Optoelectronic and low temperature thermoelectric studies on nanostructured thin films of silver gallium selenide

Science.gov (United States)

Jacob, Rajani; Philip, Rachel Reena; Nazer, Sheeba; Abraham, Anitha; Nair, Sinitha B.; Pradeep, B.; Urmila, K. S.; Okram, G. S.

2014-01-01

Polycrystalline thin films of silver gallium selenide were deposited on ultrasonically cleaned soda lime glass substrates by multi-source vacuum co-evaporation technique. The structural analysis done by X-ray diffraction ascertained the formation of nano structured tetragonal chalcopyrite thin films. The compound formation was confirmed by X-ray photo-electron spectroscopy. Atomic force microscopic technique has been used for surface morphological analysis. Direct allowed band gap ˜1.78eV with high absorption coefficient ˜106/m was estimated from absorbance spectra. Low temperature thermoelectric effects has been investigated in the temperature range 80-330K which manifested an unusual increase in Seebeck coefficient with negligible phonon drag toward the very low and room temperature regime. The electrical resistivity of these n-type films was assessed to be ˜2.6Ωm and the films showed good photo response.

The Mobility Enhancement of Indium Gallium Zinc Oxide Transistors via Low-temperature Crystallization using a Tantalum Catalytic Layer

OpenAIRE

Shin, Yeonwoo; Kim, Sang Tae; Kim, Kuntae; Kim, Mi Young; Oh, Saeroonter; Jeong, Jae Kyeong

2017-01-01

High-mobility indium gallium zinc oxide (IGZO) thin-film transistors (TFTs) are achieved through low-temperature crystallization enabled via a reaction with a transition metal catalytic layer. For conventional amorphous IGZO TFTs, the active layer crystallizes at thermal annealing temperatures of 600??C or higher, which is not suitable for displays using a glass substrate. The crystallization temperature is reduced when in contact with a Ta layer, where partial crystallization at the IGZO bac...

Optoelectronic and low temperature thermoelectric studies on nanostructured thin films of silver gallium selenide

International Nuclear Information System (INIS)

Jacob, Rajani; Philip, Rachel Reena; Nazer, Sheeba; Abraham, Anitha; Nair, Sinitha B.; Pradeep, B.; Urmila, K. S.; Okram, G. S.

2014-01-01

Polycrystalline thin films of silver gallium selenide were deposited on ultrasonically cleaned soda lime glass substrates by multi-source vacuum co-evaporation technique. The structural analysis done by X-ray diffraction ascertained the formation of nano structured tetragonal chalcopyrite thin films. The compound formation was confirmed by X-ray photo-electron spectroscopy. Atomic force microscopic technique has been used for surface morphological analysis. Direct allowed band gap ∼1.78eV with high absorption coefficient ∼10 6 /m was estimated from absorbance spectra. Low temperature thermoelectric effects has been investigated in the temperature range 80–330K which manifested an unusual increase in Seebeck coefficient with negligible phonon drag toward the very low and room temperature regime. The electrical resistivity of these n-type films was assessed to be ∼2.6Ωm and the films showed good photo response

Gallium hydride complexes stabilised by multidentate alkoxide ligands: precursors to thin films of Ga2O3 at low temperatures.

Science.gov (United States)

Pugh, David; Bloor, Leanne G; Parkin, Ivan P; Carmalt, Claire J

2012-05-07

The donor-functionalised alkoxides {Me(3-x)N(CH(2)CH(2)O)(x)} (L(x); x = 1, 2) have been used to form gallium hydride complexes [{GaH(2)(L(1))}(2)] and [{GaH(L(2))}(2)] that are stable and isolable at room temperature. Along with a heteroleptic gallium tris(alkoxide) complex [Ga(L(1))(3)] and the dimeric complex [{GaMe(L(2))}(2)], these compounds have been used as single-source precursors for the deposition of Ga(2)O(3) by aerosol-assisted chemical vapour deposition (AACVD) with toluene as solvent. The resulting films were mostly transparent, indicating low levels of carbon contamination, and they were also mainly amorphous. However, [Ga(L(1))(3)] did contain visibly crystalline material deposited at a substrate temperature of 450 °C, by far the lowest ever observed for the CVD of gallium oxide. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

High-Temperature Decomposition of Brønsted Acid Sites in Gallium-Substituted Zeolites

Energy Technology Data Exchange (ETDEWEB)

K Al-majnouni; N Hould; W Lonergan; D Vlachos; R Lobo

2011-12-31

The dehydroxylation of Broensted acid sites (BAS) in Ga-substituted zeolites was investigated at temperatures up to 850 C using X-ray absorption spectroscopy (XAS), Fourier transform infrared spectroscopy (FTIR), and mass spectrometry-temperature programmed desorption (MS-TPD). X-ray absorption near-edge spectroscopy (XANES) revealed that the majority of gallium has tetrahedral coordination even after complete dehydroxylation. The interatomic gallium-oxygen distance and gallium coordination number determined by extended X-ray absorption fine structure (EXAFS) are consistent with gallium in tetrahedral coordination at low T (< 550 C). Upon heating Ga-Beta and Ga-ZSM5 to 850 C, analysis of the EXAFS showed that 70 and 80% of the gallium was still in tetrahedral coordination. The remainder of the gallium was found to be in octahedral coordination. No trigonal Ga atoms were observed. FTIR measurements carried out at similar temperatures show that the intensity of the OH vibration due to BAS has been eliminated. MS-TPD revealed that hydrogen in addition to water evolved from the samples during dehydroxylation. This shows that dehydrogenation in addition to dehydration is a mechanism that contributes to BAS decomposition. Dehydrogenation was further confirmed by exposing the sample to hydrogen to regenerate some of the BAS as monitored by FTIR and MS-TPD.

Ultra-low threshold gallium nitride photonic crystal nanobeam laser

Energy Technology Data Exchange (ETDEWEB)

Niu, Nan, E-mail: nanniu@fas.harvard.edu; Woolf, Alexander; Wang, Danqing; Hu, Evelyn L. [School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138 (United States); Zhu, Tongtong; Oliver, Rachel A. [Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS (United Kingdom); Quan, Qimin [Rowland Institute at Harvard University, Cambridge, Massachusetts 02142 (United States)

2015-06-08

We report exceptionally low thresholds (9.1 μJ/cm{sup 2}) for room temperature lasing at ∼450 nm in optically pumped Gallium Nitride (GaN) nanobeam cavity structures. The nanobeam cavity geometry provides high theoretical Q (>100 000) with small modal volume, leading to a high spontaneous emission factor, β = 0.94. The active layer materials are Indium Gallium Nitride (InGaN) fragmented quantum wells (fQWs), a critical factor in achieving the low thresholds, which are an order-of-magnitude lower than obtainable with continuous QW active layers. We suggest that the extra confinement of photo-generated carriers for fQWs (compared to QWs) is responsible for the excellent performance.

Ultra-low threshold gallium nitride photonic crystal nanobeam laser

International Nuclear Information System (INIS)

Niu, Nan; Woolf, Alexander; Wang, Danqing; Hu, Evelyn L.; Zhu, Tongtong; Oliver, Rachel A.; Quan, Qimin

2015-01-01

We report exceptionally low thresholds (9.1 μJ/cm 2 ) for room temperature lasing at ∼450 nm in optically pumped Gallium Nitride (GaN) nanobeam cavity structures. The nanobeam cavity geometry provides high theoretical Q (>100 000) with small modal volume, leading to a high spontaneous emission factor, β = 0.94. The active layer materials are Indium Gallium Nitride (InGaN) fragmented quantum wells (fQWs), a critical factor in achieving the low thresholds, which are an order-of-magnitude lower than obtainable with continuous QW active layers. We suggest that the extra confinement of photo-generated carriers for fQWs (compared to QWs) is responsible for the excellent performance

Optical and Micro-Structural Characterization of MBE Grown Indium Gallium Nitride Polar Quantum Dots

KAUST Repository

El Afandy, Rami

2011-07-07

Gallium nitride and related materials have ushered in scientific and technological breakthrough for lighting, mass data storage and high power electronic applications. These III-nitride materials have found their niche in blue light emitting diodes and blue laser diodes. Despite the current development, there are still technological problems that still impede the performance of such devices. Three-dimensional nanostructures are proposed to improve the electrical and thermal properties of III-nitride optical devices. This thesis consolidates the characterization results and unveils the unique physical properties of polar indium gallium nitride quantum dots grown by molecular beam epitaxy technique. In this thesis, a theoretical overview of the physical, structural and optical properties of polar III-nitrides quantum dots will be presented. Particular emphasis will be given to properties that distinguish truncated-pyramidal III-nitride quantum dots from other III-V semiconductor based quantum dots. The optical properties of indium gallium nitride quantum dots are mainly dominated by large polarization fields, as well as quantum confinement effects. Hence, the experimental investigations for such quantum dots require performing bandgap calculations taking into account the internal strain fields, polarization fields and confinement effects. The experiments conducted in this investigation involved the transmission electron microscopy and x-ray diffraction as well as photoluminescence spectroscopy. The analysis of the temperature dependence and excitation power dependence of the PL spectra sheds light on the carrier dynamics within the quantum dots, and its underlying wetting layer. A further analysis shows that indium gallium nitride quantum dots through three-dimensional confinements are able to prevent the electronic carriers from getting thermalized into defects which grants III-nitrides quantum dot based light emitting diodes superior thermally induced optical

High-temperature performance of gallium-nitride-based pin alpha-particle detectors grown on sapphire substrates

Science.gov (United States)

Zhu, Zhifu; Zhang, Heqiu; Liang, Hongwei; Tang, Bin; Peng, Xincun; Liu, Jianxun; Yang, Chao; Xia, Xiaochuan; Tao, Pengcheng; Shen, Rensheng; Zou, Jijun; Du, Guotong

2018-06-01

The temperature-dependent radiation-detection performance of an alpha-particle detector that was based on a gallium-nitride (GaN)-based pin structure was studied from 290 K to 450 K. Current-voltage-temperature measurements (I-V-T) of the reverse bias show the exponential dependence of leakage currents on the voltage and temperature. The current transport mechanism of the GaN-based pin diode from the reverse bias I-V fitting was analyzed. The temperature-dependent pulse-height spectra of the detectors were studied using an 241 Am alpha-particle source at a reverse bias of 10 V, and the peak positions shifted from 534 keV at 290 K to 490 keV at 450 K. The variation of full width at half maximum (FWHM) from 282 keV at 290 K to 292 keV at 450 K is almost negligible. The GaN-based pin detectors are highly promising for high-temperature environments up to 450 K.

