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Sample records for beo wurtzite structure

  1. Stability of the Wurtzite Structure

    DEFF Research Database (Denmark)

    Lawætz, Peter

    1972-01-01

    An analysis of available data for 20 wurtzite compounds of the ANB8-N type shows that the stability as compared with zinc blende is closely connected with deviations of the c / a ratio from the ideal value of 1.633. A simple qualitative model is proposed to account for this feature. The variation...... in c / a is then correlated with the charge parameter ZC / ℏωp, where Z is the (effective) valence, C Phillips's electronegativity difference, and ℏωp the plasma energy of the free-valence-electron gas. The results indicate that c / a may be predicted with an uncertainty of 0.1%....

  2. Ab-initio investigations of the electronic properties of bulk wurtzite Beryllia and its derived nanofilms

    KAUST Repository

    Goumri-Said, Souraya; Kanoun, Mohammed

    2010-01-01

    In this Letter we investigate the electronic properties of the bulk and the nanofilm BeO in wurtzite structure. We performed a first-principles pseudo-potential method within the generalized gradient approximation. We will give more importance

  3. Evidence for an ultrafast breakdown of the BeO band structure due to swift argon and xenon ions.

    Science.gov (United States)

    Schiwietz, G; Czerski, K; Roth, M; Grande, P L; Koteski, V; Staufenbiel, F

    2010-10-29

    Auger-electron spectra associated with Be atoms in the pure metal lattice and in the stoichiometric oxide have been investigated for different incident charged particles. For fast incident electrons, for Ar7+ and Ar15+ ions as well as Xe15+ and Xe31+ ions at velocities of 6% to 10% the speed of light, there are strong differences in the corresponding spectral distributions of Be-K Auger lines. These differences are related to changes in the local electronic band structure of BeO on a femtosecond time scale after the passage of highly charged heavy ions.

  4. Theoretical analysis of the structural phase transformation from B3 to B1 in BeO under high pressure

    Science.gov (United States)

    Jain, Arvind; Verma, Saligram; Nagarch, R. K.; Shah, S.; Kaurav, Netram

    2018-05-01

    We have performed the phase transformation and elastic properties of BeO at high pressure by formulating effective interionic interaction potential. The elastic constants, including the long-range Coulomb and van der Waals (vdW) interactions and the short-range repulsive interaction of up to second-neighbor ions within the Hafemeister and Flygare approach, are derived. Assuming that both the ions are polarizable, we employed the Slater-Kirkwood variational method to estimate the vdW coefficients, a structural phase transition (Pt) from ZnS structure (B3) to NaCl structure (B1) at 108 GPa has been predicted for BeO. The estimated value of the phase transition pressure (Pt) and the magnitude of the discontinuity in volume at the transition pressure are consistent as compared to the theoretical data. The variations of elastic constants with pressure follow a systematic trend identical to that observed in others compounds of ZnS type structure family.

  5. Crystal and electronic structure study of Mn doped wurtzite ZnO nanoparticles

    Directory of Open Access Journals (Sweden)

    O.M. Ozkendir

    2016-08-01

    Full Text Available The change in the crystal and electronic structure properties of wurtzite ZnO nanoparticles was studied according to Mn doping in the powder samples. The investigations were conducted by X-ray Absorption Fine Structure Spectroscopy (XAFS technique for the samples prepared with different heating and doping processes. Electronic analysis was carried out by the collected data from the X-ray Absorption Near-Edge Structure Spectroscopy (XANES measurements. Additional crystal structure properties were studied by Extended-XAFS (EXAFS analysis. Longer heating periods for the undoped wurtzite ZnO samples were determined to own stable crystal geometries. However, for some doped samples, the distortions in the crystal were observed as a result of the low doping amounts of Mn which was treated as an impurity. Besides, the changes in oxygen locations were determined to create defects and distortions in the samples.

  6. Ab initio electronic band structure calculation of InP in the wurtzite phase

    Science.gov (United States)

    Dacal, Luis C. O.; Cantarero, Andrés

    2011-05-01

    We present ab initio calculations of the InP band structure in the wurtzite phase and compare it with that of the zincblende phase. In both calculations, we use the full potential linearized augmented plane wave method as implemented in the WIEN2k code and the modified Becke-Johnson exchange potential, which provides an improved value of the bandgap. The structural optimization of the wurtizte InP gives a=0.4150 nm, c=0.6912 nm, and an internal parameter u=0.371, showing the existence of a spontaneous polarization along the growth axis. As compared to the ideal wurtzite structure (that with the lattice parameter derived from the zincblende structure calculations), the actual wurtzite structure is compressed (-1.3%) in plane and expanded (0.7%) along the c-direction. The value of the calculated band gaps agrees well with recent optical experiments. The calculations are also consistent with the optical transitions found using polarized light.

  7. Ab initio calculations of indium arsenide in the wurtzite phase: structural, electronic and optical properties

    International Nuclear Information System (INIS)

    Dacal, Luis C O; Cantarero, A

    2014-01-01

    Most III–V semiconductors, which acquire the zinc-blende phase as bulk materials, adopt the metastable wurtzite phase when grown in the form of nanowires. These are new semiconductors with new optical properties, in particular, a different electronic band gap when compared with that grown in the zinc-blende phase. The electronic gap of wurtzite InAs at the Γ–point of the Brillouin zone (E 0 gap) has been recently measured, E 0 =0.46 eV at low temperature. The electronic gap at the A–point of the Brillouin zone (equivalent to the L–point in the zinc-blende structure, E 1 ) has also been obtained recently based on a resonant Raman scattering experiment. In this work, we calculate the band structure of InAs in the zinc-blende and wurtzite phases, using the full potential linearized augmented plane wave method, including spin-orbit interaction. The electronic band gap has been improved through the modified Becke–Johnson exchange-correlation potential. Both the E 0 and E 1 gaps agree very well with the experiment. From the calculations, a crystal field splitting of 0.122 eV and a spin-orbit splitting of 0.312 eV (the experimental value in zinc-blende InAs is 0.4 eV) has been obtained. Finally, we calculate the dielectric function of InAs in both the zinc-blende and wurtzite phases and a comparative discussion is given. (paper)

  8. Ab initio calculations of indium arsenide in the wurtzite phase: structural, electronic and optical properties

    Science.gov (United States)

    Dacal, Luis C. O.; Cantarero, A.

    2014-03-01

    Most III-V semiconductors, which acquire the zinc-blende phase as bulk materials, adopt the metastable wurtzite phase when grown in the form of nanowires. These are new semiconductors with new optical properties, in particular, a different electronic band gap when compared with that grown in the zinc-blende phase. The electronic gap of wurtzite InAs at the \\Gamma -point of the Brillouin zone ({{E}_{0}} gap) has been recently measured, {{E}_{0}}=0.46 eV at low temperature. The electronic gap at the A-point of the Brillouin zone (equivalent to the L-point in the zinc-blende structure, {{E}_{1}}) has also been obtained recently based on a resonant Raman scattering experiment. In this work, we calculate the band structure of InAs in the zinc-blende and wurtzite phases, using the full potential linearized augmented plane wave method, including spin-orbit interaction. The electronic band gap has been improved through the modified Becke-Johnson exchange-correlation potential. Both the {{E}_{0}} and {{E}_{1}} gaps agree very well with the experiment. From the calculations, a crystal field splitting of 0.122 eV and a spin-orbit splitting of 0.312 eV (the experimental value in zinc-blende InAs is 0.4 eV) has been obtained. Finally, we calculate the dielectric function of InAs in both the zinc-blende and wurtzite phases and a comparative discussion is given.

  9. Electronic structure and photocatalytic activity of wurtzite Cu–Ga–S nanocrystals and their Zn substitution

    KAUST Repository

    Kandiel, Tarek

    2015-03-23

    Stoichiometric and gallium-rich wurtzite Cu-Ga-S ternary nanocrystals were synthesized via a facile solution-based hot injection method using 1-dodecanethiol as a sulfur source. The use of 1-dodecanethiol was found to be essential not only as a sulfur source but also as a structure-directing reagent to form a metastable wurtzite structure. In addition, the substitution of zinc in the wurtzite gallium-rich Cu-Ga-S nanocrystals was also investigated. The obtained nanocrystals were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS), photoluminescence (PL), and inductively coupled plasma atomic emission spectroscopy (ICP-OES). Electronic structures of pristine and the Zn-substituted Cu-Ga-S system were investigated using density functional theory (DFT) with HSE06 exchange-correlation functional. The calculated bandgaps accurately reflect the measured ones. The allowed electronic transitions occur upon the photon absorption from the (Cu + S) band towards the (Ga + S) one. The Zn substitution was found not to contribute to the band edge structure and hence altered the bandgaps only slightly, the direct transition nature remaining unchanged with the Zn substitution. The photocatalytic activities of H2 evolution from an aqueous Na2S/Na2SO3 solution under visible-light illumination on the synthesized nanocrystals were investigated. While the stoichiometric CuGaS2 exhibited negligible activity, the gallium-rich Cu-Ga-S ternary nanocrystals displayed reasonable activity. The optimum Zn substitution in the gallium-rich Cu-Ga-S ternary nanocrystals enhanced the H2 evolution rate, achieving an apparent quantum efficiency of >6% at 400 nm. © 2015 The Royal Society of Chemistry.

  10. Ab-initio investigations of the electronic properties of bulk wurtzite Beryllia and its derived nanofilms

    International Nuclear Information System (INIS)

    Goumri-Said, Souraya; Kanoun, Mohammed Benali

    2010-01-01

    In this Letter we investigate the electronic properties of the bulk and the nanofilm BeO in wurtzite structure. We performed a first-principles pseudo-potential method within the generalized gradient approximation. We will give more importance to the changes in band structure and density of states between the bulk structure and its derived nanofilms. The bonding characterization will be investigated via the analysis Mulliken population and charge density contours. It is found that the nanofilm retains the same properties as its bulk structure with slight changes in electronic properties and band structure which may offer some unusual transport properties.

  11. Ab-initio investigations of the electronic properties of bulk wurtzite Beryllia and its derived nanofilms

    KAUST Repository

    Goumri-Said, Souraya

    2010-08-01

    In this Letter we investigate the electronic properties of the bulk and the nanofilm BeO in wurtzite structure. We performed a first-principles pseudo-potential method within the generalized gradient approximation. We will give more importance to the changes in band structure and density of states between the bulk structure and its derived nanofilms. The bonding characterization will be investigated via the analysis Mulliken population and charge density contours. It is found that the nanofilm retains the same properties as its bulk structure with slight changes in electronic properties and band structure which may offer some unusual transport properties. © 2010 Elsevier B.V. All rights reserved.

  12. Mechanism of polarization switching in wurtzite-structured zinc oxide thin films

    Science.gov (United States)

    Konishi, Ayako; Ogawa, Takafumi; Fisher, Craig A. J.; Kuwabara, Akihide; Shimizu, Takao; Yasui, Shintaro; Itoh, Mitsuru; Moriwake, Hiroki

    2016-09-01

    The properties of a potentially new class of ferroelectric materials based on wurtzite-structured ZnO thin films are examined using the first-principles calculations. Theoretical P-E hysteresis loops were calculated using the fixed-D method for both unstrained and (biaxially) strained single crystals. Ferroelectric polarization switching in ZnO (S.G. P63mc) is shown to occur via an intermediate non-polar structure with centrosymmetric P63/mmc symmetry by displacement of cations relative to anions in the long-axis direction. The calculated coercive electric field (Ec) for polarization switching was estimated to be 7.2 MV/cm for defect-free monocrystalline ZnO. During switching, the short- and long-axis lattice parameters expand and contract, respectively. The large structural distortion required for switching may explain why ferroelectricity in this compound has not been reported experimentally for pure ZnO. Applying an epitaxial tensile strain parallel to the basal plane is shown to be effective in lowering Ec during polarization, with a 5% biaxial expansion resulting in a decrease of Ec to 3.5 MV/cm. Comparison with calculated values for conventional ferroelectric materials suggests that the ferroelectric polarization switching of wurtzite-structured ZnO may be achievable by preparing high-quality ZnO thin films with suitable strain levels and low defect concentrations.

  13. Structural refinement, photoluminescence and Raman spectroscopy of wurtzite Mn-doped Zn O pellets

    Energy Technology Data Exchange (ETDEWEB)

    Marquina, J.; Martin, J.; Luengo, J.; Vera, F.; Roa, L. [Centro de Estudios Avanzados en Optica, Universidad de los Andes, Merida 5101 (Venezuela, Bolivarian Republic of); Gonzalez, J. [Centro de Estudios de Semiconductores, Universidad de los Andes, Merida 5101 (Venezuela, Bolivarian Republic of); Rodriguez, F.; Renero L, C.; Valiente, R. [Malta-Consolider Team, CITIMAC, Facultad de Ciencias, Universidad de Cantabria, Santander 69005 (Spain); Delgado, G. E., E-mail: marquinajesus@gmail.com [Laboratorio de Cristalografia, Facultad de Ciencias, Universidad de los Andes, Merida 5101 (Venezuela, Bolivarian Republic of)

    2017-11-01

    We report the results of the Rietveld refinement, photoluminescence and Raman spectroscopy of Mn-doped Zn O ceramic pellets. Rietveld refinement shows that samples crystallize in the wurtzite structure and for the Mn-doped sample indicated that the Mn atoms substitute the Zn tetrahedral crystallographic sites in the Zn O host lattice. The emission and absorption spectra of Mn-doped Zn O have been investigated in the visible-UV region and the data have been interpreted in terms of the wurtzite Zn O electronic structure. Two broad bands, one due to superposition between donor bound excitons (DX) and free excitons (FX) and other due free-to bond excitonic recombination (FB) dominates the low-temperature photoluminescence spectra of Mn-doped Zn O bulk. In the Raman spectrum, an extra mode at ∼520 cm{sup -1} has been observed in agreement with earlier works, and it is an indicator for the incorporation of Mn{sup +2} ions into the Zn O host matrix since it is not is observed in Zn O pristine. Rietveld refinement of the X-ray diffraction patterns, energy-dispersive X-ray spectroscopy (EDS) technique, and Raman spectroscopies were performed to study these effects. (Author)

  14. Structural study of the AlP, GaAs and AlAs semiconductors with wurtzite structure

    International Nuclear Information System (INIS)

    Bautista H, A.; Perez A, L.; Pal, U.; Rivas S, J.F.

    2003-01-01

    In this work we present ab initio calculations of optimization geometries, lattice constant and electronic structure for semiconductors wurtzite type, like AIN, CdS, Zn S, Zn Se, Ga N and GaAs. For this, we used the CASTEP program of CERUIS with LDA and GGA approximations, in the framework of Functional Density Theory. The used pseudopotentials are available in that program and were generated using the optimization scheme of Troullier-Martins. With the lattice constant just optimized, we calculate then the X-ray spectra for studied semiconductors.We analyzed the effect of used pseudopotentials on function of the results obtained. Finally, we predicted the geometry and X-ray pattern for AIP, AlAs and GaAs with wurtzite structure, giving evidence about the semiconductor character of these materials. (Author)

  15. Structural and electronic properties of wurtzite Bx Al1-x N from first-principles calculations

    KAUST Repository

    Zhang, Muwei; Li, Xiaohang

    2017-01-01

    The structural and electronic properties of wurtzite BAlN (0≤x≤1) are studied using density functional theory. The change of lattice parameters with increased B composition shows small bowing parameters and thus slightly nonlinearity. The bandgap exhibits strong dependence on the B composition, where transition from direct to indirect bandgap occurs at a relatively low B composition (x∼0.12) is observed, above which the bandgap of BAlN maintained indirect, thus desirable for low-absorption optical structures. The Γ-A and Γ-K indirect bandgaps are dominant at lower and higher B compositions, respectively. Density of states (DOS) of the valence band is susceptible to the B incorporation. Strong hybridization of Al, B, and N in p-states leads to high DOS near the valence band maximum. The hybridization of Al and B in s-states at lower B compositions and p-states of B at higher B compositions give rise to high DOS near lower end of the upper valence band. Charge density analysis reveals the B-N chemical bond is more covalent than the Al-N bond. This will lead to more covalent crystal with increasing B composition. Dramatic change of the heavy hole effective mass is found due to significant curvature increase of the band by minor B incorporation.

  16. Structural and electronic properties of wurtzite Bx Al1-x N from first-principles calculations

    KAUST Repository

    Zhang, Muwei

    2017-06-14

    The structural and electronic properties of wurtzite BAlN (0≤x≤1) are studied using density functional theory. The change of lattice parameters with increased B composition shows small bowing parameters and thus slightly nonlinearity. The bandgap exhibits strong dependence on the B composition, where transition from direct to indirect bandgap occurs at a relatively low B composition (x∼0.12) is observed, above which the bandgap of BAlN maintained indirect, thus desirable for low-absorption optical structures. The Γ-A and Γ-K indirect bandgaps are dominant at lower and higher B compositions, respectively. Density of states (DOS) of the valence band is susceptible to the B incorporation. Strong hybridization of Al, B, and N in p-states leads to high DOS near the valence band maximum. The hybridization of Al and B in s-states at lower B compositions and p-states of B at higher B compositions give rise to high DOS near lower end of the upper valence band. Charge density analysis reveals the B-N chemical bond is more covalent than the Al-N bond. This will lead to more covalent crystal with increasing B composition. Dramatic change of the heavy hole effective mass is found due to significant curvature increase of the band by minor B incorporation.

  17. Electronic structure and optical properties of the scintillation material wurtzite ZnS(Ag)

    Institute of Scientific and Technical Information of China (English)

    Dong-Yang Jiang; Zheng Zhang; Rui-Xue Liang; Zhi-Hong Zhang; Yang Li; Qiang Zhao; Xiao-Ping Ouyang

    2017-01-01

    In order to investigate the effect of Ag doping (ZnS(Ag)) and Zn vacancy (Vzn) on the alpha particle detection performance of wurtzite (WZ) ZnS as a scintillation cell component,the electronic structure and optical properties of ZnS,ZnS(Ag),and Vzn were studied by firstprinciple calculation based on the density functional theory.The results show that the band gaps of ZnS,ZnS(Ag),and Vzn are 2.17,1.79,and 2.37 eV,respectively.Both ZnS(Ag) and Vzn enhance the absorption and reflection of the low energy photons.A specific energy,about 2.9 eV,leading to decrease of detection efficiency is observed.The results indicate that Ag doping has a complex effect on the detection performance.It is beneficial to produce more visible light photons than pure WZ ZnS when exposed to the same amount of radiation,while the increase of the absorption to visible light photons weakens the detection performance.Zn vacancy has negative effect on the detection performance.If we want to improve the detection performance of WZ ZnS,Ag doping will be a good way,but we should reduce the absorption to visible light photons and control the number of Zn vacancy rigorously.

  18. Quasi-two-dimensional superconductivity in wurtzite-structured InN films

    International Nuclear Information System (INIS)

    Ling, D.C.; Cheng, J.H.; Lo, Y.Y.; Du, C.H.; Chiu, A.P.; Chang, P.H.; Chang, C.A.

    2007-01-01

    C-axis oriented InN films with wurtzite structure were grown on sapphire(0001) substrate by MOCVD method. Superconductivity with transition onset temperature T c,onset around 3.5 K has been characterized by magnetotransport measurements in fields up to 9 Tesla for films with carrier concentration in the range of 1 x 10 19 cm -3 to 7 x 10 20 cm -3 . Among them, the film with a nitridation buffer layer has the highest zero-resistance temperature T c0 of 2 K. The normal-state magnetoresistance follows Kohler's rule ΔR/R∝(H/R) 2 , indicating that there is a single species of charge carrier with single scattering time at all points on the Fermi surface. The extrapolated value of zero-temperature upper critical field H c2 ab (0) and H c2 c (0) is estimated to be 5900 G and 2800 G, respectively, giving rise to the anisotropy parameter γ about 2.1. The angular dependence of the upper critical field is in good agreement with the behavior predicted by Lawrence-Doniach model in the two-dimensional (2D) limit strongly suggesting that the InN film is a quasi-2D superconductor. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  19. Unit cell structure of the wurtzite phase of GaP nanowires : X-ray diffraction studies and density functional theory calculations

    OpenAIRE

    Kriegner, D.; Assali, S.; Belabbes, A.; Etzelstorfer, T.; Holy, V.; Schülli, T.U.; Bechstedt, F.; Bakkers, E.P.A.M.; Bauer, G.; Stangl, J.

    2013-01-01

    We present structural characterization of the wurtzite crystal structure of GaP nanowires, which were recently shown to have a direct electronic band gap. The structural parameters of the wurtzite phase do consist of two lattice parameters and one internal degree of freedom, determining the Ga-P bond length along the c direction. Using density functional theory calculations, we study the influence of the internal degree of freedom on the band structure. By synchrotron x-ray diffraction studie...

  20. Lattice stability of metastable AlN and wurtzite-to-rock-salt structural transformation by CALPHAD modeling

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Yanhui, E-mail: yanhui.z@hotmail.com [Karlsruhe Institute of Technology (KIT), Institute for Applied Materials-Applied Materials Physics (IAM-AWP), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany); High-performance Ceramics Division, Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 110016, Shenyang (China); Franke, Peter; Li, Dajian; Seifert, Hans Jürgen [Karlsruhe Institute of Technology (KIT), Institute for Applied Materials-Applied Materials Physics (IAM-AWP), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany)

    2016-12-01

    Reliable lattice stability of cubic AlN with rock-salt structure (rs-AlN) is the prerequisite of accurate thermodynamic modeling of cubic (M, Al)N solid solutions (M = Ti, Zr, Cr etc.). In order to derive the Gibbs energy of metastable rs-AlN, and then its lattice stability, we did the pressure-temperature (P-T) assessment of AlN phases by equations-of-state modeling. Meanwhile, the molar volumes and the heat capacities of wurtzite and rock-salt AlN, as well as the wurtzite-to-rock-salt structural transition at high P&T were successfully incorporated in CALPHAD-type database by integrating thermodynamic data from experiments and ab-initio calculations. These results promise subsequent investigations on phase stabilities and transitions of solid solutions with AlN component and the development of novel multicomponent coatings. - Highlights: • Phase stability investigation for novel multi-component metastable coatings. • Structural transition at high temperature and high pressure. • Integrating thermodynamic data from ab-initio calculations and experiments. • Thermal expansion, isothermal compressibility and heat capacity of w-AlN and rs-AlN.

  1. Optical study of the band structure of wurtzite GaP nanowires

    OpenAIRE

    Assali, S.; Greil, J.; Zardo, I.; Belabbes, A.; de Moor, M.W.A.; Kölling, S.; Koenraad, P.M.; Bechstedt, F.; Bakkers, E.P.A.M.; Haverkort, J.E.M.

    2016-01-01

    We investigated the optical properties of wurtzite (WZ) GaP nanowires by performing photoluminescence (PL) and time-resolved PL measurements in the temperature range from 4 K to 300 K, together with atom probe tomography to identify residual impurities in the nanowires. At low temperature, the WZ GaP luminescence shows donor-acceptor pair emission at 2.115 eV and 2.088 eV, and Burstein-Moss band-filling continuum between 2.180 and 2.253 eV, resulting in a direct band gap above 2.170 eV. Sharp...

  2. Al{sub 4}SiC{sub 4} wurtzite crystal: Structural, optoelectronic, elastic, and piezoelectric properties

    Energy Technology Data Exchange (ETDEWEB)

    Pedesseau, L., E-mail: laurent.pedesseau@insa-rennes.fr, E-mail: jacky.even@insa-rennes.fr; Even, J., E-mail: laurent.pedesseau@insa-rennes.fr, E-mail: jacky.even@insa-rennes.fr; Durand, O. [Fonctions Optiques pour les Technologies de l’Information, FOTON UMR 6082, CNRS, INSA de Rennes, 35708 Rennes (France); Modreanu, M. [Tyndall National Institute, University College Cork, Lee Maltings, Cork (Ireland); Chaussende, D.; Sarigiannidou, E.; Chaix-Pluchery, O. [LMGP, CNRS, Université Grenoble Alpes, 38000 Grenoble (France)

    2015-12-01

    New experimental results supported by theoretical analyses are proposed for aluminum silicon carbide (Al{sub 4}SiC{sub 4}). A state of the art implementation of the density functional theory is used to analyze the experimental crystal structure, the Born charges, the elastic properties, and the piezoelectric properties. The Born charge tensor is correlated to the local bonding environment for each atom. The electronic band structure is computed including self-consistent many-body corrections. Al{sub 4}SiC{sub 4} material properties are compared to other wide band gap wurtzite materials. From a comparison between an ellipsometry study of the optical properties and theoretical results, we conclude that the Al{sub 4}SiC{sub 4} material has indirect and direct band gap energies of about 2.5 eV and 3.2 eV, respectively.

  3. Structure, phase stability, and gaps of wurtzite MgZnO and CdZnO alloys

    International Nuclear Information System (INIS)

    Eisenacher, Matthias; Schleife, Andre; Furthmueller, Juergen; Bechstedt, Friedhelm; Kuehl Teles, Lara

    2008-01-01

    Recently II-VI compounds became more and more important as materials with potential applications in optoelectronic devices. For pseudomorphic heterostructures it is highly desirable to adjust the material properties carefully. Alloys allow to tailor a certain material property. Also from a theoretical point of view the investigation of mixed crystals is a challenge. We apply density functional theory and the generalized quasichemical approximation together with a cluster approximation to study MgZnO and CdZnO alloys in the wurtzite structure. The combination of these ab initio approaches enables us to study the thermodynamics of these systems as well as the structural and electronic properties with varying composition. We construct phase diagrams versus composition and temperature and calculate bond lengths as well as gap-bowing parameters for the two alloys versus average composition

  4. Comparison of Low Field Electron Transport in Zincblende and Wurtzite SiC Structures for High Gain Device Modeling

    Directory of Open Access Journals (Sweden)

    Hadi Arabshahi

    2011-01-01

    Full Text Available Temperature and doping dependencies of electron mobility in both wurtzite and zincblende SiC structures have been calculated using an iteravive technique. The following scattering mechanisims, i.e, impurity, polar optical phonon, acoustic phonon, piezoelectric and electron plasmon are inculded in the calculation. Ionized imurity scattering has been treated beyound the Born approximation using the phase-shift analysis. It is found that the electron mobility decreases monotonically as the temperature increases from 100 to 500 K. The low temperature value of electron mobilty increases significantly with increasing doping concentration. The iterative results are in fair agreement with other recent calculations obtained using the relaxation-time approximation and experimental methods.

  5. Optical study of the band structure of wurtzite GaP nanowires

    KAUST Repository

    Assali, S.

    2016-07-25

    We investigated the optical properties of wurtzite (WZ) GaP nanowires by performing photoluminescence (PL) and time-resolved PL measurements in the temperature range from 4 K to 300 K, together with atom probe tomography to identify residual impurities in the nanowires. At low temperature, the WZ GaP luminescence shows donor-acceptor pair emission at 2.115 eV and 2.088 eV, and Burstein-Moss band-filling continuum between 2.180 and 2.253 eV, resulting in a direct band gap above 2.170 eV. Sharp exciton α-β-γ lines are observed at 2.140–2.164–2.252 eV, respectively, showing clear differences in lifetime, presence of phonon replicas, and temperature-dependence. The excitonic nature of those peaks is critically discussed, leading to a direct band gap of ∼2.190 eV and to a resonant state associated with the γ-line ∼80 meV above the Γ8C conduction band edge.

  6. Optical study of the band structure of wurtzite GaP nanowires

    KAUST Repository

    Assali, S.; Greil, J.; Zardo, I.; Belabbes, Abderrezak; de Moor, M. W. A.; Koelling, S.; Koenraad, P. M.; Bechstedt, F.; Bakkers, E. P. A. M.; Haverkort, J. E. M.

    2016-01-01

    We investigated the optical properties of wurtzite (WZ) GaP nanowires by performing photoluminescence (PL) and time-resolved PL measurements in the temperature range from 4 K to 300 K, together with atom probe tomography to identify residual impurities in the nanowires. At low temperature, the WZ GaP luminescence shows donor-acceptor pair emission at 2.115 eV and 2.088 eV, and Burstein-Moss band-filling continuum between 2.180 and 2.253 eV, resulting in a direct band gap above 2.170 eV. Sharp exciton α-β-γ lines are observed at 2.140–2.164–2.252 eV, respectively, showing clear differences in lifetime, presence of phonon replicas, and temperature-dependence. The excitonic nature of those peaks is critically discussed, leading to a direct band gap of ∼2.190 eV and to a resonant state associated with the γ-line ∼80 meV above the Γ8C conduction band edge.

  7. The effect of high non-hydrostatic pressure on III-V semiconductors: zinc blende to wurtzite structural phase transition and multiphase generation

    International Nuclear Information System (INIS)

    Pizani, P S; Jasinevicius, R G

    2014-01-01

    Raman scattering was employed to study structural phase transitions of InSb, GaSb and GaAs induced by highly non-hydrostatic pressures applied by mechanical impact, in which high compression/decompression rates are imposed to the sample. The results showed that is possible to produce several structural phases localized in different micrometric regions of the same sample: the zinc blende to possibly wurtzite structural phase transition and the generation of a multiphase state.

  8. Room temperature ferromagnetism in Zn{sub 1-x}Co{sub x}S thin films with wurtzite structure

    Energy Technology Data Exchange (ETDEWEB)

    Patel, Shiv P., E-mail: shivpoojanbhola@gmail.com [Physics Department, University of Allahabad, Allahabad 211002 (India); Pivin, J.C. [CSNSM, IN2P3-CNRS, Batiment 108, F-91405 Orsay Campus (France); Chawla, A.K.; Chandra, Ramesh [Nanoscience Laboratory, IIC, Indian Institute of Technology, Roorkee 247667 (India); Kanjilal, D. [Inter University Accelerator Centre, Aruna Asaf Ali Marg, New Delhi 110067 (India); Kumar, Lokendra, E-mail: lkumarau@gmail.com [Physics Department, University of Allahabad, Allahabad 211002 (India)

    2011-11-15

    The magnetic properties of Zn{sub 1-x}Co{sub x}S (x=0.025 and 0.05) thin films grown on {alpha}-quartz substrates at different temperatures (T{sub S}) of 200, 400 and 600 deg. C by means of pulsed laser deposition are presented. The films are crystallized with wurtzite structure. Optical absorption and transmission electron microscopy measurements indicate that Co ions are substituted to Zn on tetrahedral sites. Their magnetic response is composed of ferromagnetic and paramagnetic components of which respective strengths depend on T{sub S} and Co concentration. This behavior is interpreted as due to fluctuations in the magnetic ordering, depending on grain size and site location in grain boundaries or in crystal cores. - Highlights: > Co doped ZnS thin films have been fabricated at different substrate temperatures. > Magnetization in the films changes with changing substrate temperature. > Substitution of Co on Zn sites gives room temperature intrinsic ferromagnetism. > Magnetization in the films is composed of ferromagnetic and paramagnetic components.

  9. Structure and optical properties of cored wurtzite (Zn,Mg)O heteroepitaxial nanowires

    International Nuclear Information System (INIS)

    Heo, Y.W.; Abernathy, C.; Pruessner, K.; Sigmund, W.; Norton, D.P.; Overberg, M.; Ren, F.; Chisholm, M.F.

    2004-01-01

    The synthesis, structure, and optical properties of one-dimensional heteroepitaxial cored (Zn,Mg)O semiconductor nanowires grown by a catalyst-driven molecular beam epitaxy technique are discussed. The structures form spontaneously in a Zn, Mg and O 2 /O 3 flux, consisting of a single crystal, Zn-rich Zn 1-x Mg x O(x 1-y Mg y O(y>>0.02) sheath. High resolution Z-contrast scanning transmission electron microscopy shows core diameters as small as 4 nm. The cored structure forms spontaneously under constant flux due to a bimodal growth mechanism in which the core forms via bulk like vapor-liquid-solid growth, while the outer sheath grows as a heteroepitaxial layer. Temperature-dependent photoluminescence shows a slight blueshift in the near band edge peak, which is attributed to a few percent Mg doping in the nanoscale ZnO core. The catalyst-driven molecular beam epitaxy technique provides for site-specific nanorod growth on arbitrary substrates

  10. Electronic structures and optical properties of wurtzite type LiBSe2 (B=Al, Ga, In): A first-principles study

    International Nuclear Information System (INIS)

    Li Longhua; Li Junqian; Wu Liming

    2008-01-01

    The electronic structures of three wurtzite type isostructural compounds LiBSe 2 (B=Al, Ga, In) are studied by the density functional theory (DFT). The results reveal that the presence of Li cations has direct influence on neither the band gaps (Eg) nor the bonding levels, but plays an important role in the stabilization of the structures. The band structures and densities of states (DOS) are analyzed in detail, and the band gaps of LiBSe 2 adhere to the following trend Eg (LiAlSe2) >Eg (LiGaSe2) >Eg (LiInSe2) , which is in agreement with the decrease of the bond energy of the corresponding Se 4p-B s antibonding orbitals. The role of the active s electrons of B element on the band gaps is also discussed. Finally, the optical properties are predicted, and the results would be a guide to understand the experiments. - Graphical abstract: The electronic structures and optical properties of wurtzite type LiBSe 2 (B=Al, Ga, In) have been studied by the DFT calculations. And the correlation of the electronegative of B element and the band gap decrease-trend are discussed. The comparison between different calculation methods and the experimental results is presented

  11. Electronic structure, defect formation energy, and photovoltaic properties of wurtzite-derived CuGaO2

    Science.gov (United States)

    Okumura, H.; Sato, K.; Kakeshita, T.

    2018-04-01

    Wurtzite-derived CuGaO2 (β-CuGaO2) is a recently synthesized oxide and expected as a candidate material for photovoltaic solar cells. In this paper, we propose computational material design concerning β-CuGaO2 based on the first-principles calculations. We perform hybrid calculations by using the VASP code. It is predicted that β-CuGaO2 has a direct bandgap (Eg = 1.56 eV), which is nearly optimal for high efficiency solar cells. The calculated formation energy of Cu vacancy (VCu) is very small and can be negative depending on the Fermi level. This result reasonably explains the observed p-type conduction in this material. As for the n-type doping, Cd doping could be suitable; however, VCu formation needs to be repressed in order to realize n-type β-CuGaO2. It is also shown that halogen impurities are not suitable for n-type β-CuGaO2 because of their large formation energy. Band alignment between β-CuGaO2 and ZnO is predicted to be type-II, leading to a suggestion of photovoltaic device based on the heterojunction.

  12. Complex monitoring of aerospace and mountain environment at Beo Mussala

    International Nuclear Information System (INIS)

    Angelov, I.; Angelov, C.; Barnekov, L. and others

    2006-01-01

    The mission of BEO Moussala is the observing, complex monitoring and studies of global change processes, aerospace and mountain environment, natural hazards and technological risks. BEO Moussala is the focal point of the BEO Centre of Excellence established and promoted in the framework of FP5 project HIMONTONET essentially improving its research capacities in frame of the FP6 project BEOBAL. The basic fields of current and future activities and studies at BEO Moussala are: global change, aerospace and mountain environment, natural hazards and technological risks and not at least development, design and enhancement of measurement devices and systems. The basic parameters and characteristics of the new measuring facilities are given and discussed from the point of view of the requirements of Global Atmospheric Watch (GAW) and Global Change Programs

  13. Positron annihilation studies on BeO powders

    International Nuclear Information System (INIS)

    Brauer, G.; Kerbe, F.; Kajcsos, Z.; Ashry, A.

    1984-01-01

    The sintering behaviour of two differently produced BeO powders is studied by positron annihilation. The positron lifetime in dislocations is found to be tau/sub d/ = (185 +- 2) ps, whereas for the perfect lattice tau/sub c/ = (130 +- 2) ps. (author)

  14. 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.

  15. Young's Modulus of Wurtzite and Zinc Blende InP Nanowires.

    Science.gov (United States)

    Dunaevskiy, Mikhail; Geydt, Pavel; Lähderanta, Erkki; Alekseev, Prokhor; Haggrén, Tuomas; Kakko, Joona-Pekko; Jiang, Hua; Lipsanen, Harri

    2017-06-14

    The Young's modulus of thin conical InP nanowires with either wurtzite or mixed "zinc blende/wurtzite" structures was measured. It has been shown that the value of Young's modulus obtained for wurtzite InP nanowires (E [0001] = 130 ± 30 GPa) was similar to the theoretically predicted value for the wurtzite InP material (E [0001] = 120 ± 10 GPa). The Young's modulus of mixed "zinc blende/wurtzite" InP nanowires (E [111] = 65 ± 10 GPa) appeared to be 40% less than the theoretically predicted value for the zinc blende InP material (E [111] = 110 GPa). An advanced method for measuring the Young's modulus of thin and flexible nanostructures is proposed. It consists of measuring the flexibility (the inverse of stiffness) profiles 1/k(x) by the scanning probe microscopy with precise control of loading force in nanonewton range followed by simulations.

  16. Growth and structural investigations of epitaxial hexagonal YMnO3 thin films deposited on wurtzite GaN(001) substrates

    International Nuclear Information System (INIS)

    Balasubramanian, K.R.; Chang, Kai-Chieh; Mohammad, Feroz A.; Porter, Lisa M.; Salvador, Paul A.; DiMaio, Jeffrey; Davis, Robert F.

    2006-01-01

    Epitaxial hexagonal YMnO 3 (h-YMnO 3 ) films having sharp (00l) X-ray diffraction peaks were grown above 700 deg. C in 5 mTorr O 2 via pulsed laser deposition both on as-received wurtzite GaN/AlN/6H-SiC(001) (w-GaN) substrates as well as on w-GaN surfaces that were etched in 50% HF solution. High-resolution transmission electron microscopy revealed an interfacial layer between film and the unetched substrate; this layer was absent in those samples wherein an etched substrate was used. However, the substrate treatment did not affect the epitaxial arrangement between the h-YMnO 3 film and w-GaN substrate. The epitaxial relationships of the h-YMnO 3 films with the w-GaN(001) substrate was determined via X-ray diffraction to be (001) YMnO 3 -parallel (001) GaN : [11-bar0] YMnO 3 -parallel [110] GaN ; in other words, the basal planes of the film and the substrate are aligned parallel to one another, as are the most densely packed directions in planes of the film and the substrate. Interestingly, this arrangement has a larger lattice mismatch than if the principal axes of the unit cells were aligned

  17. Meeting regulatory standards with BeO ceramic TLD

    International Nuclear Information System (INIS)

    Gammage, R.B.; Christian, D.J.

    1978-01-01

    Measurements of exposures below 1 mR are possible with BeO ceramic TLD by signal recording that discriminates against an interfering pyroelectric incandescence. Performance under environmental monitoring conditions is considered in light of current regulatory criteria. Factors such as reproducibility and batch uniformity are satisfactory. An anomalous energy dependence causes an over-response that will probably require use of an energy compensation shield

  18. Growth of InAs Wurtzite Nanocrosses from Hexagonal and Cubic Basis

    DEFF Research Database (Denmark)

    Krizek, Filip; Kanne, Thomas; Razmadze, Davydas

    2017-01-01

    . Two methods use conventional wurtzite nanowire arrays as a 6-fold hexagonal basis for growing single crystal wurtzite nanocrosses. A third method uses the 2-fold cubic symmetry of (100) substrates to form well-defined coherent inclusions of zinc blende in the center of the nanocrosses. We show......Epitaxially connected nanowires allow for the design of electron transport experiments and applications beyond the standard two terminal device geometries. In this Letter, we present growth methods of three distinct types of wurtzite structured InAs nanocrosses via the vapor-liquid-solid mechanism...

  19. Energy and spectrum of BeO molecule under the electric field from different directions

    NARCIS (Netherlands)

    Jiang, M.; Guo, F. J.; Yan, A. Y.; Zhang, C. W.; Miao, F.

    2010-01-01

    Based on the density functional theory DFT/ B3LYP at 6-311g level, the ground states of BeO molecule are optimized. The effects of electric field on the bond length, the system energy, the charge distribution, the energy levels, the HOMO-LUMO gaps and the infrared spectrum of BeO molecule are

  20. Polarity of wurtzite crystals by photoelectron diffraction

    Czech Academy of Sciences Publication Activity Database

    Bartoš, Igor; Romanyuk, Olexandr

    2014-01-01

    Roč. 315, OCT (2014), s. 506-509 ISSN 0169-4332 Grant - others:AVČR(CZ) M100101201 Institutional support: RVO:68378271 Keywords : wurtzite semiconductors * surface polarity * X-ray photoelectron diffraction * XPD Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.711, year: 2014 http://www.sciencedirect.com/science/article/pii/S016943321400066X

  1. Towards an elastic model of wurtzite AlN nanowires

    International Nuclear Information System (INIS)

    Mitrushchenkov, A; Chambaud, G; Yvonnet, J; He, Q-C

    2010-01-01

    Starting with ab initio calculations of AlN wurtzite [0001] nanowires with diameters up to 4 nm, a finite element method is developed to deal with larger nanostructures/nanoparticles. The ab initio calculations show that the structure of the nanowires can be well represented by an internal part with AlN bulk elastic properties, and one atomic surface layer with its own elastic behavior. The proposed finite element method includes surface elements with their own elastic properties using surface elastic coefficients deduced from the ab initio calculations. The elastic properties obtained with the finite element model compare very well with those obtained with the full ab initio calculations.

  2. Effect of effective mass and spontaneous polarization on photocatalytic activity of wurtzite and zinc-blende ZnS

    International Nuclear Information System (INIS)

    Dong, Ming; Zhang, Jinfeng; Yu, Jiaguo

    2015-01-01

    Semiconductor zinc sulphide (ZnS) has two common phases: hexagonal wurtzite and cubic zinc-blende structures. The crystal structures, energy band structures, density of states (DOS), bond populations, and optical properties of wurtzite and zinc-blende ZnS were investigated by the density functional theory of first-principles. The similar band gaps and DOS of wurtzite and zinc-blende ZnS were found and implied the similarities in crystal structures. However, the distortion of ZnS 4 tetrahedron in wurtzite ZnS resulted in the production of spontaneous polarization and internal electric field, which was beneficial for the transfer and separation of photogenerated electrons and holes

  3. Novel mechanical behaviors of wurtzite CdSe nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Fu, Bing [Shanghai Normal University, Department of Physics (China); Chen, Li [MCPHS University, School of Arts and Sciences (United States); Xie, Yiqun; Feng, Jie; Ye, Xiang, E-mail: yexiang@shnu.edu.cn [Shanghai Normal University, Department of Physics (China)

    2015-09-15

    As an important semiconducting nanomaterial, CdSe nanowires have attracted much attention. Although many studies have been conducted in the electronic and optical properties of CdSe NWs, the mechanical properties of Wurtzite (WZ) CdSe nanowires remain unclear. Using molecular dynamics simulations, we have studied the tensile mechanical properties and behaviors of [0001]-oriented Wurtzite CdSe nanowires. By monitoring the stretching processes of CdSe nanowires, three distinct structures are found: the WZ wire, a body-centered tetragonal structure with four-atom rings (denoted as BCT-4), and a structure that consists of ten-atom rings with two four-atom rings (denoted as TAR-4) which is observed for the first time. Not only the elastic tensile characteristics are highly reversible under unloading, but a reverse transition between TAR-4 and BCT-4 is also observed. The stretching processes also have a strong dependence on temperature. A tubular structure similar to carbon nanotubes is observed at 150 K, a single-atom chain is formed at 300, 350 and 450 K, and a double-atom chain is found at 600 K. Our findings on tensile mechanical properties of WZ CdSe nanowires does not only provide inspiration to future study on other properties of CdSe nanomaterials but also help design and build efficient nanoscale devices.

  4. 100-nm thick single-phase wurtzite BAlN films with boron contents over 10%

    KAUST Repository

    Li, Xiaohang

    2017-01-11

    Growing thicker BAlN films while maintaining single-phase wurtzite structure and boron content over 10% has been challenging. In this study, we report on the growth of 100 nm-thick single-phase wurtzite BAlN films with boron contents up to 14.4% by MOCVD. Flow-modulated epitaxy was employed to increase diffusion length of group-III atoms and reduce parasitic reactions between the metalorganics and NH3. A large growth efficiency of ∼2000 μm mol−1 was achieved as a result. Small B/III ratios up to 17% in conjunction with high temperatures up to 1010 °C were utilized to prevent formation of the cubic phase and maintain wurtzite structure.

  5. 100-nm thick single-phase wurtzite BAlN films with boron contents over 10%

    KAUST Repository

    Li, Xiaohang; Wang, Shuo; Liu, Hanxiao; Ponce, Fernando A.; Detchprohm, Theeradetch; Dupuis, Russell D.

    2017-01-01

    Growing thicker BAlN films while maintaining single-phase wurtzite structure and boron content over 10% has been challenging. In this study, we report on the growth of 100 nm-thick single-phase wurtzite BAlN films with boron contents up to 14.4% by MOCVD. Flow-modulated epitaxy was employed to increase diffusion length of group-III atoms and reduce parasitic reactions between the metalorganics and NH3. A large growth efficiency of ∼2000 μm mol−1 was achieved as a result. Small B/III ratios up to 17% in conjunction with high temperatures up to 1010 °C were utilized to prevent formation of the cubic phase and maintain wurtzite structure.

  6. Unit cell parameters of wurtzite InP nanowires determined by x-ray diffraction.

    Science.gov (United States)

    Kriegner, D; Wintersberger, E; Kawaguchi, K; Wallentin, J; Borgström, M T; Stangl, J

    2011-10-21

    High resolution x-ray diffraction is used to study the structural properties of the wurtzite polytype of InP nanowires. Wurtzite InP nanowires are grown by metal-organic vapor phase epitaxy using S-doping. From the evaluation of the Bragg peak position we determine the lattice parameters of the wurtzite InP nanowires. The unit cell dimensions are found to differ from the ones expected from geometric conversion of the cubic bulk InP lattice constant. The atomic distances along the c direction are increased whereas the atomic spacing in the a direction is reduced in comparison to the corresponding distances in the zinc-blende phase. Using core/shell nanowires with a thin core and thick nominally intrinsic shells we are able to determine the lattice parameters of wurtzite InP with a negligible influence of the S-doping due to the much larger volume in the shell. The determined material properties will enable the ab initio calculation of electronic and optical properties of wurtzite InP nanowires.

  7. Pressure dependence of the refractive index in wurtzite and rocksalt indium nitride

    Energy Technology Data Exchange (ETDEWEB)

    Oliva, R. [Institut Jaume Almera, Consell Superior d' Investigacions Científiques (CSIC), Lluís Solé i Sabarís s.n., 08028 Barcelona, Catalonia (Spain); MALTA-Consolider Team, Departament de Física Aplicada, ICMUV, Universitat de València, c/Dr. Moliner 50, 46100 Burjassot, València (Spain); Segura, A. [MALTA-Consolider Team, Departament de Física Aplicada, ICMUV, Universitat de València, c/Dr. Moliner 50, 46100 Burjassot, València (Spain); Ibáñez, J., E-mail: jibanez@ictja.csic.es; Artús, L. [Institut Jaume Almera, Consell Superior d' Investigacions Científiques (CSIC), Lluís Solé i Sabarís s.n., 08028 Barcelona, Catalonia (Spain); Yamaguchi, T.; Nanishi, Y. [Faculty of Science and Engineering, Ritsumeikan University, Shiga 525-8577 (Japan)

    2014-12-08

    We have performed high-pressure Fourier transform infrared reflectance measurements on a freestanding InN thin film to determine the refractive index of wurtzite InN and its high-pressure rocksalt phase as a function of hydrostatic pressure. From a fit to the experimental refractive-index curves including the effect of the high-energy optical gaps, phonons, free carriers, and the direct (fundamental) band-gap in the case of wurtzite InN, we obtain pressure coefficients for the low-frequency (electronic) dielectric constant ε{sub ∞}. Negative pressure coefficients of −8.8 × 10{sup −2 }GPa{sup −1} and −14.8 × 10{sup −2 }GPa{sup −1} are obtained for the wurtzite and rocksalt phases, respectively. The results are discussed in terms of the electronic band structure and the compressibility of both phases.

  8. Pressure dependence of the refractive index in wurtzite and rocksalt indium nitride

    International Nuclear Information System (INIS)

    Oliva, R.; Segura, A.; Ibáñez, J.; Artús, L.; Yamaguchi, T.; Nanishi, Y.

    2014-01-01

    We have performed high-pressure Fourier transform infrared reflectance measurements on a freestanding InN thin film to determine the refractive index of wurtzite InN and its high-pressure rocksalt phase as a function of hydrostatic pressure. From a fit to the experimental refractive-index curves including the effect of the high-energy optical gaps, phonons, free carriers, and the direct (fundamental) band-gap in the case of wurtzite InN, we obtain pressure coefficients for the low-frequency (electronic) dielectric constant ε ∞ . Negative pressure coefficients of −8.8 × 10 −2  GPa −1 and −14.8 × 10 −2  GPa −1 are obtained for the wurtzite and rocksalt phases, respectively. The results are discussed in terms of the electronic band structure and the compressibility of both phases

  9. E1 Gap of Wurtzite InAs Single Nanowires Measured by Means of Resonant Raman Spectroscopy

    International Nuclear Information System (INIS)

    Moeller, M.; Lima, M. M. Jr. de; Cantarero, A.; Dacal, L. C. O.; Iikawa, F.; Chiaramonte, T.; Cotta, M. A.

    2011-01-01

    Indium arsenide nanowires were synthesized with an intermixing of wurtzite and zincblende structure by chemical beam epitaxy with the vapor-liquid-solid mechanism. Resonant Raman spectroscopy of the transverse optical phonon mode at 215 cm -1 reveals an E 1 gap of 2.47 eV which is assigned to the electronic band gap at the A point in the indium arsenide wurtzite phase.

  10. E1 Gap of Wurtzite InAs Single Nanowires Measured by Means of Resonant Raman Spectroscopy

    Science.gov (United States)

    Möller, M.; Dacal, L. C. O.; de Lima, M. M.; Iikawa, F.; Chiaramonte, T.; Cotta, M. A.; Cantarero, A.

    2011-12-01

    Indium arsenide nanowires were synthesized with an intermixing of wurtzite and zincblende structure by chemical beam epitaxy with the vapor-liquid-solid mechanism. Resonant Raman spectroscopy of the transverse optical phonon mode at 215 cm-1 reveals an E1 gap of 2.47 eV which is assigned to the electronic band gap at the A point in the indium arsenide wurtzite phase.

  11. Energy stored in BeO, MgO, Al2O3 and SiO2 oxides irradiated with neutrons

    International Nuclear Information System (INIS)

    Roux, Andre

    1969-01-01

    Within the field of researches on refractory oxides which may be used in structure materials in atomic pile, the objective of this research thesis has been the measurement of the energy stored in some specific oxides (BeO, MgO, Al 2 O 3 and SiO 2 ) after their irradiation in a nuclear reactor. This measurement is performed by 'healing' the irradiated substance by means of thermal treatments during which sample initial mass and morphologies are preserved. The measurement of the Wigner energy is then performed by differential enthalpy analysis. The first part reports the experimental determination of Wigner energies (measurement apparatus, method of ballistic differential enthalpy analysis, thermo-gram compensation). The second part presents the Wigner energies obtained for the sintered BeO, the sintered MgO, the sintered Al 2 O 3 , and the vitreous SiO 2 . The third part reports the result interpretation

  12. Metastable growth of pure wurtzite InGaAs microstructures.

    Science.gov (United States)

    Ng, Kar Wei; Ko, Wai Son; Lu, Fanglu; Chang-Hasnain, Connie J

    2014-08-13

    III-V compound semiconductors can exist in two major crystal phases, namely, zincblende (ZB) and wurtzite (WZ). While ZB is thermodynamically favorable in conventional III-V epitaxy, the pure WZ phase can be stable in nanowires with diameters smaller than certain critical values. However, thin nanowires are more vulnerable to surface recombination, and this can ultimately limit their performances as practical devices. In this work, we study a metastable growth mechanism that can yield purely WZ-phased InGaAs microstructures on silicon. InGaAs nucleates as sharp nanoneedles and expand along both axial and radial directions simultaneously in a core-shell fashion. While the base can scale from tens of nanometers to over a micron, the tip can remain sharp over the entire growth. The sharpness maintains a high local surface-to-volume ratio, favoring hexagonal lattice to grow axially. These unique features lead to the formation of microsized pure WZ InGaAs structures on silicon. To verify that the WZ microstructures are truly metastable, we demonstrate, for the first time, the in situ transformation from WZ to the energy-favorable ZB phase inside a transmission electron microscope. This unconventional core-shell growth mechanism can potentially be applied to other III-V materials systems, enabling the effective utilization of the extraordinary properties of the metastable wurtzite crystals.

  13. Evaluation of thermoluminescent BeO samples in standard radiotherapy beams; Avaliacao de amostras termoluminescentes de BeO em feixes padroes de radioterapia

    Energy Technology Data Exchange (ETDEWEB)

    Groppo, Daniela P.; Silva, Jonas O.; Caldas, Linda V.E., E-mail: daniela.piai.groppo@gmail.com [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-SP), Sao Paulo, SP (Brazil)

    2012-08-15

    Beryllium oxide thermoluminescent samples were evaluated in standard radiotherapy beams of low energy. Results for response reproducibility, dose-response curve and energy dependence were obtained. The lower detection limit was determined. The pellets of BeO showed their usefulness for beam dosimetry. (author)

  14. Wurtzite BAlN and BGaN alloys for heterointerface polarization engineering

    KAUST Repository

    Liu, Kaikai; Sun, Haiding; Alqatari, Feras; Guo, Wenzhe; Liu, Xinwei; Li, Jingtao; Torres Castanedo, Carlos G; Li, Xiaohang

    2017-01-01

    deformation and the dipole moment difference between the hexagonal and wurtzite structures. The PZ constants exhibit significant bowing because of the large lattice difference between binary alloys. Furthermore, the PZ constants of BxAl1-xN and BxGa1-xN become

  15. BEOS-A new approach to promote and organize industrial ISS utilization

    Science.gov (United States)

    Luttmann, Helmut; Buchholz, Henning; Bratke, Burkhard; Hueser, Detlev; Dittus, Hansjörg

    2000-01-01

    In order to develop and to market innovative services and products for the operation of the ISS and its utilization, three players have teamed up together and established an entity called BEOS (Bremen Engineering Operations Science). The team is made up of DaimlerChrysler Aerospace, OHB-System and ZARM, the Center of Applied Space Technology and Microgravity at the University of Bremen. It is the aim of BEOS to represent a competent industrial interface to potential ISS users from the space and non-space industries. In this effort BEOS is supporting and supplementing the activities of the space agencies, especially in the field of industrial and/or commercial ISS utilization. With this approach BEOS is creating new business opportunities not only for its team members but also for its customers from industry. Besides the fostering of industrial research in space, nontechnical fields of space utilization like entertainment, advertisement, education and space travel represent further key sectors for the marketing efforts of BEOS. .

  16. Wurtzite InP nanowire arrays grown by selective area MOCVD

    International Nuclear Information System (INIS)

    Chu, Hyung-Joon; Stewart, Lawrence; Yeh, Ting-Wei; Dapkus, P.D.

    2010-01-01

    InP nanowires are a unique material phase because this normally zincblende material forms in the wurtzite crystal structure below a critical diameter owing to the contribution of sidewalls to the total formation energy. This may allow control of the carrier transport and optical properties of InP nanowires for applications such as nano scale transistors, lasers and detectors. In this work, we describe the fabrication of InP nanowire arrays by selective area growth using MOCVD in the diameter range where the wurtzite structure is formed. The spatial growth rate in selective area growth is modeled by a diffusion model for the precursors. The proposed model achieves an average error of 9%. Electron microscopy shows that the grown InP nanowires are in the wurtzite crystal phase with many stacking faults. The threshold diameter of the crystal phase transition of InP nanowires is larger than the thermodynamic estimation. In order to explain this tendency, we propose a surface kinetics model based on a 2 x 2 reconstruction. This model can explain the increased tendency for wurtzite nanowire formation on InP (111)A substrates and the preferred growth direction of binary III-V compound semiconductor nanowires. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  17. Importance of hydration in exoelectron emission from ceramic BeO

    International Nuclear Information System (INIS)

    Gammage, R.B.; Cheka, J.S.

    1976-01-01

    The influence of the state of hydration on the exoelectron emitting characteristics of BeO ceramic dosimeters for TSEE is very strong and very complex. For dosimetry the most unfavorable characteristics are a ruined TSEE peak shape and loss of intensity; this occurs if atmosphere moisture is allowed to condense onto, and evaporate from, the BeO surface. For unencapsulated dosimeters this occurs when the ambient temperature falls below the dew point. Immersion of irradiated detectors directly into liquid water for a few hours causes fading at a substantial rate, but surprisingly little change in the TSEE peak shape or intensity. The different behaviors with respect to immersion in liquid water and exposure to condensing atmospheric moisture present an enigma. Ceramic BeO TSEE dosimeters can only be used with confidence in atmospheres where below dew point conditions are avoidable, such as inside air conditioned buildings or encapsulated, dry air containers

  18. A facile arrested precipitation method for synthesis of pure wurtzite Cu2ZnSnS4 nanocrystals using thiourea as a sulfur source

    International Nuclear Information System (INIS)

    Li, Chunya; Ha, Enna; Wong, Wing-Leung; Li, Cuiling; Ho, Kam-Piu; Wong, Kwok-Yin

    2012-01-01

    Graphical abstract: High-resolution TEM image of wurtzite Cu 2 ZnSnS 4 nanocrystals. Highlights: ► Wurtzite Cu 2 ZnSnS 4 nanocrystals were synthesized by arrested precipitation method. ► XRD, EDX, TEM demonstrate that the CZTS nanocrystals are purely wurtzite structure. ► The average diameter of the bulk CZTS products is found to be 10 ± 1.1 nm. ► The estimated direct bandgap energy is 1.56 eV for wurtzite CZTS nanocrystals. ► The electrical resistivity of the wurtzite CZTS nanocrystals is low. -- Abstract: A facile route for the synthesis of wurtzite Cu 2 ZnSnS 4 (CZTS) nanocrystals was developed by an arrested precipitation method at 240 °C under simple reaction conditions with diethanolamine as the solvent and thiourea as sulfur source. The structure and morphology of the CZTS nanocrystals were characterized by X-ray diffraction and transmission electron microscopy. Control experiments demonstrated that CZTS nanocrystals which are purely wurtzite structure are readily obtained. The average diameter of the bulk CZTS products is found to be 10 ± 1.1 nm. The estimated direct bandgap energy is 1.56 eV, which indicates that the CZTS nanocrystals produced by this method possess promising applications in photovoltaic devices.

  19. Synthesis of [100] Wurtzite InN Nanowires and [011] Zinc-Blende InN Nanorods

    International Nuclear Information System (INIS)

    Chao, Nie; Rong, Zhang; Zi-Li, Xie; Xiang-Qiang, Xiu; Bin, Liu; De-Yi, Fu; Qi-Jia, Liu; Ping, Han; Shu-Lin, Gu; Yi, Shi; You-Dou, Zheng

    2008-01-01

    One-dimensional wurtzite InN nanowires and zincblende InN nanorods are prepared by chemical vapour deposition (CVD) method on natural cleavage plane (110) of GaAs. The growth direction of InN nanowires is [100], with wurtzite structure. The stable crystal structure of InN is wurtzite (w-InN), zincblende structure (z-InN) is only reported for 2D InN crystals before. However, in this work, the zincblende InN nanorods [011] are synthesized and characterized. The SEM and TEM images show that every nanorod shapes a conical tip, which can be explained by the anisotropy of growth process and the theory of Ehrlich–Schwoebel barrier. (condensed matter: structure, mechanical and thermal properties)

  20. Pseudodirect to Direct Compositional Crossover in Wurtzite GaP/InxGa1–xP Core–Shell Nanowires

    KAUST Repository

    Gagliano, L.; Belabbes, Abderrezak; Albani, M.; Assali, S.; Verheijen, M. A.; Miglio, L.; Bechstedt, F.; Haverkort, J. E. M.; Bakkers, E. P. A. M.

    2016-01-01

    Thanks to their uniqueness, nanowires allow the realization of novel semiconductor crystal structures with yet unexplored properties, which can be key to overcome current technological limits. Here we develop the growth of wurtzite GaP/InGaP core

  1. Optical phonon modes of wurtzite InP

    Science.gov (United States)

    Gadret, E. G.; de Lima, M. M.; Madureira, J. R.; Chiaramonte, T.; Cotta, M. A.; Iikawa, F.; Cantarero, A.

    2013-03-01

    Optical vibration modes of InP nanowires in the wurtzite phase were investigated by Raman scattering spectroscopy. The wires were grown along the [0001] axis by the vapor-liquid-solid method. The A1(TO), E2h, and E1(TO) phonon modes of the wurtzite symmetry were identified by using light linearly polarized along different directions in backscattering configuration. Additionally, forbidden longitudinal optical modes have also been observed. Furthermore, by applying an extended 11-parameter rigid-ion model, the complete dispersion relations of InP in the wurtzite phase have been calculated, showing a good agreement with the Raman experimental data.

  2. Strain effects in polytypical wurtzite/zinc-blend nanowhiskers

    Science.gov (United States)

    Sipahi, Guilherme; Faria, Paulo

    2012-02-01

    The recent interest on III-V nanowhiskers has led to the growth of high quality samples of systems with two different crystalline structures [1]. The crystals grown in [111]-direction for the zinc-blend (ZB) phase and [0001]-direction for the wurtzite (WZ) phase are very similar and can both be described as stacked hexagonal layers. The effect of two different structural phases coexisting in the same nanostrucure is known as polytypism and creates confinement profiles similar to a heterostructure. One can notice band offsets at the interface and the formation of electronic minibands that can be explored to design systems for device applications. Although some of the III-V compounds do not present WZ structure in bulk form, recent calculations [2] presented a theoretical prediction of their band structure. However, as they considered that ZB and WZ to have the same lattice parameters no strain effects should appear on a first approach. Our theoretical approach introduces strain effects in our previous model [3] by using group theory arguments. It allows the analysis of the biaxial strain effects for both structures in a single matrix. [1] P. Caroff et al. Nature Nanotech. 4, 50, 2009. [2] A. De and C. E. Pryor, Phys. Rev. B 81, 155210, 2010 [3] http://arxiv.org/abs/1012.022

  3. Femtosecond Laser-Induced Formation of Wurtzite Phase ZnSe Nanoparticles in Air

    Directory of Open Access Journals (Sweden)

    Hsuan I Wang

    2012-01-01

    Full Text Available We demonstrate an effective method to prepare wurtzite phase ZnSe nanoparticles from zincblende ZnSe single crystal using femtosecond pulse laser ablation. The fabricated ZnSe nanoparticles are in spherical shape and uncontaminated while synthesized under ambient environment. By controlling the laser fluences, the average size of ZnSe nanoparticles can be varied from ~16 nm to ~22 nm in diameter. In Raman spectra, the surface phonon mode becomes dominant in the smaller average particle size with uniform size distribution. The interesting phase transition from the zinc blende structure of ZnSe single crystal to wurtzite structure of ZnSe nanoparticles may have been induced by the ultrahigh ablation pressure at the local area due to the sudden injection of high energy leading to solid-solid transition.

  4. Polar Mixing Optical Phonon Spectra in Wurtzite GaN Cylindrical Quantum Dots: Quantum Size and Dielectric Effects

    International Nuclear Information System (INIS)

    Zhang Li; Liao Jianshang

    2010-01-01

    The interface-optical-propagating (IO-PR) mixing phonon modes of a quasi-zero-dimensional (QoD) wurtzite cylindrical quantum dot (QD) structure are derived and studied by employing the macroscopic dielectric continuum model. The analytical phonon states of IO-PR mixing modes are given. It is found that there are two types of IO-PR mixing phonon modes, i.e. ρ-IO/z-PR mixing modes and the z-IO/ρ-PR mixing modes existing in QoD wurtzite QDs. And each IO-PR mixing modes also have symmetrical and antisymmetrical forms. Via a standard procedure of field quantization, the Froehlich Hamiltonians of electron-(IO-PR) mixing phonons interaction are obtained. Numerical calculations on a wurtzite GaN cylindrical QD are performed. The results reveal that both the radial-direction size and the axial-direction size as well as the dielectric matrix have great influence on the dispersive frequencies of the IO-PR mixing phonon modes. The limiting features of dispersive curves of these phonon modes are discussed in depth. The phonon modes 'reducing' behavior of wurtzite quantum confined systems has been observed obviously in the structures. Moreover, the degenerating behaviors of the IO-PR mixing phonon modes in wurtzite QoD QDs to the IO modes and PR modes in wurtzite Q2D QW and Q1D QWR systems are analyzed deeply from both of the viewpoints of physics and mathematics. (interdisciplinary physics and related areas of science and technology)

  5. Fabrication and Characterization of Thin Film Solar Cell Made from CuIn0.75Ga0.25S2 Wurtzite Nanoparticles

    Directory of Open Access Journals (Sweden)

    Fengyan Zhang

    2013-01-01

    Full Text Available CuIn0.75Ga0.25S2 (CIGS thin film solar cells have been successfully fabricated using CIGS Wurtzite phase nanoparticles for the first time. The structure of the cell is Glass/Mo/CIGS/CdS/ZnO/ZnO:Al/Ag. The light absorption layer is made from CIGS Wurtzite phase nanoparticles that are formed from single-source precursors through a microwave irradiation. The Wurtzite phase nanoparticles were converted to Chalcopyrite phase film through a single-step annealing process in the presence of argon and sulfur at 450°C. The solar cell made from Wurtzite phase nanoparticles showed 1.6% efficiency and 0.42 fill factor.

  6. Thermal conductivity thermal diffusivity of UO{sub 2}-BeO nuclear fuel pellets

    Energy Technology Data Exchange (ETDEWEB)

    Mansur, Fábio A.; Camarano, Denise M.; Santos, Ana M. M.; Ferraz, Wilmar B.; Silva, Mayra A.; Ferreira, Ricardo A.N., E-mail: fam@cdtn.br, E-mail: dmc@cdtn.br, E-mail: amms@cdtn.br, E-mail: ferrazw@cdtn.br, E-mail: mayra.silva@cdtn.br, E-mail: ricardoanf@yahoo.com.br [Centro de Desenvolvimento da Tecnologia Nuclear (CDTN/CNEN-MG), Belo Horizonte, MG (Brazil)

    2017-07-01

    The temperature distribution in nuclear fuel pellets is of vital importance for the performance of the reactor, as it affects the heat transfer, the mechanical behavior and the release of fission gas during irradiation, reducing safety margins in possible accident scenarios. One of the main limitation for the current uranium dioxide nuclear fuel (UO{sub 2}) is its low thermal conductivity, responsible for the higher temperature of the pellet center and, consequently, for a higher radial temperature gradient. Thus, the addition of another material to increase the UO{sub 2} fuel thermal conductivity has been considered. Among the additives that are being investigated, beryllium oxide (BeO) has been chosen due to its high thermal conductivity, with potential to optimize power generation in pressurized light water reactors (PWR). In this work, UO{sub 2}-BeO pellets were obtained by the physical mixing of the powders with additions of 2wt% and 3wt% of BeO. The thermal diffusivity and conductivity of the pellets were determined from room temperature up to 500 °C. The results were normalized to 95% of the theoretical density (TD) of the pellets and varied according to the BeO content. The range of the values of thermal diffusivity and conductivity were 1.22 mm{sup 2}∙s{sup -1} to 3.69 mm{sup 2}∙s{sup -1} and 3.80 W∙m{sup -}'1∙K{sup -1} to 9.36 W∙m{sup -1}∙K{sup -1}, respectively. (author)

  7. Neutron monochromators of BeO, MgO and ZnO single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Adib, M.; Habib, N. [Reactor Physics Department, NRC, AEAE, Cairo (Egypt); Bashter, I.I. [Physics Department, Faculty of Science, Zagazig University (Egypt); Morcos, H.N.; El-Mesiry, M.S. [Reactor Physics Department, NRC, AEAE, Cairo (Egypt); Mansy, M.S., E-mail: mohamedmansy_np@yahoo.com [Physics Department, Faculty of Science, Zagazig University (Egypt)

    2014-05-21

    The monochromatic features of BeO, MgO and ZnO single crystals are discussed in terms of orientation, mosaic spread, and thickness within the wavelength band from 0.05 up to 0.5 nm. A computer program MONO, written in “FORTRAN”, has been developed to carry out the required calculations. Calculation shows that a 5 mm thick MgO single crystal cut along its (2 0 0) plane having mosaic spread of 0.5° FWHM has the optimum parameters when it is used as a neutron monochromator. Moreover, at wavelengths shorter than 0.24 nm the reflected monochromatic neutrons are almost free from the higher order ones. The same features are seen with BeO (0 0 2) with less reflectivity than that of the former. Also, ZnO cut along its (0 0 2) plane is preferred over the others only at wavelengths longer than 0.20 nm. When the selected monochromatic wavelength is longer than 0.24 nm, the neutron intensities of higher orders from a thermal reactor flux are higher than those of the first-order one. For a cold reactor flux, the first order of BeO and MgO single crystals is free from the higher orders up to 0.4 nm, and ZnO at wavelengths up to 0.5 nm. - Highlights: • Monochromatic features of BeO, MgO and ZnO single crystals. • Calculations of neutron reflectivity using a computer program MONO. • Optimum mosaic spread, thickness and cutting plane of single crystals.

  8. Ceramic BeO exoelectron dosimeters for tritium and radon monitoring

    International Nuclear Information System (INIS)

    Gammage, R.B.

    1979-01-01

    An environmental monitoring device with BeO ceramic dosimeters can be used to measure 222 Rn in dwellings. Radon diffuses into a porous hemispheric chamber and the radon daughters are electrostatically collected on aluminized Mylar foil covering the BeO dosimeter that records the alpha activity. A 10:1 signal-to-background ratio results from a radon exposure of only pCi-h/l. This high sensitivity makes accurate radon measurement possible within one day, even at near background levels of a few tenths pCi/l. The BeO exoelectron dosimeter is also uniquely suited for monitoring occupational exposure to insoluble tritium gas. At one-fifth the maximum permissible concentration, exposure for 8 hours gives a 10:1 signal-to-background exoelectron response to the low energy beta rays. Compensation for any exoelectron response caused by photon radiation can be made by reading the thermoluminescence. The tritium exposure produces negligible thermoluminescence. Progress in these and other applications is now totally dependent on achieving reliability and long-term stability of the exoelectron dosimeter

  9. Current situation for exoelectron dosimeters of BeO ceramic in neutron dosimetry

    International Nuclear Information System (INIS)

    Gammage, R.B.

    1977-01-01

    Much of the early enthusiasm for using exoelectron dosimeters (ceramic BeO Thermalox 995) in neutron dosimetry was predicted on the belief that the response to fast neutrons, relative to gamma rays, was 0.18 to 0.28 on a R/sub γ/ equiv/tissue rad n/sub f/ basis for neutron energies between 0.1 and 16 MeV. Pairs of BeO disks had to be used, one covered with a polyethylene radiator for producing recoil protons, and the other covered with Teflon. More recent studies indicated a considerably lower ratio of 0.11 for Health Physics Reactor Research fission neutrons. In the earlier work the BeO was coated with gold to enhance the surface conductivity during reading of the thermally stimulated exoelectron emission (TSEE). No metallic coating is now deemed to be necessary. Perhaps thermal neutron contamination of the fast neutron beams due to some thermalization within the hydrogenous radiator was sufficient to cause the high apparent fast neutron sensitivity via n, γ reactions. Whatever the cause, however, the lower value of 0.11 has caused a marked subsidence of enthusiasm in this technique of fast neutron monitoring

  10. Neutron monochromators of BeO, MgO and ZnO single crystals

    Science.gov (United States)

    Adib, M.; Habib, N.; Bashter, I. I.; Morcos, H. N.; El-Mesiry, M. S.; Mansy, M. S.

    2014-05-01

    The monochromatic features of BeO, MgO and ZnO single crystals are discussed in terms of orientation, mosaic spread, and thickness within the wavelength band from 0.05 up to 0.5 nm. A computer program MONO, written in “FORTRAN”, has been developed to carry out the required calculations. Calculation shows that a 5 mm thick MgO single crystal cut along its (2 0 0) plane having mosaic spread of 0.5° FWHM has the optimum parameters when it is used as a neutron monochromator. Moreover, at wavelengths shorter than 0.24 nm the reflected monochromatic neutrons are almost free from the higher order ones. The same features are seen with BeO (0 0 2) with less reflectivity than that of the former. Also, ZnO cut along its (0 0 2) plane is preferred over the others only at wavelengths longer than 0.20 nm. When the selected monochromatic wavelength is longer than 0.24 nm, the neutron intensities of higher orders from a thermal reactor flux are higher than those of the first-order one. For a cold reactor flux, the first order of BeO and MgO single crystals is free from the higher orders up to 0.4 nm, and ZnO at wavelengths up to 0.5 nm.

  11. Determination of the kinetic parameters of BeO using isothermal decay method

    International Nuclear Information System (INIS)

    Nieto, Juan Azorin; Vega, Claudia Azorin; Montalvo, Teodoro Rivera; Cabrera, Eugenio Torijano

    2016-01-01

    Most of the existing methods for obtaining the frequency factors make use of the trap depth (activation energy) making some assumptions about the order of the kinetics. This causes inconsistencies in the reported values of trapping parameters due that the values of the activation energy obtained by different methods differ appreciably among them. Then, it is necessary to use a method independent of the trap depth making use of the isothermal luminescence decay (ILD) method. The trapping parameters associated with the prominent glow peak of BeO (280 °C) are reported using ILD method. As a check, the trap parameters are also calculated by glow curve shape (Chen's) method after isolating the prominent glow peak by thermal cleaning technique. Our results show a very good agreement between the trapping parameters calculated by the two methods. ILD method was used for determining the trapping parameters of BeO. Results obtained applying this method are in good agreement with those obtained using other methods, except in the value of the frequency factor. - Highlights: • Kinetic parameters of BeO were determined. • Isothermal decay method was used. • Frecuency factor not agree with those obtained by other methods.

  12. A versatile light-switchable nanorod memory: Wurtzite ZnO on perovskite SrTiO3

    KAUST Repository

    Kumar, Anup Bera; Peng, Haiyang; Lourembam, James; Shen, Youde; Sun, Xiaowei; Wu, Tao

    2013-01-01

    heterojunction memory made of wurtzite ZnO nanorods grown on perovskite Nb-doped SrTiO3 (NSTO) is reported, the electronic properties of which can be drastically reconfigured by applying a voltage and light. Despite of the distinct lattice structures of Zn

  13. Predicted bond length variation in wurtzite and zinc-blende InGaN and AlGaN alloys

    International Nuclear Information System (INIS)

    Mattila, T.; Zunger, A.

