 20}S{sub 30} was obtained using a differential scanning calorimetry (DSC) with heating rate of 7.5 K/min. The glass transition temperature T{sub g}, crystallization temperature T{sub c} and peak crystallization temperature T{sub p} were identified. The X-ray diffraction (XRD) examination indicates the amorphous nature of the as-deposited film and polycrystalline structure of the thermal annealed ones. The dark electrical resistivity (ρ) measurements were taken in temperature range (300-500 K) and thickness range (200-450 nm). Analysis of the electrical resistivity results revealed two types of conduction mechanisms: conduction due to extended states in the temperature range (T > T{sub c}) and variable range hopping in the temperature range (T < T{sub c}). The effect of the heat treatment and thickness on the density of localized states at the Fermi level N(E{sub F}) and hopping parameters were studied. (orig.)

  4. Effect of fluctuations on electron and phonon processes and thermodynamic parameters of Ag2Te and Ag2Se in the region of phase transition

    International Nuclear Information System (INIS)

    Aliev, S. A.; Aliev, F. F.

    2008-01-01

    Temperature dependences of electrical conductivity σ, thermoelectric power α, results of differential thermal analysis ΔT y , thermal conductivity χ, temperature conductivity κ, and heat capacity C p were studied in Ag 2 Te and Ag 2 Se semiconductors in the region of the phase transition. Two extrema are observed in the temperature dependence χ(T): a maximum in the region of the α' → β' transition and a minimum in the region of the β' → β transition; these extrema are caused by the similar dependence C p (T). It is shown that the α → α' and β' → β transitions are displacement transitions, while the α' → β' transition is of reconstruction type. It is established that the disorder parameter η in silver chalcogenides is highly smeared in the region of the phase transition; therefore, disordering of phases at the point of the phase transition is incomplete: 73, 62, and 48% in Ag 2 Te, Ag 2 Se, and Ag 2 S, respectively. The minimum volumes V ph for new phases are calculated; it is shown that the value of V ph in displacement transitions is larger than in the reconstruction-type transitions

  5. Reformulación teórica de los elementos fonológicos básicos en la lengua de señas colombiana

    Directory of Open Access Journals (Sweden)

    Bermúdez Guzmán Floralba

    2003-06-01

    Full Text Available

    En primera instancia se presenta de manera sucinta el estado actual de la investigación lingüística en la lengua de señas colombiana (LSC; luego enfatiza el propósito del artículo de presentar una propuesta de reformulación de los elementos fonológicos básicos de la lengua de señas colombiana partiendo de reflexiones y del interés por enriquecer la teoría particular de dicha lengua. En este proceso se hace aclaración sobre la terminología lingüística adoptada en el texto y se presenta un sustento teórico con la explicación de los modelos de descripción fonológica más usados en esta lengua (simultaneidad de Stokôc  y secuencialidad de Liddell. Luego, se plantean las dificultades de descripción en la aplicación de estos modelos sobre fenómenos de articulación particulares en la LSC (identificación de las variantes de realización segmental y la restricción semántica de los términos para denominar los segmentos. Allí, y con base en la explicación de algunos ejemplos, se argumenta la propuesta de reformulación y complementación de los modelos descriptivos, en cuya definición concluye el artículo.

  6. Effect of Indium nano-sandwiching on the structural and optical performance of ZnSe films

    Directory of Open Access Journals (Sweden)

    S.E. Al Garni

    Full Text Available In the current study, we attempted to explore the effects of the Indium nanosandwiching on the mechanical and optical properties of the physically evaporated ZnSe thin films by means of X-ray diffractions and ultraviolet spectrophotometry techniques. While the thickness of each layer of ZnSe was fixed at 1.0 μm, the thickness of the nanosandwiched Indium thin films was varied in the range of 25–100 nm. It was observed that the as grown ZnSe films exhibits cubic and hexagonal nature of crystallization as those of the ZnSe powders before the film deposition. The cubic phases weighs ∼70% of the structure. The analysis of this phases revealed that there is a systematic variation process presented by the decreasing of; the lattice constant, compressing strain, stress, stacking faults and dislocation intensity and increasing grain size resulted from increasing the Indium layer thickness in the range of 50–100 nm. In addition, the nanosandwiching of Indium between two layers of ZnSe is observed to enhance the absorbability of the ZnSe. Particularly, at incident photon energy of 2.38 eV the absorbability of the ZnSe films which are sandwiched with 100 nm Indium is increased by 13.8 times. Moreover, increasing the thickness of the Indium layer shrinks the optical energy band gap. These systematic variations in mechanical and optical properties are assigned to the better recrystallization process that is associated with Indium insertion which in turn allows total internal energy redistribution in the ZnSe films through the enlargement of grains. Keywords: ZnSe, Nanosandwiching, Mechanical, Optical gap

  7. The development of the room temperature LWIR HgCdTe detectors for free space optics communication systems

    Science.gov (United States)

    Martyniuk, Piotr; Gawron, Waldemar; Mikołajczyk, Janusz

    2017-10-01

    There are many room temperature applications to include free space optics (FSO) communication system combining quantum cascade lasers sources where HgCdTe long-wave (8-12 micrometer) infrared radiation (LWIR) detector reaching ultrafast response time 109 cmHz1/2/W. Since commercially available FSO could operate separately in SWIR, MWIR and LWIR range - the dual band detectors should be implemented into FSO. This paper shows theoretical performance of the dual band back-to-back MWIR and LWIR HgCdTe detector operating at 300 K pointing out the MWIR active layer influence on LWIR operating regime.

  8. Electronic and optical properties of defect CdIn_2Te_4 chalcopyrite semiconductor: A first principle approach

    International Nuclear Information System (INIS)

    Mishra, S.; Ganguli, B.

    2016-01-01

    We present detailed study of structural, electronic and optical properties of CdIn_2Te_4 compound. The calculations are carried out using Density Functional theory based Tight Binding Linear Muffin Tin Orbital method. The compound is found to be direct band gap semiconductor with a band gap of 1.03 eV. The band gap is within the limit of LDA underestimation. The calculated structural parameters agree well with the available experimental values. We find a decrements of 9.6% in band gap and significant effects on overall electronic and optical properties due to structural distortions. These effects on optical properties come mainly from the change in transition probability. An-isotropic nature of optical properties get enhanced due to structural distortion. The Calculated real & imaginary parts of dielectric constant and static dielectric constant agree well with the available experimental result. - Highlights: • We present ab-initio calculations of electronic & optical properties of CdIn_2Te_4. • Band gap get reduced by 9.6% due to structural distortion. • Structural distortion has significant effects on optical properties. • Anisotropic nature of optical response functions get enhanced by structural distortion. • Calculated dielectric constant agrees with experimental value.

  9. Synthesis and crystal structure of Fe[(Te1.5Se0.5)O5]Cl, the first iron compound with selenate(IV) and tellurate(IV) groups

    Science.gov (United States)

    Akhrorov, Akhmad Yu; Kuznetsova, Elena S.; Aksenov, Sergey M.; Berdonosov, Peter S.; Kuznetsov, Alexey N.; Dolgikh, Valery A.

    2017-12-01

    During the search for selenium analogues of FeTe2O5Cl, the new iron (III) tellurate(IV) selenate(IV) chloride with the composition Fe[(Te1.5Se0.5)O5]Cl was synthesized by chemical vapor transport (CVT) reaction and characterized by TGA-, EDX-,SCXRD-analysis, as well as IR and Raman spectroscopy. It was found that Fe[(Te1.5Se0.5)O5]Cl crystallizes in the monoclinic space group P21/c with unitcell parameters a = 5.183(3) Å, b = 15.521(9) Å, c = 7.128(5) Å and β = 107.16(1)°. The crystal structure of Fe[(Te1.5Se0.5)O5]Cl represents a new structure type and contains electroneutral heteropolyhedral layers formed by dimers of the [FeO5Cl]8- octahedra, linked via common O-O edges, and mixed [Te3SeO10]4- tetramers. Adjacent layers are stacked along the b axis and linked by weak residual bonds. The new compound is stable up to 420 °C. DFT calculations predict Fe[(Te1.5Se0.5)O5]Cl to be a wide-gap semiconductor with the band gap of ca. 2.7 eV.

  10. Fabrication of highly nonlinear germano-silicate glass optical fiber incorporated with PbTe semiconductor quantum dots using atomization doping process and its optical nonlinearity.

    Science.gov (United States)

    Ju, Seongmin; Watekar, Pramod R; Han, Won-Taek

    2011-01-31

    Germano-silicate glass optical fiber incorporated with PbTe semiconductor quantum dots (SQDs) in the core was fabricated by using the atomization process in modified chemical vapor deposition (MCVD) process. The absorption bands attributed to PbTe semiconductor quantum dots in the fiber core were found to appear at around 687 nm and 1055 nm. The nonlinear refractive index measured by the long-period fiber grating (LPG) pair method upon pumping with laser diode at 976.4 nm was estimated to be ~1.5 × 10(-16) m2/W.

  11. Optics of the CuGaSe{sub 2} solar cell for highly efficient tandem concepts; Optik der CuGaSe{sub 2}-Solarzelle fuer hocheffiziente Tandemkonzepte

    Energy Technology Data Exchange (ETDEWEB)

    Schmid, Martina

    2010-01-25

    A principle aim of solar cell research lies in optimizing the exploitation of the incident solar light. Yet, for single junction solar cells there exists an efficiency limit as described by Shockley and Queisser. The only concept realized so far to overcome this threshold is - apart from concentration - the multijunction solar cell. However, any kind of multijunction design poses new challenges: The upper wide-gap solar cell (top cell) needs to show efficient light absorption in the short-wavelength region. At the same time sufficient transmission for long-wavelength light is required which then needs to be absorbed effectively by the low-gap bottom cell. In tandem solar cells a proper light management in top and bottom solar cell is of great importance. This work focuses on chalcopyrite-based tandem solar cells. For the wide-bandgap IR-transparent ZnO:Al/i-ZnO/CdS/CuGaSe{sub 2}/SnO{sub 2}:F/glass solar cell an optical model has been established. Starting from modeling each of the individual layers building the stack the optical behavior of the complete thin film system of the top cell could be described. Carefully selected layer combinations and comparison of experimental and calculated data allowed for the attribution of transmission losses to the distinct material properties. Defects in the absorber are of crucial importance but also free carrier absorption in the window and in the transparent back contact contribute significantly to optical losses. The quantification of the losses was achieved by calculating the effects of reduced top cell transmission on the photo current of a simplified bottom cell. An extension of the optical model allowed to calculate the effective absorption in the individual layers and to determine reflection losses at the interfaces. From these results an optimized top cell stack was derived which is characterized by A) simulation of the monolithic integration, B) reduced layer thicknesses wherever possible from the electrical point of

  12. Study of structural and optical properties of Cd{sub 1-x}Zn{sub x}Se thin films

    Energy Technology Data Exchange (ETDEWEB)

    Wahab, L.A., E-mail: aly_lo2003@yahoo.com [National Center for Radiation Research and Technology, Nasr City, Cairo (Egypt); Zayed, H.A. [University Collage of Women for Art, Science and Education, Ain Shams University, Cairo (Egypt); El-Galil, A.A. Abd [National Center for Radiation Research and Technology, Nasr City, Cairo (Egypt)

    2012-06-01

    Cd{sub 1-x}Zn{sub x}Se (x = 0, 0.5 and 1) thin films have been deposited onto glass substrates using thermal evaporation technique. The lattice constants, grain size, microstrain and dislocation density were studied by using X-ray diffraction. In addition the optical constants were calculated in the wavelength range 400-2500 nm. Transmittance and reflectance were used to calculate the absorption coefficient {alpha} and the optical band gap E{sub g}. The linear relation of ({alpha}h{upsilon}){sup 2} as a function of photon energy h{upsilon} for the thin films illustrated that the films exhibit a direct band gap, which increases with increasing Zn content. This increasing of optical band gap was interpreted in accordance to the increasing in the cohesive energy. Optical constants, such as refractive index n, optical conductivity {sigma}{sub opt}, complex dielectric constant, relaxation time {tau} and dissipation factor tan{delta} were determined. The optical dispersion parameters E{sub 0}, E{sub d} were determined according to Wemple and Di Domenico method. - Highlights: Black-Right-Pointing-Pointer ZnSe thin film has cubic zinc blende structure while CdSe and Cd{sub 0.5}Zn{sub 0.5}Se thin films have hexagonal structure. Black-Right-Pointing-Pointer Grain size of Cd{sub 1-x}Zn{sub x}Se decreases with increasing x (x = 0, 0.5 and 1). Black-Right-Pointing-Pointer Optical band gap increases with increasing x.

  13. Analysis on nonlinear optical properties of Cd (Zn) Se quantum dots synthesized using three different stabilizing agents

    Science.gov (United States)

    J, Joy Sebastian Prakash; G, Vinitha; Ramachandran, Murugesan; Rajamanickam, Karunanithi

    2017-10-01

    Three different stabilizing agents, namely, L-cysteine, Thioglycolic acid and cysteamine hydrochloride were used to synthesize Cd(Zn)Se quantum dots (QDs). It was characterized using UV-vis spectroscopy, x-ray diffraction (XRD) and transmission electron microscopy (TEM). The non-linear optical properties (non-linear absorption and non-linear refraction) of synthesized Cd(Zn)Se quantum dots were studied with z-scan technique using diode pumped continuous wavelaser system at a wavelength of 532 nm. Our (organic) synthesized quantum dots showed optical properties similar to the inorganic materials reported elsewhere.

  14. Electro-optical and dielectric properties of CdSe quantum dots and 6CHBT liquid crystals composites

    Energy Technology Data Exchange (ETDEWEB)

    Singh, U. B.; Pandey, M. B., E-mail: mbpandey@gmail.com [Department of Physics, Vikramajit Singh Sanatan Dharama College, Kanpur-208002 (India); Dhar, R; Pandey, A. S. [Centre of Material Sciences, Institute of Interdisciplinary Studies, University of Allahabad, Allahabad-211002 (India); Kumar, S. [Raman Research Institute, C. V. Raman Avenue, Bangalore-560080 (India); Dabrowski, R. [Institute of Applied Sciences and Chemistry, Military University of Technology, 00-908-Warswa (Poland)

    2014-11-15

    We have prepared the composites of a room temperature nematic liquid crystal namely 4-(trans-4-n-hexylcyclohexyl) isothiocyanatobenzoate (6CHBT) and Cadmium Selenide Quantum Dots (CdSe-QDs) and investigated their electro-optical and dielectric properties. Effect of dispersion of CdSe-QDs on various electro-optical and display parameters of host liquid crystalline material have been studied. Physical parameters, such as switching threshold voltage and splay elastic constant have been altered drastically for composites. Dispersion of QDs in a liquid crystals medium destabilizes nematic ordering of the host and decreases the nematic-to-isotropic transition temperature.

  15. Electro-optical and dielectric properties of CdSe quantum dots and 6CHBT liquid crystals composites

    International Nuclear Information System (INIS)

    Singh, U. B.; Pandey, M. B.; Dhar, R; Pandey, A. S.; Kumar, S.; Dabrowski, R.