Low-lying Photoexcited States of a One-Dimensional Ionic Extended Hubbard Model

Science.gov (United States)

Yokoi, Kota; Maeshima, Nobuya; Hino, Ken-ichi

2017-10-01

We investigate the properties of low-lying photoexcited states of a one-dimensional (1D) ionic extended Hubbard model at half-filling. Numerical analysis by using the full and Lanczos diagonalization methods shows that, in the ionic phase, there exist low-lying photoexcited states below the charge transfer gap. As a result of comparison with numerical data for the 1D antiferromagnetic (AF) Heisenberg model, it was found that, for a small alternating potential Δ, these low-lying photoexcited states are spin excitations, which is consistent with a previous analytical study [Katsura et al., link ext-link-type="uri" xlink:href="https://doi.org/10.1103/PhysRevLett.103.177402" xlink:type="simple">Phys. Rev. Lett. 103, 177402 (2009)link>]. As Δ increases, the spectral intensity of the 1D ionic extended Hubbard model rapidly deviates from that of the 1D AF Heisenberg model and it is clarified that this deviation is due to the neutral-ionic domain wall, an elementary excitation near the neutral-ionic transition point.

Gallium-Based Room-Temperature Liquid Metals: Actuation and Manipulation of Droplets and Flows

Directory of Open Access Journals (Sweden)

Leily Majidi

2017-08-01

Full Text Available Gallium-based room-temperature liquid metals possess extremely valuable properties, such as low toxicity, low vapor pressure, and high thermal and electrical conductivity enabling them to become suitable substitutes for mercury and beyond in wide range of applications. When exposed to air, a native oxide layer forms on the surface of gallium-based liquid metals which mechanically stabilizes the liquid. By removing or reconstructing the oxide skin, shape and state of liquid metal droplets and flows can be manipulated/actuated desirably. This can occur manually or in the presence/absence of a magnetic/electric field. These methods lead to numerous useful applications such as soft electronics, reconfigurable devices, and soft robots. In this mini-review, we summarize the most recent progresses achieved on liquid metal droplet generation and actuation of gallium-based liquid metals with/without an external force.

Gallium Oxide Nanostructures for High Temperature Sensors

Energy Technology Data Exchange (ETDEWEB)

Chintalapalle, Ramana V. [Univ. of Texas, El Paso, TX (United States)

2015-04-30

Gallium oxide (Ga₂O₃) thin films were produced by sputter deposition by varying the substrate temperature (T_s) in a wide range (T_s=25-800 °C). The structural characteristics and electronic properties of Ga₂O₃ films were evaluated using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDS), Rutherford backscattering spectrometry (RBS) and spectrophotometric measurements. The effect of growth temperature is significant on the chemistry, crystal structure and morphology of Ga₂O₃ films. XRD and SEM analyses indicate that the Ga₂O₃ films grown at lower temperatures were amorphous while those grown at T_s≥500 oC were nanocrystalline. RBS measurements indicate the well-maintained stoichiometry of Ga₂O₃ films at T_s=300-800 °C. The electronic structure determination indicated that the nanocrystalline Ga₂O₃films exhibit a band gap of ~5 eV. Tungsten (W) incorporated Ga₂O₃ films were produced by co-sputter deposition. W-concentration was varied by the applied sputtering-power. No secondary phase formation was observed in W-incorporated Ga₂O₃ films. W-induced effects were significant on the structure and electronic properties of Ga2O3 films. The band gap of Ga₂O₃ films without W-incorporation was ~5 eV. Oxygen sensor characteristics evaluated using optical and electrical methods indicate a faster response in W-doped Ga₂O₃ films compared to intrinsic Ga₂O₃ films. The results demonstrate the applicability of both intrinsic and W-doped Ga-oxide films for oxygen sensor application at temperatures ≥700 °C.

Raman study of low-temperature-grown Al0.29Ga0.71ASGaAs photorefractive materials

International Nuclear Information System (INIS)

Guo, L.W.; Han, Y.J.; Hu, C.Y.; Tan, P.H.; Yang, F.H.; Huang, Q.; Zhou, J.M.

2002-01-01

We report on the observation of resonant Raman scattering in low-temperature-grown AlGaASGaAs structure. Two kinds of excitation lights, 632.8 and 488 nm laser lines, were used to detect scattering signal from different regions based on different penetration depths. Under the outgoing resonant condition, up to fourth-order resonant Raman peaks were observed in the low-temperature-grown AlGaAs alloy, owing to a broad exciton luminescence in low-temperature-grown AlGaAs alloy induced by intrinsic defects and As cluster after post-annealing. These resonant peaks were assigned according to their fundamental modes. Among the resonant peaks, besides the overtones of the GaAs- or AlAs-like mode, there exist combination bands of these two kinds of modes. In addition, a weak scattering peak similar to the bulk GaAs longitudinal optical mode was observed in low-temperature Raman experiments. We consider the weak signal correlated with GaAs clusters appearing in AlGaAs alloys. The accumulation of GaAs in AlGaAs alloys was enhanced after annealing at high temperatures. A detailed study of the dependence of vibration modes on measuring temperature and post-annealing conditions is given also. In light of our experiments, it is suggested that a Raman scattering experiment is a sensitive microscopic probe of local disorder and, especially performed at low temperature, is a superior method in detecting and analyzing the weak interaction between phonons and electrons

Dramatic improvement of crystal quality for low-temperature-grown rabbit muscle aldolase

International Nuclear Information System (INIS)

Park, HaJeung; Rangarajan, Erumbi S.; Sygusch, Jurgen; Izard, Tina

2010-01-01

Rabbit muscle aldolase (RMA) was crystallized in complex with the low-complexity domain (LC4) of sorting nexin 9. Monoclinic crystals were obtained at room temperature that displayed large mosaicity and poor X-ray diffraction. However, orthorhombic RMA–LC4 crystals grown at 277 K under similar conditions exhibited low mosaicity, allowing data collection to 2.2 Å Bragg spacing and structure determination. Rabbit muscle aldolase (RMA) was crystallized in complex with the low-complexity domain (LC4) of sorting nexin 9. Monoclinic crystals were obtained at room temperature that displayed large mosaicity and poor X-ray diffraction. However, orthorhombic RMA–LC4 crystals grown at 277 K under similar conditions exhibited low mosaicity, allowing data collection to 2.2 Å Bragg spacing and structure determination. It was concluded that the improvement of crystal quality as indicated by the higher resolution of the new RMA–LC4 complex crystals was a consequence of the introduction of new lattice contacts at lower temperature. The lattice contacts corresponded to an increased number of interactions between high-entropy side chains that mitigate the lattice strain incurred upon cryocooling and accompanying mosaic spread increases. The thermodynamically unfavorable immobilization of high-entropy side chains used in lattice formation was compensated by an entropic increase in the bulk-solvent content owing to the greater solvent content of the crystal lattice

Temperature-dependent structure evolution in liquid gallium

International Nuclear Information System (INIS)

Xiong, L.H.; Wang, X.D.; Yu, Q.; Zhang, H.; Zhang, F.; Sun, Y.; Cao, Q.P.; Xie, H.L.; Xiao, T.Q.; Zhang, D.X.; Wang, C.Z.; Ho, K.M.

2017-01-01

Temperature-dependent atomistic structure evolution of liquid gallium (Ga) has been investigated by using in situ high energy X-ray diffraction experiment and ab initio molecular dynamics simulation. Both experimental and theoretical results reveal the existence of a liquid structural change around 1000 K in liquid Ga. Below and above this temperature the liquid exhibits differences in activation energy for self-diffusion, temperature-dependent heat capacity, coordination numbers, density, viscosity, electric resistivity and thermoelectric power, which are reflected from structural changes of the bond-orientational order parameter Q_6, fraction of covalent dimers, averaged string length and local atomic packing. This finding will trigger more studies on the liquid-to-liquid crossover in metallic melts. - Graphical abstract: Atomistic structure evolution of liquid gallium has been investigated by using in situ high energy X-ray diffraction and ab initio molecular dynamics simulations, which both demonstrate the existence of a liquid structural change together with reported density, viscosity, electric resistivity and absolute thermoelectric power data.

Gallium--A smart metal

Science.gov (United States)

Foley, Nora; Jaskula, Brian W.