    1999-01-01

    Valence force field simulations utilizing large supercells are used to investigate the bond lengths in wurtzite and zinc-blende In x Ga 1-x N and Al x Ga 1-x N random alloys. We find that (i) while the first-neighbor cation endash anion shell is split into two distinct values in both wurtzite and zinc-blende alloys (R Ga-N 1 ≠R In-N 1 ), the second-neighbor cation endash anion bonds are equal (R Ga-N 2 =R In-N 2 ). (ii) The second-neighbor cation endash anion bonds exhibit a crucial difference between wurtzite and zinc-blende binary structures: in wurtzite we find two bond distances which differ in length by 13% while in the zinc-blende structure there is only one bond length. This splitting is preserved in the alloy, and acts as a fingerprint, distinguishing the wurtzite from the zinc-blende structure. (iii) The small splitting of the first-neighbor cation endash anion bonds in the wurtzite structure due to nonideal c/a ratio is preserved in the alloy, but is obscured by the bond length broadening. (iv) The cation endash cation bond lengths exhibit three distinct values in the alloy (Ga endash Ga, Ga endash In, and In endash In), while the anion endash anion bonds are split into two values corresponding to N endash Ga endash N and N endash In endash N. (v) The cation endash related splitting of the bonds and alloy broadening are considerably larger in InGaN alloy than in AlGaN alloy due to larger mismatch between the binary compounds. (vi) The calculated first-neighbor cation endash anion and cation endash cation bond lengths in In x Ga 1-x N alloy are in good agreement with the available experimental data. The remaining bond lengths are provided as predictions. In particular, the predicted splitting for the second-neighbor cation endash anion bonds in the wurtzite structure awaits experimental testing. copyright 1999 American Institute of Physics

  14. OSL response bleaching of BeO samples, using fluorescent light and blue LEDs

    International Nuclear Information System (INIS)

    Groppo, Daniela Piai; Caldas, Linda V.E.

    2015-01-01

    The optically stimulated luminescence (OSL) is widely used as a dosimetric technique for many applications. In this work, the OSL response bleaching of BeO samples was studied. The samples were irradiated using a beta radiation source ( 90 Sr+ 90 Y); the bleaching treatments (fluorescent light and blue LEDs) were performed, and the results were compared. Various optical treatment time intervals were tested until reaching the complete bleaching of the OSL response. The best combination of the time interval and bleaching type was analyzed. (author)

  15. Surface effects during exoelectron-emission of BeO ceramics

    International Nuclear Information System (INIS)

    Siegel, V.; Kirchner, H.H.

    1979-01-01

    Studying the behaviour of the two thermally stimulated exoelectron emission (TSEE) maxima of BeO ceramics at about 270 0 C und 325 0 C it can be shown that the TSEE maximum at 270 0 C is closely connected with adsorption and desorption processes occuring on the surface of the samples. In particular, this TSEE maximum is strongly influenced as well by donor-like behaviour of adsorbed hydrogen and lithium as by acceptor-like behaviour of alcohols and nitrides of the lithium. The detailed surface processes leading to the apperance or disapperance of the TSEE maximum at 270 0 C are discussed. (orig.) [de

  16. OSL response bleaching of BeO samples, using fluorescent light and blue LEDs

    International Nuclear Information System (INIS)

    Groppo, D P; Caldas, L V E

    2016-01-01

    The optically stimulated luminescence (OSL) is widely used as a dosimetric technique for many applications. In this work, the OSL response bleaching of BeO samples was studied. The samples were irradiated using a beta radiation source ("9"0Sr+"9"0Y); the bleaching treatments (fluorescent light and blue LEDs) were performed, and the results were compared. Various optical treatment time intervals were tested until reaching the complete bleaching of the OSL response. The best combination of the time interval and bleaching type was analyzed. (paper)

  17. Polarity effects in the x-ray photoemission of ZnO and other wurtzite semiconductors

    International Nuclear Information System (INIS)

    Allen, M. W.; Zemlyanov, D. Y.; Waterhouse, G. I. N.; Metson, J. B.; Veal, T. D.; McConville, C. F.; Durbin, S. M.

    2011-01-01

    Significant polarity-related effects were observed in the near-surface atomic composition and valence band electronic structure of ZnO single crystals, investigated by x-ray photoemission spectroscopy using both Al K α (1486.6 eV) and synchrotron radiation (150 to 1486 eV). In particular, photoemission from the lowest binding energy valence band states was found to be significantly more intense on the Zn-polar face compared to the O-polar face. This is a consistent effect that can be used as a simple, nondestructive indicator of crystallographic polarity in ZnO and other wurtzite semiconductors.

  18. Study of vibrational modes and specific heat of wurtzite phase of BN

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Daljit, E-mail: daljit.jt@gmail.com; Sinha, M. M. [Department of Physics, SLIET, Longowal (India)

    2016-05-06

    In these days of nanotechnology the materials like BN is of utmost importance as in hexagonal phase it is among hardest materials. The phonon mode study of the materials is most important factor to find structural and thermodynamcal properties. To study the phonons de launey angular force (DAF) constant model is best suited as it involves many particle interactions. Therefore in this presentation we have studied the lattice dynamical properties and specific heat of BN in wurtzite phase using DAF model. The obtained results are in excellent agreement with existing results.

  19. Study of vibrational modes and specific heat of wurtzite phase of BN

    International Nuclear Information System (INIS)

    Singh, Daljit; Sinha, M. M.

    2016-01-01

    In these days of nanotechnology the materials like BN is of utmost importance as in hexagonal phase it is among hardest materials. The phonon mode study of the materials is most important factor to find structural and thermodynamcal properties. To study the phonons de launey angular force (DAF) constant model is best suited as it involves many particle interactions. Therefore in this presentation we have studied the lattice dynamical properties and specific heat of BN in wurtzite phase using DAF model. The obtained results are in excellent agreement with existing results.

  20. Determination of the kinetic parameters of BeO thermoluminescent samples using different methods

    Energy Technology Data Exchange (ETDEWEB)

    Algarve, Fábio J.; Caldas, Linda V.E., E-mail: fjalgarve@ipen.br, E-mail: lcaldas@ipen.br [Instituto de Pesquisas Energéticas e Nucleares (IPEN/CNEN-SP), São Paulo, SP (Brazil)

    2017-07-01

    The objective of this work was to determine the kinetic parameters of BeO thermoluminescent (TL) samples. The knowledge of the kinetic parameters is important for the general description of the physical characteristics of a thermoluminescent material. Using a linear heating rate of 5K/s{sup -1}, the BeO peak temperatures obtained were (474.7 ± 1.2) K and (620.5 ± 1.2) K, respectively, for the first and second TL peaks. The peak shape and the glow curve area measurement methods and the Urbach formula have been used for the trap parameter determination. A kinetic order of about two was determined for the first peak, whereas the second peak followed the first-order kinetics according to the geometrical factor. The energy activation values obtained using different kinds of measurements are in good agreement, including the Kitis method for deconvolution of the glow curve. Furthermore the results agree with those presented by other authors. (author)

  1. Subcritical multiplication measurements with a BeO reflected 233U uranyl nitrate solution system

    International Nuclear Information System (INIS)

    Job, P.K.; Srinivasan, M.; Nargundkar, V.R.; Chandramoleshwar, K.; Pasupathy, C.S.; Das, S.; Mayankutty, P.C.

    1978-01-01

    A series of subcritical multiplication measurements were carried out in PURNIMA with 233 U uranyl nitrate solution contained in all 11 x 11 cm 2 square sectional tank and reflected by 30 cm thickness of BeO on all sides. The objective of these experiments was to determine the 'Minimum critical mass' of the system in rectangular parellelopiped geometry. The rectangular aluminium core tank was attached to the bottom of an alpha tight glove box. BeO reflector was arranged below the glove box outside the core tank. The system multiplication was measured as a function of solution concentration and core volume by means of neutron detectors placed outside the assembly. The extrapolated critical mass was obtained through conventional inverse counts plot. The maximum amount of 233 U used was 120 gms. The rectangular geometry was estimated to be 235 +- 10 gms, in the concentration range of 80 to 120 gms/litre of 233 U. The experimental set up, procedure adopted, method of analysis and the details of the results are described. (author)

  2. Nanoscale size dependence parameters on lattice thermal conductivity of Wurtzite GaN nanowires

    International Nuclear Information System (INIS)

    Mamand, S.M.; Omar, M.S.; Muhammad, A.J.

    2012-01-01

    Graphical abstract: Temperature dependence of calculated lattice thermal conductivity of Wurtzite GaN nanowires. Highlights: ► A modified Callaway model is used to calculate lattice thermal conductivity of Wurtzite GaN nanowires. ► A direct method is used to calculate phonon group velocity for these nanowires. ► 3-Gruneisen parameter, surface roughness, and dislocations are successfully investigated. ► Dislocation densities are decreases with the decrease of wires diameter. -- Abstract: A detailed calculation of lattice thermal conductivity of freestanding Wurtzite GaN nanowires with diameter ranging from 97 to 160 nm in the temperature range 2–300 K, was performed using a modified Callaway model. Both longitudinal and transverse modes are taken into account explicitly in the model. A method is used to calculate the Debye and phonon group velocities for different nanowire diameters from their related melting points. Effect of Gruneisen parameter, surface roughness, and dislocations as structure dependent parameters are successfully used to correlate the calculated values of lattice thermal conductivity to that of the experimentally measured curves. It was observed that Gruneisen parameter will decrease with decreasing nanowire diameters. Scattering of phonons is assumed to be by nanowire boundaries, imperfections, dislocations, electrons, and other phonons via both normal and Umklapp processes. Phonon confinement and size effects as well as the role of dislocation in limiting thermal conductivity are investigated. At high temperatures and for dislocation densities greater than 10 14 m −2 the lattice thermal conductivity would be limited by dislocation density, but for dislocation densities less than 10 14 m −2 , lattice thermal conductivity would be independent of that.

  3. Nanoscale size dependence parameters on lattice thermal conductivity of Wurtzite GaN nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Mamand, S.M., E-mail: soran.mamand@univsul.net [Department of Physics, College of Science, University of Sulaimani, Sulaimanyah, Iraqi Kurdistan (Iraq); Omar, M.S. [Department of Physics, College of Science, University of Salahaddin, Arbil, Iraqi Kurdistan (Iraq); Muhammad, A.J. [Department of Physics, College of Science, University of Kirkuk, Kirkuk (Iraq)

    2012-05-15

    Graphical abstract: Temperature dependence of calculated lattice thermal conductivity of Wurtzite GaN nanowires. Highlights: Black-Right-Pointing-Pointer A modified Callaway model is used to calculate lattice thermal conductivity of Wurtzite GaN nanowires. Black-Right-Pointing-Pointer A direct method is used to calculate phonon group velocity for these nanowires. Black-Right-Pointing-Pointer 3-Gruneisen parameter, surface roughness, and dislocations are successfully investigated. Black-Right-Pointing-Pointer Dislocation densities are decreases with the decrease of wires diameter. -- Abstract: A detailed calculation of lattice thermal conductivity of freestanding Wurtzite GaN nanowires with diameter ranging from 97 to 160 nm in the temperature range 2-300 K, was performed using a modified Callaway model. Both longitudinal and transverse modes are taken into account explicitly in the model. A method is used to calculate the Debye and phonon group velocities for different nanowire diameters from their related melting points. Effect of Gruneisen parameter, surface roughness, and dislocations as structure dependent parameters are successfully used to correlate the calculated values of lattice thermal conductivity to that of the experimentally measured curves. It was observed that Gruneisen parameter will decrease with decreasing nanowire diameters. Scattering of phonons is assumed to be by nanowire boundaries, imperfections, dislocations, electrons, and other phonons via both normal and Umklapp processes. Phonon confinement and size effects as well as the role of dislocation in limiting thermal conductivity are investigated. At high temperatures and for dislocation densities greater than 10{sup 14} m{sup -2} the lattice thermal conductivity would be limited by dislocation density, but for dislocation densities less than 10{sup 14} m{sup -2}, lattice thermal conductivity would be independent of that.

  4. Formation of cellular films consisting of wurtzite-type zinc oxide nanosheets by mediation of phosphate anions

    International Nuclear Information System (INIS)

    Yamabi, Satoshi; Yahiro, Junko; Iwai, Satoko; Imai, Hiroaki

    2005-01-01

    We successfully prepared a wide variety of wurtzite-type zinc oxide films exhibiting columnar, cellular and densely packed morphologies in a simple aqueous solution system containing phosphate anions. As the phosphate concentration increased, the shape of crystalline units composing the films varied from hexagonal needles into seaweed-like sheets. A novel type of open cellular structures was obtained by assembly of nanoscale zinc oxide sheets covered with phosphate. Specific adsorption of phosphate anions on (001) of the wurtzite-type crystal flattened the crystal grains, and then induced the structural evolution into a cellular form. A blue shift of the absorption edge suggested that the quantum size effect occurred in the nanoscale platy crystals composing the cellular films

  5. More on the TR-OSL signal from BeO ceramics

    International Nuclear Information System (INIS)

    Bulur, Enver

    2014-01-01

    Time Resolved Optically Stimulated Luminescence (TR-OSL) from BeO ceramics was investigated using blue (445 nm) and near-IR light (852 nm) for stimulation. Stimulation spectrum of the TR-OSL signal – as measured in the interval 700 to 420 nm- was observed to increase monotonically with the decreasing stimulation wavelength. In addition to the “fast” and “slow” components observed with blue light stimulation, IR stimulated TR-OSL spectra of irradiated BeO ceramics were observed to have two components with average lifetimes around ∼2.5 μs and ∼17 μs. Emission spectra of the both IR stimulated TR-OSL components were observed to have a broad emission band peaking around 330 nm. Thermal stability of the IR stimulated TR-OSL signal was studied by making preheating experiments in the range from 100 °C to 190 °C. It was observed that the IR stimulated OSL signal is stable up to ∼150 °C and decay afterwards. Radiation dose response of the IR stimulated luminescence signal was obtained in the range from 5 to 500 Gy. Both blue and IR stimulated TR-OSL signals grew up to 100 Gy and exhibited saturation for higher doses. Additionally, measurement temperature dependence of the components was also investigated and for the ∼2 μs component thermal assistance with activation energy around 0.16 eV was observed. It seems that the fast component of the blue stimulated TR-OSL component can be correlated to the ∼2 μs IR stimulated TR-OSL component. - Highlights: • IR Stimulated Time-Resolved OSL from BeO was studied. • Two components with lifetimes ∼2 and ∼17us were observed. • IR stimulated TR-OSL signal is found to be stable up to 150 °C. • Thermal quenching energy of the 2us component was found as 0.16 eV

  6. Manufacture of a UO2-Based Nuclear Fuel with Improved Thermal Conductivity with the Addition of BeO

    Science.gov (United States)

    Garcia, Chad B.; Brito, Ryan A.; Ortega, Luis H.; Malone, James P.; McDeavitt, Sean M.

    2017-12-01

    The low thermal conductivity of oxide nuclear fuels is a performance-limiting parameter. Enhancing this property may provide a contribution toward establishing accident-tolerant fuel forms. In this study, the thermal conductivity of UO2 was increased through the fabrication of ceramic-ceramic composite forms with UO2 containing a continuous BeO matrix. Fuel with a higher thermal conductivity will have reduced thermal gradients and lower centerline temperatures in the fuel pin. Lower operational temperatures will reduce fission gas release and reduce fuel restructuring. Additions of BeO were made to UO2 fuel pellets in 2.5, 5, 7.5, and 10 vol pct concentrations with the goals of establishing reliable lab-scale processing procedures, minimizing porosity, and maximizing thermal conductivity. The microstructure was characterized with electron probe microanalysis, and the thermal properties were assessed by light flash analysis and differential scanning calorimetry. Reliable, high-density samples were prepared using compaction pressure between 200 and 225 MPa and sintering times between 4 and 6 hours. It was found that the thermal conductivity of UO2 improved approximately 10 pct for each 1 vol pct BeO added over the measured temperature range 298.15 K to 523.15 K (25 °C to 250 °C) with the maximum observed improvement being ˜ 100 pct, or doubled, at 10 vol pct BeO.

  7. Effects of lattice parameters on piezoelectric constants in wurtzite materials: A theoretical study using first-principles and statistical-learning methods

    Science.gov (United States)

    Momida, Hiroyoshi; Oguchi, Tamio

    2018-04-01

    Longitudinal piezoelectric constant (e 33) values of wurtzite materials, which are listed in a structure database, are calculated and analyzed by using first-principles and statistical learning methods. It is theoretically shown that wurtzite materials with high e 33 generally have small lattice constant ratios (c/a) almost independent of constituent elements, and approximately expressed as e 33 ∝ c/a - (c/a)0 with ideal lattice constant ratio (c/a)0. This relation also holds for highly-piezoelectric ternary materials such as Sc x Al1- x N. We conducted a search for high-piezoelectric wurtzite materials by identifying materials with smaller c/a values. It is proposed that the piezoelectricity of ZnO can be significantly enhanced by substitutions of Zn with Ca.

  8. Modeling the natural UV irradiation and comparative UV measurements at Moussala BEO (BG)

    Science.gov (United States)

    Tyutyundzhiev, N.; Angelov, Ch; Lovchinov, K.; Nitchev, Hr; Petrov, M.; Arsov, T.

    2018-03-01

    Studies of and modeling the impact of natural UV irradiation on the human population are of significant importance for human activity and economics. The sharp increase of environmental problems – extraordinary temperature changes, solar irradiation abnormalities, icy rains – raises the question of developing novel means of assessing and predicting potential UV effects. In this paper, we discuss new UV irradiation modeling based on recent real-time measurements at Moussala Basic Environmental Observatory (BEO) on Moussala Peak (2925 m ASL) in Rila Mountain, Bulgaria, and highlight the development and initial validation of portable embedded devices for UV-A, UV-B monitoring using open-source software architecture, narrow bandpass UV sensors, and the popular Arduino controllers. Despite the high temporal resolution of the VIS and UV irradiation measurements, the results obtained reveal the need of new assumptions in order to minimize the discrepancy with available databases.

  9. In-situ x-ray characterization of wurtzite formation in GaAs nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Krogstrup, Peter; Hannibal Madsen, Morten; Nygaard, Jesper; Feidenhans' l, Robert [Nano-Science Center, Niels Bohr Institute, University of Copenhagen, Copenhagen (Denmark); Hu Wen [Quantum Beam Science Directorate, Japan Atomic Energy Agency, 1-1-1 Koto, Sayo, Hyogo 679-5148 (Japan); Kozu, Miwa; Nakata, Yuka [University of Hyogo, 3-2-1 Koto, Kamigori, Hyogo 678-1297 (Japan); Takahasi, Masamitu [Quantum Beam Science Directorate, Japan Atomic Energy Agency, 1-1-1 Koto, Sayo, Hyogo 679-5148 (Japan); University of Hyogo, 3-2-1 Koto, Kamigori, Hyogo 678-1297 (Japan)

    2012-02-27

    In-situ monitoring of the crystal structure formation during Ga-assisted GaAs nanowire growth on Si(111) substrates has been performed in a combined molecular beam epitaxy growth and x-ray characterization experiment. Under Ga rich conditions, we show that an increase in the V/III ratio increases the formation rate of the wurtzite structure. Moreover, the response time for changes in the structural phase formation to changes in the beam fluxes is observed to be much longer than predicted time scales of adatom kinetics and liquid diffusion. This suggests that the morphology of the growth interface plays the key role for the relative growth structure formation rates.

  10. Analysis of UO{sub 2}-BeO fuel under transient using fuel performance code

    Energy Technology Data Exchange (ETDEWEB)

    Gomes, Daniel S.; Abe, Alfredo Y.; Muniz, Rafael O.R.; Giovedi, Claudia, E-mail: dsgomes@ipen.br, E-mail: alfredo@ctmsp.mar.mil.br, E-mail: rafael.orm@gmail.com, E-mail: claudia.giovedi@ctmsp.mar.mil.br [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-SP), Sao Paulo, SP (Brazil); Universidade de São Paulo (USP), São Paulo, SP (Brazil). Departamento de Engenharia Naval e Oceânica

    2017-11-01

    Recent research has appointed the need to replace the classic fuel concept, used in light water reactors. Uranium dioxide has a weak point due to the low thermal conductivity, that produce high temperatures on the fuel. The ceramic composite fuel formed of uranium dioxide (UO{sub 2}), with the addition of beryllium oxide (BeO), presents high thermal conductivity compared with UO{sub 2}. The oxidation of zirconium generates hydrogen gas that can create a detonation condition. One of the preferred options are the ferritic alloys formed of iron-chromium and aluminum (FeCrAl), that should avoid the hydrogen release due to oxidation. In general, the FeCrAl alloys containing 10 - 20Cr, 3 - 5Al, and 0 - 0.12Y in weight percent. The FeCrAl alloys should exhibit a slow oxidation kinetics due to chemical composition. Resistance to oxidation in the presence of steam is improved as a function of the content of chromium and aluminum. In this way, the thermal and mechanical properties of the UO{sub 2}-BeO-10%vol, composite fuel were coupled with FeCrAl alloys and added to the fuel codes. In this work, we examine the fuel rod behavior of UO{sub 2}-10%vol-BeO/FeCrAl, including a simulated transient of reactivity. The fuels behavior shown reduced temperature with UO{sub 2}-BeO/Zr, UO{sub 2}-BeO/FeCrAl also were compared with UO{sub 2}/Zr system. The case reactivity initiated accident analyzed, reproducing the fuel rod called VA-1 using UO{sub 2}/Zr alloys and compared with UO{sub 2}-BeO/FeCrAl. (author)

  11. Diffusion Parameters of BeO by the Pulsed Neutron Method

    International Nuclear Information System (INIS)

    Joshi, B.V.; Nargundkar, V.R.; Subbarao, K.

    1965-01-01

    The use of the pulsed neutron method for the precise determination of the diffusion parameters of moderators is described. The diffusion parameters of BeO have been obtained by this method. The neutron bursts were produced from a cascade accelerator by pulsing the ion source and using the Be (d, n) reaction. The detector was an enriched boron trifluoride proportional counter. It is shown that by a proper choice of the counter position arid length, and the source position, most of the space harmonics can be eliminated. Any constant background can be accounted for in the calculation of the decay constant. Very large bucklings were not used to avoid time harmonics. Any remaining harmonic content was rendered ineffective by the use of adequate time delay. The decay constant of the fundamental mode of the thermal neutron population was determined for several bucklings. Conditions to be satisfied for an accurate determination of the diffusion cooling constant C are discussed. The following values are obtained for BeO: λ 0 = absorption constant = 156.02 ± 4.37 s -1 D = diffusion coefficient = (1.3334 ± 0.0128) x 10 5 cm 2 /s C = diffusion cooling constant = (-4.8758 ± 0.5846) x 10 5 cm 4 /s. The effect of neglecting the contribution of the B 6 term on the determination of the diffusion parameters was estimated and is shown to be considerable. The reason for the longstanding discrepancy between the values of C obtained for the same moderator by different workers is attributed to this. (author) [fr

  12. Valence band offset of β-Ga2O3/wurtzite GaN heterostructure measured by X-ray photoelectron spectroscopy.

    Science.gov (United States)

    Wei, Wei; Qin, Zhixin; Fan, Shunfei; Li, Zhiwei; Shi, Kai; Zhu, Qinsheng; Zhang, Guoyi

    2012-10-10

    A sample of the β-Ga2O3/wurtzite GaN heterostructure has been grown by dry thermal oxidation of GaN on a sapphire substrate. X-ray diffraction measurements show that the β-Ga2O3 layer was formed epitaxially on GaN. The valence band offset of the β-Ga2O3/wurtzite GaN heterostructure is measured by X-ray photoelectron spectroscopy. It is demonstrated that the valence band of the β-Ga2O3/GaN structure is 1.40 ± 0.08 eV.

  13. Valence-band splitting energies in wurtzite InP nanowires: Photoluminescence spectroscopy and ab initio calculations

    Science.gov (United States)

    Gadret, E. G.; Dias, G. O.; Dacal, L. C. O.; de Lima, M. M., Jr.; Ruffo, C. V. R. S.; Iikawa, F.; Brasil, M. J. S. P.; Chiaramonte, T.; Cotta, M. A.; Tizei, L. H. G.; Ugarte, D.; Cantarero, A.

    2010-09-01

    We investigated experimentally and theoretically the valence-band structure of wurtzite InP nanowires. The wurtzite phase, which usually is not stable for III-V phosphide compounds, has been observed in InP nanowires. We present results on the electronic properties of these nanowires using the photoluminescence excitation technique. Spectra from an ensemble of nanowires show three clear absorption edges separated by 44 meV and 143 meV, respectively. The band edges are attributed to excitonic absorptions involving three distinct valence-bands labeled: A, B, and C. Theoretical results based on “ab initio” calculation gives corresponding valence-band energy separations of 50 meV and 200 meV, respectively, which are in good agreement with the experimental results.

  14. Atomic-scale origin of piezoelectricity in wurtzite ZnO.

    Science.gov (United States)

    Lee, Jung-Hoon; Lee, Woo-Jin; Lee, Sung-Hoon; Kim, Seong Min; Kim, Sungjin; Jang, Hyun Myung

    2015-03-28

    ZnO has been extensively studied by virtue of its remarkably high piezoelectric responses, especially in nanowire forms. Currently, the high piezoelectricity of wurtzite ZnO is understood in terms of the covalent-bonding interaction between Zn 3d and O 2p orbitals. However, the Zn 3d orbitals are not capable of forming hybridized orbitals with the O 2pz orbitals since the Zn ion is characterized by fully filled non-interacting 3d orbitals. To resolve this puzzling problem, we have investigated the atomic-scale origin of piezoelectricity by exploiting density-functional theory calculations. On the basis of the computed orbital-resolved density of states and the band structure over the Γ-M first Brillouin zone, we propose an intriguing bonding mechanism that accounts for the observed high piezoelectricity - intra-atomic 3dz(2)-4pz orbital self-mixing of Zn, followed by asymmetric hybridization between the Zn 3dz(2)-4pz self-mixed orbital and the O 2pz orbital along the polar c-axis of the wurtzite ZnO.

  15. Spin-relaxation time in the impurity band of wurtzite semiconductors

    Science.gov (United States)

    Tamborenea, Pablo I.; Wellens, Thomas; Weinmann, Dietmar; Jalabert, Rodolfo A.

    2017-09-01

    The spin-relaxation time for electrons in the impurity band of semiconductors with wurtzite crystal structure is determined. The effective Dresselhaus spin-orbit interaction Hamiltonian is taken as the source of the spin relaxation at low temperature and for doping densities corresponding to the metallic side of the metal-insulator transition. The spin-flip hopping matrix elements between impurity states are calculated and used to set up a tight-binding Hamiltonian that incorporates the symmetries of wurtzite semiconductors. The spin-relaxation time is obtained from a semiclassical model of spin diffusion, as well as from a microscopic self-consistent diagrammatic theory of spin and charge diffusion in doped semiconductors. Estimates are provided for particularly important materials. The theoretical spin-relaxation times compare favorably with the corresponding low-temperature measurements in GaN and ZnO. For InN and AlN we predict that tuning of the spin-orbit coupling constant induced by an external potential leads to a potentially dramatic increase of the spin-relaxation time related to the mechanism under study.

  16. Structural property of platinum mononitride

    International Nuclear Information System (INIS)

    Yu, L.H.; Yao, K.L.; Liu, Z.L.; Zhang, Y.S.

    2007-01-01

    The structural stability and pressure-induced structural phase transition of platinum mononitride (PtN), as well as its electronic structure, were studied using the full potential augmented plane wave plus local orbitals method with the generalized gradient approximation (GGA) exchange-correlation functional. The total energy calculations show that the optimized wurtzite structure is most stable energetically among four structures: zinc blende, rocksalt, CsCl and wurtzite, which reveals the platinum mononitride PtN perhaps crystallizes in the wurtzite structure; the pressure of phase transition from wurtzite to rocksalt is predicted to be 41.4 GPa.The calculated bulk modulus of the wurtzite structure is 99.41 GPa, which is smaller than that of the other three structures and face-centered cubic Pt. The band structure calculations show wurtzite PtN is metallic

  17. Fabrication of hollow-sphere films of wurtzite CuInS{sub 2} on copper substrate

    Energy Technology Data Exchange (ETDEWEB)

    Lei, Shuijin, E-mail: shjlei@ncu.edu.cn [School of Materials Science and Engineering, Nanchang University, Nanchang, Jiangxi 330031 (China); Wang, Chunying [School of Materials Science and Engineering, Nanchang University, Nanchang, Jiangxi 330031 (China); Huang, Qiang [School of Electromechanical Engineering, Nanchang University, Nanchang, Jiangxi 330031 (China); Liu, Lei; Ge, Yang; Tang, Qingliu; Cheng, Baochang; Xiao, Yanhe; Zhou, Lang [School of Materials Science and Engineering, Nanchang University, Nanchang, Jiangxi 330031 (China)

    2013-12-16

    As important semiconductors, I–III–VI{sub 2} compounds have attracted wide attention, among which the wurtzite structured CuInS{sub 2} has been the research focus due to its metastable phase. In this paper, the wurtzite CuInS{sub 2} hollow-sphere films have been successfully prepared on copper substrate in a self-designed solvothermal detached system. The films of Cu(OH){sub 2} one-dimensional nanostructure arrays and thioacetamide were used as the precursors and triethylene glycol was used as the solvent. Experiments showed that the amount of indium trichloride played a determinative role in the final morphology of the products. Meanwhile, the one-dimensional nanostructure arrays and the detached solvothermal system have great influences on the crystal shape as well. Based on the experimental results, a possible formation mechanism for the CuInS{sub 2} hollow spheres was also proposed. The UV–Vis absorption spectrum showed a broad absorption over the entire visible light and extending into the near-infrared region and presented the band gap of 1.53 eV for the as-prepared wurtzite CuInS{sub 2}, which indicates the potential applications in solar cells. - Highlights: • A self-designed detached system along with solvothermal treatment was developed. • Wurtzite CuInS{sub 2} hollow-sphere films were successfully fabricated on Cu substrate. • The detached system and InCl{sub 3} usage were crucial for the hollow spheres. • The broadband absorption and 1.53 eV band-gap indicates its potentials in PV.

  18. An in-situ chemical reaction deposition of nanosized wurtzite CdS thin films

    International Nuclear Information System (INIS)

    Chu Juan; Jin Zhengguo; Cai Shu; Yang Jingxia; Hong Zhanglian

    2012-01-01

    Nanocrystalline CdS thin films were deposited on glass substrates by an ammonia-free in-situ chemical reaction synthesis technique using cadmium cationic precursor solid films as reaction source and sodium sulfide based solutions as anionic reaction medium. Effects of ethanolamine addition to the cadmium cationic precursor solid films, deposition cycle numbers and annealing treatments in Ar atmosphere on structure, morphology, chemical composition and optical properties of the resultant films were investigated by X-ray diffraction, field emission scanning electron microscope, energy dispersive X-ray analysis and UV–Vis spectra measurements. The results show that CdS thin films deposited by the in-situ chemical reaction synthesis have wurtzite structure with (002) plane preferential orientation and crystallite size is in the range of 16 nm–19 nm. The growth of film thickness is almost constant with deposition cycle numbers and about 96 nm per cycle.

  19. Dosimetric characterization of BeO samples in alpha, beta and X radiation beams using luminescent techniques

    International Nuclear Information System (INIS)

    Groppo, Daniela Piai

    2013-01-01

    In the medical field, the ionizing radiation is used both for therapeutic and diagnostic purposes, in a wide range of radiation doses. In order to ensure that the objective is achieved in practice, detailed studies of detectors and devices in different types of radiations beams are necessary. In this work a dosimetric characterization of BeO samples was performed using the techniques of thermoluminescence (TL) and optically stimulated luminescence (OSL) by a comparison of their response for alpha, beta and X radiations and the establishment of an appropriated system for use in monitoring of these radiations beams. The main results are: the high sensitivity to beta radiation for both techniques, good reproducibility of TL and OSL response (coefficients of variation lower than 5%), maximum energy dependence of the X radiation of 28% for the TL technique, and only 7% for the OSL technique, within the studied energy range. The dosimetric characteristics obtained in this work show the possibility of applying BeO samples to dosimetry of alpha, beta and X radiations, considering the studied dose ranges, using the TL and OSL techniques. From the results obtained, the samples of BeO showed their potential use for beam dosimetry in diagnostic radiology and radiotherapy. (author)

  20. Critical Temperature for the Conversion from Wurtzite to Zincblende of the Optical Emission of InAs Nanowires

    KAUST Repository

    Rota, Michele B.

    2017-07-12

    One hour annealing at 300 degrees C changes the optical emission characteristics of InAs nanowires (NWs) from the wurtzite (WZ) phase into that of zincblende (ZB). These results are accounted for by the conversion of a small fraction of the NW WZ metastable structure into the stable ZB structure. Several paths toward the polytype transformation in the configuration space are also demonstrated using first-principles calculations. For lower annealing temperatures, emission which is likely related to WZ polytypes is observed at energies that agree with theoretical predictions. These results demonstrate severe constraints on thermal processes to which devices made from InAs WZ NWs can be exposed.

  1. Crystal orientation effects on wurtzite quantum well electromechanical fields

    DEFF Research Database (Denmark)

    Duggen, Lars; Willatzen, Morten

    2010-01-01

    in the literature for semiconductors, is inaccurate for ZnO/MgZnO heterostructures where shear-strain components play an important role. An interesting observation is that a growth direction apart from [1̅ 21̅ 0] exists for which the electric field in the quantum well region becomes zero. This is important for, e......A one-dimensional continuum model for calculating strain and electric field in wurtzite semiconductor heterostructures with arbitrary crystal orientation is presented and applied to GaN/AlGaN and ZnO/MgZnO heterostructure combinations. The model is self-consistent involving feedback couplings...... of spontaneous polarization, strain, and electric field. Significant differences between fully coupled and semicoupled models are found for the longitudinal and shear-strain components as a function of the crystal-growth direction. In particular, we find that the semicoupled model, typically used...

  2. The Upper Miocene Lake Pannon marl from the Filijala Open Pit (Beočin, northern Serbia: New geological and paleomagnetic data

    Directory of Open Access Journals (Sweden)

    Ganić Meri

    2010-01-01

    Full Text Available This work presents major lithological, structural, paleontological and paleomagnetic characteristics of the Upper Miocene Pannonian marl in the Filijala Open Pit of the La Farge Cement Plant near Beočin, northern Serbia. Pannonian marl lies between the underlying heterogeneous Sarmatian deposits and the overlying set of Pontian sand beds and Quaternary sediments. The open pit is located on the NE range of Fruška Gora, a horst structure with a core of Paleozoic, Mesozoic and Paleogene rocks in a complex structural pattern. Pannonian sediments, which are part of a younger structural stage, deposited on the horst limbs. The Pannonian marl strata dip at angles from 12° to 26° (to the NNW, forming a monocline. The strata deformations are a consequence of radial tectonics and are a potential source of landslides. The many mollusks (7 gastropod and 9 bivalve species and ostracodes (27 species and their biostratigraphical position indicate marl deposition throughout the Pannonian age. A paleomagnetic investigation established that the marl has inconsistent remanent magnetization (with bad statistical parameters, which originates from neoformed magnetite.

  3. Exciton binding energy in wurtzite InGaN/GaN quantum wells

    International Nuclear Information System (INIS)

    Park, Seoung-Hwan; Kim, Jong-Jae; Kim, Hwa-Min

    2004-01-01

    The internal field and carrier density effects on the exciton binding energies in wurtzite (WZ) InGaN/GaN quantum-well (QW) structures are investigated using the multiband effective-mass theory, and are compared with those obtained from the at-band model and with those of GaN/AlGaN QW structures. The exciton binding energy is significantly reduced with increasing sheet carrier density, suggesting that excitons are nearly bleached at densities around 10 12 cm -2 for both InGaN/GaN and GaN/AlGaN QW structures. With the inclusion of the internal field, the exciton binding energy is substantialy reduced compared to that of the at-band model in the investigated region of the wells. This can be explained by a decrease in the momentum matrix element and an increase in the inverse screening length due to the internal field. The exciton binding energy of the InGaN/GaN structure is smaller than that of the GaN/AlGaN structure because InGaN/GaN structures have a smaller momentum matrix element and a larger inverse screening length than GaN/AlGaN structures.

  4. Diffusion Parameters of BeO by the Pulsed Neutron Method; Calcul des Parametres de Diffusion de BeO par la Methode des Neutrons Pulses; Opredelenie diffuzionnykh parametrov BeO s pomoshch'yu metoda impul'snykh nejtronov; Determinacion de los Parametros de Difusion en el BeO por el Metodo de los Neutrones Pulsados

    Energy Technology Data Exchange (ETDEWEB)

    Joshi, B. V.; Nargundkar, V. R.; Subbarao, K. [Atomic Energy Establishment Trombay, Bombay (India)

    1965-08-15

    The use of the pulsed neutron method for the precise determination of the diffusion parameters of moderators is described. The diffusion parameters of BeO have been obtained by this method. The neutron bursts were produced from a cascade accelerator by pulsing the ion source and using the Be (d, n) reaction. The detector was an enriched boron trifluoride proportional counter. It is shown that by a proper choice of the counter position arid length, and the source position, most of the space harmonics can be eliminated. Any constant background can be accounted for in the calculation of the decay constant. Very large bucklings were not used to avoid time harmonics. Any remaining harmonic content was rendered ineffective by the use of adequate time delay. The decay constant of the fundamental mode of the thermal neutron population was determined for several bucklings. Conditions to be satisfied for an accurate determination of the diffusion cooling constant C are discussed. The following values are obtained for BeO: {lambda}{sub 0} = absorption constant = 156.02 {+-} 4.37 s{sup -1} D = diffusion coefficient = (1.3334 {+-} 0.0128) x 10{sup 5} cm{sup 2}/s C = diffusion cooling constant = (-4.8758 {+-} 0.5846) x 10{sup 5} cm{sup 4}/s. The effect of neglecting the contribution of the B{sup 6} term on the determination of the diffusion parameters was estimated and is shown to be considerable. The reason for the longstanding discrepancy between the values of C obtained for the same moderator by different workers is attributed to this. (author) [French] Les auteurs decrivent l'emploi de la methode des neutrons puises pour la determination precise des parametres de diffusion des ralentisseurs. Ils ont calculi ceux de la glucine par cette methode. Des deuterons puises au moyen d'un accelerateur a cascade produisaient les bouffees de neutrons par la reaction Be (d, n). Le detecteur etait constitue par un compteur proportionnel au BF{sub 3} enrichi. En choisissant convenablement

  5. Characteristics of poly- and mono-crystalline BeO and SiO{sub 2} as thermal and cold neutron filters

    Energy Technology Data Exchange (ETDEWEB)

    Adib, M.; Habib, N. [Reactor Physics Department, NRC, Atomic Energy Authority, Cairo (Egypt); Bashter, I.I. [Physics Department, Faculty of Science, Zagazig University (Egypt); Morcos, H.N.; El-Mesiry, M.S. [Reactor Physics Department, NRC, Atomic Energy Authority, Cairo (Egypt); Mansy, M.S., E-mail: drmohamedmansy88@hotmail.com [Reactor Physics Department, NRC, Atomic Energy Authority, Cairo (Egypt)

    2015-09-01

    Highlights: • Neutron filtering features of BeO and SiO{sub 2} poly- and mono-crystals. • Calculations of the cold and thermal neutron cross sections and transmission with the code “HEXA-FILTERS”. • Optimal mosaic spread, thicknesses and cutting planes for BeO and SiO{sub 2} mono-crystals. - Abstract: A simple model along with a computer code “HEXA-FILTERS” is used to carry out the calculation of the total cross-sections of BeO and SiO{sub 2} having poly or mono-crystalline form as a function of neutron wavelength at room (R.T.) and liquid nitrogen (L.N.) temperatures. An overall agreement is indicated between the calculated neutron cross-sections and experimental data. Calculation shows that 25 cm thick of polycrystalline BeO cooled at liquid nitrogen temperature was found to be a good filter for neutron wavelengths longer than 0.46 nm. While, 50 cm of SiO{sub 2}, with much less transmission, for neutrons with wavelengths longer than 0.85 nm. It was also found that 10 cm of BeO and 15 cm SiO{sub 2} thick mono-crystals cut along their (0 0 2) plane, with 0.5° FWHM on mosaic spread and cooled at L.N., are a good thermal neutron filter, with high effect-to-noise ratio.

  6. Mobility in n-doped wurtzite III-Nitrides

    Directory of Open Access Journals (Sweden)

    C.G. Rodrigues

    2003-01-01

    Full Text Available A study of the mobility of n-doped wurtzite III-Nitrides is reported. We have determined the nonequilibrium thermodynamic state of the III-Nitrides systems driven far away from equilibrium by a strong electric field in the steady state, which follows after a very fast transient. The dependence of the mobility (which depends on the nonequilibrium thermodynamic state of the sample on the electric field strength is derived, which decreases with the strength of electric field. We analyzed the contributions to the mobility arising out of the different channels of electron scattering, namely, the polar optic, deformation, piezoelectric, interactions with the phonons, and with impurities. The case of n-InN, n-GaN, and n-AlN have been analyzed: as expected the main contribution comes from the polar-optic interactions in these strongly polar semiconductors. The other interactions are in decreasing order, the deformation acoustic, the piezoelectric, and the one due to impurities.

  7. Optical Properties of Strained Wurtzite Gallium Phosphide Nanowires

    KAUST Repository

    Greil, J.

    2016-06-08

    Wurtzite gallium phosphide (WZ GaP) has been predicted to exhibit a direct bandgap in the green spectral range. Optical transitions, however, are only weakly allowed by the symmetry of the bands. While efficient luminescence has been experimentally shown, the nature of the transitions is not yet clear. Here we apply tensile strain up to 6% and investigate the evolution of the photoluminescence (PL) spectrum of WZ GaP nanowires (NWs). The pressure and polarization dependence of the emission together with a theoretical analysis of strain effects is employed to establish the nature and symmetry of the transitions. We identify the emission lines to be related to localized states with significant admixture of Γ7c symmetry and not exclusively related to the Γ8c conduction band minimum (CBM). The results emphasize the importance of strongly bound state-related emission in the pseudodirect semiconductor WZ GaP and contribute significantly to the understanding of the optoelectronic properties of this novel material.

  8. Mechanical, Thermodynamic and Electronic Properties of Wurtzite and Zinc-Blende GaN Crystals

    Science.gov (United States)

    Luan, Xinghe; Feng, Chuang; Yang, Daoguo; Zhang, Guoqi

    2017-01-01

    For the limitation of experimental methods in crystal characterization, in this study, the mechanical, thermodynamic and electronic properties of wurtzite and zinc-blende GaN crystals were investigated by first-principles calculations based on density functional theory. Firstly, bulk moduli, shear moduli, elastic moduli and Poisson’s ratios of the two GaN polycrystals were calculated using Voigt and Hill approximations, and the results show wurtzite GaN has larger shear and elastic moduli and exhibits more obvious brittleness. Moreover, both wurtzite and zinc-blende GaN monocrystals present obvious mechanical anisotropic behavior. For wurtzite GaN monocrystal, the maximum and minimum elastic moduli are located at orientations [001] and , respectively, while they are in the orientations and for zinc-blende GaN monocrystal, respectively. Compared to the elastic modulus, the shear moduli of the two GaN monocrystals have completely opposite direction dependences. However, different from elastic and shear moduli, the bulk moduli of the two monocrystals are nearly isotropic, especially for the zinc-blende GaN. Besides, in the wurtzite GaN, Poisson’s ratios at the planes containing [001] axis are anisotropic, and the maximum value is 0.31 which is located at the directions vertical to [001] axis. For zinc-blende GaN, Poisson’s ratios at planes (100) and (111) are isotropic, while the Poisson’s ratio at plane (110) exhibits dramatically anisotropic phenomenon. Additionally, the calculated Debye temperatures of wurtzite and zinc-blende GaN are 641.8 and 620.2 K, respectively. At 300 K, the calculated heat capacities of wurtzite and zinc-blende are 33.6 and 33.5 J mol−1 K−1, respectively. Finally, the band gap is located at the G point for the two crystals, and the band gaps of wurtzite and zinc-blende GaN are 3.62 eV and 3.06 eV, respectively. At the G point, the lowest energy of conduction band in the wurtzite GaN is larger, resulting in a wider band gap

  9. Mechanical, Thermodynamic and Electronic Properties of Wurtzite and Zinc-Blende GaN Crystals

    Directory of Open Access Journals (Sweden)

    Hongbo Qin

    2017-12-01

    Full Text Available For the limitation of experimental methods in crystal characterization, in this study, the mechanical, thermodynamic and electronic properties of wurtzite and zinc-blende GaN crystals were investigated by first-principles calculations based on density functional theory. Firstly, bulk moduli, shear moduli, elastic moduli and Poisson’s ratios of the two GaN polycrystals were calculated using Voigt and Hill approximations, and the results show wurtzite GaN has larger shear and elastic moduli and exhibits more obvious brittleness. Moreover, both wurtzite and zinc-blende GaN monocrystals present obvious mechanical anisotropic behavior. For wurtzite GaN monocrystal, the maximum and minimum elastic moduli are located at orientations [001] and <111>, respectively, while they are in the orientations <111> and <100> for zinc-blende GaN monocrystal, respectively. Compared to the elastic modulus, the shear moduli of the two GaN monocrystals have completely opposite direction dependences. However, different from elastic and shear moduli, the bulk moduli of the two monocrystals are nearly isotropic, especially for the zinc-blende GaN. Besides, in the wurtzite GaN, Poisson’s ratios at the planes containing [001] axis are anisotropic, and the maximum value is 0.31 which is located at the directions vertical to [001] axis. For zinc-blende GaN, Poisson’s ratios at planes (100 and (111 are isotropic, while the Poisson’s ratio at plane (110 exhibits dramatically anisotropic phenomenon. Additionally, the calculated Debye temperatures of wurtzite and zinc-blende GaN are 641.8 and 620.2 K, respectively. At 300 K, the calculated heat capacities of wurtzite and zinc-blende are 33.6 and 33.5 J mol−1 K−1, respectively. Finally, the band gap is located at the G point for the two crystals, and the band gaps of wurtzite and zinc-blende GaN are 3.62 eV and 3.06 eV, respectively. At the G point, the lowest energy of conduction band in the wurtzite GaN is larger

  10. Mechanical, Thermodynamic and Electronic Properties of Wurtzite and Zinc-Blende GaN Crystals.

    Science.gov (United States)

    Qin, Hongbo; Luan, Xinghe; Feng, Chuang; Yang, Daoguo; Zhang, Guoqi

    2017-12-12

    For the limitation of experimental methods in crystal characterization, in this study, the mechanical, thermodynamic and electronic properties of wurtzite and zinc-blende GaN crystals were investigated by first-principles calculations based on density functional theory. Firstly, bulk moduli, shear moduli, elastic moduli and Poisson's ratios of the two GaN polycrystals were calculated using Voigt and Hill approximations, and the results show wurtzite GaN has larger shear and elastic moduli and exhibits more obvious brittleness. Moreover, both wurtzite and zinc-blende GaN monocrystals present obvious mechanical anisotropic behavior. For wurtzite GaN monocrystal, the maximum and minimum elastic moduli are located at orientations [001] and , respectively, while they are in the orientations and for zinc-blende GaN monocrystal, respectively. Compared to the elastic modulus, the shear moduli of the two GaN monocrystals have completely opposite direction dependences. However, different from elastic and shear moduli, the bulk moduli of the two monocrystals are nearly isotropic, especially for the zinc-blende GaN. Besides, in the wurtzite GaN, Poisson's ratios at the planes containing [001] axis are anisotropic, and the maximum value is 0.31 which is located at the directions vertical to [001] axis. For zinc-blende GaN, Poisson's ratios at planes (100) and (111) are isotropic, while the Poisson's ratio at plane (110) exhibits dramatically anisotropic phenomenon. Additionally, the calculated Debye temperatures of wurtzite and zinc-blende GaN are 641.8 and 620.2 K, respectively. At 300 K, the calculated heat capacities of wurtzite and zinc-blende are 33.6 and 33.5 J mol -1 K -1 , respectively. Finally, the band gap is located at the G point for the two crystals, and the band gaps of wurtzite and zinc-blende GaN are 3.62 eV and 3.06 eV, respectively. At the G point, the lowest energy of conduction band in the wurtzite GaN is larger, resulting in a wider band gap. Densities of

  11. Carrier thermalization dynamics in single zincblende and wurtzite InP Nanowires.

    Science.gov (United States)

    Wang, Yuda; Jackson, Howard E; Smith, Leigh M; Burgess, Tim; Paiman, Suriati; Gao, Qiang; Tan, Hark Hoe; Jagadish, Chennupati

    2014-12-10

    Using transient Rayleigh scattering (TRS) measurements, we obtain photoexcited carrier thermalization dynamics for both zincblende (ZB) and wurtzite (WZ) InP single nanowires (NW) with picosecond resolution. A phenomenological fitting model based on direct band-to-band transition theory is developed to extract the electron-hole-plasma density and temperature as a function of time from TRS measurements of single nanowires, which have complex valence band structures. We find that the thermalization dynamics of hot carriers depends strongly on material (GaAs NW vs InP NW) and less strongly on crystal structure (ZB vs WZ). The thermalization dynamics of ZB and WZ InP NWs are similar. But a comparison of the thermalization dynamics in ZB and WZ InP NWs with ZB GaAs NWs reveals more than an order of magnitude slower relaxation for the InP NWs. We interpret these results as reflecting their distinctive phonon band structures that lead to different hot phonon effects. Knowledge of hot carrier thermalization dynamics is an essential component for effective incorporation of nanowire materials into electronic devices.

  12. Quinary wurtzite Zn-Ga-Ge-N-O solid solutions and their photocatalytic properties under visible light irradiation

    Science.gov (United States)

    Xie, Yinghao; Wu, Fangfang; Sun, Xiaoqin; Chen, Hongmei; Lv, Meilin; Ni, Shuang; Liu, Gang; Xu, Xiaoxiang

    2016-01-01

    Wurtzite solid solutions between GaN and ZnO highlight an intriguing paradigm for water splitting into hydrogen and oxygen using solar energy. However, large composition discrepancy often occurs inside the compound owing to the volatile nature of Zn, thereby prescribing rigorous terms on synthetic conditions. Here we demonstrate the merits of constituting quinary Zn-Ga-Ge-N-O solid solutions by introducing Ge into the wurtzite framework. The presence of Ge not only mitigates the vaporization of Zn but also strongly promotes particle crystallization. Synthetic details for these quinary compounds were systematically explored and their photocatalytic properties were thoroughly investigated. Proper starting molar ratios of Zn/Ga/Ge are of primary importance for single phase formation, high particle crystallinity and good photocatalytic performance. Efficient photocatalytic hydrogen and oxygen production from water were achieved for these quinary solid solutions which is strongly correlated with Ge content in the structure. Apparent quantum efficiency for optimized sample approaches 1.01% for hydrogen production and 1.14% for oxygen production. Theoretical calculation reveals the critical role of Zn for the band gap reduction in these solid solutions and their superior photocatalytic acitivity can be understood by the preservation of Zn in the structure as well as a good crystallinity after introducing Ge.

  13. Wurtzite BAlN and BGaN alloys for heterointerface polarization engineering

    KAUST Repository

    Liu, Kaikai

    2017-11-30

    The spontaneous polarization (SP) and piezoelectric (PZ) constants of BxAl1-xN and BxGa1-xN (0 ≤ x ≤ 1) ternary alloys were calculated with the hexagonal structure as reference. The SP constants show moderate nonlinearity due to the volume deformation and the dipole moment difference between the hexagonal and wurtzite structures. The PZ constants exhibit significant bowing because of the large lattice difference between binary alloys. Furthermore, the PZ constants of BxAl1-xN and BxGa1-xN become zero at boron compositions of ∼87% and ∼74%, respectively, indicating non-piezoelectricity. The large range of SP and PZ constants of BxAl1-xN (BAlN) and BxGa1-xN (BGaN) can be beneficial for the compound semiconductor device development. For instance, zero heterointerface polarization ΔP can be formed for BAlN and BGaN based heterojunctions with proper B compositions, potentially eliminating the quantum-confined Stark effect for c-plane optical devices and thus removing the need of non-polar layers and substrates. Besides, large heterointerface polarization ΔP is available that is desirable for electronic devices.

  14. Photoluminescence study of as-grown vertically standing wurtzite InP nanowire ensembles.

    Science.gov (United States)

    Iqbal, Azhar; Beech, Jason P; Anttu, Nicklas; Pistol, Mats-Erik; Samuelson, Lars; Borgström, Magnus T; Yartsev, Arkady

    2013-03-22

    We demonstrate a method that enables the study of photoluminescence of as-grown nanowires on a native substrate by non-destructively suppressing the contribution of substrate photoluminescence. This is achieved by using polarized photo-excitation and photoluminescence and by making an appropriate choice of incident angle of both excitation beam and photoluminescence collection direction. Using TE-polarized excitation at a wavelength of 488 nm at an incident angle of ∼70° we suppress the InP substrate photoluminescence relative to that of the InP nanowires by about 80 times. Consequently, the photoluminescence originating from the nanowires becomes comparable to and easily distinguishable from the substrate photoluminescence. The measured photoluminescence, which peaks at photon energies of ∼1.35 eV and ∼1.49 eV, corresponds to the InP substrate with zinc-blende crystal structure and to the InP nanowires with wurtzite crystal structure, respectively. The photoluminescence quantum yield of the nanowires was found to be ∼20 times lower than that of the InP substrate. The nanowires, grown vertically in a random ensemble, neither exhibit substantial emission polarization selectivity to the axis of the nanowires nor follow excitation polarization preferences observed previously for a single nanowire.

  15. Impact of pulse duration in high power impulse magnetron sputtering on the low-temperature growth of wurtzite phase (Ti,Al)N films with high hardness

    Energy Technology Data Exchange (ETDEWEB)

    Shimizu, Tetsuhide, E-mail: simizu-tetuhide@tmu.ac.jp [Division of Human Mechatronics Systems, Graduate School of System Design, Tokyo Metropolitan University, 6-6, Asahigaoka, Hino-shi, 191-0065 Tokyo (Japan); Teranishi, Yoshikazu; Morikawa, Kazuo; Komiya, Hidetoshi; Watanabe, Tomotaro; Nagasaka, Hiroshi [Surface Finishing Technology Group, Tokyo Metropolitan Industrial Technology Research Institute, 2-4-10, Aomi, Kohtoh-ku, 135-0064 Tokyo (Japan); Yang, Ming [Division of Human Mechatronics Systems, Graduate School of System Design, Tokyo Metropolitan University, 6-6, Asahigaoka, Hino-shi, 191-0065 Tokyo (Japan)

    2015-04-30

    (Ti,Al)N films were deposited from a Ti{sub 0.33}Al{sub 0.67} alloy target with a high Al content at a substrate temperature of less than 150 °C using high power impulse magnetron sputtering (HIPIMS) plasma. The pulse duration was varied from 60 to 300 μs with a low frequency of 333 Hz to investigate the effects on the dynamic variation of the substrate temperature, microstructural grain growth and the resulting mechanical properties. The chemical composition, surface morphology and phase composition of the films were analyzed by energy dispersive spectroscopy, scanning electron microscopy and X-ray diffraction, respectively. Mechanical properties were additionally measured by using a nanoindentation tester. A shorter pulse duration resulted in a lower rate of increase in the substrate temperature with an exponentially higher peak target current. The obtained films had a high Al content of 70–73 at.% with a mixed highly (0002) textured wurtzite phase and a secondary phase of cubic (220) grains. Even with the wurtzite phase and the relatively high Al contents of more than 70 at.%, the films exhibited a high hardness of more than 30 GPa with a relatively smooth surface of less than 2 nm root-mean-square roughness. The hardest and smoothest surfaces were obtained for pulses with an intermediate duration of 150 μs. The differences between the obtained film properties under different pulse durations are discussed on the basis of the grain growth process observed by transmission electron microscopy. The feasibility of the low-temperature synthesis of AlN rich wurtzite phase (Ti,Al)N films with superior hardness by HIPIMS plasma duration was demonstrated. - Highlights: • Low temperature synthesis of AlN rich wurtzite phase (Ti,Al)N film was demonstrated. • 1 μm-thick TiAlN film was deposited under the temperature less than 150 °C by HIPIMS. • High Al content with highly (0002) textured wurtzite phase structure was obtained. • High hardness of 35 GPa were

  16. Pseudodirect to Direct Compositional Crossover in Wurtzite GaP/InxGa1–xP Core–Shell Nanowires

    KAUST Repository

    Gagliano, L.

    2016-11-29

    Thanks to their uniqueness, nanowires allow the realization of novel semiconductor crystal structures with yet unexplored properties, which can be key to overcome current technological limits. Here we develop the growth of wurtzite GaP/InGaP core-shell nanowires with tunable indium concentration and optical emission in the visible region from 590 nm (2.1 eV) to 760 nm (1.6 eV). We demonstrate a pseudodirect (δ-δ) to direct (δ-δ) transition crossover through experimental and theoretical approach. Time resolved and temperature dependent photoluminescence measurements were used, which led to the observation of a steep change in carrier lifetime and temperature dependence by respectively one and 3 orders of magnitude in the range 0.28 ± 0.04 ≤ x ≤ 0.41 ± 0.04. Our work reveals the electronic properties of wurtzite InGaP.

  17. Growth of wurtzite CdTe nanowires on fluorine-doped tin oxide glass substrates and room-temperature bandgap parameter determination

    Science.gov (United States)

    Choi, Seon Bin; Song, Man Suk; Kim, Yong

    2018-04-01

    The growth of CdTe nanowires, catalyzed by Sn, was achieved on fluorine-doped tin oxide glass by physical vapor transport. CdTe nanowires grew along the 〈0001〉 direction, with a very rare and phase-pure wurtzite structure, at 290 °C. CdTe nanowires grew under Te-limited conditions by forming SnTe nanostructures in the catalysts and the wurtzite structure was energetically favored. By polarization-dependent and power-dependent micro-photoluminescence measurements of individual nanowires, heavy and light hole-related transitions could be differentiated, and the fundamental bandgap of wurtzite CdTe at room temperature was determined to be 1.562 eV, which was 52 meV higher than that of zinc-blende CdTe. From the analysis of doublet photoluminescence spectra, the valence band splitting energy between heavy hole and light hole bands was estimated to be 43 meV.

  18. Structural and thermal analysis of a solid-cooled, low energy booster, radio-frequency-cavity tuner at the Superconducting Super Collider

    International Nuclear Information System (INIS)

    Ranganathan, R.; Propp, A.; Dao, B.; Campbell, B.

    1993-04-01

    A three-dimensional heat conduction and structural model was developed to analyze and optimize the design of a solid-cooled low energy booster (LEB) radio-frequency (RF) cavity tuner concept. Consideration was given to three cooling options: (1) using beryllium oxide (BeO) disks, (2) using aluminum nitride (A1N) disks and (3) using neither BeO nor AlN disks. The results indicate that solid cooling is feasible from thermal and structural viewpoints if a minimum of two BeO disks or four AlN disks are used

  19. Structural and thermal analysis of a solid-cooled, low energy booster, radio-frequency-cavity tuner at the Superconducting Super Collider

    Energy Technology Data Exchange (ETDEWEB)

    Ranganathan, R.; Propp, A.; Dao, B.; Campbell, B.

    1993-04-01

    A three-dimensional heat conduction and structural model was developed to analyze and optimize the design of a solid-cooled low energy booster (LEB) radio-frequency (RF) cavity tuner concept. Consideration was given to three cooling options: (1) using beryllium oxide (BeO) disks, (2) using aluminum nitride (A1N) disks and (3) using neither BeO nor AlN disks. The results indicate that solid cooling is feasible from thermal and structural viewpoints if a minimum of two BeO disks or four AlN disks are used.

  20. Thermodynamic properties of diamond and wurtzite model fluids from computer simulation and thermodynamic perturbation theory

    Science.gov (United States)

    Zhou, S.; Solana, J. R.

    2018-03-01

    Monte Carlo NVT simulations have been performed to obtain the thermodynamic and structural properties and perturbation coefficients up to third order in the inverse temperature expansion of the Helmholtz free energy of fluids with potential models proposed in the literature for diamond and wurtzite lattices. These data are used to analyze performance of a coupling parameter series expansion (CPSE). The main findings are summarized as follows, (1) The CPSE provides accurate predictions of the first three coefficient in the inverse temperature expansion of Helmholtz free energy for the potential models considered and the thermodynamic properties of these fluids are predicted more accurately when the CPSE is truncated at second or third order. (2) The Barker-Henderson (BH) recipe is appropriate for determining the effective hard sphere diameter for strongly repulsive potential cores, but its performance worsens with increasing the softness of the potential core. (3) For some thermodynamic properties the first-order CPSE works better for the diamond potential, whose tail is dominated by repulsive interactions, than for the potential, whose tail is dominated by attractive interactions. However, the first-order CPSE provides unsatisfactory results for the excess internal energy and constant-volume excess heat capacity for the two potential models.

  1. Resonance Raman spectra of wurtzite and zincblende CdSe nanocrystals

    Energy Technology Data Exchange (ETDEWEB)

    Kelley, Anne Myers, E-mail: amkelley@ucmerced.edu [Chemistry and Chemical Biology, School of Natural Sciences, University of California, 5200 North Lake Road, Merced, CA 95343 (United States); Dai, Quanqin; Jiang, Zhong-jie; Baker, Joshua A.; Kelley, David F. [Chemistry and Chemical Biology, School of Natural Sciences, University of California, 5200 North Lake Road, Merced, CA 95343 (United States)

    2013-08-30

    Highlights: ► Very similar resonance Raman spectra of wurtzite and zincblende CdSe nanocrystals. ► First absolute resonance Raman cross-sections reported for CdSe nanocrystals. ► LO overtones suggest slightly stronger electron–phonon coupling in wurtzite form. - Abstract: Resonance Raman spectra and absolute differential Raman cross-sections have been measured for CdSe nanocrystals in both the wurtzite and zincblende crystal forms at four excitation wavelengths from 457.9 to 514.5 nm. The frequency and bandshape of the longitudinal optical (LO) phonon fundamental is essentially identical for both crystal forms at each excitation wavelength. The LO phonon overtone to fundamental intensity ratio appears to be slightly higher for the wurtzite form, which may suggest slightly stronger exciton–phonon coupling from the Fröhlich mechanism in the wurtzite form. The LO fundamental Raman cross-sections are very similar for both crystal forms at each excitation wavelength.

  2. An analytical model of anisotropic low-field electron mobility in wurtzite indium nitride

    International Nuclear Information System (INIS)

    Wang, Shulong; Liu, Hongxia; Song, Xin; Guo, Yulong; Yang, Zhaonian

    2014-01-01

    This paper presents a theoretical analysis of anisotropic transport properties and develops an anisotropic low-field electron analytical mobility model for wurtzite indium nitride (InN). For the different effective masses in the Γ-A and Γ-M directions of the lowest valley, both the transient and steady state transport behaviors of wurtzite InN show different transport characteristics in the two directions. From the relationship between velocity and electric field, the difference is more obvious when the electric field is low in the two directions. To make an accurate description of the anisotropic transport properties under low field, for the first time, we present an analytical model of anisotropic low-field electron mobility in wurtzite InN. The effects of different ionized impurity scattering models on the low-field mobility calculated by Monte Carlo method (Conwell-Weisskopf and Brooks-Herring method) are also considered. (orig.)

  3. EPE analysis of sub-N10 BEoL flow with and without fully self-aligned via using Coventor SEMulator3D

    Science.gov (United States)

    Franke, Joern-Holger; Gallagher, Matt; Murdoch, Gayle; Halder, Sandip; Juncker, Aurelie; Clark, William

    2017-03-01

    During the last few decades, the semiconductor industry has been able to scale device performance up while driving costs down. What started off as simple geometrical scaling, driven mostly by advances in lithography, has recently been accompanied by advances in processing techniques and in device architectures. The trend to combine efforts using process technology and lithography is expected to intensify, as further scaling becomes ever more difficult. One promising component of future nodes are "scaling boosters", i.e. processing techniques that enable further scaling. An indispensable component in developing these ever more complex processing techniques is semiconductor process modeling software. Visualization of complex 3D structures in SEMulator3D, along with budget analysis on film thicknesses, CD and etch budgets, allow process integrators to compare flows before any physical wafers are run. Hundreds of "virtual" wafers allow comparison of different processing approaches, along with EUV or DUV patterning options for defined layers and different overlay schemes. This "virtual fabrication" technology produces massively parallel process variation studies that would be highly time-consuming or expensive in experiment. Here, we focus on one particular scaling booster, the fully self-aligned via (FSAV). We compare metal-via-metal (mevia-me) chains with self-aligned and fully-self-aligned via's using a calibrated model for imec's N7 BEoL flow. To model overall variability, 3D Monte Carlo modeling of as many variability sources as possible is critical. We use Coventor SEMulator3D to extract minimum me-me distances and contact areas and show how fully self-aligned vias allow a better me-via distance control and tighter via-me contact area variability compared with the standard self-aligned via (SAV) approach.

  4. Dependence of some characteristics of granulated wurtzite boron nitride powders on conditions of their production

    International Nuclear Information System (INIS)

    Volkogon, V.M.

    1986-01-01

    Compaction of wurtzite boron nitride powders (both pure and with plasticizers) by different methods is studied for its peculiarities. Compaction of powders in all cases is established to obey basic regularities of compaction. Such physical and technological characteristics of wurtzite boron nitride powders granulated after preliminary compaction as specific surface, bulk weight and yield point are studied. It is shown that properties of these powders depend on the method of their compaction prior to granulation. Powders produced after preliminary compaction of initial BN W powders under high static and dynamic pressures possess the best characteristics

  5. Thermal Conductivity of Wurtzite Zinc-Oxide from First-Principles Lattice Dynamics – a Comparative Study with Gallium Nitride

    Science.gov (United States)

    Wu, Xufei; Lee, Jonghoon; Varshney, Vikas; Wohlwend, Jennifer L.; Roy, Ajit K.; Luo, Tengfei

    2016-01-01

    Wurtzite Zinc-Oxide (w-ZnO) is a wide bandgap semiconductor that holds promise in power electronics applications, where heat dissipation is of critical importance. However, large discrepancies exist in the literature on the thermal conductivity of w-ZnO. In this paper, we determine the thermal conductivity of w-ZnO using first-principles lattice dynamics and compare it to that of wurtzite Gallium-Nitride (w-GaN) – another important wide bandgap semiconductor with the same crystal structure and similar atomic masses as w-ZnO. However, the thermal conductivity values show large differences (400 W/mK of w-GaN vs. 50 W/mK of w-ZnO at room temperature). It is found that the much lower thermal conductivity of ZnO originates from the smaller phonon group velocities, larger three-phonon scattering phase space and larger anharmonicity. Compared to w-GaN, w-ZnO has a smaller frequency gap in phonon dispersion, which is responsible for the stronger anharmonic phonon scattering, and the weaker interatomic bonds in w-ZnO leads to smaller phonon group velocities. The thermal conductivity of w-ZnO also shows strong size effect with nano-sized grains or structures. The results from this work help identify the cause of large discrepancies in w-ZnO thermal conductivity and will provide in-depth understanding of phonon dynamics for the design of w-ZnO-based electronics. PMID:26928396

  6. Electric field dependence of the electron mobility in bulk wurtzite ZnO

    Indian Academy of Sciences (India)

    Electric field dependence of the electron mobility in bulk wurtzite ZnO. K ALFARAMAWI ... tion to ultraviolet light emitters, gas sensors, surface acoustic wave devices and ..... Dorkel J M and Leturcq P H 1981 Solid-State Electron. 24 8211.

  7. Characterization of the nitrogen split interstitial defect in wurtzite aluminum nitride using density functional theory

    International Nuclear Information System (INIS)

    Szállás, A.; Szász, K.; Trinh, X. T.; Son, N. T.; Janzén, E.; Gali, A.

    2014-01-01

    We carried out Heyd-Scuseria-Ernzerhof hybrid density functional theory plane wave supercell calculations in wurtzite aluminum nitride in order to characterize the geometry, formation energies, transition levels, and hyperfine tensors of the nitrogen split interstitial defect. The calculated hyperfine tensors may provide useful fingerprint of this defect for electron paramagnetic resonance measurement.

  8. Characterization of the nitrogen split interstitial defect in wurtzite aluminum nitride using density functional theory

    Energy Technology Data Exchange (ETDEWEB)

    Szállás, A., E-mail: szallas.attila@wigner.mta.hu [Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, P.O. Box 49, H-1525 Budapest (Hungary); Szász, K. [Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, P.O. Box 49, H-1525 Budapest (Hungary); Institute of Physics, Eötvös University, Pázmány Péter sétány 1/A, H-1117 Budapest (Hungary); Trinh, X. T.; Son, N. T.; Janzén, E. [Department of Physics, Chemistry and Biology, Linköping University, SE-581 83 Linköping (Sweden); Gali, A., E-mail: gali.adam@wigner.mta.hu [Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, P.O. Box 49, H-1525 Budapest (Hungary); Department of Atomic Physics, Budapest University of Technology and Economics, Budafoki út 8, H-1111 Budapest (Hungary)

    2014-09-21

    We carried out Heyd-Scuseria-Ernzerhof hybrid density functional theory plane wave supercell calculations in wurtzite aluminum nitride in order to characterize the geometry, formation energies, transition levels, and hyperfine tensors of the nitrogen split interstitial defect. The calculated hyperfine tensors may provide useful fingerprint of this defect for electron paramagnetic resonance measurement.

  9. Mechanical, thermodynamic and electronic properties of wurtzite and zinc-blende GaN crystals

    NARCIS (Netherlands)

    Qin, Hongbo; Luan, Xinghe; Feng, Chuang; Yang, Daoguo; Zhang, G.Q.

    2017-01-01

    For the limitation of experimental methods in crystal characterization, in this study, the mechanical, thermodynamic and electronic properties of wurtzite and zinc-blende GaN crystals were investigated by first-principles calculations based on density functional theory. Firstly, bulk moduli,

  10. Reaction Cross Section Calculations in Neutron Induced Reactions and GEANT4 Simulation of Hadronic Interactions for the Reactor Moderator Material BeO

    Directory of Open Access Journals (Sweden)

    Veli ÇAPALI

    2016-05-01

    Full Text Available BeO is one of the most common moderator material for neutron moderation; due to its high density, neutron capture cross section and physical-chemical properties that provides usage at elevated temperatures. As it’s known, for various applications in the field of reactor design and neutron capture, reaction cross–section data are required. The cross–sections of (n,α, (n,2n, (n,t, (n,EL and (n,TOT reactions for 9Be and 16O nuclei have been calculated by using TALYS 1.6 Two Component Exciton model and EMPIRE 3.2 Exciton model in this study. Hadronic interactions of low energetic neutrons and generated isotopes–particles have been investigated for a situation in which BeO was used as a neutron moderator by using GEANT4, which is a powerful simulation software. In addition, energy deposition along BeO material has been obtained. Results from performed calculations were compared with the experimental nuclear reaction data exist in EXFOR.

  11. Characteristics of poly- and mono-crystalline BeO and SiO2 as thermal and cold neutron filters

    Science.gov (United States)

    Adib, M.; Habib, N.; Bashter, I. I.; Morcos, H. N.; El-Mesiry, M. S.; Mansy, M. S.

    2015-09-01

    A simple model along with a computer code "HEXA-FILTERS" is used to carry out the calculation of the total cross-sections of BeO and SiO2 having poly or mono-crystalline form as a function of neutron wavelength at room (R.T.) and liquid nitrogen (L.N.) temperatures. An overall agreement is indicated between the calculated neutron cross-sections and experimental data. Calculation shows that 25 cm thick of polycrystalline BeO cooled at liquid nitrogen temperature was found to be a good filter for neutron wavelengths longer than 0.46 nm. While, 50 cm of SiO2, with much less transmission, for neutrons with wavelengths longer than 0.85 nm. It was also found that 10 cm of BeO and 15 cm SiO2 thick mono-crystals cut along their (0 0 2) plane, with 0.5° FWHM on mosaic spread and cooled at L.N., are a good thermal neutron filter, with high effect-to-noise ratio.

  12. In vitro responses of canine alveolar lymphocytes to BeSO4 after inhalation exposure to BeO: comparisons with human chronic berylliosis

    International Nuclear Information System (INIS)

    Haley, P.J.; Finch, G.L.; Mewhinney, J.A.; Hahn, F.F.; Hoover, M.D.; Bice, D.E.

    1988-01-01

    Alveolar lymphocytes obtained by broncho-alveolar lavage (BAL) and peripheral blood lymphocytes from 20 dogs exposed once by inhalation to achieve low or high initial lung burdens (ILB) of beryllium oxide (BeO) calcined at one of two different temperatures, 500 deg. C or 1000 deg. C, were cultured in vitro with BeSO 4 . Positive BAL lymphocyte responses were observed at 6 and 7 mo after exposure, with peak responses occurring at 7 mo followed by a rapid decline. Peak BAL SI values ranged from a high of 64 at 6 mo to a low of 6 at 7 mo. Positive blood SI were observed at 7, 15, 18, and 22 mo after exposure in some, but not all, dogs with high or low ILBs of 500 deg. C or 1000 deg. C BeO. Lymphocytes from lung and blood of control dogs did not respond in vitro to BeSO 4 . These data indicate that a single exposure of dogs to an aerosol of BeO can result in beryllium-specific immune responses by alveolar lymphocytes. (author)

  13. Composition Dependence of Surface Phonon Polariton Mode in Wurtzite InxGa1−xN (0 ≤ x ≤ 1) Ternary Alloy

    International Nuclear Information System (INIS)

    Ng, S. S.; Hassan, Z.; Hassan, H. Abu

    2008-01-01

    We present a theoretical study on the composition dependence of the surface phonon polariton (SPP) mode in wurtzite structure α-In x Ga 1-x N ternary alloy over the whole composition range. The SPP modes are obtained by the theoretical simulations by means of an anisotropy model. The results reveal that the SPP mode of α-In x Ga 1-x N semiconductors exhibits one-mode behaviour. From these data, composition dependence of the SPP mode with bowing parameter of −28.9 cm −1 is theoretically obtained

  14. Wurtzite gallium phosphide has a direct-band gap

    NARCIS (Netherlands)

    Assali, S.; Zardo, I.; Plissard, S.; Verheijen, M.A.; Haverkort, J.E.M.; Bakkers, E.P.A.M.

    2013-01-01

    Gallium Phosphide (GaP) with the normal cubic crystal structure has an indirect band gap, which severely limits the emission efficiency. We report the fabrication of GaP nanowires with pure hexagonal crystal structure and demonstrate the direct nature of the band gap. We observe strong

  15. [BEO'S - physical activity and healthy eating at schools in Oberfranken, Bavaria concept and first results of a resource-oriented, systemic approach in school-based health promotion].