    2014-01-01

    We have prepared the composites of a room temperature nematic liquid crystal namely 4-(trans-4-n-hexylcyclohexyl) isothiocyanatobenzoate (6CHBT) and Cadmium Selenide Quantum Dots (CdSe-QDs) and investigated their electro-optical and dielectric properties. Effect of dispersion of CdSe-QDs on various electro-optical and display parameters of host liquid crystalline material have been studied. Physical parameters, such as switching threshold voltage and splay elastic constant have been altered drastically for composites. Dispersion of QDs in a liquid crystals medium destabilizes nematic ordering of the host and decreases the nematic-to-isotropic transition temperature

  16. Thickness dependent structural, optical and electrical properties of Se85In12Bi3 nanochalcogenide thin films

    Science.gov (United States)

    Tripathi, Ravi P.; Zulfequar, M.; Khan, Shamshad A.

    2018-04-01

    Our aim is to study the thickness dependent effects on structure, electrical and optical properties of Se85In12Bi3 nanochalcogenide thin films. Bulk alloy of Se85In12Bi3 was synthesized by melt-quenching technique. The amorphous as well as glassy nature of Se85In12Bi3 chalcogenide was confirmed by non-isothermal Differential Scanning Calorimetry (DSC) measurements. The nanochalcogenide thin films of thickness 30, 60 and 90 nm were prepared on glass/Si wafer substrate using Physical Vapour Condensation Technique (PVCT). From XRD studies it was found that thin films have amorphous texture. The surface morphology and particle size of films were studied by Field Emission Scanning Electron Microscope (FESEM). From optical studies, different optical parameters were estimated for Se85In12Bi3 thin films at different thickness. It was found that the absorption coefficient (α) and extinction coefficient (k) increases with photon energy and decreases with film thickness. The optical absorption process followed the rule of indirect transitions and optical band gap were found to be increase with film thickness. The value of Urbach energy (Et) and steepness parameter (σ) were also calculated for different film thickness. For electrical studies, dc-conductivity measurement was done at different temperature and activation energy (ΔEc) were determined and found to be increase with film thickness.

  17. Tuning the Electronic, Optical, and Magnetic Properties of Monolayer GaSe with a Vertical Electric Field

    Science.gov (United States)

    Ke, Congming; Wu, Yaping; Guo, Guang-Yu; Lin, Wei; Wu, Zhiming; Zhou, Changjie; Kang, Junyong

    2018-04-01

    Inspired by two-dimensional material with their unique physical properties and innovative device applications, here we report a design framework on monolayer GaSe, an important member of the two-dimensional material family, in an effort to tune the electronic, optical, and magnetic properties through a vertical electric field. A transition from indirect to direct band gap in monolayer GaSe is found with an electric field of 0.09 V /Å . The giant Stark effect results in a reduction of the band gap with a Stark coefficient of 3.54 Å. Optical and dielectric properties of monolayer GaSe are dependent on the vertical electric field. A large regulation range for polarization E ∥c ^ is found for the static dielectric constant. The optical anisotropy with the dipole transition from E ∥c ^ to E ⊥c ^ is achieved. Induced by the spin-orbit coupling, spin-splitting energy at the valence band maximum increases linearly with the electric field. The effective mass of holes is highly susceptible to the vertical electric field. Switchable spin-polarization features in spin texture of monolayer GaSe are predicted. The tunable electronic, optical, and magnetic properties of monolayer GaSe hold great promise for applications in both the optoelectronic and spintronic devices.

  18. Preparation of InSe Thin Films by Thermal Evaporation Method and Their Characterization: Structural, Optical, and Thermoelectrical Properties

    Directory of Open Access Journals (Sweden)

    Sarita Boolchandani

    2018-01-01

    Full Text Available The indium selenium (InSe bilayer thin films of various thickness ratios, InxSe(1-x (x = 0.25, 0.50, 0.75, were deposited on a glass substrate keeping overall the same thickness of 2500 Ǻ using thermal evaporation method under high vacuum atmosphere. Electrical, optical, and structural properties of these bilayer thin films have been compared before and after thermal annealing at different temperatures. The structural and morphological characterization was done using XRD and SEM, respectively. The optical bandgap of these thin films has been calculated by Tauc’s relation that varies within the range of 1.99 to 2.05 eV. A simple low-cost thermoelectrical power measurement setup is designed which can measure the Seebeck coefficient “S” in the vacuum with temperature variation. The setup temperature variation is up to 70°C. This setup contains a Peltier device TEC1-12715 which is kept between two copper plates that act as a reference metal. Also, in the present work, the thermoelectric power of indium selenide (InSe and aluminum selenide (AlSe bilayer thin films prepared and annealed in the same way is calculated. The thermoelectric power has been measured by estimating the Seebeck coefficient for InSe and AlSe bilayer thin films. It was observed that the Seebeck coefficient is negative for InSe and AlSe thin films.

  19. Characterization of the phase composition, crystal structure and superconducting properties of Fe{sub 1.02}Se{sub y}Te{sub 1−y−x}S{sub x}

    Energy Technology Data Exchange (ETDEWEB)

    Abouhaswa, A.S., E-mail: aliabohaswa@hotmail.com [Institute of Natural Sciences, Ural Federal University, 620083, Ekaterinburg (Russian Federation); Merentsov, A.I. [Institute of Natural Sciences, Ural Federal University, 620083, Ekaterinburg (Russian Federation); Baranov, N.V. [Institute of Natural Sciences, Ural Federal University, 620083, Ekaterinburg (Russian Federation); M.N. Miheev Institute of Metal Physics, Ural Branch of RAS, 620990, Ekaterinburg (Russian Federation)

    2016-08-15

    Highlights: • The Fe{sub 1.02}Se{sub 0.5}Te{sub 0.5−x}S{sub x} and Fe{sub 1.02}Se{sub 0.4}Te{sub 0.6−x}S{sub x} samples have been synthesized. • The S for Te substitution results in a small expansion of the crystal lattice of the PbO-type phase. • This expansion is attributed to changes in the phase relation and chemical composition of phases. • There is a correlation between the changes of T{sub c} and lattice parameters of the PbO-type phase. - Abstract: Two series of the Fe{sub 1.02}Se{sub 0.5}Te{sub 0.5–x}S{sub x} (I) and Fe{sub 1.02}Se{sub 0.4}Te{sub 0.6–x}S{sub x} (II) samples with the sulfur for tellurium substitution and with the invariable Se concentrations have been synthesized and studied by means of X-ray diffraction, scanning electron microscopy, electrical resistivity and magnetic susceptibility measurements. The superconducting PbO-type phase is found to persists in the first series up to x = 0.4 and in the second one up to x = 0.5. Despite the lower ionic radius of sulfur in comparison with tellurium the replacement of tellurium by sulfur does not lead to contraction of the unit cell volume of the superconducting phase in both I and II series with ternary mixture of chalcogens. Variations of the lattice parameters caused by the S for Te substitution in the Fe{sub 1.02}Se{sub 0.5}Te{sub 0.5–x}S{sub x} and Fe{sub 1.02}Se{sub 0.4}Te{sub 0.6–x}S{sub x} samples are found to be less pronounced than that reported for the Fe{sub 1.02}Te{sub 0.5}Se{sub 0.5-x}S{sub x} system and are accompanied by lowering of the critical temperature. The behavior of the lattice parameters and critical temperature of Fe(S,Se,Te) materials with the ternary mixture of chalcogens at substitutions is ascribed to the changes in the volume fraction and chemical compositions of the coexisting tetragonal and hexagonal phases.

  20. Molecular structures of Se(SCH3)2 and Te(SCH3)2 using gas-phase electron diffraction and ab initio and DFT geometry optimisations.

    Science.gov (United States)

    Fleischer, Holger; Wann, Derek A; Hinchley, Sarah L; Borisenko, Konstantin B; Lewis, James R; Mawhorter, Richard J; Robertson, Heather E; Rankin, David W H

    2005-10-07

    The molecular structures of Se(SCH(3))(2) and Te(SCH(3))(2) were investigated using gas-phase electron diffraction (GED) and ab initio and DFT geometry optimisations. While parameters involving H atoms were refined using flexible restraints according to the SARACEN method, parameters that depended only on heavy atoms could be refined without restraints. The GED-determined geometric parameters (r(h1)) are: rSe-S 219.1(1), rS-C 183.2(1), rC-H 109.6(4) pm; angleS-Se-S 102.9(3), angleSe-S-C 100.6(2), angleS-C-H (mean) 107.4(5), phiS-Se-S-C 87.9(20), phiSe-S-C-H 178.8(19) degrees for Se(SCH(3))(2), and rTe-S 238.1(2), rS-C 184.1(3), rC-H 110.0(6) pm; angleS-Te-S 98.9(6), angleTe-S-C 99.7(4), angleS-C-H (mean) 109.2(9), phiS-Te-S-C 73.0(48), phiTe-S-C-H 180.1(19) degrees for Te(SCH(3))(2). Ab initio and DFT calculations were performed at the HF, MP2 and B3LYP levels, employing either full-electron basis sets [3-21G(d) or 6-31G(d)] or an effective core potential with a valence basis set [LanL2DZ(d)]. The best fit to the GED structures was achieved at the MP2 level. Differences between GED and MP2 results for rS-C and angleS-Te-S were explained by the thermal population of excited vibrational states under the experimental conditions. All theoretical models agreed that each compound exists as two stable conformers, one in which the methyl groups are on the same side (g(+)g(-) conformer) and one in which they are on different sides (g(+)g(+) conformer) of the S-Y-S plane (Y = Se, Te). The conformational composition under the experimental conditions could not be resolved from the GED data. Despite GED R-factors and ab initio and DFT energies favouring the g(+)g(+) conformer, it is likely that both conformers are present, for Se(SCH(3))(2) as well as for Te(SCH(3))(2).

  1. The optical, vibrational, structural and elasto-optic properties of Zn_0_._2_5Cd_0_._7_5S_ySe_1_-_y quaternary alloys

    International Nuclear Information System (INIS)

    Paliwal, U.; Swarkar, C. B.; Sharma, M. D.; Joshi, K. B.

    2016-01-01

    The optical, vibrational, structural and elasto-optic properties of quaternary II-VI alloys Zn_0_._2_5Cd_0_._7_5S_0_._2_5Se_0_._7_5, Zn_0_._2_5Cd_0_._7_5S_0_._5_0Se_0_._5_0 and Zn_0_._2_5Cd_0_._7_5S_0_._7_5Se_0_._2_5 are presented. Within the empirical pseudopotential method (EPM) the disorder effects are modeled via modified virtual crystal approximation (MVCA). The computed bandgaps and the refined form factors are utilized to evaluate optical, vibrational, structural and elasto-optic properties. The refractive index (n), static (ε_0) and high frequency dielectric (ε_∞) constants are calculated to reveal optical behavior of alloys. The longitudinal ω_L_O(0) and transverse ω_T_O(0) optical frequencies are obtained to see vibrational characteristics. Moreover, the elastic constants (c_i_j) and bulk moduli (B) are computed by combining the EPM with Harrison bond orbital model. The elasto-optic nature of alloys is examined by computing the photo-elastic constants. These values are significant with regard to the opto-electronic applications especially when no experimental data are available on this system.

  2. Interlocked chiral/polar domain walls and large optical rotation in Ni3TeO6

    Directory of Open Access Journals (Sweden)

    Xueyun Wang

    2015-07-01

    Full Text Available Chirality, i.e., handedness, pervades much of modern science from elementary particles, DNA-based biology to molecular chemistry; however, most of the chirality-relevant materials have been based on complex molecules. Here, we report inorganic single-crystalline Ni3TeO6, forming in a corundum-related R3 structure with both chirality and polarity. These chiral Ni3TeO6 single crystals exhibit a large optical specific rotation (α—1355° dm−1 cm3 g−1. We demonstrate, for the first time, that in Ni3TeO6, chiral and polar domains form an intriguing domain pattern, resembling a radiation warning sign, which stems from interlocked chiral and polar domain walls through lowering of the wall energy.

  3. Optical properties of electrochemically deposited CuInSe sub 2 thin films

    Energy Technology Data Exchange (ETDEWEB)

    Guillen, C; Herrero, J [Inst. de Energias Renovables (CIEMAT), Madrid (Spain)

    1991-11-01

    Polycrystalline thin films of CuInSe{sub 2} within a wide composition range have been electrochemically deposited. Their optical properties in the near-infrared and visible range, 400-2000 nm, have been studied in relation to the deposition potential and film thickness. An absorption coefficient ({alpha}) as high as 10{sup 5} cm{sup -1} is observed at short wavelength ({lambda} < 700 nm), but near the band edge {alpha} has a value about 10{sup 4} cm{sup -1}. The observed absorption coefficient variation is due to an allowed direct transition with an energy in the range 0.88-0.96 eV and an additional forbidden direct transition with an energy in the range 1.32-1.41 eV, where the absorption coefficient depends on the deposition potential, and the possible phase nature of the material, with band gap narrowing when the potential becomes anodic. The values of {alpha} and transition energies also depend on the film thickness for samples up to 0.6 {mu}m thick. (orig.).

  4. Exciton diamagnetic shift and optical properties in CdSe nanocrystal quantum dots in magnetic fields

    Science.gov (United States)

    Wu, Shudong; Cheng, Liwen

    2018-04-01

    The magnetic field dependence of the optical properties of CdSe nanocrystal quantum dots (NQDs) is investigated theoretically using a perturbation method within the effective-mass approximation. The results show that the magnetic field lifts the degeneracy of the electron (hole) states. A blue-shift in the absorption spectra of m ≥ 0 exciton states is observed while the absorption peak of m attributed to the interplay of the orbital Zeeman effect and the additive confinement induced by the magnetic field. The excitonic absorption coefficient is almost independent of B in the strong confinement regime. The applied magnetic field causes the splitting of degenerated exciton states, resulting in the new absorption peaks. Based on the first-order perturbation theory, we propose the analytical expressions for the exciton binding energy, exciton transition energy and exciton diamagnetic shift of 1s, 1p-1, 1p0, 1p1, 1d-2, 1d-1, 1d0, 1d1, 1d2 and 2s exciton states on the applied magnetic field in the strong confinement regime.

  5. Optical and structural properties of FeSe2 thin films obtained by selenization of sprayed amorphous iron oxide films

    International Nuclear Information System (INIS)

    Ouertani, B.; Ouerfelli, J.; Saadoun, M.; Zribi, M.; Rabha, M.Ben; Bessais, B.; Ezzaouia, H.

    2006-01-01

    We report in this work the optical and structural properties of iron diselenide films (FeSe 2 ) obtained by selenization under vacuum of amorphous iron oxide films predeposited by spray pyrolysis. The structure of the FeSe 2 films was investigated by scanning electron microscopy (SEM), microprobe analyses, atomic force microscopy (AFM) and X-ray diffraction (XRD). XRD and micro-probe analyses showed that FeSe 2 as well as FeSe 2-x phases begin to appear at a selenization temperature of 500 deg. C. As the selenization temperature rises, the iron diselenide films become more stoichiometric with a dominance of the FeSe 2 phase. At 550 deg. C, a single FeSe 2 phase having good crystallinity was obtained. At 600 deg. C, two phases were detected: the major one corresponds to Fe 3 O 4 , and the minor one to FeSe 2 . SEM surface views show that FeSe 2 films have granular structure with small spherical crystallites. However, layered and clustered FeSe 2 films were found, respectively, at 550 deg. C and 600 deg. C. Absorption measurements show that iron diselenide films have a direct and an indirect gaps of about 1.03 eV and 0.3 eV, which were suggested to be due to the stoichiometric FeSe 2 phase and to a Fe-rich non-stoichiometric phase, respectively

  6. The lanthanoid(III) chloride oxoselenates(IV) MCl[SeO3] (M = Sm - Lu) with HoCl[TeO3]- or B-type structure

    International Nuclear Information System (INIS)

    Lipp, C.; Schleid, T.