2013-01-01

Gallium is a soft, silvery metallic element with an atomic number of 31 and the chemical symbol Ga. The French chemist Paul-Emile Lecoq de Boisbaudran discovered gallium in sphalerite (a zinc-sulfide mineral) in 1875 using spectroscopy. He named the element "gallia" after his native land of France (formerly Gaul; in Latin, Gallia). The existence of gallium had been predicted in 1871 by Dmitri Mendeleev, the Russian chemist who published the first periodic table of the elements. Mendeleev noted a gap in his table and named the missing element "eka-aluminum" because he determined that its location was one place away from aluminum in the table. Mendeleev thought that the missing element (gallium) would be very much like aluminum in its chemical properties, and he was right. Solid gallium has a low melting temperature (~29 degrees Celsius, or °C) and an unusually high boiling point (~2,204 °C). Because of these properties, the earliest uses of gallium were in high-temperature thermometers and in designing metal alloys that melt easily. The development of a gallium-based direct band-gap semiconductor in the 1960s led to what is now one of the most well-known applications for gallium-based products--the manufacture of smartphones and data-centric networks.

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.

Low temperature synthesis and field emission characteristics of single to few layered graphene grown using PECVD

Energy Technology Data Exchange (ETDEWEB)

Kumar, Avshish; Khan, Sunny; Zulfequar, M.; Harsh; Husain, Mushahid, E-mail: mush_reslab@rediffmail.com

2017-04-30

Highlights: • Graphene was synthesized by PECVD system at a low temperature of 600 °C. • From different characterization techniques, the presence of single and few layered graphene was confirmed. • X-ray diffraction pattern of the graphene showed single crystalline nature of the film. • The as-grown graphene films were observed extremely good field emitters with long term emission current stability. - Abstract: In this work, high-quality graphene has successfully been synthesized on copper (Cu) coated Silicon (Si) substrate at very large-area by plasma enhanced chemical vapor deposition system. This method is low cost and highly effective for synthesizing graphene relatively at low temperature of 600 °C. Electron microscopy images have shown that surface morphology of the grown samples is quite uniform consisting of single layered graphene (SLG) to few layered graphene (FLG). Raman spectra reveal that graphene has been grown with high-quality having negligible defects and the observation of G and G' peaks is also an indicative of stokes phonon energy shift caused due to laser excitation. Scanning probe microscopy image also depicts the synthesis of single to few layered graphene. The field emission characteristics of as-grown graphene samples were studied in a planar diode configuration at room temperature. The graphene samples were observed to be a good field emitter having low turn-on field, higher field amplification factor and long term emission current stability.

Dramatic improvement of crystal quality for low-­temperature-grown rabbit muscle aldolase

OpenAIRE

Park, HaJeung; Rangarajan, Erumbi S.; Sygusch, Jurgen; Izard, Tina

2010-01-01

Rabbit muscle aldolase (RMA) was crystallized in complex with the low-complexity domain (LC4) of sorting nexin 9. Monoclinic crystals were obtained at room temperature that displayed large mosaicity and poor X-ray diffraction. However, orthorhombic RMA–LC4 crystals grown at 277 K under similar conditions exhibited low mosaicity, allowing data collection to 2.2 Å Bragg spacing and structure determination.

Metal Contacts to Gallium Arsenide.

Science.gov (United States)

Ren, Fan

1991-07-01

While various high performance devices fabricated from the gallium arsenide (GaAs) and related materials have generated considerable interest, metallization are fundamental components to all semiconductor devices and integrated circuits. The essential roles of metallization systems are providing the desired electrical paths between the active region of the semiconductor and the external circuits through the metal interconnections and contacts. In this work, in-situ clean of native oxide, high temperature n-type, low temperature n-type and low temperature p-type ohmic metal systems have been studied. Argon ion mill was used to remove the native oxide prior to metal deposition. For high temperature process n-type GaAs ohmic contacts, Tungsten (W) and Tungsten Silicide (WSi) were used with an epitaxial grown graded Indium Gallium Arsenide (InGaAs) layer (0.2 eV) on GaAs. In addition, refractory metals, Molybdenum (Mo), was incorporated in the Gold-Germanium (AuGe) based on n-type GaAs ohmic contacts to replace conventional silver as barrier to prevent the reaction between ohmic metal and chlorine based plasma as well as the ohmic metallization intermixing which degrades the device performance. Finally, Indium/Gold-Beryllium (In/Au-Be) alloy has been developed as an ohmic contact for p-type GaAs to reduce the contact resistance. The Fermi-level pinning of GaAs has been dominated by the surface states. The Schottky barrier height of metal contacts are about 0.8 V regardless of the metal systems. By using p-n junction approach, barrier height of pulsed C-doped layers was achieved as high as 1.4 V. Arsenic implantation into GaAs method was also used to enhance the barrier height of 1.6 V.

Sodium enhances indium-gallium interdiffusion in copper indium gallium diselenide photovoltaic absorbers.

Science.gov (United States)

Colombara, Diego; Werner, Florian; Schwarz, Torsten; Cañero Infante, Ingrid; Fleming, Yves; Valle, Nathalie; Spindler, Conrad; Vacchieri, Erica; Rey, Germain; Guennou, Mael; Bouttemy, Muriel; Manjón, Alba Garzón; Peral Alonso, Inmaculada; Melchiorre, Michele; El Adib, Brahime; Gault, Baptiste; Raabe, Dierk; Dale, Phillip J; Siebentritt, Susanne

2018-02-26

Copper indium gallium diselenide-based technology provides the most efficient solar energy conversion among all thin-film photovoltaic devices. This is possible due to engineered gallium depth gradients and alkali extrinsic doping. Sodium is well known to impede interdiffusion of indium and gallium in polycrystalline Cu(In,Ga)Se 2 films, thus influencing the gallium depth distribution. Here, however, sodium is shown to have the opposite effect in monocrystalline gallium-free CuInSe 2 grown on GaAs substrates. Gallium in-diffusion from the substrates is enhanced when sodium is incorporated into the film, leading to Cu(In,Ga)Se 2 and Cu(In,Ga) 3 Se 5 phase formation. These results show that sodium does not decrease per se indium and gallium interdiffusion. Instead, it is suggested that sodium promotes indium and gallium intragrain diffusion, while it hinders intergrain diffusion by segregating at grain boundaries. The deeper understanding of dopant-mediated atomic diffusion mechanisms should lead to more effective chemical and electrical passivation strategies, and more efficient solar cells.

Robustness of the charge-ordered phases in IrTe2 against photoexcitation

Science.gov (United States)

Monney, C.; Schuler, A.; Jaouen, T.; Mottas, M.-L.; Wolf, Th.; Merz, M.; Muntwiler, M.; Castiglioni, L.; Aebi, P.; Weber, F.; Hengsberger, M.

2018-02-01

We present a time-resolved angle-resolved photoelectron spectroscopy study of IrTe2, which undergoes two first-order structural and charge-ordered phase transitions on cooling below 270 K and below 180 K. The possibility of inducing a phase transition by photoexcitation with near-infrared femtosecond pulses is investigated in the charge-ordered phases. We observe changes of the spectral function occurring within a few hundreds of femtoseconds and persisting up to several picoseconds, which we interpret as a partial photoinduced phase transition (PIPT). The necessary time for photoinducing these spectral changes increases with increasing photoexcitation density and reaches time scales longer than the rise time of the transient electronic temperature. We conclude that the PIPT is driven by a transient increase of the lattice temperature following the energy transfer from the electrons. However, the photoinduced changes of the spectral function are small, which indicates that the low-temperature phase is particularly robust against photoexcitation. We suggest that the system might be trapped in an out-of-equilibrium state, for which only a partial structural transition is achieved.

Interactions of zircaloy cladding with gallium -- 1997 status

International Nuclear Information System (INIS)

Wilson, D.F.; DiStefano, J.R.; King, J.F.; Manneschmidt, E.T.; Strizak, J.P.

1997-11-01

A four phase program has been implemented to evaluate the effect of gallium in mixed oxide (MOX) fuel derived from weapons grade (WG) plutonium on Zircaloy cladding performance. The objective is to demonstrate that low levels of gallium will not compromise the performance of the MOX fuel system in LWR. This graded, four phase experimental program will evaluate the performance of prototypic Zircaloy cladding materials against: (1) liquid gallium (Phase 1), (2) various concentrations of Ga 2 O 3 (Phase 2), (3) centrally heated surrogate fuel pellets with expected levels of gallium (Phase 3), and (4) centrally heated prototypic MOX fuel pellets (Phase 4). This status report describes the results of an initial series of tests for phases 1 and 2. Three types of tests are being performed: (1) corrosion, (2) liquid metal embrittlement (LME), and (3) corrosion mechanical. These tests are designed to determine the corrosion mechanisms, thresholds for temperature and concentration of gallium that may delineate behavioral regimes, and changes in mechanical properties of Zircaloy. Initial results have generally been favorable for the use of WG-MOX fuel. The MOX fuel cladding, Zircaloy, does react with gallium to form intermetallic compounds at ≥ 300 C; however, this reaction is limited by the mass of gallium and is therefore not expected to be significant with a low level (in parts per million) of gallium in the MOX fuel. While continued migration of gallium into the initially formed intermetallic compound results in large stresses that can lead to distortion, this is also highly unlikely because of the low mass of gallium or gallium oxide present and expected clad temperatures below 400 C. Furthermore, no evidence for grain boundary penetration by gallium has been observed

Annealing of low-temperature GaAs studied using a variable energy positron beam

International Nuclear Information System (INIS)

Keeble, D.J.; Umlor, M.T.; Asoka-Kumar, P.; Lynn, K.G.; Cooke, P.W.