    Science.gov (United States)

    Eichhorn, C; Bodner, L; Liebl, S; Scholz, U; Wozniak, D; Möstl, M; Ungerer-Röhrich, U; Nagel, E; Loss, J

    2012-02-01

    The high prevalence of overweight among children and adolescents has led to an increase in school-based prevention programmes. The aim of the present paper is to present the concept of an initiative called "BEO'S" as well as the experience made with the implementation und acceptance of this programme in the participating schools. Different from the majority of school-based projects for healthy eating and physical activity, BEO'S pursues a systemic approach that includes the whole school and is tailored to the school's respective resources. Characteristics are (1) the participation of teachers, students, parents, and caretakers, (2) the motivation and empowerment of schools to plan and implement activities by themselves, (3) the focus on environmental approaches, and (4) addressing and considering the individual school's needs and resources. The university project team supports the schools by individual counselling as well as providing information materials, trainings and workshops for teachers, an internet page, newsletters, and financial support. In the school years 2007/08 and 2008/09, BEO'S was conducted at 14 primary and secondary schools in the district of Oberfranken, Bavaria. It was extended to other schools in 2009/10. The short- and mid-term goals are the improvement of the school's environments as well as the eating behaviour and physical activity of the students. In the long run, it is intended to prevent obesity and improve the students' health and school performance. The implementation processes showed that the teachers for physical education and domestic science as well as the headmasters were especially committed. The participation of the teaching staff, the students and the parents proved to be difficult, however. The schools implemented many activities for healthy eating and physical activity, but the planning process was not very systematic: needs assessment, status quo analysis, identification of successful strategies and definition of aims was

  16. Investigation of intrinsic defect magnetic properties in wurtzite ZnO materials

    Science.gov (United States)

    Fedorov, A. S.; Visotin, M. A.; Kholtobina, A. S.; Kuzubov, A. A.; Mikhaleva, N. S.; Hsu, Hua Shu

    2017-10-01

    Theoretical and experimental investigations of the ferromagnetism induced by intrinsic defects inside wurtzite zinc oxide structures are performed using magnetic field-dependent circular dichroism (MCD-H), direct magnetization measurement (M-H) by superconducting quantum interference device (SQUID) as well as by generalized gradient density functional theory (GGA-DFT). To investigate localized magnetic moments of bulk material intrinsic defects - vacancies, interstitial atoms and Frenkel defects, various-size periodic supercells are calculated. It is shown that oxygen interstitial atoms (Oi) or zinc vacancies (Znv) generate magnetic moments of 1,98 и 1,26 μB respectively, however, the magnitudes are significantly reduced when the distance between defects increases. At the same time, the magnetic moments of oxygen Frenkel defects are large ( 1.5-1.8 μB) and do not depend on the distance between the defects. It is shown that the origin of the induced ferromagnetism in bulk ZnO is the extra spin density on the oxygen atoms nearest to the defect. Also dependence of the magnetization of ZnO (10 1 ̅ 0) and (0001) thin films on the positions of Oi and Znv in subsurface layers were investigated and it is shown that the magnetic moments of both defects are significantly different from the values inside bulk material. In order to check theoretical results regarding the defect induced ferromagnetism in ZnO, two thin films doped by carbon (C) and having Zn interstitials and oxygen vacancies were prepared and annealed in vacuum and air, respectively. According to the MCD-H and M-H measurements, the film, which was annealed in air, exhibits a ferromagnetic behavior, while the other does not. One can assume annealing of ZnO in vacuum should create oxygen vacancies or Zn interstitial atoms. At that annealing of the second C:ZnO film in air leads to essential magnetization, probably by annihilation of oxygen vacancies, formation of interstitial oxygen atoms or zinc vacancies

  17. A versatile light-switchable nanorod memory: Wurtzite ZnO on perovskite SrTiO3

    KAUST Repository

    Kumar, Anup Bera

    2013-04-25

    Integrating materials with distinct lattice symmetries and dimensions is an effective design strategy toward realizing novel devices with unprecedented functionalities, but many challenges remain in synthesis and device design. Here, a heterojunction memory made of wurtzite ZnO nanorods grown on perovskite Nb-doped SrTiO3 (NSTO) is reported, the electronic properties of which can be drastically reconfigured by applying a voltage and light. Despite of the distinct lattice structures of ZnO and NSTO, a consistent nature of single crystallinity is achieved in the heterojunctions via the low-temperature solution-based hydrothermal growth. In addition to a high and persistent photoconductivity, the ZnO/NSTO heterojunction diode can be turned into a versatile light-switchable resistive switching memory with highly tunable ON and OFF states. The reversible modification of the effective interfacial energy barrier in the concurrent electronic and ionic processes most likely gives rise to the high susceptibility of the ZnO/NSTO heterojunction to external electric and optical stimuli. Furthermore, this facile synthesis route is promising to be generalized to other novel functional nanodevices integrating materials with diverse structures and properties. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Increase of thermal conductivity of uranium dioxide nuclear fuel pellets with beryllium oxide addition; Condutividade termica de pastilhas de combustivel nuclear de UO{sub 2}-BeO nas temperaturas de 25 deg C e 100 deg C

    Energy Technology Data Exchange (ETDEWEB)

    Camarano, D.M.; Mansur, F.A.; Santos, A.M.M. dos; Ferraz, W.B., E-mail: dmc@cdtn.br [Centro de Desenvolvimento da Tecnologia Nuclear (CDTM/CNEN-MG), Belo Horizonte, MG (Brazil)

    2016-07-01

    The UO{sub 2} fuel is one of the most used nuclear fuel in thermal reactors and has many advantages such as high melting point, chemical compatibility with cladding, etc. However, its thermal conductivity is relatively low, which leads to a premature degradation of the fuel pellets due to a high radial temperature gradient during reactor operation. An alternative to avoid this problem is to increase the thermal conductivity of the fuel pellets, by adding beryllium oxide (BeO). Pellets of UO{sub 2} and UO{sub 2}-BeO were obtained from a homogenized mixture of powders of UO{sub 2} and BeO, containing 2% and 3% by weight of BeO and sintering at 1750 °C for 3 h under H{sub 2} atmosphere after uniaxial pressing at 400 MPa. The pellet densities were obtained by xylol penetration-immersion method and the thermal diffusivity, specific heat and thermal conductivity were determined according to ASTM E-1461 at room temperature (25 deg C) and 100 deg C. The thermal diffusivity measurements were carried out employing the laser flash method. The thermal conductivity obtained at 25 deg C showed an increase with the addition of 2% and 3% of BeO corresponding to 19% and 28%, respectively. As for the measurements carried out at 100 deg C, there was an increase in the thermal conductivity for the same BeO contents of 20% and 31%. These values as a percentage of increased conductivity were obtained in relation to the UO{sub 2} pellets. (author)

  19. Piezoelectric Field Enhanced Second-Order Nonlinear Optical Susceptibilities in Wurtzite GaN/AlGaN Quantum Wells

    Science.gov (United States)

    Liu, Ansheng; Chuang, S.-L.; Ning, C. Z.; Woo, Alex (Technical Monitor)

    1999-01-01

    Second-order nonlinear optical processes including second-harmonic generation, optical rectification, and difference-frequency generation associated with intersubband transitions in wurtzite GaN/AlGaN quantum well (QW) are investigated theoretically. Taking into account the strain-induced piezoelectric (PZ) effects, we solve the electronic structure of the QW from coupled effective-mass Schrodinger equation and Poisson equation including the exchange-correlation effect under the local-density approximation. We show that the large PZ field in the QW breaks the symmetry of the confinement potential profile and leads to large second-order susceptibilities. We also show that the interband optical pump-induced electron-hole plasma results in an enhancement in the maximum value of the nonlinear coefficients and a redshift of the peak position in the nonlinear optical spectrum. By use of the difference-frequency generation, THz radiation can be generated from a GaN/Al(0.75)Ga(0.25)N with a pump laser of 1.55 micron.

  20. Minor component ordering in wurtzite Ga1-xInxN and Ga1-xAlxN

    International Nuclear Information System (INIS)

    Laaksonen, K.; Ganchenkova, M.G.; Nieminen, R.M.

    2006-01-01

    The electronic and thermodynamic properties of materials are defined largely by their internal structure, in particular, composition uniformity. In this work the homogeneity of the minor component distribution in ternary Ga(In/Al)N alloys in the wurtzite polytype is studied. For this aim, the stability of different configurations of small clusters of the second component atoms is examined using Daft-based code Vas. The hydrostatic strain, induced in the matrix by the component atomic size mismatch, as well as external hydrostatic strain are taken under consideration. Clustering of In atoms along the [0001] direction is shown to be energetically favourable, whereas in the (0001) plane they repel each other. In contrast, Al atoms in GaN do not interact, irrespective of strain conditions. According to these results In in GaN should form [0001] aligned pairs or chains and, at higher In concentrations, zigzag chains in the c-direction, while Al forms a random alloy with the matrix material. The effect of the minor component (In/Al) ordering pattern on the band gap of the ternary Ga(In/Al)N alloy is also discussed

  1. Band gaps of wurtzite Sc{sub x}Ga{sub 1−x}N alloys

    Energy Technology Data Exchange (ETDEWEB)

    Tsui, H. C. L.; Moram, M. A. [Department of Materials, Imperial College London, Exhibition Road, London SW7 2AZ (United Kingdom); Goff, L. E. [Department of Materials, Imperial College London, Exhibition Road, London SW7 2AZ (United Kingdom); Department of Physics, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE (United Kingdom); Rhode, S. K. [Department of Materials Science and Metallurgy, University of Cambridge, Charles Babbage Road, Cambridge CB3 0FS (United Kingdom); Pereira, S. [CICECO and Dept. Physics, Universidade de Aveiro, 3810-193 Aveiro (Portugal); Beere, H. E.; Farrer, I.; Nicoll, C. A.; Ritchie, D. A. [Department of Physics, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE (United Kingdom)

    2015-03-30

    Optical transmittance measurements on epitaxial, phase-pure, wurtzite-structure Sc{sub x}Ga{sub 1−x}N films with 0 ≤ x ≤ 0.26 showed that their direct optical band gaps increased from 3.33 eV to 3.89 eV with increasing x, in agreement with theory. These films contained I{sub 1}- and I{sub 2}-type stacking faults. However, the direct optical band gaps decreased from 3.37 eV to 3.26 eV for Sc{sub x}Ga{sub 1−x}N films, which additionally contained nanoscale lamellar inclusions of the zinc-blende phase, as revealed by aberration-corrected scanning transmission electron microscopy. Therefore, we conclude that the apparent reduction in Sc{sub x}Ga{sub 1−x}N band gaps with increasing x is an artefact resulting from the presence of nanoscale zinc-blende inclusions.

  2. Ab initio study of the stability and electronic properties of wurtzite and zinc-blende BeS nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Faraji, Somayeh [Simulation Laboratory, Department of Physics, Faculty of Science, Shahrekord University, Shahrekord (Iran, Islamic Republic of); Mokhtari, Ali, E-mail: mokhtari@sci.sku.ac.i [Simulation Laboratory, Department of Physics, Faculty of Science, Shahrekord University, Shahrekord (Iran, Islamic Republic of); Nanotechnology Research Center, Shahrekord University, Shahrekord (Iran, Islamic Republic of)

    2010-07-19

    In this work we study the structural stability and electronic properties of the Beryllium sulfide nanowires (NWs) in zinc-blende (ZB) and wurtzite (WZ) phases (with triangle and hexagonal cross sections), using first principle calculations within the plane-wave pseudopotential method. A phenomenological model is used to explain the role of dangling bonds in the stability of the NWs. In contrast to the bulk phase, the ZB-NWs with diameters less than 133.3 A are found to be less favorable over the WZ-NWs, in which the surface dangling bonds (DBs) on the NW facets play an important role to stabilize the NWs. Furthermore, both ZB- and WZ-NWs are predicted to be semiconductor and the values of the band gaps are dependent on the surface DBs as well as the size and shape of the NWs. Finally, we obtain atom projected density of states (PDOSs) by calculating the localized density of states on the surface atoms, as well as on the core and edge atoms.

  3. Ab initio study of the stability and electronic properties of wurtzite and zinc-blende BeS nanowires

    International Nuclear Information System (INIS)

    Faraji, Somayeh; Mokhtari, Ali

    2010-01-01

    In this work we study the structural stability and electronic properties of the Beryllium sulfide nanowires (NWs) in zinc-blende (ZB) and wurtzite (WZ) phases (with triangle and hexagonal cross sections), using first principle calculations within the plane-wave pseudopotential method. A phenomenological model is used to explain the role of dangling bonds in the stability of the NWs. In contrast to the bulk phase, the ZB-NWs with diameters less than 133.3 A are found to be less favorable over the WZ-NWs, in which the surface dangling bonds (DBs) on the NW facets play an important role to stabilize the NWs. Furthermore, both ZB- and WZ-NWs are predicted to be semiconductor and the values of the band gaps are dependent on the surface DBs as well as the size and shape of the NWs. Finally, we obtain atom projected density of states (PDOSs) by calculating the localized density of states on the surface atoms, as well as on the core and edge atoms.

  4. Dynamical properties and their strain-dependence of ZnSe(ZnSe:N: Zinc-blende and wurtzite

    Directory of Open Access Journals (Sweden)

    Dandan Wang

    2014-06-01

    Full Text Available The lattice dynamical properties of ZnSe and ZnSe with substitutional N incorporation(ZnSe:N are investigated in both the zinc-blend(ZB and wurtzite(WZ structures using first-principles calculations. The optical phonon modes of ZB-ZnSe at the Γ-point locate at 250 cm−1 for LO and 213 cm−1 for TO. The characteristic E2 phonon modes at about 50 cm−1 and the E1 and another E2 phonon modes around 200 cm−1 of WZ-ZnSe are suggested to be the fingerprint for distinguishing the two polytypes of ZnSe. For substitutional N incorporated ZnSe, the N incorporation introduces three new high energy modes above 500 cm−1, and the splitting of them is much larger in the WZ phase than that in ZB phase. The strain dependence of phonon frequency which could be useful for corresponding spectroscopic strain characterization are also studied. The simple linear dependence is determined for ZB-ZnSe, while the situation for WZ-ZnSe looks more complicated.

  5. Low temperature synthesis, photoluminescence, magnetic properties of the transition metal doped wurtzite ZnS nanowires

    International Nuclear Information System (INIS)

    Cao, Jian; Han, Donglai; Wang, Bingji; Fan, Lin; Fu, Hao; Wei, Maobin; Feng, Bo; Liu, Xiaoyan; Yang, Jinghai

    2013-01-01

    In this paper, we synthesized the transition metal ions (Mn, Cu, Fe) doped and co-doped ZnS nanowires (NWs) by a one-step hydrothermal method. The results showed that the solid solubility of the Fe 2+ ions in the ZnS NWs was about two times larger than that of the Mn 2+ or Cu 2+ ions in the ZnS NWs. There was no phase transformation from hexagonal to cubic even in a large quantity transition metal ions introduced for all the samples. The Mn 2+ /Cu 2+ /Fe 2+ related emission peaks can be observed in the Mn 2+ ,Cu 2+ and Fe 2+ doped ZnS NWs. The ferromagnetic properties of the co-doped samples were investigated at room temperature. - graphical abstract: The stable wurtzite ZnS:TM 2+ (TM=Mn, Cu, Fe) nanowires with room temperature ferromagnetism properties were obtained. The different elongation of unit cell caused by the different doped ions was observed. Highlights: ► The transition metal ions doped wurtzite ZnS nanowires were synthesized at 180 °C. ► There was no phase transformation from hexagonal to cubic even in a large quantity introduced for all the samples. ► The room temperature ferromagnetism properties of the co-doped nanowires were investigated

  6. Nonlinear elasticity in wurtzite GaN/AlN planar superlattices and quantum dots

    International Nuclear Information System (INIS)

    Lepkowski, S.P.; Majewski, J.A.; Jurczak, G.

    2005-01-01

    The elastic stiffness tensor for wurtzite GaN and AlN show a significant hydrostatic pressure dependence, which id the evidence of nonlinear elasticity of these compounds. We have examined how the pressure dependence of elastic constants for wurtzite nitrides influences elastic and piezoelectric properties of GaN/AlN planar superlattices and quantum dots. Particularly we show that built-in hydrostatic pressure, present in both quantum wells of the GaN/AlN superlattices and GaN/AlN quantum dots, increases significantly by 0.3-0.7 GPa when nonlinear elasticity is used. Consequently, the compressive volumetric strain in quantum wells and quantum dots decreases in comparison to the case of the linear elastic theory, However, the-component of the built-in electric field in the quantum wells and quantum dots increases considerably when nonlinear elasticity is taken into account. Both effects, i.e., a decrease in the compressive volumetric strain as well as an increase in the built-in electric field, decrease the band-to-band transition energies in the quantum wells and quantum dots. (author)

  7. Optical characterization of InAs quantum wells and dots grown radially on wurtzite InP nanowires

    International Nuclear Information System (INIS)

    Lindgren, David; Kawaguchi, Kenichi; Heurlin, Magnus; Borgström, Magnus T; Pistol, Mats-Erik; Samuelson, Lars; Gustafsson, Anders

    2013-01-01

    Correlated micro-photoluminescence (μPL) and cathodoluminescence (CL) measurements are reported for single core–shell InP–InAs wurtzite nanowires grown using metal–organic vapor phase epitaxy. Samples covering a radial InAs shell thickness of 1–12 ML were investigated. The effective masses for the wurtzite material were determined from the transition energy dependence of the InAs shell thickness, using a model based on linear deformation potential theory. InP cores with segments of mixed zincblende and wurtzite, on which quantum dots nucleated selectively, were also investigated. Narrow peaks were observed by μPL and the spatial origin of the emission was identified with CL imaging. (paper)

  8. Wurtzite InP/InAs/InP core-shell nanowires emitting at telecommunication wavelengths on Si substrate

    International Nuclear Information System (INIS)

    Hadj Alouane, M H; Anufriev, R; Chauvin, N; Bru-Chevallier, C; Khmissi, H; Ilahi, B; Maaref, H; Naji, K; Gendry, M; Patriarche, G

    2011-01-01

    Optical properties of wurtzite InP/InAs/InP core-shell nanowires grown on silicon substrates by solid source molecular beam epitaxy are studied by means of photoluminescence and microphotoluminescence. The growth conditions were optimized to obtain purely wurtzite radial quantum wells emitting in the telecom bands with a radiative lifetime in the 5-7 ns range at 14 K. Optical studies on single nanowires reveal that the polarization is mainly parallel to the growth direction. A 20-fold reduction of the photoluminescence intensity is observed between 14 and 300 K confirming the very good quality of the nanowires.

  9. MCSCF wave functions for excited states of polar molecules - Application to BeO. [Multi-Configuration Self-Consistent Field

    Science.gov (United States)

    Bauschlicher, C. W., Jr.; Yarkony, D. R.

    1980-01-01

    A previously reported multi-configuration self-consistent field (MCSCF) algorithm based on the generalized Brillouin theorem is extended in order to treat the excited states of polar molecules. In particular, the algorithm takes into account the proper treatment of nonorthogonality in the space of single excitations and invokes, when necessary, a constrained optimization procedure to prevent the variational collapse of excited states. In addition, a configuration selection scheme (suitable for use in conjunction with extended configuration interaction methods) is proposed for the MCSCF procedure. The algorithm is used to study the low-lying singlet states of BeO, a system which has not previously been studied using an MCSCF procedure. MCSCF wave functions are obtained for three 1 Sigma + and two 1 Pi states. The 1 Sigma + results are juxtaposed with comparable results for MgO in order to assess the generality of the description presented here.

  10. Molecular dynamics simulation of ZnO wurtzite phase under high and low pressures and temperatures

    Science.gov (United States)

    Chergui, Y.; Aouaroun, T.; Hadley, M. J.; Belkada, R.; Chemam, R.; Mekki, D. E.

    2017-11-01

    Isothermal and isobaric ensembles behaviours of ZnO wurtzite phase have been investigated, by parallel molecular dynamics method and using Buckingham potential, which contains long-range Coulomb, repulsive exponential, and attractive dispersion terms. To conduct our calculations, we have used dl_poly 4 software, under which the method is implemented. We have examined the influence of the temperature and pressure on molar volume in the ranges of 300-3000 K and 0-200 GPa. Isothermal-isobaric relationships, fluctuations, standard error, equilibrium time, molar volume and its variation versus time are predicted and analyzed. Our results are close to available experimental data and theoretical results.

  11. Adsorption configuration of magnesium on wurtzite gallium nitride surface using first-principles calculations

    International Nuclear Information System (INIS)

    Yan Han; Gan Zhiyin; Song Xiaohui; Chen Zhaohui; Xu Jingping; Liu Sheng

    2009-01-01

    First-principles calculations of magnesium adsorption at the Ga-terminated and N-terminated {0 0 0 1} basal plane wurtzite gallium nitride surfaces have been carried out to explain the atomic-scale insight into the initial adsorption processes of magnesium doping in gallium nitride. The results reveal that magnesium adsorption on N-terminated surfaces is preferred than that on Ga-terminated surfaces. Furthermore, the surface diffusivity of magnesium atom on the N-terminated surface is much lower than that on the Ga-terminated surface, which is due to both the larger average adsorption energies and the lower adsorption distance on N-terminated surface than that on Ga-terminated surface. The results indicate that the p-type doping on the Ga-terminated surface will be better distributed than that on the N-terminated surface.

  12. Critical Temperature for the Conversion from Wurtzite to Zincblende of the Optical Emission of InAs Nanowires

    KAUST Repository

    Rota, Michele B.; Ameruddin, Amira S.; Wong-Leung, Jennifer; Belabbes, Abderrezak; Gao, Qiang; Miriametro, Antonio; Mura, Francesco; Tan, Hark Hoe; Polimeni, Antonio; Bechstedt, Friedhelm; Jagadish, Chennupati; Capizzi, Mario

    2017-01-01

    One hour annealing at 300 degrees C changes the optical emission characteristics of InAs nanowires (NWs) from the wurtzite (WZ) phase into that of zincblende (ZB). These results are accounted for by the conversion of a small fraction of the NW WZ

  13. Electronic properties of wurtzite-phase InP nanowires determined by optical and magneto-optical spectroscopy

    Science.gov (United States)

    De Luca, Marta; Polimeni, Antonio

    2017-12-01

    Thanks to their peculiar shape and dimensions, semiconductor nanowires (NWs) are emerging as building components of novel devices. The presence of wurtzite (WZ) phase in the lattice structure of non-nitride III-V NWs is one of the most surprising findings in these nanostructures: this phase, indeed, cannot be found in the same materials in the bulk form, where the zincblende (ZB) structure is ubiquitous, and therefore the WZ properties are poorly known. This review focuses on WZ InP NWs, because growth techniques have reached a high degree of control on the structural properties of this material, and optical studies performed on high-quality samples have allowed determining the most useful electronic properties, which are reviewed here. After an introduction summarizing the reasons for the interest in WZ InP nanowires (Sec. I), we give an overview on growth process and structural and optical properties of WZ InP NWs (Sec. II). In Sec. III, a complete picture of the energy and symmetry of the lowest-energy conduction and valence bands, as assessed by polarization-resolved photoluminescence (PL) and photoluminescence-excitation (PLE) studies is drawn and compared to all the available theoretical information. The elastic properties of WZ InP (determined by PL under hydrostatic pressure) and the radiative recombination dynamics of spatially direct and indirect (namely, occurring across the WZ/ZB interfaces) transitions are also discussed. Section IV, focuses on the magneto-optical studies of WZ InP NWs. The diagram of the energy levels of excitons in WZ materials—with and without magnetic field—is first provided. Then, all theoretical and experimental information available about the changes in the transport properties (i.e., carrier effective mass) caused by the ZB→WZ phase variation are reviewed. Different NW/magnetic field geometrical configurations, sensitive to polarization selection rules, highlight anisotropies in the diamagnetic shifts, Zeeman splitting

  14. Electronic structure and photocatalytic activity of wurtzite Cu–Ga–S nanocrystals and their Zn substitution

    KAUST Repository

    Kandiel, Tarek; Anjum, Dalaver H.; Sautet, Philippe; Le Bahers, Tangui; Takanabe, Kazuhiro

    2015-01-01

    by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS), photoluminescence (PL), and inductively coupled plasma atomic emission spectroscopy (ICP-OES). Electronic

  15. Neutron Spectra in H{sub 2}O, D{sub 2}O, BeO and CH{sub 2}; Spectres de Neutrons dans H{sub 2}O, D{sub 2}O, BeO et CH{sub 2}; Spektry nejtronov v H{sub 2}O, D{sub 2}O, BeO i CH{sub 2}; Espectros Neutronicos en H{sub 2}O, D{sub 2}O, BeO y CH{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Neill, J. M.; Young, J. C.; Trimble, G. D.; Beyster, J. R. [General Atomic Division of General Dynamics Corporation, John Jay Hopkins Laboratory for Pure and Applied Science, San Diego, CA (United States)

    1965-08-15

    Thermal neutron spectral measurements in moderators of interest to reactor technology are being made at General Atomic. The purpose of these measurements is to provide an integral check of the adequacy of proposed scattering models for these moderators. At present the scattering kernels are obtained by measuring the double differential scattering cross-sections directly, or by inferring them from a study of the vibrational and rotational motions of the molecules in a liquid or the lattice vibrational spectrum in a solid. The direct measurement has suffered from some experimental difficulties, such as obtaining the desired intensity and resolution and making the proper corrections for multiple scattering in the sample. From the standpoint of the application to reactor technology, the latter procedure for obtaining the scattering kernel has been more satisfactory in many instances. The integral measurements that have been made, coupled to comparative calculations of the neutron spectra, allow comment to be made on the status of the theoretical scattering models for H{sub 2}O, D{sub 2}O and BeO. In this paper, angular- and position-dependent spectra measured in H{sub 2}O and D{sub 2}O poisoned with boron or cadmium are presented and show improved agreement with the theoretical values. It appears that the Nelkin model for H{sub 2}O provides a reasonable first description for the scattering by that moderator. It also appears that the Honeck model for D{sub 2}O, an extension of the incoherent model for H{sub 2}O of Nelkin, is also an adequate description for some applications. This is surprising since deuterium, unlike hydrogen, is mostly a coherent scatterer; however it supports recent studies by Koppel which showed that the intramolecular and intermolecular interference scattering terms in D{sub 2}O tend to cancel. Measured angularly-dependent neutron spectra in BeO poisoned with borated stainless steel are also presented. In general the agreement of measurement with

  16. On the martensite character of the transformation of the wurtzite modification of BN into a graphite-like one

    International Nuclear Information System (INIS)

    Kurdyumov, A.V.; Ostrovskaya, N.F.; Pilyankevich, A.N.

    1977-01-01

    A comparative analysis of regularities in the transformation of the wurtzite BNsub(w) and sphalerite BNsub(sp) modifications of boron nitride was carried out, which confirmed the assumption about the martensitic nature of the transformation of wurtzite BNsub(w) to graphite-like BNsub(g). New experimental data were considered, which served as a basis for a proposed atomic mechamism of lattice rearrangement in the course of the BNsub(w) → BNsub(g) martensitic transformation. The investigation was carried out on particles of the BNsub(w) powder obtained by impact compression, with an average size of monocrystal grains apptoximately 1. The BNsub(w) → BNsub(g) transformation was achieved by means of an electron beam. It is shown that electron irradiation causes grain cracking

  17. Pressure-Dependent Photoluminescence Study of Wurtzite InP Nanowires.

    Science.gov (United States)

    Chauvin, Nicolas; Mavel, Amaury; Patriarche, Gilles; Masenelli, Bruno; Gendry, Michel; Machon, Denis

    2016-05-11

    The elastic properties of InP nanowires are investigated by photoluminescence measurements under hydrostatic pressure at room temperature and experimentally deduced values of the linear pressure coefficients are obtained. The pressure-induced energy shift of the A and B transitions yields a linear pressure coefficient of αA = 88.2 ± 0.5 meV/GPa and αB = 89.3 ± 0.5 meV/GPa with a small sublinear term of βA = βB = -2.7 ± 0.2 meV/GPa(2). Effective hydrostatic deformation potentials of -6.12 ± 0.04 and -6.2 ± 0.04 eV are derived from the results for the A and B transitions, respectively. A decrease of the integrated intensity is observed above 0.5 GPa and is interpreted as a carrier transfer from the first to the second conduction band of the wurtzite InP.

  18. Transport and mobility properties of wurtzite InN and GaN

    International Nuclear Information System (INIS)

    Yarar, Zeki

    2007-01-01

    The results of an ensemble Monte Carlo model of the electron transport in wurtzite gallium nitride (GaN) and indium nitride (InN) are presented. There is a controversy over the material parameters of InN, therefore the recently reported and the traditionally accepted parameter values for InN are used in simulations and the results are compared. The steady-state and transient electron transport characteristics are analyzed and the valley populations of electrons are determined as a function of electric field. The low-field mobility of electrons is also obtained as a function of temperature and over a wide range of carrier concentrations. It is seen that with the recently published material parameters the peak velocity of carriers in InN increases significantly, while the field at which it is attained decreases. The calculated maximum low field mobility at 300 K in InN with the recent material parameters is about 10000 cm 2 /V s for low carrier concentrations. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  19. First-principles study of size-, surface- and mechanical strain-dependent electronic properties of wurtzite and zinc-blende InSb nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Yong [School of Mathematics, Physics and Energy Engineering, Hunan Institute of Technology, Hengyang 421002 (China); Xie, Zhong-Xiang, E-mail: xiezxhu@163.com [School of Mathematics, Physics and Energy Engineering, Hunan Institute of Technology, Hengyang 421002 (China); Yu, Xia; Wang, Hai-Bin; Deng, Yuan-Xiang [School of Mathematics, Physics and Energy Engineering, Hunan Institute of Technology, Hengyang 421002 (China); Ning, Feng, E-mail: fning@gxtc.edu.cn [College of Physics and Electronic Engineering, Guangxi Teachers Education University, Nanning 530001 (China)

    2016-08-06

    Using first-principle calculations with density functional theory, we investigated the modification of electronic properties in zinc-blende (ZB) and wurtzite (WZ) InSb nanowires (NWs) grown along the [111] and [0001] directions for different size, different surface coverage and different mechanical strain. The results show that before the surface passivation, ZBNWs and WZNWs exhibit the metallic character and the semiconductor character, respectively. WZNWs show a crossover from a direct to an indirect as diameter decreases. After the surface passivation, both ZBNWs and WZNWs are found to be direct-gap character. The electronic band structure shows a significant response to changes in surface passivation with pseudo hydrogen and halogen. The band structure with mechanical strain is strongly dependent on the crystal orientation and the NW diameter. In ZBNWs, compressive strain induces the indirect band gap character, whereas tensile strain can not form it. WZNWs have various strain dependence in that both compressive and tensile strain make InSb show a direct band gap character. A brief analysis of these results is given. - Highlights: • InSb nanowires with different surfaces can show the different band structures. • Band gap magnitude of InSb nanowires depends on the suppression of surface states. • Different types of mechanical strains show the different effect on the band structure of the InSb nanowires.

  20. Temperature Dependence of Interband Transitions in Wurtzite InP Nanowires.

    Science.gov (United States)

    Zilli, Attilio; De Luca, Marta; Tedeschi, Davide; Fonseka, H Aruni; Miriametro, Antonio; Tan, Hark Hoe; Jagadish, Chennupati; Capizzi, Mario; Polimeni, Antonio

    2015-04-28

    Semiconductor nanowires (NWs) formed by non-nitride III-V compounds grow preferentially with wurtzite (WZ) lattice. This is contrary to bulk and two-dimensional layers of the same compounds, where only zincblende (ZB) is observed. The absorption spectrum of WZ materials differs largely from their ZB counterparts and shows three transitions, referred to as A, B, and C in order of increasing energy, involving the minimum of the conduction band and different critical points of the valence band. In this work, we determine the temperature dependence (T = 10-310 K) of the energy of transitions A, B, and C in ensembles of WZ InP NWs by photoluminescence (PL) and PL excitation (PLE) spectroscopy. For the whole temperature and energy ranges investigated, the PL and PLE spectra are quantitatively reproduced by a theoretical model taking into account contribution from both exciton and continuum states. WZ InP is found to behave very similarly to wide band gap III-nitrides and II-VI compounds, where the energy of A, B, and C displays the same temperature dependence. This finding unveils a general feature of the thermal properties of WZ materials that holds regardless of the bond polarity and energy gap of the crystal. Furthermore, no differences are observed in the temperature dependence of the fundamental band gap energy in WZ InP NWs and ZB InP (both NWs and bulk). This result points to a negligible role played by the WZ/ZB differences in determining the deformation potentials and the extent of the electron-phonon interaction that is a direct consequence of the similar nearest neighbor arrangement in the two lattices.

  1. Wurtzite-Phased InP Micropillars Grown on Silicon with Low Surface Recombination Velocity.

    Science.gov (United States)

    Li, Kun; Ng, Kar Wei; Tran, Thai-Truong D; Sun, Hao; Lu, Fanglu; Chang-Hasnain, Connie J

    2015-11-11

    The direct growth of III-V nanostructures on silicon has shown great promise in the integration of optoelectronics with silicon-based technologies. Our previous work showed that scaling up nanostructures to microsize while maintaining high quality heterogeneous integration opens a pathway toward a complete photonic integrated circuit and high-efficiency cost-effective solar cells. In this paper, we present a thorough material study of novel metastable InP micropillars monolithically grown on silicon, focusing on two enabling aspects of this technology-the stress relaxation mechanism at the heterogeneous interface and the microstructure surface quality. Aberration-corrected transmission electron microscopy studies show that InP grows directly on silicon without any amorphous layer in between. A set of periodic dislocations was found at the heterointerface, relaxing the 8% lattice mismatch between InP and Si. Single crystalline InP therefore can grow on top of the fully relaxed template, yielding high-quality micropillars with diameters expanding beyond 1 μm. An interesting power-dependence trend of carrier recombination lifetimes was captured for these InP micropillars at room temperature, for the first time for micro/nanostructures. By simply combining internal quantum efficiency with carrier lifetime, we revealed the recombination dynamics of nonradiative and radiative portions separately. A very low surface recombination velocity of 1.1 × 10(3) cm/sec was obtained. In addition, we experimentally estimated the radiative recombination B coefficient of 2.0 × 10(-10) cm(3)/sec for pure wurtzite-phased InP. These values are comparable with those obtained from InP bulk. Exceeding the limits of conventional nanowires, our InP micropillars combine the strengths of both nanostructures and bulk materials and will provide an avenue in heterogeneous integration of III-V semiconductor materials onto silicon platforms.

  2. Value and Anisotropy of the Electron and Hole Mass in Pure Wurtzite InP Nanowires.

    Science.gov (United States)

    Tedeschi, D; De Luca, M; Granados Del Águila, A; Gao, Q; Ambrosio, G; Capizzi, M; Tan, H H; Christianen, P C M; Jagadish, C; Polimeni, A

    2016-10-12

    The effective mass of electrons and holes in semiconductors is pivotal in determining the dynamics of carriers and their confinement energy in nanostructured materials. Surprisingly, this quantity is still unknown in wurtzite (WZ) nanowires (NWs) made of III-V compounds (e.g., GaAs, InAs, GaP, InP), where the WZ phase has no bulk counterpart. Here, we investigate the magneto-optical properties of InP WZ NWs grown by selective-area epitaxy that provides perfectly ordered NWs featuring high-crystalline quality. The combined analysis of the energy of free exciton states and impurity levels under magnetic field (B up to 29 T) allows us to disentangle the dynamics of oppositely charged carriers from the Coulomb interaction and thus to determine the values of the electron and hole effective mass. By application of B⃗ along different crystallographic directions, we also assess the dependence of the transport properties with respect to the NW growth axis (namely, the WZ ĉ axis). The effective mass of electrons along ĉ is m e ∥ = (0.078 ± 0.002) m 0 (m 0 is the electron mass in vacuum) and perpendicular to ĉ is m e ⊥ = (0.093 ± 0.001) m 0 , resulting in a 20% mass anisotropy. Holes exhibit a much larger (∼320%) and opposite mass anisotropy with their effective mass along and perpendicular to ĉ equal to m h ∥ = (0.81 ± 0.18) m 0 and m h ⊥ = (0.250 ± 0.016) m 0 , respectively. While no full consensus is found with current theoretical results on WZ InP, our findings show trends remarkably similar to the experimental data available in WZ bulk materials, such as InN, GaN, and ZnO.

  3. Study of wurtzite and zincblende GaN/InN based solar cells alloys: First-principles investigation within the improved modified Becke-Johnson potential

    KAUST Repository

    Ul Haq, Bakhtiar

    2014-09-01

    Wurtzite GaInN alloys with flexible energy gaps are pronounced for their potential applications in optoelectronics and solar cell technology. Recently the unwanted built-in fields caused by spontaneous polarization and piezoelectric effects in wurtzite (WZ) GaInN, has turned the focus towards zinc-blende (ZB) GaInN alloys. To comprehend merits and demerits of GaInN alloys in WZ and ZB structures, we performed a comparative study of the structural, electronic and optical properties of Ga1-xInxN alloys with different In concentration using first-principles methodology with density function theory with generalized gradient approximations (GGA) and modified Becke-Johnson (mBJ) potential. Investigations pertaining to total energy of GaInN for the both phases, demonstrate a marginal difference, reflecting nearly equivalent stability of the ZB-GaInN to WZ-GaInN. The larger ionic radii of indium (In), result in larger values of lattice parameters of Ga1-xInxN with higher In concentration. For In deficient Ga1-xInxN, at first, the formation enthalpies increase rapidly as the In content approaches to 45% in WZ and 47% in ZB, and then decreases with the further increase in In concentration. ZB-Ga1-xInxN alloys exhibit comparatively narrower energy gaps than WZ, and get smaller with increase in In contents. The smaller values of effective masses of free carriers, in WZ phase, than ZB phase, reflect higher carrier mobility and electrical conductivity of WZ-Ga1-xInxN. Moreover wide energy gap of WZ-Ga1-xInxN results in large values of the absorption coefficients comparatively and smaller static refractive indices compared to ZB-Ga1-xInxN. Comparable electronic and optical characteristics of the ZB-Ga1-xInxN to WZ-Ga1-xInxN endorses it a material of choice for optoelectronics and solar cell applications besides the WZ-Ga1-xInxN. © 2014 Elsevier Ltd.

  4. Study of wurtzite and zincblende GaN/InN based solar cells alloys: First-principles investigation within the improved modified Becke-Johnson potential

    KAUST Repository

    Ul Haq, Bakhtiar; Ahmed, Rashid; Shaari, Amiruddin; El Haj Hassan, Fouad; Kanoun, Mohammed; Goumri-Said, Souraya

    2014-01-01

    Wurtzite GaInN alloys with flexible energy gaps are pronounced for their potential applications in optoelectronics and solar cell technology. Recently the unwanted built-in fields caused by spontaneous polarization and piezoelectric effects in wurtzite (WZ) GaInN, has turned the focus towards zinc-blende (ZB) GaInN alloys. To comprehend merits and demerits of GaInN alloys in WZ and ZB structures, we performed a comparative study of the structural, electronic and optical properties of Ga1-xInxN alloys with different In concentration using first-principles methodology with density function theory with generalized gradient approximations (GGA) and modified Becke-Johnson (mBJ) potential. Investigations pertaining to total energy of GaInN for the both phases, demonstrate a marginal difference, reflecting nearly equivalent stability of the ZB-GaInN to WZ-GaInN. The larger ionic radii of indium (In), result in larger values of lattice parameters of Ga1-xInxN with higher In concentration. For In deficient Ga1-xInxN, at first, the formation enthalpies increase rapidly as the In content approaches to 45% in WZ and 47% in ZB, and then decreases with the further increase in In concentration. ZB-Ga1-xInxN alloys exhibit comparatively narrower energy gaps than WZ, and get smaller with increase in In contents. The smaller values of effective masses of free carriers, in WZ phase, than ZB phase, reflect higher carrier mobility and electrical conductivity of WZ-Ga1-xInxN. Moreover wide energy gap of WZ-Ga1-xInxN results in large values of the absorption coefficients comparatively and smaller static refractive indices compared to ZB-Ga1-xInxN. Comparable electronic and optical characteristics of the ZB-Ga1-xInxN to WZ-Ga1-xInxN endorses it a material of choice for optoelectronics and solar cell applications besides the WZ-Ga1-xInxN. © 2014 Elsevier Ltd.

  5. Investigation into structure of berylliumaluminium silicate glasses and crystals by X-ray spectroscopy

    International Nuclear Information System (INIS)

    Tykachinskij, I.D.; Gorbachev, V.V.; Petrakov, V.N.; Varshal, B.G.; Bystrakov, A.S.; Dmitriev, I.D.; Zatsepin, A.F.; Blaginina, L.A.

    1983-01-01

    For the purpose of elucidating the structural state of Be 2+ and Al 3+ ions as well as the nature of Be-O bond the investigation of glasses obtained from BeO, Al 2 O 3 and SiO 2 with different component composition is undertaken by X-ray spectroscopy. In three-component beryllium alumosilicate glasses at the ratio γ=Al 2 O 3 /BeO=0.34-1.92 the main part of Al 3+ cations forms AlO 4 groups. Be 2+ cations probably occupy several non-equivalent states. At the ''crystal-glass'' transition the reorganization of near structure of beryllium alumosilicate frame with appearance in a glass in contrast to crystal analog of beryllium cations playing the role of a glass former (being a part of glass net) as well as a modifier role occurs. For compositions with γ=1 the degree of ionic character of the Be-O bond is the greatest. The increase of Be 2+ cations fraction being a part of the glass net is characteristic feature of the glasses with parameter values γ not equal to 1

  6. Valence band offset of wurtzite InN/SrTiO3 heterojunction measured by x-ray photoelectron spectroscopy

    Directory of Open Access Journals (Sweden)

    Li Zhiwei

    2011-01-01

    Full Text Available Abstract The valence band offset (VBO of wurtzite indium nitride/strontium titanate (InN/SrTiO3 heterojunction has been directly measured by x-ray photoelectron spectroscopy. The VBO is determined to be 1.26 ± 0.23 eV and the conduction band offset is deduced to be 1.30 ± 0.23 eV, indicating the heterojunction has a type-I band alignment. The accurate determination of the valence and conduction band offsets paves a way to the applications of integrating InN with the functional oxide SrTiO3.

  7. Determination of the spin orbit coupling and crystal field splitting in wurtzite InP by polarization resolved photoluminescence

    Science.gov (United States)

    Chauvin, Nicolas; Mavel, Amaury; Jaffal, Ali; Patriarche, Gilles; Gendry, Michel

    2018-02-01

    Excitation photoluminescence spectroscopy is usually used to extract the crystal field splitting (ΔCR) and spin orbit coupling (ΔSO) parameters of wurtzite (Wz) InP nanowires (NWs). However, the equations expressing the valence band splitting are symmetric with respect to these two parameters, and a choice ΔCR > ΔSO or ΔCR InP NWs grown on silicon. The experimental results combined with a theoretical model and finite difference time domain calculations allow us to conclude that ΔCR > ΔSO in Wz InP.

  8. Polarized infrared reflectance studies for wurtzite InN epilayers on Si(111) grown by molecular beam expitaxy

    International Nuclear Information System (INIS)

    Ooi, P.K.; Lee, S.C.; Ng, S.S.; Hassan, Z.; Abu Hassan, H.; Chen, W.L.

    2011-01-01

    Room temperature polarized infrared reflectance technique is employed to study the optical properties of wurtzite InN epilayers on Si(111) grown by molecular beam expitaxy. The reflection spectra are compared to the calculated spectra generated based on the anisotropic dielectric function model. Good agreement between the measured and calculated spectra is obtained. From the fit of the experimental curve, the reststrahlen parameters at the center of Brillouin zone, the carrier concentration and mobility as well as the epilayers thicknesses are determined. The values of the carrier concentration and mobility are in good agreement with the results obtained from the Hall effects measurements.

  9. Minor component ordering in wurtzite Ga{sub 1-x}In{sub x}N and Ga{sub 1-x}Al{sub x}N

    Energy Technology Data Exchange (ETDEWEB)

    Laaksonen, K. [Laboratory of Physics, Helsinki University of Technology, P.O. Box 1100, FIN-02015 HUT (Finland)]. E-mail: kml@fyslab.hut.fi; Ganchenkova, M.G. [Laboratory of Physics, Helsinki University of Technology, P.O. Box 1100, FIN-02015 HUT (Finland); Nieminen, R.M. [Laboratory of Physics, Helsinki University of Technology, P.O. Box 1100, FIN-02015 HUT (Finland)

    2006-04-01

    The electronic and thermodynamic properties of materials are defined largely by their internal structure, in particular, composition uniformity. In this work the homogeneity of the minor component distribution in ternary Ga(In/Al)N alloys in the wurtzite polytype is studied. For this aim, the stability of different configurations of small clusters of the second component atoms is examined using Daft-based code Vas. The hydrostatic strain, induced in the matrix by the component atomic size mismatch, as well as external hydrostatic strain are taken under consideration. Clustering of In atoms along the [0001] direction is shown to be energetically favourable, whereas in the (0001) plane they repel each other. In contrast, Al atoms in GaN do not interact, irrespective of strain conditions. According to these results In in GaN should form [0001] aligned pairs or chains and, at higher In concentrations, zigzag chains in the c-direction, while Al forms a random alloy with the matrix material. The effect of the minor component (In/Al) ordering pattern on the band gap of the ternary Ga(In/Al)N alloy is also discussed.

  10. Characterization of individual stacking faults in a wurtzite GaAs nanowire by nanobeam X-ray diffraction.

    Science.gov (United States)

    Davtyan, Arman; Lehmann, Sebastian; Kriegner, Dominik; Zamani, Reza R; Dick, Kimberly A; Bahrami, Danial; Al-Hassan, Ali; Leake, Steven J; Pietsch, Ullrich; Holý, Václav

    2017-09-01

    Coherent X-ray diffraction was used to measure the type, quantity and the relative distances between stacking faults along the growth direction of two individual wurtzite GaAs nanowires grown by metalorganic vapour epitaxy. The presented approach is based on the general property of the Patterson function, which is the autocorrelation of the electron density as well as the Fourier transformation of the diffracted intensity distribution of an object. Partial Patterson functions were extracted from the diffracted intensity measured along the [000\\bar{1}] direction in the vicinity of the wurtzite 00\\bar{1}\\bar{5} Bragg peak. The maxima of the Patterson function encode both the distances between the fault planes and the type of the fault planes with the sensitivity of a single atomic bilayer. The positions of the fault planes are deduced from the positions and shapes of the maxima of the Patterson function and they are in excellent agreement with the positions found with transmission electron microscopy of the same nanowire.

  11. Wurtzite/zinc-blende electronic-band alignment in basal-plane stacking faults in semi-polar GaN

    Science.gov (United States)

    Monavarian, Morteza; Hafiz, Shopan; Izyumskaya, Natalia; Das, Saikat; Özgür, Ümit; Morkoç, Hadis; Avrutin, Vitaliy

    2016-02-01

    Heteroepitaxial semipolar and nonpolar GaN layers often suffer from high densities of extended defects including basal plane stacking faults (BSFs). BSFs which are considered as inclusions of cubic zinc-blende phase in wurtzite matrix act as quantum wells strongly affecting device performance. Band alignment in BSFs has been discussed as type of band alignment at the wurtzite/zinc blende interface governs the response in differential transmission; fast decay after the pulse followed by slow recovery due to spatial splitting of electrons and heavy holes for type- II band alignment in contrast to decay with no recovery in case of type I band alignment. Based on the results, band alignment is demonstrated to be of type II in zinc-blende segments in wurtzite matrix as in BSFs.

  12. Facile in situ synthesis of wurtzite ZnS/ZnO core/shell heterostructure with highly efficient visible-light photocatalytic activity and photostability

    Science.gov (United States)

    Xiao, Jian-Hua; Huang, Wei-Qing; Hu, Yong-sheng; Zeng, Fan; Huang, Qin-Yi; Zhou, Bing-Xin; Pan, Anlian; Li, Kai; Huang, Gui-Fang

    2018-02-01

    High photocatalytic activity and photostability are the pursuit of the goal for designing promising photocatalysts. Herein, using ZnO to encapsulate ZnS nanoparticles is proposed as an effective strategy to enhance photocatalytic activity and anti-photocorrosion. The ZnS/ZnO core/shell heterostructures are obtained via an annealing treatment of ZnS nanoparticles produced by a facile wet chemical approach. Due to its small size, the nascent cubic sphalerite ZnS (s-ZnS) converts into a hexagonal wurtzite ZnS (w-ZnS)/ZnO core/shell structure after annealing treatment. In situ oxidation leads to increasing ZnO, simultaneously decreasing the w-ZnS content in the resultant w-ZnS/ZnO with thermal annealing time. The w-ZnS/ZnO core/shell heterostructures show high photocatalytic activity, demonstrated by the photodegradation rate of methylene blue being up to ten-fold and seven-fold higher than that of s-ZnS under UV and visible light irradiation, respectively, and the high capability of degrading rhodamine B. The enhanced photocatalytic activity may be attributed to the large specific surface and improved charge carrier separation at the core/shell interface. Moreover, it displays high photostability owing to the protection of the ZnO shell, greatly inhibiting the photocorrosion of ZnS. This facile in situ oxidation is effective and easily scalable, providing opportunities for developing novel core/shell structure photocatalysts with high activity and photostability.

  13. Room-temperature heteroepitaxy of single-phase Al1−xInxN films with full composition range on isostructural wurtzite templates

    International Nuclear Information System (INIS)

    Hsiao, Ching-Lien; Palisaitis, Justinas; Junaid, Muhammad; Persson, Per O.Å.; Jensen, Jens; Zhao, Qing-Xiang; Hultman, Lars; Chen, Li-Chyong; Chen, Kuei-Hsien; Birch, Jens

    2012-01-01

    Al 1−x In x N heteroepitaxial layers covering the full composition range have been realized by magnetron sputter epitaxy on basal-plane AlN, GaN, and ZnO templates at room temperature (RT). Both Al 1−x In x N single layers and multilayers grown on these isostructural templates show single phase, single crystal wurtzite structure. Even at large lattice mismatch between the film and the template, for instance InN/AlN (∼ 13% mismatch), heteroepitaxy is achieved. However, RT-grown Al 1−x In x N films directly deposited on non-isostructural c-plane sapphire substrate exhibit a polycrystalline structure for all compositions, suggesting that substrate surface structure is important for guiding the initial nucleation. Degradation of Al 1−x In x N structural quality with increasing indium content is attributed to the formation of more point- and structural defects. The defects result in a prominent hydrostatic tensile stress component, in addition to the biaxial stress component introduced by lattice mismatch, in all RT-grown Al 1−x In x N films. These effects are reflected in the measured in-plane and out-of-plane strains. The effect of hydrostatic stress is negligible compared to the effects of lattice mismatch in high-temperature grown AlN layers thanks to their low amount of defects. We found that Vegard’s rule is applicable to determine x in the RT-grown Al 1−x In x N epilayers if the lattice constants of RT-sputtered AlN and InN films are used instead of those of the strain-free bulk materials. - Highlights: ► Magnetron sputter epitaxy of single-phase Al 1−x In x N(0001) at room temperature ► Growing Al 1−x In x N onto temperature sensitive substrates is desirable. ► Substrate surface structure plays a vital role at nucleation stage. ► Point and extended defects produce hydrostatic tensile stress. ► The applicability of Vegard's rule for these compounds is confirmed.

  14. The influence of the (n, 2n) and (n, α) reactions of beryllium on the neutron balance in a BeO or Be moderated reactor and its consequences on the long term reactivity changes

    International Nuclear Information System (INIS)

    Sahai, K.; Benoist, P.; Horowitz, J.

    1958-01-01

    The reaction probabilities in an infinite and homogeneous medium of BeO or Be have been calculated from neutron cross-section curves, for a neutron produced with an energy distribution similar to a fission spectrum; the calculation shows that, after several elastic collisions, the neutron has yet an appreciable probability to undergo a reaction, in spite of the energy degradation in the spectrum due to each collision. This degradation has been calculated, taking into account of anisotropy of the collisions. The gain of the reactivity in a reactor has been obtained after correcting these probabilities for the attenuation of the flux of fission neutrons due to the inelastic scattering in the uranium. Finally, the calculation shows that in a power reactor, this gain of reactivity is in practice destroyed in a few years by the accumulation of poisonous nuclei such as Li 6 and He 3 following (n, α) reaction. (author) [fr

  15. Thermodynamic properties of beryllium hydroxide; Proprietes thermodynamiques de l'hydroxyde de beryllium. Etude du systeme BeO - H{sub 2}O - BE(OH){sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Baur, A; Lecocq, A [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

    1964-07-01

    The study of the hydro-thermal decomposition of beryllium hydroxide has made it possible to determine the free energy of formation and the entropy. The results obtained are in good agreement with the theoretical values calculated from the solubility product of this substance. They give furthermore the possibility of acquiring a better understanding of the BeO-H{sub 2}O-Be (OH){sub 2} system between 20 and 1500 C. (authors) [French] L'etude de la decomposition hydrothermale de l'hydroxyde de beryllium a permis de determiner l'energie libre de formation et l'entropie. Les resultats obtenus sont en bon accord avec les valeurs theoriques calculees a partir du produit de solubilite de ce corps. Ils donnent en outre la possibilite d'acceder a une meilleure comprehension du systeme BeO - H{sub 2}O - Be(OH){sub 2}, entre 20 C et 1500 C. (auteurs)

  16. Biologically-induced precipitation of sphalerite-wurtzite nanoparticles by sulfate-reducing bacteria: implications for acid mine drainage treatment.

    Science.gov (United States)

    Castillo, Julio; Pérez-López, Rafael; Caraballo, Manuel A; Nieto, José M; Martins, Mónica; Costa, M Clara; Olías, Manuel; Cerón, Juan C; Tucoulou, Rémi

    2012-04-15

    Several experiments were conducted to evaluate zinc-tolerance of sulfate-reducing bacteria (SRB) obtained from three environmental samples, two inocula from sulfide-mining districts and another inoculum from a wastewater treatment plant. The populations of SRB resisted zinc concentrations of 260 mg/L for 42 days in a sulfate-rich medium. During the experiments, sulfate was reduced to sulfide and concentrations in solution decreased. Zinc concentrations also decreased from 260 mg/L to values below detection limit. Both decreases were consistent with the precipitation of newly-formed sphalerite and wurtzite, two polymorphs of ZnS, forming <2.5-μm-diameter spherical aggregates identified by microscopy and synchrotron-μ-XRD. Sulfate and zinc are present in high concentrations in acid mine drainage (AMD) even after passive treatments based on limestone dissolution. The implementation of a SRB-based zinc removal step in these systems could completely reduce the mobility of all metals, which would improve the quality of stream sediments, water and soils in AMD-affected landscapes. Copyright © 2012 Elsevier B.V. All rights reserved.

  17. Correlated electron—hole transitions in wurtzite GaN quantum dots: the effects of strain and hydrostatic pressure

    International Nuclear Information System (INIS)

    Zheng Dongmei; Wang Zongchi; Xiao Boqi

    2012-01-01

    Within the effective-mass and finite-height potential barrier approximation, a theoretical study of the effects of strain and hydrostatic pressure on the exciton emission wavelength and electron—hole recombination rate in wurtzite cylindrical GaN/Al x Ga 1−x N quantum dots (QDs) is performed using a variational approach. Numerical results show that the emission wavelength with strain effect is higher than that without strain effect when the QD height is large (> 3.8 nm), but the status is opposite when the QD height is small (< 3.8 nm). The height of GaN QDs must be less than 5.5 nm for an efficient electron—hole recombination process due to the strain effect. The emission wavelength decreases linearly and the electron—hole recombination rate increases almost linearly with applied hydrostatic pressure. The hydrostatic pressure has a remarkable influence on the emission wavelength for large QDs, and has a significant influence on the electron—hole recombination rate for small QDs. Furthermore, the present numerical outcomes are in qualitative agreement with previous experimental findings under zero pressure. (semiconductor physics)

  18. Simulation of pure and defective wurtzite-type ZnO

    Energy Technology Data Exchange (ETDEWEB)

    Maldonado, Frank; Stashans, Arvids [Grupo de FisicoquImica de Materiales, Instituto de Quimica Aplicada, Universidad Tecnica Particular de Loja, Apartado 11-01-608, Loja (Ecuador)], E-mail: arvids@utpl.edu.ec

    2009-12-15

    Changes in the structural and electronic properties of zinc oxide (ZnO) due to the O vacancy and F-centre were studied using a semi-empirical quantum-chemical approach based on Hartree-Fock theory. A periodic supercell of 128 atoms was exploited throughout the study. The semi-empirical parameters for the Zn atom are obtained by reproducing the main properties of the ZnO crystal as well as the first three ionization potentials of the Zn atom. The perturbation imposed by the defect leads to atomic relaxation, which is computed and discussed in detail. It is found that electron density redistribution in the vicinity of defects plays an important role in the determination of atomic movements. The introduction of an oxygen vacancy generates a local one-electron energy level placed below the conduction band while the presence of an F-centre produces a local energy level just above the upper valence band of the material. The deep situation of the local energy level corresponding to the F-centre implies that the F-centre cannot serve as a source of unintentional n-type electrical conductivity in ZnO. Changes in the chemical bonding are observed, showing that it becomes slightly more covalent because of oxygen-vacancy-type defects.

  19. Simulation of pure and defective wurtzite-type ZnO

    International Nuclear Information System (INIS)

    Maldonado, Frank; Stashans, Arvids

    2009-01-01

    Changes in the structural and electronic properties of zinc oxide (ZnO) due to the O vacancy and F-centre were studied using a semi-empirical quantum-chemical approach based on Hartree-Fock theory. A periodic supercell of 128 atoms was exploited throughout the study. The semi-empirical parameters for the Zn atom are obtained by reproducing the main properties of the ZnO crystal as well as the first three ionization potentials of the Zn atom. The perturbation imposed by the defect leads to atomic relaxation, which is computed and discussed in detail. It is found that electron density redistribution in the vicinity of defects plays an important role in the determination of atomic movements. The introduction of an oxygen vacancy generates a local one-electron energy level placed below the conduction band while the presence of an F-centre produces a local energy level just above the upper valence band of the material. The deep situation of the local energy level corresponding to the F-centre implies that the F-centre cannot serve as a source of unintentional n-type electrical conductivity in ZnO. Changes in the chemical bonding are observed, showing that it becomes slightly more covalent because of oxygen-vacancy-type defects.

  20. Physical and biophysical assessment of highly fluorescent, magnetic quantum dots of a wurtzite-phase manganese selenide system

    Science.gov (United States)

    Sarma, Runjun; Das, Queen; Hussain, Anowar; Ramteke, Anand; Choudhury, Amarjyoti; Mohanta, Dambarudhar

    2014-07-01

    Combining fluorescence and magnetic features in a non-iron based, select type of quantum dots (QDs) can have immense value in cellular imaging, tagging and other nano-bio interface applications, including targeted drug delivery. Herein, we report on the colloidal synthesis and physical and biophysical assessment of wurtzite-type manganese selenide (MnSe) QDs in cell culture media. Aiming to provide a suitable colloidal system of biological relevance, different concentrations of reactants and ligands (e.g., thioglycolic acid, TGA) have been considered. The average size of the QDs is ˜7 nm, which exhibited a quantum yield of ˜75% as compared to rhodamine 6 G dye®. As revealed from time-resolved photoluminescence (TR-PL) response, the near band edge emission followed a bi-exponential decay feature with characteristic times of ˜0.64 ns and 3.04 ns. At room temperature, the QDs were found to exhibit paramagnetic features with coercivity and remanence impelled by TGA concentrations. With BSA as a dispersing agent, the QDs showed an improved optical stability in Dulbecco’s Modified Eagle Media® (DMEM) and Minimum Essential Media® (MEM), as compared to the Roswell Park Memorial Institute® (RPMI-1640) media. Finally, the cell viability of lymphocytes was found to be strongly influenced by the concentration of MnSe QDs, and had a safe limit upto 0.5 μM. With BSA inclusion in cell media, the cellular uptake of MnSe QDs was observed to be more prominent, as revealed from fluorescence imaging. The fabrication of water soluble, nontoxic MnSe QDs would open up an alternative strategy in nanobiotechnology, while preserving their luminescent and magnetic properties intact.

  1. Epitaxially grown zinc-blende structured Mn doped ZnO nanoshell on ZnS nanoparticles

    International Nuclear Information System (INIS)

    Limaye, Mukta V.; Singh, Shashi B.; Date, Sadgopal K.; Gholap, R.S.; Kulkarni, Sulabha K.

    2009-01-01

    Zinc oxide in the bulk as well as in the nanocrystalline form is thermodynamically stable in the wurtzite structure. However, zinc oxide in the zinc-blende structure is more useful than that in the wurtzite structure due to its superior electronic properties as well as possibility of efficient doping. Therefore, zinc oxide shell is grown epitaxially on zinc sulphide core nanoparticles having zinc-blende structure. It is shown that doping of manganese could be achieved in zinc oxide nanoshell with zinc-blende structure

  2. First-principle-based full-dispersion Monte Carlo simulation of the anisotropic phonon transport in the wurtzite GaN thin film

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Ruikang; Hu, Run, E-mail: hurun@hust.edu.cn, E-mail: luoxb@hust.edu.cn; Luo, Xiaobing, E-mail: hurun@hust.edu.cn, E-mail: luoxb@hust.edu.cn [State Key Laboratory of Coal Combustion and Thermal Packaging Laboratory, School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan 430074 (China)

    2016-04-14

    In this study, we developed a first-principle-based full-dispersion Monte Carlo simulation method to study the anisotropic phonon transport in wurtzite GaN thin film. The input data of thermal properties in MC simulations were calculated based on the first-principle method. The anisotropy of thermal conductivity in bulk wurtzite GaN is found to be strengthened by isotopic scatterings and reduced temperature, and the anisotropy reaches 40.08% for natural bulk GaN at 100 K. With the GaN thin film thickness decreasing, the anisotropy of the out-of-plane thermal conductivity is heavily reduced due to both the ballistic transport and the less importance of the low-frequency phonons with anisotropic group velocities. On the contrary, it is observed that the in-plane thermal conductivity anisotropy of the GaN thin film is strengthened by reducing the film thickness. And the anisotropy reaches 35.63% when the natural GaN thin film thickness reduces to 50 nm at 300 K with the degree of specularity being zero. The anisotropy is also improved by increasing the surface roughness of the GaN thin film.

  3. Valence-band discontinuities of wurtzite GaN, AlN, and InN heterojunctions measured by x-ray photoemission spectroscopy

    International Nuclear Information System (INIS)

    Martin, G.; Botchkarev, A.; Rockett, A.; Morkoc, H.

    1996-01-01

    The valence-band discontinuities at various wurtzite GaN, AlN, and InN heterojunctions were measured by means of x-ray photoemission spectroscopy. A significant forward endash backward asymmetry was observed in the InN/GaN endash GaN/InN and InN/AlN endash AlN/InN heterojunctions. The asymmetry was understood as a piezoelectric strain effect. We report the valence band discontinuities for InN/GaN=1.05±0.25 eV, GaN/AlN=0.70±0.24 eV, and InN/AlN=1.81±0.20 eV, all in the standard type I lineup. These values obey transitivity to within the experimental accuracy. Tables of photoemission core level binding energies are reported for wurtzite GaN, AlN, and InN. copyright 1996 American Institute of Physics

  4. Electronic Structure of Cdse Nanowires Terminated With Gold ...

    African Journals Online (AJOL)

    Cadmium selenide nanowires in the wurtzite bulk phase, connected to gold electrodes are studied using local density approximation. The short wire is fully metalized by metal-induced gap states. For longer wires, a gap similar to that in bare cadmium selenide nanowires is observed near the center while sub-gap structure ...

  5. Atomic structure and orientation relations of interfaces between Ag and ZnO

    NARCIS (Netherlands)

    Vellinga, W.P.; Hosson, de J.Th.M.

    1997-01-01

    This paper presents the results of investigations of Ag-ZnO interfaces, produced by internal oxidation of an Ag-Zn alloy. ZnO precipitates with the wurtzite structure were found exhibiting mainly one orientation relation with the Ag matrix. However, closely related ORs were found, rotated by small

  6. Temperature-dependence on the structural, optical, andparamagnetic properties of ZnO nanostructures

    CSIR Research Space (South Africa)

    Mhlongo, GH

    2014-02-01

    Full Text Available of the phonon peak at 580 cm(sup-1) was gradually enhanced with the increase of annealing temperature. X-ray diffraction and X-ray photoelectron spectroscopy (XPS) measurements showed that all ZnO samples possess a typical wurtzite structure with high...

  7. The effects of optical phonon on the binding energy of bound polaron in a wurtzite ZnO/MgxZn1−xO quantum well

    International Nuclear Information System (INIS)

    Zhao, Feng-Qi; Guo, Zi-Zheng; Zhu, Jun

    2014-01-01

    An improved Lee-Low-Pines intermediate coupling method is used to study the energies and binding energies of bound polarons in a wurtzite ZnO/Mg x Zn 1−x O quantum well. The contributions from different branches of long-wave optical phonons, i.e., confined optical phonons, interface optical phonons, and half-space optical phonons are considered. In addition to electron-phonon interaction, the impurity-phonon interaction, and the anisotropy of material parameters, such as phonon frequency, electron effective mass, and dielectric constant, are also included in our computation. Ground-state energies, binding energies and detailed phonon contributions from various phonons as functions of well width, impurity position and composition are presented. Our result suggests that total phonon contribution to ground state and binding energies in the studied wurtzite ZnO/Mg 0.3 Zn 0.7 O quantum wells varies between 28–23 meV and 62–45 meV, respectively, which are much larger than the corresponding values (about 3.2–1.8 meV and 1.6–0.3 meV) in GaAs/Al 0.3 Ga 0.7 As quantum wells. For a narrower quantum well, the phonon contribution mainly comes from interface and half-space phonons, for a wider quantum well, most of phonon contribution originates from confined phonons. The contribution from all the phonon modes to binding energies increases slowly either when impurity moves far away from the well center in the z direction or with the increase in magnesium composition (x). It is found that different phonons have different influences on the binding energies of bound polarons. Furthermore, the phonon contributions to binding energies as functions of well width, impurity position, and composition are very different from one another. In general, the electron-optical phonon interaction and the impurity center-optical phonon interaction play an important role in electronic states of ZnO-based quantum wells and cannot be neglected.

  8. Infrared optical responses of wurtzite In{sub x}Ga{sub 1−x}N thin films with porous surface morphology

    Energy Technology Data Exchange (ETDEWEB)

    Yew, P., E-mail: paulinevcu@hotmail.com [Institute of Nano-Optoelectronics Research and Technology (INOR), Universiti Sains Malaysia, 11800 Minden, Penang (Malaysia); School of Physics, Universiti Sains Malaysia, 11800 Minden, Penang (Malaysia); Lee, S.C. [School of Physics, Universiti Sains Malaysia, 11800 Minden, Penang (Malaysia); Centre of Excellence for Pre-University Studies, INTI International College Penang, Laureate International University, 1-Z, Lebuh Bukit Jambul, 11900 Penang (Malaysia); Ng, S.S. [Institute of Nano-Optoelectronics Research and Technology (INOR), Universiti Sains Malaysia, 11800 Minden, Penang (Malaysia); Hassan, H. Abu [School of Physics, Universiti Sains Malaysia, 11800 Minden, Penang (Malaysia); Chen, W.L. [Department of Electronic Engineering, National Changhua University of Education, 500, Taiwan, ROC (China); Osipowicz, T.; Ren, M.Q. [Centre for Ion Beam Applications (CIBA), Department of Physics, National University of Singapore, Singapore 119260 (Singapore)

    2016-03-31

    Room temperature infrared (IR) optical responses of wurtzite indium gallium nitride (In{sub x}Ga{sub 1−x}N) in the composition range of 0.174 ≤ x ≤ 0.883 were investigated by the polarized IR reflectance spectroscopy. Analyses of the amplitudes of oscillation fringes in the non-reststrahlen region revealed that the high frequency dielectric constants of the samples were unusually smaller than the values predicted from the Clausius–Mossotti relation. This odd behavior was attributed to the porous surface morphology of the In{sub x}Ga{sub 1−x}N samples. The E{sub 1} optical phonon modes of the In{sub x}Ga{sub 1−x}N were deduced from the composition dependent reststrahlen features. The obtained values were compared to those calculated through the modified random element iso-displacement (MREI) model. The deviation between the measured data and the MREI model prediction were explained in detail from the aspects of strain, thermal expansion and anharmonic phonon-coupling. Finally, it was found that the large discrepancy of the E{sub 1}(LO) mode is mainly attributed to the effects of the longitudinal phonon–plasmon coupling. - Highlights: • Composition dependence of E{sub 1} modes of In{sub x}Ga{sub 1−x}N alloys (x = 0.174 to 0.883) • Dependence of porous morphology on infrared (IR) optical properties • Longitudinal phonon–plasmon coupling obscures determination of E{sub 1}(LO) mode.

  9. Effects of hydrostatic pressure on ionized donor bound exciton states in strained wurtzite GaN/AlxGa1-xN cylindrical quantum dots

    International Nuclear Information System (INIS)

    Zheng Dongmei; Wang Zongchi; Xiao Boqi

    2012-01-01

    Based on the effective-mass approximation and variational procedure, ionized donor bound exciton (D + , X) states confined in strained wurtzite (WZ) GaN/Al x Ga 1-x N cylindrical (disk-like) quantum dots (QDs) with finite-height potential barriers are investigated, with considering the influences of the built-in electric field (BEF), the biaxial strain dependence of material parameters and the applied hydrostatic pressure. The Schrödinger equation via the proper choice of the donor bound exciton trial wave function is solved. The behaviors of the binding energy of (D + , X) and the optical transition associated with (D + , X) are examined at different pressures for different QD sizes and donor positions. In our calculations, the effective masses of electron and hole, dielectric constants, phonon frequencies, energy gaps, and piezoelectric polarizations are taken into account as functions of biaxial strain and hydrostatic pressure. Our results show that the hydrostatic pressure, the QD size and the donor position have a remarkable influence on (D + , X) states. The hydrostatic pressure generally increases the binding energy of (D + , X). However, the binding energy tends to decrease for the QDs with large height and lower Al composition (x 0 ≤0. The optical transition energy has a blue-shift (red-shift) if the hydrostatic pressure (QD height) increases. For the QDs with small height and low Al composition, the hydrostatic pressure dependence of the optical transition energy is more obvious. Furthermore, the relationship between the radiative decay time and hydrostatic pressure (QD height) is also investigated. It is found that the radiative decay time increases with pressure and the increment tendency is more prominent for the QDs with large height. The radiative decay time increases exponentially reaching microsecond order with increasing QD height. The physical reason has been analyzed in depth.

  10. Real space pseudopotential calculations for size trends in Ga- and Al-doped zinc oxide nanocrystals with wurtzite and zincblende structures

    Energy Technology Data Exchange (ETDEWEB)

    Bobbitt, N. Scott; Kim, Minjung [Department of Chemical Engineering, The University of Texas at Austin, Austin, Texas 78712 (United States); Sai, Na [Department of Physics, The University of Texas at Austin, Austin, Texas 78712 (United States); Marom, Noa [Department of Physics and Engineering Physics, Tulane University, New Orleans, Louisiana, 70118 (United States); Chelikowsky, James R. [Center for Computational Materials, Institute for Computational Engineering and Sciences, Departments of Physics and Chemical Engineering, The University of Texas at Austin, Austin, Texas 78712 (United States)

    2014-09-07

    Zinc oxide is often used as a popular inexpensive transparent conducting oxide. Here, we employ density functional theory and local density approximation to examine the effects of quantum confinement in doped nanocrystals of this material. Specifically, we examine the addition of Ga and Al dopants to ZnO nanocrystals on the order of 1.0 nm. We find that the inclusion of these dopants is energetically less favorable in smaller particles and that the electron binding energy, which is associated with the dopant activation, decreases with the nanocrystal size. We find that the introduction of impurities does not alter significantly the Kohn-Sham eigenspectrum for small nanocrystals of ZnO. The added electron occupies the lowest existing state, i.e., no new bound state is introduced in the gap. We verify this assertion with hybrid functional calculations.

  11. Real space pseudopotential calculations for size trends in Ga- and Al-doped zinc oxide nanocrystals with wurtzite and zincblende structures

    International Nuclear Information System (INIS)

    Bobbitt, N. Scott; Kim, Minjung; Sai, Na; Marom, Noa; Chelikowsky, James R.

    2014-01-01

    Zinc oxide is often used as a popular inexpensive transparent conducting oxide. Here, we employ density functional theory and local density approximation to examine the effects of quantum confinement in doped nanocrystals of this material. Specifically, we examine the addition of Ga and Al dopants to ZnO nanocrystals on the order of 1.0 nm. We find that the inclusion of these dopants is energetically less favorable in smaller particles and that the electron binding energy, which is associated with the dopant activation, decreases with the nanocrystal size. We find that the introduction of impurities does not alter significantly the Kohn-Sham eigenspectrum for small nanocrystals of ZnO. The added electron occupies the lowest existing state, i.e., no new bound state is introduced in the gap. We verify this assertion with hybrid functional calculations

  12. Chemical substitution of Cd ions by Hg in CdSe nanorods and nanodots: Spectroscopic and structural examination

    International Nuclear Information System (INIS)

    Prudnikau, Anatol; Artemyev, Mikhail; Molinari, Michael; Troyon, Michel; Sukhanova, Alyona; Nabiev, Igor; Baranov, Alexandr V.; Cherevkov, Sergey A.; Fedorov, Anatoly V.

    2012-01-01

    Highlights: ► We studied cadmium-by-mercury chemical substitution in CdSe nanocrystals. ► Zinc blende CdSe quantum dots can be easily converted to isostructural Cd x Hg 1−x Se. ► Wurtzite CdSe QDs require longer time to convert to a zinc blende Cd x Hg 1−x Se. ► Wurtzite CdSe nanorods transform to nanoheterogeneous luminescent Cd x Hg 1−x Se rods. - Abstract: The chemical substitution of cadmium by mercury in colloidal CdSe quantum dots (QDs) and nanorods has been examined by absorption, photoluminescence and Raman spectroscopy. The crystalline structure of original CdSe QDs used for Cd/Hg substitution (zinc blende versus wurtzite) shows a strong impact on the optical and structural properties of resultant Cd x Hg 1−x Se nanocrystals. Substitution of Cd by Hg in isostructural zinc blende CdSe QDs converts them to ternary Cd x Hg 1−x Se zinc blende nanocrystals with significant NIR emission. Whereas, the wurtzite CdSe QDs transformed first to ternary nanocrystals with almost no emission followed by slow structural reorganization to a NIR-emitting zinc blende Cd x Hg 1−x Se QDs. CdSe nanorods with intrinsic wurtzite structure show unexpectedly intense NIR emission even at early Cd/Hg substitution stage with PL active zinc blende Cd x Hg 1−x Se regions.

  13. Electronic structure and physical properties of ScN in pressure: density-functional theory calculations

    International Nuclear Information System (INIS)

    Guan Pengfei; Wang Chongyu; Yu Tao

    2008-01-01

    Local density functional is investigated by using the full-potential linearized augmented plane wave (FP-LAPW) method for ScN in the hexagonal structure and the rocksalt structure and for hexagonal structures linking a layered hexagonal phase with wurtzite structure along a homogeneous strain transition path. It is found that the wurtzite ScN is unstable and the layered hexagonal phase, labelled as h o , in which atoms are approximately fivefold coordinated, is metastable, and the rocksalt ScN is stable. The electronic structure, the physical properties of the intermediate structures and the energy band structure along the transition are presented. It is found that the band gaps change from 4.0 to 1.0 eV continuously when c/a value varies from 1.68 to 1.26. It is noticeable that the study of ScN provides an opportunity to apply this kind of material (in wurtzite[h]-derived phase). (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  14. Phase discrimination in CdSe structures by means of Raman scattering

    International Nuclear Information System (INIS)

    Cusco, R.; Artus, L.; Consonni, V.; Bellet-Amalric, E.; Andre, R.