    2008-01-01

    The B-type lanthanoid(III) chloride oxoselenates(IV) MCl[SeO 3 ] (M = Sm - Lu) crystallize in the orthorhombic space group Pnma (no. 62) with Z = 4 in the structure type of HoCl[TeO 3 ]. Their lattice constants are decreasing following the lanthanoid contraction from a = 730.01(7), b = 707.90(7), c 895.64(9) pm for SmCl[SeO 3 ] to a = 714.63(7), b = 681.76(7), c = 864.05(9) pm for LuCl[SeO 3 ]. In contrast to NdCl[SeO 3 ], the only representative of the A-type structure, where the coordination numbers of the Nd 3+ cations are 7+2 and 8, the B-type structure is dominated by pentagonal bipyramids [MO 5 Cl 2 ] 9- (CN(M 3+ ) = 7), which are connected via trans-oriented O..O edges to ∞ 1 {[MO 4/2 e O 1/1 t Cl 2/1 t ] 5- } chains (e = edge-sharing, t = terminal) running parallel to the [010] direction. Their inclination relative to each other allows for an alternating interconnection of these chains via Cl - and ψ 1 -tetrahedral [SeO 3 ] 2- anions to form a three-dimensional structure. The distances within the [SeO 3 ] 2- groups are in the normal range (d(Se-O) = 165 - 172 pm), while those of the O 2- and Cl - anions to the central M 3+ cation diminish in dependence of the increasing atomic number (d(M-O) = 226 - 244 pm / 216 - 232 pm, d(M-Cl) 277 - 278 pm / 266 - 270 pm, M = Sm / Lu). For the synthesis of the chloride oxoselenates(IV) MCl[SeO 3 ] the respective lanthanoid sesquioxide (M 2 O 3 ) and selenium dioxide (SeO 2 ) were reacted with either an eutectic mixture of RbCl and LiCl or with the corresponding lanthanoid trichloride (MCl 3 ) in evacuated silica ampoules for either five weeks at 500 C or one week at 850 C. (orig.)

  7. Evaluation of TeO2 content on the optical and spectroscopic properties of Yb3 +-doped calcium borotellurite glasses

    Science.gov (United States)

    Lima, A. M. O.; Gomes, J. F.; Hegeto, F. L.; Medina, A. N.; Steimacher, A.; Barboza, M. J.

    2018-03-01

    This paper reports the synthesis and the characterization of Yb3 +-doped calcium borotellurite (CaBTeX) glasses with composition 10CaF2-(29.5 - 0.4x)CaO-(60 - 0.6x)B2O3-xTeO2-0.5Yb2O3 (x = 10, 16, 22, 31 and 54 mol%). The results of XRD confirm the amorphous character of all the samples. The density, molar volume, refractive index and electronic polarizability values show an increase with TeO2 content. Otherwise, the optical band gap energy shows a decrease with the increase of TeO2 content. The replacement of CaO and B2O3 by TeO2 changes the glass structure, which decreases the excited Yb3 +/cm3 and, consequently, the luminescence intensity. The temperature dependence of luminescence was studied for all the samples up to 420 K. The fluorescence lifetime does not change significantly due to TeO2 addition. In addition, absorption and emission cross section were calculated and present high values as compared to other tellurite and phosphate glasses.

  8. Single-step in-situ synthesis and optical properties of ZnSe nanostructured dielectric nanocomposites

    Energy Technology Data Exchange (ETDEWEB)

    Dey, Chirantan; Rahaman Molla, Atiar; Tarafder, Anal; Karmakar, Basudeb, E-mail: basudebk@cgcri.res.in [CSIR-Central Glass and Ceramic Research Institute, Glass Science and Technology Section, Glass Division, 196, Raja S. C. Mullick Road, 700032 Kolkata (India); Kr Mishra, Manish; De, Goutam [CSIR-Central Glass and Ceramic Research Institute, Nano-Structured Materials Division, 196, Raja S. C. Mullick Road, 700032 Kolkata (India); Goswami, Madhumita; Kothiyal, G. P. [Glass and Advanced Ceramics Division, Bhaba Atomic Research Centre, Trombay, 400085 Mumbai (India)

    2014-04-07

    This work provides the evidence of visible red photoluminescent light emission from ZnSe nanocrystals (NCs) grown within a dielectric (borosilicate glass) matrix synthesized by a single step in-situ technique for the first time and the NC sizes were controlled by varying only the concentration of ZnSe in glass matrix. The ZnSe NCs were investigated by UV-Vis optical absorption spectroscopy, Raman spectroscopy, and transmission electron microscopy (TEM). The sizes of the ZnSe NCs estimated from the TEM images are found to alter in the range of 2–53 nm. Their smaller sizes of the NCs were also calculated by using the optical absorption spectra and the effective mass approximation model. The band gap enlargements both for carrier and exciton confinements were evaluated and found to be changed in the range of 0–1.0 eV. The Raman spectroscopic studies showed blue shifted Raman peaks of ZnSe at 295 and 315 cm{sup −1} indicating phonon confinement effect as well as compressive stress effect on the surface atoms of the NCs. Red photoluminescence in ZnSe-glass nanocomposite reveals a broad multiple-peak structure due to overlapping of emission from NC size related electron-hole recombination (∼707 nm) and emissions from defects to traps, which were formed due to Se and Zn vacancies signifying potential application in photonics.

  9. Thermoelectric properties of n-type Bi{sub 2}(Te{sub 1{minus}x}Se{sub x}){sub 3} fabricated by mechanical alloying and hot pressing

    Energy Technology Data Exchange (ETDEWEB)

    Kim, H J; Choi, J S; Oh, T S; Hyun, D B

    1997-07-01

    Thermoelectric properties of polycrystalline Bi{sub 2}(Te{sub 1{minus}x}Se{sub x}){sub 3} (0.05 {le} x {le} 0.25), fabricated by mechanical alloying and hot pressing, have been investigated. Formation of n-type Bi{sub 2}(Te{sub 0.9}Se{sub 0.1}){sub 3} alloy powders was completed by mechanical alloying for 3 hours at ball-to-material ratio of 5:1, and processing time for Bi{sub 2}(Te{sub 1{minus}x}Se{sub x}){sub 3} formation increased with Bi{sub 2}Se{sub 3} content x. Figure-of-merit of Bi{sub 2}(Te{sub 0.9}Se{sub 0.1}) was markedly increased by hot pressing at temperatures above 450 C, and maximum value of 1.9 x 10{sup {minus}3}/K was obtained by hot pressing at 550 C. With addition of 0.015 wt% Bi as acceptor dopant, figure-of-merit of Bi{sub 2}(Te{sub 0.9}Se{sub 0.1}){sub 3} was hot pressed at 550 C, could be improved to 2.1 x 10{sup {minus}3}/K. When Bi{sub 2}(Te{sub 1{minus}x}Se{sub x}){sub 3} was hot pressed at 550 C, figure-of-merit increased from 1.14 x 10{sup {minus}3}/K to 1.92 x 10{sup {minus}3}/K with increasing Bi{sub 2}Se{sub 3} content x from 0.05 to 0.15, and then decreased to 1.30 x 10{sup {minus}3}/K for x = 0.25 composition.

  10. Optical and structural characterization of GaSb and Te-doped GaSb single crystals

    International Nuclear Information System (INIS)

    Tirado-Mejia, L.; Villada, J.A.; Rios, M. de los; Penafiel, J.A.; Fonthal, G.; Espinosa-Arbelaez, D.G.; Ariza-Calderon, H.; Rodriguez-Garcia, M.E.

    2008-01-01

    Optical and structural properties of GaSb and Te-doped GaSb single crystals are reported herein. Utilizing the photoreflectance technique, the band gap energy for doped samples was obtained at 0.814 eV. Photoluminescence (PL) spectra showed a peak at 0.748 eV that according to this research, belongs to electronic states of pure GaSb and not to the longitudinal optical (LO) phonon replica as has been reported by other authors. Analysis of the full width at half maximum (FWHM) values of X-ray diffraction, as well as micro-Raman peaks showed that the inclusion of Te decreases the crystalline quality

  11. Optical spectroscopy of lanthanide ions in ZnO-TeO2 glasses.

    Science.gov (United States)

    Rolli, R; Wachtler, K; Wachtler, M; Bettinelli, M; Speghini, A; Ajò, D

    2001-09-01

    Zinc tellurite glasses of compositions 19ZnO-80TeO2-1Ln2O3 with Ln = Eu, Er, Nd and Tm were prepared by melt quenching. The absorption spectra were measured and from the experimental oscillator strengths of the f-->f transitions the Judd-Ofelt parameters ohm(lambda) were obtained. The values of the ohm(lambda) parameters are in the range usually observed for oxide glasses. For Nd3+ and Er3+, luminescence spectra in the near infrared were measured and the stimulated emission cross sections sigma(p) were evaluated for some laser transitions. The high values of sigma(p), especially for Nd3+, make them possible candidates for optical applications. Fluorescence line narrowing (FLN) spectra of the Eu3+ doped glass were measured at 20 K, and the energies of the Stark components of the 7F1 and 7F2 states were obtained. A crystal field analysis was carried out assuming a C2v site symmetry. The behaviour of the crystal field ratios B22/B20 and B44/B40 agrees reasonably well with the values calculated using the geometric model proposed by Brecher and Riseberg. The crystal field strength at the Eu3+ sites appears to be very low compared to other oxide glasses.

  12. Optically detected electron spin-flip resonance in CdMnTe

    International Nuclear Information System (INIS)

    Zeng, S.; Smith, L.C.; Davies, J.J.; Wolverson, D.; Bingham, S.J.; Aliev, G.N.

    2006-01-01

    We show that the spin-flip of electrons at neutral donors in a dilute magnetic semiconductor can be observed directly by means of optically-detected magnetic resonance (ODMR). Spectra obtained at 105 GHz for a bulk crystal of Cd 1-x Mn x Te with x = 0.005 showed strong signals with g -values ranging between 12 (at 4.2 K) and 35 (at 1.7 K), with magnetic resonance linewidths ranging from 0.3 Tesla to 0.1 Tesla at the lowest temperature. In energy terms, these linewidths are independent of temperature and agree with those in spin-flip Raman spectra from the same specimen. The line broadening is caused by fluctuations in the number of manganese ions that interact with a particular donor and an analysis of this leads to a value for the donor Bohr radius of 4.5 nm. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  13. EFECTO DEL ESPESOR EN LAS PROPIEDADES SUPERCONDUCTORAS Y ESTRUCTURALES DE PELÍCULAS DELGADAS DE FeSe0,5Te0,5

    Directory of Open Access Journals (Sweden)

    Oscar Rodríguez

    2012-07-01

    Full Text Available En este trabajo se investiga la influencia del espesor de la capa de FeSe0,5Te0,5 en las propiedades cristalinas y superconductoras de las películas depositadas sobre una capa buffer de hierro (Fe en sustratos de MgAl2O4, por el método de deposición por láser pulsado (PLD. El espesor de las capas superconductoras producidas son ~55nm y ~134nm. La película con menor espesor presenta mejores propiedades de textura (crecimiento orientado y una menor rugosidad superficial (RMS; verificadas por difracción de rayos X y AFM respectivamente. Esta misma película presenta una transición marcada al estado superconductor y una mayor temperatura crítica a diferencia de la película de mayor espesor. Se discute el efecto del espesor en las tensiones de la red superconductora.

  14. Effect of high pressure sintering and annealing on microstructure and thermoelectric properties of nanocrystalline Bi2Te2.7Se0.3 doped with Gd

    Institute of Scientific and Technical Information of China (English)

    Ping Zou; Guiying Xun; Song Wang; Penglei Chen; Fengzhu Huang

    2014-01-01

    Bi2Te2.7Se0.3 of high performance doped with Gd bulk materials was prepared by a high pressure (6.0 GPa) sintering (HPS) method at 593 K, 633 K, 673 K and 693 K. The sample was then annealed for 36 h in a vacuum at 633 K. The phase composition, crystal structure and morphology of the sample were analyzed by X-ray diffraction and scanning electron microscopy. The electric conductivity, Seebeck coefficient, and thermal conductivity aspects of the sample were measured from 298 K to 473 K. The results show that high pressure sintering and the doping with Gd has a great effect on the crystal structure and the thermoelectric properties of the samples. The samples are consisted of nanoparticles before and after annealing, and these nanostructures have good stability at high temperature. HPS together with annealing can improve the TE properties of the sample by decreasing the thermal conductivity of the sample with nanostructures. The maximum ZT value of 0.74 was obtained at 423 K for the sample, which was sintered at 673 K and then annealed at 633 K for 36 h. Compared with the zone melting sample, it was increased by 85%at 423 K. Hence the temperature of the maximum of figure of merit was increased. The results can be applied to the field of thermoelectric power generation materials.

  15. Systematic research on Ag2X (X = O, S, Se, Te) as visible and near-infrared light driven photocatalysts and effects of their electronic structures

    Science.gov (United States)

    Jiang, Wei; Wu, Zhaomei; Zhu, Yingming; Tian, Wen; Liang, Bin

    2018-01-01

    Four silver chalcogen compounds, Ag2O, Ag2S, Ag2Se and Ag2Te, can be utilized as visible-light-driven photocatalysts. In this research, the electronic structures of these compounds were analyzed by simulation and experiments to systematically reveal the relationship between photocatalytic performance and energetic structure. All four chalcogenides exhibited interesting photocatalytic activities under ultraviolet, visible and near-infrared light. However, their photocatalytic performances and stability significantly depended on the band gap width, and the valence band and conduct band position, which was determined by their composition. Increasing the X atomic number from O to Te resulted in the upward movement of the valence band top and the conduct band bottom, which resulted in narrower band gaps, a wider absorption spectrum, a weaker photo-oxidization capacity, a higher recombination probability of hole and electron pairs, lower quantum efficiency, and worse stability. Among them, Ag2O has the highest photocatalytic performance and stability due to its widest band gap and lowest position of VB and CB. The combined action of photogenerated holes and different radicals, depending on the different electronic structures, including anion ozone radical, hydroxide radical, and superoxide radical, was observed and understood. The results of experimental observations and simulations of the four silver chalcogen compounds suggested that a proper electronic structure is necessary to obtain a balance between photocatalytic performance and absorbable light region in the development of new photocatalysts.

  16. Recent Progress in the Design of Advanced Cathode Materials and Battery Models for High-Performance Lithium-X (X = O2 , S, Se, Te, I2 , Br2 ) Batteries.