1993-01-01

The annihilation characteristics of monoenergetic positrons implanted in a molecular beam epitaxy layer of low-temperature (LT) GaAs annealed at temperatures from 300 to 600 degree C were measured. A gallium vacancy concentration of approximately 3x10 17 cm -3 is inferred for the as-grown material. The S parameter increased significantly upon anneal to 500 degree C. The dominant positron traps in samples annealed at and below 400 degree C are distinct from those acting for samples annealed to 500 or 600 degree C. The change in S parameter for the 600 degree C annealed sample compared to the GaAs substrate, S LT,600 =1.047S sub , is consistent with divacancies or larger open volume defects

Structural analysis of as-deposited and annealed low-temperature gallium arsenide

Science.gov (United States)

Matyi, R. J.; Melloch, M. R.; Woodall, J. M.

1993-04-01

The structure of GaAs grown at low substrate temperatures (LT-GaAs) by molecular beam epitaxy has been studied using high resolution X-ray diffraction methods. Double crystal rocking curves from the as-deposited LT-GaAs show well defined interference fringes, indicating a high level of structural perfection. Triple crystal diffraction analysis of the as-deposited sample showed significantly less diffuse scattering near the LT-GaAs 004 reciprocal lattice point compared with the substrate 004 reciprocal lattice point, suggesting that despite the incorporation of approximately 1% excess arsenic, the epitaxial layer had superior crystalline perfection than did the GaAs substrate. Triple crystal scans of annealed LT-GaAs showed an increase in the integrated diffuse intensity by approximately a factor of three as the anneal temperature was increased from 700 to 900°C. Analogous to the effects of SiO2 precipitates in annealed Czochralski silicon, the diffuse intensity is attributed to distortions in the epitaxial LT-GaAs lattice by arsenic precipitates.

α-Ga2O3 grown by low temperature atomic layer deposition on sapphire

Science.gov (United States)

Roberts, J. W.; Jarman, J. C.; Johnstone, D. N.; Midgley, P. A.; Chalker, P. R.; Oliver, R. A.; Massabuau, F. C.-P.

2018-04-01

α-Ga2O3 is a metastable phase of Ga2O3 of interest for wide bandgap engineering since it is isostructural with α-In2O3 and α-Al2O3. α-Ga2O3 is generally synthesised under high pressure (several GPa) or relatively high temperature (∼500 °C). In this study, we report the growth of α-Ga2O3 by low temperature atomic layer deposition (ALD) on sapphire substrate. The film was grown at a rate of 0.48 Å/cycle, and predominantly consists of α-Ga2O3 in the form of (0001) -oriented columns originating from the interface with the substrate. Some inclusions were also present, typically at the tips of the α phase columns and most likely comprising ε-Ga2O3. The remainder of the Ga2O3 film - i.e. nearer the surface and between the α-Ga2O3 columns, was amorphous. The film was found to be highly resistive, as is expected for undoped material. This study demonstrates that α-Ga2O3 films can be grown by low temperature ALD and suggests the possibility of a new range of ultraviolet optoelectronic and power devices grown by ALD. The study also shows that scanning electron diffraction is a powerful technique to identify the different polymorphs of Ga2O3 present in multiphase samples.

Epitaxially-grown Gallium Nitride on Gallium Oxide substrate for photon pair generation in visible and telecomm wavelengths

KAUST Repository

Awan, Kashif M.

2016-08-11

Gallium Nitride (GaN), along with other III-Nitrides, is attractive for optoelectronic and electronic applications due to its wide direct energy bandgap, as well as high thermal stability. GaN is transparent over a wide wavelength range from infra-red to the visible band, which makes it suitable for lasers and LEDs. It is also expected to be a suitable candidate for integrated nonlinear photonic circuits for a wide range of applications from all-optical signal processing to quantum computing and on-chip wavelength conversion. Despite its abundant use in commercial devices, there is still need for suitable substrate materials to reduce high densities of threading dislocations (TDs) and other structural defects like stacking faults, and grain boundaries. All these defects degrade the optical quality of the epi-grown GaN layer as they act as non-radiative recombination centers.

Epitaxially-grown Gallium Nitride on Gallium Oxide substrate for photon pair generation in visible and telecomm wavelengths

KAUST Repository

Awan, Kashif M.; Dolgaleva, Ksenia; Mumthaz Muhammed, Mufasila; Roqan, Iman S.

2016-01-01

Gallium Nitride (GaN), along with other III-Nitrides, is attractive for optoelectronic and electronic applications due to its wide direct energy bandgap, as well as high thermal stability. GaN is transparent over a wide wavelength range from infra-red to the visible band, which makes it suitable for lasers and LEDs. It is also expected to be a suitable candidate for integrated nonlinear photonic circuits for a wide range of applications from all-optical signal processing to quantum computing and on-chip wavelength conversion. Despite its abundant use in commercial devices, there is still need for suitable substrate materials to reduce high densities of threading dislocations (TDs) and other structural defects like stacking faults, and grain boundaries. All these defects degrade the optical quality of the epi-grown GaN layer as they act as non-radiative recombination centers.

The Mobility Enhancement of Indium Gallium Zinc Oxide Transistors via Low-temperature Crystallization using a Tantalum Catalytic Layer.

Science.gov (United States)

Shin, Yeonwoo; Kim, Sang Tae; Kim, Kuntae; Kim, Mi Young; Oh, Saeroonter; Jeong, Jae Kyeong

2017-09-07

High-mobility indium gallium zinc oxide (IGZO) thin-film transistors (TFTs) are achieved through low-temperature crystallization enabled via a reaction with a transition metal catalytic layer. For conventional amorphous IGZO TFTs, the active layer crystallizes at thermal annealing temperatures of 600 °C or higher, which is not suitable for displays using a glass substrate. The crystallization temperature is reduced when in contact with a Ta layer, where partial crystallization at the IGZO back-channel occurs with annealing at 300 °C, while complete crystallization of the active layer occurs at 400 °C. The field-effect mobility is significantly boosted to 54.0 cm 2 /V·s for the IGZO device with a metal-induced polycrystalline channel formed at 300 °C compared to 18.1 cm 2 /V·s for an amorphous IGZO TFT without a catalytic layer. This work proposes a facile and effective route to enhance device performance by crystallizing the IGZO layer with standard annealing temperatures, without the introduction of expensive laser irradiation processes.

Low temperature step-graded InAlAs/GaAs metamorphic buffer layers grown by molecular beam epitaxy

International Nuclear Information System (INIS)

Shang, X Z; Wu, S D; Liu, C; Wang, W X; Guo, L W; Huang, Q; Zhou, J M

2006-01-01

Low-temperature step-graded InAlAs metamorphic buffer layers on GaAs substrate grown by molecular beam epitaxy were investigated. The strain relaxation and the composition of the top InAlAs layer were determined by high-resolution triple-axis x-ray diffraction measurements, which show that the top InAlAs layer is nearly fully relaxed. Surface morphology was observed by reflection high-energy electron diffraction pattern and atomic force microscopy. Under a selected range of growth parameters, the root mean square surface roughness of the sample grown at 380 deg. C is 0.802 nm, which has the smallest value compared with those of other samples. Furthermore, The ω-2θ and ω scans of the triple-axis x-ray diffraction, and photoluminescence show the sample grown at 380 deg. C has better crystalline quality. With decreasing As overpressure at this growth temperature, crystalline quality became poor and could not maintain two dimensional growth with increasing overpressure. The carrier concentrations and Hall mobilities of the InAlAs/ InGaAs/GaAs MM-HEMT structure on low-temperature step-graded InAlAs metamorphic buffer layers grown in optimized conditions are high enough to make devices

Surface cleaning procedures for thin films of indium gallium nitride grown on sapphire

Energy Technology Data Exchange (ETDEWEB)

Douglass, K.; Hunt, S. [Department of Chemistry and Biochemistry, University of Delaware, Newark, DE 19716 (United States); Teplyakov, A., E-mail: andrewt@udel.edu [Department of Chemistry and Biochemistry, University of Delaware, Newark, DE 19716 (United States); Opila, R.L. [Department of Material Science and Engineering, University of Delaware, Newark, DE 19716 (United States)

2010-12-15

Surface preparation procedures for indium gallium nitride (InGaN) thin films were analyzed for their effectiveness for carbon and oxide removal as well as for the resulting surface roughness. Aqua regia (3:1 mixture of concentrated hydrochloric acid and concentrated nitric acid, AR), hydrofluoric acid (HF), hydrochloric acid (HCl), piranha solution (1:1 mixture of sulfuric acid and 30% H{sub 2}O{sub 2}) and 1:9 ammonium sulfide:tert-butanol were all used along with high temperature anneals to remove surface contamination. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) were utilized to study the extent of surface contamination and surface roughness, respectively. The ammonium sulfide treatment provided the best overall removal of oxygen and carbon. Annealing over 700 deg. C after a treatment showed an even further improvement in surface contamination removal. The piranha treatment resulted in the lowest residual carbon, while the ammonium sulfide treatment leads to the lowest residual oxygen. AFM data showed that all the treatments decreased the surface roughness (with respect to as-grown specimens) with HCl, HF, (NH{sub 4}){sub 2}S and RCA procedures giving the best RMS values ({approx}0.5-0.8 nm).

Disorder in silicon films grown epitaxially at low temperature

International Nuclear Information System (INIS)

Schwarzkopf, J.; Selle, B.; Bohne, W.; Roehrich, J.; Sieber, I.; Fuhs, W.

2003-01-01

Homoepitaxial Si films were prepared by electron cyclotron resonance plasma enhanced chemical vapor deposition on Si(100) substrates at temperatures of 325-500 deg. C using H 2 , Ar, and SiH 4 as process gases. The gas composition, substrate temperature, and substrate bias voltage were systematically varied to study the breakdown of epitaxial growth. Information from ion beam techniques, like Rutherford backscattering and heavy-ion elastic recoil detection analysis, was combined with transmission and scanning electron micrographs to examine the transition from ordered to amorphous growth. The results suggest that the breakdown proceeds in two stages: (i) highly defective but still ordered growth with a defect density increasing with increasing film thickness and (ii) formation of conically shaped amorphous precipitates. The hydrogen content is found to be directly related to the degree of disorder which acts as sink for excessive hydrogen. Only in almost perfect epitaxially grown films is the hydrogen level low, and an exponential tail of the H concentration into the crystalline substrate is observed as a result of the diffusive transport of hydrogen

Gallium-67 imaging with low collimators and energy weighted acquisition

International Nuclear Information System (INIS)

Hamill, J.J.; DeVito, R.P.