    2017-01-01

    Raman spectra of epitaxial layers of CdSe grown by molecular beam epitaxy have been measured for the cubic (zincblende) and hexagonal (wurtzite) phases. The Raman spectra are examined in the light of density functional calculations for these two highly similar structures. Characteristic Raman frequencies and spectral features associated with the different symmetry are discussed and reliable criteria for phase discrimination based on Raman spectroscopy are proposed. Although LO frequencies are virtually identical in both structures and may be affected by size effects, the observation of a low energy E 2 mode at 33 cm -1 unambiguously identifies the wurtzite structure and can be used as a specific fingerprint to distinguish between these two phases in CdSe-based nanostructures. The slightly lower LO frequency measured in the zincblende epitaxial layer is ascribed to residual tensile strain. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  15. Phase discrimination in CdSe structures by means of Raman scattering

    Energy Technology Data Exchange (ETDEWEB)

    Cusco, R.; Artus, L. [Institut Jaume Almera (ICTJA-CSIC), Consejo Superior de Investigaciones Cientificas, Lluis Sole i Sabaris s.n., 08028 Barcelona (Spain); Consonni, V. [Universite Grenoble Alpes and CNRS, LMGP, 38016 Grenoble (France); Bellet-Amalric, E. [Universite Grenoble Alpes and CEA, INAC-PHEILQS, Nanophysique et Semiconducteurs Group, 38000 Grenoble (France); Andre, R. [Universite Grenoble Alpes and CNRS, Institut Neel, Nanophysique et Semiconducteurs Group, 38000 Grenoble (France)

    2017-05-15

    Raman spectra of epitaxial layers of CdSe grown by molecular beam epitaxy have been measured for the cubic (zincblende) and hexagonal (wurtzite) phases. The Raman spectra are examined in the light of density functional calculations for these two highly similar structures. Characteristic Raman frequencies and spectral features associated with the different symmetry are discussed and reliable criteria for phase discrimination based on Raman spectroscopy are proposed. Although LO frequencies are virtually identical in both structures and may be affected by size effects, the observation of a low energy E{sub 2} mode at 33 cm{sup -1} unambiguously identifies the wurtzite structure and can be used as a specific fingerprint to distinguish between these two phases in CdSe-based nanostructures. The slightly lower LO frequency measured in the zincblende epitaxial layer is ascribed to residual tensile strain. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  16. New crystal structures in hexagonal CuInS2 nanocrystals

    Science.gov (United States)

    Shen, Xiao; Hernández-Pagan, Emil A.; Zhou, Wu; Puzyrev, Yevgeniy S.; Idrobo, Juan C.; MacDonald, Janet E.; Pennycook, Stephen J.; Pantelides, Sokrates T.

    2013-03-01

    CuInS2 is one of the best candidate materials for solar energy harvesting. Its nanocrystals with a hexagonal lattice structure that is different from the bulk chalcopyrite phase have been synthesized by many groups. The structure of these CuInS2 nanocrystals has been previously identified as the wurtzite structure in which the copper and indium atoms randomly occupy the cation sites. Using first-principles total energy and electronic structure calculations based on density functional theory, UV-vis absorption spectroscopy, X-ray diffraction, and atomic resolution Z-contrast images obtained in an aberration-corrected scanning transmission electron microscope, we show that CuInS2 nanocrystals do not form random wurtzite structure. Instead, the CuInS2 nanocrystals consist of several wurtzite- related crystal structures with ordered cation sublattices, some of which are reported for the first time here. This work is supported by the NSF TN-SCORE (JEM), by NSF (WZ), by ORNL's Shared Research Equipment User Program (JCI) sponsored by DOE BES, by DOE BES Materials Sciences and Engineering Division (SJP, STP), and used resources of the National Energy Research Scientific Computing Center, supported by the DOE Office of Science under Contract No. DE-AC02-05CH11231.

  17. Crystal Structures of GaN Nanodots by Nitrogen Plasma Treatment on Ga Metal Droplets

    Directory of Open Access Journals (Sweden)

    Yang-Zhe Su

    2018-06-01

    Full Text Available Gallium nitride (GaN is one of important functional materials for optoelectronics and electronics. GaN exists both in equilibrium wurtzite and metastable zinc-blende structural phases. The zinc-blende GaN has superior electronic and optical properties over wurtzite one. In this report, GaN nanodots can be fabricated by Ga metal droplets in ultra-high vacuum and then nitridation by nitrogen plasma. The size, shape, density, and crystal structure of GaN nanodots can be characterized by transmission electron microscopy. The growth parameters, such as pre-nitridation treatment on Si surface, substrate temperature, and plasma nitridation time, affect the crystal structure of GaN nanodots. Higher thermal energy could provide the driving force for the phase transformation of GaN nanodots from zinc-blende to wurtzite structures. Metastable zinc-blende GaN nanodots can be synthesized by the surface modification of Si (111 by nitrogen plasma, i.e., the pre-nitridation treatment is done at a lower growth temperature. This is because the pre-nitridation process can provide a nitrogen-terminal surface for the following Ga droplet formation and a nitrogen-rich condition for the formation of GaN nanodots during droplet epitaxy. The pre-nitridation of Si substrates, the formation of a thin SiNx layer, could inhibit the phase transformation of GaN nanodots from zinc-blende to wurtzite phases. The pre-nitridation treatment also affects the dot size, density, and surface roughness of samples.

  18. First principles total energy calculations of the structural and electronic properties of ScxGa1-xN

    International Nuclear Information System (INIS)

    Moreno-Armenta, Maria Guadalupe; Mancera, Luis; Takeuchi, Noboru

    2003-01-01

    Using first principles total energy calculations within the the full-potential linearized augmented plane wave (FP-LAPW) method, we have investigated the structural and electronic properties of Sc x Ga 1-x N, with Sc concentrations varying from 0% up to 100%. In particular we have studied the relative stability of several configurations of Sc x Ga 1-x N in wurtzite-like structures (the ground state configuration of GaN), or in rocksalt-like structures (the ground state configuration of ScN). It is found that for Sc concentrations less than ∼65%, the favored structure is a wurtzite-like one, while for Sc concentrations greater than ∼65%, the favored structure is a NaCl-like structure. It is also found that for the wurtzite-like crystals, the fundamental gap is large and direct. For the rocksalt crystals the fundamental gap is small and indirect, but with an additional larger direct gap. In agreement with the experiments of Little and Kordesch [Appl. Phys. Lett. 78, 2891 (2001)] we found a decrease of the band gap with the increase of the Sc concentration. (Abstract Copyright [2003], Wiley Periodicals, Inc.)

  19. 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.

  20. The influence of the (n, 2n) and (n, {alpha}) reactions of beryllium on the neutron balance in a BeO or Be moderated reactor and its consequences on the long term reactivity changes; Influence des reactions (n, 2n) et (n, {alpha}) du beryllium sur le bilan neutronique d'un reacteur modere a l'oxyde de beryllium ou au beryllium. Consequences sur l'evolution a long terme de la reactivite

    Energy Technology Data Exchange (ETDEWEB)

    Sahai, K; Benoist, P; Horowitz, J [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

    1958-07-01

    The reaction probabilities in an infinite and homogeneous medium of BeO or Be have been calculated from neutron cross-section curves, for a neutron produced with an energy distribution similar to a fission spectrum; the calculation shows that, after several elastic collisions, the neutron has yet an appreciable probability to undergo a reaction, in spite of the energy degradation in the spectrum due to each collision. This degradation has been calculated, taking into account of anisotropy of the collisions. The gain of the reactivity in a reactor has been obtained after correcting these probabilities for the attenuation of the flux of fission neutrons due to the inelastic scattering in the uranium. Finally, the calculation shows that in a power reactor, this gain of reactivity is in practice destroyed in a few years by the accumulation of poisonous nuclei such as Li{sup 6} and He{sup 3} following (n, {alpha}) reaction. (author) [French] Les probabilites de reaction en milieu infini et homogene de glucine (BeO) ou de beryllium ont ete calculees a partir des courbes de section efficace pour un neutron naissant suivant un spectre de fission; le calcul montre qu'apres plusieurs diffusions elastiques le neutron a encore une probabilite appreciable de subir une reaction, malgre la degradation du spectre a chaque diffusion; cette degradation a ete calculee en tenant compte de l'anisotropie du choc. Le gain de reactivite dans un reacteur a ensuite ete obtenu en corrigeant les probabilites en milieu homogene de l'effet l'attenuation du flux des neutrons de fission par les chocs inelastiques dans les barres d'uranium. Enfin, le calcul montre que, dans un reacteur de puissance, ce gain de reactivite est pratiquement detruit en peu d'annees par l'accumulation de noyaux poisons Li{sup 6} et He{sup 3} consecutive a la reaction (n, {alpha}). (auteur)

  1. Structuralism.

    Science.gov (United States)

    Piaget, Jean

    Provided is an overview of the analytical method known as structuralism. The first chapter discusses the three key components of the concept of a structure: the view of a system as a whole instead of so many parts; the study of the transformations in the system; and the fact that these transformations never lead beyond the system but always…

  2. Optical and Structural Characterizations of GaN Nano structures

    International Nuclear Information System (INIS)

    Shekari, L.; Abu Hassan, H.; Thahab, S.M.

    2011-01-01

    We have grown wurtzite GaN nano wires (NWs) on polished silicon (Si) either with or without Au as catalyst, using commercial GaN powder by thermal evaporation in an atmosphere of argon (Ar) gas. Structural and optical characterizations were performed using high resolution X-ray diffraction (HR-XRD), scanning electron microscopy (SEM), photoluminescence (PL) and energy-dispersive X-ray spectroscopy (EDX) spectroscopy. Results indicate that the nano wires are of single-crystal hexagonal GaN and the nano wires on Si with Au catalyst are more oriented than those without Au catalyst; and using catalyst make the NWs grow much faster and quite well-ordered. The compositional quality of the grown nano wires on the substrates are mostly same, however the nano wires on the Au coated silicon are of low density, while the nano wires on the Si are of high density. (author)

  3. Electronic structure of layered ferroelectric high-k titanate Pr2Ti2O7

    Science.gov (United States)

    Atuchin, V. V.; Gavrilova, T. A.; Grivel, J.-C.; Kesler, V. G.; Troitskaia, I. B.

    2012-11-01

    The spectroscopic parameters and electronic structure of binary titanate Pr2Ti2O7 have been studied by IR-, Raman and X-ray photoelectron spectroscopy (XPS) for the powder sample prepared by solid state synthesis. The spectral features of valence band and all constituent element core levels have been considered. The Auger parameters of titanium and oxygen in Pr2Ti2O7 have been determined as αTi=872.8 and αO=1042.3 eV. Variations of cation-anion bond ionicity have been discussed using binding energy differences ΔTi=(BE O 1s-BE Ti 2p3/2)=71.6 eV and ΔPr=BE(Pr 3d5/2)-BE(O 1s)=403.8 eV as key parameters in comparison with those of other titanium- and praseodymium-bearing oxides.

  4. Hydrostatic Pressure and Built-In Electric Field Effects on the Donor Impurity States in Cylindrical Wurtzite GaN/AlxGa1−xN Quantum Rings

    Directory of Open Access Journals (Sweden)

    Guangxin Wang

    2015-01-01

    Full Text Available Within the framework of the effective mass approximation, the ground-state binding energy of a hydrogenic impurity is investigated in cylindrical wurtzite GaN/AlxGa1-xN strained quantum ring (QR by means of a variational approach, considering the influence of the applied hydrostatic pressure along the QR growth direction and the strong built-in electric field (BEF due to the piezoelectricity and spontaneous polarization. Numerical results show that the donor binding energy for a central impurity increases inchmeal firstly as the QR radial thickness (ΔR decreases gradually and then begins to drop quickly. In addition, the donor binding energy is an increasing (a decreasing function of the inner radius (height. It is also found that the donor binding energy increases almost linearly with the increment of the applied hydrostatic pressure. Moreover, we also found that impurity positions have an important influence on the donor binding energy. The physical reasons have been analyzed in detail.

  5. The structure and morphology of semiconductor nanocrystals

    Energy Technology Data Exchange (ETDEWEB)

    Kadavanich, Andreas V. [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry

    1997-11-01

    Colloidal semiconductor nanocrystals were studied using High Resolution Transmission Electron Microscopy (HRTEM). Organically capped nanocrystals were found to have faceted shapes consistent with Wulff polyhedra after the effects of capping ligands on surface energies were taken into account. The basic shape thus derived for wurtzite (WZ) structure CdSe nanocrystals capped by tri-octyl phosphine oxide (TOPO) was a truncated hexagonal prism, elongated alone the <001> axis with (100) and (002) facets. This structure has C{sub 3v} point group symmetry. The main defect in this structure is a stacking fault (a single layer of zinc blende type stacking), which does not significantly affect the shape (does not alter the point group).

  6. Electronic structure and optical properties of AIN under high pressure

    International Nuclear Information System (INIS)

    Li Zetao; Dang Suihu; Li Chunxia

    2011-01-01

    We have calculated the electronic structure and optical properties of Wurtzite structure AIN under different high pressure with generalized gradient approximation (GGA) in this paper. The total energy, density of state, energy band structure and optical absorption and reflection properties under high pressure are calculated. By comparing the changes of the energy band structure, we obtained AIN phase transition pressure for 16.7 GPa, which is a direct band structure transforming to an indirect band structure. Meanwhile, according to the density of states distribution and energy band structure, we analyzed the optical properties of AIN under high-pressure, the results showed that the absorption spectra moved from low-energy to high-energy. (authors)

  7. Die Bedeutung von Interleukon-1 beo der Entstehung der Knochenerosion

    Directory of Open Access Journals (Sweden)

    Graninger W

    2002-01-01

    Full Text Available Die chronische Polyarthritis ist eine immunmediierte entzündliche Erkrankung, die morphologisch durch eine Zerstörung der Gelenksstrukturen und des subchondralen Knochens charakterisiert ist. Obwohl schon in frühen Krankheitsstadien eine gelenksnahe Osteoporose im Nativröntgen sichtbar wird, ist die Richtigkeit der Diagnose radiologisch erst durch den Nachweis jener typischen Knochenzerstörung zu beweisen, die als Usur oder Erosion bezeichnet wird. An der Grenze zwischen dem entzündlichen Zellinfiltrat, das als Pannus makroskopisch und histologisch imponiert, und dem Gelenksknorpel (cartilage-pannus junction kommt es unter dem Einfluß aktivierter Synoviafibroblasten und ihrer Sekretionsprodukte zum Knorpelzelluntergang und zur Zerstörung der Knorpelmatrix. Gleichzeitig kommt es zur Aktivierung von Osteoklasten, die schließlich in der Entstehung der gelenksnahen Erosion und der subchondralen Knochenzysten resultiert.

  8. X-ray absorption in GaGdN: A study of local structure

    Science.gov (United States)

    Martínez-Criado, G.; Sancho-Juan, O.; Garro, N.; Sans, J. A.; Cantarero, A.; Susini, J.; Roever, M.; Mai, D.-D.; Bedoya-Pinto, A.; Malindretos, J.; Rizzi, A.

    2008-07-01

    In this study, we report on the incorporation of dilute Gd amounts into GaN films grown by molecular beam epitaxy. A combination of x-ray fluorescence with x-ray absorption spectroscopic techniques enabled us to examine not only the distribution of rare earth atoms in the GaN matrix but also the short-range structural order. Our results show Gd atoms in a trivalent state with tetrahedral coordination, thus substituting Ga in the wurtzite GaN structure.

  9. X-ray absorption in GaGdN: A study of local structure

    International Nuclear Information System (INIS)

    Martinez-Criado, G.; Sans, J. A.; Susini, J.; Sancho-Juan, O.; Cantarero, A.; Garro, N.; Roever, M.; Mai, D.-D.; Bedoya-Pinto, A.; Malindretos, J.; Rizzi, A.

    2008-01-01

    In this study, we report on the incorporation of dilute Gd amounts into GaN films grown by molecular beam epitaxy. A combination of x-ray fluorescence with x-ray absorption spectroscopic techniques enabled us to examine not only the distribution of rare earth atoms in the GaN matrix but also the short-range structural order. Our results show Gd atoms in a trivalent state with tetrahedral coordination, thus substituting Ga in the wurtzite GaN structure

  10. Effects of hydrostatic pressure on ionized donor bound exciton states in strained wurtzite GaN/Al{sub x}Ga{sub 1-x}N cylindrical quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Zheng Dongmei, E-mail: smdmzheng@163.com [College of Physics and Electromechanical Engineering, Sanming University, Sanming 365004 (China); Wang Zongchi; Xiao Boqi [College of Physics and Electromechanical Engineering, Sanming University, Sanming 365004 (China)

    2012-11-01

    Based on the effective-mass approximation and variational procedure, ionized donor bound exciton (D{sup +}, X) states confined in strained wurtzite (WZ) GaN/Al{sub x}Ga{sub 1-x}N cylindrical (disk-like) quantum dots (QDs) with finite-height potential barriers are investigated, with considering the influences of the built-in electric field (BEF), the biaxial strain dependence of material parameters and the applied hydrostatic pressure. The Schroedinger equation via the proper choice of the donor bound exciton trial wave function is solved. The behaviors of the binding energy of (D{sup +}, X) and the optical transition associated with (D{sup +}, X) are examined at different pressures for different QD sizes and donor positions. In our calculations, the effective masses of electron and hole, dielectric constants, phonon frequencies, energy gaps, and piezoelectric polarizations are taken into account as functions of biaxial strain and hydrostatic pressure. Our results show that the hydrostatic pressure, the QD size and the donor position have a remarkable influence on (D{sup +}, X) states. The hydrostatic pressure generally increases the binding energy of (D{sup +}, X). However, the binding energy tends to decrease for the QDs with large height and lower Al composition (x<0.3) if the donor is located at z{sub 0}{<=}0. The optical transition energy has a blue-shift (red-shift) if the hydrostatic pressure (QD height) increases. For the QDs with small height and low Al composition, the hydrostatic pressure dependence of the optical transition energy is more obvious. Furthermore, the relationship between the radiative decay time and hydrostatic pressure (QD height) is also investigated. It is found that the radiative decay time increases with pressure and the increment tendency is more prominent for the QDs with large height. The radiative decay time increases exponentially reaching microsecond order with increasing QD height. The physical reason has been analyzed in depth.

  11. Synthesis and characterization of porous structured ZnO thin film for dye sensitized solar cell applications

    Energy Technology Data Exchange (ETDEWEB)

    Marimuthu, T.; Anandhan, N., E-mail: anandhan-kn@rediffmail.com; Mummoorthi, M. [School of Physics, Alagappa University, Karaikudi – 630 003 (India); Dharuman, V. [Department of Bioelectronics and Biosensors, Alagappa University, Karaikudi – 630 003 (India)

    2016-05-23

    Zinc oxide (ZnO) and zinc oxide/eosin yellow (ZnO/EY) thin films were potentiostatically deposited onto fluorine doped tin oxide (FTO) glass substrate. Effect of eosin yellow dye on structural, morphological and optical properties was studied. X-ray diffraction patterns, micro Raman spectra and photoluminescence (PL) spectra reveal hexagonal wurtzite structure with less atomic defects in 101 plane orientation of the ZnO/EY film. Scanning electron microscopy (SEM) images show flower for ZnO and porous like structure for ZnO/EY thin film, respectively. DSSC was constructed and evaluated by measuring the current density verses voltage curve.

  12. Study of defects and vacancies in structural properties of Mn, co-doped oxides: ZnO

    Science.gov (United States)

    Kumar, Harish; Kaushik, A.; Alvi, P. A.; Dalela, B.; Dalela, S.

    2018-05-01

    The paper deals with the Structural properties on Mn, Co doped oxides ZnO samples using XRD, Positron Annihilation Lifetime (PAL) Spectra and Raman Spectra. The Mn, Co doped ZnO samples crystallize in a wurtzite structure without any impurity phases in XRD Spectra. The defect state of these samples has been investigated by using positron annihilation lifetime (PAL) spectroscopy technique in which all the relevant lifetime parameters are measured for all the spectra. The results are explained in the direction of doping concentration in these samples in terms of defects structure on Zn lattice site VZn and oxygen defects Vo.

  13. Studies on electronic structure of GaN(0001) surface

    CERN Document Server

    Xie Chang Kun; Xu Fa Qiang; Deng Rui; Liu Feng; Yibulaxin, K

    2002-01-01

    An electronic structure investigation on GaN(0001) is reported. The authors employ a full-potential linearized augmented plane-wave (FPLAPW) approach to calculate the partial density of state, which is in agreement with previous experimental results. The effects of the Ga3d semi-core levels on the electronic structure of GaN are discussed. The valence-electronic structure of the wurtzite GaN(0001) surface is investigated using synchrotron radiation excited angle-resolved photoemission spectroscopy. The bulk bands dispersion along GAMMA A direction in the Brillouin zones is measured using normal-emission spectra by changing photon-energy. The band structure derived from authors' experimental data is compared well with the results of authors' FPLAPW calculation. Furthermore, off-normal emission spectra are also measured along the GAMMA K and GAMMA M directions. Two surface states are identified, and their dispersions are characterized

  14. Electron transport in wurtzite InN

    Indian Academy of Sciences (India)

    InN transport; mobility; energy and momentum relaxation; impurity scattering. ... future generation solar cell because the nitride alloys can cover the whole ... We apply the ensemble Monte Carlo method to investigate the electron transport in.

  15. Structural, optoelectronic, luminescence and thermal properties of Ga-doped zinc oxide thin films

    International Nuclear Information System (INIS)

    Shinde, S.S.; Shinde, P.S.; Oh, Y.W.; Haranath, D.; Bhosale, C.H.; Rajpure, K.Y.

    2012-01-01

    Highlights: ► The ecofriendly deposition of Ga-doped zinc oxide. ► Influence of Ga doping onto physicochemical properties in aqueous media. ► Electron–phonon coupling by Raman. ► Chemical bonding structure and valence band analysis by XPS. - Abstract: Ga-doped ZnO thin films are synthesized by chemical spray pyrolysis onto corning glass substrates in aqueous media. The influence of gallium doping on to the photoelectrochemical, structural, Raman, XPS, morphological, optical, electrical, photoluminescence and thermal properties have been investigated in order to achieve good quality films. X-ray diffraction study depicts the films are polycrystalline and fit well with hexagonal (wurtzite) crystal structure with strong orientations along the (0 0 2) and (1 0 1) planes. Presence of E 2 high mode in Raman spectra indicates that the gallium doping does not change the wurtzite structure. The coupling strength between electron and LO phonon has experimentally estimated. In order to understand the chemical bonding structure and electronic states of the Ga-doped ZnO thin films XPS analysis have been studied. SEM images shows the films are adherent, compact, densely packed with hexagonal flakes and spherical grains. Optical transmittance and reflectance measurements have been carried out. Room temperature PL spectra depict violet, blue and green emission in deposited films. The specific heat and thermal conductivity study shows the phonon conduction behavior is dominant in these polycrystalline films.

  16. Electronic Structures of Strained InAs x P1-x by Density Functional Theory.

    Science.gov (United States)

    Lee, Seung Mi; Kim, Min-Young; Kim, Young Heon

    2018-09-01

    We investigated the effects of strain on the electronic structures of InAsxP1-x using quantum mechanical density functional theory calculations. The electronic band gap and electron effective mass decreased with the increase of the uniaxial tensile strain along the [0001] direction of wurtzite InAs0.75P0.25. Therefore, faster electron movements are expected. These theoretical results are in good agreement with the experimental measurements of InAs0.75P0.25 nanowire.

  17. Effects of tellurium concentration on the structure of melt-grown ZnSe crystals

    International Nuclear Information System (INIS)

    Atroshchenko, Lyubov V.; Galkin, Sergey N.; Rybalka, Irina A.; Voronkin, Evgeniy F.; Lalayants, Alexandr I.; Ryzhikov, Vladimir D.; Fedorov, Alexandr G.

    2005-01-01

    It has been shown that isovalent doping by tellurium positively affects the structural perfection of ZnSe crystals related to the completeness of the wurtzite-sphalerite phase transition. The optimum concentration range of tellurium in ZnSe crystals is 0.3-0.6 mass %. X-ray diffraction studies have shown that in ZnSe 1-x Te x crystals at tellurium concentrations below 0.3 mass % twinning and packing defects occur, while tellurium concentrations above 0.6 mass % lead to formation of tetragonal crystal lattice

  18. Nanoparticles of ZnO doped with Mn: structural and morphological characteristics

    Energy Technology Data Exchange (ETDEWEB)

    Bonifacio, Maria Aparecida Ribeiro; Lira, Helio de Lucena; Gama, Lucianna, E-mail: m_aparecidaribeiro@yahoo.com.br [Universidade Federal de Campina Grande (UFCG), PB (Brazil). Departamento de Engenharia de Materiais; Neiva, Laedna Souto [Universidade Federal do Cariri (UFCA), Juazeiro do Norte, CE (Brazil). Unidade Academica de Materiais; Kiminami, Ruth H. G. A. [Universidade Federal de Sao Carlos (USCar), SP (Brazil). Departamento de Engenharia de Materiais

    2017-07-15

    In this study, the effects of dopant concentrations on the structural and morphological characteristics of Zn{sub 1-x}Mn{sub x} O powders (x= 0.025, 0.05, 0.075, and 0.1 mole) synthesized by the Pechini method has been investigated. The powder was characterized by X-ray diffraction (XRD), Brunauer-Emmet-Teller (BET) specific surface, energy dispersive X-ray (EDX), scanning electron microscopy (SEM) and Spectroscopy with Fourier transform (FTIR). An XRD analysis of the powder showed the formation of ZnO phase with a typical single phase wurtzite structure. The EDX analysis revealed Mn incorporated in the ZnO structure. The particle size calculated by BET ranged from 24 to 63 nm, confirming the nanometric size of the powder particles. The SEM analysis revealed irregular shaped particle agglomerates and the presence of nanosheets. From FTIR it was confirmed the wurtzite structure in ZnO and ZnO nanoparticles doped with Mn. (author)

  19. Structural and electronic properties of ScxAl1−xN: First principles study

    International Nuclear Information System (INIS)

    Berkok, Houria; Tebboune, Abdelghani; Saim, Asmaa; Belbachir, Ahmed H

    2013-01-01

    The structural and electronic properties of Sc x Al 1−x N ternary semiconductor alloys are investigated in the rocksalt, zinc blend and wurtzite structures using the full potential linear muffin tin orbitals (FP-LMTO) method. The local density approximation (LDA) was used for the exchange and correlation energy density functional. In particular, the lattice constant, bulk modulus and band gap energies of ScN and AlN compounds and their ternary alloys Sc x Al 1−x N are calculated in rocksalt, zinc blend and wurtzite structures and discussed. A linear relationship has obtained for equilibrium lattice constants versus Sc concentration for rocksalt and zinc blend structures. The band gap is decreased with the increasing of Sc concentration in the rocksalt phase. For ZB-Sc x Al 1−x N, the band gap is the largest one at x=0.25 and changes from indirect to direct when x is more than 0.25

  20. Structural and optical properties of nano-structured CdS thin films prepared by chemical bath deposition

    Energy Technology Data Exchange (ETDEWEB)

    Bai, Rekha, E-mail: rekha.mittal07@gmail.com; Kumar, Dinesh; Chaudhary, Sujeet; Pandya, Dinesh K. [Thin Film Laboratory, Physics Department, Indian Institute of Technology Delhi, New Delhi-110016 (India)

    2016-05-06

    Cadmium sulfide (CdS) thin films have been deposited on conducting glass substrates by chemical bath deposition (CBD) technique. The effect of precursor concentration on the structural, morphological, compositional, and optical properties of the CdS films has been studied. Crystal structure of these CdS films is characterized by X-ray diffraction (XRD) and it reveals polycrystalline structure with mixture of cubic and wurtzite phases with grain size decreasing as precursor concentration is increased. Optical studies reveal that the CdS thin films have high transmittance in visible spectral region reaching 90% and the films possess direct optical band gap that decreases from 2.46 to 2.39 eV with decreasing bath concentration. Our study suggests that growth is nucleation controlled.

  1. Structural and optical properties of nano-structured CdS thin films prepared by chemical bath deposition

    International Nuclear Information System (INIS)

    Bai, Rekha; Kumar, Dinesh; Chaudhary, Sujeet; Pandya, Dinesh K.

    2016-01-01

    Cadmium sulfide (CdS) thin films have been deposited on conducting glass substrates by chemical bath deposition (CBD) technique. The effect of precursor concentration on the structural, morphological, compositional, and optical properties of the CdS films has been studied. Crystal structure of these CdS films is characterized by X-ray diffraction (XRD) and it reveals polycrystalline structure with mixture of cubic and wurtzite phases with grain size decreasing as precursor concentration is increased. Optical studies reveal that the CdS thin films have high transmittance in visible spectral region reaching 90% and the films possess direct optical band gap that decreases from 2.46 to 2.39 eV with decreasing bath concentration. Our study suggests that growth is nucleation controlled.

  2. Band Structure and Quantum Confined Stark Effect in InN/GaN superlattices

    DEFF Research Database (Denmark)

    Gorczyca, I.; Suski, T.; Christensen, Niels Egede

    2012-01-01

    InN/GaN superlattices offer an important way of band gap engineering in the blue-green range of the spectrum. This approach represents a more controlled method than the band gap tuning in quantum well systems by application of InGaN alloys. The electronic structures of short-period wurtzite InN/G...... wells and barriers one may tune band gaps over a wide spectral range, which provides flexibility in band gap engineering.......InN/GaN superlattices offer an important way of band gap engineering in the blue-green range of the spectrum. This approach represents a more controlled method than the band gap tuning in quantum well systems by application of InGaN alloys. The electronic structures of short-period wurtzite In......N/GaN(0001) superlattices are investigated, and the variation of the band gap with the thicknesses of the well and the barrier is discussed. Superlattices of the form mInN/nGaN with n ≥ m are simulated using band structure calculations in the Local Density Approximation with a semiempirical correction...

  3. Compton profiles and band structure calculations of CdS and CdTe

    International Nuclear Information System (INIS)

    Heda, N.L.; Mathur, S.; Ahuja, B.L.; Sharma, B.K.

    2007-01-01

    In this paper we present the isotropic Compton profiles of zinc-blende CdS and CdTe measured at an intermediate resolution of 0.39 a.u. using our 20 Ci 137 Cs Compton spectrometer. The electronic band structure calculations for both the zinc-blende structure compounds and also wurtzite CdS have been undertaken using various schemes of ab-initio linear combination of atomic orbitals calculations implemented in CRYSTAL03 code. The band structure and Mulliken's populations are reported using density functional scheme. In case of wurtzite CdS, our theoretical anisotropies in directional Compton profiles are compared with available experimental data. In case of both the zinc-blende compounds, the isotropic experimental profiles are found to be in better agreement with the present Hartree-Fock calculations. A study of the equal-valence-electron-density experimental profiles of zinc-blende CdS and CdTe shows that the CdS is more ionic than CdTe. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  4. Electronic structure of CdTe using GGA+USIC

    International Nuclear Information System (INIS)

    Menéndez-Proupin, E.; Amézaga, A.; Cruz Hernández, N.

    2014-01-01

    A simple method to obtain a gap-corrected band structure of cadmium telluride within density functional theory is presented. On-site Coulomb self-interaction-like correction potential has been applied to the 5p-shell of Te and the 4d-shell of Cd. The predicted physical properties are similar to or better than those obtained with hybrid functionals and at largely reduced computational cost. In addition to the corrected electronic structure, the lattice parameters and the bulk modulus are improved. The relative stabilities of the different phases (zincblende, wurtzite, rocksalt and cinnabar) are preserved. The formation energy of the cadmium vacancy remains close to the values obtained from hybrid functional calculations

  5. Theoretical prediction of low-density hexagonal ZnO hollow structures

    Energy Technology Data Exchange (ETDEWEB)

    Tuoc, Vu Ngoc, E-mail: tuoc.vungoc@hust.edu.vn [Institute of Engineering Physics, Hanoi University of Science and Technology, 1 Dai Co Viet Road, Hanoi (Viet Nam); Huan, Tran Doan [Institute of Materials Science, University of Connecticut, Storrs, Connecticut 06269-3136 (United States); Thao, Nguyen Thi [Institute of Engineering Physics, Hanoi University of Science and Technology, 1 Dai Co Viet Road, Hanoi (Viet Nam); Hong Duc University, 307 Le Lai, Thanh Hoa City (Viet Nam); Tuan, Le Manh [Hong Duc University, 307 Le Lai, Thanh Hoa City (Viet Nam)

    2016-10-14

    Along with wurtzite and zinc blende, zinc oxide (ZnO) has been found in a large number of polymorphs with substantially different properties and, hence, applications. Therefore, predicting and synthesizing new classes of ZnO polymorphs are of great significance and have been gaining considerable interest. Herein, we perform a density functional theory based tight-binding study, predicting several new series of ZnO hollow structures using the bottom-up approach. The geometry of the building blocks allows for obtaining a variety of hexagonal, low-density nanoporous, and flexible ZnO hollow structures. Their stability is discussed by means of the free energy computed within the lattice-dynamics approach. Our calculations also indicate that all the reported hollow structures are wide band gap semiconductors in the same fashion with bulk ZnO. The electronic band structures of the ZnO hollow structures are finally examined in detail.

  6. Effect of the electrochemical technique on nanocrystalline ZnO electrodeposition, its structural, morphological and photoelectrochemical properties

    Energy Technology Data Exchange (ETDEWEB)

    Chettah, Hamdane; Abdi, Djamila, E-mail: naimadjam@hotmail.com

    2013-06-30

    This article reports the influence of the electrochemical technique on the electrodeposition of nanoscopic zinc oxide from aqueous mixed bath of zinc nitrate and potassium chloride at 70 °C onto fluorine doped tin oxide coated glass substrates. ZnO thin films were elaborated via cyclic voltamperometry and chronoamperometry techniques. This study shows structural and morphological differences in films deposited according to both methods. Thin and adherent films obtained via cyclic voltamperometry have been obtained after 100 cycles, and those obtained using the chronoampermetric method grown at potential of − 1 V vs. Ag/AgCl during 1 h. The structural characterisation of such films was performed using X-ray diffraction, which showed the most important peaks of ZnO wurtzite structure with preferential orientation along the (002) axis for deposits obtained via cyclic voltamperometry presenting nanometric grain sizes (42 nm). Atomic force microscopy was used to study surface morphology and estimate the surface roughness factor for two deposits. Photoelectrochemical study indicates that both kinds of films had n-type electrical conductivity and presents high photoanodic-generated currents. - Highlights: • Zinc oxide films were electrodeposited on fluorine doped tin oxide substrates at 70 °C. • Two electrochemical techniques were used cyclic voltamperometry and chronoamperometry. • X-ray diffraction showed the most important peaks of ZnO wurtzite structure. • Preferential orientation along the (002) axis for cyclic voltamperometry films. • Deposits had n-type electrical conductivity and high photoanodic-generated currents.

  7. Structural, optical and magnetic properties of nanocrystalline Co-doped ZnO thin films grown by sol-gel

    Energy Technology Data Exchange (ETDEWEB)

    Kayani, Zohra Nazir; Shah, Iqra; Zulfiqar, Bareera; Sabah, Aneeqa [Lahore College for Women Univ., Lahore (Pakistan); Riaz, Saira; Naseem, Shahzad [Univ. of the Punjab, Lahore (Pakistan). Centre of Excellence in Solid State Physics

    2018-04-01

    Cobalt-doped ZnO thin films have been deposited using a sol-gel route by changing the number of coats on the substrate from 6 to 18. This project deals with various film thicknesses by increasing the number of deposited coats. The effect of thickness on structural, magnetic, surface morphology and optical properties of Co-doped ZnO thin film was studied. The crystal structure of the Co-doped ZnO films was investigated by X-ray diffraction. The films have polycrystalline wurtzite hexagonal structures. A Co{sup 2+} ion takes the place of a Zn{sup 2+} ion in the lattice without creating any distortion in its hexagonal wurtzite structure. An examination of the optical transmission spectra showed that the energy band gap of the Co-doped ZnO films increased from 3.87 to 3.97 eV with an increase in the number of coatings on the substrate. Ferromagnetic behaviour was confirmed by measurements using a vibrating sample magnetometer. The surface morphology of thin films was assessed by scanning electron microscope. The grain size on the surface of thin films increased with an increase in the number of coats.

  8. Growth, structure and phase transitions of epitaxial nanowires of III-V semiconductors

    International Nuclear Information System (INIS)

    Glas, F; Patriarche, G; Harmand, J C

    2010-01-01

    We review and illustrate the impact of TEM on the study of nanowires of non-nitride III-V semiconductors, with particular emphasis on the understanding of the thermodynamics and kinetics of their formation assisted by nano-sized catalyst particles. Besides providing basic information about the morphology of the nanowires and their growth rate as a function of diameter, TEM offers insights into the peculiar crystalline structure that they adopt. We discuss the formation of the unusual wurtzite hexagonal crystalline phase and that of planar stacking defects in these nanowires and show that they are kinetically controlled. We also demonstrate the transformation of wurtzite into cubic sphalerite upon epitaxial burying of the nanowires. Nanowires are particularly interesting in that they allow the fabrication of precisely positioned quantum dots with well-defined geometries. In this respect, we discuss the formation of strained quantum-size inclusions in nanowires, their critical dimensions and the kinetic and thermodynamic factors governing the changes of the crystalline structure that sometimes occur around a hetero-interface.

  9. Electronic structure and local distortions in epitaxial ScGaN films

    International Nuclear Information System (INIS)

    Knoll, S M; Zhang, S; Rovezzi, M; Joyce, T B; Moram, M A

    2014-01-01

    High energy resolution fluorescence-detected x-ray absorption spectroscopy and density functional theory calculations were used to investigate the local bonding and electronic structure of Sc in epitaxial wurtzite-structure Sc x Ga 1−x N films with x ≤ 0.059. Sc atoms are found to substitute for Ga atoms, accompanied by a local distortion involving an increase in the internal lattice parameter u around the Sc atoms. The local bonding and electronic structure at Sc are not affected strongly by the strain state or the defect microstructure of the films. These data are consistent with theoretical predictions regarding the electronic structure of dilute Sc x Ga 1−x N alloys. (paper)

  10. The Influence of Doping with Transition Metal Ions on the Structure and Magnetic Properties of Zinc Oxide Thin Films

    Directory of Open Access Journals (Sweden)

    Jenica Neamtu

    2014-01-01

    Full Text Available Zn1−xNixO (x=0.03÷0.10 and Zn1−xFexO (x=0.03÷0.15 thin films were synthesized by sol-gel method. The structure and the surface morphology of zinc oxide thin films doped with transition metal (TM ions have been investigated by X-ray diffraction (XRD and atomic force microscopy (AFM. The magnetic studies were done using vibrating sample magnetometer (VSM at room temperature. Experimental results revealed that the substitution of Ni ions in ZnO wurtzite lattice for the contents x=0.03÷0.10 (Ni2+ leads to weak ferromagnetism of thin films. For Zn1-xFexO with x=0.03÷0.05, the Fe3+ ions are magnetic coupling by superexchange interaction via oxygen ions in wurtzite structure. For x=0.10÷0.15 (Fe3+ one can observe the increasing of secondary phase of ZnFe2O4 spinel. The Zn0.9Fe0.1O film shows a superparamagnetic behavior due to small crystallite sizes and the net spin magnetic moments arisen from the interaction between the iron ions through an oxygen ion in the spinel structure.

  11. First-principles study of electronic and structural properties and examining the effect of pressure on structure and energy gap in In N phases

    International Nuclear Information System (INIS)

    Bouchani, A.; Arabi, H.; Abolhasani, M. R.

    2007-01-01

    The electronic and structural properties of both zinc-blende and wurtzite phases of In N were investigated by using full potential augmented plane wave method within density functional theory. For exchange correlation potential, local density approximation, generalized gradient approximation and an alternative form of generalized gradient approximation proposed by Engel and Vosko (EV-generalized gradient approximation ) have been used. Results obtained for band structure of these compounds have been compared with experimental results as well as other theoretical work and closer to experimental data. The lattice constants, bulk modulus are calculated for each of both phases. We have also investigated the structural transitions of In N and have calculated the transition pressure between zinc-blende and rock salt phases.

  12. 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.

  13. Structural and optical properties of magnetron sputtered MgxZn1-xO thin films

    International Nuclear Information System (INIS)

    Kumar, Sanjeev; Gupte, Vinay; Sreenivas, K

    2006-01-01

    Mg x Zn 1-x O (MZO) thin films prepared by an rf magnetron sputtering technique are reported. The films were grown at room temperature and at relatively low rf power of 50 W. MZO thin films were found to possess preferred c-axis orientation and exhibited hexagonal wurtzite structure of ZnO up to a Mg concentration of 42 mol%. A small variation in the c-axis lattice parameter of around 0.3% was observed with increasing Mg composition, showing the complete solubility of Mg in ZnO. The band gap of the MZO films in the wurtzite phase varied linearly with the Mg concentration and a maximum band gap ∼4.19 eV was achieved at x = 0.42. The refractive indices of the MgO films were found to decrease with increasing Mg content. The observed optical dispersion data are in agreement with the single oscillator model. A photoluminescence study revealed a blue shift in the near band edge emission peak with increasing Mg content in the MZO films. The results show the potential of MZO films in various opto-electronic applications

  14. LDA+U and tight-binding electronic structure of InN nanowires

    Science.gov (United States)

    Molina-Sánchez, A.; García-Cristóbal, A.; Cantarero, A.; Terentjevs, A.; Cicero, G.

    2010-10-01

    In this paper we employ a combined ab initio and tight-binding approach to obtain the electronic and optical properties of hydrogenated Indium nitride (InN) nanowires. We first discuss InN band structure for the wurtzite structure calculated at the LDA+U level and use this information to extract the parameters needed for an empirical tight-binging implementation. These parameters are then employed to calculate the electronic and optical properties of InN nanowires in a diameter range that would not be affordable by ab initio techniques. The reliability of the large nanowires results is assessed by explicitly comparing the electronic structure of a small diameter wire studied both at LDA+U and tight-binding level.

  15. Structure, magnetic, and electrical properties of Zn1-xMnxO material

    Science.gov (United States)

    Sebayang, P.; Hulu, S. F.; Nasruddin, Aryanto, D.; Kurniawan, C.; Subhan, A.; Sudiro, T.; Ginting, M.

    2017-07-01

    ZnO and MnO2 powder were synthesized using solid state reaction method to produce Zn1-xMnxO materials. Effect of dopant concentrations at the material of Zn1-xMnxO (x = 0.015, 0.02, 0.025) to the change of crystal structure, electrical and magnetic properties was studied. The X-ray diffraction (XRD) result of the samples that were doped with Mn showed a hexagonal wurtzite polycrystalline structure. The addition of Mn dopant resulting the decrease of lattice parameters and peaks intensity. The significant increase of the peak intensity occurred at x = 0.02, which also indicated an increase in the crystal quality of ZnO. The change of the ZnO structure affected the electrical and magnetic properties of the samples.

  16. Low-temperature growth of aligned ZnO nanorods: effect of annealing gases on the structural and optical properties.

    Science.gov (United States)

    Umar, Ahmad; Hahn, Yoon-Bong; Al-Hajry, A; Abaker, M

    2014-06-01

    Aligned ZnO nanorods were grown on ZnO/Si substrate via simple aqueous solution process at low-temperature of - 65 degrees C by using zinc nitrate and hexamethylenetetramine (HMTA). The detailed morphological and structural properties measured by FESEM, XRD, EDS and TEM confirmed that the as-grown nanorods are vertically aligned, well-crystalline possessing wurtzite hexagonal phase and grown along the [0001] direction. The room-temperature photoluminescence spectrum of the grown nanorods exhibited a strong and broad green emission and small ultraviolet emission. The as-prepared ZnO nanorods were post-annealed in nitrogen (N2) and oxygen (O2) environments and further characterized in terms of their morphological, structural and optical properties. After annealing the nanorods exhibit well-crystallinity and wurtzite hexagonal phase. Moreover, by annealing the PL spectra show the enhancement in the UV emission and suppression in the green emission. The presented results demonstrate that simply by post-annealing process, the optical properties of ZnO nanostructures can be controlled.

  17. Quantitative size-dependent structure and strain determination of CdSe nanoparticles using atomic pair distribution function analysis

    Energy Technology Data Exchange (ETDEWEB)

    Masadeh, A S; Bozin, E S; Farrow, C L; Paglia, G; Juhas, P; Billinge, S J. L.; Karkamkar, A; Kanatzidis, M G [Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824-1116 (United States); Department of Chemistry, Michigan State University, East Lansing, Michigan 48824-1116 (United States)

    2007-09-15

    The size-dependent structure of CdSe nanoparticles, with diameters ranging from 2 to 4 nm, has been studied using the atomic pair distribution function (PDF) method. The core structure of the measured CdSe nanoparticles can be described in terms of the wurtzite atomic structure with extensive stacking faults. The density of faults in the nanoparticles is {approx}50%. The diameter of the core region was extracted directly from the PDF data and is in good agreement with the diameter obtained from standard characterization methods, suggesting that there is little surface amorphous region. A compressive strain was measured in the Cd-Se bond length that increases with decreasing particle size being 0.5% with respect to bulk CdSe for the 2 nm diameter particles. This study demonstrates the size-dependent quantitative structural information that can be obtained even from very small nanoparticles using the PDF approach.

  18. The effect of laser irradiation on electrical and structural properties of ZnO thin films

    Directory of Open Access Journals (Sweden)

    P Kameli

    2013-03-01

    Full Text Available  In this paper, ZnO thin film was prepared by sol-gel process on glass substrates. The deposited films were dried at 100 and 240 ˚C and then annealed at 300, 400 and 500 ˚C. The two-probe measurement showed that resistance of as-prepared films is very high. The KrF excimer (λ=248 nm laser irradiation with 1000 pulses, frequency of 1 Hz and 90 mJ/cm2 energy on surface of film resulted in the reduction of the films electrical resistance. X-ray diffraction (XRD patterns confirmed the improved hexagonal wurtzite structure of film, and AFM and FE-SEM analyses showed regular and spherical grain was formed on the surface. The particle size was increased from ~10 to ~30 nm after leaser irradiation. Generally, it was showed that electrical, structural and morphological properties of films improve considerably by laser irradiation.

  19. Characterization of structural and electrical properties of ZnO tetrapods

    Science.gov (United States)

    Gu, Yu-Dong; Mai, Wen-Jie; Jiang, Peng

    2011-12-01

    ZnO tetrapods were synthesized by a typical thermal vapor-solid deposition method in a horizontal tube furnace. Structural characterization was carried out by transmission electron microscopy (TEM) and select-area electron diffraction (SAED), which shows the presence of zinc blende nucleus in the center of tetrapods while the four branches taking hexagonal wurtzite structure. The electrical transport property of ZnO tetrapods was investigated through an in-situ nanoprobe system. The three branches of a tetrapod serve as source, drain, and "gate", respectively; while the fourth branch pointing upward works as the force trigger by vertically applying external force downward. The conductivity of each branch of ZnO-tetrapods increases 3-4 times under pressure. In such situation, the electrical current through the branches of ZnO tetrapods can be tuned by external force, and therefore a simple force sensor based on ZnO tetrapods has been demonstrated for the first time.

  20. Effect of Cu-Dopant on the Structural, Magnetic and Electrical Properties of ZnO

    Science.gov (United States)

    Aryanto, D.; Kurniawan, C.; Subhan, A.; Sudiro, T.; Sebayang, P.; Ginting, M.; Siregar, S. M. K.; Nasruddin, M. N.

    2017-05-01

    Zn1- x Cu x O (x = 0, 2, 3, and 4 at.%) was synthesized by using solid-state reaction technique. The ZnO and CuO powders were mixed and then milled by using high-speed shaker mill. The influence of Cu dopants on the structure, magnetic, and electrical properties was investigated by using XRD, VSM, and I-V and C-V measurements. The XRD analysis showed that the Zn1- x Cu x O had hexagonal wurtzite polycrystalline. The diffraction intensity decreased and the peak position shifted directly to a higher 2θ angle with increasing the dopant concentration. Furthermore, the lattice parameters decreased when the ZnO was doped with x = 0.04, which indicated that the crystal structure changed. The increase of Cu dopants was believed to affect the magnetic and electrical properties of ZnO.

  1. Structural, Optical, and Vibrational Properties of ZnO Microrods Deposited on Silicon Substrate

    Science.gov (United States)

    Lahlouh, Bashar I.; Ikhmayies, Shadia J.; Juwhari, Hassan K.

    2018-03-01

    Zinc oxide (ZnO) microrod films deposited by spray pyrolysis on silicon substrate at 350 ± 5°C have been studied and evaluated, and compared with thin films deposited by electron beam to confirm the identity of the studied samples. The films were characterized using different techniques. The microrod structure was studied and confirmed by scanning electron microscopy. Fourier-transform infrared (FTIR) spectroscopy and x-ray diffraction analysis confirmed successful deposition of ZnO thin films with the expected wurtzite structure. Reflectance data showed a substantial drop across the whole studied wavelength range. The photoluminescence (PL) spectra of the studied samples showed a peak at ˜ 360 nm, representing a signature of ZnO. The shift in the PL peak position is due to defects and other species present in the films, as confirmed by FTIR and energy-dispersive x-ray spectroscopy results.

  2. A first principle study of band structure of III-nitride compounds

    Energy Technology Data Exchange (ETDEWEB)

    Ahmed, Rashid [Centre for High Energy Physics University of the Punjab, Lahore-54590 (Pakistan)]. E-mail: rasofi@hotmail.com; Akbarzadeh, H. [Department of Physics, Isfahan University of Technology, 841546 Isfahan (Iran, Islamic Republic of); Fazal-e-Aleem [Centre for High Energy Physics University of the Punjab, Lahore-54590 (Pakistan)

    2005-12-15

    The band structure of both phases, zinc-blende and wurtzite, of aluminum nitride, indium nitride and gallium nitride has been studied using computational methods. The study has been done using first principle full-potential linearized augmented plane wave (FP-LAPW) method, within the framework of density functional theory (DFT). For the exchange correlation potential, generalized gradient approximation (GGA) and an alternative form of GGA proposed by Engel and Vosko (GGA-EV) have been used. Results obtained for band structure of these compounds have been compared with experimental results as well as other first principle computations. Our results show a significant improvement over other theoretical work and are closer to the experimental data.

  3. Electronic structure of CdTe using GGA+U{sup SIC}

    Energy Technology Data Exchange (ETDEWEB)

    Menéndez-Proupin, E., E-mail: emenendez@uchile.cl [Departamento de Física, Facultad de Ciencias, Universidad de Chile, Las Palmeras 3425, 780-0003 Ñuñoa, Santiago (Chile); Instituto de Energía Solar and Dept. Tecnologías Especiales, E.T.S.I. Telecomunicación, Universidad Politécnica de Madrid (Spain); Amézaga, A. [Departamento de Física, Facultad de Ciencias, Universidad de Chile, Las Palmeras 3425, 780-0003 Ñuñoa, Santiago (Chile); Instituto de Ciencias Físicas y Matemáticas, Universidad Austral de Chile, Casilla 567, Valdivia (Chile); Cruz Hernández, N. [Departamento de Física Aplicada I, Escuela Técnica Superior de Ingeniería Informática, Universidad de Sevilla, Av. Reina Mercedes, 41012 Sevilla (Spain)

    2014-11-01

    A simple method to obtain a gap-corrected band structure of cadmium telluride within density functional theory is presented. On-site Coulomb self-interaction-like correction potential has been applied to the 5p-shell of Te and the 4d-shell of Cd. The predicted physical properties are similar to or better than those obtained with hybrid functionals and at largely reduced computational cost. In addition to the corrected electronic structure, the lattice parameters and the bulk modulus are improved. The relative stabilities of the different phases (zincblende, wurtzite, rocksalt and cinnabar) are preserved. The formation energy of the cadmium vacancy remains close to the values obtained from hybrid functional calculations.

  4. Structural and optical properties of magnetron sputtered Mg{sub x}Zn{sub 1-x}O thin films

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Sanjeev; Gupte, Vinay; Sreenivas, K [Department of Physics and Astrophysics, University of Delhi, Delhi-110007 (India)

    2006-04-05

    Mg{sub x}Zn{sub 1-x}O (MZO) thin films prepared by an rf magnetron sputtering technique are reported. The films were grown at room temperature and at relatively low rf power of 50 W. MZO thin films were found to possess preferred c-axis orientation and exhibited hexagonal wurtzite structure of ZnO up to a Mg concentration of 42 mol%. A small variation in the c-axis lattice parameter of around 0.3% was observed with increasing Mg composition, showing the complete solubility of Mg in ZnO. The band gap of the MZO films in the wurtzite phase varied linearly with the Mg concentration and a maximum band gap {approx}4.19 eV was achieved at x = 0.42. The refractive indices of the MgO films were found to decrease with increasing Mg content. The observed optical dispersion data are in agreement with the single oscillator model. A photoluminescence study revealed a blue shift in the near band edge emission peak with increasing Mg content in the MZO films. The results show the potential of MZO films in various opto-electronic applications.

  5. Structural, optical and magnetic characterization of Ru doped ZnO nanorods

    International Nuclear Information System (INIS)

    Kumar, Sanjeev; Kaur, Palvinder; Chen, C.L.; Thangavel, R.; Dong, C.L.; Ho, Y.K.; Lee, J.F.; Chan, T.S.; Chen, T.K.; Mok, B.H.; Rao, S.M.; Wu, M.K.

    2014-01-01

    Graphical abstract: Ruthenium (Ru = 0%, 1% and 2%) doped nano-crystalline zinc oxide (ZnO) nanorods were synthesized by using well-known sol–gel technique. X-ray diffraction (XRD) results show that Ru (0%, 1% and 2%) doped ZnO nanorods crystallized in the wurtzite structure having space group C 3v (P6 3 mc). Williamson and Hall plot reveal that in the nanoscale dimensions, incorporation of Ru induced the tensile strain in ZnO host matrix. Photoluminescence (PL) and Raman studies of Ru doped ZnO nanorods show the formation of singly ionized oxygen vacancies which may account for the observed room temperature ferromagnetism (RTFM) in 2% Ru doped ZnO. X-ray absorption spectroscopy (XAS) reveals that Ru replace the Zn atoms in the host lattice and maintain the crystal symmetry with slightly lattice distortion. Highlights: • Ru doped ZnO nanorods crystallized in the wurtzite structure having space group C 3v (P6 3 mc). • PL and Raman studies show the formation of singly ionized oxygen vacancies in 2% Ru doped ZnO. • XAS reveals that Ru replace the Zn atoms in the host lattice with slightly lattice distortion. • Doping of Ru in ZnO nanostructures gives rise to RTFM ordering. -- Abstract: Ruthenium (Ru = 0%, 1% and 2%) doped nano-crystalline zinc oxide (ZnO) nanorods were synthesized by using well-known sol–gel technique. X-ray diffraction (XRD) results show that Ru (0%, 1% and 2%) doped ZnO nanorods crystallized in the wurtzite structure having space group C 3v (P6 3 mc). Williamson and Hall plot reveal that in the nanoscale dimensions, incorporation of Ru induced the tensile strain in ZnO host matrix. Photoluminescence (PL) and Raman studies of Ru doped ZnO nanorods show the formation of singly ionized oxygen vacancies which may account for the observed room temperature ferromagnetism (RTFM) in 2% Ru doped ZnO. X-ray absorption spectroscopy (XAS) reveals that Ru replace the Zn atoms in the host lattice and maintain the crystal symmetry with slightly lattice

  6. Electronic structure, magnetic and structural properties of Ni doped ZnO nanoparticles

    International Nuclear Information System (INIS)

    Kumar, Shalendra; Vats, Prashant; Gautam, S.; Gupta, V.P.; Verma, K.D.; Chae, K.H.; Hashim, Mohd; Choi, H.K.

    2014-01-01

    Highlights: • XRD, and HR-TEM results show the single phase nature of Ni doped ZnO nanoparticles. • dc magnetization results indicate the RT-FM in Ni doped ZnO nanoparticles. • Ni L 3,2 edge NEXAFS spectra infer that Ni ions are in +2 valence state. • O K edge NEXAFS spectra show that O vacancy increases with Ni doping in ZnO. - Abstract: We report structural, magnetic and electronic structural properties of Ni doped ZnO nanoparticles prepared by auto-combustion method. The prepared nanoparticles were characterized by using X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM), near edge X-ray absorption fine structure (NEXAFS) spectroscopy, and dc magnetization measurements. The XRD and HR-TEM results indicate that Ni doped ZnO nanoparticles have single phase nature with wurtzite lattice and exclude the presence of secondary phase. NEXAFS measurements performed at Ni L 3,2 -edges indicates that Ni ions are in +2 valence state and exclude the presence of Ni metal clusters. O K-edge NEXAFS spectra indicate an increase in oxygen vacancies with Ni-doping, while Zn L 3,2 -edge show the absence of Zn-vacancies. The magnetization measurements performed at room temperature shows that pure and Ni doped ZnO exhibits ferromagnetic behavior

  7. The digital structural analysis of cadmium selenide crystals by a method of ion beam thinning for high resolution electron microscopy

    International Nuclear Information System (INIS)

    Kanaya, Koichi; Baba, Norio; Naka, Michiaki; Kitagawa, Yukihisa; Suzuki, Kunio

    1986-01-01

    A digital processing method using a scanning densitometer system for structural analysis of electron micrographs was successfully applied to a study of cadmium selenide crystals, which were prepared by an argon-ion beam thinning method. Based on Fourier techniques for structural analysis from a computer-generated diffractogram, it was demonstrated that when cadmium selenide crystals were sufficiently thin to display the higher order diffraction spots at a high resolution approaching the atomic level, they constitute an alternative hexagonal lattice of imperfect wurtzite phase from a superposition of individual harmonic images by the enhanced scattering amplitude and corrected phase. From the structural analysis data, a Fourier synthetic lattice image was reconstructed, representing the precise location and three-dimensional arrangement of each of the atoms in the unit cell. Extensively enhanced lattice defect images of dislocations and stacking faults were also derived and shown graphically. (author)

  8. Size-dependent structure of CdSe nanoclusters formed after ion implantation in MgO

    International Nuclear Information System (INIS)

    Huis, M.A. van; Veen, A. van; Schut, H.; Eijt, S.W.H.; Kooi, B.J.; Hosson, J.Th.M. de

    2005-01-01

    The band gap as well as the optical and structural properties of semiconductor CdSe nanoclusters change as a function of the nanocluster size. Embedded CdSe nanoclusters in MgO were created by means of sequential Cd and Se ion implantation followed by thermal annealing. Changes during annealing were monitored using optical absorption and positron annihilation spectroscopy. High-resolution TEM on cross-sections after annealing at a temperature of 1300 K showed that clusters with a size below 5 nm have the high-pressure rock-salt structure and are in a cube-on-cube orientation relation with MgO, whereas clusters larger than 5 nm adopt the stable wurtzite crystal structure and were observed in two different orientation relations with MgO

  9. Ab initio investigation of thermodynamic stability and structure of cell molecules B3N4H8 and Be4O4H8

    International Nuclear Information System (INIS)

    Minyaev, R.M.

    2000-01-01

    Ab initio calculation methods (RHF/6-31G, MP2(full)/6-31G and MP2(full)/6-311++G) ) are used to investigate thermodynamic stability, energy and structural characteristics of different position isomers of isoelectron B 3 N 4 H 8 (1) and Be 4 O 4 H 8 (2) systems with cubane structure. High thermodynamic stability of these system is shown. Decomposition of structure (1) into two 1,3,2,4-diazadiborethidine molecules or four molecules of iminoborane HBNH is an endothermal process and needs 10.1 (RHF/6-31G), 39/6 (MP2(full)/6-31G) Cal/mol and 140.6 (RHF/6-31G), 161.4 (MP2(full)/6-31G) Cal/mol accordingly. Decomposition of structure (2) into two 1,3,2,4-dioxydiberyllotidine or four molecules of HBeOH is an endothermal process too and needs 22.1 (RHF/6-31G), 39.8 (MP2(full)/6-31G) Cal/mol and 127.1(RHF/6-31G), 155.2 MP2(full)/6-31G) Cal/mol accordingly. Geometrical characteristics of simple BeH 2 , Be 2 , Be 2 H 2 , Be 2 H 4 , BeO, Be 2 O 2 molecules are calculated [ru

  10. Structural and optical properties of Co-doped ZnO nanocrystallites prepared by a one-step solution route

    International Nuclear Information System (INIS)

    Li Ping; Wang Sha; Li Jibiao; Wei Yu

    2012-01-01

    Zinc oxide (ZnO) nanocrystallites with different Co-doping levels were successfully synthesized by a simple one-step solution route at low temperature (95 deg. C) in this study. The structure and morphology of the samples thus obtained were characterized by XRD, EDS, XPS and FESEM. Results show that cobalt ions, in the oxidation state of Co 2+ , replace Zn 2+ ions in the ZnO lattice without changing its wurtzite structure. The dopant content varies from 0.59% to 5.39%, based on Co-doping levels. The pure ZnO particles exhibit well-defined 3D flower-like morphology with an average size of 550 nm, while the particles obtained after Co-doping are mostly cauliflower-like nanoclusters with an average size of 120 nm. Both the flower-like pure ZnO and the cauliflower-like Co:ZnO nanoclusters are composed of densely arrayed nanorods. The optical properties of the ZnO nanocrystallites following Co-doping were also investigated by UV-Visible absorption and Photoluminescence spectra. Our results indicate that Co-doping can change the energy-band structure and effectively adjust the luminescence properties of ZnO nanocrystallites. - Highlights: → Co-doped ZnO nanocrystallites were synthesized via a simple one-step solution route. → Co 2+ ions incorporated into the ZnO lattice without changing its wurtzite structure. → Co-doping changed the energy band structure of ZnO. → Co-doping effectively adjusted the luminescence properties of ZnO nanocrystallites.

  11. Structural and optical properties of Co-doped ZnO nanocrystallites prepared by a one-step solution route

    Energy Technology Data Exchange (ETDEWEB)

    Li Ping, E-mail: lipingchina@yahoo.com.cn [Provincial Key Laboratory of Inorganic Nanomaterials, School of Chemistry and Materials Science, Hebei Normal University, 113 Yuhua Road, Shijiazhuang 050016, Hebei (China); Wang Sha; Li Jibiao; Wei Yu [Provincial Key Laboratory of Inorganic Nanomaterials, School of Chemistry and Materials Science, Hebei Normal University, 113 Yuhua Road, Shijiazhuang 050016, Hebei (China)

    2012-01-15

    Zinc oxide (ZnO) nanocrystallites with different Co-doping levels were successfully synthesized by a simple one-step solution route at low temperature (95 deg. C) in this study. The structure and morphology of the samples thus obtained were characterized by XRD, EDS, XPS and FESEM. Results show that cobalt ions, in the oxidation state of Co{sup 2+}, replace Zn{sup 2+} ions in the ZnO lattice without changing its wurtzite structure. The dopant content varies from 0.59% to 5.39%, based on Co-doping levels. The pure ZnO particles exhibit well-defined 3D flower-like morphology with an average size of 550 nm, while the particles obtained after Co-doping are mostly cauliflower-like nanoclusters with an average size of 120 nm. Both the flower-like pure ZnO and the cauliflower-like Co:ZnO nanoclusters are composed of densely arrayed nanorods. The optical properties of the ZnO nanocrystallites following Co-doping were also investigated by UV-Visible absorption and Photoluminescence spectra. Our results indicate that Co-doping can change the energy-band structure and effectively adjust the luminescence properties of ZnO nanocrystallites. - Highlights: > Co-doped ZnO nanocrystallites were synthesized via a simple one-step solution route. > Co{sup 2+} ions incorporated into the ZnO lattice without changing its wurtzite structure. > Co-doping changed the energy band structure of ZnO. > Co-doping effectively adjusted the luminescence properties of ZnO nanocrystallites.

  12. Electronic structure of layered ferroelectric high-k titanate Pr{sub 2}Ti{sub 2}O{sub 7}

    Energy Technology Data Exchange (ETDEWEB)

    Atuchin, V.V., E-mail: atuchin@thermo.isp.nsc.ru [Laboratory of Optical Materials and Structures, Institute of Semiconductor Physics, SB RAS, Novosibirsk 90, 630090 (Russian Federation); Gavrilova, T.A. [Laboratory of Nanodiagnostics and Nanolithography, Institute of Semiconductor Physics, SB RAS, Novosibirsk 90, 630090 (Russian Federation); Grivel, J.-C. [Materials Research Division, National Laboratory for Sustainable Energy, Technical University of Denmark, Frederiksborgvej 399, DK-4000, Roskilde (Denmark); Kesler, V.G. [Laboratory of Physical Bases of Integrated Microelectronics, Institute of Semiconductor Physics, SB RAS, Novosibirsk 90, 630090 (Russian Federation); Troitskaia, I.B. [Laboratory of Optical Materials and Structures, Institute of Semiconductor Physics, SB RAS, Novosibirsk 90, 630090 (Russian Federation)

    2012-11-15

    The spectroscopic parameters and electronic structure of binary titanate Pr{sub 2}Ti{sub 2}O{sub 7} have been studied by IR-, Raman and X-ray photoelectron spectroscopy (XPS) for the powder sample prepared by solid state synthesis. The spectral features of valence band and all constituent element core levels have been considered. The Auger parameters of titanium and oxygen in Pr{sub 2}Ti{sub 2}O{sub 7} have been determined as {alpha}{sub Ti}=872.8 and {alpha}{sub O}=1042.3 eV. Variations of cation-anion bond ionicity have been discussed using binding energy differences {Delta}{sub Ti}=(BE O 1s-BE Ti 2p{sub 3/2})=71.6 eV and {Delta}{sub Pr}=BE(Pr 3d{sub 5/2})-BE(O 1s)=403.8 eV as key parameters in comparison with those of other titanium- and praseodymium-bearing oxides. Highlights: Black-Right-Pointing-Pointer Solid state synthesis of polar titanate Pr{sub 2}Ti{sub 2}O{sub 7}. Black-Right-Pointing-Pointer Structural and spectroscopic properties and electronic structure determination. Black-Right-Pointing-Pointer Ti-O and Pr-O bonding analysis using Ti 2p{sub 3/2}, Pr 3d{sub 5/2} and O 1s core levels.

  13. Green synthesis of ZnO nanoparticles by Aspalathus linearis: Structural & optical properties

    International Nuclear Information System (INIS)

    Diallo, A.; Ngom, B.D.; Park, E.; Maaza, M.

    2015-01-01

    This contribution reports for the 1st time on the synthesis and the main physical properties of ZnO nanoparticles synthesized by an entirely green physical-chemistral process using Aspalathus linearis's natural extract as an efficient reduction/oxidizing agent. Their structural and optical properties by electron microscopy, X-rays diffraction, Raman and X-rays photoemission spectroscopies as well as room temperature photoluminescence are reported. - Highlights: • 1st time report on synthesis of ZnO nanoparticles by a green process via Aspalathus linearis extract. • A. linearis's natural extract was used as an effective reduction/oxidizing agent. • Wurtzite nature of ZnO nanoparticles was confirmed via XRD, Raman, XPS and PL

  14. Green synthesis of ZnO nanoparticles by Aspalathus linearis: Structural & optical properties

    Energy Technology Data Exchange (ETDEWEB)

    Diallo, A.; Ngom, B.D. [UNESCO-UNISA Africa Chair in Nanosciences-Nanotechnology, College of Graduate Studies, University of South Africa, Muckleneuk Ridge, PO Box 392, Pretoria (South Africa); Nanosciences African Network (NANOAFNET), iThemba LABS-National Research Foundation, 1 Old Faure road, Somerset West 7129, PO Box 722, Somerset West, Western Cape (South Africa); Park, E. [UNESCO-UNISA Africa Chair in Nanosciences-Nanotechnology, College of Graduate Studies, University of South Africa, Muckleneuk Ridge, PO Box 392, Pretoria (South Africa); Nanosciences African Network (NANOAFNET), iThemba LABS-National Research Foundation, 1 Old Faure road, Somerset West 7129, PO Box 722, Somerset West, Western Cape (South Africa); Nelson Mandela African Institute for Science & Technology, Arusha (Tanzania, United Republic of); Maaza, M., E-mail: Maaza@tlabs.ac.za [UNESCO-UNISA Africa Chair in Nanosciences-Nanotechnology, College of Graduate Studies, University of South Africa, Muckleneuk Ridge, PO Box 392, Pretoria (South Africa); Nanosciences African Network (NANOAFNET), iThemba LABS-National Research Foundation, 1 Old Faure road, Somerset West 7129, PO Box 722, Somerset West, Western Cape (South Africa)

    2015-10-15

    This contribution reports for the 1st time on the synthesis and the main physical properties of ZnO nanoparticles synthesized by an entirely green physical-chemistral process using Aspalathus linearis's natural extract as an efficient reduction/oxidizing agent. Their structural and optical properties by electron microscopy, X-rays diffraction, Raman and X-rays photoemission spectroscopies as well as room temperature photoluminescence are reported. - Highlights: • 1st time report on synthesis of ZnO nanoparticles by a green process via Aspalathus linearis extract. • A. linearis's natural extract was used as an effective reduction/oxidizing agent. • Wurtzite nature of ZnO nanoparticles was confirmed via XRD, Raman, XPS and PL.

  15. Compositional and structural properties of pulsed laser-deposited ZnS:Cr films

    Science.gov (United States)

    Nematollahi, Mohammadreza; Yang, Xiaodong; Seim, Eivind; Vullum, Per Erik; Holmestad, Randi; Gibson, Ursula J.; Reenaas, Turid W.

    2016-02-01

    We present the properties of Cr-doped zinc sulfide (ZnS:Cr) films deposited on Si(100) by pulsed laser deposition. The films are studied for solar cell applications, and to obtain a high absorption, a high Cr content (2.0-5.0 at.%) is used. It is determined by energy-dispersive X-ray spectroscopy that Cr is relatively uniformly distributed, and that local Cr increases correspond to Zn decreases. The results indicate that most Cr atoms substitute Zn sites. Consistently, electron energy loss and X-ray photoelectron spectroscopy showed that the films contain mainly Cr2+ ions. Structural analysis showed that the films are polycrystalline and textured. The films with ~4 % Cr are mainly grown along the hexagonal [001] direction in wurtzite phase. The average lateral grain size decreases with increasing Cr content, and at a given Cr content, increases with increasing growth temperature.

  16. Comparative study of Ni and Cu doped ZnO nanoparticles: Structural and optical properties

    Science.gov (United States)

    Thakur, Shaveta; Thakur, Samita; Sharma, Jyoti; Kumar, Sanjay

    2018-05-01

    Nanoparticles of undoped and doped (0.1 M Ni2+ and Cu2+) ZnO are synthesized using chemical precipitation method. The crystallite size, morphology, chemical bonding and optical properties of as prepared nanoparticles are determined by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and UV-visible spectra. XRD analysis shows that the prepared samples are single phase and have hexagonal wurtzite structure. The crystallite size of the doped and undoped nanoparticles is determined using Scherrer method. The crystallite size is found to be increased with concentration of nickel and copper. All stretching and vibrational bands are observed at their specific positions through FTIR. The increase in band gap can be attributed to the different chemical nature of dopant and host cation.

  17. Doping dependent room-temperature ferromagnetism and structural properties of dilute magnetic semiconductor ZnO:Cu2+ nanorods

    International Nuclear Information System (INIS)

    Sharma, Prashant K.; Dutta, Ranu K.; Pandey, Avinash C.

    2009-01-01

    Copper doped ZnO nanoparticles were synthesized by the chemical technique based on the hydrothermal method. The crystallite structure, morphology and size were determined by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM) for different doping percentages of Cu 2+ (1-10%). TEM/SEM images showed formation of uniform nanorods, the aspect ratio of which varied with doping percentage of Cu 2+ . The wurtzite structure of ZnO gradually degrades with the increasing Cu 2+ doping concentration and an additional CuO associated diffraction peak was observed above 8% of Cu 2+ doping. The change in magnetic behavior of the nanoparticles of ZnO with varying Cu 2+ doping concentrations was investigated using a vibrating sample magnetometer (VSM). Initially these nanoparticles showed strong room-temperature ferromagnetic behavior, however at higher doping percentage of copper the ferromagnetic behavior was suppressed and paramagnetic nature was enhanced.

  18. Effect of nickel doping concentration on structural and magnetic properties of ultrafine diluted magnetic semiconductor ZnO nanoparticles

    International Nuclear Information System (INIS)

    Sharma, Prashant K.; Dutta, Ranu K.; Pandey, Avinash C.

    2009-01-01

    The ZnO:Ni 2+ nanoparticles of mean size 2-12 nm were synthesized at room temperature by the simple co-precipitation method. The crystallite structure, morphology and size were determined by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). The wurtzite structure of ZnO gradually degrades with the increasing Ni doping concentration and an additional NiO-associated diffraction peak was observed above 15% of Ni 2+ doping. The change in magnetic behavior of the nanoparticles of ZnO with varying Ni 2+ doping concentration was investigated using a vibrating sample magnetometer (VSM). Initially, these nanoparticles showed strong ferromagnetic behavior, however, at higher doping percentage of Ni 2+ , the ferromagnetic behavior was suppressed and paramagnetic nature was observed. The enhanced antiferromagnetic interaction between neighboring Ni-Ni ions suppressed the ferromagnetism at higher doping concentrations of Ni 2+ .

  19. Tuning effect of polysaccharide Chitosan on structural, morphological, optical and photoluminescence properties of ZnO nanoparticles

    Science.gov (United States)

    Magesh, G.; Bhoopathi, G.; Nithya, N.; Arun, A. P.; Ranjith Kumar, E.

    2018-05-01

    Chitosan/ZnO nanocomposites was synthesized by in-situ chemical precipitation method. The effect of polysaccharide Chitosan concentration (0.1 g, 0.5 g, 1 g and 3 g) was investigated by X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM) with Energy dispersive spectroscopy (EDX), High Resolution Transmission Electron Microscopy (HRTEM), UV-visible (UV), Fourier Transform Infrared (FTIR) and Photoluminescence Spectroscopy (PL). XRD pattern confirms the hexagonal wurtzite structure of the Chitosan/ZnO nanocomposites. The structural morphology and the elemental composition of the samples were analysed by FESEM and EDX respectively. From TEM analysis, it is observed that the particles in spindle shape morphology with average particle size ranges 10-20 nm. UV-Vis analysis reveals that the Chitosan concentration affect the absorption band edge and shift towards lower wavelength. The oxygen vacancy induced photoluminescence of ZnO nanoparticles was observed and its intensity decreases by tuning the Chitosan concentration.

  20. Investigation of the near-surface structures of polar InN films by chemical-state-discriminated hard X-ray photoelectron diffraction

    International Nuclear Information System (INIS)

    Yang, A. L.; Yamashita, Y.; Kobata, M.; Yoshikawa, H.; Sakata, O.; Kobayashi, K.; Matsushita, T.; Píš, I.; Imura, M.; Yamaguchi, T.; Nanishi, Y.