    Science.gov (United States)

    Xu, Jiantie; Ma, Jianmin; Fan, Qinghua; Guo, Shaojun; Dou, Shixue

    2017-07-01

    Recent advances and achievements in emerging Li-X (X = O 2 , S, Se, Te, I 2 , Br 2 ) batteries with promising cathode materials open up new opportunities for the development of high-performance lithium-ion battery alternatives. In this review, we focus on an overview of recent important progress in the design of advanced cathode materials and battery models for developing high-performance Li-X (X = O 2 , S, Se, Te, I 2 , Br 2 ) batteries. We start with a brief introduction to explain why Li-X batteries are important for future renewable energy devices. Then, we summarize the existing drawbacks, major progress and emerging challenges in the development of cathode materials for Li-O 2 (S) batteries. In terms of the emerging Li-X (Se, Te, I 2 , Br 2 ) batteries, we systematically summarize their advantages/disadvantages and recent progress. Specifically, we review the electrochemical performance of Li-Se (Te) batteries using carbonate-/ether-based electrolytes, made with different electrode fabrication techniques, and of Li-I 2 (Br 2 ) batteries with various cell designs (e.g., dual electrolyte, all-organic electrolyte, with/without cathode-flow mode, and fuel cell/solar cell integration). Finally, the perspective on and challenges for the development of cathode materials for the promising Li-X (X = O 2 , S, Se, Te, I 2 , Br 2 ) batteries is presented. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Synchronous γ (Co60) photons and thermal processing induced insulator metal transition in amorphous chalcogenide As4Se3Te3 composition

    Science.gov (United States)

    El-Sayed, S. A.; Morsy, M. A.

    2018-05-01

    Amorphous chalcogenide composition AS4Se3Te3 is prepared by conventional quenching technique. The separate annealing or γ quanta irradiation not effect on the dc conductivity properties of the prepared composition. When the prepared samples are subjected to simultaneous annealing at temperature 413 K and γ quanta irradiation the dc conductivity increases. The dark dc conductivity increases by increasing the time of exposure to γ irradiation. At irradiation dose 1.47 × 104 Gy the dc conductivity starts to have metallic like conductivity character. These samples could be used as high temperature γ quanta dosimeter. By applying scaling theory on the samples irradiated with different dose of γ irradiation the critical exponents are determined and found to be temperature tends to zero. The steric value is low in the insulator side of conductivity, but high and almost saturated in the metallic side of conductivity.

  18. Research Update: Point defects in CdTexSe1−x crystals grown from a Te-rich solution for applications in detecting radiation

    International Nuclear Information System (INIS)

    Gul, R.; Roy, U. N.; Bolotnikov, A. E.; Camarda, G. S.; Cui, Y.; Hossain, A.; Yang, G.; James, R. B.; Lee, W.; Cui, Y.; Burger, A.

    2015-01-01

    We investigated cadmium telluride selenide (CdTeSe) crystals, newly grown by the Traveling Heater Method (THM), for the presence and abundance of point defects. Current Deep Level Transient spectroscopy (I-DLTS) was used to determine the energies of the traps, their capture cross sections, and densities. The bias across the detectors was varied from 1 to 30 V. Four types of point defects were identified, ranging from 10 meV to 0.35 eV. Two dominant traps at energies of 0.18 eV and 0.14 eV were studied in depth. Cd vacancies are found at lower concentrations than other point defects present in the material

  19. Contribution to the study of electronic structure of crystalline semiconductors (Si, Ge, GaAs, Gap, ZnTe, ZnSe

    Directory of Open Access Journals (Sweden)

    Bouhafs B.

    2012-06-01

    Full Text Available The band structure of semiconductors was described by several theorists since the Fifties. The main objective of the present paper is to do a comparative study between various families of semi-conductors IV (Si,Ge, III-V (GaAs, GaP and II-VI (ZnSe, ZnTe with both methods; tight Binding1 method and pseudo potential method2. This work enables us to understand as well as the mechanism of conduction process in these semiconductors and powers and limits of the above methods. The obtained results allow to conclude that both methods are in a good agreement to describe the morphology of band structures of the cited semiconductors. This encourages us to study in the future the electronic behaviour through the structure of bands for more complex systems such as the heterostructures.

  20. Jahn-Teller coupling of Cr2+ ion with degenerate modes in ZnS, ZnSe, and ZnTe crystals: microscopic treatment

    International Nuclear Information System (INIS)

    Natadze, A.L.; Ryskin, A.I.

    1980-01-01

    The Jahn-Teller (JT) interaction energy is calculated for 5 T 2 and 5 E states of the Cr 2+ ion in ZnS, ZnSe, and ZnTe crystals. The calculations are made within the framework of a particular microscopic model of the crystal field in the distorted crystal (model of point-like exchange charges), the multimode interaction is taken into account. For the 5 T 2 term the energies of interaction with tetragonal and trigonal modes are of the same order of magnitude. This circumstance results in a small height of the barriers that separate various minima of the adiabatic potential and is responsible for the dynamic aspect of the static JT effect in these systems. (author)

  1. Magnetic-field-induced crossover from the inverse Faraday effect to the optical orientation in EuTe

    Science.gov (United States)

    Pavlov, V. V.; Pisarev, R. V.; Nefedov, S. G.; Akimov, I. A.; Yakovlev, D. R.; Bayer, M.; Henriques, A. B.; Rappl, P. H. O.; Abramof, E.

    2018-05-01

    A time-resolved optical pump-probe technique has been applied for studying the ultrafast dynamics in the magnetic semiconductor EuTe near the absorption band gap. We show that application of external magnetic field up to 6 T results in crossover from the inverse Faraday effect taking place on the femtosecond time scale to the optical orientation phenomenon with an evolution in the picosecond time domain. We propose a model which includes both these processes, possessing different spectral and temporal properties. The circularly polarized optical pumping induces the electronic transition 4 f 7 5 d 0 → 4 f 6 5 d 1 forming the absorption band gap in EuTe. The observed crossover is related to a strong magnetic-field shift of the band gap in EuTe at low temperatures. It was found that manipulation of spin states on intrinsic defect levels takes place on a time scale of 19 ps in the applied magnetic field of 6 T.

  2. Composition determination of CdS sub x Se sub 1-x mixed crystals by optical dispersion

    Energy Technology Data Exchange (ETDEWEB)

    Iliev, I; Dimov, T; Ribarov, D [Pedagogical High School, Schumen (Bulgaria); Lange, H [Akademie der Wissenschaften der DDR, Berlin (German Democratic Republic). Zentralinstitut fuer Elektronenphysik

    1989-10-16

    An optical dispersion method has been developed determining the CdS/CdSe ratio in CdS{sub x}Se{sub 1-x} mixed crystals from the relationship between position of the isotropic point (birefrigence becomes zero for a definite wavelength at the absorption edge) and chemical composition x. Birefrigence spectra and piezo-optic spectra of samples with x = 0.2, 0.6, and 0.875 give the spectral position of the isotropic point (ip). A curve of wavelength of ip versus x of CdS{sub x}Se{sub 1-x} is evaluated by the least-squares procedure and tested by X-ray fluorescence analysis.

  3. Hydride generation atomic fluorescence spectrometric determination of As, Bi, Sb, Se(IV) and Te(IV) in aqua regia extracts from atmospheric particulate matter using multivariate optimization

    International Nuclear Information System (INIS)

    Moscoso-Perez, Carmen; Moreda-Pineiro, Jorge; Lopez-Mahia, Purificacion; Muniategui-Lorenzo, Soledad; Fernandez-Fernandez, Esther; Prada-Rodriguez, Dario

    2004-01-01

    A highly sensitive and simple method, based on hydride generation and atomic fluorescence detection, has been developed for the determination of As, Bi, Sb, Se(IV) and Te(IV) in aqua regia extracts from atmospheric particulate matter samples. Atmospheric particulates matter was collected on glass fiber filters using a medium volume sampler (PM1 particulate matter). Two-level factorial designs have been used to optimise the hydride generation atomic fluorescence spectrometry (HG-AFS) procedure. The effects of several parameters affecting the hydride generation efficiency (hydrochloric acid, sodium tetrahydroborate and potassium iodide concentrations and flow rates) have been evaluated using a Plackett-Burman experimental design. In addition, parameters affecting the hydride measurement (delay, analysis and memory times) have been also investigated. The significant parameters obtained (sodium tetrahydroborate concentration, sodium tetrahydroborate flow rate and analysis time for As; hydrochloric acid concentration and sodium tetrahydroborate flow rate for Se(IV); and sodium tetrahydroborate concentration and sodium tetrahydroborate flow rate for Te(IV)) have been optimized by using 2 n + star central composite design. Hydrochloric acid concentration and sodium tetrahydroborate flow rate were the significant parameters obtained for Sb and Bi determination, respectively. Using a univariate approach these parameters were optimized. The accuracy of methods have been verified by using several certified reference materials: SRM 1648 (urban particulate matter) and SRM 1649a (urban dust). Detection limits in the range of 6 x 10 -3 to 0.2 ng m -3 have been achieved. The developed methods were applied to several atmospheric particulate matter samples corresponding to A Coruna city (NW Spain)

  4. Flux free growth of large FeSe1/2Te1/2 superconducting single crystals by an easy high temperature melt and slow cooling method

    Directory of Open Access Journals (Sweden)

    P. K. Maheshwari

    2015-09-01

    Full Text Available We report successful growth of flux free large single crystals of superconducting FeSe1/2Te1/2 with typical dimensions of up to few cm. The AC and DC magnetic measurements revealed the superconducting transition temperature (Tc value of around 11.5K and the isothermal MH showed typical type-II superconducting behavior. The lower critical field (Hc1 being estimated by measuring the low field isothermal magnetization in superconducting regime is found to be above 200Oe at 0K. The temperature dependent electrical resistivity ρ(T  showed the Tc (onset to be 14K and the Tc(ρ = 0 at 11.5K. The electrical resistivity under various magnetic fields i.e., ρ(TH for H//ab and H//c demonstrated the difference in the width of Tc with applied field of 14Tesla to be nearly 2K, confirming the anisotropic nature of superconductivity. The upper critical and irreversibility fields at absolute zero temperature i.e., Hc2(0 and Hirr(0 being determined by the conventional one-band Werthamer–Helfand–Hohenberg (WHH equation for the criteria of normal state resistivity (ρn falling to 90% (onset, and 10% (offset is 76.9Tesla, and 37.45Tesla respectively, for H//c and 135.4Tesla, and 71.41Tesla respectively, for H//ab. The coherence length at the zero temperature is estimated to be above 20Å ´ by using the Ginsburg-Landau theory. The activation energy for the FeSe1/2Te1/2 in both directions H//c and H//ab is determined by using Thermally Activation Flux Flow (TAFF model.

  5. Optical properties and surface morphology of ZnTe thin films prepared by multiple potential steps

    Energy Technology Data Exchange (ETDEWEB)

    Gromboni, Murilo F.; Lucas, Francisco W. S.; Mascaro, Lucia H., E-mail: lmascaro@ufscar.br [Universidade de Federal de Sao Carlos (LIEC/UFSCar), SP (Brazil). Departamento de Quimica. Lab. de Eletroquimica e Ceramica

    2014-03-15

    In this work, the ZnTe thin films were electrodeposited using potentiostatic steps, on Pt substrate. The effect of steps number, the deposition time for each element (Zn or Te) and layer order (Zn/Te or Te/Zn) in the morphology, composition, band gap energy and photocurrent was evaluated. Microanalysis data showed that the ratio Zn/Te ranged from 0.12 and 0.30 and the film was not stoichiometric. However, the band-gap value obtained from in all experimental conditions used in this work was 2.28 eV, indicating film growth of ZnTe. The samples with higher Zn showed higher photocurrent, which was of the order of 2.64 μA cm{sup -2} and dendritic morphology (author)

  6. Optical properties of ZnTe epilayers with submonolayer planar narrow gap inclusions

    Energy Technology Data Exchange (ETDEWEB)

    Agekian, V. F.; Filosofov, N. G., E-mail: n.filosofov@spbu.ru; Serov, A. Yu. [St. Petersburg State University, Universitetskaya nab. 7 – 9, 199034 Si. Petersburg (Russian Federation); Shtrom, I. V. [St. Petersburg State University, Universitetskaya nab. 7 – 9, 199034 Si. Petersburg (Russian Federation); Ioffe Physicotechnical Institute, Russian Academy of Sciences, Politekhnicheskaya 26, 194021 St. Petersburg (Russian Federation); St. Petersburg Academic University — Nanotechnology Research and Education Centre, Russian Academy of Sciences, Khlopina 8/3, 194021 St. Petersburg (Russian Federation); Karczewski, G. [Institute of Physics Polish Academy of Science, Ał. Lotnikov 32/46, 02-668 Warsaw (Poland)

    2016-06-17

    The exciton luminescence of ZnTe matrices with the embedded CdTe submonolayer inclusions is investigated. It is shown that the exciton localized by CdTe narrow gap component dominates in the emission spectrum. These localized excitons are coupled mainly with the phonons belonging to the cadmium enriched layers. The real distribution of cadmium in the direction of the heterostructure growth is determined from the energy position of the localized exciton emission bands.

  7. Cytotoxicity assessment of functionalized CdSe, CdTe and InP quantum dots in two human cancer cell models.

    Science.gov (United States)

    Liu, Jing; Hu, Rui; Liu, Jianwei; Zhang, Butian; Wang, Yucheng; Liu, Xin; Law, Wing-Cheung; Liu, Liwei; Ye, Ling; Yong, Ken-Tye

    2015-12-01

    The toxicity of quantum dots (QDs) has been extensively studied over the past decade. Some common factors that originate the QD toxicity include releasing of heavy metal ions from degraded QDs and the generation of reactive oxygen species on the QD surface. In addition to these factors, we should also carefully examine other potential QD toxicity causes that will play crucial roles in impacting the overall biological system. In this contribution, we have performed cytotoxicity assessment of four types of QD formulations in two different human cancer cell models. The four types of QD formulations, namely, mercaptopropionic acid modified CdSe/CdS/ZnS QDs (CdSe-MPA), PEGylated phospholipid encapsulated CdSe/CdS/ZnS QDs (CdSe-Phos), PEGylated phospholipid encapsulated InP/ZnS QDs (InP-Phos) and Pluronic F127 encapsulated CdTe/ZnS QDs (CdTe-F127), are representatives for the commonly used QD formulations in biomedical applications. Both the core materials and the surface modifications have been taken into consideration as the key factors for the cytotoxicity assessment. Through side-by-side comparison and careful evaluations, we have found that the toxicity of QDs does not solely depend on a single factor in initiating the toxicity in biological system but rather it depends on a combination of elements from the particle formulations. More importantly, our toxicity assessment shows different cytotoxicity trend for all the prepared formulations tested on gastric adenocarcinoma (BGC-823) and neuroblastoma (SH-SY5Y) cell lines. We have further proposed that the cellular uptake of these nanocrystals plays an important role in determining the final faith of the toxicity impact of the formulation. The result here suggests that the toxicity of QDs is rather complex and it cannot be generalized under a few assumptions reported previously. We suggest that one have to evaluate the QD toxicity on a case to case basis and this indicates that standard procedures and comprehensive

  8. Investigation of the structural, optical and electrical transport properties of n-doped CdSe thin films

    Science.gov (United States)

    Ali, H. M.; Abd El-Ghanny, H. A.

    2008-04-01

    Thin films of (CdSe)90(In2O3)10, (CdSe)90(SnO2)10 and (CdSe)90(ZnO)10 have been grown on glass substrates by the electron beam evaporation technique. It has been found that undoped and Sn or In doped CdSe films have two direct transitions corresponding to the energy gaps Eg and Eg+Δ due to spin-orbit splitting of the valence band. The electrical resistivity for n-doped CdSe thin films as a function of light exposure time has been studied. The influence of doping on the structural, optical and electrical characteristics of In doped CdSe films has been investigated in detail. The lattice parameters, grain size and dislocation were determined from x-ray diffraction patterns. The optical transmittance and band gap of these films were determined using a double beam spectrophotometer. The DC conductivity of the films was measured in vacuum using a two-probe technique.