1990-01-01

This paper reports that the medium and high energy collimators used in 67 Ga imaging have poorer resolution than low-energy collimators, such as the LEAP. The low energy collimators could be used for gallium imaging if the background under the 93 and 185 keV peaks could be reduced without degrading the signal-to-noise ratio unacceptably. energy weighted acquisition provides a means of accomplishing this background reduction. The authors have developed weighing functions for gallium imaging through LEAP and high resolution collimators. The resolution of the low energy collimators is realized while the background is comparable to, or better than, the background in normal, energy-window imaging with the medium energy collimator. The pixel noise is somewhat greater than the Poisson noise in normal gallium imaging, and some noise correlations, or noise texture, is introduced

Interactions of Zircaloy cladding with gallium: 1998 midyear status

International Nuclear Information System (INIS)

Wilson, D.F.; DiStefano, J.R.; Strizak, J.P.; King, J.F.; Manneschmidt, E.T.

1998-06-01

A program has been implemented to evaluate the effect of gallium in mixed-oxide (MOX) fuel derived from weapons-grade (WG) plutonium on Zircaloy cladding performance. The objective is to demonstrate that low levels of gallium will not compromise the performance of the MOX fuel system in a light-water reactor. The graded, four-phase experimental program was designed to evaluate the performance of prototypic Zircaloy cladding materials against (1) liquid gallium (Phase 1), (2) various concentrations of Ga 2 O 3 (Phase 2), (3) centrally heated surrogate fuel pellets with expected levels of gallium (Phase 3), and (4) centrally heated prototypic MOX fuel pellets (Phase 4). This status report describes the results of a series of tests for Phases 1 and 2. Three types of tests are being performed: (1) corrosion, (2) liquid metal embrittlement, and (3) corrosion-mechanical. These tests will determine corrosion mechanisms, thresholds for temperature and concentration of gallium that may delineate behavioral regimes, and changes in the mechanical properties of Zircaloy. Initial results have generally been favorable for the use of WG-MOX fuel. The MOX fuel cladding, Zircaloy, does react with gallium to form intermetallic compounds at ≥300 C; however, this reaction is limited by the mass of gallium and is therefore not expected to be significant with a low level (parts per million) of gallium in the MOX fuel. Although continued migration of gallium into the initially formed intermetallic compound can result in large stresses that may lead to distortion, this was shown to be extremely unlikely because of the low mass of gallium or gallium oxide present and expected clad temperatures below 400 C. Furthermore, no evidence for grain boundary penetration by gallium has been observed

GaSb grown from Sn solvent at low temperatures by LPE

Energy Technology Data Exchange (ETDEWEB)

Compean, V H; Anda, F de; Mishurnyi, V A; Gorbatchev, A Yu, E-mail: fdeanda@cactus.iico.uaslp.m [Universidad Autonoma de San Luis Potosi, Instituto de Investigacion en Comunicacion Optica, Av. Karakorum 1470, Col. Lomas 4a Sec., San Luis Potosi, SLP, CP 78210 (Mexico)

2009-05-01

The LPE growth of GaSb using Sn as a solvent has been studied in the temperature range 250-370 C and using liquid solutions covering a wide range of compositions. In order to find the growth conditions the phase diagram has been determined experimentally around the same temperature region. It is shown the Sn incorporates into the grown layers and that it behaves as an acceptor. The photoluminescence spectra of the grown layers with different Sn contents show characteristic peaks that can be attributed to different recombination processes.

Suppression of self-interstitials in silicon during ion implantation via in-situ photoexcitation

International Nuclear Information System (INIS)

Ravi, J.; Erokhin, Yu.; Christensen, K.; Rozgonyi, G.A.; Patnaik, B.K.; White, C.W.

1995-02-01

The influence of in-situ photoexcitation during low temperature implantation on self-interstitial agglomeration following annealing has been investigated using transmission electron microscopy (TEM). A reduction in the level of as-implanted damage determined by RBS and TEM occurs athermally during 150 keV self-ion implantation. The damage reduction following a 300 C anneal suggests that it is mostly divacancy related. Subsequent thermal annealing at 800 C resulted in the formation of (311) rod like defects or dislocation loops for samples with and without in-situ photoexcitation, respectively. Estimation of the number of self-interstitials bound by these defects in the sample without in-situ photoexcitation corresponds to the implanted dose; whereas for the in-situ photoexcitation sample a suppression of ∼2 orders in magnitude is found. The kinetics of the athermal annealing process are discussed within the framework of either a recombination enhanced defect reaction mechanism, or a charge state enhanced defect migration and Coulomb interaction

Determination of lattice orientation in aluminium alloy grains by low energy gallium ion-channelling

Energy Technology Data Exchange (ETDEWEB)

Silk, Jonathan R. [Aerospace Metal Composites Ltd., RAE Road, Farnborough, GU14 6XE (United Kingdom); Dashwood, Richard J. [WMG, University of Warwick, Coventry, CV4 7AL (United Kingdom); Chater, Richard J., E-mail: r.chater@imperial.ac.u [Department of Materials, Imperial College, London SW7 2AZ (United Kingdom)

2010-06-15

Polished sections of a fine-grained aluminium, silicon carbide metal matrix composite (MMC) alloy were prepared by sputtering using a low energy gallium ion source and column (FIB). The MMC had been processed by high temperature extrusion. Images of the polished surface were recorded using the ion-induced secondary electron emission. The metal matrix grains were distinguished by gallium ion-channelling contrast from the silicon carbide component. The variation of the contrast from the aluminium grains with tilt angle can be recorded and used to determine lattice orientation with the contrast from the silicon carbide (SiC) component as a reference. This method is rapid and suits site-specific investigations where classical methods of sample preparation fail.

Motional spin relaxation in photoexcited triplet states

International Nuclear Information System (INIS)

Harryvan, D.; Faassen, E. van

1997-01-01

Transient EPR experiments were performed on photoexcited spin triplet states of the luminescent dye EOSIN-Y in diluted (order of 1 nMol) frozen propane-1-ol solutions at various temperatures. Photoexcitation was achieved by irradiation with intense, short laser pulses. The details of the spin relaxation, in particular the dependence on time, magnetic field and microwave field strength are all reproduced by a model which computes the total magnetization in a population of photoexcited triplet states undergoing random reorientational motion. Using this model, we estimated the motional correlation times to be around a microsecond. This timescale is two orders of magnitude slower than the phase memory time of the triplets. (author)

Trapping of positron in gallium arsenide: evidencing of vacancies and of ions with a negative charge

International Nuclear Information System (INIS)

Pierre, F.

1989-12-01

Vacancy type defects in Ga As as grown and irradiated by electrons are characterized by lifetime of positrons. Positron lifetime increases from 230 ps to 258 and 295 ps in presence of native vacancies in n type Ga As. Configuration of native vacancies changes when Fermi level crosses energy levels localized in the forbidden zone at 0.035eV and at 0.10eV from the bottom of the conduction band. Native vacancies are identified to arsenic vacancies with or without other point defects. Positron lifetime increases from 230 to 260 ps in presence of vacancies produced by low temperature irradiation negative ions are also produced. In irradiated Ga As, these ions trap positrons in competition with vacancies produced by irradiation, showing they have a negative charge. Two annealing zones between 180-300K and 300-600K are presented by vacancies. Ions do not anneal below ambient temperature. Vacancies and negative ions are identified respectively to gallium vacancies and gallium antisite [fr

Reducing the layer number of AB stacked multilayer graphene grown on nickel by annealing at low temperature.

Science.gov (United States)

Velasco, J Marquez; Giamini, S A; Kelaidis, N; Tsipas, P; Tsoutsou, D; Kordas, G; Raptis, Y S; Boukos, N; Dimoulas, A

2015-10-09

Controlling the number of layers of graphene grown by chemical vapor deposition is crucial for large scale graphene application. We propose here an etching process of graphene which can be applied immediately after growth to control the number of layers. We use nickel (Ni) foil at high temperature (T = 900 °C) to produce multilayer-AB-stacked-graphene (MLG). The etching process is based on annealing the samples in a hydrogen/argon atmosphere at a relatively low temperature (T = 450 °C) inside the growth chamber. The extent of etching is mainly controlled by the annealing process duration. Using Raman spectroscopy we demonstrate that the number of layers was reduced, changing from MLG to few-layer-AB-stacked-graphene and in some cases to randomly oriented few layer graphene near the substrate. Furthermore, our method offers the significant advantage that it does not introduce defects in the samples, maintaining their original high quality. This fact and the low temperature our method uses make it a good candidate for controlling the layer number of already grown graphene in processes with a low thermal budget.