    2013-01-01

    Near-surface structures of polar InN films were investigated by laboratory-based hard X-ray photoelectron diffraction (HXPD) with chemical-state-discrimination. HXPD patterns from In 3d 5/2 and N 1s core levels of the In-polar and N-polar InN films were different from each other and compared with the simulation results using a multiple-scattering cluster model. It was found that the near-surface structure of the In-polar InN film was close to the ideal wurtzite structure. On the other hand, on the N-polar InN film, defects-rich surface was formed. In addition, the existence of the In-polar domains was observed in the HXPD patterns.

  1. The structural, electrical and optical properties of Mg-doped ZnO with different interstitial Mg concentration

    Energy Technology Data Exchange (ETDEWEB)

    Hu, Yonghong, E-mail: hchyh@njust.edu.cn [School of Nuclear Technology and Chemistry & Biology, Hubei University of Science and Technology, Xianning 437100 (China); Institute of Optoelectronics & Nanomaterials, College of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094 (China); Zeng, Haibo [Institute of Optoelectronics & Nanomaterials, College of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094 (China); Du, Jifu [School of Nuclear Technology and Chemistry & Biology, Hubei University of Science and Technology, Xianning 437100 (China); Hu, Ziyu [Beijing Computational Science Research Center, Beijing 100084 (China); Zhang, Shengli [Institute of Optoelectronics & Nanomaterials, College of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094 (China)

    2016-10-01

    Through first principle calculations, we studied the structural, electronic and optical properties of ZnO doped by interstitial Mg. With the increase of Mg content (x), the derivations of lattice parameters from the wurtzite ZnO become more and more significant. The Mg-doped ZnO with x below 15.79% is found to be n-type semiconductor. The minimum of energy band gap and light transmittance in high energy region (7.5–25 eV) decrease while the conductivity and refractive index increase with increasing x. Further increasing x up to 20%, the Mg-doped ZnO is found to be direct-band-gap semiconductor with great structural derivation from wurtzite phase. The light transmittance increases while the refractive index decreases with the increase of x due to the change of geometry and electronic structure. So, it’s concluded that the electronic and optical properties of ZnO doped by interstitial Mg may be greatly influenced by Mg content. - Graphical abstract: The minimum of energy gap decreases while the corresponding relative number of electrons into the conduction bands increases when the interstitial Mg content x in Mg-doped ZnO increases (0 ≤ x ≤ 15.79%). - Highlights: • The energy band gap decreases with the increase of interstitial Mg content from 5.88% to 15.79%. • The conductivity increases with the increase of interstitial Mg content from 5.88% to 15.79%. • The Mg{sub x}Zn{sub 1-x}O (interstitial Mg content x= 20%) is found to be a direct-band-gap semiconductor. • The light transmittance decreases with the increase of interstitial Mg content from 5.88% to 15.79%. • The refractive index increases with the increase of interstitial Mg content from 5.88% to 15.79%.

  2. Structure and defect studies of In2O3:Zn,Zr for higher stability TCO

    Science.gov (United States)

    Herwadkar, Aditi; Kim, Kwiseon

    2010-03-01

    The defects structures among the transparent conducting oxides (TCO) plays a major role in determining stability of the oxide over a temperature range and in tuning electrical and optical properties for the different TCO applications In2O3 crystallizes in the cubic bixbyite structure. The structure can be derived from the related fluorite structure by removing one fourth of the anions and allowing for small shifts of the ionic positions. In2O3 has two non-equivalent six-fold coordinated cation sites. For one of the sites, the cation is bounded by two structural vacancy along the body diagonal and for the other non-equivalent site the vacancies lie along the face diagonal. These vacancies are actually empty oxygen vacancy positions. Indium is in +3 charge state. ZnO on the other hand crystallizes to form wurtzite structure with four-fold coordination for Zn and is in +2 charge state where as the crystal structure of ZrO is rulite with Zr in +4 charge state and is four fold coordinated. Co-doping of Zn and Zr with each substituting the In atom satisfies the octet rule and is lower in energy then the individual substitutions with overall neutrality. The formation enthalpy as a function of pair (Zn, Zr) shows a minimum at experimental composition of In2(Zn,Zr)3O24. We in this work present the electronic structure optimization and study the defect states in this material.

  3. Influence of the precursors in the morphology, structure, vibrational order and optical gap of nano structured Zn O

    Energy Technology Data Exchange (ETDEWEB)

    Jurado, J. F.; Londono C, A.; Jurado L, F. F.; Romero S, J. D., E-mail: jfjurado@unal.edu.co [Universidad Nacional de Colombia, Laboratorio de Propiedades Termicas Dielectricas de Compositos, A. A. 127, Manizales (Colombia)

    2014-07-01

    The synthesis of Zn O by reaction in solid state from two precursor salts (zinc acetate and zinc sulfate), presented significant differences concerning morphology, structure, vibrational order and optical gap. As well as covering in the size of the compounds, a homogeneous distribution of nanoparticles of 21±3 nm and micro stars of 1.03±0.19 μm respectively. The Zn O showed a structural phase with a vibrational state of the hexagonal type (wurtzite). The variation in the morphology due to the precursor is attributed to the disorder within of lattice, which contributes to vibrational changes and is correlated to the degrees of freedom of molecules. Measurements of UV-Vis of nanoparticles displayed a band gap (E{sub g}) lower than the one reported for the bulk material. The structural characterization of the compounds was carried out by using a X-ray Bruker D8 Advance diffractometer. The vibrational order was assessed throughout micro-Raman with a monochromatic radiation source of 473 nm). (Author)

  4. Investigation on structural and electrical properties of Fe doped ZnO nanoparticles synthesized by solution combustion method

    International Nuclear Information System (INIS)

    Ram, Mast; Bala, Kanchan; Sharma, Hakikat; Kumar, Arun; Negi, N. S.

    2016-01-01

    In the present study, nanoparticles of Fe doped zinc oxide (ZnO) [Zn_1_-_xFe_xO where x=0.0, 0.01, 0.02, 0.03 and 0.05] were prepared by cost effective solution combustion method. The powder X-ray diffractometry confirms the formation of single phase wurtzite structure. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to investigate the micrsostructure of Fe-doped ZnO nanoparticles. The DC electrical conductivity was found to increase with temperature and measurement was carried out in the temperature range of 300-473K. DC electrical conductivity increases with temperature and decreases with Fe doping concentration.

  5. Structural, magnetic and electronic structure properties of Co doped ZnO nanoparticles

    International Nuclear Information System (INIS)

    Kumar, Shalendra; Song, T.K.; Gautam, Sanjeev; Chae, K.H.; Kim, S.S.; Jang, K.W.

    2015-01-01

    Highlights: • XRD and HR-TEM results show the single phase nature of Co doped ZnO nanoparticles. • XMCD and dc magnetization results indicate the RT-FM in Co doped ZnO nanoparticles. • Co L 3,2 NEXAFS spectra infer that Co ions are in 2+ valence state. • O K edge NEXAFS spectra show that O vacancy increases with Co doping in ZnO. - Abstract: We reported structural, magnetic and electronic structure studies of Co doped ZnO nanoparticles. Doping of Co ions in ZnO host matrix has been studied and confirmed using various methods; such as X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersed X-ray (EDX), high resolution transmission electron microscopy (HR-TEM), Fourier transform infrared spectroscopy (FT-IR), near edge X-ray absorption fine structure (NEXAFS) spectroscopy, magnetic hysteresis loop measurements and X-ray magnetic circular dichroism (XMCD). From the XRD and HR-TEM results, it is observed that Co doped ZnO nanoparticles have single phase nature with wurtzite structure and exclude the possibility of secondary phase formation. FE-SEM and TEM micrographs show that pure and Co doped nanoparticles are nearly spherical in shape. O K edge NEXAFS spectra indicate that O vacancies increase with Co doping. The Co L 3,2 edge NEXAFS spectra revealed that Co ions are in 2+ valence state. DC magnetization hysteresis loops and XMCD results clearly showed the intrinsic origin of temperature ferromagnetism in Co doped ZnO nanoparticles

  6. Investigation on the structural changes of ZnO:Er:Yb thin film during laser annealing to fabricate a transparent conducting upconverter

    Energy Technology Data Exchange (ETDEWEB)

    Lluscà, Marta, E-mail: marta.llusca@gmail.com [Department of Applied Physics, Universitat de Barcelona, 08028 Barcelona (Spain); Future Industries Institute, University of South Australia, Mawson Lakes, 5095 South Australia (Australia); López-Vidrier, Julian [Department of Electronics, Universitat de Barcelona, 08028 Barcelona (Spain); IMTEK, Faculty of Engineering, Albert-Ludwigs-University Freiburg, Georges-Köhler-Allee 103, 79110 Freiburg (Germany); Lauzurica, Sara; Canteli, David; Sánchez-Aniorte, Maria I.; Molpeceres, Carlos [Centro Láser, Universidad Politécnica de Madrid, 28031 Madrid (Spain); Antony, Aldrin [Department of Applied Physics, Universitat de Barcelona, 08028 Barcelona (Spain); Indian Institute of Technology Bombay, 400076 Mumbai (India); Hernández, Sergi [Department of Electronics, Universitat de Barcelona, 08028 Barcelona (Spain); Alcobé, Xavier [Unitat de Difracció de Raigs X, Centres Científics i Tecnològics, Universitat de Barcelona, 08028 Barcelona (Spain); Garrido, Blas [Department of Electronics, Universitat de Barcelona, 08028 Barcelona (Spain); Bertomeu, Joan [Department of Applied Physics, Universitat de Barcelona, 08028 Barcelona (Spain)

    2017-05-15

    A transparent and conducting ZnO:Er:Yb thin film with upconversion properties has been achieved after being annealed with continuous laser radiation just before the ablation point of the material. This work demonstrates that the laser energy preserves the conductivity of the film and at the same time creates an adequate surrounding for Er and Yb to produce visible upconversion at 660, 560, 520, and 480 nm under 980 nm laser excitation. The relation between the structural, electrical and upconversion properties is discussed. It is observed that the laser energy melts part of the material, which recrystallizes creating rare earth oxides and two different wurtzite structures, one with substitutional rare earths and oxygen vacancies (responsible for the conductivity) and the other without substitutional rare earth ions (responsible for the upconversion emission).

  7. Effect of Ni doping on structural and optical properties of Zn{sub 1−x}Ni{sub x}O nanopowder synthesized via low cost sono-chemical method

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Budhendra, E-mail: bksingh@ua.pt [TEMA-NRD, Mechanical Engineering Department, Aveiro Institute of Nanotechnology (AIN), University of Aveiro, 3810-193 Aveiro (Portugal); Kaushal, Ajay, E-mail: ajay.kaushal@ua.pt [Department of Ceramic and Glass Engineering, CICECO, University of Aveiro, 3810-193 Aveiro (Portugal); Bdikin, Igor [TEMA-NRD, Mechanical Engineering Department, Aveiro Institute of Nanotechnology (AIN), University of Aveiro, 3810-193 Aveiro (Portugal); Venkata Saravanan, K. [Department of Physics, School of Basic and Applied Sciences, Central University of Tamil Nadu, Thiruvarur 610101 (India); Ferreira, J.M.F. [Department of Ceramic and Glass Engineering, CICECO, University of Aveiro, 3810-193 Aveiro (Portugal)

    2015-10-15

    Highlights: • Pure and Ni doped ZnO nanopowders were synthesized by low cost sonochemical method. • The optical properties of Zn{sub 1−x}Ni{sub x}O nanopowders can be tuned by varying Ni content. • The results reveal the solubility limit of Ni into ZnO matrix as below 8%. - Abstract: Zn{sub 1−x}Ni{sub x}O nanopowders with different Ni contents of x = 0.0, 0.04 and 0.08 were synthesized via cost effective sonochemical reaction method. X-ray diffraction (XRD) pattern reveals pure wurtzite phase of prepared nanostructures with no additional impurity peaks. The morphology and dimensions of nanoparticles were investigated using scanning electron microscope (SEM). A sharp and strong peak for first order optical mode for wurtzite zinc oxide (ZnO) structure was observed at ∼438 cm{sup −1} in Raman spectra. The calculated optical band gap (E{sub g}) from UV–vis transmission data was found to decrease with increase in Ni content. The observed red shift in E{sub g} with increasing Ni content in ZnO nanopowders were in agreement with band gap behaviours found in their photoluminescence (PL) spectra. The synthesised ZnO nanopowders with controlled band gap on Ni doping reveals their potential for use in various electronic and optical device applications. The results were discussed in detail.

  8. Effect of temperature on the optical and structural properties of hexadecylamine capped ZnS nanoparticles using Zinc(II) N-ethyl-N-phenyldithiocarbamate as single source precursor

    Energy Technology Data Exchange (ETDEWEB)

    Onwudiwe, Damian C., E-mail: dconwudiwe@webmail.co.za [Chemical Resource Beneficiation, North-West University, Private Bag X6001, Potchefstroom 2520 (South Africa); Strydom, Christien [Chemical Resource Beneficiation, North-West University, Private Bag X6001, Potchefstroom 2520 (South Africa); Oluwafemi, Oluwatobi S., E-mail: oluwafemi.oluwatobi@gmail.com [Department of Chemistry and Chemical Technology, Walter Sisulu University, Mthatha Campus, Private Bag X1, Mthatha (South Africa); Songca, Sandile P. [Faculty of Science, Engineering and Technology, Walter Sisulu University, P.O. Box 19712, Tecoma, East London (South Africa)

    2012-12-15

    Graphical abstract: Display Omitted Highlights: ► HDA-capped ZnS nanoparticles were synthesized via thermolysis of a single source precursor. ► Zinc(II) N-ethyl-N-phenyldithiocarbamate was used as the single source precursor. ► The growth temperature was varied to study the optical properties of the nanocrystals. ► Change in growth temperature affects the structural properties of the ZnS nanoparticles. ► Hexagonal wurtzite phase was obtained at lower temperatures while cubic sphalerite phase was obtained at higher growth temperatures. -- Abstract: Reported in this work is the synthesis of HDA (hexadecylamine)-capped ZnS nanoparticles by a single source route using Zinc(II) N-ethyl-N-phenyldithiocarbamate as a precursor. By varying the growth temperature, the temporal evolution of the optical properties and morphology of the nanocrystals were investigated. The as-synthesized nanoparticles were characterized using UV–vis absorption and photoluminescence (PL) spectroscopy, transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD). All the particles exhibited quantum confinement in their optical properties with band edge emission at the early stage of the reaction. The XRD showed transition from hexagonal wurtzite phase to cubic sphalerite phase as the growth temperature increases. The TEM image showed that the particles are small and spherical in shape while the HRTEM image confirmed the crystalline nature of the material.

  9. Chemically stabilized epitaxial wurtzite-BN thin film

    Science.gov (United States)

    Vishal, Badri; Singh, Rajendra; Chaturvedi, Abhishek; Sharma, Ankit; Sreedhara, M. B.; Sahu, Rajib; Bhat, Usha; Ramamurty, Upadrasta; Datta, Ranjan

    2018-03-01

    We report on the chemically stabilized epitaxial w-BN thin film grown on c-plane sapphire by pulsed laser deposition under slow kinetic condition. Traces of no other allotropes such as cubic (c) or hexagonal (h) BN phases are present. Sapphire substrate plays a significant role in stabilizing the metastable w-BN from h-BN target under unusual PLD growth condition involving low temperature and pressure and is explained based on density functional theory calculation. The hardness and the elastic modulus of the w-BN film are 37 & 339 GPa, respectively measured by indentation along direction. The results are extremely promising in advancing the microelectronic and mechanical tooling industry.

  10. Optical Properties of Strained Wurtzite Gallium Phosphide Nanowires

    KAUST Repository

    Greil, J.; Assali, S.; Isono, Y.; Belabbes, Abderrezak; Bechstedt, F.; Valega Mackenzie, F. O.; Silov, A. Yu.; Bakkers, E. P. A. M.; Haverkort, J. E. M.

    2016-01-01

    with a theoretical analysis of strain effects is employed to establish the nature and symmetry of the transitions. We identify the emission lines to be related to localized states with significant admixture of Γ7c symmetry and not exclusively related

  11. Structure and performance of ZnO/PVC nanocomposites

    Energy Technology Data Exchange (ETDEWEB)

    Elashmawi, I.S., E-mail: islam_shukri2000@yahoo.co [Spectroscopy department, Physics division, National Research Centre, Dokki (Egypt); Hakeem, N.A. [Spectroscopy department, Physics division, National Research Centre, Dokki (Egypt); Marei, L.K.; Hanna, F.F. [Faculty of Petroleum and Mining Engineering, Suez Canal University, Suez (Egypt)

    2010-10-01

    ZnO/PVC nanocomposites films have been prepared by the solvent casting method and investigated by various techniques. All results show good dispersion of ZnO nanoparticles in the polymeric matrix. XRD revealed that pure PVC films are partially crystalline with hallow peak but ZnO nanoparticles have wurtzite structure and the nanocomposite films were almost the same as those of ZnO with decrease in the degree of crystallization, causing increase in the amorphous region. FT-IR presented the same spectra for nanocomposites in the wavenumber range 700-3100 cm{sup -1}, weak band located at 500-700 cm{sup -1},which can be attributed to stretching of Zn---O bond and an increase of the bending band of O-H at 1631 cm{sup -1} was observed. The surface of the films was analyzed by SEM, which becomes rough with some small aggregates compared with pure PVC with good distribution in the entire surface region with bright spots. TEM revealed a regular crystalline lattice superimposed on an amorphous background due to carbon support and PVC matrix and the structure of these particles is hexagonal. In addition, the nanocomposites films have higher glass transition temperature, specific heat and thermal stability relative to those of pure PVC because of strong interaction among ZnO nanoparticles and PVC.

  12. Further characteristics important in the operation of ceramic BeO TLD

    International Nuclear Information System (INIS)

    Gammage, R.B.

    1977-01-01

    There is now a considerable volume of published research dealing with ceramic BeO--TLD (Crase and Gammage, 1975; Yamashita et al., 1974; Scarpa et al., 1971). Its high sensitivity to radiation (1 mR), cheapness, commercial availability, non-toxicity, chemical stability, an atomic number of near tissue equivalence, and resistance to thermal fading, suggest that it should, by now, have found widespread acceptance as a TLD phosphor. It has not. There are only a small handful of reports dealing with the practical application of this type of dosimeter (Puite et al., 1974; Gammage and Haywood, 1976; Gesell et al., 1975). It seems wise, therefore, to look at the phosphor more closely and to focus on characteristics likely to cause problems under real operating conditions, especially those which are acting as a deterrent to its widespread acceptance. Operational characteristics were studied and the results are discussed

  13. Application of electron crystallography to structure characterization of ZnS nanocrystals

    Directory of Open Access Journals (Sweden)

    Jin-Gyu Kim

    2011-07-01

    Full Text Available We chracterized the structure properties of two types of ZnS nanocrystals by electron crystallography. X-ray diffraction analysis for these ZnS nanocrystals was performed to determine their initial structures. Their crystallite sizes were about 5.9 nm and 8.1 nm and their crystal systems were hexagonal and cubic, respectively. Their atomic structures, however, could not be determined because of the weak diffraction intensities as well as the unexpected intensities from impurty. To overcome these problems, the structures of ZnS nanocrystals were resolved by electron crystallography using EF-EPD (energy-filtered electron powder diffraction and HRTEM (high resolution transmission electron microscopy methods. The structrues determined by Rietveld analysis are P63mc (a = 3.8452 Å, c = 18.5453 Å and F-43m (a = 5.4356 Å, respectively. Their crystallite shapes were nanorods and quasi-nanoparticles and the nanorod crystal were grown along the [001] direction. It was revealed that the phase transformation between the cubic sphalerite to the hexagonal wurtzite structure of ZnS nanocrytals was related to their shapes and growth mechanism. Electron cryststallogrpahy, employing EF-EPD and HRTEM methods together, has advantages for structure analysis and property chracterization of nano-sized materials.

  14. Effect of Al dopants on the structural, optical and gas sensing properties of spray-deposited ZnO thin films

    Energy Technology Data Exchange (ETDEWEB)

    Prajapati, C.S. [Department of Physics, Motilal Nehru National Institute of Technology, Allahabad 211 004 (India); Kushwaha, Ajay [Department of Physics, Indian Institute of Technology Bombay, Powai, Mumbai 400076 (India); Sahay, P.P., E-mail: dr_ppsahay@rediffmail.com [Department of Physics, Motilal Nehru National Institute of Technology, Allahabad 211 004 (India)

    2013-10-01

    Undoped and Al-doped ZnO thin films were deposited on glass substrates by the spray pyrolysis method. The structural, morphological and optical properties of these films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), UV–Vis spectroscopy, photoluminescence (PL) and photoconductivity (PC) measurements, respectively. XRD analyses confirm that the films are polycrystalline zinc oxide with the hexagonal wurtzite structure, and the crystallite size has been found to be in the range 20–40 nm. SEM and AFM analyses reveal that the films have continuous surface without visible holes or faulty zones, and the surface roughness decreases on Al doping. The Al-doped films have been found to be highly transparent (>85%) and show normal dispersion behavior in the wavelength range 450–700 nm. The doped films show only ultraviolet emission and are found to be highly photosensitive. Among all the films examined, at 300 °C the 1.0 at% Al-doped film shows the selective high response (98.2%) to 100 ppm acetone concentration over to methanol, ethanol, propan-2-ol, formaldehyde and hydrogen. - Highlights: • ZnO films possess hexagonal wurtzite structure with crystallite size: 20–40 nm. • On Al doping, the surface roughness decreases and optical transmission increases. • Al-doped films exhibit the normal dispersion behavior for (450–700 nm) wavelength. • All the films are photosensitive and the photocurrent enhances on Al doping. • 1 at% Al-doped films exhibit high sensitivity and selectivity to acetone at 300 °C.

  15. Electrical and physical characteristics for crystalline atomic layer deposited beryllium oxide thin film on Si and GaAs substrates

    International Nuclear Information System (INIS)

    Yum, J.H.; Akyol, T.; Lei, M.; Ferrer, D.A.; Hudnall, Todd W.; Downer, M.; Bielawski, C.W.; Bersuker, G.; Lee, J.C.; Banerjee, S.K.

    2012-01-01

    In a previous study, atomic layer deposited (ALD) BeO exhibited less interface defect density and hysteresis, as well as less frequency dispersion and leakage current density, at the same equivalent oxide thickness than Al 2 O 3 . Furthermore, its self-cleaning effect was better. In this study, the physical and electrical characteristics of ALD BeO grown on Si and GaAs substrates are further evaluated as a gate dielectric layer in III–V metal-oxide-semiconductor devices using transmission electron microscopy, selective area electron diffraction, second harmonic generation, and electrical analysis. An as-grown ALD BeO thin film was revealed as a layered single crystal structure, unlike the well-known ALD dielectrics that exhibit either poly-crystalline or amorphous structures. Low defect density in highly ordered ALD BeO film, less variability in electrical characteristics, and great stability under electrical stress were demonstrated. - Highlights: ► BeO is an excellent electrical insulator, but good thermal conductor. ► Highly crystalline film of BeO has been grown using atomic layer deposition. ► An ALD BeO precursor, which is not commercially available, has been synthesized. ► Physical and electrical characteristics have been investigated.

  16. Exciting imperfection. Real-structure effects in magnesium-, cadmium-, and zinc-oxide

    Energy Technology Data Exchange (ETDEWEB)

    Schleife, Andre

    2010-07-01

    We employ recent ab-initio methods and theoretical spectroscopy techniques that rely on heavy numerical calculations to describe electronic excitations in non-ideal crystals of three group-II oxides. We study the ideal equilibrium polymorphs of these oxides, for gaining a thorough understanding as well as the necessary confidence in our approaches to generalize and apply them to the electronic excitations in imperfect crystals. As such imperfections we take the influence of strain, the alloying of the different oxides, an intrinsic point defect, and free electrons in the lowest conduction band into account. We employ the DFT results as input in order to compute quasiparticle electronic structures, which are in good agreement with experimental findings. According to Hedin's equations for interacting electrons, the electron-hole interaction is taken into account by solving a Bethe-Salpeter equation for the polarization function. Thereafter the equilibrium polymorphs of ideal bulk MgO, ZnO, and CdO and investigates the structure of their valence and conduction bands are described. We present densities of states and effective masses, as well as natural band discontinuities. Furthermore, our description of the dielectric function, which takes excitonic effects into account, enables us to derive the electron-energy loss function. The influence of uniaxial and biaxial strain on the ordering of the valence bands in ZnO is investigated. In addition, we explore the electronic band structure of the non-equilibrium wurtzite structures of MgO and CdO. We predict valence-band splittings and band gaps as they might occur at interfaces of Mgo or CdO with ZnO substrates. Thereafter we study pseudobinary alloys by means of a cluster expansion method. Due to the different crystal structures of the respective oxides, i.e. rocksalt and wurtzite, the description of their heterostructural combination has to be achieved. The electronic and optical properties of the group-II oxide

  17. Exciting imperfection. Real-structure effects in magnesium-, cadmium-, and zinc-oxide

    International Nuclear Information System (INIS)

    Schleife, Andre

    2010-01-01

    We employ recent ab-initio methods and theoretical spectroscopy techniques that rely on heavy numerical calculations to describe electronic excitations in non-ideal crystals of three group-II oxides. We study the ideal equilibrium polymorphs of these oxides, for gaining a thorough understanding as well as the necessary confidence in our approaches to generalize and apply them to the electronic excitations in imperfect crystals. As such imperfections we take the influence of strain, the alloying of the different oxides, an intrinsic point defect, and free electrons in the lowest conduction band into account. We employ the DFT results as input in order to compute quasiparticle electronic structures, which are in good agreement with experimental findings. According to Hedin's equations for interacting electrons, the electron-hole interaction is taken into account by solving a Bethe-Salpeter equation for the polarization function. Thereafter the equilibrium polymorphs of ideal bulk MgO, ZnO, and CdO and investigates the structure of their valence and conduction bands are described. We present densities of states and effective masses, as well as natural band discontinuities. Furthermore, our description of the dielectric function, which takes excitonic effects into account, enables us to derive the electron-energy loss function. The influence of uniaxial and biaxial strain on the ordering of the valence bands in ZnO is investigated. In addition, we explore the electronic band structure of the non-equilibrium wurtzite structures of MgO and CdO. We predict valence-band splittings and band gaps as they might occur at interfaces of Mgo or CdO with ZnO substrates. Thereafter we study pseudobinary alloys by means of a cluster expansion method. Due to the different crystal structures of the respective oxides, i.e. rocksalt and wurtzite, the description of their heterostructural combination has to be achieved. The electronic and optical properties of the group-II oxide alloys

  18. Structural, optical, and hydrogenation properties of ZnO nanowall networks grown on a Si (1 1 1) substrate by plasma-assisted molecular beam epitaxy

    International Nuclear Information System (INIS)

    Su, S.C.; Lu, Y.M.; Zhang, Z.Z.; Li, B.H.; Shen, D.Z.; Yao, B.; Zhang, J.Y.; Zhao, D.X.; Fan, X.W.

    2008-01-01

    ZnO nanowall networks were grown on a Si (1 1 1) substrate by plasma-assisted molecular beam epitaxy (P-MBE) without using catalysts. Scanning electronic microscopy (FE-SEM) confirmed the formation of nanowalls with a thickness of about 10-20 nm. X-ray diffraction (XRD) showed that the ZnO nanowall networks were crystallized in a wurtzite structure with their height parallel to the direction. Photoluminescence (PL) of the ZnO nanowall networks exhibited free excitons (FEs), donor-bound exciton (D 0 X), donor-acceptor pair (DAP), and free exciton to acceptor (FA) emissions. The growth mechanism of the ZnO nanowall networks was discussed, and their hydrogenation was also studied

  19. A geo-economical study of beryl, specially the bery from the northeast (of Brazil)

    International Nuclear Information System (INIS)

    Argentiere, R.

    1977-01-01

    The crystalline structure of beryl and the BeO proportion in minerals are presented. The geoeconomics areas are studied and tables of the Brazilian beryl productions and its relative position in the world-wide production are presented [pt

  20. Structural and magnetic characterization of mixed valence Co(II, III)xZn1−xO epitaxial thin films

    International Nuclear Information System (INIS)

    Negi, D.S.; Loukya, B.; Dileep, K.; Sahu, R.; Shetty, S.; Kumar, N.; Ghatak, J.; Pachauri, N.; Gupta, A.; Datta, R.

    2014-01-01

    In this article, we report on the Co atom incorporation, secondary phase formation and composition-dependent magnetic and optical properties of mixed valence Co(II, III) x Zn 1−x O epitaxial thin films grown by pulsed laser deposition. The intended total Co concentration is varied between ∼6–60 at.% with relatively higher concentration of +3 over +2 charge state. Mixed valence Co(II, III) shows high solubility in ZnO (up to 38 at.%) and ferromagnetism is observed in samples with total Co incorporation of ∼29 and 38 at.%. Electron diffraction pattern and high resolution transmission electron microscopy images reveal single crystalline nature of the thin films with wurtzite structure. Co oxide interlayer, with both rock salt and spinel structure, are observed to be formed between the substrate and wurtzite film for total Co concentration at ∼17 at.% and above. Magnetization shows composition dependence with a saturation moment value of ∼93 emu cm −3 and a coercive field of ∼285 Oe observed for ∼38 at.% Co:ZnO films. Ferromagnetism was not observed for films with Co concentration 17 and 9 at.%. The Co oxide interlayer does not show any ferromagnetism. All the films are n-type with carrier concentration ∼10 19 cm −3 . The observed magnetism is probably resulting from direct antiferromagntic exchange interaction between Co 2+ and Co 3+ ions favored by heavy Co alloying giving rise to ferrimagnetism in the system. - Highlights: • Mixed valence Co doped ZnO ferromagnetic single crystal thin film. • Secondary phase formation in terms of CoO and Co3O4 and magnetism is observed only for high Co alloying. • Cathodoluminescence (CL) data showing increase in band gap with Co concentrations

  1. Structure of AlN films deposited by magnetron sputtering method

    Directory of Open Access Journals (Sweden)

    Nowakowska-Langier K.

    2015-09-01

    Full Text Available AlN films on a Si substrate were synthesized by magnetron sputtering method. A dual magnetron system operating in AC mode was used in the experiment. Processes of synthesis were carried out in the atmosphere of a mixture of Ar/N2. Morphology and phase structure of the AlN films were investigated at different pressures. Structural characterizations were performed by means of SEM and X-ray diffraction methods. Our results show that the use of magnetron sputtering method in a dual magnetron sputtering system is an effective way to produce AlN layers which are characterized by a good adhesion to the silicon substrate. The morphology of the films is strongly dependent on the Ar/N2 gas mixture pressure. An increase of the mixture pressure is accompanied by a columnar growth of the layers. The films obtained at the pressure below 1 Pa are characterized by finer and compacter structure. The AlN films are characterized by a polycrystalline hexagonal (wurtzite structure in which the crystallographic orientation depends on the gas mixture pressure.

  2. Growth of InAs/InP core-shell nanowires with various pure crystal structures.

    Science.gov (United States)

    Gorji Ghalamestani, Sepideh; Heurlin, Magnus; Wernersson, Lars-Erik; Lehmann, Sebastian; Dick, Kimberly A

    2012-07-20

    We have studied the epitaxial growth of an InP shell on various pure InAs core nanowire crystal structures by metal-organic vapor phase epitaxy. The InP shell is grown on wurtzite (WZ), zinc-blende (ZB), and {111}- and {110}-type faceted ZB twin-plane superlattice (TSL) structures by tuning the InP shell growth parameters and controlling the shell thickness. The growth results, particularly on the WZ nanowires, show that homogeneous InP shell growth is promoted at relatively high temperatures (∼500 °C), but that the InAs nanowires decompose under the applied conditions. In order to protect the InAs core nanowires from decomposition, a short protective InP segment is first grown axially at lower temperatures (420-460 °C), before commencing the radial growth at a higher temperature. Further studies revealed that the InP radial growth rate is significantly higher on the ZB and TSL nanowires compared to WZ counterparts, and shows a strong anisotropy in polar directions. As a result, thin shells were obtained during low temperature InP growth on ZB structures, while a higher temperature was used to obtain uniform thick shells. In addition, a schematic growth model is suggested to explain the basic processes occurring during the shell growth on the TSL crystal structures.

  3. Growth of InAs/InP core–shell nanowires with various pure crystal structures

    International Nuclear Information System (INIS)

    Gorji Ghalamestani, Sepideh; Heurlin, Magnus; Lehmann, Sebastian; Dick, Kimberly A; Wernersson, Lars-Erik

    2012-01-01

    We have studied the epitaxial growth of an InP shell on various pure InAs core nanowire crystal structures by metal–organic vapor phase epitaxy. The InP shell is grown on wurtzite (WZ), zinc-blende (ZB), and {111}- and {110}-type faceted ZB twin-plane superlattice (TSL) structures by tuning the InP shell growth parameters and controlling the shell thickness. The growth results, particularly on the WZ nanowires, show that homogeneous InP shell growth is promoted at relatively high temperatures (∼500 °C), but that the InAs nanowires decompose under the applied conditions. In order to protect the InAs core nanowires from decomposition, a short protective InP segment is first grown axially at lower temperatures (420–460 °C), before commencing the radial growth at a higher temperature. Further studies revealed that the InP radial growth rate is significantly higher on the ZB and TSL nanowires compared to WZ counterparts, and shows a strong anisotropy in polar directions. As a result, thin shells were obtained during low temperature InP growth on ZB structures, while a higher temperature was used to obtain uniform thick shells. In addition, a schematic growth model is suggested to explain the basic processes occurring during the shell growth on the TSL crystal structures. (paper)

  4. First principles study of structural and electronic properties of different phases of boron nitride

    Energy Technology Data Exchange (ETDEWEB)

    Ahmed, Rashid [Centre for High Energy Physics, University of the Punjab, Lahore 54590 (Pakistan)], E-mail: rasofi@hotmail.com; Fazal-e-Aleem [Centre for High Energy Physics, University of the Punjab, Lahore 54590 (Pakistan); Hashemifar, S. Javad; Akbarzadeh, Hadi [Department of Physics, Isfahan University of Technology, 84156 Isfahan (Iran, Islamic Republic of)

    2007-11-15

    A theoretical study of structural and electronic properties of the four phases of BN (zincblende, wurtzite, hexagonal and rhombohedral) is presented. The calculations are done by full potential (linear) augmented plane wave plus local orbitals (APW+lo) method based on the density functional theory (DFT) as employed in WIEN2k code. Using the local density approximation (LDA) and generalized gradient approximation (GGA-PBE) for the exchange correlation energy functional, we have calculated lattice parameters, bulk modulus, its pressure derivative and cohesive energy. In order to calculate electronic band structure, another form of the generalized gradient approximation proposed by Engel and Vosko (GGA-EV) has been employed along with LDA and GGA-PBE. It is found that all the three approximations exhibit similar band structure qualitatively. However, GGA-EV gives energy band gap values closer to the measured data. Our results for structural and electronic properties are compared with the experimental and other theoretical results wherever these are available.

  5. Structural and Optical Properties of Eu Doped ZnO Nanorods prepared by Pulsed Laser Deposition

    KAUST Repository

    Alarawi, Abeer

    2014-06-23

    Nano structured wide band gap semiconductors have attracted attention of many researchers due to their potential electronic and optoelectronic applications. In this thesis, we report successful synthesis of well aligned Eu doped ZnO nano-rods prepared, for the first time to our knowledge, by pulsed laser deposition (PLD) without any catalyst. X-ray diffraction (XRD) patterns shows that these Eu doped ZnO nanorods are grown along the c-axis of ZnO wurtzite structure. We have studied the effect of the PLD growth conditions on forming vertically aligned Eu doped ZnO nanorods. The structural properties of the material are investigated using a -scanning electron microscope (SEM). The PLD parameters must be carefully controlled in order to obtain c-axis oriented ZnO nanorods on sapphire substrates, without the use of any catalyst. The experiments conducted in order to identify the optimal growth conditions confirmed that, by adjusting the target-substrate distance, substrate temperature, laser energy and deposition duration, the nanorod size could be successfully controlled. Most importantly, the results indicated that the photoluminescence (PL) properties reflect the quality of the ZnO nanorods. These parameters can change the material’s structure from one-dimensional to two-dimensional however the laser energy and frequency affect the size and the height of the nanorods; the xygen pressure changes the density of the nanorods.

  6. Synthesis of assembled ZnO structures by precipitation method in aqueous media

    International Nuclear Information System (INIS)

    Sepulveda-Guzman, S.; Reeja-Jayan, B.; Rosa, E. de la; Torres-Castro, A.; Gonzalez-Gonzalez, V.; Jose-Yacaman, M.

    2009-01-01

    In this work, arrays of submicron ZnO structures were successfully synthesized using a one-step aqueous precipitation method. Snowflake-like and flower-like morphologies were obtained by changing the reaction temperature. X-ray diffraction (XRD) patterns indicated that the ZnO arrays have a wurtzite crystal structure. A possible growth mechanism based on the analysis done by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and high-angle annular dark field (HAADF) is proposed. Our findings suggest that the growth mechanism of the ZnO arrays is by self-aggregation, and that such an oriented aggregation is enhanced by increasing the reaction temperature. The results also revealed that the aggregation process introduces several structural defects such as differences in mass distribution and crystalline structure. In order to study the surface chemical composition the samples were also characterized by XPS. The results showed the presence of Zn(OH) 2 and absorbed carbon species on the ZnO surface. In addition, the photoluminescence characterization showed that on UV excitation (λ = 360 nm) all samples present the characteristic UV emission centered at 390 nm, and for the sample synthesized at 60 deg. C, a visible emission was also observed

  7. Synthesis of assembled ZnO structures by precipitation method in aqueous media

    Energy Technology Data Exchange (ETDEWEB)

    Sepulveda-Guzman, S. [Centro de Innovacion, Investigacion y Desarrollo en Ingenieria y Tecnologia, UANL Km. 10 de la nueva carretera al Aeropuerto Internacional de Monterrey, PIIT Monterrey, Apodaca NL (Mexico); Facultad de Ingenieria Mecanica y Electrica de la UANL, Ciudad Universitaria San Nicolas de los Garza, Nuevo Leon C.P. 66451 (Mexico)], E-mail: ssepulveda@mail.uanl.mx; Reeja-Jayan, B. [Texas Materials Institute, University of Texas at Austin, 1 University Station C0803 (United States); Rosa, E. de la [Centro de Investigaciones en Optica, A.C. Loma del Bosque 115 Col. Lomas del Campestre, Leon Gto. C.P. 37150 (Mexico); Torres-Castro, A.; Gonzalez-Gonzalez, V. [Centro de Innovacion, Investigacion y Desarrollo en Ingenieria y Tecnologia, UANL Km. 10 de la nueva carretera al Aeropuerto Internacional de Monterrey, PIIT Monterrey, Apodaca NL (Mexico); Facultad de Ingenieria Mecanica y Electrica de la UANL, Ciudad Universitaria San Nicolas de los Garza, Nuevo Leon C.P. 66451 (Mexico); Jose-Yacaman, M. [Physics and Astronomy Department, University of Texas at San Antonio, 1604 Campus San Antonio, TX 78249 (United States)

    2009-05-15

    In this work, arrays of submicron ZnO structures were successfully synthesized using a one-step aqueous precipitation method. Snowflake-like and flower-like morphologies were obtained by changing the reaction temperature. X-ray diffraction (XRD) patterns indicated that the ZnO arrays have a wurtzite crystal structure. A possible growth mechanism based on the analysis done by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and high-angle annular dark field (HAADF) is proposed. Our findings suggest that the growth mechanism of the ZnO arrays is by self-aggregation, and that such an oriented aggregation is enhanced by increasing the reaction temperature. The results also revealed that the aggregation process introduces several structural defects such as differences in mass distribution and crystalline structure. In order to study the surface chemical composition the samples were also characterized by XPS. The results showed the presence of Zn(OH){sub 2} and absorbed carbon species on the ZnO surface. In addition, the photoluminescence characterization showed that on UV excitation ({lambda} = 360 nm) all samples present the characteristic UV emission centered at 390 nm, and for the sample synthesized at 60 deg. C, a visible emission was also observed.

  8. Structural and optical analysis of ZnBeMgO powder and thin films

    International Nuclear Information System (INIS)

    Panwar, Neeraj; Liriano, J.; Katiyar, Ram S.

    2011-01-01

    Research highlights: → Structural and optical studies of Zn 1-x-y Be x Mg y O (0 ≤ x ≤0.10; 0 ≤ y ≤ 0.20) powders and thin films. → Raman studies of the pure ZnO powder showed all the characteristic peaks of the wurtzite hexagonal structure and with (Be, Mg) co-doping new modes appeared which can be attributed to arise as a result of doping effect. → The XRD of the films prepared from the powders using pulsed laser deposition (PLD) technique exhibited the preferential orientation and with doping the (0 0 0 2) peak also shifts to higher 2θ values suggesting the incorporation of Be/Mg at the Zn-site. → From the UV-visible optical band gap measurement it was noticed that the band gap of the pristine ZnO film is 3.3 eV which enhanced up to 4.51 eV for Zn 0.7 Be 0.1 Mg 0.2 O film which lies in the solar blind region and is very useful for the deep UV detection. - Abstract: We here report the structural and optical studies of Zn 1-x-y Be x Mg y O (0 ≤ x ≤ 0.15; 0 ≤ y ≤ 0.20) powders and thin films. From the Rietveld refinement of the powder X-ray diffraction (XRD) patterns it was revealed that the value of 'a' lattice parameter remains almost unchanged whereas 'c' parameter reduces with Be and Mg co-doping in ZnO. The Zn-O bond length also decreases in co-doped samples. Raman studies of the pure ZnO powder showed all the characteristic peaks of the wurtzite hexagonal structure and with (Be, Mg) co-doping new modes appeared which can be attributed to arise as a result of substitution. The XRD of the films prepared from the powders using pulsed laser deposition (PLD) technique exhibited the preferential orientation and with increase in co-doping the (0 0 0 2) peak also shifts to higher 2θ values suggesting the incorporation of Be/Mg at the Zn-site. From the UV-visible optical transmittance measurement it was noticed that the band gap of the pristine ZnO film is 3.3 eV which enhanced up to 4.51 eV for Zn 0.7 Be 0.1 Mg 0.2 O film which lies in the

  9. Electronic structure calculations on nitride semiconductors and their alloys

    International Nuclear Information System (INIS)

    Dugdale, D.

    2000-09-01

    Calculations of the electronic properties of AIN, GaN, InN and their alloys are presented. Initial calculations are performed using the first principles pseudopotential method to obtain accurate lattice constants. Further calculations then investigate bonding in the nitrides through population analysis and density of state calculations. The empirical pseudopotential method is also used in this work. Pseudopotentials for each of the nitrides are constructed using a functional form that allows strained material and alloys to be studied. The conventional k.p valence band parameters for both zincblende and wurtzite are obtained from the empirical band structure using two different methods. A Monte-Carlo fitting of the k.p band structure to the pseudopotential data (or an effective mass method for the zincblende structure) is used to produce one set. Another set is obtained directly from the momentum matrix elements and energy eigenvalues at the centre of the Brillouin zone. Both methods of calculating k.p parameters produce band structure in excellent agreement with the original empirical band calculations near the centre of the Brillouin zone. The advantage of the direct method is that it produces consistent sets of parameters, and can be used in studies involving a series of alloy compositions. Further empirical pseudopotential method calculations are then performed for alloys of the nitrides. In particular, the variation of the band gap with alloy composition is investigated, and good agreement with theory and experiment is found. The direct method is used to obtain k.p parameters for the alloys, and is contrasted with the fitting approach. The behaviour of the nitrides under strain is also studied. In particular. valence band offsets for nitride heterojunctions are calculated, and a strong forward- backward asymmetry in the band offset is found, in good agreement with other results in the literature. (author)

  10. Structural and Optical Properties of ZnO Thin Film Prepared by Oxidation of Zn Metal Powders

    International Nuclear Information System (INIS)

    Hassan, N.K.; Hashim, M.R.

    2013-01-01

    High quality ZnO nano structures have been fabricated at room temperature by a simple vacuum thermal evaporator from metallic Zn powders (99.999 % purity) on a silicon (100) substrate. The Zn thin films were then transferred into a thermal tube furnace for oxidation at 700 degree Celsius for different time durations. Time was found to be a critical factor in the synthesis. This was followed by characterization of their morphological, structural and optical properties. The morphology of the grown ZnO nano structures exhibited several large grains, which increased gradually with increasing oxidation time. The crystallinity of the grown nano structures was investigated using X-ray diffraction, revealing that the synthesized ZnO was in hexagonal wurtzite phase. The photoluminescence (PL) spectra of the fabricated ZnO nano structures showed high intensity peak in the UV region due to near-band-edge (NBE) emission in which the structures oxidized for 30 min showing highest intensity. (author)

  11. Structure of Ga2O3(ZnO)6: a member of the homologous series Ga2O3(ZnO)m

    International Nuclear Information System (INIS)

    Michiue, Yuichi; Kanke, Yasushi; Kimizuka, Noboru

    2008-01-01

    The structure of Ga 2 O 3 (ZnO) 6 was determined using singlecrystal X-ray diffraction techniques in the space group Cmcm. The metal ion sublattice resembles some of the Zn ions in the wurtzite ZnO structure. The oxygen ion sublattice in Ga 2 O 3 (ZnO) 6 also resembles some of the O ions in ZnO. Structural relationships between Ga 2 O 3 (ZnO) 6 and ZnO are discussed, illustrating the process for obtaining the centrosymmetric Ga 2 O 3 (ZnO) 6 structure from the noncentrosymmetric ZnO. Structures of phases in the homologous series Ga 2 O 3 (ZnO) m are predicted on the basis of the structural data for Ga 2 O 3 (ZnO) 6 . The structures of even m are constructed by simply extending the structure units seen in Ga 2 O 3 (ZnO) 6 , while those of odd m consist of structure units which are of different types from those used for even m. (orig.)

  12. Synthesis and self-assembly of dumbbell shaped ZnO sub-micron structures using low temperature chemical bath deposition technique

    Energy Technology Data Exchange (ETDEWEB)

    Borade, P. [National Centre for Nanoscience and Nanotechnology, University of Mumbai, Kalina Campus, Santacruz (E), Mumbai 400098 (India); Joshi, K.U. [Anton-Paar India Pvt. Ltd., Thane (W), 400607 (India); Gokarna, A.; Lerondel, G. [Laboratoire de Nanotechnologie et D' Instrumentation Optique, Institut Charles Delaunay, CNRS UMR 6281, Université de Technologie de Troyes, 12 Rue Marie Curie, BP 2060, 10010 Troyes (France); Walke, P. [National Centre for Nanoscience and Nanotechnology, University of Mumbai, Kalina Campus, Santacruz (E), Mumbai 400098 (India); Late, D. [National Chemical Laboratory (NCL), Pune 400027 (India); Jejurikar, S.M., E-mail: jejusuhas@gmail.com [National Centre for Nanoscience and Nanotechnology, University of Mumbai, Kalina Campus, Santacruz (E), Mumbai 400098 (India)

    2016-02-01

    We report well dispersed horizontal growth of ZnO sub-micron structures using simplest technique ever known i.e. chemical bath deposition (CBD). A set of samples were prepared under two different cases A) dumbbell shaped ZnO grown in CBD bath and B) tubular ZnO structures evolved from dumbbell shaped structures by dissolution mechanism. Single phase wurtzite ZnO formation is confirmed using X-ray diffraction (XRD) technique in both cases. From the morphological investigations performed using scanning electron microscopy (SEM), sample prepared under case A indicate formation of hex bit tool (HBT) shaped ZnO crystals, which observed to self-organize to form dumbbell structures. Further these microstructures are then converted into tubular structures as a fragment of post CBD process. The possible mechanism responsible for the self-assembly of HBT units to form dumbbell structures is discussed. Observed free excitonic peak located at 370 nm in photoluminescence (PL) spectra recorded at 18 K indicate that the micro/nanostructures synthesized using CBD are of high optical quality. - Highlights: • Controlled growth of Dumbbell shaped ZnO using Chemical Bath Deposition (CBD). • Growth mechanism of dumbbell shaped ZnO by self-assembling was discussed. • Quick Transformation of ZnO dumbbell structures in to tubular structures by dissolution. • Sharp UV Emission at 370 nm from both dumbbell and tubular structures.

  13. Theoretical investigation of the structural, electronic, and thermodynamic properties of CdS1-xSex alloys

    Science.gov (United States)

    Long, Debing; Li, Mingkai; Meng, Dongxue; Ahuja, Rajeev; He, Yunbin

    2018-03-01

    In this work, the structural, electronic, and thermodynamic properties of wurtzite (WZ) and zincblende (ZB) CdS1-xSex alloys are investigated using the density functional theory (DFT) and the cluster expansion method. A special quasirandom structure containing 16 atoms is constructed to calculate the band structures of random alloys. The band gaps of CdS1-xSex alloys are direct and decrease as the Se content increases. The delta self-consistent-field method is applied to correct band gaps that are underestimated by DFT. The band offsets clearly reflect the variation in valence band maxima and conduction band minima, thus providing information useful to the design of relevant quantum well structures. The positive formation enthalpies of both phases imply that CdS1-xSex is an immiscible system and tends to phase separate. The influence of lattice vibrations on the phase diagram is investigated by calculating the phonon density of states. Lattice vibration effects can reduce the critical temperature Tc and increase alloy solid solubilities. This influence is especially significant in the ZB structure. When only chemical interactions are present, the Tc values for WZ- and ZB-CdS1-xSex are 260 K and 249 K, respectively. The lattice vibration enthalpy and entropy lower the Tc to 255 K and 233 K, respectively.

  14. Structural and optical properties of Na doped ZnO nanocrystals: Application to solar photocatalysis

    Energy Technology Data Exchange (ETDEWEB)

    Tabib, Asma; Bouslama, Wiem [Laboratoire de Physico-Chimie des Matériaux Minéraux et leurs Applications, Centre National de Recherches en Sciences des Matériaux, B.P. 95 Hammam-Lif, 2050 (Tunisia); Sieber, Brigitte; Addad, Ahmed [UMET, UMR, CNRS 8207, Université Lille 1, 59665 Villeneuve d’Ascq Cédex (France); Elhouichet, Habib, E-mail: habib.elhouichet@fst.rnu.tn [Laboratoire de Physico-Chimie des Matériaux Minéraux et leurs Applications, Centre National de Recherches en Sciences des Matériaux, B.P. 95 Hammam-Lif, 2050 (Tunisia); Département de Physique, Faculté des Sciences de Tunis, University of Tunis, ElManar 2092 (Tunisia); Férid, Mokhtar [Laboratoire de Physico-Chimie des Matériaux Minéraux et leurs Applications, Centre National de Recherches en Sciences des Matériaux, B.P. 95 Hammam-Lif, 2050 (Tunisia); Boukherroub, Rabah [Institut d’Electronique de Microélectronique et de Nanotechnologie (IEMN), UMR, CNRS, 8520 Avenue Pointcarré, BP 60069, 59652 Villeneuve d’Ascq (France)

    2017-02-28

    Highlights: • Na doped ZnO nanocrystals were prepared via sol–gel method. • A substitution of Zn{sup 2+} by Na{sup +} was demonstrated. • Low Na concentration induces higher photocatalytic activity under solar irradiation. • Oxygen vacancies guided the processes of charge separation. - Abstract: Na doped ZnO nanocrystals (NCs) were successfully produced by sol–gel process and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution TEM (HRTEM), Raman scattering, UV–vis diffuse reflectance spectroscopy and photoluminescence (PL). XRD analysis indicated that all the prepared samples present pure hexagonal wurtzite structure without any Na related phases. The lattice distortion, calculated using Williamson hall equation, induces stress and a reduction of NCs size from 71.4 to 24.5 nm. TEM images showed NCs with hexagonal shape and a rather uniform size distribution. The selected area electron diffraction (SAED) patterns confirmed the high crystal quality along the 〈101〉 direction and is consistent with the hexagonal wurtzite structure of ZnO. The Raman spectra are dominated by E{sub 2}{sup high} mode of ZnO. High Na doping shows the occurrence of anomalous local vibrational Raman modes close to 270 and 513 cm{sup −1} that are related to intrinsic host lattice defects and distortion, respectively. Optical band gap was found to vary with Na content. Photoluminescence (PL) spectra indicate the presence of a high density of defects in ZnO NCs which are mainly oxygen vacancies. Finally, the obtained NCs were used as a photocatalyst to degrade Rhodamine B (RhB) in solution, under solar irradiation. Na doping enhances the photocatalytic activity of ZnO NCs till an optimum concentration of 0.5% where a full degradation was observed after 120 min of sun light irradiation. Furthermore, this sample presents a good cycling stability and reusability. Based on scavangers test, it was found that both superoxide and

  15. Structural and dielectric properties of Al x Zn1- x O ( x = 0, 0.02, 0.04, 0.06, 0.08 and 0.10) nanoparticles

    Science.gov (United States)

    Sharma, Neha; Kumar, Sanjay; Sharma, Varun

    2018-05-01

    The chemical precipitation method is followed for the synthesis of Al-doped ZnO nanoparticles (NPs) with varying doping concentrations (0, 0.02, 0.04, 0.06, 0.08, and 0.10 M). A single hexagonal crystalline phase of wurtzite structure has been confirmed for all the samples by X-ray diffraction. Crystalline size and microstrain of the un-doped and doped ZnO (NPs) is determined by the Williamson-Hall (W-H) analysis. The optical properties like band gap and Urbach energy are found out by the UV-visible spectroscopy. The functional bonds are detailed by Fourier transmission infrared spectroscopy. The dielectric properties have been shown by doped sample due to hopping mechanisms as compared to the undoped. The loss factor (tan δ) follows an inverse direction as correspond to frequency due to the presence of dielectric dispersion.

  16. Structural, elastic, mechanical and thermodynamic properties of Terbium oxide: First-principles investigations

    Directory of Open Access Journals (Sweden)

    Samah Al-Qaisi

    Full Text Available First-principles investigations of the Terbium oxide TbO are performed on structural, elastic, mechanical and thermodynamic properties. The investigations are accomplished by employing full potential augmented plane wave FP-LAPW method framed within density functional theory DFT as implemented in the WIEN2k package. The exchange-correlation energy functional, a part of the total energy functional, is treated through Perdew Burke Ernzerhof scheme of the Generalized Gradient Approximation PBEGGA. The calculations of the ground state structural parameters, like lattice constants a0, bulk moduli B and their pressure derivative B′ values, are done for the rock-salt RS, zinc-blende ZB, cesium chloride CsCl, wurtzite WZ and nickel arsenide NiAs polymorphs of the TbO compound. The elastic constants (C11, C12, C13, C33, and C44 and mechanical properties (Young’s modulus Y, Shear modulus S, Poisson’s ratio σ, Anisotropic ratio A and compressibility β, were also calculated to comprehend its potential for valuable applications. From our calculations, the RS phase of TbO compound was found strongest one mechanically amongst the studied cubic structures whereas from hexagonal phases, the NiAs type structure was found stronger than WZ phase of the TbO. To analyze the ductility of the different structures of the TbO, Pugh’s rule (B/SH and Cauchy pressure (C12–C44 approaches are used. It was found that ZB, CsCl and WZ type structures of the TbO were of ductile nature with the obvious dominance of the ionic bonding while RS and NiAs structures exhibited brittle nature with the covalent bonding dominance. Moreover, Debye temperature was calculated for both cubic and hexagonal structures of TbO in question by averaging the computed sound velocities. Keywords: DFT, TbO, Elastic properties, Thermodynamic properties

  17. Influence of the processing conditions on the structural properties of ZnO layers obtained by PECVD

    Energy Technology Data Exchange (ETDEWEB)

    Kitova, S; Danev, G, E-mail: skitova@clf.bas.b [Institute of Optical Materials and Technology ' Acad. J. Malinowski' , Bulgarian Academy of Sciences, Acad. G. Bonchev str., bl.109, 1113 Sofia (Bulgaria)

    2010-11-01

    The plasma enhanced chemical vapor deposition (PECVD) is a powerful and flexible instrument for depositing thin layers, nanocomposites or nanostructures. In this work ZnO layers have been grown by metal-organic PECVD (RF - 13.56 MHz) on Si wafers. Zn acetylacetonate has been used as a precursor and oxygen as oxidant. The influence of the oxygen content in gas mixture, the total pressure, substrate temperature and ZnO seed layer on the structural properties of the layers deposited on Si wafers has been studied. ZnO layer properties were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD data have shown that all layers are crystalline with hexagonal wurtzite structure. The crystallites are preferentially oriented along c-axis direction perpendicular to the substrate surfaces. The results obtained indicate that by controlling the oxygen content in gas mixture, the total pressure and substrate temperature during the film growth one can control the formation of c-axis phase and the crystallite grain size. Nanorods with good alignment, vertically orientated to the substrate surface can be observed in the layers deposited at low content of O{sub 2} in plasma at substrate temperature of 400 {sup o}C. Due to their structural characteristics these layers are potential materials for preparing chemical- and biosensors where inherently large surface to volume ratio of structured materials are important prerequisite for enhanced sensitivity.

  18. Influence of crystal structure on the CoII diffusion behavior in the Zn1-xCoxO system

    International Nuclear Information System (INIS)

    Peiteado, M.; Makovec, D.; Villegas, M.; Caballero, A.C.

    2008-01-01

    The solid state interaction of the Zn 1-x Co x O nominal system is investigated by means of diffusion couples and analysis of co-precipitated samples. The formation of a homogeneous Co:ZnO solid solution is found to be determined by the crystal structure from which Co II ions diffuse into the wurtzite lattice. No diffusion is observed whenever the CoO rock-salt structure is formed from the Co II precursor. On the contrary, the diffusion from the Co 3 O 4 spinel phase is feasible but has a limited temperature range defined by the reduction at a high temperature of Co III -Co II , since this process again leads to the formation of the rock-salt structure. However, when using a highly reactive and homogeneous co-precipitated starting powder, neither the spinel phase nor the rock-salt structure is formed, and a Co II :ZnO solid solution is obtained, which remains stable up to high temperatures. - Graphical abstract: Maximum diffusion distance for the ZnO-CoO x couple as a function of temperature. Dashed gray lines represent the temperature values at which the transformations between CoO and Co 3 O 4 compounds take place

  19. Structural and optical properties of chromium doped zinc oxide nanoparticles synthesized by sol-gel method

    Energy Technology Data Exchange (ETDEWEB)

    Naqvi, Syed Mohd. Adnan, E-mail: adiaks2004@yahoo.co.in [Department of Fundamental and Applied Sciences, Universiti Teknologi Petronas, Bandar Seri Iskandar, Perak (Malaysia); Irshad, Kashif, E-mail: alig.kashif@gmail.com [Department of Mechanical Engineering, Universiti Teknologi Petronas, Bandar Seri Iskandar, Perak (Malaysia); Soleimani, Hassan, E-mail: hassan.soleimani@petronas.com.my, E-mail: noorhana-yahya@petronas.com.my; Yahya, Noorhana, E-mail: hassan.soleimani@petronas.com.my, E-mail: noorhana-yahya@petronas.com.my

    2014-10-24

    Nanosized Cr-doped ZnO nano particles were synthesized by facile sol-gel auto combustion method. The structural and optical properties of Cr-doped ZnO nanoparticles have been investigated by XRD and UV-Vis spectroscopy at room temperature for 0% to 8% concentration. X-ray diffraction analysis reveals that the Cr-doped ZnO crystallizes in a single phase polycrystalline nature with wurtzite lattice. With every % of doping, the peaks are shifting scarcely and doping of Cr is possible up to 7%. After that, the last peak vanishes, that signifies its structure is transmuted from 8% doping. The average crystallite size decreases with increase in Cr concentration (i.e. 28.9 nm for 0% to 25.8 nm for 8%). The UV-Vis spectra of the nanoparticles betoken an incrementation in the band gap energy from 3.401, 3.415, 3.431, 3.437,3.453, 3.514,3.521, 3.530 and 3.538 eV respectively, for 0,1, 2, 3, 4, 5, 6, 7 and 8 % doping concentration.

  20. Influences of Co doping on the structural and optical properties of ZnO nanostructured

    Science.gov (United States)

    Majeed Khan, M. A.; Wasi Khan, M.; Alhoshan, Mansour; Alsalhi, M. S.; Aldwayyan, A. S.

    2010-07-01

    Pure and Co-doped ZnO nanostructured samples have been synthesized by a chemical route. We have studied the structural and optical properties of the samples by using X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), field-emission transmission electron microscope (FETEM), energy-dispersive X-ray (EDX) analysis and UV-VIS spectroscopy. The XRD patterns show that all the samples are hexagonal wurtzite structures. Changes in crystallite size due to mechanical activation were also determined from X-ray measurements. These results were correlated with changes in particle size followed by SEM and TEM. The average crystallite sizes obtained from XRD were between 20 to 25 nm. The TEM images showed the average particle size of undoped ZnO nanostructure was about 20 nm whereas the smallest average grain size at 3% Co was about 15 nm. Optical parameters such as absorption coefficient ( α), energy band gap ( E g ), the refractive index ( n), and dielectric constants ( σ) have been determined using different methods.

  1. Structural and plasmonic properties of noble metal doped ZnO nanomaterials

    Science.gov (United States)

    Pathak, Trilok K.; Swart, H. C.; Kroon, R. E.

    2018-04-01

    Noble metal doped ZnO has been synthesized by the combustion method and the effect of different metals (Ag, Au, Pd) on the structural, morphological, optical, photoluminescence and localized surface plasmon resonance (LSPR) properties has been investigated. X-ray diffraction analysis revealed that the ZnO had a hexagonal wurtzite structure and the crystallite sizes were affected by the doping. The formation of noble metal nanoparticles (NPs) was investigated using transmission electron microscopy and diffuse reflectance spectra. The LSPR of the metallic NPs was predicted using Mie theory calculations. The absorption spectra were calculated using the Kubelka-Munk function and the optical bandgap varied from 3.06 to 3.18 eV for the different doping materials. The experimental results suggest that the origin of enhanced emission was due to direct interaction between the laser photons and the noble material NPs which in turn leads to photoemission transfer of electrons from the noble metals NPs to the conduction band of ZnO.

  2. Structural and optical properties of chromium doped zinc oxide nanoparticles synthesized by sol-gel method

    International Nuclear Information System (INIS)

    Naqvi, Syed Mohd. Adnan; Irshad, Kashif; Soleimani, Hassan; Yahya, Noorhana

    2014-01-01

    Nanosized Cr-doped ZnO nano particles were synthesized by facile sol-gel auto combustion method. The structural and optical properties of Cr-doped ZnO nanoparticles have been investigated by XRD and UV-Vis spectroscopy at room temperature for 0% to 8% concentration. X-ray diffraction analysis reveals that the Cr-doped ZnO crystallizes in a single phase polycrystalline nature with wurtzite lattice. With every % of doping, the peaks are shifting scarcely and doping of Cr is possible up to 7%. After that, the last peak vanishes, that signifies its structure is transmuted from 8% doping. The average crystallite size decreases with increase in Cr concentration (i.e. 28.9 nm for 0% to 25.8 nm for 8%). The UV-Vis spectra of the nanoparticles betoken an incrementation in the band gap energy from 3.401, 3.415, 3.431, 3.437,3.453, 3.514,3.521, 3.530 and 3.538 eV respectively, for 0,1, 2, 3, 4, 5, 6, 7 and 8 % doping concentration

  3. Structural, linear and nonlinear optical properties of co-doped ZnO thin films

    Science.gov (United States)

    Shaaban, E. R.; El-Hagary, M.; Moustafa, El Sayed; Hassan, H. Shokry; Ismail, Yasser A. M.; Emam-Ismail, M.; Ali, A. S.

    2016-01-01

    Different compositions of Co-doped zinc oxide [(Zn(1- x)Co x O) ( x = 0, 0.02, 0.04, 0.06, 0.08 and 0.10)] thin films were evaporated onto highly clean glass substrates by thermal evaporation technique using a modified source. The structural properties investigated by X-ray diffraction revealed hexagonal wurtzite ZnO-type structure. The crystallite size of the films was found to decrease with increasing Co content. The optical characterization of the films has been carried out using spectral transmittance and reflectance obtained in the wavelength range from 300 to 2500 nm. The refractive index has been found to increase with increasing Co content. It was further found that optical energy gap decreases from 3.28 to 3.03 eV with increasing Co content from x = 0 to x = 0.10, respectively. The dispersion of refractive index has been analyzed in terms of Wemple-DiDomenico (WDD) single-oscillator model. The oscillator parameters, the single-oscillator energy ( E o), the dispersion energy ( E d), and the static refractive index ( n 0), were determined. The nonlinear refractive index of the Zn(1- x)Co x O thin films was calculated and revealed well correlation with the linear refractive index and WDD parameters which in turn depend on the density and molar volume of the system.

  4. Optical and structural properties of thin films of ZnO at elevated temperature

    International Nuclear Information System (INIS)

    Kayani, Zohra N.; Afzal, Tosif; Riaz, Saira; Naseem, Shahzad

    2014-01-01

    Highlights: • Thin films of ZnO are prepared on glass substrates using dip-coating. • The X-ray diffraction showed that films are crystalline. • Optical measurements show that the film possesses high transmittance in visible region. • The transmission decreased with increased withdrawal speed. • The films has direct band gap in range 3.78-3.48 eV. - Abstract: Zinc oxide (ZnO) thin films were prepared on glass substrate by sol–gel dip-coating method. The paper presents the properties of zinc oxide thin films deposited on soda-lime-glass substrate via dip-coating technique, using zinc acetate dehydrate and ethanol as raw materials. The effect of withdrawal speed on the crystalline structure, surface morphology and optical properties of the thin films has been investigated using XRD, SEM and UV–Vis spectrophotometer. X-ray diffraction study shows that all the films have hexagonal wurtzite structure with preferred orientation in (0 0 2) direction and transmission spectra showed highly transparent films with band gap ranging from 3.78 to 3.48 eV

  5. Investigation of Structural, Magnetic, and Optical Properties of ZnO Codoped with Co and Cd

    Directory of Open Access Journals (Sweden)

    Lubna Mustafa

    2014-01-01

    Full Text Available Co and Cd have been codoped in ZnO using a simple solid state reaction technique to synthesize dilute magnetic oxide semiconductors of composition Zn0.9Co0.1−xCdxO (x = 0.0-0.1 with an increment of 0.02. Hexagonal wurtzite structure has been obtained for samples up to x = 0.06, using X-ray diffractometry. However, at x = 0.08 and 0.1, secondary peak of CdO is observed. Raman spectra of the samples have been obtained in 200–800 cm−1 range. UV-VIS spectrophotometer is used to study the optical properties, which shows that band gap energy decreases with the increase in Cd concentration. A weak ferromagnetic behavior was evident which decreased further by adding Cd in the series. Room temperature resistivity measurements performed using four-point probe technique showed that their values lie in the semiconductor range. Structural morphology of the samples has been investigated by a scanning electron microscope and grain size has been determined. Raman spectra and Fourier transform infrared spectroscopy revealed the successful incorporation of Co and Cd ions into the host ZnO lattice.

  6. Structural cladding /clad structures:

    DEFF Research Database (Denmark)

    Beim, Anne

    2013-01-01

    tendencies, which can be traced in the use of materials, the structural features and the construction details of building systems in selected architectural works. With a particular focus at heavy constructions made of solid wood and masonry, and light weight constructions made of wooden frame structures...... and steel profiles, it is the intention to analyze, compare, and discuss how these various construction solutions point out strategies for development based on fundamentally different mindsets. The research questions address the following issues: How to learn from traditional construction principles: When...

  7. Structural, morphological and electroluminescence studies of Zno:Co nanophosphor

    Science.gov (United States)

    Singh, Anju; Vishwakarma, H. L.

    2016-09-01

    The nanoparticles of zinc oxide (ZnO) doped with various concentrations of cobalt (Co) were synthesized by chemical precipitation method in the presence of capping agent polyvinylpyrrolidone (PVP). The effect of doping concentration on structural and morphological properties has been studied by X-ray diffraction (XRD) and scanning electron microscope (SEM). Cell volume, bond length, texture coefficient, lattice constants and dislocation density are also studied. Here, we also compared the interplaner spacing and relative peak intensities from their standard values with different angles. Crystallite sizes have been calculated by Debye-Scherrer's formula whose values are decreasing with increase in cobalt content up to 3 %. It has been seen that the growth orientation of the prepared ZnO nanorods was (101). The XRD analysis also ensures that ZnO has a hexagonal (wurtzite) crystal structure. The electroluminescence (EL) cells were prepared by placing pure and cobalt-doped ZnO nanoparticles between ITO-coated conducting glass plate and aluminium foil. Alternating voltage of various frequencies was applied, and EL brightness at different voltages was measured and corresponding current was also recorded. The voltage dependence of electroluminescence (EL) brightness of the ZnO:Co shows exponential increase. The linear voltage-current characteristic indicates ohmic nature. The EL brightness at a particular voltage is found to increase by increasing Co doping, but for higher percentage of Co the EL brightness is reduced. It is also seen that Co does not influence the threshold voltage. The brightness is also affected by increasing the frequency of AC signal.

  8. Structural cladding /clad structures

    DEFF Research Database (Denmark)

    Beim, Anne

    2012-01-01

    Structural Cladding /Clad Structures: Studies in Tectonic Building Practice A. Beim CINARK – Centre for Industrialized Architecture, Institute of Architectural Technology, The Royal Danish Academy of Fine Arts School of Architecture, Copenhagen, Denmark ABSTRACT: With point of departure in the pr......Structural Cladding /Clad Structures: Studies in Tectonic Building Practice A. Beim CINARK – Centre for Industrialized Architecture, Institute of Architectural Technology, The Royal Danish Academy of Fine Arts School of Architecture, Copenhagen, Denmark ABSTRACT: With point of departure...... to analyze, compare, and discuss how these various construction solutions point out strategies for development based on fundamentally different mindsets. The research questions address the following issues: How to learn from traditional construction principles: When do we see limitations of tectonic maneuver......, to ask for more restrictive building codes. As an example, in Denmark there are series of increasing demands in the current building legislations that are focused at enhancing the energy performance of buildings, which consequently foster rigid insulation standards and ask for improvement of air...

  9. Electronic structure of nitride-based quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Winkelnkemper, Momme

    2008-11-07

    In the present work the electronic and optical properties of In{sub x}Ga{sub 1-x}N/GaN and GaN/AlN QDs are studied by means of eight-band k.p theory. Experimental results are interpreted in detail using the theoretical results. The k.p model for the QD electronicstructure calculations accounts for strain, piezo- and pyroelectric effects, spin-orbit and crystal-field splitting, and is implemented for arbitrarily shaped QDs on a finite differences grid. Few-particle corrections are included using the self-consistent Hartree method. Band parameters for the wurtzite and zinc-blende phases of GaN, AlN, and InN are derived from first-principle G{sub 0}W{sub 0} band-structure calculations. Reliable values are also provided for parameters that have not been determined experimentally yet. The electronic properties of nitride QDs are dominated by the large built-in piezo- and pyroelectric fields, which lead to a pronounced red-shift of excitonic transition energies and extremely long radiative lifetimes in large GaN/AlN QDs. In In{sub x}Ga{sub 1-x}N/GaN QDs these fields induce a pronounced dependence of the radiative excitonic lifetimes on the exact QD shape and composition. It is demonstrated that the resulting variations of the radiative lifetimes in an inhomogeneous QD ensemble are the origin of the multi-exponential luminescence decay frequently observed in time-resolved ensemble measurements on In{sub x}Ga{sub 1-x}N/GaN QDs. A polarization mechanism in nitride QDs based on strain-induced valence-band mixing effects is discovered. Due to the valence-band structure of wurtzite group-III nitrides and the specific strain situation in c-plane QDs, the confined hole states are formed predominantly by the two highest valence bands. In particular, the hole ground state (h{sub 0} {identical_to} h{sub A}) is formed by the A band, and the first excited hole state (h{sub 1} {identical_to} h{sub B}) by the B band. It is shown that the interband transitions involving h{sub A} or h

  10. Effects of grinding on certain crystalline structures; Influence de broyage sur quelques structures cristallines

    Energy Technology Data Exchange (ETDEWEB)

    Tekiz, Y [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

    1965-06-15

    The effects of grinding on certain crystalline substances (ZnO, ZnS, Sb), have been studied using X-ray diffraction and electron microscopy. The treatments were carried out using a vibrating mill which involves a higher energy than more conventional equipment such as ball-mills. Various methods have been proposed for determining the width of the intrinsic profile ({beta}). In the case of zinc oxide it has been shown possible to differentiate the respective contributions of the fragmentation effects and of lattice deformation effects to the overall effects of the grinding. For the two types of zinc sulfide (blend and Wurtzite) it has been shown that the blend-wurtzite) transition point is very much decreased, and that the rate of transformation of wurtzite into the stable form (blend) at room temperature is considerably increased by the grinding. In the case of antimony, the method of fragmentation shows the existence of an anisotropy which appears to be connected with easily cleavable planes. These observations show that in the case of grinding carried out with sufficient energy, the accumulation of this energy in the matter through the creation of lattice defects can accelerate the reaction rate or bring about physical transformations. (author) [French] Les effets du broyage sur certains corps cristallises (ZnO, ZnS, Sb) ont ete etudies a l'aide de la diffraction de rayons X et de la microscopie electronique. Les broyages ont ete effectues au moyen d'un vibro-broyeur qui met en jeu une energie superieure par rapport aux appareils plus conventionnels tels que les broyeurs a boulets. Diverses methodes concernant la determination de la largeur du profil intrinseque ({beta}) ont ete proposees. Dans le cas de l'oxyde de zinc on a montre la possibilite de differencier les contributions de l'effet de fragmentation et celui de perturbation du reseau, a l'effet total du broyage. Avec les deux varietes de sulfure de zinc (blende et Wurtzite) on a montre que le point de

  11. Effects of grinding on certain crystalline structures

    International Nuclear Information System (INIS)

    Tekiz, Y.

    1965-06-01

    The effects of grinding on certain crystalline substances (ZnO, ZnS, Sb), have been studied using X-ray diffraction and electron microscopy. The treatments were carried out using a vibrating mill which involves a higher energy than more conventional equipment such as ball-mills. Various methods have been proposed for determining the width of the intrinsic profile (β). In the case of zinc oxide it has been shown possible to differentiate the respective contributions of the fragmentation effects and of lattice deformation effects to the overall effects of the grinding. For the two types of zinc sulfide (blend and Wurtzite) it has been shown that the blend-wurtzite) transition point is very much decreased, and that the rate of transformation of wurtzite into the stable form (blend) at room temperature is considerably increased by the grinding. In the case of antimony, the method of fragmentation shows the existence of an anisotropy which appears to be connected with easily cleavable planes. These observations show that in the case of grinding carried out with sufficient energy, the accumulation of this energy in the matter through the creation of lattice defects can accelerate the reaction rate or bring about physical transformations. (author) [fr

  12. Evaluation of the structural, optical and electrical properties of AZO thin films prepared by chemical bath deposition for optoelectronics

    Science.gov (United States)

    Kumar, K. Deva Arun; Valanarasu, S.; Rosario, S. Rex; Ganesh, V.; Shkir, Mohd.; Sreelatha, C. J.; AlFaify, S.