  9. The synthesis of CdSe quantum dots with carboxyl group and study on their optical characteristics

    International Nuclear Information System (INIS)

    Ye, Chen; Park, Sangjoon; Kim, Jongsung

    2009-01-01

    Quantum dots are nanocrystal semiconductors which attract lots of research interests due to their peculiar optical properties. CdSe/ZnS quantum dots have been synthesized via pyrolysis of organometallic reagents. The color of the quantum dot changes from yellow-green to red as their size increases with reaction time. Photoluminescence quantum efficiency of CdSe quantum dots have been enhanced by passivating the surface of CdSe quantum dots with ZnS layers. Quantum dots are nanocrystal semiconductors which attract lots of research interests due to their peculiar optical properties. CdSe/ZnS quantum dots have been synthesized via pyrolysis of organometallic reagents. The color of the quantum dot changes from yellow-green to red as their size increases with reaction time. Photoluminescence quantum efficiency of CdSe quantum dots have been enhanced by passivating the surface of CdSe quantum dots with ZnS layers. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  10. Study of structural, optical and thermal properties of nanostructured SnSe{sub 2} prepared by mechanical alloying

    Energy Technology Data Exchange (ETDEWEB)

    Borges, Z.V. [Faculdade de Tecnologia, Universidade Federal do Amazonas, 3000 Japiim, 69077-000 Manaus, Amazonas (Brazil); Poffo, C.M., E-mail: claudio.poffo@ufsc.br [Universidade Federal de Santa Catarina, Campus de Araranguá, 88900-000, Santa Catarina (Brazil); Lima, J.C. de [Departamento de Física, Universidade Federal de Santa Catarina, Campus Trindade, C.P. 476, 88040-900 Florianópolis, Santa Catarina (Brazil); Souza, S.M. de; Trichês, D.M.; Nogueira, T.P.O. [Departamento de Física, Universidade Federal do Amazonas, 3000 Japiim, 69077-000 Manaus, Amazonas (Brazil); Manzato, L. [Instituto Federal de Educação, Ciência e Tecnologia do Amazonas, 1672, 69075-351 Manaus, Amazonas (Brazil); Biasi, R.S. de [Seção de Engenharia Mecânica e de Materiais, Instituto Militar de Engenharia, 22290-270 Rio de Janeiro (Brazil)

    2016-02-01

    A nanostructured SnSe{sub 2} phase was successfully produced by mechanical alloying. The influence of defect centers on the structural, optical and photoacoustic properties of the alloy was investigated by annealing the as-milled SnSe{sub 2} powder. From optical absorbance and photoacoustic absorption measurements, the energy band gap, E{sub g}, and the thermal diffusivity, α, values were determined for as-milled and annealed samples. The thermal conductivity values for the as-milled and annealed samples were estimated by using the α values obtained from the photoacoustic measurements, the density values obtained from the Rietveld refinement of the X-ray diffraction patterns and the specific heat value for the bulk SnSe{sub 2} phase. These values were used to estimate the dimensionless figure of merit ZT. It was evidenced that the ZT parameter of the as-milled nanostructured SnSe{sub 2} sample is almost twice larger than the ZT of the annealed sample. - Highlights: • Nanostructured SnSe{sub 2} was produced using Mechanical Alloying technique. • As milled sample has a high fraction of interfacial component (80%). • Thermal diffusivity value for nanostructured SnSe{sub 2} was a new report in literature.

  11. Synthesis of ZnSe and ZnSe:Cu quantum dots by a room temperature photochemical (UV-assisted) approach using Na2 SeO3 as Se source and investigating optical properties.

    Science.gov (United States)

    Khafajeh, R; Molaei, M; Karimipour, M

    2017-06-01

    In this study, ZnSe and ZnSe:Cu quantum dots (QDs) were synthesized using Na 2 SeO 3 as the Se source by a rapid and room temperature photochemical (UV-assisted) approach. Thioglycolic acid (TGA) was employed as the capping agent and UV illumination activated the chemical reactions. Synthesized QDs were successfully characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), photoluminescence (PL) and UV-visible (UV-vis) spectroscopy, Fourier transform-infrared (FT-IR), and energy dispersive X-ray spectroscopy (EDX). XRD analysis demonstrated the cubic zinc blend phase QDs. TEM images indicated that round-shaped particles were formed, most of which had a diameter of about 4 nm. The band gap of the ZnSe QDs was higher than that for ZnSe in bulk. PL spectra indicated an emission with three peaks related to the excitonic, surface trap states and deep level (DL) states. The band gap and QD emission were tunable only by UV illumination time during synthesis. ZnSe:Cu showed green emission due to transition of electrons from the Conduction band (CB) or surface trap states to the 2 T 2 acceptor levels of Cu 2 + . The emission was increased by increasing the Cu 2 + ion concentration, such that the optimal value of PL intensity was obtained for the nominal mole ratio of Cu:Zn 1.5%. Copyright © 2016 John Wiley & Sons, Ltd.

  12. Unexpected Ge-Ge contacts in the two-dimensional Ge{sub 4}Se{sub 3}Te phase and analysis of their chemical cause with the density of energy (DOE) function

    Energy Technology Data Exchange (ETDEWEB)

    Kuepers, Michael; Konze, Philipp M.; Maintz, Stefan; Steinberg, Simon [Institute of Inorganic Chemistry, Chair of Solid-State and Quantum Chemistry, RWTH Aachen University (Germany); Mio, Antonio M.; Cojocaru-Miredin, Oana; Zhu, Min; Wuttig, Matthias [I. Physikalisches Institut, RWTH Aachen University (Germany); Mueller, Merlin; Mayer, Joachim [Gemeinschaftslabor fuer Elektronenmikroskopie, RWTH Aachen University (Germany); Luysberg, Martina [Ernst-Ruska-Center, Forschungszentrum Juelich GmbH (Germany); Dronskowski, Richard [Institute of Inorganic Chemistry, Chair of Solid-State and Quantum Chemistry, RWTH Aachen University (Germany); Juelich-Aachen Research Alliance (JARA-HPC), RWTH Aachen University (Germany)

    2017-08-14

    A hexagonal phase in the ternary Ge-Se-Te system with an approximate composition of GeSe{sub 0.75}Te{sub 0.25} has been known since the 1960s but its structure has remained unknown. We have succeeded in growing single crystals by chemical transport as a prerequisite to solve and refine the Ge{sub 4}Se{sub 3}Te structure. It consists of layers that are held together by van der Waals type weak chalcogenide-chalcogenide interactions but also display unexpected Ge-Ge contacts, as confirmed by electron microscopy analysis. The nature of the electronic structure of Ge{sub 4}Se{sub 3}Te was characterized by chemical bonding analysis, in particular by the newly introduced density of energy (DOE) function. The Ge-Ge bonding interactions serve to hold electrons that would otherwise go into antibonding Ge-Te contacts. (copyright 2017 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim)

  13. Sensing application of an optical fiber dip coated with L-Cystein ethyl ester hydrochloride capped ZnTe quantum dots

    Directory of Open Access Journals (Sweden)

    Sundaray Madhulita

    2016-09-01

    Full Text Available Optical fiber in conjunction with ZnTe quantum dots (QDs is investigated for sensing application. ZnTe QDs, are synthesized by a simple chemical bottom up approach. Quantum dots are capped with L-Cystein ethyl ester hydrochloride (LEEH, to increase their stability. Then LEEH capped ZnTe QDs, whose size is estimated as 2.29 nm by effective mass approximation (EMA, are dip-coated on a cladding removed optical fiber. Different concentrations of alcohol and ammonia are used to investigate the sensing behavior. It is found that sensitivity of the sensor increases with the use of QDs for both alcohol and ammonia.

  14. Strain/size analysis in ternary compounds AgIn{sub 5} VI{sub 8} (Vi = S, Se, Te) by X-ray diffraction; Analisis de tension/tamano en compuestos ternarios AgIn{sub 5} VI{sub 8} (VI = S, Se, Te) mediante difraccion de rayos X

    Energy Technology Data Exchange (ETDEWEB)

    Fermin, J. R.; Salcedo, D. Y.; Durante R, C.; Castro, J. A. [Universidad del Zulia, Facultad Experimental de Ciencias, Departamento de Fisica, Maracaibo, Zulia (Venezuela, Bolivarian Republic of)

    2017-11-01

    In this work, we have study the microstructural properties of the ternary compounds AgIn{sub 5} VI{sub 8} (Vi = S, Se, Te) by X-ray diffraction technique (XRD). The linewidth of the XRD profile is measured as function of the diffraction angle. Structural parameters such as, average grain size, micro strains, and crystalline dislocation density, are obtained on the framework of a strain/size analysis based on the modified Scherrer equation for Gaussian profiles. The crystalline dislocation arrange according to a Gaussian distribution function, indicating that these dislocations are randomly distributed within the grains. (Author)

  15. Band alignment and charge transfer predictions of ZnO/ZnX (X = S, Se or Te) interfaces applied to solar cells: a PBE+U theoretical study.

    Science.gov (United States)

    Flores, Efracio Mamani; Gouvea, Rogério Almeida; Piotrowski, Maurício Jeomar; Moreira, Mário Lucio

    2018-02-14

    The engineering of semiconductor materials for the development of solar cells is of great importance today. Two topics are considered to be of critical importance for the efficiency of Grätzel-type solar cells, the efficiency of charge separation and the efficiency of charge carrier transfer. Thus, one research focus is the combination of semiconductor materials with the aim of reducing charge recombination, which occurs by spatial charge separation. From an experimental point of view, the combining of materials can be achieved by decorating a core with a shell of another material resulting in a core-shell system, which allows control of the desired photoelectronic properties. In this context, a computational simulation is mandatory for the atomistic understanding of possible semiconductor combinations and for the prediction of their properties. Considering the construction of ZnO/ZnX (X = S, Se or Te) interfaces, we seek to investigate the electronic influence of the shell (ZnX) on the core (ZnO) and, consequently, find out which of the interfaces would present the appropriate properties for (Grätzel-type) solar cell applications. To perform this study, we have employed density functional theory (DFT) calculations, considering the Perdew-Burke-Ernzerhof (PBE) functional. However, it is well-known that plain DFT fails to describe strong electronic correlated materials where, in general, an underestimation of the band gap is obtained. Thus, to obtain the correct description of the electronic properties, a Hubbard correction was employed, i.e. PBE+U calculations. The PBE+U methodology provided the correct electronic structure properties for bulk ZnO in good agreement with experimental values (99.4%). The ZnO/ZnX interfaces were built and were composed of six ZnO layers and two ZnX layers, which represents the decoration process. The core-shell band gap was 2.2 eV for ZnO/ZnS, ∼1.71 eV for ZnO/ZnSe and ∼0.95 eV for ZnO/ZnTe, which also exhibited a type-II band

  16. Electronic structure and optical properties of LiGa0.5In0.5Se2 single crystal, a nonlinear optical mid-IR material

    Science.gov (United States)

    Lavrentyev, A. A.; Gabrelian, B. V.; Vu, Tuan V.; Isaenko, L. I.; Yelisseyev, A. P.; Khyzhun, O. Y.

    2018-06-01

    Measurements of X-ray photoelectron core-level and valence-band spectra for pristine and irradiated with Ar+ ions surfaces of LiGa0.5In0.5Se2 single crystal, novel nonlinear optical mid-IR selenide grown by a modified vertical Bridgman-Stockbarger technique, are reported. Electronic structure of LiGa0.5In0.5Se2 is elucidated from theoretical and experimental points of view. Notably, total and partial densities of states (DOSs) of the LiGa0.5In0.5Se2 compound are calculated based on density functional theory (DFT) using the augmented plane wave + local orbitals (APW + lo) method. In accordance with the DFT calculations, the principal contributors to the valence band are the Se 4p states, making the main input at the top and in the upper part of the band, while its bottom is dominated by contributions of the valence s states associated with Ga and In atoms. The theoretical total DOS curve peculiarities are found to be in excellent agreement with the shape of the X-ray photoelectron valence-band spectrum of the LiGa0.5In0.5Se2 single crystal. The bottom of the conduction band of LiGa0.5In0.5Se2 is formed mainly by contributions of the unoccupied Ga 4s and In 5s states in almost equal proportion, with somewhat smaller contributions of the unoccupied Se 4p states as well. Our calculations indicate that the LiGa0.5In0.5Se2 compound is a direct gap semiconductor. The principal optical constants of LiGa0.5In0.5Se2 are calculated in the present work.

  17. Structural and optical analysis of 60Co gamma-irradiated thin films of polycrystalline Ga10Se85Sn5

    Science.gov (United States)

    Ahmad, Shabir; Asokan, K.; Shahid Khan, Mohd.; Zulfequar, M.

    2015-12-01

    The present study focuses on the effects of gamma irradiation on structural and optical properties of polycrystalline Ga10Se85Sn5 thin films with a thickness of ∼300 nm deposited by the thermal evaporation technique on cleaned glass substrates. X-ray diffraction patterns of the investigated thin films show that crystallite growth occurs in the orthorhombic phase structure. The surface study carried out by using the scanning electron microscope (SEM) confirms that the grain size increases with gamma irradiation. The optical parameters were estimated from optical transmission spectra data measured from a UV-vis-spectrophotometer in the wavelength range of 200-1100 nm. The refractive index dispersion data of the investigated thin films follow the single oscillator model. The estimated values of static refractive index n0, oscillator strength Ed, zero frequency dielectric constant ε0, optical conductivity σoptical and the dissipation factor increases after irradiation, while the single oscillator energy Eo decreases after irradiation. It was found that the value of the optical band gap of the investigated thin films decreases and the corresponding absorption coefficient increases continuously with an increase in the dose of gamma irradiation. This post irradiation changes in the values of optical band gap and absorption coefficient were interpreted in terms of the bond distribution model.

  18. Role of Mn2+ concentration in the linear and nonlinear optical properties of Ni1-xMnxSe nanoparticles

    Science.gov (United States)

    Anugop, B.; Prasanth, S.; Rithesh Raj, D.; Vineeshkumar, T. V.; Pranitha, S.; Mahadevan Pillai, V. P.; Sudarsanakumar, C.

    2016-12-01

    Ni1-xMnxSe nanoparticles (x = 0.1, 0.3, 0.5, 0.7, 0.9) were successfully synthesized by chemical co-precipitation method and their structural and optical properties were studied using X-ray diffraction, transmission electron microscopy, UV-Visible absorption and photo luminescence spectroscopy. XRD pattern reveals the hexagonal structure of the particles and the peak positions were shifted to higher 2θ values with increase in Mn2+ concentration. The average particle size determined from XRD varies from 6 to 11 nm. The UV-Visible absorption spectrum shows absorption edge around the blue region and is red-shifted with increasing Mn2+ concentration consequently the optical bandgap energy is decreasing. The PL emission spectrum shows a broad emission around 380 nm, and the intensity of the emission decreases with increase in Mn2+ concentration. The nonlinear optical properties of the samples were analysed using Z-scan technique and the samples show optical limiting behaviour and the 2 PA coefficient increases with increasing Mn2+ concentration. Overall, manganese concentration influences the linear and nonlinear optical properties of Ni1-xMnxSe nanoparticles.