Dramatic Improvement of Crystal Quality for Low-temperature-grown Rabbit Muscle Aldolase

Energy Technology Data Exchange (ETDEWEB)

Park, H.; Rangarajan, E; Sygusch, J; Izard, T

2010-01-01

Rabbit muscle aldolase (RMA) was crystallized in complex with the low-complexity domain (LC4) of sorting nexin 9. Monoclinic crystals were obtained at room temperature that displayed large mosaicity and poor X-ray diffraction. However, orthorhombic RMA-LC4 crystals grown at 277 K under similar conditions exhibited low mosaicity, allowing data collection to 2.2 {angstrom} Bragg spacing and structure determination. It was concluded that the improvement of crystal quality as indicated by the higher resolution of the new RMA-LC4 complex crystals was a consequence of the introduction of new lattice contacts at lower temperature. The lattice contacts corresponded to an increased number of interactions between high-entropy side chains that mitigate the lattice strain incurred upon cryocooling and accompanying mosaic spread increases. The thermodynamically unfavorable immobilization of high-entropy side chains used in lattice formation was compensated by an entropic increase in the bulk-solvent content owing to the greater solvent content of the crystal lattice.

Dramatic improvement of crystal quality for low-temperature-grown rabbit muscle aldolase.

Science.gov (United States)

Park, Hajeung; Rangarajan, Erumbi S; Sygusch, Jurgen; Izard, Tina

2010-05-01

Rabbit muscle aldolase (RMA) was crystallized in complex with the low-complexity domain (LC4) of sorting nexin 9. Monoclinic crystals were obtained at room temperature that displayed large mosaicity and poor X-ray diffraction. However, orthorhombic RMA-LC4 crystals grown at 277 K under similar conditions exhibited low mosaicity, allowing data collection to 2.2 A Bragg spacing and structure determination. It was concluded that the improvement of crystal quality as indicated by the higher resolution of the new RMA-LC4 complex crystals was a consequence of the introduction of new lattice contacts at lower temperature. The lattice contacts corresponded to an increased number of interactions between high-entropy side chains that mitigate the lattice strain incurred upon cryocooling and accompanying mosaic spread increases. The thermodynamically unfavorable immobilization of high-entropy side chains used in lattice formation was compensated by an entropic increase in the bulk-solvent content owing to the greater solvent content of the crystal lattice.

Observation of the exciton and Urbach band tail in low-temperature-grown GaAs using four-wave mixing spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Webber, D.; Yildirim, M.; Hacquebard, L.; March, S.; Mathew, R.; Gamouras, A.; Hall, K. C. [Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia B3H 4R2 (Canada); Liu, X.; Dobrowolska, M.; Furdyna, J. K. [Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556 (United States)

2014-11-03

Four-wave mixing (FWM) spectroscopy reveals clear signatures associated with the exciton, free carrier inter-band transitions, and the Urbach band tail in low-temperature-grown GaAs, providing a direct measure of the effective band gap as well as insight into the influence of disorder on the electronic structure. The ability to detect (and resolve) these contributions, in contrast to linear spectroscopy, is due to an enhanced sensitivity of FWM to the optical joint density of states and to many-body effects. Our experiments demonstrate the power of FWM for studying the near-band-edge optical properties and coherent carrier dynamics in low-temperature-grown semiconductors.

Above band gap absorption spectra of the arsenic antisite defect in low temperature grown GaAs and AlGaAs

DEFF Research Database (Denmark)

Dankowski, S. U.; Streb, D.; Ruff, M.

1996-01-01

coefficients at the band gap are twice as high as for high temperature grown materials. By annealing the samples, we obtained a drastic reduced absorption coefficient below as well as above the band gap. We observed absorption changes up to 17 000 cm(-1) for LT-GaAs and 9000 cm(-1) for LT-AlGaAs taking place......Room temperature absorption spectra of low temperature molecular beam epitaxy grown GaAs (LT-GaAs) and AlGaAs (LT-AlGaAs) are reported. We performed measurements in an extended spectral range from 0.8 eV to photon energies of 2.8 eV far above the band gap. For as-grown LT-materials, the absorption...

Photoexcited iron porphyrin as biomimetic catalysts

International Nuclear Information System (INIS)

Bartocci, C.; Maldotti, A.; Varani, G.; Consiglio Nazionale delle Ricerche, Ferrara

1996-01-01

Photoexcited iron porphyrins can be of some interest in both fine and industrial chemistry in view of the preparation of new efficient biomimetic catalysts, working with high selectivity under mild temperature and pressure

Influence of arsenic flow on the crystal structure of epitaxial GaAs grown at low temperatures on GaAs (100) and (111)A substrates

Energy Technology Data Exchange (ETDEWEB)

Galiev, G. B.; Klimov, E. A. [Russian Academy of Sciences, Institute of Ultra High Frequency Semiconductor Electronics (Russian Federation); Vasiliev, A. L.; Imamov, R. M. [Russian Academy of Sciences, Shubnikov Institute of Crystallography, Federal Scientific Research Centre “Crystallography and Photonics,” (Russian Federation); Pushkarev, S. S., E-mail: s-s-e-r-p@mail.ru [Russian Academy of Sciences, Institute of Ultra High Frequency Semiconductor Electronics (Russian Federation); Trunkin, I. N. [National Research Centre “Kurchatov Institute” (Russian Federation); Maltsev, P. P. [Russian Academy of Sciences, Institute of Ultra High Frequency Semiconductor Electronics (Russian Federation)

2017-01-15

The influence of arsenic flow in a growth chamber on the crystal structure of GaAs grown by molecular-beam epitaxy at a temperature of 240°C on GaAs (100) and (111)A substrates has been investigated. The flow ratio γ of arsenic As4 and gallium was varied in the range from 16 to 50. GaAs films were either undoped, or homogeneously doped with silicon, or contained three equidistantly spaced silicon δ-layers. The structural quality of the annealed samples has been investigated by transmission electron microscopy. It is established for the first time that silicon δ-layers in “low-temperature” GaAs serve as formation centers of arsenic precipitates. Their average size, concentration, and spatial distribution are estimated. The dependence of the film structural quality on γ is analyzed. Regions 100–150 nm in size have been revealed in some samples and identified (by X-ray microanalysis) as pores. It is found that, in the entire range of γ under consideration, GaAs films on (111)A substrates have a poorer structural quality and become polycrystalline beginning with a thickness of 150–200 nm.

Structural variations in nanosized confined gallium

Energy Technology Data Exchange (ETDEWEB)

Lee, Min Kai [Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan (China); Tien Cheng [Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan (China)] [Center for Micro/Nano Science of Technology, National Cheng Kung University, Tainan 70101, Taiwan, ROC (China); Charnaya, E.V., E-mail: charnaya@live.co [Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan (China)] [Institute of Physics, St. Petersburg State University, St. Petersburg, Petrodvorets 198504 (Russian Federation); Sheu, Hwo-Shuenn [National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan (China); Kumzerov, Yu.A. [A.F. Ioffe Physico-Technical Institute RAS, St. Petersburg, 194021 (Russian Federation)

2010-03-29

The complex crystalline structure of gallium under nanoconfinement was revealed by synchrotron radiation x-ray powder diffraction. Nanoconfinement was shown to stabilize delta-Ga which is metastable in bulk. Two new gallium phases named iota- and kappa-Ga were found upon cooling below room temperature. These crystalline modifications were stable and coexisted with known gallium phases. Correlations between confined gallium particle shapes and emergence of particular crystalline phases were observed. Melting and freezing temperatures for different gallium phases were obtained. Remarkable supercooling of liquid gallium was seen in 3.5 nm pores.

Increasing minority carrier lifetime in as-grown multicrystalline silicon by low temperature internal gettering

Energy Technology Data Exchange (ETDEWEB)

Al-Amin, M., E-mail: m.al-amin@warwick.ac.uk; Murphy, J. D., E-mail: john.d.murphy@warwick.ac.uk [School of Engineering, University of Warwick, Coventry, CV4 7AL (United Kingdom)

2016-06-21

We report a systematic study into the effects of long low temperature (≤500 °C) annealing on the lifetime and interstitial iron distributions in as-grown multicrystalline silicon (mc-Si) from different ingot height positions. Samples are characterised in terms of dislocation density, and lifetime and interstitial iron concentration measurements are made at every stage using a temporary room temperature iodine-ethanol surface passivation scheme. Our measurement procedure allows these properties to be monitored during processing in a pseudo in situ way. Sufficient annealing at 300 °C and 400 °C increases lifetime in all cases studied, and annealing at 500 °C was only found to improve relatively poor wafers from the top and bottom of the block. We demonstrate that lifetime in poor as-grown wafers can be improved substantially by a low cost process in the absence of any bulk passivation which might result from a dielectric surface film. Substantial improvements are found in bottom wafers, for which annealing at 400 °C for 35 h increases lifetime from 5.5 μs to 38.7 μs. The lifetime of top wafers is improved from 12.1 μs to 23.8 μs under the same conditions. A correlation between interstitial iron concentration reduction and lifetime improvement is found in these cases. Surprisingly, although the interstitial iron concentration exceeds the expected solubility values, low temperature annealing seems to result in an initial increase in interstitial iron concentration, and any subsequent decay is a complex process driven not only by diffusion of interstitial iron.

Effects of low-temperature (120 °C) annealing on the carrier concentration and trap density in amorphous indium gallium zinc oxide thin film transistors

Energy Technology Data Exchange (ETDEWEB)

Kim, Jae-sung; Piao, Mingxing; Jang, Ho-Kyun; Kim, Gyu-Tae, E-mail: gtkim@korea.ac.kr [School of Electrical Engineering, Korea University, Seoul 136-701 (Korea, Republic of); Oh, Byung Su [School of Electrical Engineering, Korea University, Seoul 136-701 (Korea, Republic of); Samsung Display Company, Yongin (Korea, Republic of); Joo, Min-Kyu [School of Electrical Engineering, Korea University, Seoul 136-701 (Korea, Republic of); IMEP-LAHC, Grenoble INP, Minatec, CS 50257, 38016 Grenoble (France); Ahn, Seung-Eon [School of Electrical Engineering, Korea University, Seoul 136-701 (Korea, Republic of); Samsung Advanced Institute of Technology, Samsung Electronics Corporations, Yongin 446-712 (Korea, Republic of)

2014-12-28

We report an investigation of the effects of low-temperature annealing on the electrical properties of amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs). X-ray photoelectron spectroscopy was used to characterize the charge carrier concentration, which is related to the density of oxygen vacancies. The field-effect mobility was found to decrease as a function of the charge carrier concentration, owing to the presence of band-tail states. By employing the transmission line method, we show that the contact resistance did not significantly contribute to the changes in device performance after annealing. In addition, using low-frequency noise analyses, we found that the trap density decreased by a factor of 10 following annealing at 120 °C. The switching operation and on/off ratio of the a-IGZO TFTs improved considerably after low-temperature annealing.