    2018-04-01

    Aluminum doped zinc oxide (AZO) thin films for electrode applications were deposited on glass substrates using chemical bath deposition (CBD) method. The influence of deposition time on the structural, morphological, and opto-electrical properties of AZO films were investigated. Structural studies confirmed that all the deposited films were hexagonal wurtzite structure with polycrystalline nature and exhibited (002) preferential orientation. There is no other impurity phases were detected for different deposition time. Surface morphological images shows the spherically shaped grains are uniformly arranged on to the entire film surface. The EDS spectrum confirms the presence of Zn, O and Al elements in deposited AZO film. The observed optical transmittance is high (87%) in the visible region, and the calculated band gap value is 3.27 eV. In this study, the transmittance value is decreased with increasing deposition time. The room temperature PL spectrum exposed that AZO thin film deposited at (60 min) has good optical quality with less defect density. The minimum electrical resistivity and maximum carrier concentration values were observed as 8.53 × 10-3(Ω cm) and 3.53 × 1018 cm-3 for 60 min deposited film, respectively. The obtained figure of merit (ϕ) value 3.05 × 10-3(Ω/sq)- 1 is suggested for an optoelectronic device.

  13. Structural and room temperature ferromagnetic properties of Ni doped ZnO nanoparticles via low-temperature hydrothermal method

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Kun; Liu, Changzhen, E-mail: liuchangzhen94@163.com; Chen, Rui; Fang, Xiaoxiang; Wu, Xiuling; Liu, Jie

    2016-12-01

    A series of Zn{sub 1−x}Ni{sub x}O (x=0, 1%, 3%, 5%) nanoparticles have been synthesized via a low-temperature hydrothermal method. Influence of Ni doping concentration on the structure, morphology, optical properties and magnetism of the samples was investigated by means of X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, UV–vis spectrophotometer and vibrating sample magnetometer instruments. The results show that the undoped and doped ZnO nanoparticles are both hexagonal wurtzite structures. The surface analysis was performed using X-ray photoelectron spectroscopic studies. The images of SEM reveal that the structure of pure ZnO and Ni doped samples are nanoparticles which intended to form flakes with thickness of few nanometers, being overlain with each one to develop the network with some pores and voids. Based on the ultraviolet–visible (UV–vis) spectroscopy analysis, it indicates that the band gap energy decreases with the increasing concentration of Ni. Furthermore, The Ni doped ZnO samples didn't exhibit higher ultraviolet-light-driven photocatalytic activity compared to the undoped ZnO sample. Vibrating sample magnetometer was used for the magnetic property investigations, and the result indicates that room temperature ferromagnetism property of 3% Ni doped sample is attributed to oxygen vacancy and interaction between doped ions.

  14. Investigation of Zinc Oxide-Loaded Poly(Vinyl Alcohol) Nanocomposite Films in Tailoring Their Structural, Optical and Mechanical Properties

    Science.gov (United States)

    Aslam, Muhammad; Kalyar, Mazhar Ali; Raza, Zulfiqar Ali

    2018-04-01

    Wurtzite ZnO nanoparticles, as a nanofiller, were incorporated in a poly(vinyl alcohol) (PVA) matrix to prepare multipurpose nanocomposite films using a solution casting approach. Some advanced analytical techniques were used to investigate the properties of prepared nanocomposite films. The mediation of ZnO nanofillers resulted in modification of structural, optical and mechanical properties of nanocomposite films. A comprehensive band structure investigation might be useful for designing technological applications like in optoelectronic devices. The experimental results were found to be closely dependent on the nanofiller contents. Some theoretical models like Tauc's and Wemple-DiDomenico, were employed to investigate the band structure parameters. The imaginary part of the dielectric constant was used to investigate the band gap. Then, the Helpin-Tsai model was employed to predict Young's moduli of the prepared nanocomposite films. On 3 wt.% ZnO nanofiller loading, the optical band gap of the PVA-based nanocomposite film was decreased from 5.26 eV to 3 eV, the tensile strength increased from 25.3 MPa to 48 MPa and Young's modulus increased from 144 MPa to 544 MPa.

  15. Extended x-ray absorption fine structure in Ga1-xMnxN/SiC films with high Mn content

    Science.gov (United States)

    Sancho-Juan, O.; Martínez-Criado, O.; Cantarero, A.; Garro, N.; Salomé, M.; Susini, J.; Olguín, D.; Dhar, S.; Ploog, K.

    2011-05-01

    In this study, the local atomic structure of highly homogeneous Ga1-xMnxN alloy films (0.03structure measurements. From the curve fitting, the structural parameters corresponding to the first two atomic shells surrounding both Ga and Mn atoms are reported. In the Ga1-xMnxN films, grown by molecular beam epitaxy, the Mn atoms are in tetrahedral configuration, independent of the Mn concentration; that is, they are in a substitutional site, MnGa, in the wurtzite structure. A small increase in the interatomic distances has been found with increasing Mn content. The Debye-Waller factor does not show a significant trend as Mn content increases, which suggests the presence of short-range disorder in the GaN lattice. Ab initio calculations of the structural parameter for two different Mn concentrations are consistent with the experimental results.

  16. Mosaic Structure Characterization of the AlInN Layer Grown on Sapphire Substrate

    Directory of Open Access Journals (Sweden)

    Engin Arslan

    2014-01-01

    Full Text Available The 150 nm thick, (0001 orientated wurtzite-phase Al1−xInxN epitaxial layers were grown by metal organic chemical vapor deposition on GaN (2.3 µm template/(0001 sapphire substrate. The indium (x concentration of the Al1−xInxN epitaxial layers was changed as 0.04, 0.18, 0.20, 0.47, and 0.48. The Indium content (x, lattice parameters, and strain values in the AlInN layers were calculated from the reciprocal lattice mapping around symmetric (0002 and asymmetric (10–15 reflection of the AlInN and GaN layers. The mosaic structure characteristics of the AlInN layers, such as lateral and vertical coherence lengths, tilt and twist angle, heterogeneous strain, and dislocation densities (edge and screw type dislocations of the AlInN epilayers, were investigated by using high-resolution X-ray diffraction measurements and with a combination of Williamson-Hall plot and the fitting of twist angles.

  17. Annealing effect on structural and optical properties of chemical bath deposited MnS thin film

    Energy Technology Data Exchange (ETDEWEB)

    Ulutas, Cemal, E-mail: cemalulutas@hakkari.edu.tr [Faculty of Education, Hakkari Universty, 30000, Hakkari (Turkey); Gumus, Cebrail [Faculty of Science and Letters, Cukurova University, 01330, Adana (Turkey)

    2016-03-25

    MnS thin film was prepared by the chemical bath deposition (CBD) method on commercial microscope glass substrate deposited at 30 °C. The as-deposited film was given thermal annealing treatment in air atmosphere at various temperatures (150, 300 and 450 °C) for 1 h. The MnS thin film was characterized by using X-ray diffraction (XRD), UV-vis spectrophotometer and Hall effect measurement system. The effect of annealing temperature on the structural, electrical and optical properties such as optical constants of refractive index (n) and energy band gap (E{sub g}) of the film was determined. XRD measurements reveal that the film is crystallized in the wurtzite phase and changed to tetragonal Mn{sub 3}O{sub 4} phase after being annealed at 300 °C. The energy band gap of film decreased from 3.69 eV to 3.21 eV based on the annealing temperature.

  18. Morphology evolution of hydrothermally grown ZnO nanostructures on gallium doping and their defect structures

    Energy Technology Data Exchange (ETDEWEB)

    Pineda-Hernandez, G. [Facultad de Ingenieria Quimica, Benemerita Universidad Autonoma de Puebla, C.P. 72570 Puebla, Pue. (Mexico); Escobedo-Morales, A., E-mail: alejandroescobedo@hotmail.com [Facultad de Ingenieria Quimica, Benemerita Universidad Autonoma de Puebla, C.P. 72570 Puebla, Pue. (Mexico); Pal, U. [Instituto de Fisica, Benemerita Universidad Autonoma de Puebla, Apdo. Postal J-48, C.P. 72570 Puebla, Pue. (Mexico); Chigo-Anota, E. [Facultad de Ingenieria Quimica, Benemerita Universidad Autonoma de Puebla, C.P. 72570 Puebla, Pue. (Mexico)

    2012-08-15

    In the present article, the effect of gallium doping on the morphology, structural, and vibrational properties of hydrothermally grown ZnO nanostructures has been studied. It has been observed that incorporated gallium plays an important role on the growth kinetics and hence on the morphology evolution of the ZnO crystals. Ga doping in high concentration results in the contraction of ZnO unit cell, mainly along c-axis. Although Ga has high solubility in ZnO, heavy doping promotes the segregation of Ga atoms as a secondary phase. Incorporated Ga atoms strongly affect the vibrational characteristics of ZnO lattice and induce anomalous Raman modes. Possible mechanisms of morphology evolution and origin of anomalous Raman modes in Ga doped ZnO nanostructures are discussed. -- Highlights: Black-Right-Pointing-Pointer Ga doped ZnO nanostructures were successfully grown by hydrothermal chemical route. Black-Right-Pointing-Pointer Ga doping has strong effect on the resulting morphology of ZnO nanostructures. Black-Right-Pointing-Pointer Anomalous vibrational modes in wurtzite ZnO lattice are induced by Ga doping. Black-Right-Pointing-Pointer Incorporated Ga atoms accommodate at preferential lattice sites.

  19. Structure evolution of zinc oxide thin films deposited by unbalance DC magnetron sputtering

    Energy Technology Data Exchange (ETDEWEB)

    Aryanto, Didik, E-mail: didi027@lipi.go.id [Research Center for Physics, Indonesian Institute of Sciences, Serpong 15314, Tangerang Selatan (Indonesia); Materials Research Group, Physics Department, Universitas Negeri Semarang, Gunungpati, Semarang 50229 Jawa Tengah (Indonesia); Marwoto, Putut; Sugianto [Physics Department, Faculty of Mathematics and Science, Universitas Negeri Semarang, Gunungpati, Semarang 50229 Jawa Tengah (Indonesia); Materials Research Group, Physics Department, Universitas Negeri Semarang, Gunungpati, Semarang 50229 Jawa Tengah (Indonesia); Sudiro, Toto [Research Center for Physics, Indonesian Institute of Sciences, Serpong 15314, Tangerang Selatan (Indonesia); Birowosuto, Muhammad D. [Research Center for Physics, Indonesian Institute of Sciences, Serpong 15314, Tangerang Selatan (Indonesia); CINTRA UMI CNRS/NTU/THALES 3288 Research Techno Plaza, 50 Nanyang Drive, Border X Block, level 6, 637553 (Singapore); Sulhadi [Physics Department, Faculty of Mathematics and Science, Universitas Negeri Semarang, Gunungpati, Semarang 50229 Jawa Tengah (Indonesia)

    2016-04-19

    Zinc oxide (ZnO) thin films are deposited on corning glass substrates using unbalanced DC magnetron sputtering. The effect of growth temperature on surface morphology and crystallographic orientation of ZnO thin film is studied using atomic force microscopy (AFM) and X-ray diffraction (XRD) techniques. The surface morphology and crystallographic orientation of ZnO thin film are transformed against the increasing of growth temperature. The mean grain size of film and the surface roughness are inversely and directly proportional towards the growth temperature from room temperature to 300 °C, respectively. The smaller grain size and finer roughness of ZnO thin film are obtained at growth temperature of 400 °C. The result of AFM analysis is in good agreement with the result of XRD analysis. ZnO thin films deposited in a series of growth temperatures have hexagonal wurtzite polycrystalline structures and they exhibit transformations in the crystallographic orientation. The results in this study reveal that the growth temperature strongly influences the surface morphology and crystallographic orientation of ZnO thin film.

  20. Structural and optical investigations of oxygen defects in zinc oxide nanoparticles

    International Nuclear Information System (INIS)

    Sahai, Anshuman; Goswami, Navendu

    2015-01-01

    ZnO nanoparticles (NPs) were prepared implementing chemical precipitation method. Structural and optical characterizations of synthesized ZnO NPs were thoroughly probed applying X-ray diffraction (XRD), transmission electron microscope (TEM), energy dispersive X-ray (EDX) analysis, X-ray photoelectron spectroscopy (XPS), UV- Visible absorption and fluorescence (FL) spectroscopy. The XRD and TEM analyses revealed hexagonal wurtzite phase with 25-30 nm size. EDX analysis indicated oxygen (O) rich composition of nanoparticles. In accordance with EDX, XPS analysis verifies O i rich stoichiometry of prepared NPs. Furthermore, concurrence of lattice oxygen (O L ), interstitial oxygen (O i ) and oxygen vacancy (V O ) in ZnO NPs was demonstrated through XPS analysis. Size quantization of nanoparticles is evident by blue shift of UV-Visible absorption energy. The FL spectroscopic investigations ascertain the existence of several discrete and defect states and radiative transitions occurring therein. Display of visible emission from oxygen defect states and most importantly, excess of O i defects in prepared ZnO nanoparticles, was well established through FL study

  1. Role of Fe doping on structural and vibrational properties of ZnO nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Pandiyarajan, T.; Udayabhaskar, R.; Karthikeyan, B. [National Institute of Technology, Department of Physics, Tiruchirappalli (India)

    2012-05-15

    In this report, Raman and Fourier Transform Infrared (FTIR) measurements were carried out to study the phonon modes of pure and Fe doped ZnO nanoparticles. The nanoparticles were prepared by sol-gel technique at room temperature. The X-ray diffraction measurements reveal that the nanoparticles are in hexagonal wurtzite structure and doping makes the shrinkage of the lattice parameters, whereas there is no alteration in the unit cell. Raman measurements show both E{sub 2}{sup low} and E{sub 2}{sup High} optical phonon mode is shifted towards lower wave number with Fe incorporation and explained on the basis of force constant variation, stress measurements, respectively. In addition, Fe related local vibrational modes (LVM) were observed for higher concentration of Fe doping. FTIR spectra reveal a band at 444 cm{sup -1} which is specific to E{sub 1} (TO) mode; a red-shift of this mode in Fe doped samples and some surface phonon modes were observed. Furthermore, the observation of additional IR modes, which is considered to have an origin related to Fe dopant in the ZnO nanostructures, is also reported. These additional mode features can be regarded as an indicator for the incorporation of Fe ions into the lattice position of the ZnO nanostructures. (orig.)

  2. Synthesis Structural and Optical Properties Of (Co, Al) co-doped ZnO Nano Particles

    Science.gov (United States)

    Swapna, P.; Venkatramana Reddy, S.

    2018-02-01

    We prepared (Co, Al) co-doped ZnO nanostructures using the method chemical co-precipitation successfully, at room temperature using PEG (Poly ethylene glycol) as stabilizing agent. Samples are prepared with different concentrations by keeping aluminium at 5 mol percent constant and varying the concentration of cobalt from 1 to 5 mol percent. After the preparation all the samples are carefully subjected to characterizations such as XRD, SEM with EDS, TEM, PL and UV-VIS-NIR. XRD pattern shows that all the samples possess hexagonal wurtzite crystal structure having no secondary phases pertaining to Al or cobalt, which shows successful dissolution of the dopents. TEM results shows the accurate size of particles and is confirmed the XRD data. SEM images of all the samples shows that particles are in nearly spherical shape, EDS spectrum reveals that incorporation of cobalt and aluminum in host lattice. PL spectrum shows that all the samples containing two prominent peaks centered at 420 nm and 446 nm. UV-VIS-NIR spectra has shown three absorptions peaks in the range of wavelength 550 nm to 700 nm, which are ascribed as typical d-d transitions of cobalt ions.

  3. Synthesis, optical, structural, and electrical properties of single-crystalline CdS nanobelts

    Energy Technology Data Exchange (ETDEWEB)

    Alqahtani, Mohammed S. [King Saud University, Department of Physics and Astronomy, Riyadh (Saudi Arabia); Hadia, N.M.A.; Mohamed, S.H. [Sohag University, Physics Department, Faculty of Science, Sohag (Egypt)

    2017-04-15

    CdS nanobelts (NBs) were synthesized by vapor transport of CdS powders. The growth was carried out without any catalyst on quartz and Si (100) substrates. The synthesized CdS NBs were examined by transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM) and selected area electron diffraction (SAED), high-resolution transmission electron microscopy (HR-TEM), X-ray powder diffraction (XRD), energy dispersion analysis of X-ray (EDAX), spectrophotometer, and photoluminescence spectroscopy. CdS NBs were indexed as hexagonal wurtzite structure. The growth was via vapor-solid growth mechanism and along the [100] direction. The refractive index was evaluated in the transparent region, as suggested by Swanepoel, using the envelope method. The refractive index values and the extinction coefficient were decreased by increasing the wavelength. The calculated optical band gap was 2.50 eV. The photoluminescence (PL) spectrum of the synthesized CdS NBs exhibited a green emission peak at 510 nm and a broad red emission peak at 696 nm. The conductivity measurements were achieved, in the temperature range from 300 to 600 K, using the conventional two-probe technique. Two different slopes with different activation energies of 0.618 and 0.215 eV were obtained. The CdS NBs are likely being novel functional materials. Thus, they can be used in the manufacture of innovative optoelectronic nanodevices. (orig.)

  4. Catalyst-free fabrication of novel ZnO/CuO core-Shell nanowires heterojunction: Controlled growth, structural and optoelectronic properties

    Science.gov (United States)

    Khan, Muhammad Arif; Wahab, Yussof; Muhammad, Rosnita; Tahir, Muhammad; Sakrani, Samsudi

    2018-03-01

    Development of controlled growth and vertically aligned ZnO/CuO core-shell heterojunction nanowires (NWs) with large area by a catalyst free vapor deposition and oxidation approach has been investigated. Structural characterization reveals successful fabrication of a core ZnO nanowire having single crystalline hexagonal wurtzite structure along [002] direction and CuO nanostructure shell with thickness (8-10 nm) having polycrystalline monoclinic structure. The optical property analysis suggests that the reflectance spectrum of ZnO/CuO heterostructure nanowires is decreased by 18% in the visible range, which correspondingly shows high absorption in this region as compared to pristine ZnO nanowires. The current-voltage (I-V) characteristics of core-shell heterojunction nanowires measured by conductive atomic force microscopy (C-AFM) shows excellent rectifying behavior, which indicates the characteristics of a good p-n junction. The high-resolution transmission electron microscopy (HRTEM) has confirmed the sharp junction interface between the core-shell heterojunction nanowire arrays. The valence band offset and conduction band offset at ZnO/CuO heterointerfaces are measured to be 2.4 ± 0.05 and 0.23 ± 0.005 eV respectively, using X-ray photoelectron spectroscopy (XPS) and a type-II band alignment structure is found. The results of this study contribute to the development of new advanced device heterostructures for solar energy conversion and optoelectronics applications.

  5. Influence of the Al distribution on the structure, elastic properties, and phase stability of supersaturated Ti1-xAlxN

    International Nuclear Information System (INIS)

    Mayrhofer, P. H.; Music, D.; Schneider, J. M.

    2006-01-01

    Ti 1-x Al x N films and/or their alloys are employed in many industrial applications due to their excellent mechanical and thermal properties. Synthesized by plasma-assisted vapor deposition, Ti 1-x Al x N is reported to crystallize in the cubic NaCl (c) structure for AlN mole fractions below 0.4-0.91, whereas at larger Al contents the hexagonal ZnS-wurtzite (w) structure is observed. Here we use ab initio calculations to analyze the effect of composition and Al distribution on the metal sublattice on phase stability, structure, and elastic properties of c-Ti 1-x Al x N and w-Ti 1-x Al x N. We show that the phase stability of supersaturated c-Ti 1-x Al x N not only depends on the chemical composition but also on the Al distribution of the metal sublattice. An increase of the metastable solubility limit of AlN in c-Ti 1-x Al x N from 0.64 to 0.74 is obtained by decreasing the number of Ti-Al bonds. This can be understood by considering the Al distribution induced changes of the electronic structure, bond energy, and configurational entropy. This may in part explain the large variation of the metastable solubility limit reported in the literature

  6. Effect of the substrate surface topology and temperature on the structural properties of ZnO layers obtained by plasma enhanced chemical vapour deposition

    Energy Technology Data Exchange (ETDEWEB)

    Kitova, S; Danev, G, E-mail: skitova@clf.bas.b [Acad. J .Malinowski Central Laboratory of Photoprocesses, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl.109, 1113 Sofia (Bulgaria)

    2010-04-01

    In this work thin ZnO layers were grown by metal-organic PECVD (RF 13.56 MHz) on Si wafers. Zn acetylacetonate was used as a precursor and oxygen as oxidant. A system for dosed injection of the precursor and oxidant into the plasma reactor was developed. The influence of the substrate surface topology and temperature on the structural properties of the deposited layers was studied. ZnO and graphite powder dispersions were used to modify the silicon wafers before starting the deposition process of the layers. Some of the ZnO layers were deposited on the back, unpolished, side of Si wafers. Depositions at 400 {sup 0}C were performed to examine the effect of the substrate temperatures on the layer growth. The film structure was examined by XRD and SEM. The results show that all layers are crystalline with hexagonal wurtzite structure. The crystallites are preferentially oriented along the c-axis direction perpendicular to the substrate surfaces. ZnO layers deposited on thin ZnO seed films and clean Si surface exhibit well-developed grain structures and more c-axis preferred phase with better crystal quality than that of the layers deposited on graphite seed layer or rough, unpolished Si wafer.

  7. Growth of highly transparent Cd{sub x}Zn{sub 1−x}O (CZO) thin films: Structural and optical studies

    Energy Technology Data Exchange (ETDEWEB)

    Gautam, Naina, E-mail: nainagtm@gmail.com [Department of Electronic Science, University of Delhi South Campus, New Delhi 110023 (India); Singh, Fouran, E-mail: fouran@gmail.com [Inter University Accelerator Centre, Aruna Asaf Ali Marg, New Delhi 110067 (India); Gautam, Subodh K. [Inter University Accelerator Centre, Aruna Asaf Ali Marg, New Delhi 110067 (India); Singh, R.G. [Department of Physics, Bhagini Nivedita College, Delhi University, Delhi 110043 (India); Ojha, S. [Inter University Accelerator Centre, Aruna Asaf Ali Marg, New Delhi 110067 (India); Kapoor, A. [Department of Electronic Science, University of Delhi South Campus, New Delhi 110023 (India)

    2015-11-25

    The deposition of Cd{sub x}Zn{sub 1−x}O thin films with different cadmium concentrations i.e., x = 0.0, 0.05, 0.20 by sol–gel spin coating is reported. The doping fraction of Cd in ZnO films was measured by Rutherford backscattering spectrometry (RBS), while the surface morphology was studied by scanning electron microscopy (SEM). Grazing incidence X-ray diffraction (GIXRD) study was carried out for the structural investigations and reveals hexagonal wurtzite structure with polycrystalline nature. The various structural parameters are calculated including the lattice constants ‘a’ and ‘c’, stress (σ), strain (ε) and internal parameter (u). For x = 0.20 Cd content, the formation of secondary phase of the cubic CdO at 33.12° (111) and 38.41° (200) is observed and this is further confirmed by micro-Raman studies, where the TO mode emerges at ∼261.5 cm{sup −1}. The basic wurtzite structure is maintained as ‘c/a’ ratio and internal parameter ‘u’ found to be closer to the ideal values. All the films are found to be highly transparent in the visible region and a bending of the near band edge (NBE) absorption is observed with Cd doping. It is further confirmed by calculating the Urbach energy (E{sub u}), which is found to be increased from 0.14 eV (for x = 0.0) to 0.26 eV (for x = 0.20) with maximum value for the lightly doped films i.e. x = 0.05. However, the optical band gap is found to decrease from 3.26 eV (for x = 0.0) to 3.08 eV (for x = 0.20). - Highlights: • High transparent Cd{sub x}Zn{sub 1−x}O (CZO) thin films with an average transparency of ∼85% in the visible region. • Band-gap tuning is achieved by Cd doping in ZnO. • Segregation of cubic rock-salt CdO phase upon high doping as confirmed by Micro-Raman and SEM investigations.

  8. Structure and properties of nanoparticles fabricated by laser ablation of Zn metal targets in water and ethanol

    Science.gov (United States)

    Svetlichnyi, V. A.; Lapin, I. N.

    2013-10-01

    Size characteristics, structure, and spectral and luminescent properties of nanoparticles fabricated by laser ablation of zinc metal targets in water and ethanol are experimentally investigated upon excitation by Nd:YAG-laser radiation (1064 nm, 7 ns, and 15 Hz). It is demonstrated that zinc oxide nanoparticles with average sizes of 10 nm (in water) and 16 nm (in ethanol) are formed in the initial stage as a result of ablation. The kinetics of the absorption and luminescence spectra, transmission electron microscopy, and x-ray structural analysis demonstrate that during long storage of water dispersions and their drying, nanoparticles efficiently interact with carbon dioxide gas of air that leads to the formation of water-soluble Zn(CO3)2(OH)6. In ethanol, Zn oxidation leads to the formation of stable dispersions of ZnO nanoparticles with 99% of the wurtzite phase; in this case, the fluorescence spectra of ZnO nanoparticles change with time, shifting toward longer wavelength region from 550 to 620 nm, which is caused by the changed nature of defects.

  9. Preparation and Study the Electrical, Structural and Gas Sensing Properties of ZnO Thick Film Resistor

    Directory of Open Access Journals (Sweden)

    M. K. DEORE

    2010-08-01

    Full Text Available Thick films of AR grade ZnO were prepared on glass substrate by screen-printing technique. These films were dried and fired at different temperatures between 550 oC, 600 oC and 650 oC for one hour in air atmosphere. The gas sensing performance of thick films was tested for various gases. ZnO films showed larger response (sensitivity to H2S gas (100 ppm at 250 oC for firing temperature 650 oC. The Morphological, Compositional and Structural properties of the ZnO thick films were performed by Scanning electron microscopy (SEM, Energy dispersive spectroscopy (EDX and XRD technique respectively. Chemical composition of ZnO film samples changes with firing temperature showing non-stoichiometric behaviours. XRD study indicated the formation of polycrystalline ZnO films with hexagonal wurtzite structure. The gas response (sensitivity, selectivity, response and recovery time of the sensor were measured and presented.

  10. Electronic structure engineering of ZnO with the modified Becke-Johnson exchange versus the classical correlation potential approaches

    KAUST Repository

    Ul Haq, Bakhtiar

    2013-12-01

    In this study, we report investigations of structural and electronic properties of ZnO in wurtzite (WZ), rock salt (RS) and zinc-blende (ZB) phases. Calculations have been done with full-potential linearized augmented plane wave plus local orbital method developed within the frame work of Density Functional Theory (DFT). For structural properties investigations, Perdew and Wang proposed local density approximations (LDA) and Perdew et al. proposed generalized gradient approximations (GGA) have been applied. Where for electronic properties in addition to these, Tran-Blaha modified Becke-Johnson (mBJ) potential has been used. Our computed band gap values of ZnO in WZ and ZB phases with mBJ potential are significantly improved compared to those with LDA and GGA; however, in RS phase, energy gap is significantly overestimated compared to experimental measurements. The Zn-d band was found to be more narrower with mBJ potential than that of LDA and GGA. On the other hand, our evaluated crystal field splitting energy values overestimate the experimental values. © 2013 Taylor and Francis.

  11. Structural, electrical and optical properties of indium chloride doped ZnO films synthesized by Ultrasonic Spray Pyrolysis technique

    International Nuclear Information System (INIS)

    Zaleta-Alejandre, E.; Camargo-Martinez, J.; Ramirez-Garibo, A.; Pérez-Arrieta, M.L.; Balderas-Xicohténcatl, R.; Rivera-Alvarez, Z.; Aguilar-Frutis, M.; Falcony, C.

    2012-01-01

    Indium chloride doped zinc oxide (ZnO:In) thin films were deposited onto glass substrates using zinc acetate by Ultrasonic Spray Pyrolysis technique. The effect of substrate temperature, deposition time and acetic acid added to the spraying solution on the structural, electrical and optical properties of these ZnO:In films is reported. The films were in all cases polycrystalline with a hexagonal (wurtzite) structure, a transparency over 80% and resistivity of the order of 10 −3 –10 −2 Ω·cm. The resistivity was dependent on the volume % of acetic acid added to the spraying solution. The minimum resistivity value was obtained with a 5 vol.% acetic acid (pH = 3.71) at substrate temperature of 450 °C. The deposition rates obtained were as high as 180 Å·min −1 at a substrate temperature of 450 °C. - Highlights: ► Conductive ZnO:In thin films were deposited by Ultrasonic Spray Pyrolysis (USP). ► USP is of low cost, high growth rates and scalable for industrial applications. ► USP is appropriate for the deposition of metallic oxide films. ► We studied the effect of acetic acid, time deposition and substrate temperature. ► Zinc acetate and indium chloride were used as precursor materials.

  12. Structural, electrical and optical properties of indium chloride doped ZnO films synthesized by Ultrasonic Spray Pyrolysis technique

    Energy Technology Data Exchange (ETDEWEB)

    Zaleta-Alejandre, E., E-mail: ezaleta@fis.cinvestav.mx [Centro de Investigacion y de Estudios Avanzados-IPN, Departamento de Fisica, Apdo, Postal 14-470, Del. Gustavo A. Madero, C.P. 07000, Mexico, D.F. (Mexico); Camargo-Martinez, J.; Ramirez-Garibo, A. [Centro de Investigacion y de Estudios Avanzados-IPN, Departamento de Fisica, Apdo, Postal 14-470, Del. Gustavo A. Madero, C.P. 07000, Mexico, D.F. (Mexico); Perez-Arrieta, M.L. [Universidad Autonoma de Zacatecas, Unidad Academica de Fisica, Calzada Solidaridad esq. Paseo, La Bufa s/n, C.P. 98060, Zacatecas, Mexico (Mexico); Balderas-Xicohtencatl, R.; Rivera-Alvarez, Z. [Centro de Investigacion y de Estudios Avanzados-IPN, Departamento de Fisica, Apdo, Postal 14-470, Del. Gustavo A. Madero, C.P. 07000, Mexico, D.F. (Mexico); Aguilar-Frutis, M. [Centro de Investigacion en Ciencia Aplicada y Tecnologia Avanzada-IPN, Legaria 694, Col. Irrigacion, Del. Miguel Hidalgo, Mexico, D.F. (Mexico); Falcony, C. [Centro de Investigacion y de Estudios Avanzados-IPN, Departamento de Fisica, Apdo, Postal 14-470, Del. Gustavo A. Madero, C.P. 07000, Mexico, D.F. (Mexico)

    2012-12-01

    Indium chloride doped zinc oxide (ZnO:In) thin films were deposited onto glass substrates using zinc acetate by Ultrasonic Spray Pyrolysis technique. The effect of substrate temperature, deposition time and acetic acid added to the spraying solution on the structural, electrical and optical properties of these ZnO:In films is reported. The films were in all cases polycrystalline with a hexagonal (wurtzite) structure, a transparency over 80% and resistivity of the order of 10{sup -3}-10{sup -2} Ohm-Sign {center_dot}cm. The resistivity was dependent on the volume % of acetic acid added to the spraying solution. The minimum resistivity value was obtained with a 5 vol.% acetic acid (pH = 3.71) at substrate temperature of 450 Degree-Sign C. The deposition rates obtained were as high as 180 A{center_dot}min{sup -1} at a substrate temperature of 450 Degree-Sign C. - Highlights: Black-Right-Pointing-Pointer Conductive ZnO:In thin films were deposited by Ultrasonic Spray Pyrolysis (USP). Black-Right-Pointing-Pointer USP is of low cost, high growth rates and scalable for industrial applications. Black-Right-Pointing-Pointer USP is appropriate for the deposition of metallic oxide films. Black-Right-Pointing-Pointer We studied the effect of acetic acid, time deposition and substrate temperature. Black-Right-Pointing-Pointer Zinc acetate and indium chloride were used as precursor materials.

  13. Structural and magnetic properties of Co-doped ZnO thin films grown by ultrasonic spray pyrolysis method

    Science.gov (United States)

    Baghdad, R.; Lemée, N.; Lamura, G.; Zeinert, A.; Hadj-Zoubir, N.; Bousmaha, M.; Bezzerrouk, M. A.; Bouyanfif, H.; Allouche, B.; Zellama, K.

    2017-04-01

    Cobalt-doped ZnO thin films with several different percentage of Co from 0 up to 15 at% were synthesized via a cheap, simple and versatile method i.e. ultrasonic spray pyrolysis at atmospheric pressure and a substrate temperature of 350 °C. The structure of the as-prepared samples was characterized by X-ray diffraction (XRD), Raman spectroscopy and FTIR. The Co-doping effect is revealed by the presence of three additional peaks around 235, 470 and 538 cm-1 respect to the Raman spectra of the unsubstituted film. Fourier transform infrared spectroscopy (FTIR) put in evidence the decrease of the bond force constant f with increasing Co-doping. By ultra-violet visible near infrared (UV-Vis-NIR) spectroscopy on Co-doped samples it was possible to show the presence of additional absorption bands at approximately 570, 620 and 660 nm suggesting that Co2+ ions do not change their oxidation when substituted to zinc and the ZnO lattice does not change its wurtzite structure as well. Finally, all our samples exhibit a paramagnetic behavior without any trace of intrinsic room temperature ferromagnetism.

  14. VLS growth of alternating InAsP/InP heterostructure nanowires for multiple-quantum-dot structures.

    Science.gov (United States)

    Tateno, Kouta; Zhang, Guoqiang; Gotoh, Hideki; Sogawa, Tetsuomi

    2012-06-13

    We investigated the Au-assisted growth of alternating InAsP/InP heterostructures in wurtzite InP nanowires on InP(111)B substrates for constructing multiple-quantum-dot structures. Vertical InP nanowires without stacking faults were obtained at a high PH(3)/TMIn mole flow ratio of 300-1000. We found that the growth rate changed largely when approximately 40 min passed. Ten InAsP layers were inserted in the InP nanowire, and it was found that both the InP growth rate and the background As level increased after the As supply. We also grew the same structure using TBAs/TBP and could reduce the As level in the InP segments. A simulation using a finite-difference time-domain method suggests that the nanowire growth was dominated by the diffusion of the reaction species with long residence time on the surface. For TBAs/TBP, when the source gases were changed, the formed surface species showed a short diffusion length so as to reduce the As background after the InAsP growth.

  15. Substrate temperature effects on the structure and properties of ZnMnO films prepared by pulsed laser deposition

    Science.gov (United States)

    Riascos, H.; Duque, J. S.; Orozco, S.

    2017-01-01

    ZnMnO thin films were grown on silicon substrates by pulsed laser deposition (PLD). Pulsed Nd:YAG laser was operated at a wavelength of 1064 nm and 100 mJ. ZnMnO thin films were deposited at the vacuum pressure of 10-5 Torr and with substrate temperature from room temperature to 600 °C. The effects of substrate temperature on the structural and Optical properties of ZnMnO thin films have been investigated by X-ray diffraction (XRD), Raman spectroscopy and Uv-vis spectroscopy. From XRD data of the samples, it can be showed that temperature substrate does not change the orientation of ZnMnO thin films. All the films prepared have a hexagonal wurtzite structure, with a dominant (002) peak around 2θ=34.44° and grow mainly along the c-axis orientation. The substrate temperature improved the crystallinity of the deposited films. Uv-vis analysis showed that, the thin films exhibit high transmittance and low absorbance in the visible region. It was found that the energy band to 300 ° C is 3.2 eV, whereas for other temperatures the values were lower. Raman reveals the crystal quality of ZnMnO thin films.

  16. Study of copper doping effects on structural, optical and electrical properties of sprayed ZnO thin films

    International Nuclear Information System (INIS)

    Mhamdi, A.; Mimouni, R.; Amlouk, A.; Amlouk, M.; Belgacem, S.

    2014-01-01

    Highlights: • The sprayed Cu-doped ZnO thin layers films were well crystallised in hexagonal wurtzite phase. • Nanoncrystallites on clusters were observed whose density decreases especially at 2% Cu content. • This parallel circuit R–C represents the contribution of the grain boundaries delineating the oriented columnar microcrystallites along c-axis. - Abstract: Copper-doped zinc oxide thin films (ZnO:Cu) at different percentages (1–3%) were deposited on glass substrates using a chemical spray technique. The effect of Cu concentration on the structural, morphology and optical properties of the ZnO:Cu thin films were investigated. XRD analysis revealed that all films consist of single phase ZnO and were well crystallised in würtzite phase with the crystallites preferentially oriented towards (0 0 2) direction parallel to c-axis. The Film surface was analyzed by contact atomic force microscopy (AFM) in order to understand the effect of the doping on the surface structure. Doping by copper resulted in a slight decrease in the optical band gap energy of the films and a noticeably change in optical constants. From the spectroscopy impedance analysis we investigated the frequency relaxation phenomenon and the circuit equivalent circuit of such thin layers. Finally, all results have been discussed in terms of the copper doping concentration

  17. Effect of Er3+ doping on structural, morphological and photocatalytical properties of ZnO thin films

    Science.gov (United States)

    Bouhouche, S.; Bensouici, F.; Toubane, M.; Azizi, A.; Otmani, A.; Chebout, K.; Kezzoula, F.; Tala-Ighil, R.; Bououdina, M.

    2018-05-01

    In this research work, structure, microstructure, optical and photocatalytic properties of undoped and Erbium doped nanostructured ZnO thin films prepared by sol-gel dip-coating are investigated. X-ray diffraction (XRD) analysis indicates that the deposited films crystallize within the hexagonal wurtzite-type structure with a preferential growth orientation along (002) plane. Morphological observations using scanning electron microscopy (SEM) reveal important influence of Er concentration; displaying homogeneous and dense aspect for undoped to 0.3% then grid-like morphology for 0.4 and 0.5%. UV/vis/NIR transmittance spectroscopy spectra display a transmittance over 70%, and small variation in the energy gap energy 3.263–3.278 eV. Wettability test of ZnO thin films surface ranges from hydrophilic aspect for pure ZnO to hydrophobic one for Er doped ZnO, and the contact angle is found to increase from 58.7° for pure ZnO up to 98.4° for 0.4% Er doped ZnO. The photocatalytic activity measurements evaluated using the degradation of methylene blue (MB) under UV light irradiation demonstrate that undoped ZnO film shows higher photocatalytic activity compared to Er doped ZnO films, which may be attributed to the deterioration of films’crystallinity resulting in lower transmittance.

  18. The structural evolution of InN nanorods to microstructures on Si (111) by molecular beam epitaxy

    International Nuclear Information System (INIS)

    Anyebe, E A; Zhuang, Q; Kesaria, M; Krier, A

    2014-01-01

    We report the catalyst free growth of wurtzite InN nanorods (NRs) and microislands on bare Si (111) by plasma-assisted molecular beam epitaxy at various temperatures. The morphological evolution from NRs to three dimensional (3D) islands as a function of growth temperature is investigated. A combination of tapered, non-tapered, and pyramidal InN NRs are observed at 490 °C, whereas the InN evolves to faceted microislands with an increase in growth temperature to 540 °C and further developed to indented and smooth hemispherical structures at extremely high temperatures (630 °C). The evolution from NRs to microislands with increase in growth temperature is attributed to the lowering of the surface free energy of the growing crystals with disproportionate growth velocities along different growth fronts. The preferential adsorption of In atoms on the (0001) c-plane and (10-10) m-plane promotes the growth of NRs at relatively low growth temperature and 3D microislands at higher temperatures. The growth rate imbalance along different planes facilitates the development of facets on 3D microislands. A strong correlation between the morphological and structural properties of the 3D films is established. XRD studies reveal that the NRs and the faceted microislands are crystalline, whereas the hemispherical microislands grown at extremely high growth temperature contain In adlayers. Finally, photoluminescent emissions were observed at ∼0.75 eV from the InN NRs. (paper)

  19. Structural and rectifying junction properties of self-assembled ZnO nanoparticles in polystyrene diblock copolymers on (1 0 0)Si substrates

    Science.gov (United States)

    Ali, H. A.; Iliadis, A. A.; Martinez-Miranda, L. J.; Lee, U.

    2006-06-01

    The structural and electronic transport properties of self-assembled ZnO nanoparticles in polystyrene-acrylic acid, [PS] m/[PAA] n, diblock copolymer on p-type (1 0 0)Si substrates are reported for the first time. Four different block repeat unit ratios ( m/ n) of 159/63, 139/17,106/17, and 106/4, were examined in order to correlate the physical parameters (size, density) of the nanoparticles with the copolymer block lengths m and n. We established that the self-assembled ZnO nanoparticle average size increased linearly with minority block length n, while the average density decreased exponentially with majority block length m. Average size varied from 20 nm to 250 nm and average density from 3.5 × 10 7 cm -2 to 1 × 10 10 cm -2, depending on copolymer parameters. X-ray diffraction studies showed the particles to have a wurtzite crystal structure with the (1 0 0) being the dominant orientation. Room temperature current-voltage characteristics measured for an Al/ZnO-nanocomposite/Si structure exhibited rectifying junction properties and indicated the formation of Al/ZnO-nanocomposite Schottky type junction with a barrier height of 0.7 V.

  20. A Comparative Study on Structural and Optical Properties of ZnO Micro-Nanorod Arrays Grown on Seed Layers Using Chemical Bath Deposition and Spin Coating Methods

    Directory of Open Access Journals (Sweden)

    Sibel MORKOÇ KARADENİZ

    2016-11-01

    Full Text Available In this study, Zinc Oxide (ZnO seed layers were prepared on Indium Tin Oxide (ITO substrates by using Chemical Bath Deposition (CBD method and Sol-gel Spin Coating (SC method. ZnO micro-nanorod arrays were grown on ZnO seed layers by using Hydrothermal Synthesis method. Seed layer effects of structural and optical properties of ZnO arrays were characterized. X-ray diffractometer (XRD, Scanning Electron Microscopy (SEM and Ultraviolet Visible (UV-Vis Spectrometer were used for analyses. ZnO micro-nanorod arrays consisted of a single crystalline wurtzite ZnO structure for each seed layer. Besides, ZnO rod arrays were grown smoothly and vertically on SC seed layer, while ZnO rod arrays were grown randomly and flower like structures on CBD seed layer. The optical absorbance peaks found at 422 nm wavelength in the visible region for both ZnO arrays. Optical bandgap values were determined by using UV-Vis measurements at 3.12 and 3.15 eV for ZnO micro-nanorod arrays on CBD seed layer and for ZnO micro-nanorod arrays on SC-seed layer respectively.DOI: http://dx.doi.org/10.5755/j01.ms.22.4.13443

  1. Broad range tuning of structural and optical properties of Znx Mg1−x O nanostructures grown by vapor transport method

    International Nuclear Information System (INIS)

    Vanjaria, Jignesh V; Azhar, Ebraheem Ali; Yu, Hongbin

    2016-01-01

    One-dimensional (1D) Zn x Mg 1−x O nanomaterials have drawn global attention due to their remarkable chemical and physical properties, and their diverse current and future technological applications. In this work, 1D ZnMgO nanostructures with different magnesium concentrations and different morphologies were grown directly on zinc oxide-coated silicon substrates by thermal evaporation of zinc oxide, magnesium boride and graphite powders. Highly well-defined Mg-rich ZnMgO nanorods with a rock salt structure and Zn-rich ZnMgO nanostructures with a wurtzite structure have been deposited individually by careful optimization of the source mixture and process parameters. Structural and optical properties of the deposited products were studied by scanning electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction, and Raman spectroscopy. Cathodoluminescence measurements demonstrate strong dominant peaks at 3.3 eV in Mg poor ZnMgO nanostructures and 4.8 eV in Mg rich nanostructures implying that the ZnMgO nanostructures can be used for the fabrication of deep UV optoelectronic devices. A mechanism for the formation and achieved diverse morphology of the ZnMgO nanostructures was proposed based on the characterization results. (paper)

  2. Structural and electrical properties of ZnO/Zn0.85Mg0.15O thin film prepared by pulsed laser deposition

    Science.gov (United States)

    Yang, Jing-Jing; Wang, Gang; Du, Wen-Han; Xiong, Chao

    2017-07-01

    The electrical transport properties are the key factors to determine the performance of ZnO-based quantum effect device. ZnMgO is a typical material to regulate the band of ZnO. In order to investigate the electrical properties of the interface of ZnO/Zn0.85Mg0.15O films, three kinds of ZnO/Zn0.85Mg0.15O films have been fabricated with different thickness. After comparing the structural and electrical properties of the samples, we found that the independent Zn0.85Mg0.15O hexagonal wurtzite structure (002) peak can be detected in XRD spectra. Hall-effect test data confirmed that the two-dimensional electron gas (2DEG) became lower because of the decrease of thickness of Zn0.85Mg0.15O films, increase of impurity scattering and lattice structure distortion caused by the increase of Mg content.

  3. Structural and optical properties of nano-structured tungsten-doped ZnO thin films grown by pulsed laser deposition

    Energy Technology Data Exchange (ETDEWEB)

    Ngom, B.D. [African Laser Centre, CSIR campus, P.O. Box 395, Pretoria (South Africa); Groupes de Laboratoires de physique des Solides et Sciences des Materiaux, Faculte des sciences et Techniques Universite Cheikh Anta Diop de Dakar (UCAD), B.P. 25114 Dakar-Fann Dakar (Senegal); NANO-Sciences Laboratories, Materials Research Group, iThemba LABS, National Research Foundation (South Africa)], E-mail: bdngom@tlabs.ac.za; Mpahane, T. [NANO-Sciences Laboratories, Materials Research Group, iThemba LABS, National Research Foundation (South Africa); Manyala, N. [Department of Physics and Electronics National University of Lesotho (Lesotho); Nemraoui, O. [NANO-Sciences Laboratories, Materials Research Group, iThemba LABS, National Research Foundation (South Africa); Buttner, U. [Engineering Department, University of Stellenbosch (South Africa); Kana, J.B. [Department of Physique University of Yaounde 1 (Cameroon); Fasasi, A.Y. [Centre for Energy Research and Development, Obafemi Awolowo University, Ile-Ife, Osun State (Nigeria); Maaza, M. [African Laser Centre, CSIR campus, P.O. Box 395, Pretoria (South Africa); NANO-Sciences Laboratories, Materials Research Group, iThemba LABS, National Research Foundation (South Africa); Beye, A.C. [African Laser Centre, CSIR campus, P.O. Box 395, Pretoria (South Africa); Groupes de Laboratoires de physique des Solides et Sciences des Materiaux, Faculte des sciences et Techniques Universite Cheikh Anta Diop de Dakar (UCAD), B.P. 25114 Dakar-Fann Dakar (Senegal)

    2009-01-15

    Novel highly c-oriented tungsten-doped zinc oxide (WZO) thin films with 1 wt% were grown by pulsed laser deposition (PLD) technique on corning 1737F glass substrate. The effects of laser energy on the structural, morphological as well as optical transmission properties of the films were studied. The films were highly transparent with average transmittance exceeding 87% in the wavelength region lying between 400 and 2500 nm. X-ray diffraction analysis (XRD) results indicated that the WZO films had c-axis preferred orientation with wurtzite structure. Film thickness and the full width at half maximum (FWHM) of the (0 0 2) peaks of the films were found to be dependent on laser fluence. The composition determined through Rutherford backscattering spectroscopy (RBS) appeared to be independent of the laser fluence. By assuming a direct band gap transition, the band gap values of 3.36, 3.34 and 3.31 eV were obtained for corresponding laser fluence of 1, 1.7 and 2.7 J cm{sup -2}, respectively. Compared with the reported undoped ZnO band gap value of 3.37 eV, it is conjectured that the observed low band gap values obtained in this study may be attributable to tungsten incorporation in the films as well as the increase in laser fluence. The high transparency makes the films useful as optical windows while the high band gap values support the idea that the films could be good candidates for optoelectronic applications.

  4. Scintillator structures

    International Nuclear Information System (INIS)

    Cusano, D.A.; Prener, J.S.

    1978-01-01

    Distributed phosphor scintillator structures providing superior optical coupling to photoelectrically responsive devices together with methods for fabricating said scintillator structures are disclosed. In accordance with one embodiment of the invention relating to scintillator structures, the phosphor is distributed in a 'layered' fashion with certain layers being optically transparent so that the visible wavelength output of the scintillator is better directed to detecting devices. In accordance with another embodiment of the invention relating to scintillator structures, the phosphor is distributed throughout a transparent matrix in a continuous fashion whereby emitted light is more readily transmitted to a photodetector. Methods for fabricating said distributed phosphor scintillator structures are also disclosed. (Auth.)

  5. Single layers and multilayers of GaN and AlN in square-octagon structure: Stability, electronic properties, and functionalization

    Science.gov (United States)

    Gürbüz, E.; Cahangirov, S.; Durgun, E.; Ciraci, S.

    2017-11-01

    Further to planar single-layer hexagonal structures, GaN and AlN can also form free-standing, single-layer structures constructed from squares and octagons. We performed an extensive analysis of dynamical and thermal stability of these structures in terms of ab initio finite-temperature molecular dynamics and phonon calculations together with the analysis of Raman and infrared active modes. These single-layer square-octagon structures of GaN and AlN display directional mechanical properties and have wide, indirect fundamental band gaps, which are smaller than their hexagonal counterparts. These density functional theory band gaps, however, increase and become wider upon correction. Under uniaxial and biaxial tensile strain, the fundamental band gaps decrease and can be closed. The electronic and magnetic properties of these single-layer structures can be modified by adsorption of various adatoms, or by creating neutral cation-anion vacancies. The single-layer structures attain magnetic moment by selected adatoms and neutral vacancies. In particular, localized gap states are strongly dependent on the type of vacancy. The energetics, binding, and resulting electronic structure of bilayer, trilayer, and three-dimensional (3D) layered structures constructed by stacking the single layers are affected by vertical chemical bonds between adjacent layers. In addition to van der Waals interaction, these weak vertical bonds induce buckling in planar geometry and enhance their binding, leading to the formation of stable 3D layered structures. In this respect, these multilayers are intermediate between van der Waals solids and wurtzite crystals, offering a wide range of tunability.

  6. Experimental study on structural, optoelectronic and room temperature sensing performance of Nickel doped ZnO based ethanol sensors

    Science.gov (United States)

    Sudha, M.; Radha, S.; Kirubaveni, S.; Kiruthika, R.; Govindaraj, R.; Santhosh, N.

    2018-04-01

    Nano crystalline undoped (1Z) Zinc Oxide (ZnO) and 5, 10 and 15 Wt. % (1ZN, 2ZN and 3ZN) of Nickel doped ZnO based sensors were fabricated using the hydrothermal approach on Fluorine doped Tin Oxide (FTO) glass substrates. X-ray diffraction (XRD) analysis proved the hexagonal Wurtzite structure of ZnO. Parametric variations in terms of dislocation density, bond length, lattice parameters and micro strain with respect to dopant concentration were analysed. The prominent variations in the crystallite size, optical band gap and Photoluminescence peak ratio of devices fabricated was observed. The Field Emission Scanning Electron Microscope (FESEM) images showed a change in diameter and density of the nanorods. The effect of the operating temperature, concentration of ethanol and the different doping levels of sensitivity, response and recovery time were investigated. It was inferred that 376% of sensitivity with a very quick response and recovery time of <5 s and 10 s respectively at 150 °C of 3ZN sensor has better performance compared to other three sensors. Also 3ZN sensor showed improved sensitivity of 114%, even at room temperature with response and recovery time of 35 s and 45 s respectively.

  7. The structure, composition, and dimensions of TiO2 and ZnO nanomaterials in commercial sunscreens

    Science.gov (United States)

    Lewicka, Zuzanna A.; Benedetto, Angelo F.; Benoit, Denise N.; Yu, William W.; Fortner, John D.; Colvin, Vicki L.

    2011-09-01

    TiO2 and ZnO nanomaterials are widely used to block ultraviolet radiation in many skin care products, yet product labels do not specify their dimensions, shape, or composition. The absence of this basic information creates a data gap for both researchers and consumers alike. Here, we investigate the structural similarity of pigments derived from actual sunscreen products to nanocrystals which have been the subject of intense scrutiny in the nanotoxicity literature. TiO2 and ZnO particles were isolated from eight out of nine commercial suncare products using three extraction methods. Their dimension, shape, crystal phase, surface area, and elemental composition were examined using transmission and scanning electron microscopy, X-ray diffraction, Brunauer-Emmett-Teller (BET) specific surface area analysis, energy dispersive X-ray and inductively coupled plasma optical emission spectroscopy. TiO2 pigments were generally rutile nanocrystals (dimensions 25 nm) with needle-like or near-spherical shapes. ZnO pigments were wurtzite rods with a short axes less than 40 nm and longer dimensions often in excess of 100 nm. We identify two commercial sources of TiO2 and ZnO nanocrystals whose physical and chemical features are similar to the pigments found in sunscreens. These particular materials would be effective surrogates for the commercial product and could be used in studies of the health and environmental impacts of engineered nanomaterials contained in sunscreens.

  8. Structural, optical, and magnetic studies of manganese-doped zinc oxide hierarchical microspheres by self-assembly of nanoparticles.

    Science.gov (United States)

    Hao, Yao-Ming; Lou, Shi-Yun; Zhou, Shao-Min; Yuan, Rui-Jian; Zhu, Gong-Yu; Li, Ning

    2012-02-02

    In this study, a series of manganese [Mn]-doped zinc oxide [ZnO] hierarchical microspheres [HMSs] are prepared by hydrothermal method only using zinc acetate and manganese acetate as precursors and ethylene glycol as solvent. X-ray diffraction indicates that all of the as-obtained samples including the highest Mn (7 mol%) in the crystal lattice of ZnO have a pure phase (hexagonal wurtzite structure). A broad Raman spectrum from as-synthesized doping samples ranges from 500 to 600 cm-1, revealing the successful doping of paramagnetic Mn2+ ions in the host ZnO. Optical absorption analysis of the samples exhibits a blueshift in the absorption band edge with increasing dopant concentration, and corresponding photoluminescence spectra show that Mn doping suppresses both near-band edge UV emission and defect-related blue emission. In particular, magnetic measurements confirm robust room-temperature ferromagnetic behavior with a high Curie temperature exceeding 400 K, signifying that the as-formed Mn-doped ZnO HMSs will have immense potential in spintronic devices and spin-based electronic technologies.

  9. The structure, composition, and dimensions of TiO{sub 2} and ZnO nanomaterials in commercial sunscreens

    Energy Technology Data Exchange (ETDEWEB)

    Lewicka, Zuzanna A. [Rice University, Department of Electrical and Computer Engineering (United States); Benedetto, Angelo F. [Rice University, Smalley Institute for Nanoscale Science and Technology (United States); Benoit, Denise N.; Yu, William W.; Fortner, John D.; Colvin, Vicki L., E-mail: colvin@rice.edu [Rice University, Department of Chemistry (United States)

    2011-09-15

    TiO{sub 2} and ZnO nanomaterials are widely used to block ultraviolet radiation in many skin care products, yet product labels do not specify their dimensions, shape, or composition. The absence of this basic information creates a data gap for both researchers and consumers alike. Here, we investigate the structural similarity of pigments derived from actual sunscreen products to nanocrystals which have been the subject of intense scrutiny in the nanotoxicity literature. TiO{sub 2} and ZnO particles were isolated from eight out of nine commercial suncare products using three extraction methods. Their dimension, shape, crystal phase, surface area, and elemental composition were examined using transmission and scanning electron microscopy, X-ray diffraction, Brunauer-Emmett-Teller (BET) specific surface area analysis, energy dispersive X-ray and inductively coupled plasma optical emission spectroscopy. TiO{sub 2} pigments were generally rutile nanocrystals (dimensions {approx}25 nm) with needle-like or near-spherical shapes. ZnO pigments were wurtzite rods with a short axes less than 40 nm and longer dimensions often in excess of 100 nm. We identify two commercial sources of TiO{sub 2} and ZnO nanocrystals whose physical and chemical features are similar to the pigments found in sunscreens. These particular materials would be effective surrogates for the commercial product and could be used in studies of the health and environmental impacts of engineered nanomaterials contained in sunscreens.

  10. The structure, composition, and dimensions of TiO2 and ZnO nanomaterials in commercial sunscreens

    International Nuclear Information System (INIS)

    Lewicka, Zuzanna A.; Benedetto, Angelo F.; Benoit, Denise N.; Yu, William W.; Fortner, John D.; Colvin, Vicki L.

    2011-01-01

    TiO 2 and ZnO nanomaterials are widely used to block ultraviolet radiation in many skin care products, yet product labels do not specify their dimensions, shape, or composition. The absence of this basic information creates a data gap for both researchers and consumers alike. Here, we investigate the structural similarity of pigments derived from actual sunscreen products to nanocrystals which have been the subject of intense scrutiny in the nanotoxicity literature. TiO 2 and ZnO particles were isolated from eight out of nine commercial suncare products using three extraction methods. Their dimension, shape, crystal phase, surface area, and elemental composition were examined using transmission and scanning electron microscopy, X-ray diffraction, Brunauer–Emmett–Teller (BET) specific surface area analysis, energy dispersive X-ray and inductively coupled plasma optical emission spectroscopy. TiO 2 pigments were generally rutile nanocrystals (dimensions ∼25 nm) with needle-like or near-spherical shapes. ZnO pigments were wurtzite rods with a short axes less than 40 nm and longer dimensions often in excess of 100 nm. We identify two commercial sources of TiO 2 and ZnO nanocrystals whose physical and chemical features are similar to the pigments found in sunscreens. These particular materials would be effective surrogates for the commercial product and could be used in studies of the health and environmental impacts of engineered nanomaterials contained in sunscreens.

  11. Structural characteristics and UV-light enhanced gas sensitivity of La-doped ZnO nanoparticles

    International Nuclear Information System (INIS)

    Ge Chunqiao; Xie Changsheng; Hu Mulin; Gui Yanghai; Bai Zikui; Zeng Dawen

    2007-01-01

    La-doped ZnO nanoparticles were synthesized by sol-gel method starting from zinc acetate dihydrate, lanthanum sesquioxide, alcohol and nitric acid. The crystal structure and morphology of the nanoparticles were characterized by XRD, FESEM, respectively. The thermal decomposition behavior of the the ZnO-based xerogel was detected by TG-DSC. The results show that as-prepared nanoparticles with the hexagonal wurtzite contain the adsorbed water and some organic compounds below 300 o C, which is the key to the calcinations of the ZnO-based xerogel. Pure ZnO and La-doped ZnO thick film sensors were prepared and tested for specific sensitivity to alcohol and benzene with (and without) UV-light excitation. Among all, 10 at.%La-ZnO-based sensors are significantly sensitive to 100 ppm alcohol and 100 ppm benzene. There is an obvious enhancement of the gas-sensing performances with UV-light excitation. That is, the sensitivity to 100 ppm benzene rises twice. The observed sensitivity to alcohol and benzene could be explained with the surface adsorption theory and the conduction-band theory

  12. Femtosecond UV laser non-ablative surface structuring of ZnO crystal: impact on exciton photoluminescence

    Energy Technology Data Exchange (ETDEWEB)

    Museur, Luc [Laboratoire de Physique des Lasers (LPL), UMR 7538 CNRS, Institut Galilee, Universite Paris 13, 93430 Villetaneuse (France); Michel, Jean-Pierre [Laboratoire des Proprietes Mecaniques et Thermodynamiques des Materiaux (LPMTM), UMR 9001 CNRS, Institut Galilee, Universite Paris 13, 93430 Villetaneuse (France); Portes, Patrick; Kanaev, Andrei V. [Laboratoire d' Ingenierie des Materiaux et des Hautes Pressions (LIMHP), UMR 1311 CNRS, Institut Galilee, Universite Paris 13, 93430 Villetaneuse (France); Englezis, Apostolis; Stassinopoulos, Andreas; Anglos, Demetrios [Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas (IESL-FORTH), 71110 Heraklion, Crete (Greece)

    2010-03-15

    The ultraviolet (UV) laser irradiation (248 nm) of monocrystalline wurtzite ZnO with 450 fs pulses results in surface modification. A formation of two orthogonal ripple structures with a period of 400-500 nm was observed oriented parallel and perpendicular to the laser beam polarization. The UV exciton emission obtained on the irradiated domains is found greatly enhanced locally up to {approx}10{sup 3} times. The photoluminescence band is redshifted by 2-3 nm and 40% narrower (full width at half-maximum), while at the same time the E{sub 2} (439 cm{sup -1}) Raman band intensity increases up to {approx}50 times. The process is found irreversible with the threshold fluence of 11 mJ/cm{sup 2}, which is considerably lower than the ablation threshold 115 mJ/cm{sup 2}. Fine surface nanostructuring on the scale of {approx}10 nm may be responsible for the observed effect. (c) 2008 Optical Society of America.

  13. Role of structural relaxations and chemical substitutions on piezoelectric fields and potential lineup in GaN/Al junctions

    Science.gov (United States)

    Picozzi, S.; Profeta, G.; Continenza, A.; Massidda, S.; Freeman, A. J.

    2002-04-01

    First-principles full-potential linearized augmented plane wave calculations are performed to clarify the role of the interface geometry on piezoelectric fields and potential lineups in [0001] wurtzite and [111]-zincblende GaN/Al junctions. The electric field (polarity and magnitude) is found to be strongly affected by atomic relaxations in the interface region. A procedure is used to evaluate the Schottky-barrier height in the presence of electric fields, showing that their effect is relatively small (a few tenths of an eV). These calculations assess the rectifying behavior of the GaN/Al contact, in agreement with experimental values for the barrier. We disentangle chemical and structural effects on the relevant properties (such as the potential discontinuity and the electric field) by studying unrelaxed ideal nitride/metal systems. Using simple electronegativity arguments, we outline the leading mechanisms that define the values of the electric field and Schottky barrier in these ideal systems. Finally, the transitivity rule is proved to be well satisfied.

  14. Effect of self purification on the structural optical and electrical properties of copper doped oxidized Zn films

    International Nuclear Information System (INIS)

    Koshy, Obey; Abdul Khadar, M.

    2015-01-01

    The effect of self purification mechanism is studied on oxidized Cu–Zn thin films. Oxidized Cu–Zn thin films were prepared by thermal evaporation on glass substrates. XRD studies indicate that the oxidized Cu–Zn thin films are of hexagonal wurtzite structure. AFM images shows that with increase in copper wt. percent the nanoparticle morphology of oxidized Zn film turned to one dimensional nanorod morphology. XPS spectra of the oxidized Cu–Zn thin films shows the oxidized state of zinc and copper. The PL spectra of oxidized Zn film showed a strong and narrow near band edge emission at 380 nm whereas in the case of oxidized Cu–Zn thin films the emission showed peak near 410 nm corresponding to peak related to copper. With increase in copper content, the intensity of the defect emission decreased due to the self purification mechanism in nanomaterials. In addition the resistivity of doped films increased due to the self purification mechanism in nanomaterials. - Highlights: • Copper doping in ZnO resulted in the increase in blue emission due to defect levels formed. • The intensity of the luminescence peak of the doped film sample decreased and resistivity increased due to the self purification mechanism in nanomaterials.

  15. Influence of bismuth doping on the structural and optical properties of ZnS thin films and nanopowders

    International Nuclear Information System (INIS)

    Mageswari, S; Palanivel, Balan; Dhivya, L; Murugan, Ramaswamy

    2013-01-01

    Zn (1−x/2) Bi x/3 S (x = 0, 0.03, 0.09) thin films and nanopowders synthesized by the simple chemical bath deposition technique were characterized using x-ray diffraction (XRD), scanning electron microscope, energy dispersive x-ray analysis, an atomic force microscope (AFM) and ultraviolet visible (UV–Vis) and photoluminescence spectroscopy. XRD analysis revealed a sphalerite structure for Zn (1−x/2) Bi x/3 S (x = 0, 0.03, 0.09) thin films. However, the XRD pattern of Zn (1−x/2) Bi x/3 S (x = 0.09) nanopowder revealed the co-existence of both sphalerite and hexagonal (wurtzite) phases. The crystallite size of Zn (1−x/2) Bi x/3 S (x = 0, 0.03, 0.09) nanopowders were found to be in the range of 2–4 nm. AFM studies revealed that the film quality of Zn (1−x/2) Bi x/3 S (x = 0.09) was relatively good compared to other films. A notable decrease in the band gap of both the thin films and nanopowders were observed with incorporation of Bi 3+ in ZnS. These results indicate that Bi doped ZnS can be used to enhance the photocatalytic H 2 -production activity under visible and UV light. (paper)

  16. Structural Characterization and Magnetic Properties of Undoped and Ti-Doped ZnO Nanoparticles Prepared by Modified Oxalate Route

    Directory of Open Access Journals (Sweden)

    Ekane Peter Etape

    2018-01-01

    Full Text Available Ti-doped zinc oxide and pure zinc oxide nanoparticles were synthesized by a modified oxalate route using Averrhoa carambola fruit juice as a natural source of oxalate. The characteristics of the precursors have been investigated by FTIR, TGA, and XRD. The results from the investigation revealed that the precursors are zinc oxalate and Ti-doped zinc oxalate which readily decompose at 450°C. The as-prepared precursors were calcined at 450°C for 4 hours, and the decomposition products have been characterized by XRD, SEM, EDX, and VSM. XRD results revealed crystallinity with hexagonal wurtzite structure, while the average grain size was found to be 26 nm for Ti-doped ZnO and 29 nm for ZnO, using calculations based on Debye-Scherrer equation. Furthermore, the morphological studies by SEM showed particle agglomeration, while the presence of Ti3+ in the zinc oxide lattice is indicated by EDS analysis. Finally the hysteresis loop from VSM results shows that Ti-doped ZnO exhibits ferromagnetism.

  17. Crystal structure and composition of BAlN thin films: Effect of boron concentration in the gas flow

    KAUST Repository

    Wang, Shuo; Li, Xiaohang; Fischer, Alec M.; Detchprohm, Theeradetch; Dupuis, Russell D.; Ponce, Fernando A.

    2017-01-01

    We have investigated the microstructure of BxAl1-xN films grown by flow-modulated epitaxy at 1010 oC, with B/(B+Al) gas-flow ratios ranging from 0.06 to 0.18. The boron content obtained from X-ray diffraction (XRD) patterns ranges from x = 0.02 to 0.09. On the other hand, boron content deduced from the aluminum signal in the Rutherford backscattering spectra (RBS) ranges x = 0.06 to 0.16, closely following gas-flow ratios. Transmission electron microscopy indicates the sole presence of wurtzite crystal structure in the BAlN films, and a tendency towards columnar growth for B/(B+Al) gas-flow ratios below 0.12. For higher ratios, the BAlN films exhibit a tendency towards twin formation and finer microstructure. Electron energy loss spectroscopy has been used to profile spatial variations in the composition of the films.The RBS data suggest that the incorporation of B is highly efficient for our growth method, while the XRD data indicate that the epitaxial growth may be limited by a solubility limit in the crystal phase at about 9%, for the range of B/(B+Al) gas-flow ratios that we used, which is significantly higher than previously thought.

  18. Crystal structure and composition of BAlN thin films: Effect of boron concentration in the gas flow

    KAUST Repository

    Wang, Shuo

    2017-07-20

    We have investigated the microstructure of BxAl1-xN films grown by flow-modulated epitaxy at 1010 oC, with B/(B+Al) gas-flow ratios ranging from 0.06 to 0.18. The boron content obtained from X-ray diffraction (XRD) patterns ranges from x = 0.02 to 0.09. On the other hand, boron content deduced from the aluminum signal in the Rutherford backscattering spectra (RBS) ranges x = 0.06 to 0.16, closely following gas-flow ratios. Transmission electron microscopy indicates the sole presence of wurtzite crystal structure in the BAlN films, and a tendency towards columnar growth for B/(B+Al) gas-flow ratios below 0.12. For higher ratios, the BAlN films exhibit a tendency towards twin formation and finer microstructure. Electron energy loss spectroscopy has been used to profile spatial variations in the composition of the films.The RBS data suggest that the incorporation of B is highly efficient for our growth method, while the XRD data indicate that the epitaxial growth may be limited by a solubility limit in the crystal phase at about 9%, for the range of B/(B+Al) gas-flow ratios that we used, which is significantly higher than previously thought.

  19. Micro and nano-structured green gallium indium nitride/gallium nitride light-emitting diodes

    Science.gov (United States)

    Stark, Christoph J. M.

    Light-emitting diodes (LEDs) are commonly designed and studied based on bulk material properties. In this thesis different approaches based on patterns in the nano and micrometer length scale range are used to tackle low efficiency in the green spectral region, which is known as “green gap”. Since light generation and extraction are governed by microscopic processes, it is instructive to study LEDs with lateral mesa sizes scaled to the nanometer range. Besides the well-known case of the quantum size effect along the growth direction, a continuous lateral scaling could reveal the mechanisms behind the purported absence of a green gap in nanowire LEDs and the role of their extraction enhancement. Furthermore the possibility to modulate strain and piezoelectric polarization by post growth patterning is of practical interest, because the internal electric fields in conventional wurtzite GaN LEDs cause performance problems. A possible alternative is cubic phase GaN, which is free of built-in polarization fields. LEDs on cubic GaN could show the link between strong polarization fields and efficiency roll-off at high current densities, also known as droop. An additional problem for all nitride-based LEDs is efficient light extraction. For a planar GaN LED only roughly 8% of the generated light can be extracted. Novel lightextraction structures with extraction-favoring geometry can yield significant increase in light output power. To investigate the effect of scaling the mesa dimension, micro and nano-sized LED arrays of variable structure size were fabricated. The nano-LEDs were patterned by electron beam lithography and dry etching. They contained up to 100 parallel nano-stripe LEDs connected to one common contact area. The mesa width was varied over 1 μm, 200 nm, and 50 nm. These LEDs were characterized electrically and optically, and the peak emission wavelength was found to depend on the lateral structure size. An electroluminescence (EL) wavelength shift of 3 nm

  20. Impact of band structure and transition matrix elements on polarization properties of the photoluminescence of semipolar and nonpolar InGaN quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Schade, L.; Schwarz, U.T. [Department of Microsystems Engineering, University of Freiburg, Georges-Koehler-Allee 103, 79108 Freiburg (Germany); Fraunhofer Institute for Applied Solid State Physics (IAF), Tullastrasse 72, 79108 Freiburg (Germany); Wernicke, T. [Institute of Solid State Physics, Technical University, Hardenbergstrasse 36, 10623 Berlin (Germany); Weyers, M. [Ferdinand-Braun-Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Strasse 4, 12489 Berlin (Germany); Kneissl, M. [Institute of Solid State Physics, Technical University, Hardenbergstrasse 36, 10623 Berlin (Germany); Ferdinand-Braun-Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Strasse 4, 12489 Berlin (Germany)

    2011-03-15

    Partial or full linear polarization is characteristic for the spontaneous emission of light from semipolar and nonpolar InGaN quantum wells. This property is an implication of the crystalline anisotropy as a basic property of the wurtzite structure. The influence of this anisotropy on the band structure and the transition matrix elements was calculated by a k.p-method for arbitrary quantum well orientations with respect to the c-axis; results are shown here in detail. Optical polarization is a direct consequence of a broken symmetry, mainly affecting the transition matrix elements from the conduction to the valence bands. Furthermore, the strain of the InGaN quantum well strongly depends on the crystal orientation of the substrate, resulting in a valence band mixing. The composition of the eigenfunctions has emerged to be most important for the polarization dependence of strained semipolar and nonpolar InGaN QW. The matrix elements, in combination with the thermal occupation of the bands, determine the polarization of the spontaneously emitted light. Our photoluminescence measurements of nonpolar QW match well with this model. However, in contrast to calculations with standard band parameters, the two topmost subbands show a larger separation in the emitted energy. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  1. Effect of reaction time on structural, morphology and optical properties of ZnO nanoflakes prepared by chemical bath deposition method

    Energy Technology Data Exchange (ETDEWEB)

    Molefe, F.V.; Koao, L.F., E-mail: koaolf@qwa.ufs.ac.za; Dolo, J.J.; Dejene, B.F.

    2014-04-15

    ZnO nanoflakes have been successfully synthesized by the chemical bath deposition (CBD) method for different reaction times. X-ray diffraction (XRD) results confirm the initial formation of the cubic ZnO structure. However, increasing the reaction time resulted into the emergence of the well-known hexagonal wurtzite structure of ZnO. Scanning electron microscopy images showed the presence of agglomerated nanoflakes. The morphology was found not to depend on synthesis time. UV–vis spectra showed a partially increase in the percentage reflectance and the absorption edges red shifted to the higher wavelength with an increase in synthesis time. The highest band gap energy was obtained for ZnO synthesized for 1 min, with its estimated band gap energy of 3.91±0.08 eV. The estimated band gap decreased with an increase in the reaction time. The photoluminescent intensity of the emission peak at 473 nm decreased with an increase in reaction time.

  2. Effects of the Ho{sup 3+}/Yb{sup 3+} concentration ratio on the structure and photoluminescence of ZnO films

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Boxu [School of Materials Science and Engineering, Tianjin Polytechnic University, Tianjin 300387 (China); Wang, Pei [Auditing Department, Tianjin Polytechnic University, Tianjin 300387 (China); Meng, Xiaoqi; Zou, Kaishun [School of Materials Science and Engineering, Tianjin Polytechnic University, Tianjin 300387 (China); Liu, Juncheng, E-mail: jchliu@tjpu.edu.cn [School of Materials Science and Engineering, Tianjin Polytechnic University, Tianjin 300387 (China)

    2016-07-15

    To improve the efficiency of photoluminescent films, this study investigates the effects of the Ho{sup 3+}/Yb{sup 3+} concentration ratio on the structure and up-conversion photoluminescence of ZnO films prepared by the sol–gel method and the spin-coating technique. ZnO maintained its hexagonal wurtzite structure after doping with rare earth ions. The ZnO films consist of round granules, the average size of which increases as the Ho{sup 3+}/Yb{sup 3+} concentration ratio increases. Once the ratio exceeds 1:2, the film's granules significantly coarsen, and the surface roughness slightly increases. When the film is pumped with a 980-nm laser, two intense emission bands are observed in the up-conversion emission spectrum, with a green band centered at 550 nm and a red band centered at 660 nm, corresponding to the Ho{sup 3+}: {sup 5}S{sub 2}/{sup 5}F{sub 4}→{sup 5}I{sub 8}, and {sup 5}F{sub 5}→{sup 5}I{sub 8} transitions, respectively. In addition, as the Ho{sup 3+}/Yb{sup 3+} concentration ratio increases, the intensity of the film's upconversion luminescence first increases and then decreases, reaching a maximum at a concentration ratio of 1:2, with a peak of about four times the minimum value.

  3. ZnO nanorod arrays prepared by chemical bath deposition combined with rapid thermal annealing: structural, photoluminescence and field emission characteristics

    International Nuclear Information System (INIS)

    Chen, Hung-Wei; He, Hsin-Min; Lee, Yi-Mu; Yang, Hsi-Wen

    2016-01-01

    ZnO nanorod arrays were prepared by low temperature chemical bath deposition (CBD) combined with rapid thermal annealing (RTA) under different ambient conditions. The structure and morphology of the synthesized ZnO have been characterized by field-emission scanning electron microscopy (FESEM) and x-ray diffraction (XRD). The obtained ZnO samples are highly crystalline with a hexagonal wurtzite phase and also display well-aligned array structure. A pronounced effect on increased nanorod length was found for the RTA-treated ZnO as compared to the as-grown ZnO. Analysis of XRD indicates that the (0 0 2) feature peak of the as-grown ZnO was shifted towards a lower angle as compared to the peaks of RTA-treated ZnO samples due to the reduction of tensile strain along the c-axis by RTA. Photoluminescence (PL) studies reveal that the ZnO nanorod arrays receiving RTA in an O 2 environment have the sharpest UV emission band and greatest intensity ratio of near band-edge emission (NBE) to deep level emission (DLE). Additionally, the effects of RTA on the field emission properties were evaluated. The results demonstrate that RTA an O 2 environment can lower the turn-on field and improve the field enhancement factor. The stability of the field emission current was also tested for 4 h. (paper)

  4. Effect of Co doping concentration on structural properties and optical parameters of Co-doped ZnO thin films by sol-gel dip-coating method.