  19. Precipitação seletiva de tamanhos em nanopartículas semicondutoras coloidais de CdTe e CdSe: um estudo por espectroscopia UV-VIS

    Directory of Open Access Journals (Sweden)

    Lívia Cristina de Souza Viol

    2011-01-01

    Full Text Available The post-preparative size-selective precipitation technique was applied in CdTe and CdSe semiconductor nanocrystals prepared via colloidal route in water. The synthesis of CdTe and CdSe nanoparticles and the effect of the post-preparative size-selective precipitation have been characterized mainly by mean of ultraviolet and visible absorption spectroscopy (UV-Vis. It was demonstrated that the size-selective precipitation are able to isolate particles of different sizes and purify the nanoparticles as well.

  20. The variation of the energy gap with composition in the quaternary alloy system ZnTe/sub 1-2x/S/sub x/Se/sub x/

    International Nuclear Information System (INIS)

    Litvinchuk, A.P.; Vitrikhovskii, N.I.

    1983-01-01

    Studies are presented of photoluminescence spectra of the quaternary ZnTe/sub 1-2x/S/sub x/Se/sub x/ alloy (x = 0.05, 0.10, and 0.20). The determination of the energy gap variation with composition at 85 K is given. The nonlinear variation of the energy gap E/sub g/ with composition for the quaternary ZnTe/sub 1-2x/S/sub x/Se/sub x/ alloy may be interpreted in the framework of the pseudopotential theory based on the nonlinear crystal field properties

  1. Optically pumped quantum-dot Cd(Zn)Se/ZnSe laser and microchip converter for yellow-green spectral region

    Energy Technology Data Exchange (ETDEWEB)

    Lutsenko, E V; Voinilovich, A G; Rzheutskii, N V; Pavlovskii, V N; Yablonskii, G P; Sorokin, S V; Gronin, S V; Sedova, I V; Kop' ev, Petr S; Ivanov, Sergei V; Alanzi, M; Hamidalddin, A; Alyamani, A

    2013-05-31

    The room temperature laser generation in the yellow-green ({lambda} = 558.5-566.7 nm) spectral range has been demonstrated under optical pumping by a pulsed nitrogen laser of Cd(Zn)Se/ZnSe quantum dot heterostructures. The maximum achieved laser wavelength was as high as {lambda} = 566.7 nm at a laser cavity length of 945 {mu}m. High values of both the output pulsed power (up to 50 W) and the external differential quantum efficiency ({approx}60%) were obtained at a cavity length of 435 {mu}m. Both a high quality of the laser heterostructure and a low lasing threshold ({approx}2 kW cm{sup -2}) make it possible to use a pulsed InGaN laser diode as a pump source. A laser microchip converter based on this heterostructure has demonstrated a maximum output pulse power of {approx}90 mW at {lambda} = 560 nm. The microchip converter was placed in a standard TO-18 (5.6 mm in diameter) laser diode package. (semiconductor lasers. physics and technology)

  2. Synthesis and Optical Properties of Thiol Functionalized CdSe/ZnS (Core/Shell Quantum Dots by Ligand Exchange

    Directory of Open Access Journals (Sweden)

    Huaping Zhu

    2014-01-01

    Full Text Available The colloidal photoluminescent quantum dots (QDs of CdSe (core and CdSe/ZnS (core/shell were synthesized at different temperatures with different growth periods. Optical properties (i.e., UV/Vis spectra and photoluminescent emission spectra of the resulting QDs were investigated. The shell-protected CdSe/ZnS QDs exhibited higher photoluminescent (PL efficiency and stability than their corresponding CdSe core QDs. Ligand exchange with various thiol molecules was performed to replace the initial surface passivation ligands, that is, trioctylphosphine oxide (TOPO and trioctylphosphine (TOP, and the optical properties of the surface-modified QDs were studied. The thiol ligand molecules in this study included 1,4-benzenedimethanethiol, 1,16-hexadecanedithiol, 1,11-undecanedithiol, biphenyl-4,4′-dithiol, 11-mercapto-1-undecanol, and 1,8-octanedithiol. After the thiol functionalization, the CdSe/ZnS QDs exhibited significantly enhanced PL efficiency and storage stability. Besides surface passivation effect, such enhanced performance of thiol-functionalized QDs could be due to cross-linked assembly formation of dimer/trimer clusters, in which QDs are linked by dithiol molecules. Furthermore, effects of ligand concentration, type of ligand, and heating on the thiol stabilization of QDs were also discussed.

  3. Optical and electrical study of CdZnTe surfaces passivated by KOH and NH{sub 4}F solutions

    Energy Technology Data Exchange (ETDEWEB)

    Zázvorka, J., E-mail: zazvorka.jakub@gmail.com [Institute of Physics, Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 5, 121 16 Prague (Czech Republic); Franc, J.; Statelov, M.; Pekárek, J.; Veis, M.; Moravec, P. [Institute of Physics, Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 5, 121 16 Prague (Czech Republic); Mašek, K. [Department of Surface and Plasma Science, Faculty of Mathematics and Physics, Charles University in Prague, V Holešovičkách 2, CZ, 18000 Prague (Czech Republic)

    2016-12-15

    Highlights: • Surface of CdZnTe samples was passivated after chemical etching. • KOH and NH{sub 4}F solutions were used as passivation agents. • Growth of surface oxide after passivation is observed. • Surface oxide thickness was evaluated over time after chemical treatment. • Oxidation of the sample correlates with decreased leakage current. - Abstract: Performance of CdZnTe-based detectors is highly related to surface preparation. Mechanical polishing, chemical etching and passivation are routinely employed for this purpose. However, the relation between these processes and the detector performance in terms of underlying physical phenomena has not been fully explained. The dynamics and properties of CdZnTe surface oxide layers, created by passivation with KOH and NH4F/H2O2 solutions, were studied by optical ellipsometry and X-ray photoelectron spectroscopy (XPS). Thicknesses and growth rates of the surface oxide layers differed for each of the passivation methods. Leakage currents which influence the final spectral resolution of the detector were measured simultaneously with ellipsometry. Results of both optical and electrical investigation showed the same trends in the time evolution and correlated to each other. NH4F/H2O2 passivation showed to be a method which produces the most desirable properties of the surface oxide layer.

  4. Ultrafast Optical Excitation of a Persistent Surface-State Population in the Topological Insulator Bi2Se3

    Energy Technology Data Exchange (ETDEWEB)

    Sobota, Jonathan

    2012-03-14

    Using femtosecond time- and angle-resolved photoemission spectroscopy, we investigated the nonequilibrium dynamics of the topological insulator Bi{sub 2}Se{sub 3}. We studied p-type Bi{sub 2}Se{sub 3}, in which the metallic Dirac surface state and bulk conduction bands are unoccupied. Optical excitation leads to a meta-stable population at the bulk conduction band edge, which feeds a nonequilibrium population of the surface state persisting for >10 ps. This unusually long-lived population of a metallic Dirac surface state with spin texture may present a channel in which to drive transient spin-polarized currents.

  5. Structural, optical, and photoluminescence characterization of electron beam evaporated ZnS/CdSe nanoparticles thin films

    Science.gov (United States)

    Mohamed, S. H.; Ali, H. M.

    2011-01-01

    Structural, optical, and photoluminescence investigations of ZnS capped with CdSe films prepared by electron beam evaporation are presented. X-ray diffraction analysis revealed that the ZnS/CdSe nanoparticles films contain cubic cadmium selenide and hexagonal zinc sulfide crystals and the ZnS grain sizes increased with increasing ZnS thickness. The refractive index was evaluated in terms of envelope method, which has been suggested by Swanepoel in the transparent region. The refractive index values were found to increase with increasing ZnS thickness. However, the optical band gap and the extinction coefficient were decreased with increasing ZnS thickness. Photoluminescence (PL) investigations revealed the presence of two broad emission bands. The ZnS thickness significantly influenced the PL intensities.

  6. Optical study of HgCdTe infrared photodetectors using internal photoemission spectroscopy

    International Nuclear Information System (INIS)

    Lao, Yan-Feng; Unil Perera, A. G.; Wijewarnasuriya, Priyalal S.

    2014-01-01

    We report a study of internal photoemission spectroscopy (IPE) applied to a n-type Hg 1−x Cd x Te/Hg 1−y Cd y Te heterojunction. An exponential line-shape of the absorption tail in HgCdTe is identified by IPE fittings of the near-threshold quantum yield spectra. The reduction of quantum yield (at higher photon energy) below the fitting value is explained as a result of carrier-phonon scatterings. In addition, the obtained bias independence of the IPE threshold indicates a negligible electron barrier at the heterojunction interface

  7. Enhanced infrared magneto-optical response of the nonmagnetic semiconductor BiTeI driven by bulk Rashba splitting

    Energy Technology Data Exchange (ETDEWEB)

    Demko, L.; Tokura, Y. [Multiferroics Project, ERATO, JST, c/o Department of Applied Physics, University of Tokyo (Japan); Schober, G.A.H. [Institute for Theoretical Physics, University of Heidelberg (Germany); Kocsis, V.; Kezsmarki, I. [Department of Physics, Budapest University of Technology and Economics and Condensed Matter Research Group of the Hungarian Academy of Sciences (Hungary); Bahramy, M.S.; Murakawa, H. [CMRG and CERG, RIKEN ASI (Japan); Lee, J.S.; Arita, R.; Nagaosa, N. [Department of Applied Physics, University of Tokyo (Japan)

    2013-07-01

    We study the magneto-optical (MO) response of the polar semiconducting BiTeI with giant bulk Rashba spin splitting at various carrier densities. Despite being nonmagnetic, the material is found to yield a huge MO activity in the infrared region under moderate magnetic fields (up to 3 T). Our first-principles calculations show that the enhanced MO response of BiTeI comes mainly from the intraband transitions between the Rashba-split bulk conduction bands. These transitions connecting electronic states with opposite spin directions become active due to the presence of strong spin-orbit interaction and give rise to distinct features in the MO spectra with a systematic doping dependence. We predict an even more pronounced enhancement in the low-energy MO response and dc Hall effect near the crossing (Dirac) point of the conduction bands.

  8. Propuesta de Modelo Teórico que señala las variables de la Mercadotecnia política que influyen en el comportamiento electoral. Caso: Delegación D-II-IPN-7 del SNTE

    OpenAIRE

    Parra Ortega, Viridiana

    2013-01-01

    En Mexico cada vez mas se manejan estrategias de mercadotecnia política para lograr incentivar la desicion del voto, diversas variables que afectan el comportamiento electoral se encuentran inmersas dentro de la aplicación y estudio de la mercadotecnia política, pero no se han determinado las variables de mercadotecnia política que influyen en el comportamiento electoral.A partir de lo anterior el objetivo de esta investigación es: proponer un modelo teórico que señale las variables de mercad...

  9. Structural and optical properties of electrodeposited culnSe{sub 2} thin films for photovoltaic solar cells; Propiedades estructurales y opticas de laminas delgadas de CulnSe2 electrodepositadas para su aplicacion en celulas solares fotovoltaicas

    Energy Technology Data Exchange (ETDEWEB)

    Guillen, C; Herrero, J; Galiano, F

    1990-07-01

    Optical an structural properties of electrodeposited copper indium diselenide, CulnSe2, thin films were studied for its application in photovoltaic devices. X-ray diffraction patterns showed that thin films were grown in chalcopyrite phase after suitable treatments. Values of Eg for the CulnSe2 thin films showed a dependence on the deposition potential as determined by optical measurements. (Author) 47 refs.

  10. Electronic structure and optical properties of noncentrosymmetric LiGaGe{sub 2}Se{sub 6}, a promising nonlinear optical material

    Energy Technology Data Exchange (ETDEWEB)

    Lavrentyev, A.A.; Gabrelian, B.V.; Vu, V.T.; Ananchenko, L.N. [Department of Electrical Engineering and Electronics, Don State Technical University, 1 Gagarin Square, 344010 Rostov-on-Don (Russian Federation); Isaenko, L.I. [Laboratory of Crystal Growth, Institute of Geology and Mineralogy, SB RAS, 43 Russkaya Street, 630090 Novosibirsk (Russian Federation); Laboratory of Semiconductor and Dielectric Materials, Novosibirsk State University, 2 Pirogova Street, 630090 Novosibirsk (Russian Federation); Yelisseyev, A.; Krinitsin, P.G. [Laboratory of Crystal Growth, Institute of Geology and Mineralogy, SB RAS, 43 Russkaya Street, 630090 Novosibirsk (Russian Federation); Khyzhun, O.Y., E-mail: khyzhun@ipms.kiev.ua [Frantsevych Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, 3 Krzhyzhanivsky Street, UA-03142 Kyiv (Ukraine)

    2016-11-15

    X-ray photoelectron core-level and valence-band spectra are measured for pristine and Ar{sup +} ion-bombarded surfaces of LiGaGe{sub 2}Se{sub 6} single crystal grown by Bridgman-Stockbarger technique. Further, electronic structure of LiGaGe{sub 2}Se{sub 6} is elucidated from both theoretical and experimental viewpoints. Density functional theory (DFT) calculations are made using the augmented plane wave +local orbitals (APW+lo) method to study total and partial densities of states in the LiGaGe{sub 2}Se{sub 6} compound. The present calculations indicate that the principal contributors to the valence band are the Se 4p states: they contribute mainly at the top and in the central portion of the valence band of LiGaGe{sub 2}Se{sub 6}, with also their significant contributions in its lower portion. The Ge 4s and Ge 4p states are among other significant contributors to the valence band of LiGaGe{sub 2}Se{sub 6}, contributing mainly at the bottom and in the central portion, respectively. In addition, the calculations indicate that the bottom of the conduction band is composed mainly from the unoccupied Ge s and Se p states. The present DFT calculations are supported experimentally by comparison on a common energy scale of the X-ray emission bands representing the energy distribution of the 4p states associated with Ga, Ge and Se and the XPS valence-band spectrum of the LiGaGe{sub 2}Se{sub 6} single crystal. The main optical characteristics of the LiGaGe{sub 2}Se{sub 6} compound are elucidated by the first-principles calculations.

  11. Structural and optical properties of electron beam evaporated CdSe ...

    Indian Academy of Sciences (India)

    electronic applications such as photo detection or solar energy conversion, due to its optical and electrical properties, as well as its good chemical and mechanical stability. In order to explore the possibility of using this in optoelectronics, ...

  12. Screened coulomb hybrid DFT study on electronic structure and optical properties of anionic and cationic Te-doped anatase TiO2

    KAUST Repository

    Harb, Moussab

    2013-01-01

    The origin of the enhanced visible-light optical absorption in Te-doped bulk anatase TiO2 is investigated in the framework of DFT and DFPT within HSE06 in order to ensure accurate electronic structure and optical transition predictions. Various

  13. An insight into the optical properties of CdSe quantum dots during their growth in bovine serum albumin solution

    International Nuclear Information System (INIS)

    Singh, Avinash; Ahmed, M.; Guleria, A.; Singh, A.K.; Adhikari, S.; Rath, M.C.