Gallium nitride on gallium oxide substrate for integrated nonlinear optics

KAUST Repository

Awan, Kashif M.; Dolgaleva, Ksenia; Mumthaz Muhammed, Mufasila; Roqan, Iman S.

2017-01-01

Gallium Nitride (GaN), being a direct bandgap semiconductor with a wide bandgap and high thermal stability, is attractive for optoelectronic and electronic applications. Furthermore, due to its high optical nonlinearity — the characteristic of all 111-V semiconductors — GaN is also expected to be a suitable candidate for integrated nonlinear photonic circuits for a plethora of apphcations, ranging from on-chip wavelength conversion to quantum computing. Although GaN devices are in commercial production, it still suffers from lack of a suitable substrate material to reduce structural defects like high densities of threading dislocations (TDs), stacking faults, and grain boundaries. These defects significandy deteriorate the optical quality of the epi-grown GaN layer, since they act as non-radiative recombination centers. Recent studies have shown that GaN grown on (−201) β-Gallium Oxide (Ga2O3) has superior optical quality due to a better lattice matching as compared to GaN grown on Sapphire (Al2O3) [1-3]. In this work, we report on the fabrication of GaN waveguides on GaiOj substrate and their optical characterization to assess their feasibihty for efficient four-wave mixing (FWM).

Gallium nitride on gallium oxide substrate for integrated nonlinear optics

KAUST Repository

Awan, Kashif M.

2017-11-22

Gallium Nitride (GaN), being a direct bandgap semiconductor with a wide bandgap and high thermal stability, is attractive for optoelectronic and electronic applications. Furthermore, due to its high optical nonlinearity — the characteristic of all 111-V semiconductors — GaN is also expected to be a suitable candidate for integrated nonlinear photonic circuits for a plethora of apphcations, ranging from on-chip wavelength conversion to quantum computing. Although GaN devices are in commercial production, it still suffers from lack of a suitable substrate material to reduce structural defects like high densities of threading dislocations (TDs), stacking faults, and grain boundaries. These defects significandy deteriorate the optical quality of the epi-grown GaN layer, since they act as non-radiative recombination centers. Recent studies have shown that GaN grown on (−201) β-Gallium Oxide (Ga2O3) has superior optical quality due to a better lattice matching as compared to GaN grown on Sapphire (Al2O3) [1-3]. In this work, we report on the fabrication of GaN waveguides on GaiOj substrate and their optical characterization to assess their feasibihty for efficient four-wave mixing (FWM).

Dramatic improvement of crystal quality for low-­temperature-grown rabbit muscle aldolase

Science.gov (United States)

Park, HaJeung; Rangarajan, Erumbi S.; Sygusch, Jurgen; Izard, Tina

2010-01-01

Rabbit muscle aldolase (RMA) was crystallized in complex with the low-complexity domain (LC4) of sorting nexin 9. Monoclinic crystals were obtained at room temperature that displayed large mosaicity and poor X-ray diffraction. However, orthorhombic RMA–LC4 crystals grown at 277 K under similar conditions exhibited low mosaicity, allowing data collection to 2.2 Å Bragg spacing and structure determination. It was concluded that the improvement of crystal quality as indicated by the higher resolution of the new RMA–LC4 complex crystals was a consequence of the introduction of new lattice contacts at lower temperature. The lattice contacts corresponded to an increased number of interactions between high-entropy side chains that mitigate the lattice strain incurred upon cryocooling and accompanying mosaic spread increases. The thermodynamically unfavorable immobilization of high-entropy side chains used in lattice formation was compensated by an entropic increase in the bulk-solvent content owing to the greater solvent content of the crystal lattice. PMID:20445268

Proton polarization in photo-excited aromatic molecule at room temperature enhanced by intense optical source and temperature control

Energy Technology Data Exchange (ETDEWEB)

Sakaguchi, S., E-mail: sakaguchi@phys.kyushu-u.ac.jp [Department of Physics, Kyushu University, Fukuoka 812-8581 (Japan); Uesaka, T. [RIKEN Nishina Center, Saitama 351-0198 (Japan); Kawahara, T. [Department of Physics, Toho University, Chiba 274-8510 (Japan); Ogawa, T. [RIKEN Advanced Science Institute, Saitama 351-0198 (Japan); Tang, L. [Center for Nuclear Study, University of Tokyo, Tokyo 113-0001 (Japan); Teranishi, T. [Department of Physics, Kyushu University, Fukuoka 812-8581 (Japan); Urata, Y.; Wada, S. [RIKEN Advanced Science Institute, Saitama 351-0198 (Japan); Wakui, T. [Cyclotron and Radioisotope Center (CYRIC), Tohoku University, Miyagi 980-8578 (Japan)

2013-12-15

Highlights: • Proton polarization in p-terphenyl at room-temperature is enhanced by a factor of 3. • Intense laser and temperature control are critically important for high polarization. • Optimization of time structure of laser pulse is effective for further improvement. -- Abstract: Proton polarization at room temperature, produced in a p-terphenyl crystal by using electron population difference in a photo-excited triplet state of pentacene, was enhanced by utilizing an intense laser with an average power of 1.5 W. It was shown that keeping the sample temperature below 300 K is critically important to prevent the rise of the spin–lattice relaxation rate caused by the laser heating. It is also reported that the magnitude of proton polarization strongly depends on the time structure of the laser pulse such as its width and the time interval between them.

High-fluence hyperthermal ion irradiation of gallium nitride surfaces at elevated temperatures

Energy Technology Data Exchange (ETDEWEB)

Finzel, A.; Gerlach, J.W., E-mail: juergen.gerlach@iom-leipzig.de; Lorbeer, J.; Frost, F.; Rauschenbach, B.

2014-10-30

Highlights: • Irradiation of gallium nitride films with hyperthermal nitrogen ions. • Surface roughening at elevated sample temperatures was observed. • No thermal decomposition of gallium nitride films during irradiation. • Asymmetric surface diffusion processes cause local roughening. - Abstract: Wurtzitic GaN films deposited on 6H-SiC(0001) substrates by ion-beam assisted molecular-beam epitaxy were irradiated with hyperthermal nitrogen ions with different fluences at different substrate temperatures. In situ observations with reflection high energy electron diffraction showed that during the irradiation process the surface structure of the GaN films changed from two dimensional to three dimensional at elevated temperatures, but not at room temperature. Atomic force microscopy revealed an enhancement of nanometric holes and canyons upon the ion irradiation at higher temperatures. The roughness of the irradiated and heated GaN films was clearly increased by the ion irradiation in accordance with x-ray reflectivity measurements. A sole thermal decomposition of the films at the chosen temperatures could be excluded. The results are discussed taking into account temperature dependent sputtering and surface uphill adatom diffusion as a function of temperature.

Low temperature CVD growth of ultrathin carbon films

Directory of Open Access Journals (Sweden)

Chao Yang

2016-05-01

Full Text Available We demonstrate the low temperature, large area growth of ultrathin carbon films by chemical vapor deposition under atmospheric pressure on various substrates. In particularly, uniform and continuous carbon films with the thickness of 2-5 nm were successfully grown at a temperature as low as 500 oC on copper foils, as well as glass substrates coated with a 100 nm thick copper layer. The characterizations revealed that the low-temperature-grown carbon films consist on few short, curved graphene layers and thin amorphous carbon films. Particularly, the low-temperature grown samples exhibited over 90% transmittance at a wavelength range of 400-750 nm and comparable sheet resistance in contrast with the 1000oC-grown one. This low-temperature growth method may offer a facile way to directly prepare visible ultrathin carbon films on various substrate surfaces that are compatible with temperatures (500-600oC used in several device processing technologies.

Automated realization of the gallium melting and triple points

Science.gov (United States)

Yan, X.; Duan, Y.; Zhang, J. T.; Wang, W.

2013-09-01

In order to improve the automation and convenience of the process involved in realizing the gallium fixed points, an automated apparatus, based on thermoelectric and heat pipe technologies, was designed and developed. This paper describes the apparatus design and procedures for freezing gallium mantles and realizing gallium melting and triple points. Also, investigations on the melting behavior of a gallium melting point cell and of gallium triple point cells were carried out while controlling the temperature outside the gallium point cells at 30 °C, 30.5 °C, 31 °C, and 31.5 °C. The obtained melting plateau curves show dentate temperature oscillations on the melting plateaus for the gallium point cells when thermal couplings occurred between the outer and inner liquid-solid interfaces. The maximum amplitude of the temperature fluctuations was about 1.5 mK. Therefore, the temperature oscillations can be used to indicate the ending of the equilibrium phase transitions. The duration and amplitude of such temperature oscillations depend on the temperature difference between the setting temperature and the gallium point temperature; the smaller the temperature difference, the longer the duration of both the melting plateaus and the temperature fluctuations.