    Science.gov (United States)

    Nam, Giwoong; Yoon, Hyunsik; Kim, Byunggu; Lee, Dong-Yul; Kim, Jong Su; Leem, Jae-Young

    2014-11-01

    The structural and optical properties of Co-doped ZnO thin films prepared by a sol-gel dip-coating method were investigated. X-ray diffraction analysis showed that the thin films were grown with a c-axis preferred orientation. The position of the (002) peak was almost the same in all samples, irrespective of the Co concentration. It is thus clear that Co doping had little effect on the position of the (002) peak. To confirm that Co2+ was substituted for Zn2+ in the wurtzite structure, optical measurements were conducted at room temperature by a UV-visible spectrometer. Three absorption peaks are apparent in the Co-doped ZnO thin films that do not appear for the undoped ZnO thin film. As the Co concentration was increased, absorption related to characteristic Co2+ transitions increased because three absorption band intensities and the area underneath the absorption wells between 500 and 700 nm increased with increasing Co concentration. The optical band gap and static dielectric constant decreased and the Urbach energy and extinction coefficient increased with increasing Co concentration.

  5. Effect of aging time on the optical, structural and photoluminescence properties of nanocrystalline ZnO films prepared by a sol–gel method

    International Nuclear Information System (INIS)

    Ibrahim, N.B.; AL-Shomar, S.M.; Ahmad, Sahrim Hj.

    2013-01-01

    The nanocrystalline zinc oxide (ZnO) films were deposited by a sol–gel method and the effect of sol aging time 0, 1, 7 and 11 days on the structural, optical and photoluminescence properties were investigated. X-ray diffraction analysis showed that the deposited films were polycrystalline with hexagonal wurtzite structure and high orientation along c-axis direction. The grain size was in the range of 42–60 nm increased with sol aging time also the thickness increased from 70 to 147 nm with the aging time increment. The roughness of ZnO film investigated by atomic force microscope showed that roughness of the films increased then decreased with the increment of the aging time. The deposited films are highly transparent with an average transmission exceeding 82–95% in the visible range (400–800 nm), which slightly improved with aging time. The measured optical band gap values of the ZnO films were between 3.1 eV and 3.6 eV. The photoluminescence intensity increased with the aging time and the ZnO films have ultraviolet, violet and green emission.

  6. Investigations on structural, vibrational, morphological and optical properties of CdS and CdS/Co films by ultrasonic spray pyrolysis

    International Nuclear Information System (INIS)

    Aksay, S.; Polat, M.; Ozer, T.; Koese, S.; Guerbuez, G.

    2011-01-01

    CdS and CdS/Co films have been deposited on glass substrates by an ultrasonic spray pyrolysis method. The effects of Co incorporation on the structural, optical, morphological, elemental and vibrational properties of these films were investigated. XRD analysis confirmed the hexagonal wurtzite structure of all films and had no impurity phase. While CdS film has (0 0 2) as the preferred orientation, CdS/Co films have (1 1 0) as the preferred orientation. The direct optical band gap was found to decrease from 2.42 to 2.39 eV by Co incorporation. The decrease of the direct energy gaps by increasing Co contents is mainly due to the sp-d exchange interaction between the localized d-electrons of Co 2+ ions and band electrons of CdS. After the optical investigations, it was seen that the transmittance of CdS films decreased by Co content. The Raman measurements revealed two peaks corresponding to the 1LO and 2LO modes of hexagonal CdS. The vibrational modes of Cd-S were obtained in the wavenumber range (590-715 cm -1 ) using Fourier transform infrared spectroscopy (FTIR). The elemental analysis of the film was done by energy dispersive X-ray spectrometry.

  7. Investigations on structural, vibrational, morphological and optical properties of CdS and CdS/Co films by ultrasonic spray pyrolysis

    Science.gov (United States)

    Aksay, S.; Polat, M.; Özer, T.; Köse, S.; Gürbüz, G.

    2011-09-01

    CdS and CdS/Co films have been deposited on glass substrates by an ultrasonic spray pyrolysis method. The effects of Co incorporation on the structural, optical, morphological, elemental and vibrational properties of these films were investigated. XRD analysis confirmed the hexagonal wurtzite structure of all films and had no impurity phase. While CdS film has (0 0 2) as the preferred orientation, CdS/Co films have (1 1 0) as the preferred orientation. The direct optical band gap was found to decrease from 2.42 to 2.39 eV by Co incorporation. The decrease of the direct energy gaps by increasing Co contents is mainly due to the sp-d exchange interaction between the localized d-electrons of Co2+ ions and band electrons of CdS. After the optical investigations, it was seen that the transmittance of CdS films decreased by Co content. The Raman measurements revealed two peaks corresponding to the 1LO and 2LO modes of hexagonal CdS. The vibrational modes of Cd-S were obtained in the wavenumber range (590-715 cm-1) using Fourier transform infrared spectroscopy (FTIR). The elemental analysis of the film was done by energy dispersive X-ray spectrometry.

  8. The influence of annealing in nitrogen atmosphere on the electrical, optical and structural properties of spray- deposited ZnO thin films

    Energy Technology Data Exchange (ETDEWEB)

    Ikhmayies, S.J. [Applied Science Private Univ., Amman (Jordan). Dept. of Physics; Abu El-Haija, N.M.; Ahmad-Bitar, R.N. [Jordan Univ., Amman (Jordan). Dept. of Physics

    2009-07-01

    Thin-film zinc oxide (ZnO) has many applications in solar cell technology and is considered to be a candidate for the substitution of indium tin oxide and tin oxide. ZnO thin films can be prepared by thermal evaporation, rf-sputtering, atomic layer deposition, chemical vapor deposition, sol-gel, laser ablation and spray pyrolysis technique. Spray pyrolysis has received much attention because of its simplicity and low cost. In this study, large area and highly uniform polycrystalline ZnO thin films were produced by spray pyrolysis using a home-made spraying system on glass substrates at 450 degrees C. The electrical, optical and structural properties of the ZnO films were enhanced by annealing the thin films in nitrogen atmosphere. X-ray diffraction revealed that the films are polycrystalline with a hexagonal wurtzite structure. The preferential orientation did not change with annealing, but XRD patterns revealed that some very weak lines had grown. There was no noticeable increase in the grain size. The transmittance of the films increased as a result of annealing. It was concluded that post-deposition annealing is essential to improve the quality of the ZnO thin films. The electrical properties improved due to a decrease in resistivity. 13 refs., 5 figs.

  9. Structural, optical and NO{sub 2} gas sensing properties of ZnMgO thin films prepared by the sol gel method

    Energy Technology Data Exchange (ETDEWEB)

    Chebil, W., E-mail: chbil.widad@live.fr [Unité de Service Commun de Recherche « High resolution X-ray diffractometer », Département de Physique, Université de Monastir, Faculté des Sciences de Monastir, Avenue de l’Environnement, 5019, Monastir (Tunisia); Laboratoire Physico-chimie des Matériaux, Département de Physique, Université de Monastir, Faculté des Sciences de Monastir, Avenue de l' environnement, 5019 Monastir (Tunisia); Boukadhaba, M.A. [Unité de Service Commun de Recherche « High resolution X-ray diffractometer », Département de Physique, Université de Monastir, Faculté des Sciences de Monastir, Avenue de l’Environnement, 5019, Monastir (Tunisia); Laboratoire Physico-chimie des Matériaux, Département de Physique, Université de Monastir, Faculté des Sciences de Monastir, Avenue de l' environnement, 5019 Monastir (Tunisia); Madhi, I. [Laboratoire de Photovoltaïque, Centre de Recherche et des Technologies de l’Energie, Technopole de Borj-Cédria, BP 95, 2050, Hammam-Lif (Tunisia); and others

    2017-01-15

    In this present work, ZnO and ZnMgO thin films prepared by a sol-gel process were deposited on glass substrates via spin coating technique. The structural, morphological and optical properties of the obtained films were investigated. X-ray diffraction study revealed that all layers exhibit a hexagonal wurtzite structure without any secondary phase segregation. The atomic force microscopy (AFM) depicts that the grains size of ours samples decreases as magnesium content increases. The absorption spectra obtained on ZnMgO thin films show a band gap tuning from 3.19 to 3.36 eV, which is also consistent with blue shifting of near-band edge PL emission, measured at low temperature. The incorporated amount of magnesium was calculated and confirmed by EDX. The gas sensing performances were tested in air containing NO{sub 2} for different operating temperatures. The experimental result exhibited that ZnMgO sensors shows a faster response and recovery time than the ZnO thin films. The resistivity and the sensor response as function of Mg content were also investigated.

  10. Effect of Sn doping on structural, mechanical, optical and electrical properties of ZnO nanoarrays prepared by sol-gel and hydrothermal process

    Science.gov (United States)

    Agarwal, Manish Baboo; Sharma, Akash; Malaidurai, M.; Thangavel, R.

    2018-05-01

    Undoped and Sn doped Zinc oxide nanorods were prepared by two step process: initially growth of seed layers by sol-gel spin coating technique and then zinc oxide nanorods by hydrothermal process using the precursors zinc nitrate hexahydrate, hexamine and tin chloride. The effects on the electrical, optical, mechanical and structural properties for various Sn concentrations were studied. The crystalline phase determination from X-ray diffraction (XRD) confirms that Sn doped ZnO nanorods have hexagonal wurtzite structure. The variations of stress and strain with different doping concentration of Sn in ZnO nanorods were studied. The doping effect on electrical properties and optical bandgap is estimated by current voltage characteristics and absorbance spectra respectively. The surface morphology was studied with field emission scanning electron microscope (FESEM), which shows that the formation of hexagonal nanorods arrays with increasing Sn concentration. The calculated value of Young's modulus of elasticity (Y) for all the samples remains same. These results can be used in optoelectronic devices.

  11. The optoelectronic properties and role of Cu concentration on the structural and electrical properties of Cu doped ZnO nanoparticles

    Science.gov (United States)

    Omri, K.; Bettaibi, A.; Khirouni, K.; El Mir, L.

    2018-05-01

    In the current study, we synthesized a Cu-doped ZnO (CZO) nanoparticles material using a sol-gel method with different doping concentrations of Cu (0, 2, 3 and 4 at.%). The control of the Cu concentration on structural, electrical and optical properties of CZO nanoparticles was investigated in detail. The XRD analysis of the CZO nanoparticles reveals the formation of ZnO hexagonal wurtzite structure for all samples which confirm the incorporation of Cu2+ ions into the ZnO lattice by substitution. Furthermore, CZO nanoparticles showed a small red shift of absorption band with the incorporation of Cu from 0 to 4 at.%; i.e. a decreased band gap value from 3.34 eV to 3.27 eV with increasing of Cu doping content. The frequency dispersion of the electric conductivity were studied using the Jonscher universal power law, according to relation σ(ω) = σDC + A ωs(T). Alternative current conductivity increases with increasing Cu content in spite of the decrease the activation energy with copper loading. It was found that the conductivity reached its maximum value for critical Cu concentration of 3 at.%. The frequency relaxation phenomenon was also investigated and all results were discussed in term of the copper doping concentration.

  12. Structural and morphological study of Zn0.9Mn0.05Fe0.05O synthesized by sol-gel wet chemical precipitation route

    Science.gov (United States)

    Jain, S. K.; Dolia, S. N.; Choudhary, B. L.; Prashant, B. L.

    2018-04-01

    Transition metal substituted Zinc oxide (ZnO) has drawn a great deal of attention due to its excellent properties. Zn0.9Mn0.05Fe0.05O sample synthesized was by Sol-gel wet chemical precipitation route at temperature 350°C. The crystallinity and the structure of Zn0.9Mn0.05Fe0.05O was determined by X-ray diffraction by Cu-Kα radiations operated at 40kV and 35mA in the range of 20° to 80°. The pattern gets indexed in wurtzite (hexagonal) structure with lattice constants a=b=3.2525Å and c=5.2071Å and approves the single phase material with no impurity. The values of particle size assessed by Debye Scherer’s (DS) formula lie in the range of 13nm to 33nm indicating the nano-crystalline nature of the sample. The morphological analysis of the sample was performed by Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) measurements. The observed size of Zn0.9Mn0.05Fe0.05O nanoparticles by TEM micrograph exhibits the similar trend with the size calculated by Debye-Scherer formula. TEM image show the irregular shape of the nanoparticles and particle size lies in the range of 10-35nm. Similar to SEM image, the slight agglomeration of the nanoparticles have been observed from TEM.

  13. Organisational Structure

    Science.gov (United States)

    National Centre for Vocational Education Research (NCVER), 2006

    2006-01-01

    An understanding of organisational structure can provide guidance for organisations that want to change and innovate. Many writers agree that this understanding allows organisations to shape how their work is done to ultimately achieve their business goals--and that too often structure is given little consideration in business strategy and…

  14. Structural characterization of ZnO thin films grown on various substrates by pulsed laser deposition

    International Nuclear Information System (INIS)

    Novotný, M; Bulíř, J; Lančok, J; Čížek, J; Kužel, R; Connolly, J; McCarthy, E; Krishnamurthy, S; Mosnier, J-P; Anwand, W; Brauer, G

    2012-01-01

    ZnO thin films were grown by pulsed laser deposition on three different substrates: sapphire (0 0 0 1), MgO (1 0 0) and fused silica (FS). The structure and morphology of the films were characterized by x-ray diffraction and scanning electron microscopy and defect studies were carried out using slow positron implantation spectroscopy (SPIS). Films deposited on all substrates studied in this work exhibit the wurtzite ZnO structure and are characterized by an average crystallite size of 20-100 nm. However, strong differences in the microstructure of films deposited on various substrates were found. The ZnO films deposited on MgO and sapphire single-crystalline substrates exhibit local epitaxy, i.e. a well-defined relation between film crystallites and the substrate. Domains with different orientation relationships with the substrate were found in both films. On the other hand, the film deposited on the FS substrate exhibits fibre texture with random lateral orientation of crystallites. Extremely high compressive in-plane stress of σ ∼ 14 GPa was determined in the film deposited on the MgO substrate, while the film deposited on sapphire is virtually stress-free, and the film deposited on the FS substrate exhibits a tensile in-plane stress of σ ∼ 0.9 GPa. SPIS investigations revealed that the concentration of open-volume defects in the ZnO films is substantially higher than that in a bulk ZnO single crystal. Moreover, the ZnO films deposited on MgO and sapphire single-crystalline substrates exhibit a significantly higher density of defects than the film deposited on the amorphous FS substrate. (paper)

  15. Annealing effects on the structural, optical and magnetic properties of Mn implanted GaN

    International Nuclear Information System (INIS)

    Majid, Abdul; Ali, Akbar; Sharif, Rehana; Husnain, G

    2009-01-01

    Mn ions were implanted into GaN thin films with six doses ranging from 10 14 to 5 x 10 16 cm -2 and the samples were subsequently annealed isochronically in three steps at 800, 850 and 900 deg. C. Structural, optical and magnetic properties of the implanted samples were studied after each annealing. X-ray diffraction measurements exhibited new peaks on the lower angle side of the main GaN peak which are attributed to the implantation induced damage as well as the formation of a GaMnN phase. A dose dependent decrease in the optical band gap and an increase in the Urbach tail were observed from optical transmission measurements. The clear magnetic hysteresis loops were recorded by the magnetometer which revealed the room temperature ferromagnetic ordering in all the implanted samples. Unusual behaviour in the magnetic measurements was observed when saturation magnetic moment decreased in all the samples with an increase in annealing temperature from 850 to 900 deg. C. This is explained by the out-diffusion of Mn atoms from the samples during high temperature annealing. Annealing temperature of 850 deg. C for Mn implanted GaN has been suggested as suitable since the samples annealed at this temperature exhibited maximum M s and minimum Urbach energy. Bound magnetic polarons are suggested to be the origin of room temperature ferromagnetic exchange in the samples. XPS measurements indicated that the Mn ions have been incorporated into the wurtzite structure of the host lattice by substituting the Ga sites.

  16. Annealing effects on the structural, optical and magnetic properties of Mn implanted GaN

    Energy Technology Data Exchange (ETDEWEB)

    Majid, Abdul; Ali, Akbar [Advance Materials Physics Laboratory, Physics Department, Quaid-i-Azam University, Islamabad (Pakistan); Sharif, Rehana [Department of Physics, University of Engineering and Technology, Lahore (Pakistan); Husnain, G, E-mail: abdulmajid40@yahoo.co, E-mail: akbar@qau.edu.p [Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871 (China)

    2009-07-07

    Mn ions were implanted into GaN thin films with six doses ranging from 10{sup 14} to 5 x 10{sup 16} cm{sup -2} and the samples were subsequently annealed isochronically in three steps at 800, 850 and 900 deg. C. Structural, optical and magnetic properties of the implanted samples were studied after each annealing. X-ray diffraction measurements exhibited new peaks on the lower angle side of the main GaN peak which are attributed to the implantation induced damage as well as the formation of a GaMnN phase. A dose dependent decrease in the optical band gap and an increase in the Urbach tail were observed from optical transmission measurements. The clear magnetic hysteresis loops were recorded by the magnetometer which revealed the room temperature ferromagnetic ordering in all the implanted samples. Unusual behaviour in the magnetic measurements was observed when saturation magnetic moment decreased in all the samples with an increase in annealing temperature from 850 to 900 deg. C. This is explained by the out-diffusion of Mn atoms from the samples during high temperature annealing. Annealing temperature of 850 deg. C for Mn implanted GaN has been suggested as suitable since the samples annealed at this temperature exhibited maximum M{sub s} and minimum Urbach energy. Bound magnetic polarons are suggested to be the origin of room temperature ferromagnetic exchange in the samples. XPS measurements indicated that the Mn ions have been incorporated into the wurtzite structure of the host lattice by substituting the Ga sites.

  17. Structural peculiarities and point defects of bulk-ZnO single crystals

    International Nuclear Information System (INIS)

    Kaurova, I.A.; Kuz’micheva, G.M.; Rybakov, V.B.; Cousson, A.; Gayvoronsky, V.Ya.

    2014-01-01

    Highlights: • ZnO single crystals of different color were grown by the hydrothermal method. • Point defects in ZnO have been firstly investigated by neutron diffraction. • Presence of additional reflections caused by kinetic growth effects was revealed. • The relationship between the color and zinc and oxygen vacancies was found. • Photoinduced variation of transmittance versus the CW laser intensity was analyzed. - Abstract: ZnO single crystals are related to promising direct wide band gap semiconductor materials belonging to the A II B VI type of compounds with wurtzite structure. “Unintentional” n-type conductivity in ZnO may be caused by zinc and oxygen vacancies, and interstitial zinc atoms. To date, the comprehensive structural investigation and analysis of point defects in ZnO is absent in literature. Green, light green and almost colorless ZnO single crystals grown by the hydrothermal method in concentrated alkali solutions 4M(KOH) + 1M(LiOH) + 0.1M(NH 4 OH) on monohedral seeds [0 0 0 1] at crystallization temperatures in the range of 330–350 °C and pressures in the range of 30–50 MPa have been firstly investigated by neutron diffraction. It was revealed the presence of additional reflections (∼12–∼16%) for all the crystals caused by kinetic growth effects that give grounds to assign them to the space group P3 rather than to P6 3 mc. Analysis of the refined compositions together with the color of ZnO crystals does not rule out the relationship between the color and vacancies in the zinc and oxygen positions whose concentration decreases with the discoloration of the samples. The analysis of the photoinduced variation of the total and on-axis transmittance versus the CW laser intensity showed that the colored samples have profound deep defects related to oxygen vacancies

  18. Scintillator structure

    International Nuclear Information System (INIS)

    Cusano, D.A.; Prener, J.S.

    1979-01-01

    A scintillator structure comprises at least one layer of transparent fused quartz with a phosphor coating on one or both sides adjacent to at least one transparent layer of epoxy resin which directs light from the phosphor to a detector. The phosphor layer may be formed from a powder optionally with a binder, a single crystal or a melt, or by evaporation or sintering. A plurality of multiple layers may be used or the structure tilted for greater absorption. The structure may be surrounded by another such structure optionally operating in cascade with the first. Many phosphors are specified. A scintillator structure comprises phosphor particles dispersed in epoxy resin or copoly imide-silicone and cast in a multi-compartment box with long sides transparent to X-rays and dividers opaque to X-rays. (UK)

  19. Building structures

    CERN Document Server

    Ambrose, James

    2011-01-01

    James Ambrose is Editor of the Parker/Ambrose Series of Simplified Design Guides. He practiced as an architect in California and Illinois and as a structural engineer in Illinois. He was a professor of architecture at the University of Southern California. Patrick Tripeny is an Associate Professor, former director of the School of Architecture, and the current Director of the Center for Teaching and Learning Excellence at the University of Utah. He is a licensed architect in California. He has been the recipient of a number of teaching awards at the local and national level for his work in teaching structures and design. With James Ambrose, he is the coauthor of Simplified Engineering for Architects and Builders, Eleventh Edition; Simplified Design of Steel Structures, Eighth Edition; Simplified Design of Concrete Structures, Eighth Edition; and Simplified Design of Wood Structures, Sixth Edition, all published by Wiley.

  20. Gate less-FET pH Sensor Fabricated on Undoped AlGaN/ GaN HEMT Structure

    International Nuclear Information System (INIS)

    Maneea Eizadi Sharifabad; Mastura Shafinaz Zainal Abidin; Shaharin Fadzli Abd Rahman; Abdul Manaf Hashim; Abdul Rahim Abdul Rahman

    2011-01-01

    Gallium nitride with wurtzite crystal structure is a chemically stable semiconductor with high internal spontaneous and piezoelectric polarization, which make it highly suitable materials to create very sensitive and robust sensors for the detection of ions, gases and liquids. Sensing characteristics of an open-gate liquid-phase sensor fabricated on undoped-AlGaN/ GaN high-electron-mobility-transistor (HEMT) structure in aqueous solution was investigated. In ambient atmosphere, the open-gate undoped AlGaN/ GaN HEMT clearly showed only the presence of linear region of currents while Si-doped AlGaN/ GaN showed the linear and saturation regions of currents, very similar to those of gated devices. This seems to show that very low Fermi level pinning by surface states exists in undoped AlGaN/ GaN sample. In aqueous solution, the typical current-voltage (I-V) characteristics of HEMTs with good gate controllability were observed. The potential of the AlGaN surface at the open-gate area is effectively controlled via aqueous solution by Ag/ AgCl reference gate electrode. The open-gate undoped AlGaN/ GaN HEMT structure is capable of stable operation in aqueous electrolytes and exhibit linear sensitivity, and high sensitivity of 1.9 mA/ pH or 3.88 mA/ mm/ pH at drain-source voltage, VDS = 5 V was obtained. Due to large leakage current where it increases with the negative reference gate voltage, the Nernstians like sensitivity cannot be determined. Suppression of current leakage is likely to improve the device performance. The open-gate undoped-AlGaN/ GaN structure is expected to be suitable for pH sensing application. (author)

  1. Structural Behaviour of Reciprocal Structures

    DEFF Research Database (Denmark)

    Parigi, Dario; Kirkegaard, Poul Henning

    2013-01-01

    The present paper focuses on the comparison of several two-dimensional and three-dimensional reciprocal configurations. The goal of such comparison is to analyse the structural behaviour when changing the geometric parameters used to describe the geometry of reciprocal structures....

  2. Organizational structure

    NARCIS (Netherlands)

    Hendriks, P.H.J.; Schwartz, D.; Te'eni, D.

    2011-01-01

    For many decades, organization scientists have paid considerable attention to the link between knowledge and organization structure. An early contributor to these discussions was Max Weber (1922), who elaborated his concepts of professional bureaucracy. History shows a multitude of other

  3. Organizational Structures

    OpenAIRE

    2006-01-01

    drag Drag-and-Drop Exercise Interactive Media Element This interactive exercise gets the learner to identify various strengths and weaknesses of the functional, divisional, matrix, horizontal, modular, and hybrid organizational structures

  4. Hydraulic Structures

    Data.gov (United States)

    Department of Homeland Security — This table is required whenever hydraulic structures are shown in the flood profile. It is also required if levees are shown on the FIRM, channels containing the...

  5. Hydraulic structures

    CERN Document Server

    Chen, Sheng-Hong

    2015-01-01

    This book discusses in detail the planning, design, construction and management of hydraulic structures, covering dams, spillways, tunnels, cut slopes, sluices, water intake and measuring works, ship locks and lifts, as well as fish ways. Particular attention is paid to considerations concerning the environment, hydrology, geology and materials etc. in the planning and design of hydraulic projects. It also considers the type selection, profile configuration, stress/stability calibration and engineering countermeasures, flood releasing arrangements and scouring protection, operation and maintenance etc. for a variety of specific hydraulic structures. The book is primarily intended for engineers, undergraduate and graduate students in the field of civil and hydraulic engineering who are faced with the challenges of extending our understanding of hydraulic structures ranging from traditional to groundbreaking, as well as designing, constructing and managing safe, durable hydraulic structures that are economical ...

  6. Structural Origami

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 8; Issue 5. Structural Origami - A Geodesic Dome from Five Postcards. Subramania Ranganathan. General Article ... Author Affiliations. Subramania Ranganathan1. Discovery Laboratory Indian Institute of Chemical Technology Hyderabad 500 007, India.

  7. Structural Dynamics

    DEFF Research Database (Denmark)

    Nielsen, Søren R.K.

    The present textbook has been written for a course on stochastic vibration theory that is being given on the 9th semester at Aalborg University for M.Sc. students in structural engineering.......The present textbook has been written for a course on stochastic vibration theory that is being given on the 9th semester at Aalborg University for M.Sc. students in structural engineering....

  8. Nuclear structure

    International Nuclear Information System (INIS)

    Eastham, D.A.; Joy, T.

    1986-01-01

    The paper on 'nuclear structure' is the Appendix to the Daresbury (United Kingdom) Annual Report 1985/86, and contains the research work carried out at the Nuclear Structure Facility, Daresbury, within that period. During the year a total of 74 experiments were scheduled covering the main areas of activity including: nuclear collective motion, nuclei far from stability, and nuclear collisions. The Appendix contains brief reports on these experiments and associated theory. (U.K.)

  9. Unemployment - Structural

    OpenAIRE

    Lindbeck, Assar

    1999-01-01

    Structural unemployment differs from cyclical unemployment by not disappearing in cyclical booms. In economic theory, structural unemployment is usually analysed in terms of the concept of equilibrium unemployment (the "natural unemployment rate" in Friedman’s terminology). Two elaborate concepts of equilibrium unemployment – the non-accelerating inflation rate of unemployment (the NAIRU) and the unemployment rate that induces firms and workers to accept the same real wage (the PS-WS-model) a...

  10. Structural Dynamics

    International Nuclear Information System (INIS)

    Kim, Du Gi

    2005-08-01

    This book introduces summary of structural dynamics, the reason of learning of structural dynamics, single-degree of freedom system, simple harmonic vibration and application, numerical analysis method, such as time domain and frequency domain and nonlinear system, multi-degree of freedom system random vibration over discrete distribution, continuous distribution and extreme value distribution, circumstance vibration, earth quake vibration, including input earthquake, and earthquake-resistant design and capacity spectrum method, wind oscillation wave vibration, vibration control and maintenance control.

  11. Electrical and structural characteristics of metamorphic In0.38Al0.62As/In0.37Ga0.63As/In0.38Al0.62As HEMT nanoheterostructures

    International Nuclear Information System (INIS)

    Galiev, G. B.; Klimov, E. A.; Klochkov, A. N.; Maltsev, P. P.; Pushkarev, S. S.; Zhigalina, O. M.; Imamov, R. M.; Kuskova, A. N.; Khmelenin, D. N.

    2013-01-01

    The influence of the metamorphic buffer design and epitaxial growth conditions on the electrical and structural characteristics of metamorphic In 0.38 Al 0.62 As/In 0.37 Ga 0.63 As/In 0.38 Al 0.62 As high electron mobility transistor (MHEMT) nanoheterostructures has been investigated. The samples were grown on GaAs(100) substrates by molecular beam epitaxy. The active regions of the nanoheterostructures are identical, while the metamorphic buffer In x Al 1−x As is formed with a linear or stepwise (by Δ x = 0.05) increase in the indium content over depth. It is found that MHEMT nanoheterostructures with a step metamorphic buffer have fewer defects and possess higher values of two-dimensional electron gas mobility at T = 77 K. The structures of the active region and metamorphic buffer have been thoroughly studied by transmission electron microscopy. It is shown that the relaxation of metamorphic buffer in the heterostructures under consideration is accompanied by the formation of structural defects of the following types: dislocations, microtwins, stacking faults, and wurtzite phase inclusions several nanometers in size

  12. Structural and nanomechanical properties of InN films grown on Si(1 0 0) by femtosecond pulsed laser deposition

    International Nuclear Information System (INIS)

    Hafez, M A; Mamun, M A; Elmustafa, A A; Elsayed-Ali, H E

    2013-01-01

    The structural and nanomechanical properties of InN films grown on Si(1 0 0) using femtosecond pulsed laser deposition were studied for different growth conditions. Atomic nitrogen was generated by either thermal cracking or laser-induced breakdown (LIB) of ammonia. Optical emission spectroscopy was conducted on the laser plasma and used to observe atomic nitrogen formation. An indium buffer layer was initially grown on the Si substrate at low temperature. The surface structure and morphology were investigated by in situ reflection high-energy electron diffraction, ex situ atomic force microscopy and x-ray diffraction (XRD). The results show that the initial buffer indium layers were terminated with the In(2 × 1) structure and had a smooth surface. With increased coverage, the growth mode developed from two-dimensional layers to three-dimensional islands. At room temperature (RT), formation of submicrometre islands resulted in mixed crystal structure of In and InN. As the substrate temperature was increased to 250–350 °C, the crystal structure was found to be dominated by fewer In and more InN, with only InN formed at 350 °C. The XRD patterns show that the grown InN films have wurtzite crystal structure. The film hardness near the surface was observed to increase from less than 1 GPa, characteristic of In for the sample grown at RT using the thermal cracker, to a hardness of 11 GPa at 30 nm from surface, characteristic of InN for samples grown at 350 °C by LIB. The hardness at deep indents reaches the hardness of the Si substrate of ∼12 GPa. (paper)

  13. Diverter structure

    Energy Technology Data Exchange (ETDEWEB)

    Nayama, Risuke; Toyota, Masahiko; Tsujimura, Seiichi

    1995-11-21

    The present invention concerns a vacuum vessel for a tokamak-type nuclear fusion plasma experimental device, and provides a divertor structure capable of reducing a distance of a plasma facing surface of a divertor structure and an inner wall of the vacuum vessel while maintaining cooling and heat removing performance. Namely, in the divertor structure of the present invention, a compulsory cooling channel on the side receiving high temperature load is made of a highly heat conductive material such as copper. The compulsory cooling channel on the side secured to a substrate is made of a material having high mechanical strength, for example, stainless steel. With such a constitution, the compulsory cooling channel on the side receiving high temperature load transfers the heat received by an armour material from plasmas efficiently to coolants. The opposite side can be secured to the inner wall of the vacuum vessel with satisfactory mechanical strength without interposing other additional materials. As a result, the structure of the present invention can reduce the distance of the plasma facing surface of the divertor structure and the inner wall of the vacuum vessel while maintaining the cooling and heat removing performance. (I.S.).

  14. Diverter structure

    International Nuclear Information System (INIS)

    Nayama, Risuke; Toyota, Masahiko; Tsujimura, Seiichi.

    1995-01-01

    The present invention concerns a vacuum vessel for a tokamak-type nuclear fusion plasma experimental device, and provides a divertor structure capable of reducing a distance of a plasma facing surface of a divertor structure and an inner wall of the vacuum vessel while maintaining cooling and heat removing performance. Namely, in the divertor structure of the present invention, a compulsory cooling channel on the side receiving high temperature load is made of a highly heat conductive material such as copper. The compulsory cooling channel on the side secured to a substrate is made of a material having high mechanical strength, for example, stainless steel. With such a constitution, the compulsory cooling channel on the side receiving high temperature load transfers the heat received by an armour material from plasmas efficiently to coolants. The opposite side can be secured to the inner wall of the vacuum vessel with satisfactory mechanical strength without interposing other additional materials. As a result, the structure of the present invention can reduce the distance of the plasma facing surface of the divertor structure and the inner wall of the vacuum vessel while maintaining the cooling and heat removing performance. (I.S.)

  15. Microcavity structures

    International Nuclear Information System (INIS)

    Kustom, R.L.; Grudzien, D.; Feinerman, A.D.

    1994-01-01

    The feasibility of building mm-wave cavities using deep x-ray lithography techniques is being investigated. These cavities could be considered for linac accelerating structures, undulators, free electron lasers, or mm-wave amplifiers. The construction process includes making precision x-ray masks, x-ray exposure of poly-methyl-methacrylate (PMMA), removal of PMMA, and electroplating a metal. Highly precise two-dimensional features can be machined onto wafers by this technique. The challenge is to fabricate the wafers onto three-dimensional rf structures. Rectangular cavity geometry is best suited to this fabrication technique. Status of wafer manufacture, fabrication and alignment techniques using capillaries bonded in precision grooves, 2π/3 120-GHz linac structures, heat extraction analysis, and beam dynamics in a 5-meter-long 50-MeV linac will be discussed. Measurements made on 10X larger scale models that were built with conventional techniques will also be discussed

  16. Structural biophysics

    International Nuclear Information System (INIS)

    Anon.

    1979-01-01

    Summaries of research projects conducted during 1978 and 1979 are presented. The structural biophysics group explores the high-resolution structure of biological macromolecules and cell organelles. Specific subject areas include: the basic characteristics of photosynthesis in plants; the chemical composition of individual fly ash particles at the site of their damaging action in tissues; direct analysis of frozen-hydrated biological samples by scanning electron microscopy; yeast genetics; the optical activity of DNA aggregates; measurement and characterization of lipoproteins; function of lipoproteins; and the effect of radiation and pollutants on mammalian cells

  17. Foundation Structure

    DEFF Research Database (Denmark)

    2009-01-01

    Method of installing a bucket foundation structure comprising one, two, three or more skirts, into soils in a controlled manner. The method comprises two stages: a first stage being a design phase and the second stage being an installation phase. In the first stage, design parameters are determined...... relating to the loads on the finished foundation structure; soil profile on the location; allowable installation tolerances, which parameters are used to estimate the minimum diameter and length of the skirts of the bucket. The bucket size is used to simulate load situations and penetration into foundation...

  18. Energetic, structural and electronic properties of metal vacancies in strained AlN/GaN interfaces.

    Science.gov (United States)

    Kioseoglou, J; Pontikis, V; Komninou, Ph; Pavloudis, Th; Chen, J; Karakostas, Th

    2015-04-01

    AlN/GaN heterostructures have been studied using density-functional pseudopotential calculations yielding the formation energies of metal vacancies under the influence of local interfacial strains, the associated charge distribution and the energies of vacancy-induced electronic states. Interfaces are built normal to the polar direction of the wurtzite structure by joining two single crystals of AlN and GaN that are a few atomic layers thick; thus, periodic boundary conditions generate two distinct heterophase interfaces. We show that the formation energy of vacancies is a function of their distance from the interfaces: the vacancy-interface interaction is found repulsive or attractive, depending on the type of the interface. When the interaction is attractive, the vacancy formation energy decreases with increasing the associated electric charge, and hence the equilibrium vacancy concentration at the interface is greater. This finding can reveal the well-known morphological differences existing between the two types of investigated interfaces. Moreover, we found that the electric charge is strongly localized around the Ga vacancy, while in the case of Al vacancies is almost uniformly distributed throughout the AlN/GaN heterostructure. Crucially, for the applications of heterostructures, metal vacancies introduce deep states in the calculated bandgap at energy levels from 0.5 to 1 eV above the valence band maximum (VBM). It is, therefore, predicted that vacancies could initiate 'green luminescence' i.e. light emission in the energy range of 2.5 eV stemming from electronic transitions between these extra levels, and the conduction band, or energy levels, due to shallow donors.

  19. Structural anisotropy of nonpolar and semipolar InN epitaxial layers

    Science.gov (United States)

    Darakchieva, V.; Xie, M.-Y.; Franco, N.; Giuliani, F.; Nunes, B.; Alves, E.; Hsiao, C. L.; Chen, L. C.; Yamaguchi, T.; Takagi, Y.; Kawashima, K.; Nanishi, Y.

    2010-10-01

    We present a detailed study of the structural characteristics of molecular beam epitaxy grown nonpolar InN films with a- and m-plane surface orientations on r-plane sapphire and (100) γ-LiAlO2, respectively, and semipolar (101¯1) InN grown on r-plane sapphire. The on-axis rocking curve (RC) widths were found to exhibit anisotropic dependence on the azimuth angle with minima at InN [0001] for the a-plane films, and maxima at InN [0001] for the m-plane and semipolar films. The different contributions to the RC broadening are analyzed and discussed. The finite size of the crystallites and extended defects are suggested to be the dominant factors determining the RC anisotropy in a-plane InN, while surface roughness and curvature could not play a major role. Furthermore, strategy to reduce the anisotropy and magnitude of the tilt and minimize defect densities in a-plane InN films is suggested. In contrast to the nonpolar films, the semipolar InN was found to contain two domains nucleating on zinc-blende InN(111)A and InN(111)B faces. These two wurtzite domains develop with different growth rates, which was suggested to be a consequence of their different polarity. Both, a- and m-plane InN films have basal stacking fault densities similar or even lower compared to nonpolar InN grown on free-standing GaN substrates, indicating good prospects of heteroepitaxy on foreign substrates for the growth of InN-based devices.

  20. Structural anisotropy of nonpolar and semipolar InN epitaxial layers

    International Nuclear Information System (INIS)

    Darakchieva, V.; Xie, M.-Y.; Franco, N.; Alves, E.; Giuliani, F.; Nunes, B.; Hsiao, C. L.; Chen, L. C.; Yamaguchi, T.; Takagi, Y.; Kawashima, K.; Nanishi, Y.

    2010-01-01

    We present a detailed study of the structural characteristics of molecular beam epitaxy grown nonpolar InN films with a- and m-plane surface orientations on r-plane sapphire and (100) γ-LiAlO 2 , respectively, and semipolar (1011) InN grown on r-plane sapphire. The on-axis rocking curve (RC) widths were found to exhibit anisotropic dependence on the azimuth angle with minima at InN [0001] for the a-plane films, and maxima at InN [0001] for the m-plane and semipolar films. The different contributions to the RC broadening are analyzed and discussed. The finite size of the crystallites and extended defects are suggested to be the dominant factors determining the RC anisotropy in a-plane InN, while surface roughness and curvature could not play a major role. Furthermore, strategy to reduce the anisotropy and magnitude of the tilt and minimize defect densities in a-plane InN films is suggested. In contrast to the nonpolar films, the semipolar InN was found to contain two domains nucleating on zinc-blende InN(111)A and InN(111)B faces. These two wurtzite domains develop with different growth rates, which was suggested to be a consequence of their different polarity. Both, a- and m-plane InN films have basal stacking fault densities similar or even lower compared to nonpolar InN grown on free-standing GaN substrates, indicating good prospects of heteroepitaxy on foreign substrates for the growth of InN-based devices.

  1. High optical and structural quality of GaN epilayers grown on ( 2¯01) β-Ga2O3

    KAUST Repository

    Mumthaz Muhammed, Mufasila; Peres, M.; Yamashita, Y.; Morishima, Y.; Sato, S.; Franco, N.; Lorenz, K.; Kuramata, A.; Roqan, Iman S.

    2014-01-01

    Producing highly efficient GaN-based optoelectronic devices has been a challenge for a long time due to the large lattice mismatch between III-nitride materials and the most common substrates, which causes a high density of threading dislocations. Therefore, it is essential to obtain alternative substrates with small lattice mismatches, appropriate structural, thermal and electrical properties, and a competitive price. Our results show that (2̄01) oriented β-Ga2O3 has the potential to be used as a transparent and conductive substrate for GaN-growth. Photoluminescence spectra of thick GaN layers grown on (2̄01) oriented β-Ga 2O3 are found to be dominated by intense bandedge emission. Atomic force microscopy studies show a modest threading dislocation density of ∼108cm-2. X-ray diffraction studies show the high quality of the single-phase wurtzite GaN thin film on (2̄01) β-Ga2O3 with in-plane epitaxial orientation relationships between the β-Ga2O3 and the GaN thin film defined by (010) β-Ga2O3 || (112̄0) GaN and (2̄01) β-Ga2O3 || (0001) GaN leading to a lattice mismatch of ∼4.7%. Complementary Raman spectroscopy indicates that the quality of the GaN epilayer is high. © 2014 AIP Publishing LLC.

  2. Structural and optical properties of ZnO nanostructures electrochemically synthesized on AZO/Ag/AZO-multilayer-film-coated polyethersulfone substrates

    International Nuclear Information System (INIS)

    Oh, Dohyun; Yoo, Chanho; No, Youngsoo; Kim, Suyoun; Kim, Taewhan; Cho, Woonjo; Kim, Jinyoung

    2012-01-01

    ZnO nanostructures were formed on Al-doped ZnO (AZO)/Ag/AZO-multilayer-film-coated flexible polyethersulfone (PES) substrates at low temperature by using an electrochemical deposition method. The resistivity of the AZO/Ag/AZO multilayer films decreased with increasing thickness of the Ag film. X-ray diffraction patterns for the ZnO nanostructures showed that the crystal structure of the ZnO was hexagonal wurtzite and that the orientation was along the c-axis perpendicular to the substrate. Scanning electron microscopy images showed that the ZnO nanostructures grown at current densities of - 1.0 and - 1.5 mA/cm 2 were ZnO nanorods with diameters of 150 nm and ZnO nanoflowers with a planar dimension, respectively. Photoluminescence spectra showed that the band-edge emission peak of the ZnO nanostructures dominantly appeared in the ultraviolet region. These results showed that ZnO nanorods and nanoflowers with high quality were synthesized on AZO/Ag/AZO-multilayer-film-coated PES substrates.

  3. Structural studies of ZnS:Cu (5 at %) nanocomposites in porous Al{sub 2}O{sub 3} of different thicknesses

    Energy Technology Data Exchange (ETDEWEB)

    Valeev, R. G., E-mail: rishatvaleev@mail.ru; Trigub, A. L.; Chukavin, A. I.; Beltiukov, A. N. [Physical-Technical Institute, Russian Academy of Sciences (Ural Branch) (Russian Federation)

    2017-02-15

    We present EXAFS, XANES, and X-ray diffraction data on nanoscale ZnS:Cu (5 at %) structures fabricated by the thermal deposition of a ZnS and Cu powder mixture in porous anodic alumina matrices with a pore diameter of 80 nm and thicknesses of 1, 3, and 5 μm. The results obtained are compared with data on ZnS:Cu films deposited onto a polycor surface. According to X-ray diffraction data, the samples contain copper and zinc compounds with sulfur (Cu{sub 2}S and ZnS, respectively); the ZnS compound is in the cubic (sphalerite) and hexagonal (wurtzite) modifications. EXAFS and XANES studies at the K absorption edges of zinc and copper showed that, in samples deposited onto polycor and alumina with thicknesses of 3 and 5 μm, most copper atoms form the Cu{sub 2}S compound, while, in the sample deposited onto a 1-μm-thick alumina layer, copper atoms form metallic particles on the sample surface. Copper crystals affect the Zn–S interatomic distance in the sample with a 1-μm-thick porous Al{sub 2}O{sub 3} layer; this distance is smaller than in the other samples.

  4. High optical and structural quality of GaN epilayers grown on ( 2¯01) β-Ga2O3

    KAUST Repository

    Mumthaz Muhammed, Mufasila

    2014-07-28

    Producing highly efficient GaN-based optoelectronic devices has been a challenge for a long time due to the large lattice mismatch between III-nitride materials and the most common substrates, which causes a high density of threading dislocations. Therefore, it is essential to obtain alternative substrates with small lattice mismatches, appropriate structural, thermal and electrical properties, and a competitive price. Our results show that (2̄01) oriented β-Ga2O3 has the potential to be used as a transparent and conductive substrate for GaN-growth. Photoluminescence spectra of thick GaN layers grown on (2̄01) oriented β-Ga 2O3 are found to be dominated by intense bandedge emission. Atomic force microscopy studies show a modest threading dislocation density of ∼108cm-2. X-ray diffraction studies show the high quality of the single-phase wurtzite GaN thin film on (2̄01) β-Ga2O3 with in-plane epitaxial orientation relationships between the β-Ga2O3 and the GaN thin film defined by (010) β-Ga2O3 || (112̄0) GaN and (2̄01) β-Ga2O3 || (0001) GaN leading to a lattice mismatch of ∼4.7%. Complementary Raman spectroscopy indicates that the quality of the GaN epilayer is high. © 2014 AIP Publishing LLC.

  5. Effect of temperature on structural, optical and photoluminescence studies on ZnO nanoparticles synthesized by the standard co-precipitation method

    Energy Technology Data Exchange (ETDEWEB)

    Raj, K. Pradeev [Research and Development Centre, Bharathiar University, Coimbatore 641046, Tamil Nadu (India); Department of Physics, CSI College of Engineering, Ooty 643215, Tamil Nadu (India); Sadayandi, K. [Department of Physics, Alagappa Government Arts College, Karaikudi, Sivagangai 630003, Tamil Nadu (India)

    2016-04-15

    This present study brings the synthesis of Zinc oxide (ZnO) nanoparticles (NPs) by the standard aqueous chemical route technique. The impact of calcination temperature on the extent of the ZnO nanoparticles is studied for its lattice constraints. X-ray diffraction (XRD) affirms the hexagonal Wurtzite structure of the synthesized ZnO nanoparticles. From the Williamson–Hall (W–H) plot, positive slope is inferred for pure and calcined ZnO NPs and confirms the presence of tensile strain. From the SEM images it is found that the crystallinity enhances with calcination temperature. From the optical studies, it is found that the band gap energy decreases with improved transmission. The Photoluminescence (PL) spectrum reveals the UV emission is strong near the band-edge. The emission peaks around 400–480 nm result in blue emission and the peaks around 540–560 nm result in green emission. Decrease in band gap energy and enhancement in PL studies reveal the red shift of the calcined ZnO exhibiting solid quantum confinements.

  6. The effect of strontium doping on structural and morphological properties of ZnO nanofilms synthesized by ultrasonic spray pyrolysis method

    Directory of Open Access Journals (Sweden)

    A. Ouhaibi

    2018-03-01

    Full Text Available Pristine and strontium doped ZnO nanometric films were successfully synthesized on heated glass substrates by the ultrasonic spray pyrolysis technique. The samples were characterized by means of X-ray diffraction (XRD, Atomic Force Microscope (AFM, UV–visible spectroscopy and photoluminescence (PL. X-ray diffraction patterns confirmed the hexagonal (wurtzite structure, where the most pronounced (002 peak indicates the preferential orientation along the c-axis perpendicular to the sample surface. The intensity of this peak was increased rapidly from the first doping of 1% and its position was shifted toward higher angles under Sr-doping effect. For the used doping range of 1–5%, the Sr-doping at 3% attracted an especial attention. At this concentration, the particular transformation in the surface morphology of doped ZnO films was observed. The surface became granular and rough by expanding the crystallites' size. From optical measurements, transmittance and PL spectra were found to be sensitive to Sr-doping, where two different behaviors were observed before and after 3% of Sr-doping. Keywords: Ultrasonic spray pyrolysis, Sr-doped ZnO, Morphology study, Optical properties

  7. Structures manual

    Science.gov (United States)

    2001-01-01

    This manual was written as a guide for use by design personnel in the Vermont Agency of Transportation Structures Section. This manual covers the design responsibilities of the Section. It does not cover other functions that are a part of the Structu...

  8. Coastal Structures

    DEFF Research Database (Denmark)

    Oumeraci, H.; Burcharth, H. F.; Rouck, J. De

    1995-01-01

    The paper attempts to present an overview of five research projects supported by the Commission of the European Communities, Directorate General XII, under the MAST 2- Programme (Marine Sciences and Technology), with the overall objective of contributing to the development of improved rational me...... methods for the design of coastal structures....

  9. Structural optimization

    CERN Document Server

    MacBain, Keith M

    2009-01-01

    Intends to supplement the engineer's box of analysis and design tools making optimization as commonplace as the finite element method in the engineering workplace. This title introduces structural optimization and the methods of nonlinear programming such as Lagrange multipliers, Kuhn-Tucker conditions, and calculus of variations.

  10. Structural region

    Indian Academy of Sciences (India)

    First page Back Continue Last page Overview Graphics. Structural region. The two groups had 4 substitutions similar to Yawat strain. The Yawat strain had 5 unique mutations. 3 in the E2 region and 2 in the E1 region. The mutation, I702V (E2), though different from all the recent Indian and Reunion sequences was similar ...

  11. Data Structures

    DEFF Research Database (Denmark)

    Davoodi, Pooya

    We study data structures for variants of range query problems. In particular, we consider (1) the range minimum problem: given a multidimensional array, find the position of the minimum element in a query rectangle; (2) the path minima problem: given a weighted tree, find the edge with minimum...... weight in a query path; (3) the range diameter problem: given a point set in the plane, find two points that are farthest away in a query rectangle. These and similar problems arise in various applications including document retrieval, genome sequence analysis, OLAP data cubes, network flows, shape......-fitting, and clustering. The three mentioned problems are considered for either static inputs or dynamic inputs. In the static setting, we investigate the space-efficiency of data structures, which is an important aspect in massive data algorithmics. We provide lower bounds on the trade-off between the query time...

  12. Terminal structure

    Science.gov (United States)

    Schmidt, Frank [Langenhagen, DE; Allais, Arnaud [Hannover, DE; Mirebeau, Pierre [Villebon sur Yvette, FR; Ganhungu, Francois [Vieux-Reng, FR; Lallouet, Nicolas [Saint Martin Boulogne, FR

    2009-10-20

    A terminal structure (2) for a superconducting cable (1) is described. It consists of a conductor (2a) and an insulator (2b) that surrounds the conductor (2a), wherein the superconducting cable (1) has a core with a superconducting conductor (5) and a layer of insulation that surrounds the conductor (5), and wherein the core is arranged in such a way that it can move longitudinally in a cryostat. The conductor (2a) of the terminal structure (2) is electrically connected with the superconducting conductor (5) or with a normal conductor (6) that is connected with the superconducting conductor (5) by means of a tubular part (7) made of an electrically conductive material, wherein the superconducting conductor (5) or the normal conductor (6) can slide in the part (7) in the direction of the superconductor.

  13. Concrete structures

    CERN Document Server

    Setareh, Mehdi

    2017-01-01

    This revised, fully updated second edition covers the analysis, design, and construction of reinforced concrete structures from a real-world perspective. It examines different reinforced concrete elements such as slabs, beams, columns, foundations, basement and retaining walls and pre-stressed concrete incorporating the most up-to-date edition of the American Concrete Institute Code (ACI 318-14) requirements for the design of concrete structures. It includes a chapter on metric system in reinforced concrete design and construction. A new chapter on the design of formworks has been added which is of great value to students in the construction engineering programs along with practicing engineers and architects. This second edition also includes a new appendix with color images illustrating various concrete construction practices, and well-designed buildings. The ACI 318-14 constitutes the most extensive reorganization of the code in the past 40 years. References to the various sections of the ACI 318-14 are pro...

  14. Galactic structure

    International Nuclear Information System (INIS)

    1989-01-01

    The occurrence of hot, apparently normal, massive stars far from the galactic plane has been a major puzzle in an understanding of galactic structure and evolution. Such stars have been discovered and studied at the South African Astronomical Observatory (SAAO) over a number of years. During 1989 further evidence has been obtained indicating that these stars are normal, massive objects. Other studies of galactic structure conducted by the SAAO have included research on: the central bulge region of our galaxy; populations of M giants in the galaxy; a faint blue object survey; a survey of the galactic plane for distant Cepheid variables; interstellar reddening, and K-type dwarfs as tracers for the gravitational force perpendicular to the galactic plane. 1 fig

  15. Structure, microstructure and determination of optical constants from transmittance data of co-doped Zn0.90Co0.05M0.05O (M=Al, Cu, Cd, Na) films

    International Nuclear Information System (INIS)

    2 A Laboratoire des Structures, Propriétés et Interactions Inter Atomiques, Université Abbes Laghrour, Khenchela 40000 (Algeria))" data-affiliation=" (LASPI2 A Laboratoire des Structures, Propriétés et Interactions Inter Atomiques, Université Abbes Laghrour, Khenchela 40000 (Algeria))" >Roguai, S.; 2 A Laboratoire des Structures, Propriétés et Interactions Inter Atomiques, Université Abbes Laghrour, Khenchela 40000 (Algeria))" data-affiliation=" (LASPI2 A Laboratoire des Structures, Propriétés et Interactions Inter Atomiques, Université Abbes Laghrour, Khenchela 40000 (Algeria))" >Djelloul, A.; Nouveau, Corinne; Souier, T.; Dakhel, A.A.; Bououdina, M.

    2014-01-01

    Highlights: • A series of Zn 0.90 Co 0.05 M 0.05 O (M=Al, Cu, Cd, Na) films has been prepared. • Thin films of these prepared samples have been deposited using USP technique. • Absorption of electronic transition has been used to fit the transmittance data. • Optical and dispersion parameters have been determined. - Abstract: ZnO, Zn 0.95 Co 0.05 O and Zn 0.90 Co 0.05 M 0.05 O (M=Al, Cd, Na, Cu) single phase films have been successfully synthesized by ultrasonic spray pyrolysis technique. Structural analysis by X-ray diffraction show that all the films have hexagonal wurtzite structure with an average crystallite size in the range of 19–25 nm. SEM analysis revealed that Cd and Na preserve the shape of nanopetals observed with ZnO or Co-ZnO films, while the doping with Al or Cu promote the formation of dense films constituted of nanorods. By the application of Levenberg–Marquardt least square method, the experimental transmittance data were fitted perfectly with the transmittance data calculated via a combination of Wemple–DiDomenico model, absorption coefficient of an electronic transition and Tauc–Urbach model. The concentration of absorbing centres N Co and oscillator strength f of d–d transition of Co 2+ ions are calculated from Smakula’s formula

  16. Nuclear structure

    International Nuclear Information System (INIS)

    Joy, T.; Price, H.G.

    1984-01-01

    The appendix to the Daresbury Annual report contains detailed summaries of experiments carried out, or in progress, for the period 1983/84, using the Nuclear Structure Facility tandem accelerator. The experimental work is carried out by University groups from the UK and abroad, and Daresbury Staff. Developments in instrumentation, and a report on the first year of scheduled operation of the Facility, are also given. (U.K.)

  17. Structural dynamics

    CERN Document Server

    Strømmen, Einar N

    2014-01-01

    This book introduces to the theory of structural dynamics, with focus on civil engineering structures that may be described by line-like beam or beam-column type of systems, or by a system of rectangular plates. Throughout this book the mathematical presentation contains a classical analytical description as well as a description in a discrete finite element format, covering the mathematical development from basic assumptions to the final equations ready for practical dynamic response predictions. Solutions are presented in time domain as well as in frequency domain. Structural Dynamics starts off at a basic level and step by step brings the reader up to a level where the necessary safety considerations to wind or horizontal ground motion induced dynamic design problems can be performed. The special theory of the tuned mass damper has been given a comprehensive treatment, as this is a theory not fully covered elsewhere. For the same reason a chapter on the problem of moving loads on beams has been included.

  18. Structural damage

    International Nuclear Information System (INIS)

    Gray, R.E.; Bruhn, R.W.

    1992-01-01

    Virtually all structures show some signs of distress due to deterioration of the building components, to changed loads, or to changed support conditions. Changed support conditions result from ground movements. In mining regions many cases of structural distress are attributed to mining without considering alternative causes. This is particularly true of coal mining since it occurs under extensive areas. Coal mining is estimated to have already undermined more than eight million acres and may eventually undermine 40 million acres in the United States. Other nonmetal and metal underground mines impact much smaller areas. Although it is sometimes difficult, even with careful study, to identify the actual cause of damage, persons responsible for underground coal mining should at least be aware of possible causes of building stress other than mine subsidence. This paper presents information on distress to structures and briefly reviews a number of causes of ground movements other than subsidence: Mass movements, dissolution, erosion, frost action, shrinking and swelling, yield into excavations and compressibility

  19. Effects of stabilizer ratio on photoluminescence properties of sol-gel ZnO nano-structured thin films

    International Nuclear Information System (INIS)

    Boudjouan, F.; Chelouche, A.; Touam, T.; Djouadi, D.; Khodja, S.; Tazerout, M.; Ouerdane, Y.; Hadjoub, Z.

    2015-01-01

    Nanostructured ZnO thin films with different molar ratios of MEA to zinc acetate (0.5, 1.0, 1.5 and 2.0) have been deposited on glass substrates by a sol–gel dip coating technique. X-ray diffraction, Scanning Electron Microscopy, UV–visible spectrophotometry and photoluminescence spectroscopy have been employed to investigate the effect of MEA stabilizer ratio on structural, morphological, absorbance and emission properties of the ZnO thin films. Diffraction patterns have shown that all the films are polycrystalline and exhibit a wurtzite hexagonal structure. The c axis orientation has been enhanced with increasing stabilizer ratio. SEM micrographs have revealed that the morphology of the ZnO films depend on stabilizer ratio. The UV–visible absorption spectra have demonstrated that the optical absorption is affected by stabilizer ratio. The photoluminescence spectra have indicated one ultraviolet and two visible emission bands (green and red), while band intensities are found to be dependent on stabilizer ratio. ZnO thin films deposited at MEA ratio of 1.0 show the highest UV emission while the minimum UV emission intensity is observed in thin films deposited at ratio of 0.5 and the maximum green has been recorded for films deposited at MEA ratio of 2.0. - Highlight: • c axis orientation increases with increasing MEA ratio. • The increase of MEA ration from 0.5 to 1.0 enhances greatly the UV emission. • The larger I UV /I visible is obtained for the MEA to Zn ratio of 1:1. • The MEA ratio of 0.5 favors the formation of large density of V zn . • The MEA ratio of 2.0 increases the V o density

  20. Stokes shift and fine structure splitting in composition-tunable Zn{sub x}Cd{sub 1−x}Se nanocrystals: Atomistic tight-binding theory

    Energy Technology Data Exchange (ETDEWEB)

    Sukkabot, Worasak, E-mail: w.sukkabot@gmail.com

    2017-02-01

    I report on the atomistic correlation of the structural properties and excitonic splitting of ternary alloy Zn{sub x}Cd{sub 1−x}Se wurtzite nanocrystals using the sp{sup 3}s* empirical tight-binding method with the description of the first nearest neighbouring interaction and bowing effect. Based on a successful model, the computations are presented under various Zn compositions (x) and diameters of alloy Zn{sub x}Cd{sub 1−x}Se nanocrystals with the experimentally synthesized compositions and sizes. With increasing Zn contents (x), the optical band gaps and electron-hole coulomb energies are improved, while ground electron-hole wave function overlaps, electron-hole exchange energies, stokes shift and fine structure splitting are reduced. A composition-tunable emission from blue to yellow wavelength is obviously demonstrated. The optical band gaps, ground electron-hole wave function overlaps, electron-hole interactions, stokes shift and fine structure splitting are progressively decreased with the increasing diameters. Alloy Zn{sub x}Cd{sub 1−x}Se nanocrystal with Zn rich and large diameter is the best candidate to optimistically be used as a source of entangled photon pairs. The agreement with the experimental data is remarkable. Finally, the present systematic study on the structural properties and excitonic splitting predominantly opens a new perspective to understand the size- and composition-dependent properties of Zn{sub x}Cd{sub 1−x}Se nanocrystals with a comprehensive strategy to design the optoelectronic devices.

  1. Structural and Electrochemical Characterization of Zn1-xFexO-Effect of Aliovalent Doping on the Li⁺ Storage Mechanism.

    Science.gov (United States)

    Giuli, Gabriele; Eisenmann, Tobias; Bresser, Dominic; Trapananti, Angela; Asenbauer, Jakob; Mueller, Franziska; Passerini, Stefano

    2017-12-29

    In order to further improve the energy and power density of state-of-the-art lithium-ion batteries (LIBs), new cell chemistries and, therefore, new active materials with alternative storage mechanisms are needed. Herein, we report on the structural and electrochemical characterization of Fe-doped ZnO samples with varying dopant concentrations, potentially serving as anode for LIBs (Rechargeable lithium-ion batteries). The wurtzite structure of the Zn 1-x Fe x O samples (with x ranging from 0 to 0.12) has been refined via the Rietveld method. Cell parameters change only slightly with the Fe content, whereas the crystallinity is strongly affected, presumably due to the presence of defects induced by the Fe 3+ substitution for Zn 2+ . XANES (X-ray absorption near edge structure) data recorded ex situ for Zn 0.9 Fe 0.1 O electrodes at different states of charge indicated that Fe, dominantly trivalent in the pristine anode, partially reduces to Fe 2+ upon discharge. This finding was supported by a detailed galvanostatic and potentiodynamic investigation of Zn 1-x Fe x O-based electrodes, confirming such an initial reduction of Fe 3+ to Fe 2+ at potentials higher than 1.2 V (vs. Li⁺/Li) upon the initial lithiation, i.e., discharge. Both structural and electrochemical data strongly suggest the presence of cationic vacancies at the tetrahedral sites, induced by the presence of Fe 3+ (i.e., one cationic vacancy for every two Fe 3+ present in the sample), allowing for the initial Li⁺ insertion into the ZnO lattice prior to the subsequent conversion and alloying reaction.

  2. Structural and Electrochemical Characterization of Zn1−xFexO—Effect of Aliovalent Doping on the Li+ Storage Mechanism

    Directory of Open Access Journals (Sweden)

    Gabriele Giuli

    2017-12-01

    Full Text Available In order to further improve the energy and power density of state-of-the-art lithium-ion batteries (LIBs, new cell chemistries and, therefore, new active materials with alternative storage mechanisms are needed. Herein, we report on the structural and electrochemical characterization of Fe-doped ZnO samples with varying dopant concentrations, potentially serving as anode for LIBs (Rechargeable lithium-ion batteries. The wurtzite structure of the Zn1−xFexO samples (with x ranging from 0 to 0.12 has been refined via the Rietveld method. Cell parameters change only slightly with the Fe content, whereas the crystallinity is strongly affected, presumably due to the presence of defects induced by the Fe3+ substitution for Zn2+. XANES (X-ray absorption near edge structure data recorded ex situ for Zn0.9Fe0.1O electrodes at different states of charge indicated that Fe, dominantly trivalent in the pristine anode, partially reduces to Fe2+ upon discharge. This finding was supported by a detailed galvanostatic and potentiodynamic investigation of Zn1−xFexO-based electrodes, confirming such an initial reduction of Fe3+ to Fe2+ at potentials higher than 1.2 V (vs. Li+/Li upon the initial lithiation, i.e., discharge. Both structural and electrochemical data strongly suggest the presence of cationic vacancies at the tetrahedral sites, induced by the presence of Fe3+ (i.e., one cationic vacancy for every two Fe3+ present in the sample, allowing for the initial Li+ insertion into the ZnO lattice prior to the subsequent conversion and alloying reaction.

  3. Airfoil structure

    Science.gov (United States)

    Frey, G.A.; Twardochleb, C.Z.

    1998-01-13

    Past airfoil configurations have been used to improve aerodynamic performance and engine efficiencies. The present airfoil configuration further increases component life and reduces maintenance by reducing internal stress within the airfoil itself. The airfoil includes a chord and a span. Each of the chord and the span has a bow being summed to form a generally ``C`` configuration of the airfoil. The generally ``C`` configuration includes a compound bow in which internal stresses resulting from a thermal temperature gradient are reduced. The structural configuration reduces internal stresses resulting from thermal expansion. 6 figs.

  4. Vcsel structure

    DEFF Research Database (Denmark)

    2015-01-01

    .5, and wherein an index of refraction of low-index sections of the grating structure is less than 2. The core grating region defines a projection in a direction normal to the grating layer. The grating reflector further comprises a cap layer abutting the grating layer, and an index of refraction of the cap layer...... within the projection of the core grating region onto the cap layer is at least 2.5, and within the projection of the core grating region, the cap layer is abutted by a first solid dielectric low-index layer, an index of refraction of the first low-index layer or air being less than 2; and within...... the projection of the core grating region, the grating layer is also abutted by a second low-index layer and/or by air, an index of refraction of the second low-index layer or air being less than 2. The VCSEL structure furthermore comprises a first reflector and an active region for providing a cavity...

  5. Baryon structure

    International Nuclear Information System (INIS)

    Morsch, H.P.; Forschungszentrum Juelich GmbH

    1993-01-01

    A brief review on the theoretical and experimental situation of baryon spectroscopy is first given. Then, the radial structure of baryons, related to the ground state form factors and the baryonic compressibility, is discussed. An experiment has been performed at Saturne laboratory (France) in which for the first time a compression of the nucleon is observed, exciting the P 11 (1440 MeV) resonance (Roper resonance) by α-particles. The analysis of the data indicates that this excitation covers a large fraction of the available monopole strength in the nucleon. The derived compressibility is discussed as well as the consequence for other fields, as nuclear medium effects on baryon properties, high density phenomena in nuclear collisions as well as colour transparency. In the last point the spin-flip structure of the P 11 (1440 MeV) resonance is discussed. The possibility to determine isoscalar spin-flip strength by polarized deuteron scattering is contrasted with first preliminary results from photon-induced reactions studied at Mainz which indicate a non-negligible M1 excitation of the Roper resonance. (author) 10 figs., 31 refs

  6. Electric field dependence of the electron mobility in bulk wurtzite ZnO

    Indian Academy of Sciences (India)

    ZnO) material is studied. The low-field electron mobility is calculated as a function of doping concentration and lattice temperature. The results show that above nearly 50 K the electrical conduction is governed by activation through the bulk ...

  7. Microstructure analysis of chemically synthesized wurtzite-type CdS ...

    Indian Academy of Sciences (India)

    37, 4682 (1998). [12] O Z Angel and R L Morales, Phys. Rev. B 62, 13064 (2000). [13] S Wei and S B Zhang, Phys. Rev. B 62, 6944 (2000). [14] G Lin, J Zheng and R Xu, J. Phy. Chem. C 112, 7363 (2008). [15] N Bao, L Shen, T Takata, K Domen, A Gupta, K Yanagisawa and C A Grimes, J. Phys. Chem. C 111, 17527 (2007).

  8. Solar-blind wurtzite MgZnO alloy films stabilized by Be doping

    International Nuclear Information System (INIS)

    Su, Longxing; Zhu, Yuan; Zhang, Quanlin; Chen, Mingming; Ji, Xu; Wu, Tianzhun; Gui, Xuchun; Xiang, Rong; Tang, Zikang; Pan, Bicai

    2013-01-01

    Mg x Zn 1−x O alloy films were deposited on c-plane sapphire substrates by radio frequency plasma-assisted molecular beam epitaxy (rf-PMBE). The phase segregation occurred when x was larger than 33%. Be doping was found experimentally able to stabilize the high-Mg-content MgZnO alloy. By alloying 1–2% Be into MgZnO, the band gap of as-prepared quaternary alloys can be raised to the solar-blind range (4.5 eV). Calculated formation energy of the alloys based on first principle reveals that a small amount of Be incorporation can reduce the formation energy of high-Mg-content MgZnO alloys and results in a more stable system, which justifies our experimental observations. (paper)

  9. Features of the piezo-phototronic effect on optoelectronic devices based on wurtzite semiconductor nanowires.

    Science.gov (United States)

    Yang, Qing; Wu, Yuanpeng; Liu, Ying; Pan, Caofeng; Wang, Zhong Lin

    2014-02-21

    The piezo-phototronic effect, a three way coupling effect of piezoelectric, semiconductor and photonic properties in non-central symmetric semiconductor materials, utilizing the piezo-potential as a "gate" voltage to tune the charge transport/generation/recombination and modulate the performance of optoelectronic devices, has formed a new field and attracted lots of interest recently. The mechanism was verified in various optoelectronic devices such as light emitting diodes (LEDs), photodetectors and solar cells etc. The fast development and dramatic increasing interest in the piezo-phototronic field not only demonstrate the way the piezo-phototronic effects work, but also indicate the strong need for further research in the physical mechanism and potential applications. Furthermore, it is important to distinguish the contribution of the piezo-phototronic effect from other factors induced by external strain such as piezoresistance, band shifting or contact area change, which also affect the carrier behaviour and device performance. In this perspective, we review our recent progress on piezo-phototronics and especially focus on pointing out the features of piezo-phototronic effect in four aspects: I-V characteristics; c-axis orientation; influence of illumination; and modulation of carrier behaviour. Finally we proposed several criteria for describing the contribution made by the piezo-phototronic effect to the performance of optoelectronic devices. This systematic analysis and comparison will not only help give an in-depth understanding of the piezo-phototronic effect, but also work as guide for the design of devices in related areas.

  10. Structural and morphological TEM characterization of GaAs based nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Soda, Marcello

    2012-02-03

    The question of a structural and morphological characterization of GaAs based nanowires is the research interest of this thesis. For this purpose standard and analytical transmission electron microscopy techniques were employed. New investigation methodologies are introduced in order to obtain a reliable interpretation of the results. The principal motivation on developing a new investigation method is the necessity to relate the results of crystal structure and morphology characterizations to microscopic and NW-specific parameters and not to macroscopic and general growth parameters. This allows a reliable comparison of NW characteristics and enhances the comprehension of their growth mechanism.The analysis of the results on crystal structure investigations, assuming this new perspective, delivers the fundamental finding that the axial growth of Au-assisted GaAs NWs can change in a pseudo Ga-assisted growth due to a non steady-state regime of the Ga accumulation process in the liquid droplet. The attempt to associate the observed crystal structures to one of these two growth modes reveals that zinc blende segments are most probably generated when a pseudo Ga-assisted growth occurs. This experimental evidence is in accordance with investigations developed by Glas et al. and Spirkoska et al. and with the current understanding of the NW growth mechanism and unifies the interpretation of catalytic growth of GaAs NWs. A Mn doped GaAs shell deposited at low temperature on core GaAs NWs is characterized for the first time. The growth is found to be epitaxial and to confer the quality of the core crystal to the shell crystal. As a consequence a high stacking fault density of the core NW limits the temperature of the shell growth due to the formation of clusters. Cross sections of (Ga,Mn)As shells are investigated. Simple kinetic and thermodynamical considerations lead to the conclusion of morphological instability of the low temperature radial growth. Analytical

  11. Effect of Radiation and Doping on the Structure and Physical Properties of Some Oxide Materials

    International Nuclear Information System (INIS)

    Abd Elhaleem, S.M.S.

    2013-01-01

    Metal oxides thin films are used for applications in microelectronic devices, light emitting diodes, thin film, antireflection coatings, transparent electrodes in solar cell, gas sensors, surface acoustic wave devices, and lasers. In recent years, Zinc oxide (ZnO) films have been extensively studied because they exhibit high mobility, optical transparency, and electrical conductivity and have a lower material cost. ZnO films were prepared by home-made spray pyrolysis technique on preheated glass substrates. The effect of deposition parameters such as solution concentration, substrate temperature, spray time and doping level on structural, optical and electrical properties of ZnO films was investigated. The thickness of the films was measured by stylus profilometers. The structural analysis was studied by X-ray diffraction (XRD) while optical transmittance in the wavelength range (300-800 nm) was measured by double beam spectrophotometer. For electrical measurements (two- point probe) technique was used, resistance was measured as a function of temperature, in the range from room temperature to 70 Degree C. According to the structural analysis, X-ray diffraction (XRD) patterns showed that the deposited ZnO films were polycrystalline with highly preferred orientation along [002] and the crystal lattice was found to be hexagonal. The values of lattice constants, crystallite size, micro strain and dislocation density of all samples were calculated. In addition, the UV-VIS spectroscopy showed high transparency of ZnO films in the visible region. An optimization of the films has been carried out to determine the proper preparation conditions. Under variation of all of preparation conditions, all films were polycrystalline, and fit well with the hexagonal (wurtzite) structure, with preferred orientation along (002) plane. It was found that the optimum preparation conditions are solution concentration 0.2 M, substrate temperature 500 ºC and spray time 15 min. The film

  12. Scintillator structure

    International Nuclear Information System (INIS)

    Cusano, D.A.; Swank, R.K.; White, P.J.

    1978-01-01

    Scintillator structures are described in which the phosphor is embedded or suspended in an optically transparent matrix which is selected or adjusted to have an index of refraction which is approximately equal to that of the phosphor at the wavelength of the light emitted by the phosphor. The matrix may be glass, copoly 2-vinyl naphthalene/vinyl toluene or a liquid e.g. Br-naphthalene and optionally CH 3 I, the ratio of components being adjusted to give the desired refractive index. The polymer may be made in situ or a mixture of phosphor and polymer formed e.g. by freeze drying a solution and pulverizing, and then heating. Specified dyes may be used for converting the emitted light to other wavelengths. (author)

  13. Influence of the spray pyrolysis seeding and growth parameters on the structure and optical properties of ZnO nanorod arrays

    Energy Technology Data Exchange (ETDEWEB)

    Rodríguez, Juan, E-mail: jrodriguez@uni.edu.pe [Facultad de Ciencias, Universidad Nacional de Ingeniería, P.O. Box 31-139, Lima 31 (Peru); Feuillet, Guy [CEA Grenoble/LETI, 17 rue des Martyrs, F-38054 Grenoble Cedex 9 (France); Donatini, Fabrice [Univ. Grenoble Alpes, Inst NEEL, F-38000 Grenoble (France); CNRS, Inst NEEL, F-38042 Grenoble (France); Onna, Diego [DQIAQF-INQUIMAE, FCEyN-Universidad de Buenos Aires, Ciudad Universitaria, Pab. II, 1428 Buenos Aires (Argentina); Sanchez, Luis [Facultad de Ciencias, Universidad Nacional de Ingeniería, P.O. Box 31-139, Lima 31 (Peru); Candal, Roberto [DQIAQF-INQUIMAE, FCEyN-Universidad de Buenos Aires, Ciudad Universitaria, Pab. II, 1428 Buenos Aires (Argentina); ECyT, 3iA, Universidad Nacional de San Martín, Martín de Irigoyen N° 3100 (1650), San Martín, Pcia de Buenos Aires (Argentina); Marchi, M. Claudia [DQIAQF-INQUIMAE, FCEyN-Universidad de Buenos Aires, Ciudad Universitaria, Pab. II, 1428 Buenos Aires (Argentina); CMA, FCEyN-Universidad de Buenos Aires, Ciudad Universitaria, Pab. I, 1428 Buenos Aires (Argentina); Bilmes, Sara A. [DQIAQF-INQUIMAE, FCEyN-Universidad de Buenos Aires, Ciudad Universitaria, Pab. II, 1428 Buenos Aires (Argentina); Chandezon, Frédéric [University Grenoble Alpes, INAC-SPRAM, F-38000 Grenoble (France); CNRS, INAC-SPRAM, F-38000 Grenoble (France); CEA, INAC-SPRAM, F-38000 Grenoble (France)

    2015-02-01

    ZnO nanorods (NRs) were grown on fluorine doped tin oxide (FTO) substrates at low temperatures (90 °C) from Zn{sup 2+} precursors in alkaline media previously seeded with ZnO nanoparticles. These were deposited onto the FTO substrate heated at 350 °C by spray pyrolysis of a Zn acetate solution in a water ethanol mixture. The structure of seeds was tuned by the ethanol to water ratio, Γ, which controls the solvent evaporation rate of drops impinging the substrate. From a detailed characterization using a combination of scanning electron microscopy, X-ray diffraction, UV–visible absorption and cathodoluminescence spectroscopies, the dependence of the morphology and optical properties of the ZnO NRs on the seeding conditions was demonstrated. NRs grown on seeds deposited from solutions with Γ in the 0.03–0.06 range – i.e. when the surface excess of ethanol in the water–ethanol mixture has a maximum – show thinner average diameters and stacking faults due to the presence of zinc blende domains embedded into an overall wurtzite NR. They furthermore exhibit blue-shifted near band edge emission peak and a high deep level emission in cathodoluminescence. All these findings support the use of spray pyrolysis as a simple and reproducible way to control the seeds deposition, influencing the growth, the structure and the optical properties of the final ZnO NRs. - Highlights: • ZnO pyrolytic seeds tuned by the rate of solvent evaporation. • ZnO NRs grown from tuned pyrolytic seed's structure shows diameter dependence. • ZnO NRs show stacking faults due to the presence of zinc blende domains.