    2016-01-01

    Bovine serum albumin (BSA) assisted synthesis of cadmium selenide (CdSe) quantum dots (QDs) exhibits remarkable changes in the optical properties of the QDs as well as BSA during their growth. The growth of these QDs was investigated by recording the UV–visible absorption spectra and room temperature steady state fluorescence at different time intervals after the mixing of the precursors. The growth of these QDs was associated with a quenching of the fluorescence from BSA. The fluorescence from these QDs was found to be associated with several features: (1) a gradual red-shift in its peak position, (2) increase in intensity with an isoemissive point up to few minutes from the time of mixing of the two precursors, and (3) subsequent decrease in intensity reaching a minimum value, which remains almost unchanged thereafter. The decrease and increase in the fluorescence from BSA and CdSe QDs, respectively have been explained on the basis of Förster resonance energy transfer (FRET) as well as the simultaneous growth of these QDs. - Highlights: • CdSe quantum dots were synthesized in the presence of bovine serum albumin (BSA). • Fluorescence from BSA was quenched by during the growth of CdSe quantum dots. • There was an energy transfer from BSA to CdSe quantum dots during their growth. • The emission from CdSe quantum dots was associated with a red-shift.

  14. Effect of the Copper on Thermo - Mechanical and Optical Properties of S-Se-Cu Chalcogenide Glasses

    Science.gov (United States)

    Samudrala, Kavitha; Babu Devarasetty, Suresh

    2018-03-01

    The S15Se85-xCux (x = 0, 2, 4, 6, 8) chalcogenide glasses are synthesized using melt quenching technique and the effect of Copper on thermal, mechanical and optical properties of chalcogenide glasses are investigated. The glassy natures of the prepared samples were verified by X-ray diffraction and DSC studies. The optical band gap of the samples is estimated and it is observed that optical band gap is decreased with increasing of the copper content and is discussed in terms of cohesive energy and coordination number. The basic thermo-mechanical parameters such as micro-hardness, Volume (Vh) and formation energy (Eh) of micro voids in the glassy network and the modulus of Elasticity (E) are calculated in present glasses. The composition dependence of micro hardness is discussed in terms of heat of atomization energy.

  15. Structural, optical and magnetic properties of cobalt-doped CdSe ...

    Indian Academy of Sciences (India)

    Administrator

    Abstract. Pure and Co-doped CdSe nanoparticles have been synthesized by hydrothermal technique. The ... Keywords. Nanoparticles; dilute magnetic semiconductor; ferromagnetism. ... dium dodecyl sulfate (SDS) was used as a surfactant in.

  16. Numerical study of the electronic structure, elastic and optical properties of defect quaternary semiconductor CuGaSnSe4

    Science.gov (United States)

    Shen, Kesheng; Lu, Hai; Zhang, Xianzhou; Jiao, Zhaoyong

    2018-06-01

    The electronic structure, elastic and optical properties of the defect quaternary semiconductor CuGaSnSe4 in I 4 bar structure are systematically investigated using first-principles calculations. We summarize and discuss some of the studies on CuGaSnSe4 in partially ordered chalcopyrite structure and find that there are three atomic arrangements so far, but it is still uncertain which is the most stable. Through detailed simulation and comparison with the corresponding literature, we get three models and predict that M1 model should be the most stable. The band structure and optical properties of compound CuGaSnSe4, including dielectric constant, refractive index and absorption spectrum, are drawn for a more intuitive understanding. The elastic constants are also calculated, which not only prove that CuGaSnSe4 in I 4 bar structure is stable naturally but also help solve the problem of no data to accurately predict axial thermal expansion coefficients. The calculated values of the zero frequency dielectric constant and refractive index are comparable to those of the corresponding chalcopyrite structure but slightly larger.

  17. Electrodeposition of nanocrystalline CdSe thin films from dimethyl sulfoxide solution: Nucleation and growth mechanism, structural and optical studies

    International Nuclear Information System (INIS)

    Henriquez, R.; Badan, A.; Grez, P.; Munoz, E.; Vera, J.; Dalchiele, E.A.; Marotti, R.E.; Gomez, H.

    2011-01-01

    Highlights: → Electrodeposition of CdSe nanocrystalline semiconductor thin films. → Polycrystalline wurtzite structure with a slight (1010) preferred orientation. → Absorption edge shifts in the optical properties due to quantum confinement effects. - Abstract: Cadmium selenide (CdSe) nanocrystalline semiconductor thin films have been synthesized by electrodeposition at controlled potential based in the electrochemical reduction process of molecular selenium in dimethyl sulfoxide (DMSO) solution. The nucleation and growth mechanism of this process has been studied. The XRD pattern shows a characteristic polycrystalline hexagonal wurtzite structure with a slight (1 0 1 0) crystallographic preferred orientation. The crystallite size of nanocrystalline CdSe thin films can be simply controlled by the electrodeposition potential. A quantum size effect is deduced from the correlation between the band gap energy and the crystallite size.

  18. Continuous-wave infrared optical gain and amplified spontaneous emission at ultralow threshold by colloidal HgTe quantum dots

    Science.gov (United States)

    Geiregat, Pieter; Houtepen, Arjan J.; Sagar, Laxmi Kishore; Infante, Ivan; Zapata, Felipe; Grigel, Valeriia; Allan, Guy; Delerue, Christophe; van Thourhout, Dries; Hens, Zeger

    2018-01-01

    Colloidal quantum dots (QDs) raise more and more interest as solution-processable and tunable optical gain materials. However, especially for infrared active QDs, optical gain remains inefficient. Since stimulated emission involves multifold degenerate band-edge states, population inversion can be attained only at high pump power and must compete with efficient multi-exciton recombination. Here, we show that mercury telluride (HgTe) QDs exhibit size-tunable stimulated emission throughout the near-infrared telecom window at thresholds unmatched by any QD studied before. We attribute this unique behaviour to surface-localized states in the bandgap that turn HgTe QDs into 4-level systems. The resulting long-lived population inversion induces amplified spontaneous emission under continuous-wave optical pumping at power levels compatible with solar irradiation and direct current electrical pumping. These results introduce an alternative approach for low-threshold QD-based gain media based on intentional trap states that paves the way for solution-processed infrared QD lasers and amplifiers.

  19. Continuous-wave infrared optical gain and amplified spontaneous emission at ultralow threshold by colloidal HgTe quantum dots.

    Science.gov (United States)

    Geiregat, Pieter; Houtepen, Arjan J; Sagar, Laxmi Kishore; Infante, Ivan; Zapata, Felipe; Grigel, Valeriia; Allan, Guy; Delerue, Christophe; Van Thourhout, Dries; Hens, Zeger

    2018-01-01

    Colloidal quantum dots (QDs) raise more and more interest as solution-processable and tunable optical gain materials. However, especially for infrared active QDs, optical gain remains inefficient. Since stimulated emission involves multifold degenerate band-edge states, population inversion can be attained only at high pump power and must compete with efficient multi-exciton recombination. Here, we show that mercury telluride (HgTe) QDs exhibit size-tunable stimulated emission throughout the near-infrared telecom window at thresholds unmatched by any QD studied before. We attribute this unique behaviour to surface-localized states in the bandgap that turn HgTe QDs into 4-level systems. The resulting long-lived population inversion induces amplified spontaneous emission under continuous-wave optical pumping at power levels compatible with solar irradiation and direct current electrical pumping. These results introduce an alternative approach for low-threshold QD-based gain media based on intentional trap states that paves the way for solution-processed infrared QD lasers and amplifiers.

  20. The half-metallic ferromagnetism character in Be{sub 1−x}V{sub x}Y (Y=Se and Te) alloys: An ab-initio study

    Energy Technology Data Exchange (ETDEWEB)

    Sajjad, M. [School of Electronic Engineering, Beijing University of Posts and Telecommunications, Beijing 100876 (China); Manzoor, Sadia [Department of Physics, University of the Punjab, Quaid-e-Azam Campus, 54590 Lahore (Pakistan); Zhang, H.X. [School of Electronic Engineering, Beijing University of Posts and Telecommunications, Beijing 100876 (China); Beijing Key Laboratory of Work Safety Intelligent Monitoring, Beijing University of Posts and Telecommunications, Beijing 100876 (China); Noor, N.A. [Department of Physics, University of the Punjab, Quaid-e-Azam Campus, 54590 Lahore (Pakistan); Alay-e-Abbas, S.M. [Department of Physics, GC University Faisalabad, Allama Iqbal Road, Faisalabad 38000 (Pakistan); Department of Physics, University of Sargodha, Sargodha 40100 (Pakistan); Shaukat, A. [Department of Physics, University of Sargodha, Sargodha 40100 (Pakistan); Khenata, R., E-mail: khenata_rabah@yahoo.fr [Laboratoire de Physique Quantique et de Modélisation Mathématique (LPQ3M), Département de Technologie, Université de Mascara, Mascara 29000 (Algeria)

    2015-04-01

    Ab-initio calculations for V-doped BeSe and BeTe semiconductors are performed by means of all-electrons full-potential linearized augmented plane wave plus local orbital (FP-LAPW+lo) method. The structural properties are optimized using the Wu-Cohen generalized gradient approximation functional, whereas modified Becke and Jhonson local density approximation functional has been employed for evaluating the spin-polarized electronic and magnetic properties. Magnetic stability at various doping concentrations in ferromagnetic (FM) and anti-ferromagnetic (AFM) ordering is investigated by comparing the minimum total energies and enthalpies of formation (ΔH). Studied band structures, density of states, total energy, exchange interactions and magnetic moments manifest both alloys with half-metallic ferromagnetic behavior. Moreover, their valance bands are found to be paired ferromagnetically with V atoms. Furthermore, it was observed that the magnetic moment of vanadium atom reduces from free space charge value due to p–d hybridization which yields small magnetic moments on the Be, Se and Te sites. - Highlights: • Density functional calculations for V-doped BeSe and BeTe are performed. • V-doped BeSe and BeTe are found to be stable half-metallic ferromagnetism. • Improved electronic properties are achieved using mBJLDA which confirm HMF. • The half-metallic gaps show non-linear variation with increasing dopant concentration.

  1. Synthesis, structure, and characterization of two new bismuth(III) selenite/tellurite nitrates: [(Bi{sub 3}O{sub 2})(SeO{sub 3}){sub 2}](NO{sub 3}) and [Bi(TeO{sub 3})](NO{sub 3})

    Energy Technology Data Exchange (ETDEWEB)

    Meng, Chang-Yu; Wei, Ming-Fang [Department of Chemistry and Materials, Yulin Normal University,Yulin, Guangxi 537000 (China); Geng, Lei, E-mail: lgeng.cn@gmail.com [Department of Materials Science and Engineering, Huaibei Normal University, Huaibei, Anhui 235000 (China); Hu, Pei-Qing; Yu, Meng-Xia [Department of Chemistry and Materials, Yulin Normal University,Yulin, Guangxi 537000 (China); Cheng, Wen-Dan [State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002 (China)

    2016-07-15

    Two new bismuth(III) selenite/tellurite nitrates, [(Bi{sub 3}O{sub 2})(SeO{sub 3}){sub 2}](NO{sub 3}) and [Bi(TeO{sub 3})](NO{sub 3}), have been synthesized by conventional facile hydrothermal method at middle temperature 200 °C and characterized by single-crystal X-ray diffraction, powder diffraction, UV–vis–NIR optical absorption spectrum, infrared spectrum and thermal analylsis. Both [(Bi{sub 3}O{sub 2})(SeO{sub 3}){sub 2}](NO{sub 3}) and [Bi(TeO3)](NO3) crystallize in the monoclinic centronsymmetric space group P2{sub 1}/c with a=9.9403(4) Å, b=9.6857(4) Å, c=10.6864(5) Å, β=93.1150(10)° for [(Bi{sub 3}O{sub 2})(SeO{sub 3}){sub 2}](NO{sub 3}) and a=8.1489(3) Å, b=9.0663(4) Å, c=7.4729(3) Å, β=114.899(2)° for Bi(TeO3)(NO3), respectively. The two compounds, whose structures are composed of three different asymmetric building units, exhibit two different types of structures. The structure of [(Bi{sub 3}O{sub 2})(SeO{sub 3}){sub 2}](NO{sub 3}) features a three-dimensional (3D) bismuth(III) selenite cationic tunnel structure [(Bi{sub 3}O{sub 2})(SeO{sub 3}){sub 2}] {sup 3}{sub ∞} with NO{sub 3}{sup −} anion group filling in the 1D tunnel along b axis. The structure of [Bi(TeO{sub 3})](NO{sub 3}) features 2D bismuth(III) tellurite [Bi(TeO{sub 3}){sub 2}]{sup 2}{sub ∞} layers separated by NO{sub 3}{sup −} anion groups. The results of optical diffuse-reflectance spectrum measurements and electronic structure calculations based on density functional theory methods show that the two compounds are wide band-gap semiconductors. - Graphical abstract: Two novel bismuth{sup III} selenite/tellurite nitrates [(Bi{sub 3}O{sub 2})(SeO{sub 3}){sub 2}](NO{sub 3}) with 3D tunnel structure and [Bi(TeO{sub 3})](NO{sub 3}) with 2D layer structure have been firstly synthesized and characterized. Display Omitted - Highlights: • Two novel bismuth{sup III} nitrates [(Bi{sub 3}O{sub 2})(SeO{sub 3}){sub 2}](NO{sub 3}) and [Bi(TeO{sub 3})](NO{sub 3}) were firstly

  2. Theoretical estimates of the anapole magnetizabilities of C4H4X2 cyclic molecules for X=O, S, Se, and Te

    International Nuclear Information System (INIS)

    Pagola, G. I.; Ferraro, M. B.; Provasi, P. F.; Pelloni, S.; Lazzeretti, P.

    2014-01-01

    Calculations have been carried out for C 4 H 4 X 2 cyclic molecules, with X=O, S, Se, and Te, characterized by the presence of magnetic-field induced toroidal electron currents and associated orbital anapole moments. The orbital anapole induced by a static nonuniform magnetic field B, with uniform curl C=∇×B, is rationalized via a second-rank anapole magnetizability tensor a αβ , defined as minus the second derivative of the second-order interaction energy with respect to the components C α and B β . The average anapole magnetizability a ¯ equals −χ ¯ , the pseudoscalar obtained by spatial averaging of the dipole-quadrupole magnetizability χ α,βγ . It has different sign for D and L enantiomeric systems and can therefore be used for chiral discrimination. Therefore, in an isotropic chiral medium, a homogeneous magnetic field induces an electronic anapole A α , having the same magnitude, but opposite sign, for two enantiomorphs

  3. Ab initio and relativistic DFT study of spin–rotation and NMR shielding constants in XF{sub 6} molecules, X = S, Se, Te, Mo, and W

    Energy Technology Data Exchange (ETDEWEB)

    Ruud, Kenneth [Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Tromsø—The Arctic University of Norway, N-9037 Tromsø (Norway); Demissie, Taye B. [Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Tromsø—The Arctic University of Norway, N-9037 Tromsø (Norway); Institute of Physical Chemistry, Polish Academy of Sciences, 01-224 Warszawa, Kasprzaka 44 (Poland); Jaszuński, Michał, E-mail: michal.jaszunski@icho.edu.pl [Institute of Organic Chemistry, Polish Academy of Sciences, 01-224 Warszawa, Kasprzaka 44 (Poland)

    2014-05-21

    We present an analysis of the spin–rotation and absolute shielding constants of XF{sub 6} molecules (X = S, Se, Te, Mo, W) based on ab initio coupled cluster and four-component relativistic density-functional theory (DFT) calculations. The results show that the relativistic contributions to the spin–rotation and shielding constants are large both for the heavy elements as well as for the fluorine nuclei. In most cases, incorporating the computed relativistic corrections significantly improves the agreement between our results and the well-established experimental values for the isotropic spin–rotation constants and their anisotropic components. This suggests that also for the other molecules, for which accurate and reliable experimental data are not available, reliable values of spin–rotation and absolute shielding constants were determined combining ab initio and relativistic DFT calculations. For the heavy nuclei, the breakdown of the relationship between the spin–rotation constant and the paramagnetic contribution to the shielding constant, due to relativistic effects, causes a significant error in the total absolute shielding constants.