  14. The study of structural and optical properties of (Eu, La, Sm) codoped ZnO nanoparticles via a chemical route

    Energy Technology Data Exchange (ETDEWEB)

    Lang, Jihui; Zhang, Qi; Han, Qiang; Fang, Yue; Wang, Jiaying; Li, Xiuyan; Liu, Yanqing [Key Laboratory of Functional Materials Physics and Chemistry of the Ministry of Education, Jilin Normal University, Siping, 136000 (China); Wang, Dandan [Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun, 130033 (China); Yang, Jinghai, E-mail: jhyang1@jlnu.edu.cn [Key Laboratory of Functional Materials Physics and Chemistry of the Ministry of Education, Jilin Normal University, Siping, 136000 (China); Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun, 130033 (China)

    2017-06-15

    The (Eu, La, Sm) ions were doped into ZnO nanoparticles by a chemical route, and the substitution of (Eu, La, Sm) for Zn{sup 2+} ions was proved by analytic techniques of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman, transmission electron microscope (TEM), photoluminescence (PL) and UV–vis absorption spectroscopy. The results revealed that the codoping did not change the wurtzite structure of ZnO nanoparticles, but the diameter of the nanoparticles decreased with increasing the rare earth (RE) doping concentrations. The optical bandgaps calculated through UV–visible absorption spectroscopy were found to decrease from 3.26 to 3.14 eV with increasing the RE doping concentrations, which also proved by the slight shift of UV positions in PL spectra. The sharp red emissions located at 578.2, 590.1 and 615.7 nm were originated from the 4f-4f transitions in Eu{sup 3+} ions under excitation of 325 nm. And these red emissions of Eu{sup 3+} ions showed a strong correlation with the energy storage centers of oxygen vacancies in the samples which was introduced by the other RE ions of La{sup 3+} and Sm{sup 3+} codoping. - Highlights: • Doping of (Eu, La, Sm) ions into ZnO nanoparticles is realized by a chemical route. • Eu{sup 3+}-related red emissions from intra-4f follow a similar trend as broad defect emission. • Red emissions of Eu{sup 3+} enhance with RE codoping due to oxygen vacancies as energy storage centers. • The bandgap can be tuned by RE codoping, which shows a prospect for the visible utilization.

  15. Fabrication and Raman scattering of a core–shell structure based on Mn doped ZnO and barium titanate

    International Nuclear Information System (INIS)

    Sima, M.; Baibarac, M.; Vasile, E.; Sima, Ma.; Mihut, L.

    2015-01-01

    Graphical abstract: - Highlights: • ZnO/Zn_1_−_xMn_xO/BaTiO_3 nanorod array on FTO substrate. • Oxygen vacancies in the ZnO/Zn_1_−_xMn_xO nanostructure. • The interface between the ZnO/Zn_1_−_xMn_xO core and the BaTiO_3 shell without unwanted phases. - Abstract: A combination of chemical and thermal annealing techniques was used to prepare an array of ZnO/Zn_1_−_xMn_xO/BaTiO_3 nanorods. ZnO nanorod arrays were obtained by hydrothermal–electrochemical processes. The precursors for Zn_1_−_xMn_xO and BaTiO_3, prepared by sol–gel technique were deposited by spin coating on the surface of ZnO nanorods. Each deposition stage was accompanied by thermal treatment stages. Scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and photoluminescence spectroscopy reveal the presence of a film of Zn_1_−_xMn_xO with wurtzite structure on the surface of ZnO nanorods. Transmission electron microscopy images demonstrate that a layer of BaTiO_3 is deposited on the surface of each ZnO/Zn_1_−_xMn_xO core shell nanorod. BaTiO_3 film onto the ZnO/Zn_1_−_xMn_xO core shell nanorods is also evidenced in Raman scattering by broadening of the Raman band situated in the spectral range 500–750 cm"−"1.

  16. Study of structural, morphological, optical and electroluminescent properties of undoped ZnO nanorods grown by a simple chemical precipitation

    Directory of Open Access Journals (Sweden)

    Singh A.

    2015-12-01

    Full Text Available In this work, zinc oxide (ZnO nanorods were obtained by a simple chemical precipitation method in the presence of capping agent: polyvinyl pyrrolidone (PVP at room temperature. X-ray diffraction (XRD result indicates that the synthesized undoped ZnO nanorods have hexagonal wurtzite structure without any impurities. It has been observed that the growth direction of the prepared ZnO nanorods is [1 0 1]. XRD analysis revealed that the nanorods have the crystallite size of 49 nm. Crystallite size is calculated by Debye-Scherrer formula and lattice strain is calculated by Williomson-Hall equation. Cell volume, Lorentz factor, Lorentz polarization factor, bond length, texture coefficient, lattice constants and dislocation density have also been studied. We also compared the interplanar spacings and relative peak intensities with their standard values at different angles. The scanning electron microscope (SEM images confirmed the size and shape of these nanorods. It has been found that the diameter of the nanorods ranges from 1.52 μm to 1.61 μm and the length is about 4.89 μm. It has also been observed that at room temperature ultraviolet visible (UV-Vis absorption band is around 355 nm (blue shifted as compared to the bulk. The average particle size has also been calculated by mathematical model of effective mass approximation equation, using UV-Vis absorption peak. Finally, the bandgap has been calculated using UV-absorption peak. Electroluminescence (EL studies show that emission of light is possible at very small threshold voltage and it increases rapidly with increasing applied voltage. It is seen that smaller ZnO nanoparticles give higher electroluminescence brightness starting at lower threshold voltage. The brightness is also affected by increasing the frequency of AC signal.

  17. Role of nickel doping on structural, optical, magnetic properties and antibacterial activity of ZnO nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Vijayaprasath, G.; Murugan, R. [School of Physics, Alagappa University, Karaikudi 630 004, Tamil Nadu (India); Palanisamy, S.; Prabhu, N.M. [Department of Animal Health and Management, Alagappa University, Karaikudi 630 004, Tamil Nadu (India); Mahalingam, T. [Department of Electrical and Computer Engineering, Ajou University, Suwon 443-749 (Korea, Republic of); Hayakawa, Y. [Research Institute of Electronics, Shizuoka University, Hamamatsu 432-8011 (Japan); Ravi, G., E-mail: gravicrc@gmail.com [School of Physics, Alagappa University, Karaikudi 630 004, Tamil Nadu (India)

    2016-04-15

    Highlights: • The XRD analyses revealed that the synthesizes nickel doped ZnO (Zn{sub 1−x}Ni{sub x}O, x = 0.0, 0.03, 0.06 and 0.09) nanostructures have hexagonal wurtzite structure. • The photoluminescence measurements revealed that the broad emission was composed of different bands due to zinc and oxygen vacancies. • X-ray photoelectron spectroscopy (XPS) confirmed the Ni incorporation in ZnO lattice as Ni{sup 2+} ions. • Room temperature ferromagnetism was observed due to the oxygen vacancies and zinc interstitials are the main reasons for ferromagnetism in Ni doped ZnO NPs. - Abstract: Zn{sub 1−x}Ni{sub x}O nanoparticles were synthesized by co-precipitation method. The crystallite sizes of the synthesized samples found to decrease from 38 to 26 nm with increase in nickel concentration. FTIR spectra confirmed the presence of Zn−O stretching bands at 577, 573, 569 and 565 cm{sup −1} in the respective ZnO NPs. Optical absorption spectra revealed the red shifted and estimated band gap is found to decrease with increase of Ni doping concentration. The PL spectra of all the samples exhibited a broad emission at 390 nm in the visible range. The carriers (donors) bounded on the Ni sites were observed from the micro Raman spectroscopic studies. Pure and Ni doped ZnO NPs showed significant changes in the M–H loop, especially the diamagnetic behavior changed into ferromagnetic nature for Ni doped samples. The antiferromagnetic super-exchange interactions between Ni{sup 2+} ions is increased in higher Ni doped ZnO NPs and also their antibacterial activity has been studied.

  18. Fabrication and Raman scattering of a core–shell structure based on Mn doped ZnO and barium titanate

    Energy Technology Data Exchange (ETDEWEB)

    Sima, M., E-mail: msima@infim.ro [National Institute of Materials Physics, 105 bis Atomistilor Street, PO Box MG 7, 077125 Magurele (Romania); Baibarac, M. [National Institute of Materials Physics, 105 bis Atomistilor Street, PO Box MG 7, 077125 Magurele (Romania); Vasile, E. [University “Politehnica” of Bucharest, Faculty of Applied Chemistry and Material Science, Department of Oxide Materials and Nanomaterials, No. 1-7 Gh. Polizu Street, 011061 Bucharest (Romania); Sima, Ma.; Mihut, L. [National Institute of Materials Physics, 105 bis Atomistilor Street, PO Box MG 7, 077125 Magurele (Romania)

    2015-11-15

    Graphical abstract: - Highlights: • ZnO/Zn{sub 1−x}Mn{sub x}O/BaTiO{sub 3} nanorod array on FTO substrate. • Oxygen vacancies in the ZnO/Zn{sub 1−x}Mn{sub x}O nanostructure. • The interface between the ZnO/Zn{sub 1−x}Mn{sub x}O core and the BaTiO{sub 3} shell without unwanted phases. - Abstract: A combination of chemical and thermal annealing techniques was used to prepare an array of ZnO/Zn{sub 1−x}Mn{sub x}O/BaTiO{sub 3} nanorods. ZnO nanorod arrays were obtained by hydrothermal–electrochemical processes. The precursors for Zn{sub 1−x}Mn{sub x}O and BaTiO{sub 3}, prepared by sol–gel technique were deposited by spin coating on the surface of ZnO nanorods. Each deposition stage was accompanied by thermal treatment stages. Scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and photoluminescence spectroscopy reveal the presence of a film of Zn{sub 1−x}Mn{sub x}O with wurtzite structure on the surface of ZnO nanorods. Transmission electron microscopy images demonstrate that a layer of BaTiO{sub 3} is deposited on the surface of each ZnO/Zn{sub 1−x}Mn{sub x}O core shell nanorod. BaTiO{sub 3} film onto the ZnO/Zn{sub 1−x}Mn{sub x}O core shell nanorods is also evidenced in Raman scattering by broadening of the Raman band situated in the spectral range 500–750 cm{sup −1}.

  19. Structural, spectroscopic and anti-microbial inspection of PEG capped ZnO nanoparticles for biomedical applications

    Science.gov (United States)

    Meshram, J. V.; Koli, V. B.; Kumbhar, S. G.; Borde, L. C.; Phadatare, M. R.; Pawar, S. H.

    2018-04-01

    Zinc oxide (ZnO) nanoparticles (NPs) have a wide range of biomedical applications. Present study demonstrates the new methodology in sol-gel technology for synthesizing Polyethylene glycol (PEG) capped ZnO NPs and its size effect on anti-microbial activity. The reaction time was increased from 1 h to 5 h for the synthesis of ZnO NPs at 130 °C. The size of PEG capped ZnO NPs is increased from 10 to 84 nm by increasing the reaction upto 5 h. The x-ray diffraction studies and transmission electron microscopy analysis reveals the phase purity and hexagonal wurtzite crystal structure with uniform PEG capping on the surface of ZnO NPs. UV–visible spectroscopy exhibits the peak at 366 nm which is attributed to ZnO NPs. No adverse effect is observed in case of absorbance spectroscopy. Further, Fourier transforms infrared spectroscopy and thermo gravimetric analysis depicts the adsorption of PEG molecules on the ZnO NPs surface. The anti-microbial activities for both Gram-positive (S. aureus) and Gram-negative (E. coli) bacteria were studied by optical density (OD) mesurement. The remarkable anti-microbial activity was observed for PEG capped ZnO NPs synthesized at 1 h reaction time showing higher activity in comparison with that synthesized from 2 h to 5 h reaction time. The microbial growth was found to be inhibited after 10 h OD measurement for both the bacteria. The anti-microbial activity may be attributed to the generation of ROS and H2O2. However, these generated species plays a vital role in inhibition of microbial growth. Hence, PEG capped ZnO NPs has promising biomedical applications.

  20. Optical emission of InAs nanowires

    International Nuclear Information System (INIS)

    Möller, M; De Lima Jr, M M; Cantarero, A; Chiaramonte, T; Cotta, M A; Iikawa, F

    2012-01-01

    Wurtzite InAs nanowire samples grown by chemical beam epitaxy have been analyzed by photoluminescence spectroscopy. The nanowires exhibit two main optical emission bands at low temperatures. They are attributed to the recombination of carriers in quantum well structures, formed by zincblende–wurtzite alternating layers, and to the donor–acceptor pair. The blue-shift observed in the former emission band when the excitation power is increased is in good agreement with the type-II band alignment between the wurtzite and zincblende sections predicted by previous theoretical works. When increasing the temperature and the excitation power successively, an additional band attributed to the band-to-band recombination from wurtzite InAs appears. We estimated a lower bound for the wurtzite band gap energy of approximately 0.46 eV at low temperature. (paper)

  1. Optical emission of InAs nanowires

    Science.gov (United States)

    Möller, M.; de Lima, M. M., Jr.; Cantarero, A.; Chiaramonte, T.; Cotta, M. A.; Iikawa, F.

    2012-09-01

    Wurtzite InAs nanowire samples grown by chemical beam epitaxy have been analyzed by photoluminescence spectroscopy. The nanowires exhibit two main optical emission bands at low temperatures. They are attributed to the recombination of carriers in quantum well structures, formed by zincblende-wurtzite alternating layers, and to the donor-acceptor pair. The blue-shift observed in the former emission band when the excitation power is increased is in good agreement with the type-II band alignment between the wurtzite and zincblende sections predicted by previous theoretical works. When increasing the temperature and the excitation power successively, an additional band attributed to the band-to-band recombination from wurtzite InAs appears. We estimated a lower bound for the wurtzite band gap energy of approximately 0.46 eV at low temperature.

  2. First-principles study of structural stabilities, elastic and electronic properties of transition metal monocarbides (TMCs) and mononitrides (TMNs)

    Energy Technology Data Exchange (ETDEWEB)

    Rached, H.; Rached, D.; Benalia, S. [Laboratoire des Matériaux Magnétiques, Faculté des Sciences, Université Djillali Liabès de Sidi Bel-Abbès, Sidi Bel-Abbès 22000 (Algeria); Reshak, A.H., E-mail: maalidph@yahoo.co.uk [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); Rabah, M. [Laboratoire des Matériaux Magnétiques, Faculté des Sciences, Université Djillali Liabès de Sidi Bel-Abbès, Sidi Bel-Abbès 22000 (Algeria); Khenata, R. [Laboratoire de Physique Quantique et de Modélisation Mathématique de la Matière (LPQ3M), université de Mascara, Mascara 29000 (Algeria); Bin Omran, S. [Department of Physics and Astronomy, Faculty of Science, King Saud University, Riyadh 11451 (Saudi Arabia)

    2013-12-16

    The structural stabilities, elastic and electronic properties of 5d transition metal mononitrides (TMNs) XN with (X = Ir, Os, Re, W and Ta) and 5d transition metal monocarbides (TMCs) XC with (X = Ir, Os, Re and Ta) were investigated using the full-potential linear muffin-tin orbital (FP-LMTO) method, in the framework of the density functional theory (DFT) within the local density approximation (LDA) for the exchange correlation functional. The ground state quantities such as the lattice parameter, bulks modulus and its pressure derivatives for the six considered crystal structures, Rock-salt (B1), CsCl (B2), zinc-blend (B3), Wurtzite (B4), NiAs (B8{sub 1}) and the tungsten carbides (B{sub h}) are calculated. The elastic constants of TMNs and TMCs compounds in its different stable phases are determined by using the total energy variation with strain technique. The elastic modulus for polycrystalline materials, shear modulus (G), Young's modulus (E), and Poisson's ratio (ν) are calculated. The Debye temperature (θ{sub D}) and sound velocities (v{sub m}) were also derived from the obtained elastic modulus. The analysis of the hardness of the herein studied compounds classifies OsN – (B4 et B8{sub 1}), ReN – (B8{sub 1}), WN – (B8{sub 1}) and OsC – (B8{sub 1}) as superhard materials. Our results for the band structure and densities of states (DOS), show that TMNs and TMCs compounds in theirs energetically and mechanically stable phase has metallic characteristic with strong covalent nature Metal–Nonmetal elements. - Highlights: • Structural stabilities, elastic, electronic properties of 5d TMNs XN are investigated. • 5d TMCs XC with (X = Ir, Os, Re and Ta) were investigated. • The ground state properties for the six considered crystal structure are calculated. • The elastic constants of TMNs and TMCs in its different stable phases are determined. • The elastic modulus for polycrystalline materials, G, E, and ν are calculated.

  3. Investigation of structural, surface morphological, optical properties and first-principles study on electronic and magnetic properties of (Ce, Fe)-co doped ZnO

    International Nuclear Information System (INIS)

    Arul Mary, J.; Judith Vijaya, J.; Bououdina, M.; John Kennedy, L.; Daie, J.H.; Song, Y.

    2015-01-01

    We report on the synthesis of ((Zn 1−2x Ce x Fe x ) O (x=0.00, 0.01, 0.02, 0.03, 0.04 and 0.05)) nanoparticles via microwave combustion by using urea as a fuel. To understand how the dopant influenced the structural, magnetic and optical properties of nanoparticles, it was characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), diffuse reflectance spectroscopy (DRS), photoluminescence (PL) spectra and vibrating sample magnetometer (VSM). The stability and magnetic properties of Ce and Fe co-doped ZnO were probed by first principle calculations. From the analysis of X-ray diffraction, the samples are identified with the wurtzite crystal structure. The change in lattice parameters, micro-strain, and a small shift in XRD peaks confirms the substitution of co dopants into the ZnO lattice. Morphological investigation of the products revealed the existence of irregular shapes, such as spherical, spherodial and hexagonal. DRS measurements showed a decrease in the energy gap with increasing dopants contents, probably due to an increase in the lattice parameters. PL spectra consist of visible emission, due to the electronic defects, which are related to deep level emissions, such as oxide antisite (O Zn ), interstitial zinc (Zn i ), interstitial oxygen (O i ) and zinc vacancy (V Zn ). Magnetic measurements showed a ferromagnetic behavior for all the doped samples at room temperature. The first principle calculation results showed that the Ce governs the stability, while the Fe adjusts the magnetic characteristics in the Ce and Fe co-doped ZnO

  4. Synthesis, structural and optical properties of ZnO spindle/reduced graphene oxide composites with enhanced photocatalytic activity under visible light irradiation

    Science.gov (United States)

    Prabhu, S.; Pudukudy, M.; Sohila, S.; Harish, S.; Navaneethan, M.; Navaneethan, D.; Ramesh, R.; Hayakawa, Y.

    2018-05-01

    In the present work, spindle-shaped ZnO and reduced graphene oxide sheets were successfully synthesized by a hydrothermal method and then ZnO/r-GO composite was prepared by a direct solution mixing method. Various characterization results confirmed the interior and surface decoration of spindle-shaped ZnO on the reduced graphene oxide sheets. The phase formation, crystalline structure, morphology, surface states and optical properties were characterized using Powder X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier Transform Infrared Spectroscopy (FTIR) and UV-Vis spectroscopy. The X-ray diffraction analysis showed the formation of the hexagonal wurtzite crystalline structure of ZnO with high crystalline quality. The band gap of the ZnO/r-GO composite was found to be low (3.03eV) compared to the band gap of spindle shaped ZnO (3.13 eV), as calculated from optical studies. The spindle-like morphology of the single crystalline ZnO was clearly shown in the electron microscopic images. The chemical bonding and surface states of the samples were studied using XPS measurement. Moreover, a possible growth mechanism for the ZnO spindle was proposed. The catalytic activity of the as-synthesized samples was evaluated for the photodegradation of methylene blue under visible light irradiation. Among the synthesized samples, the ZnO/r-GO composite showed higher degradation efficiency of 93% and successfully reused for four consecutive run without any activity loss.

  5. Investigation of structural, surface morphological, optical properties and first-principles study on electronic and magnetic properties of (Ce, Fe)-co doped ZnO

    Energy Technology Data Exchange (ETDEWEB)

    Arul Mary, J. [Catalysis and Nanomaterials Research Laboratory, Department of Chemistry Loyola College, Chennai 600 034 (India); Judith Vijaya, J., E-mail: jjvijayaloyola@yahoo.co.in [Catalysis and Nanomaterials Research Laboratory, Department of Chemistry Loyola College, Chennai 600 034 (India); Bououdina, M. [Departments of Physics, College of Science, University of Bahrain, PO Box 32038 Kingdom of Bahrain (Bahrain); John Kennedy, L. [Materials Division, School of Advanced Sciences, Vellore Institute of Technology (VIT) University, Chennai Campus, Chennai 600 127 (India); Daie, J.H.; Song, Y. [School of Materials Science and Engineering, Harbin Institute of Technology at Weihai, 2 West Wenhua Road, Weiahi 264209 (China)

    2015-01-01

    We report on the synthesis of ((Zn{sub 1−2x}Ce{sub x}Fe{sub x}) O (x=0.00, 0.01, 0.02, 0.03, 0.04 and 0.05)) nanoparticles via microwave combustion by using urea as a fuel. To understand how the dopant influenced the structural, magnetic and optical properties of nanoparticles, it was characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), diffuse reflectance spectroscopy (DRS), photoluminescence (PL) spectra and vibrating sample magnetometer (VSM). The stability and magnetic properties of Ce and Fe co-doped ZnO were probed by first principle calculations. From the analysis of X-ray diffraction, the samples are identified with the wurtzite crystal structure. The change in lattice parameters, micro-strain, and a small shift in XRD peaks confirms the substitution of co dopants into the ZnO lattice. Morphological investigation of the products revealed the existence of irregular shapes, such as spherical, spherodial and hexagonal. DRS measurements showed a decrease in the energy gap with increasing dopants contents, probably due to an increase in the lattice parameters. PL spectra consist of visible emission, due to the electronic defects, which are related to deep level emissions, such as oxide antisite (O{sub Zn}), interstitial zinc (Zn{sub i}), interstitial oxygen (O{sub i}) and zinc vacancy (V{sub Zn}). Magnetic measurements showed a ferromagnetic behavior for all the doped samples at room temperature. The first principle calculation results showed that the Ce governs the stability, while the Fe adjusts the magnetic characteristics in the Ce and Fe co-doped ZnO.

  6. Effect of calcination temperature on the structural, optical and magnetic properties of pure and Fe-doped ZnO nanoparticles

    Directory of Open Access Journals (Sweden)

    Pal Singh Raminder Preet

    2016-06-01

    Full Text Available In the present study, pure ZnO and Fe-doped ZnO (Zn0.97Fe0.03O nanoparticles were synthesized by simple coprecipitation method with zinc acetate, ferric nitrate and sodium hydroxide precursors. Pure ZnO and Fe-doped ZnO were further calcined at 450 °C, 600 °C and 750 °C for 2 h. The structural, morphological and optical properties of the samples were characterized by X-ray diffractometer (XRD, scanning electron microscope (SEM, energy dispersive spectroscopy (EDS and UV-Vis absorption spectroscopy. The X-ray diffraction studies revealed that the as-synthesized pure and doped ZnO nanoparticles have hexagonal wurtzite structure. The average crystallite size was calculated using Debye-Scherrer’s formula. The particle size was found to be in nano range and increased with an increase in calcination temperature. SEM micrographs confirmed the formation of spherical nanoparticles. Elemental compositions of various elements in pure and doped ZnO nanoparticles were determined by EDX spectroscopy. UV-Vis absorption spectra showed red shift (decrease in band gap with increasing calcination temperature. Effect of calcination on the magnetic properties of Fe-doped ZnO sample was also studied using vibrating sample magnetometer (VSM. M-H curves at room temperature revealed that coercivity and remanent polarization increase with an increase in calcination temperature from 450 °C to 750 °C, whereas reverse effect was observed for magnetization saturation.

  7. Effect of 50 MeV Li3+ irradiation on structural and electrical properties of Mn-doped ZnO

    International Nuclear Information System (INIS)

    Neogi, S K; Chattopadhyay, S; Banerjee, Aritra; Bandyopadhyay, S; Sarkar, A; Kumar, Ravi

    2011-01-01

    The present work aims to study the effect of ion irradiation on structural and electrical properties and their correlation with the defects in the Zn 1-x Mn x O-type system. Zn 1-x Mn x O (x = 0.02, 0.04) samples have been synthesized by the solid-state reaction method and have been irradiated with 50 MeV Li 3+ ions. The concomitant changes have been probed by x-ray diffraction (XRD), temperature-dependent electrical resistivity and positron annihilation lifetime (PAL) spectroscopy. The XRD result shows a single-phase wurtzite structure for Zn 0.98 Mn 0.02 O, whereas for the Zn 0.96 Mn 0.04 O sample an impurity phase has been found, apart from the usual peaks of ZnO. Ion irradiation removes this impurity peak. The grain size of the samples is found to be uniform. For Zn 0.98 Mn 0.02 O, the observed sharp decrease in room temperature resistivity (ρ RT ) with irradiation is consistent with the lowering of the full width at half maximum of the XRD peaks. However, for Zn 0.96 Mn 0.04 O, ρ RT decreases for the initial fluence but increases for a further increase in fluence. All the irradiated Zn 0.98 Mn 0.02 O samples show a metal-semiconductor transition in temperature-dependent resistivity measurements at low temperature. But all the irradiated Zn 0.96 Mn 0.04 O samples show a semiconducting nature in the whole range of temperatures. Results of room temperature resistivity, XRD and PAL measurements are consistent with each other.

  8. Effect of 50 MeV Li{sup 3+} irradiation on structural and electrical properties of Mn-doped ZnO

    Energy Technology Data Exchange (ETDEWEB)

    Neogi, S K; Chattopadhyay, S; Banerjee, Aritra; Bandyopadhyay, S [Department of Physics, University of Calcutta, 92 Acharya Prafulla Chandra Road, Kolkata 700009, West Bengal (India); Sarkar, A [Department of Physics, Bangabasi Morning College, 19 Rajkumar Chakraborty Sarani, Kolkata 700009, West Bengal (India); Kumar, Ravi, E-mail: arbphy@caluniv.ac.in [Department of Material Science and Engineering, NIT, Hamirpur-177005, Himachal Pradesh (India)

    2011-05-25

    The present work aims to study the effect of ion irradiation on structural and electrical properties and their correlation with the defects in the Zn{sub 1-x}Mn{sub x}O-type system. Zn{sub 1-x}Mn{sub x}O (x = 0.02, 0.04) samples have been synthesized by the solid-state reaction method and have been irradiated with 50 MeV Li{sup 3+} ions. The concomitant changes have been probed by x-ray diffraction (XRD), temperature-dependent electrical resistivity and positron annihilation lifetime (PAL) spectroscopy. The XRD result shows a single-phase wurtzite structure for Zn{sub 0.98}Mn{sub 0.02}O, whereas for the Zn{sub 0.96}Mn{sub 0.04}O sample an impurity phase has been found, apart from the usual peaks of ZnO. Ion irradiation removes this impurity peak. The grain size of the samples is found to be uniform. For Zn{sub 0.98}Mn{sub 0.02}O, the observed sharp decrease in room temperature resistivity ({rho}{sub RT}) with irradiation is consistent with the lowering of the full width at half maximum of the XRD peaks. However, for Zn{sub 0.96}Mn{sub 0.04}O, {rho}{sub RT} decreases for the initial fluence but increases for a further increase in fluence. All the irradiated Zn{sub 0.98}Mn{sub 0.02}O samples show a metal-semiconductor transition in temperature-dependent resistivity measurements at low temperature. But all the irradiated Zn{sub 0.96}Mn{sub 0.04}O samples show a semiconducting nature in the whole range of temperatures. Results of room temperature resistivity, XRD and PAL measurements are consistent with each other.

  9. Effect of 50 MeV Li3 + irradiation on structural and electrical properties of Mn-doped ZnO

    Science.gov (United States)

    Neogi, S. K.; Chattopadhyay, S.; Banerjee, Aritra; Bandyopadhyay, S.; Sarkar, A.; Kumar, Ravi

    2011-05-01

    The present work aims to study the effect of ion irradiation on structural and electrical properties and their correlation with the defects in the Zn1 - xMnxO-type system. Zn1 - xMnxO (x = 0.02, 0.04) samples have been synthesized by the solid-state reaction method and have been irradiated with 50 MeV Li3 + ions. The concomitant changes have been probed by x-ray diffraction (XRD), temperature-dependent electrical resistivity and positron annihilation lifetime (PAL) spectroscopy. The XRD result shows a single-phase wurtzite structure for Zn0.98Mn0.02O, whereas for the Zn0.96Mn0.04O sample an impurity phase has been found, apart from the usual peaks of ZnO. Ion irradiation removes this impurity peak. The grain size of the samples is found to be uniform. For Zn0.98Mn0.02O, the observed sharp decrease in room temperature resistivity (ρRT) with irradiation is consistent with the lowering of the full width at half maximum of the XRD peaks. However, for Zn0.96Mn0.04O, ρRT decreases for the initial fluence but increases for a further increase in fluence. All the irradiated Zn0.98Mn0.02O samples show a metal-semiconductor transition in temperature-dependent resistivity measurements at low temperature. But all the irradiated Zn0.96Mn0.04O samples show a semiconducting nature in the whole range of temperatures. Results of room temperature resistivity, XRD and PAL measurements are consistent with each other.

  10. Structural evolution of self-assisted GaAs nanowires grown on Si(111)

    Energy Technology Data Exchange (ETDEWEB)

    Biermanns, Andreas; Davydok, Anton; Pietsch, Ullrich [University of Siegen, Solid State Physics Group, Walter-Flex-Str. 3, 57072 Siegen (Germany); Breuer, Steffen; Geelhaar, Lutz [Paul-Drude-Institut fuer Festkoerperelektronik, Hausvogteiplatz 5-7, 10117 Berlin (Germany)

    2011-04-15

    GaAs nanowires are grown on Si(111) by self-assisted molecular beam epitaxy, and the ratio between wurtzite and zinc-blende phases is determined as function of nanowire length using asymmetric X-ray diffraction. We show that under the applied growth conditions, nanowires grow in both phases during the initial stage of growth, whereas the zinc-blende content increases with growth time and dominates in long nanowires. Compared to the zinc-blende units, the vertical lattice parameter of the wurtzite segments is 0.7% larger, as measured by the positions of respective diffraction peaks. (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  11. Study on structural integrity in box structures

    International Nuclear Information System (INIS)

    Asano, Masayuki; Ueta, Masahiro; Kanaoka, Tadashi; Ikeuchi, Toshiaki; Kodama, Tetsuhiro.

    1991-01-01

    This study was carried out to give an experimental foundation to the structural integrity of a box structure. Crack growth tests were performed on the reduced scale models, simulating typical portions of the box structure, in air at room temperature. The results show that the amount of crack growth is too small to injure the structural integrity of the models for the postulated loading cycle, and make clear the effective structure against crack growth. (author)

  12. Structural Biology Fact Sheet

    Science.gov (United States)

    ... NIGMS NIGMS Home > Science Education > Structural Biology Structural Biology Tagline (Optional) Middle/Main Content Area PDF Version (688 KB) Other Fact Sheets What is structural biology? Structural biology is the study of how biological ...

  13. Structural and Morphological Properties of Zn{sub 1−x}Zr{sub x}O with Room-Temperature Ferromagnetism and Fabricated by Using the Co-Precipitation Technique

    Energy Technology Data Exchange (ETDEWEB)

    Hassan, M.; Irfan, R.; Riaz, S.; Naseem, S.; Hussain, S. S. [University of the Punjab, Lahore (Pakistan); Murtaza, G. [Government College University, Lahore (Pakistan)

    2017-03-15

    In this study, ZnO was doped with various concentrations of zirconium (x{sub Zr} = 0 - 5 mole%), by using the co-precipitation method so as to achieve successful formation of a single-phase diluted magnetic semiconductor. X-Ray diffraction results showed that the crystal structure of Zn{sub 1−x}Zr{sub x}O was that of hexagonal wurtzite. The structural properties showed no additional phases at low impurity contents (x{sub Zr} < 3%); however, impurity peaks belonging to ZrO{sub 2} appeared at high impurity contents (x{sub Zr} ≥ 3%). The calculated ZnO lattice constants 'a' and 'c' were found to be 3.256 Å and 5.203 Å, respectively, which are in close match to the values found in the literature. For undoped ZnO, the average calculated particle size was 75.35 nm, and calculated bond length was 1.98 Å. The residual strains and the secondary phases of ZrO{sub 2} were found to affect the lattice parameters and the bond lengths. The scanning electron microscopy images showed a porous structure with non-uniform surface morphology. However, a few nano-scale dendrite-type structures were also present, indicating the potential applications of Zr-doped ZnO in nano-devices. Vibrating sample magnetometry (VSM) was employed to measure the magnetic properties, and the measurements showed undoped ZnO to be diamagnetic; however, doping with Zr induced a small ferromagnetic character at small magnetic fields. On the other hand, a paramagnetic behavior was evident at higher magnetic fields. The magnetization at 1T was observed to degrade with increasing Zr content in the ZnO host lattice, which was due to the residual strains and the secondary phases.

  14. Ab initio study of phase transition of boron nitride between zinc-blende and rhombohedral structures

    Energy Technology Data Exchange (ETDEWEB)

    Nishida, S.; Funashima, H.; Sato, K.; Katayama-Yoshida, H. [Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531 (Japan)

    2013-12-04

    Boron nitride has polymorphs such as zinc-blende (c-BN), wurtzite (w-BN), rhombohedral (r-BN), and graphite-like (h-BN) forms. We simulate the direct conversion of r-BN to c-BN through electronic excitation. In our calculation, the conversion is made possible by increasing the hole concentration to over 0.06/atom. This conversion should be experimentally possible by hole-doping via an electric double layer transistor (EDLT) or capacitor.

  15. Magnetic multilayer structure

    Science.gov (United States)

    Herget, Philipp; O'Sullivan, Eugene J.; Romankiw, Lubomyr T.; Wang, Naigang; Webb, Bucknell C.

    2016-07-05

    A mechanism is provided for an integrated laminated magnetic device. A substrate and a multilayer stack structure form the device. The multilayer stack structure includes alternating magnetic layers and diode structures formed on the substrate. Each magnetic layer in the multilayer stack structure is separated from another magnetic layer in the multilayer stack structure by a diode structure.

  16. Fluid-structure interaction of submerged structures

    International Nuclear Information System (INIS)

    Tang, H.T.; Becker, E.B.; Taylor, L.M.

    1979-01-01

    The purpose of the paper is to investigate fluid-structure interaction (FSI) of submerged structures in a confined fluid-structure system. Our particular interest is the load experienced by a rigid submerged structure subject to a pressure excitation in a fluid domain bounded by a structure which is either flexible or rigid. The objective is to see whether the load experienced by the submerged structure will be influenced by its confinement conditions. This investigation is intended to provide insight into the characteristics of FSI and answer the question as to whether one can obtain FSI independent data by constructing a small scale rigid submerged structure inside a flexible fluid-structure system. (orig.)

  17. Computational structural mechanics for engine structures

    Science.gov (United States)

    Chamis, C. C.

    1989-01-01

    The computational structural mechanics (CSM) program at Lewis encompasses: (1) fundamental aspects for formulating and solving structural mechanics problems, and (2) development of integrated software systems to computationally simulate the performance/durability/life of engine structures. It is structured to mainly supplement, complement, and whenever possible replace, costly experimental efforts which are unavoidable during engineering research and development programs. Specific objectives include: investigate unique advantages of parallel and multiprocesses for: reformulating/solving structural mechanics and formulating/solving multidisciplinary mechanics and develop integrated structural system computational simulators for: predicting structural performances, evaluating newly developed methods, and for identifying and prioritizing improved/missing methods needed. Herein the CSM program is summarized with emphasis on the Engine Structures Computational Simulator (ESCS). Typical results obtained using ESCS are described to illustrate its versatility.

  18. Lightweight Materials and Structures (LMS): Inflatable Structures

    Data.gov (United States)

    National Aeronautics and Space Administration —  Current inflatable structures are designed on the restraint layer’s short term properties with a Factor of Safety of 4 due to lack of long-term data on structural...

  19. Organisational StructureStructures for Growth

    OpenAIRE

    Ramskill, Jason

    2011-01-01

    Summary Rexam Plc has articulated that part of the company’s strategy is to make a carefully managed expansion into the emerging markets. In this report I suggest an alternative structure for Rexam to enable implementation of such a strategy and propose a business process for designing effective organisational structures. The work of Chandler (1962) charts the evolution of company organisational structures from the early centralised structures of the 1920s to the multidivisional str...

  20. Structural, optical, photoluminescence and photocatalytic assessment of Sr-doped ZnO nanoparticles

    International Nuclear Information System (INIS)

    Pradeev Raj, K.; Sadaiyandi, K.; Kennedy, A.; Thamizselvi, R.

    2016-01-01

    ZnO nanoparticles (NPs) and Strontium doped ZnO nanoparticles (2–6 mol %) (SZ-NPs) were synthesized via Co-precipitation method. Synthesized samples were investigated by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Elemental dispersive spectroscopy (EDS), UV–visible, and Photoluminescence (PL) spectroscopy. Photocatalytic studies for Rhodamine B (RhB) dye in aqueous solution under UV–Vis radiation. XRD analysis confirms that all the samples have hexagonal wurtzite structure. The average crystallite size of the nanoparticles was in the range of 29–51 nm. From the Williamson –Hall (W-H) plot, a positive slope is inferred for pure and SZ-NPs, confirming the presence of tensile strain. SEM images reveal the synthesized NPs are in nanometer range with various shapes are observed. The presence of strontium (Sr) in the host lattice was confirmed by EDS spectroscopy. The optical analysis shows the absorption decreases on doping and shifts slightly towards the longer wavelength region. The band gap energy (Eg) decreases (3.32–3.03 eV) with the increase of Sr dopant concentration. The photoluminescence (PL) spectrum reveals the UV emission is strong near the band-edge region (NBE) (392 nm) and intrinsic defects resulted in series of Vis emissions around 400–560 nm. Kinetic studies on RhB dye indicates the degradation rate has increased with dopant concentration. The improved photocatalytic activity is observed due to the efficient charge separation, improved visible light absorption, inhibition of the electron-hole pair's recombination and better adsorptive of RhB dye molecule on the surface of SZ-NPs. Moreover, the reduction in the total organic carbon (TOC) results reveals the improved photocatalytic activity of strontium doped ZnO NPs. - Highlights: • Effective synthesis of ZnO and Sr−ZnO nanoparticles by co-precipitation method. • Samples were characterized by XRD, SEM, EDS, UV–Vis and PL technique. • Higher optical absorption and

  1. Structural, optical, photoluminescence and photocatalytic assessment of Sr-doped ZnO nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Pradeev Raj, K., E-mail: pradeevraj@gmail.com [Research and Development Centre, Bharathiar University, Coimbatore, 641 046, Tamilnadu (India); Department of Physics, CSI College of Engineering, Ooty, The Nilgiris, 643 215, Tamil Nadu (India); Sadaiyandi, K. [Department of Physics, Alagappa Government Arts College, Karaikudi, Sivagangai, 630 003, Tamil Nadu (India); Kennedy, A. [Department of Physics, CSI College of Engineering, Ooty, The Nilgiris, 643 215, Tamil Nadu (India); Thamizselvi, R. [Department of Chemistry, L.R.G. Govt Arts College for Women, Tirupur, 641604, Tamil Nadu (India)

    2016-11-01

    ZnO nanoparticles (NPs) and Strontium doped ZnO nanoparticles (2–6 mol %) (SZ-NPs) were synthesized via Co-precipitation method. Synthesized samples were investigated by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Elemental dispersive spectroscopy (EDS), UV–visible, and Photoluminescence (PL) spectroscopy. Photocatalytic studies for Rhodamine B (RhB) dye in aqueous solution under UV–Vis radiation. XRD analysis confirms that all the samples have hexagonal wurtzite structure. The average crystallite size of the nanoparticles was in the range of 29–51 nm. From the Williamson –Hall (W-H) plot, a positive slope is inferred for pure and SZ-NPs, confirming the presence of tensile strain. SEM images reveal the synthesized NPs are in nanometer range with various shapes are observed. The presence of strontium (Sr) in the host lattice was confirmed by EDS spectroscopy. The optical analysis shows the absorption decreases on doping and shifts slightly towards the longer wavelength region. The band gap energy (Eg) decreases (3.32–3.03 eV) with the increase of Sr dopant concentration. The photoluminescence (PL) spectrum reveals the UV emission is strong near the band-edge region (NBE) (392 nm) and intrinsic defects resulted in series of Vis emissions around 400–560 nm. Kinetic studies on RhB dye indicates the degradation rate has increased with dopant concentration. The improved photocatalytic activity is observed due to the efficient charge separation, improved visible light absorption, inhibition of the electron-hole pair's recombination and better adsorptive of RhB dye molecule on the surface of SZ-NPs. Moreover, the reduction in the total organic carbon (TOC) results reveals the improved photocatalytic activity of strontium doped ZnO NPs. - Highlights: • Effective synthesis of ZnO and Sr−ZnO nanoparticles by co-precipitation method. • Samples were characterized by XRD, SEM, EDS, UV–Vis and PL technique. • Higher optical absorption

  2. Structural, optical and vibrational studies of Na{sup +} doped Cd{sub 0.8}Zn{sub 0.2}S semiconductor compounds

    Energy Technology Data Exchange (ETDEWEB)

    Yellaiah, G., E-mail: johngolluri@yahoo.com; Hadasa, K.; Nagabhushanam, M., E-mail: mamidala_nb@yahoo.com

    2013-12-25

    Graphical abstract: FTIR spectra of Cd{sub 0.8}Zn{sub 0.2}S: N{sub x} (x = 0.2 mol%). Highlights: •The energy band gaps of Cd{sub 0.8}Zn{sub 02}S: Nasamples were estimated. •Density and porosity percentages were calculated. •From the FTIR study CdS and ZnS stretching bonds were detected. -- Abstract: Cd{sub 0.8}Zn{sub 0.2}S semiconductor powders doped with different amounts of sodium have been synthesized by controlled co-precipitation technique. X-ray diffraction (XRD), Scanning electron microscope (SEM), Optical absorption and Fourier transform infrared spectroscope (FTIR) studies have been done on all these samples. XRD studies have revealed that the samples are polycrystalline with an average crystallite size ranging from 29 to 55 nm and they crystallize in the hexagonal form with wurtzite structure. The optical measurements revealed that the samples possess direct band gap and the band gap increases with an increase in the dopant concentration. The vibrational modes of Cd–S and Zn–S were obtained from FTIR studies and found to be at 812–618 cm{sup −1} respectively. Experimental and theoretical (XRD) densities were calculated and analyzed. Density from XRD and porosity in percentage varied from 92% to 94% and 5% to 8% respectively. The elemental analysis of the compounds was done by energy dispersive spectroscopy (EDS) and found that the cadmium, zinc, sulphur and sodium elements were present in the compound as per the composition taken. From the theoretical estimations it is understood that the dopant (Na) occupies the interstitial of CdZnS.

  3. Synthesis of Zinc Oxide Nanorods via the Formation of Sea Urchin Structures and Their Photoluminescence after Heat Treatment.

    Science.gov (United States)

    Karlsson, Mattias E; Mamie, Yann C; Calamida, Andrea; Gardner, James M; Ström, Valter; Pourrahimi, Amir Masoud; Olsson, Richard T

    2018-05-01

    A protocol for the aqueous synthesis of ca. 1-μm-long zinc oxide (ZnO) nanorods and their growth at intermediate reaction progression is presented, together with photoluminescence (PL) characteristics after heat treatment at temperatures of up to 1000 °C. The existence of solitary rods after the complete reaction (60 min) was traced back to the development of sea urchin structures during the first 5 s of the precipitation. The rods primarily formed in later stages during the reaction due to fracture, which was supported by the frequently observed broken rod ends with sharp edges in the final material, in addition to tapered uniform rod ends consistent with their natural growth direction. The more dominant rod growth in the c direction (extending the length of the rods), together with the appearance of faceted surfaces on the sides of the rods, occurred at longer reaction times (>5 min) and generated zinc-terminated particles that were more resistant to alkaline dissolution. A heat treatment for 1 h at 600 or 800 °C resulted in a smoothing of the rod surfaces, and PL measurements displayed a decreased defect emission at ca. 600 nm, which was related to the disappearance of lattice imperfections formed during the synthesis. A heat treatment at 1000 °C resulted in significant crystal growth reflected as an increase in luminescence at shorter wavelengths (ca. 510 nm). Electron microscopy revealed that the faceted rod structure was lost for ZnO rods exposed to temperatures above 600 °C, whereas even higher temperatures resulted in particle sintering and/or mass redistribution along the initially long and slender ZnO rods. The synthesized ZnO rods were a more stable Wurtzite crystal structure than previously reported ball-shaped ZnO consisting of merging sheets, which was supported by the shifts in PL spectra occurring at ca. 200 °C higher annealing temperature, in combination with a smaller thermogravimetric mass loss occurring upon heating the rods to 800 °C.

  4. Mg doping induced high structural quality of sol–gel ZnO nanocrystals: Application in photocatalysis

    Energy Technology Data Exchange (ETDEWEB)

    Abed, Chayma; Bouzidi, Chaker [Laboratoire de Physico-chimie des Matériaux Minéraux et leurs Applications, Centre National de Recherches en Sciences des Matériaux, BP 95, Hammam-Lif 2050 (Tunisia); Elhouichet, Habib, E-mail: Habib.elhouichet@fst.rnu.tn [Laboratoire de Physico-chimie des Matériaux Minéraux et leurs Applications, Centre National de Recherches en Sciences des Matériaux, BP 95, Hammam-Lif 2050 (Tunisia); Département de Physique, Faculté des Sciences de Tunis, Université Tunis El Manar, Tunis 2092 (Tunisia); Gelloz, Bernard [Graduate School of Engineering, Nagoya University, 2-24-16 Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8603 (Japan); Ferid, Mokhtar [Laboratoire de Physico-chimie des Matériaux Minéraux et leurs Applications, Centre National de Recherches en Sciences des Matériaux, BP 95, Hammam-Lif 2050 (Tunisia)

    2015-09-15

    Highlights: • ZnO nancrystals doped with Mg were prepared from sol–gel method. • Structural and optical properties of ZnO:Mg nanocrystals were investigated. • Good crystalline quality of ZnO nanocrystals was reported after Mg doping. • Good photocatalytic activity of Mg doped ZnO nanocrystals was demonstrated under sun light illumination. - Abstract: Undoped and Mg doped ZnO nanocrystals (NCs) ZnO:x%Mg (x = 1, 2, 3, and 5) were synthesized using sol–gel method. The structural and optical properties were investigated by X-ray diffraction (XRD), Raman spectroscopy, diffuse reflectivity, and photoluminescence (PL). XRD analysis demonstrates that all prepared samples present pure hexagonal wurtzite structure without any Mg related phases. The NCs size varies from 26.82 nm to 42.96 nm with Mg concentrations; it presents an optimal value for 2% of Mg. The Raman spectra are dominated by the E{sub 2high} mode. For highly Mg doping (5%), the occurrence of silent B{sub 1(low)} mode suggested that the Mg ions do substitute at Zn sites in the ZnO lattice The band gap energy was estimated from both Tauc and Urbach methods and found to be 3.39 eV for ZnO:2%Mg. The PL spectra exhibit two emission bands in the UV and visible range. Their evolution with Mg doping reveals the reduction of defect density in ZnO at low Mg doping by filling Zn vacancies. In addition, it was found that further Mg doping, above 2%, improves the photocatalytic activity of ZnO NCs for photodegradation of Rhodamine B (RhB) under sunlight irradiation. The efficient electron–hole separation is the main factor responsible for the enhancement of photocatalytic performance of Mg doped ZnO NCs. Through this work, we show that by varying the Mg contents in ZnO, this material can be a potential candidate for both optoelectronic and photocatalytic applications.

  5. GaN Nanowires Synthesized by Electroless Etching Method

    KAUST Repository

    Najar, Adel; Anjum, Dalaver H.; Ng, Tien Khee; Ooi, Boon S.; Ben Slimane, Ahmed

    2012-01-01

    Ultra-long Gallium Nitride Nanowires is synthesized via metal-electroless etching method. The morphologies and optical properties of GaN NWs show a single crystal GaN with hexagonal Wurtzite structure and high luminescence properties.

  6. Distributed Structure Searchable Toxicity

    Data.gov (United States)

    U.S. Environmental Protection Agency — The Distributed Structure Searchable Toxicity (DSSTox) online resource provides high quality chemical structures and annotations in association with toxicity data....

  7. Composite Structures Manufacturing Facility

    Data.gov (United States)

    Federal Laboratory Consortium — The Composite Structures Manufacturing Facility specializes in the design, analysis, fabrication and testing of advanced composite structures and materials for both...

  8. Structural patterns in nature

    DEFF Research Database (Denmark)

    Wester, Ture

    2003-01-01

    be an inspiration to structural morphologists and other dealing with the shaping of structures for buildings and other objects. Often the patterns appear in "dual" materializations, which indicate two radically different structural types of action. Randomness as a generator for optimal and basic structural action...

  9. Structural patterns in nature

    DEFF Research Database (Denmark)

    Wester, Ture

    2004-01-01

    be an inspiration to structural morphologists and other dealing with the shaping of structures for buildings and other objects. Often the patterns appear in "dual" materializations, which indicate two radically different structural types of action. Randomness as a generator for optimal and basic structural action...

  10. Single and multi-layered core-shell structures based on ZnO nanorods obtained by aerosol assisted chemical vapor deposition

    Energy Technology Data Exchange (ETDEWEB)

    Sáenz-Trevizo, A.; Amézaga-Madrid, P.; Pizá-Ruiz, P.; Antúnez-Flores, W.; Ornelas-Gutiérrez, C.; Miki-Yoshida, M., E-mail: mario.miki@cimav.edu.mx

    2015-07-15

    Core–shell nanorod structures were prepared by a sequential synthesis using an aerosol assisted chemical vapor deposition technique. Several samples consisting of ZnO nanorods were initially grown over TiO{sub 2} film-coated borosilicate glass substrates, following the synthesis conditions reported elsewhere. Later on, a uniform layer consisting of individual Al, Ni, Ti or Fe oxides was grown onto ZnO nanorod samples forming the so-called single MO{sub x}/ZnO nanorod core–shell structures, where MO{sub x} was the metal oxide shell. Additionally, a three-layer core–shell sample was developed by growing Fe, Ti and Fe oxides alternately, onto the ZnO nanorods. The microstructure of the core–shell materials was characterized by grazing incidence X-ray diffraction, scanning and transmission electron microscopy. Energy dispersive X-ray spectroscopy was employed to corroborate the formation of different metal oxides. X-ray diffraction outcomes for single core–shell structures showed solely the presence of ZnO as wurtzite and TiO{sub 2} as anatase. For the multi-layered shell sample, the existence of Fe{sub 2}O{sub 3} as hematite was also detected. Morphological observations suggested the existence of an outer material grown onto the nanorods and further microstructural analysis by HR-STEM confirmed the development of core–shell structures in all cases. These studies also showed that the individual Al, Fe, Ni and Ti oxide layers are amorphous; an observation that matched with X-ray diffraction analysis where no apparent extra oxides were detected. For the multi-layered sample, the development of a shell consisting of three different oxide layers onto the nanorods was found. Overall results showed that no alteration in the primary ZnO core was produced during the growth of the shells, indicating that the deposition technique used herein was and it is suitable for the synthesis of homogeneous and complex nanomaterials high in quality and purity. In addition

  11. Structure, morphology and optical properties of undoped and MN-doped ZnO{sub (1−x)}S{sub x} nano-powders prepared by precipitation method

    Energy Technology Data Exchange (ETDEWEB)

    Dejene, F.B., E-mail: dejenebf@qwa.ufs.ac.za [Department of Physics, University of the Free State, (Qwa-Qwa campus), Private Bag X-13, Phuthaditjhaba 9866 (South Africa); Onani, M.O. [Chemistry Department, University of the Western Cape, Private Bag x17, Bellville 7535 (South Africa); Koao, L.F.; Wako, A.H.; Motloung, S.V.; Yihunie, M.T. [Department of Physics, University of the Free State, (Qwa-Qwa campus), Private Bag X-13, Phuthaditjhaba 9866 (South Africa)

    2016-01-01

    The undoped and Mn-doped ZnO{sub (1−x)}S{sub x} nano-powders were successfully synthesized by precipitation method without using any capping agent. Its structure, morphology, elemental analysis, optical and luminescence properties were determined by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), UV–vis spectroscopy (UV) and photoluminescence spectroscopy (PL). A typical SEM image of the un-doped ZnO{sub (1−x)}S{sub x} nanoparticles exhibit flake like structures that changes to nearly spherical particles with Mn-doping. The XRD of undoped and Mn doped ZnO{sub (1−x)}S{sub x} pattern reveals the formation of a product indexed to the hexagonal wurtzite phase of ZnS. The nanopowders have crystallite sizes estimated from XRD measurements were in the range of 10–20 nm. All the samples showed absorption maximum of ZnO{sub (1−x)}S{sub x} at 271 nm and high transmittance in UV and visible region, respectively. The undoped ZnO{sub (1−x)}S{sub x} nanoparticles show strong room-temperature photoluminescence with four emission bands centering at 338 nm, 384 nm, 448 nm and 705 nm that may originate to the impurity of ZnO{sub (1−x)}S{sub x}, existence of oxide related defects. The calculated bandgap of the nanocrystalline ZnO{sub (1−x)}S{sub x} showed a blue-shift with respect to the Mn-doping. The PL spectra of the Mn-doped samples exhibit a strong orange emission at around 594 nm attributed to the {sup 4}T{sub 1}–{sup 6}A{sub 1} transition of the Mn{sup 2+} ions.

  12. Structure-soil-structure interaction of nuclear structures

    International Nuclear Information System (INIS)

    Snyder, M.D.; Shaw, D.E.; Hall, J.R. Jr.

    1975-01-01

    Structure-to-structure interaction resulting from coupling of the foundations through the soil has traditionally been neglected in the seismic analysis of nuclear power plants. This paper examines the phenomenon and available methods of analytical treatment, including finite element and lumped parameter methods. Finite element techniques have lead to the treatment of through soil coupling of structural foundations using two dimensional plane strain models owing to the difficulty of considering three dimensional finite element models. The coupling problem is treated by means of a lumped parameter model derived from elastic half-space considerations. Consequently, the method is applicable to the interaction of any number of foundations and allows the simultaneous application of tri-directional excitation. The method entails the idealization of interacting structures as lumped mass/shear beams with lumped soil springs and dampers beneath each foundation plus a coupling matrix between the interacting foundations. Utilizing classical elastic half-space methods, the individual foundation soil springs and dampers may be derived, accounting for the effects of embedment and soil layering, analogous to the methods used for single soil-structure, interaction problems. The coupling matrix is derived by generating influence coefficients based on the geometric relationship of the structures using classical half-space solutions. The influence coefficients form the coupling flexibility matrix which is inverted to yield the coupling matrix for the lumped parameter model

  13. Strategy implemented through structuring and new structures

    DEFF Research Database (Denmark)

    Nielsen, Renate

    Research objective: With the purpose of generating a new understanding of how development in organisations take place, an interpretive perspective at continuous processes in organisations will be applied: more specifically at how organisational interpretation forms an organisation's strategy...... and how the strategy is implemented through structuring, new structures and routines....

  14. Task structure, need for structure, and creativity

    NARCIS (Netherlands)

    Rietzschel, Eric; Slijkhuis, Marjette; Van Yperen, Nico W.

    2014-01-01

    Although creativity is often seen as requiring spontaneity and flexibility, recent work suggests that there is creative potential in a structured and systematic approach as well. In a series of four experiments, we show that when Personal Need for Structure (PNS) is high, either chronic (Study 1) or

  15. Unprecedented Al supersaturation in single-phase rock salt structure VAlN films by Al+ subplantation

    Science.gov (United States)

    Greczynski, G.; Mráz, S.; Hans, M.; Primetzhofer, D.; Lu, J.; Hultman, L.; Schneider, J. M.

    2017-05-01

    Modern applications of refractory ceramic thin films, predominantly as wear-protective coatings on cutting tools and on components utilized in automotive engines, require a combination of excellent mechanical properties, thermal stability, and oxidation resistance. Conventional design approaches for transition metal nitride coatings with improved thermal and chemical stability are based on alloying with Al. It is well known that the solubility of Al in NaCl-structure transition metal nitrides is limited. Hence, the great challenge is to increase the Al concentration substantially while avoiding precipitation of the thermodynamically favored wurtzite-AlN phase, which is detrimental to mechanical properties. Here, we use VAlN as a model system to illustrate a new concept for the synthesis of metastable single-phase NaCl-structure thin films with the Al content far beyond solubility limits obtained with conventional plasma processes. This supersaturation is achieved by separating the film-forming species in time and energy domains through synchronization of the 70-μs-long pulsed substrate bias with intense periodic fluxes of energetic Al+ metal ions during reactive hybrid high power impulse magnetron sputtering of the Al target and direct current magnetron sputtering of the V target in the Ar/N2 gas mixture. Hereby, Al is subplanted into the cubic VN grains formed by the continuous flux of low-energy V neutrals. We show that Al subplantation enables an unprecedented 42% increase in metastable Al solubility limit in V1-xAlxN, from x = 0.52 obtained with the conventional method to 0.75. The elastic modulus is 325 ± 5 GPa, in excellent agreement with density functional theory calculations, and approximately 50% higher than for corresponding films grown by dc magnetron sputtering. The extension of the presented strategy to other Al-ion-assisted vapor deposition methods or materials systems is straightforward, which opens up the way for producing supersaturated single

  16. Structural and optical characterization of nanoparticulate manganese doped zinc silicate phosphors prepared by sol–gel and combustion methods

    Energy Technology Data Exchange (ETDEWEB)

    Mbule, P.S., E-mail: mbuleps@gmail.com [Department of Physics, CSET, University of South Africa, Johannesburg, 1710 (South Africa); Ntwaeaborwa, O.M. [Department of Physics, University of the Free State, P.O. Box 339, Bloemfontein 9300 (South Africa); Mothudi, B.M.; Dhlamini, M.S. [Department of Physics, CSET, University of South Africa, Johannesburg, 1710 (South Africa)

    2016-11-15

    The present study reports the synthesis, crystallographic structure and optical properties of manganese (Mn{sup 2+}) doped zinc silicate (Zn{sub 2}SiO{sub 4}) nanoparticle phosphors prepared by sol–gel and combustion methods. For samples prepared by sol–gel method, the X-ray diffraction results showed phase transformation from amorphous to α-phase Zn{sub 2}SiO{sub 4} due to annealing temperatures at 600 °C to 1100 °C, whereas for combustion samples an admixture of highly crystalline β-phase and hexagonal wurtzite structure of ZnO was observed at annealing temperature of 600 °C. Photoluminescence spectra with Mn{sup 2+} concentrations ranging from 0.015–0.09 mol% were compared for two methods. Emission band assigned to the {sup 4}T{sub 1}({sup 4}G)→{sup 6}A{sub 1}({sup 6}S) electronic transition of Mn{sup 2+} was observed with maximum intensity at ~573 nm for combustion samples and ~532 nm for sol–gel samples upon UV-excitation by a Xenon lamp. Furthermore, the photoluminescence decay curves of annealed Zn{sub 2}SiO{sub 4}:Mn{sup 2+} samples were observed to be bi-exponential. The fast and slow decay components are due to the pair or cluster formation and isolated ions at higher doping concentration, respectively. - Highlights: • Synthesis, crystallographic and optical properties of Zn{sub 2}SiO{sub 4}:Mn{sup 2+} are presented. • XRD shows amorphous diffraction peak and crystallinity improved by increase of annealing temperature. • Crystallite and particle size from XRD and SAXS techniques, respectively, are compared. • Photoluminescence (PL) spectra are compared for sol-gel and combustion method. • The photoluminescence decay curves of annealed Zn{sub 2}SiO{sub 4}:Mn{sup 2+} samples were observed to be bi-exponential.

  17. Category I structures program

    International Nuclear Information System (INIS)

    Endebrock, E.G.; Dove, R.C.

    1981-01-01

    The objective of the Category I Structure Program is to supply experimental and analytical information needed to assess the structural capacity of Category I structures (excluding the reactor cntainment building). Because the shear wall is a principal element of a Category I structure, and because relatively little experimental information is available on the shear walls, it was selected as the test element for the experimental program. The large load capacities of shear walls in Category I structures dictates that the experimental tests be conducted on small size shear wall structures that incorporates the general construction details and characteristics of as-built shear walls

  18. The Structural Integrity Centre

    International Nuclear Information System (INIS)

    Tomkins, B.

    1987-01-01

    The paper concerns the development and work of the Structural Integrity Centre (SIC) at Risley Nuclear Laboratories, United Kingdom. The centre was set up to provide authoritative advice to plant designers and operators on the integrity and life assessment of structures and components across the reactor projects in the United Kingdom. A description is given of the structure and role of the SIC, as well as the Structural Integrity Assessment work. The assessment methods are described for thermally loaded structures and welded structures. Finally, defect significance assessment and environmental effects are outlined. (U.K.)

  19. Band structure of semiconductors

    CERN Document Server

    Tsidilkovski, I M

    2013-01-01

    Band Structure of Semiconductors provides a review of the theoretical and experimental methods of investigating band structure and an analysis of the results of the developments in this field. The book presents the problems, methods, and applications in the study of band structure. Topics on the computational methods of band structure; band structures of important semiconducting materials; behavior of an electron in a perturbed periodic field; effective masses and g-factors for the most commonly encountered band structures; and the treatment of cyclotron resonance, Shubnikov-de Haas oscillatio

  20. Structural behaviour of super-light structures

    DEFF Research Database (Denmark)

    Bagger, Anne; Hertz, Kristian Dahl

    2010-01-01

    structural functions: it leads load to the skeleton, it stabilizes the compression members of the skeleton, and it redistributes loads that are not optimal for the skeleton shape. In this paper, FE analysis is used to investigated the behaviour of a series of SLS beams of concrete, under varying stiffness......A new structural concept, called Super-light Structures (SLS), has recently been invented and patented at the Technical University of Denmark. The basic concept of SLS is to construct a skeleton of a stiff and strong material, such as ordinary or high strength concrete, and stabilize this skeleton...... with a lighter and softer material, such as lightweight concrete. The combined use of stiff and light material in SLS results in structures of high stiffness and low weight. The applied technology and the advantages of SLS are elaborated upon in [1] in these proceedings. The present paper focuses...

  1. Structural system identification: Structural dynamics model validation

    Energy Technology Data Exchange (ETDEWEB)

    Red-Horse, J.R.

    1997-04-01

    Structural system identification is concerned with the development of systematic procedures and tools for developing predictive analytical models based on a physical structure`s dynamic response characteristics. It is a multidisciplinary process that involves the ability (1) to define high fidelity physics-based analysis models, (2) to acquire accurate test-derived information for physical specimens using diagnostic experiments, (3) to validate the numerical simulation model by reconciling differences that inevitably exist between the analysis model and the experimental data, and (4) to quantify uncertainties in the final system models and subsequent numerical simulations. The goal of this project was to develop structural system identification techniques and software suitable for both research and production applications in code and model validation.

  2. Optimal Priority Structure, Capital Structure, and Investment

    OpenAIRE

    Dirk Hackbarth; David C. Mauer

    2012-01-01

    We study the interaction between financing and investment decisions in a dynamic model, where the firm has multiple debt issues and equityholders choose the timing of investment. Jointly optimal capital and priority structures can virtually eliminate investment distortions because debt priority serves as a dynamically optimal contract. Examining the relative efficiency of priority rules observed in practice, we develop several predictions about how firms adjust their priority structure in res...

  3. Structural health monitoring for ship structures

    Energy Technology Data Exchange (ETDEWEB)

    Farrar, Charles [Los Alamos National Laboratory; Park, Gyuhae [Los Alamos National Laboratory; Angel, Marian [Los Alamos National Laboratory; Bement, Matthew [Los Alamos National Laboratory; Salvino, Liming [NSWC, CADEROCK

    2009-01-01

    Currently the Office of Naval Research is supporting the development of structural health monitoring (SHM) technology for U.S. Navy ship structures. This application is particularly challenging because of the physical size of these structures, the widely varying and often extreme operational and environmental conditions associated with these ships missions, lack of data from known damage conditions, limited sensing that was not designed specifically for SHM, and the management of the vast amounts of data that can be collected during a mission. This paper will first define a statistical pattern recognition paradigm for SHM by describing the four steps of (1) Operational Evaluation, (2) Data Acquisition, (3) Feature Extraction, and (4) Statistical Classification of Features as they apply to ship structures. Note that inherent in the last three steps of this process are additional tasks of data cleansing, compression, normalization and fusion. The presentation will discuss ship structure SHM challenges in the context of applying various SHM approaches to sea trials data measured on an aluminum multi-hull high-speed ship, the HSV-2 Swift. To conclude, the paper will discuss several outstanding issues that need to be addressed before SHM can make the transition from a research topic to actual field applications on ship structures and suggest approaches for addressing these issues.

  4. Space Structure Development

    Science.gov (United States)

    Smith, Thomas

    2015-01-01

    The duration of my Summer 2015 Internship Tour at NASA's Johnson Space Center was spent working in the Structural Engineering Division's Structures Branch. One of the two main roles of the Structures Branch, ES2, is to ensure the structural integrity of spacecraft vehicles and the structural subsystems needed to support those vehicles. The other main objective of this branch is to develop the lightweight structures that are necessary to take humans beyond Low-Earth Orbit. Within ES2, my four projects involved inflatable space structure air bladder material testing; thermal and impact material testing for spacecraft windows; structural analysis on a joint used in the Boeing CST-100 airbag system; and an additive manufacturing design project.

  5. Structural Measures - Hospital

    Data.gov (United States)

    U.S. Department of Health & Human Services — A list of hospitals and the structural measures they report. A structural measure reflects the environment in which hospitals care for patients, for example, whether...

  6. Cell packing structures

    KAUST Repository

    Pottmann, Helmut; Jiang, Caigui; Hö binger, Mathias; Wang, Jun; Bompas, Philippe; Wallner, Johannes

    2015-01-01

    optimization schemes for the computation of quad-based support structures. Hex-dominant structures may be designed via Voronoi tessellations, power diagrams, sphere packings and various extensions of these concepts. Apart from the obvious application as load

  7. Nonlinear Structural Analysis

    Indian Academy of Sciences (India)

    The Structures Panel of the Aeronautics Research and Development Board of India ... A great variety of topics was covered, including themes such as nonlinear finite ... or shell structures, and three are on the composite form of construction, ...

  8. Structures composing protein domains.

    Science.gov (United States)

    Kubrycht, Jaroslav; Sigler, Karel; Souček, Pavel; Hudeček, Jiří

    2013-08-01

    This review summarizes available data concerning intradomain structures (IS) such as functionally important amino acid residues, short linear motifs, conserved or disordered regions, peptide repeats, broadly occurring secondary structures or folds, etc. IS form structural features (units or elements) necessary for interactions with proteins or non-peptidic ligands, enzyme reactions and some structural properties of proteins. These features have often been related to a single structural level (e.g. primary structure) mostly requiring certain structural context of other levels (e.g. secondary structures or supersecondary folds) as follows also from some examples reported or demonstrated here. In addition, we deal with some functionally important dynamic properties of IS (e.g. flexibility and different forms of accessibility), and more special dynamic changes of IS during enzyme reactions and allosteric regulation. Selected notes concern also some experimental methods, still more necessary tools of bioinformatic processing and clinically interesting relationships. Copyright © 2013 Elsevier Masson SAS. All rights reserved.

  9. Standing wave accelerating structures

    International Nuclear Information System (INIS)

    Zavadtsev, A.A.; Zverev, B.V.; Sobepin, N.P.

    1984-01-01

    Accelerating ELA structures are considered and chosen for applied purposes of special designation. Accelerating structures with the standing wave are considered most effective for small size ELA. Designs and results of experimental investigation of two new accelerating structures are described. These are structures of the ''ring'' type with a decreased number of excitinq oscillation types and strucuture with transverse rods with a twice smaller transverse size as compared with the biperiodical structure with internal connection resonators. The accelerating biperiodical structures of the conventional type by the fact that the whole structure is not a linear chain of connected resonators, but a ring one. Model tests have shown that the homogeneous structure with transverse rods (STR) at the frequency of 2.8 GHz in the regime of the standing wave has an effective shunt resistance equalling 23 MOhm/m. It is shown that the small transverse size of biperiodic STR makes its application in logging linear electron accelerators

  10. Photon structure function - theory

    International Nuclear Information System (INIS)

    Bardeen, W.A.

    1984-12-01

    The theoretical status of the photon structure function is reviewed. Particular attention is paid to the hadronic mixing problem and the ability of perturbative QCD to make definitive predictions for the photon structure function. 11 references

  11. Fundamentals of structural dynamics

    CERN Document Server

    Craig, Roy R

    2006-01-01

    From theory and fundamentals to the latest advances in computational and experimental modal analysis, this is the definitive, updated reference on structural dynamics.This edition updates Professor Craig's classic introduction to structural dynamics, which has been an invaluable resource for practicing engineers and a textbook for undergraduate and graduate courses in vibrations and/or structural dynamics. Along with comprehensive coverage of structural dynamics fundamentals, finite-element-based computational methods, and dynamic testing methods, this Second Edition includes new and e

  12. Extended icosahedral structures

    CERN Document Server

    Jaric, Marko V

    1989-01-01

    Extended Icosahedral Structures discusses the concepts about crystal structures with extended icosahedral symmetry. This book is organized into six chapters that focus on actual modeling of extended icosahedral crystal structures. This text first presents a tiling approach to the modeling of icosahedral quasiperiodic crystals. It then describes the models for icosahedral alloys based on random connections between icosahedral units, with particular emphasis on diffraction properties. Other chapters examine the glassy structures with only icosahedral orientational order and the extent of tra

  13. Structure sensitivity in adsorption

    DEFF Research Database (Denmark)

    Hammer, Bjørk; Nielsen, Ole Holm; Nørskov, Jens Kehlet

    1997-01-01

    The structure sensitivity of CO adsorption on different flat, stepped, kinked and reconstructed Pt surfaces is studied using large-scale density-functional calculations. We find an extremely strong structure sensitivity in the adsorption energy with variations up to 1 eV (or 100%) from one...... structure to the next. We propose a model to explain this behavior, and use it to discuss more generally the origin of structure sensitivity in heterogeneous catalysis....

  14. Neutrality in bipolar structures

    DEFF Research Database (Denmark)

    Montero, Javier; Rodríguez, J. Tinguaro; Franco, Camilo

    2014-01-01

    In this paper, we want to stress that bipolar knowledge representation naturally allows a family of middle states which define as a consequence different kinds of bipolar structures. These bipolar structures are deeply related to the three types of bipolarity introduced by Dubois and Prade, but our...... approach offers a systematic explanation of how such bipolar structures appear and can be identified....

  15. HIV Structural Database

    Science.gov (United States)

    SRD 102 HIV Structural Database (Web, free access)   The HIV Protease Structural Database is an archive of experimentally determined 3-D structures of Human Immunodeficiency Virus 1 (HIV-1), Human Immunodeficiency Virus 2 (HIV-2) and Simian Immunodeficiency Virus (SIV) Proteases and their complexes with inhibitors or products of substrate cleavage.

  16. Encounters with Structure

    Science.gov (United States)

    Connell, R. W.

    2004-01-01

    A discussion of poststructuralism may be helped by reflecting on the trajectory of ideas and practices that produced it. Structuralism as an intellectual movement has had a bad press and doubtless some of that is deserved. But structuralism was more diverse and creative, and structural analysis as a procedure in social science is more important,…

  17. Modern frame structure buildings

    Directory of Open Access Journals (Sweden)

    В. М. Першаков

    2013-07-01

    Full Text Available The article deals with the design, construction and implementation of reinforced concrete frame structures with span 18, 21 m for agricultural production buildings, hall-premises of public buildings and buildings of agricultural aviation. Structures are prefabricated frame buildings and have such advantages as large space inside the structure and lower cost compared with other facilities with same purpose

  18. Growing Timber Structures

    DEFF Research Database (Denmark)

    Tamke, Martin; Evers, Henrik Leander; Stasiuk, David

    2013-01-01

    The contemporary design of timber structures has to answer questions concerning structural stability, production impact and energy implications in ever earlier stages. The interrelation of these levels creates a complexity that is difficult to resolve through contemporary linear parametric...... to integrate the behaviour of networked systems into structures made from wooden material....

  19. Basic structural dynamics

    CERN Document Server

    Anderson, James C

    2012-01-01

    A concise introduction to structural dynamics and earthquake engineering Basic Structural Dynamics serves as a fundamental introduction to the topic of structural dynamics. Covering single and multiple-degree-of-freedom systems while providing an introduction to earthquake engineering, the book keeps the coverage succinct and on topic at a level that is appropriate for undergraduate and graduate students. Through dozens of worked examples based on actual structures, it also introduces readers to MATLAB, a powerful software for solving both simple and complex structural d

  20. Shell-like structures

    CERN Document Server

    Altenbach, Holm

    2011-01-01

    In this volume, scientists and researchers from industry discuss the new trends in simulation and computing shell-like structures. The focus is put on the following problems: new theories (based on two-dimensional field equations but describing non-classical effects), new constitutive equations (for materials like sandwiches, foams, etc. and which can be combined with the two-dimensional shell equations), complex structures (folded, branching and/or self intersecting shell structures, etc.) and shell-like structures on different scales (for example: nano-tubes) or very thin structures (similar