  4. A fast and zero-biased photodetector based on GaTe-InSe vertical 2D p-n heterojunction

    Science.gov (United States)

    Feng, W.; Jin, Z.; Yuan, J.; Zhang, J.; Jia, S.; Dong, L.; Yoon, J.; Zhou, L.; Vajtai, R.; Tour, J. M.; Ajayan, P. M.; Hu, P.; Lou, J.

    2018-04-01

    p-n junctions serve as the building blocks for fundamental semiconductor devices, such as solar cells, light-emitting diodes (LEDs) and photodetectors. With recent studies unveiling the excellent optoelectronic properties of two-dimensional (2D) semiconductors, they are considered to be superb candidates for high performance p-n junctions. Here, we fabricate a vertical GaTe-InSe van der Waals (vdWs) p-n heterojunction by a PDMS-assisted transfer technique without etching. The fabricated p-n heterojunction shows gate-tunable current-rectifying behavior with a rectification factor reaching 1000. In addition, it features fast photodetection under zero bias as well as a high power conversion efficiency (PCE). Under 405 nm laser excitation, the zero-biased photodetector shows a high responsivity of 13.8 mA W-1 as well as a high external quantum efficiency (EQE) of 4.2%. Long-term stability is also observed and a response time of 20 µs is achieved due to stable and fast carrier transit through the built-in electric field in the depletion region. Fast and efficient charge separation in the vertical 2D p-n junction paves the way for developing 2D photodetectors with zero dark current, high speed and low power consumption.

  5. Order-disorder phase transitions in the two-dimensional semiconducting transition metal dichalcogenide alloys Mo1−xWxX2 (X = S, Se, and Te)

    KAUST Repository

    Gan, Liyong

    2014-10-21

    A combination of density functional theory, an empirical model, and Monte Carlo simulations is used to shed light on the evolution of the atomic distribution in the two-dimensional semiconducting transition metal dichalcogenide alloys Mo1−xWxX2 (X = S, Se, and Te) as a function of the W concentration and temperature. Both random and ordered phases are discovered and the origin of the phase transitions is clarified. While the empirical model predicts at x = 1/3 and 2/3 ordered alloys, Monte Carlo simulations suggest that they only exist at low temperature due to a small energetic preference of Mo-X-W over Mo-X-Mo and W-X-W interactions, explaining the experimental observation of random alloy Mo1−xWxS2. Negative formation energies point to a high miscibility. Tunability of the band edges and band gaps by alteration of the W concentration gives rise to a broad range of applications.

  6. Correlation between some thermo-mechanical and physico-chemical properties in multi-component glasses of Se-Te-Sn-Cd system

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Amit; Mehta, Neeraj [Banaras Hindu University, Department of Physics, Institute of Science, Varanasi (India)

    2017-06-15

    The glass transition phenomenon is guided by the swift cooling of a melt (glass-forming liquid). Consequently, the glass as a final product consists of a considerable number of micro-voids having the size of the order of atomic and/or molecular sizes. The model of free volume fluctuation helps in describing the diverse physico-chemical properties of amorphous materials (like glasses and polymers). This theory is based on the fraction of fluctuation free frozen at the glass transition temperature and it forms a basis for determination of various significant thermo-mechanical properties. In the present work, Vickers hardness test method is employed that provides useful information concerning the mechanical behavior of brittle solids. The present work emphasizes the results of micro-indentation measurements on recently synthesized novel Se{sub 78-x}Te{sub 20}Sn{sub 2}Cd{sub x} glassy system. Basic thermo-mechanical parameters such as micro-hardness, volume (V{sub h}), formation energy (E{sub h}) of micro-voids in the glassy network and modulus of elasticity (E) have been determined and their variation with glass composition has been investigated. (orig.)

  7. Small-angle x-ray scattering and density measurements of liquid Se50-Te50 mixture at high temperatures and high pressures using synchrotron radiation

    International Nuclear Information System (INIS)

    Kajihara, Y; Inui, M; Matsuda, K; Tomioka, Y

    2010-01-01

    We have carried out small-angle x-ray scattering and x-ray transmission measurements of liquid Se 50 -Te 50 mixture at SPring-8 in Japan and obtained the structure factor S(Q) at small-Q region (0.6 -1 ) and the density at high temperatures and high pressures up to 1000 0 C and 180 MPa. We report preliminary results in this paper. With increasing temperature, the density shows a minimum at around 500 0 C and a maximum at around 700 0 C. On the other hand, S(0) becomes maximum and S(Q) strongly depends on Q at around 600 0 C, which is about the middle temperature where the density shows the minimum and maximum. The temperatures shift to lower side when the pressure increases. These results prove that, with increasing temperature, the sample exhibits gradual transition from low-density structure to high-density structure, which causes mesoscopic density fluctuations in the intermediate temperature region.

  8. Correlation between some thermo-mechanical and physico-chemical properties in multi-component glasses of Se-Te-Sn-Cd system

    Science.gov (United States)

    Kumar, Amit; Mehta, Neeraj

    2017-06-01

    The glass transition phenomenon is guided by the swift cooling of a melt (glass-forming liquid). Consequently, the glass as a final product consists of a considerable number of micro-voids having the size of the order of atomic and/or molecular sizes. The model of free volume fluctuation helps in describing the diverse physico-chemical properties of amorphous materials (like glasses and polymers). This theory is based on the fraction of fluctuation free frozen at the glass transition temperature and it forms a basis for determination of various significant thermo-mechanical properties. In the present work, Vickers hardness test method is employed that provides useful information concerning the mechanical behavior of brittle solids. The present work emphasizes the results of micro-indentation measurements on recently synthesized novel Se78- x Te20Sn2Cd x glassy system. Basic thermo-mechanical parameters such as micro-hardness, volume ( V h), formation energy ( E h) of micro-voids in the glassy network and modulus of elasticity ( E) have been determined and their variation with glass composition has been investigated.

  9. Correlation between some thermo-mechanical and physico-chemical properties in multi-component glasses of Se-Te-Sn-Cd system

    International Nuclear Information System (INIS)

    Kumar, Amit; Mehta, Neeraj

    2017-01-01

    The glass transition phenomenon is guided by the swift cooling of a melt (glass-forming liquid). Consequently, the glass as a final product consists of a considerable number of micro-voids having the size of the order of atomic and/or molecular sizes. The model of free volume fluctuation helps in describing the diverse physico-chemical properties of amorphous materials (like glasses and polymers). This theory is based on the fraction of fluctuation free frozen at the glass transition temperature and it forms a basis for determination of various significant thermo-mechanical properties. In the present work, Vickers hardness test method is employed that provides useful information concerning the mechanical behavior of brittle solids. The present work emphasizes the results of micro-indentation measurements on recently synthesized novel Se_7_8_-_xTe_2_0Sn_2Cd_x glassy system. Basic thermo-mechanical parameters such as micro-hardness, volume (V_h), formation energy (E_h) of micro-voids in the glassy network and modulus of elasticity (E) have been determined and their variation with glass composition has been investigated. (orig.)

  10. Growth of niobium on the three-dimensional topological insulator Bi{sub 2}Te{sub 1.95}Se{sub 1.05}

    Energy Technology Data Exchange (ETDEWEB)

    Meixner, Philipp [Novel Materials Group, Humboldt-Universität zu Berlin, 12489 Berlin (Germany); Department of Physics and Astronomy, Seoul National University, Seoul 151-747 (Korea, Republic of); Lim, Seong Joon [Department of Physics and Astronomy, Seoul National University, Seoul 151-747 (Korea, Republic of); Park, Joonbum; Kim, Jun Sung [Department of Physics, Pohang University of Science and Technology, Pohang 790-784 (Korea, Republic of); Fischer, Saskia F. [Novel Materials Group, Humboldt-Universität zu Berlin, 12489 Berlin (Germany); Seo, Jungpil [NANOSPM Lab, Daegu Gyeongbuk Institute of Science and Technology, Daegu 711-873 (Korea, Republic of); Kuk, Young [Department of Physics and Astronomy, Seoul National University, Seoul 151-747 (Korea, Republic of)

    2016-01-15

    Graphical abstract: - Highlights: • We grew niobium on topological insulator at different substrate temperatures. • Local density of states is modified by deposited Nb islands. • We found a downward shift of the Dirac point, since niobium acts as a donor. • Nb grew in layer-by-layer growth mode up to an annealing temperature of 450 °C. • We applied a new cleaving method allowing for sample heating of flux-grown TI. - Abstract: While applying a new cleaving method, we investigated the growth of Nb on the three-dimensional (3D) topological insulator (TI) Bi{sub 2}Te{sub 1.95}Se{sub 1.05} by scanning tunneling microscopy and spectroscopy. After the deposition of nearly a full monolayer of Nb by high-energy electron-beam evaporation, we observed a downshift of the bands and the Dirac point on the TI surface, which is the result of an n-type doping of the TI by transition metal adatoms. Extra peaks in the spectroscopy results upon Nb deposition might indicate a Rashba-split of the bulk bands. Nb grew in small 10 nm wide islands upon sub-monolayer growth and in a layer-by-layer growth mode up to an annealing temperature of 450 °C.

  11. Description of vibrational properties of random alloy ZnTe{sub 1-x}Se{sub x} within the percolation model

    Energy Technology Data Exchange (ETDEWEB)

    Souhabi, Jihane; Chafi, Allal; Kassem, Mohammed; Nassour, Ayoub; Gleize, Jerome; Postnikov, A.V.; Hugel, J.; Pages, Olivier [Laboratoire de Physique des Milieux Denses, Universite Paul Verlaine - Metz, 1 Bd Arago, 57070 Metz (France)

    2009-05-15

    We discuss the classification of the phonon type behavior of semiconductor alloys as apparent in the Raman and infrared spectra, i.e. in terms of types (i) 1-bond{yields}1-mode and (ii) 2-bond{yields}1-mode (both covered by the Modified Random Element Isodisplacement model, operating at the macroscopic scale), and also (iii) the modified 2-mode type (exceptional), in the framework of the recent 1-bond{yields}2-mode percolation model based on a description of the alloy disorder at the mesoscopic scale. The leading systems of types (i) and (iii), i.e., InGaAs and InGaP, respectively, were earlier shown to obey the percolation model. The aim of this work is to investigate whether the percolation model further extends to the leading system of the last type (ii), i.e. ZnTeSe. With this end in view, we perform a careful re-examination of the Raman and infrared spectra of this alloy, as available in the literature. Special attention is awarded to the discussion and modeling of the puzzling multi-mode infrared reflectivity spectra. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  12. Thermal expansion and structural properties of (CuAlTe2)1-x(CuAlSe2)x solid solutions

    International Nuclear Information System (INIS)

    Korzun, B.V.; Fadzeyeva, A.A.; Bente, K.; Schmitz, W.; Schorr, S.

    2006-01-01

    Investigations of the thermal expansion of (CuAlTe 2 ) 1-x (CuAlSe 2 ) x solid solutions in the temperature range from 100 to 800 K have been carried out for the first time. It has been demonstrated that the thermal expansion coefficient α L grows considerably in the temperature range from 100 to 300 K, whereas the temperature dependence above 300 K is rather weak. The isotherms of composition dependence of the thermal expansion coefficient α L for 100, 293, 500 and 800 K were constructed, and it was found that linear relations could express them. The Debye temperatures θ D , the average mean-square dynamic displacements anti u 2 , the average root-mean-square amplitudes of thermal vibration RMS, the anion position parameter u using S. C. Abrahams and J. L. Bernstein (u AB ) and J. E. Jaffe and A. Zunger (u JZ ) models were calculated. The composition dependence of microhardness H using the phenomenological theory was also calculated, and it was discovered that this dependence has a non-linear character with a maximum of 383 kg/mm 2 at x=0.67. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  13. External temperature and pressure effects on thermodynamic properties and mechanical stability of yttrium chalcogenides YX (X=S, Se and Te)

    Energy Technology Data Exchange (ETDEWEB)

    Seddik, T. [Laboratoire de Physique Quantique et de Modélisation Mathématique, Université de Mascara, 29000 Mascara (Algeria); Khenata, R., E-mail: khenata_rabah@yahoo.fr [Laboratoire de Physique Quantique et de Modélisation Mathématique, Université de Mascara, 29000 Mascara (Algeria); Bouhemadou, A.; Guechi, N. [Laboratory for Developing New Materials and their Characterization, Department of Physics, Faculty of Science, University of Setif, 19000 Setif (Algeria); Sayede, A. [Université Lille Nord de France, F-59000 Lille (France); Université-Artois, UCCS, F-62300 Lens (France); CNRS, UMR 8181, F-59650 Villeneuve d’Ascq (France); Varshney, D. [Materials Science Laboratory, School of Physics, Vigyan Bhavan, Devi Ahilya University, Khandwa Road Campus, Indore 452001, Madhya Pradesh (India); Al-Douri, Y. [Institute of Nono Electronic Engineering, University Malaysia Perlis, 01000 Kangar, Perlis (Malaysia); Reshak, A.H. [Institute of Complex Systems, FFPW, CENAKVA, University of South Bohemia in CB, Nove Hrady 37333 (Czech Republic); Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis (Malaysia); Bin-Omran, S. [Department of Physics and Astronomy, Faculty of Science, King Saud University, PO Box 2455, Riyadh 11451 (Saudi Arabia)

    2013-11-01

    The full potential linearized augmented plane wave method within the framework of density functional theory is employed to investigate the structural, thermodynamic and elastic properties of the yttrium chalcogenides (YX: X=S, Se, and Te) in their low-pressure phase (Fm3{sup ¯}m) and high-pressure phase (Pm3{sup ¯}m). The exchange-correlation potential is treated with the generalized gradient approximation of Perdew–Burke–Ernzerhof (GGA-PBE). Temperature dependence of the volume and both adiabatic and isothermal bulk moduli is predicted for a temperature range from 0to1200K for the both phases of the herein considered materials. Furthermore, we have analyzed the thermodynamic properties such as the heat capacities, C{sub V} and C{sub P}, thermal expansion, α, and Debye temperature, Θ{sub D,} under variable pressure and temperature. We have calculated the isothermal elastic constants C{sub ij}{sup T} of the YX monochalcogenides in both NaCl-B1 and CsCl-B2 phases at zero pressure and a temperature range 0−1200K. The results show that rare earth yttrium monochalcogenides are mechanically stable at high temperature. The elastic anisotropy of all studied materials in the two phases has been studied using three different methods.

  14. Order-disorder phase transitions in the two-dimensional semiconducting transition metal dichalcogenide alloys Mo1−xWxX2 (X = S, Se, and Te)

    KAUST Repository

    Gan, Liyong; Zhan