The characteristics of carbon nanotubes grown at low temperature for electronic device application

Energy Technology Data Exchange (ETDEWEB)

Park, Yong Seob [Department of Photoelectronics Information, Chosun College of Science and Technology, Gwangju (Korea, Republic of); Yi, Junsin [School of Information and Communications Engineering, Sungkyunkwan University, Suwon, 440–746 (Korea, Republic of); Lee, Jaehyeong, E-mail: jaehyeong@skku.edu [School of Information and Communications Engineering, Sungkyunkwan University, Suwon, 440–746 (Korea, Republic of)

2013-11-01

For the application of carbon nanotubes (CNTs) in flexible electronic devices, the CNTs were grown on Corning 1737 glass substrate by microwave plasma enhanced chemical vapor deposition (MPECVD) method. To deposit the catalyst layer, TiN buffer layer of 200 nm thickness and Ni catalyst layer of 60 nm were first deposited on the glass by r.f. magnetron sputtering method. The CH{sub 4} and H{sub 2} gases are used as the synthesis gas of CNTs and the working pressure was about 2.13 kPa, and the substrate bias was about − 200 V. The growth time was from 2 min to 5 min and the microwave power was about 800 W. The substrate temperature as the main parameter was changed from 400 °C to 550 °C. The structural properties of CNTs synthesized with the substrate temperature were investigated using Raman, field emission scanning electron microscopy, and transmission electron microscopy methods. The surface and electrical properties of CNTs grown by MPECVD method were studied by scanning probe microscopy and four-point probe methods. We obtained the multi-walled CNTs (MW-CNTs). Multi-walled CNTs were vertically grown on Ni/TiN/glass substrates below 500 °C without any glass deformations. As the substrate temperature was increased, the crystallinity of CNTs was improved. Ni catalyst was found at the tip of CNT by the TEM observation and the grown CNTs were found to have a multi-walled with bamboo like structure. - Highlights: • Synthesis of vertically aligned carbon nanotubes. • Effects of substrate temperature on carbon nanotubes properties. • Improvement of the crystallinity with increasing substrate temperature. • Reduction of sheet resistance with increasing substrate temperature.

Chirped-pulse manipulated carrier dynamics in low-temperature molecular-beam-epitaxy grown GaAs

International Nuclear Information System (INIS)

Lee, Chao-Kuei; Lin, Yuan-Yao; Lin, Sung-Hui; Lin, Gong-Ru; Pan, Ci-Ling

2014-01-01

Chirped pulse controlled carrier dynamics in low-temperature molecular-beam-epitaxy grown GaAs are investigated by degenerate pump-probe technique. Varying the chirped condition of excited pulse from negative to positive increases the carrier relaxation time so as to modify the dispersion and reshape current pulse in time domain. The spectral dependence of carrier dynamics is analytically derived and explained by Shockley-Read Hall model. This observation enables the new feasibility of controlling carrier dynamics in ultrafast optical devices via the chirped pulse excitations

Near room temperature chemical vapor deposition of graphene with diluted methane and molten gallium catalyst.

Science.gov (United States)

Fujita, Jun-Ichi; Hiyama, Takaki; Hirukawa, Ayaka; Kondo, Takahiro; Nakamura, Junji; Ito, Shin-Ichi; Araki, Ryosuke; Ito, Yoshikazu; Takeguchi, Masaki; Pai, Woei Wu

2017-09-28

Direct growth of graphene integrated into electronic devices is highly desirable but difficult due to the nominal ~1000 °C chemical vapor deposition (CVD) temperature, which can seriously deteriorate the substrates. Here we report a great reduction of graphene CVD temperature, down to 50 °C on sapphire and 100 °C on polycarbonate, by using dilute methane as the source and molten gallium (Ga) as catalysts. The very low temperature graphene synthesis is made possible by carbon attachment to the island edges of pre-existing graphene nuclei islands, and causes no damages to the substrates. A key benefit of using molten Ga catalyst is the enhanced methane absorption in Ga at lower temperatures; this leads to a surprisingly low apparent reaction barrier of ~0.16 eV below 300 °C. The faster growth kinetics due to a low reaction barrier and a demonstrated low-temperature graphene nuclei transfer protocol can facilitate practical direct graphene synthesis on many kinds of substrates down to 50-100 °C. Our results represent a significant progress in reducing graphene synthesis temperature and understanding its mechanism.

Rutherford backscatter measurements on tellurium and cadmium implanted gallium arsenide

International Nuclear Information System (INIS)

Bell, E.C.

1979-10-01

The primary aim of the work described in this thesis was to examine implanted layers of the dopant impurities cadmium and tellurium in gallium arsenide and to experimentally assess their potential for producing electrically active layers. 1.5 MeV Rutherford backscattering measurements of lattice disorder and atom site location have been used to assess post implantation thermal annealing and elevated temperature implantations to site the dopant impurities on either gallium or arsenic lattice positions in an otherwise undisordered lattice. Pyrolitically deposited silicon dioxide was used as an encapsulant to prevent thermal dissociation of the gallium arsenide during annealing. It has been shown that high doses of cadmium and tellurium can be implanted without forming amorphous lattice disorder by heating the gallium arsenide during implantation to relatively low temperatures. Atom site location measurements have shown that a large fraction of a tellurium dose implanted at 180 0 C is located on or near lattice sites. Channeled backscatter measurements have shown that there is residual disorder or lattice strain in gallium arsenide implanted at elevated temperatures. The extent of this disorder has been shown to depend on the implanted dose and implantation temperature. The channeling effect has been used to measure annealing of the disorder. (author)

Concentration of gallium in the Permo-Carboniferous coals of China

Energy Technology Data Exchange (ETDEWEB)

Zhao, Cunliang; Qin, Shenjun; Yang, Yinchao; Li, Yanheng; Lin, Mingyue [Hebei University of Engineering, Handan (China)

2009-10-15

Gallium is widely used in electronic industry and its current price is about 500 US dollars per kilogram. It has been found that its contents are very high in Permo-Carboniferous coal of China. In order to look for valuable associated gallium deposits in coal, gallium contents of 177 coal samples were determined by using inductively coupled plasma-mass spectrometry (ICP-MS) and the data of 873 coal samples from Chinese Permo-Carboniferous coalfields were collected. The results show that the average gallium concentration of Chinese Permo-Carboniferous coals is 15.49{mu}g{center_dot}g{sup -1}. There are two concentration types of gallium in Chinese Permo-Carboniferous coals: one type is that gallium has enriched to an ore deposit, and another type is that gallium is locally enriched in coal seams, but has not formed a valuable associated gallium ore deposit. The gallium concentration in Chinese Permo-Carboniferous coal may have several different sources: concentration in sedimentation stage, magmatic hydrothermal inputs and low-temperature hydrothermal fluids.

Terahertz radiation from accelerating charge carriers in graphene under ultrafast photoexcitation

Science.gov (United States)

Rustagi, Avinash; Stanton, C. J.

2016-11-01

We study the generation of terahertz (THz) radiation from the acceleration of ultrafast photoexcited charge carriers in graphene in the presence of a dc electric field. Our model is based on calculating the transient current density from the time-dependent distribution function which is determined using the Boltzmann transport equation (BTE) within a relaxation time approximation. We include the time-dependent generation of carriers by the pump pulse by solving for the carrier generation rate using the optical Bloch equations in the rotating wave approximation (RWA). The linearly polarized pump pulse generates an anisotropic distribution of photoexcited carriers in the kx-ky plane. The collision integral in the Boltzmann equation includes a term that leads to the thermalization of carriers via carrier-carrier scattering to an effective temperature above the lattice temperature, as well as a cooling term, which leads to energy relaxation via inelastic carrier-phonon scattering. The radiated signal is proportional to the time derivative of the transient current density. In spite of the fact that the magnitude of the velocity is the same for all the carriers in graphene, there is still emitted radiation from the photoexcited charge carriers with frequency components in the THz range due to a change in the direction of velocity of the photoexcited carriers in the external electric field as well as cooling of the photoexcited carriers on a subpicosecond time scale.

Investigations in gallium removal

Energy Technology Data Exchange (ETDEWEB)

Philip, C.V.; Pitt, W.W. [Texas A and M Univ., College Station, TX (United States); Beard, C.A. [Amarillo National Resource Center for Plutonium, TX (United States)

1997-11-01

Gallium present in weapons plutonium must be removed before it can be used for the production of mixed-oxide (MOX) nuclear reactor fuel. The main goal of the preliminary studies conducted at Texas A and M University was to assist in the development of a thermal process to remove gallium from a gallium oxide/plutonium oxide matrix. This effort is being conducted in close consultation with the Los Alamos National Laboratory (LANL) personnel involved in the development of this process for the US Department of Energy (DOE). Simple experiments were performed on gallium oxide, and cerium-oxide/gallium-oxide mixtures, heated to temperatures ranging from 700--900 C in a reducing environment, and a method for collecting the gallium vapors under these conditions was demonstrated.

Investigations in gallium removal

International Nuclear Information System (INIS)

Philip, C.V.; Pitt, W.W.; Beard, C.A.

1997-11-01

Gallium present in weapons plutonium must be removed before it can be used for the production of mixed-oxide (MOX) nuclear reactor fuel. The main goal of the preliminary studies conducted at Texas A and M University was to assist in the development of a thermal process to remove gallium from a gallium oxide/plutonium oxide matrix. This effort is being conducted in close consultation with the Los Alamos National Laboratory (LANL) personnel involved in the development of this process for the US Department of Energy (DOE). Simple experiments were performed on gallium oxide, and cerium-oxide/gallium-oxide mixtures, heated to temperatures ranging from 700--900 C in a reducing environment, and a method for collecting the gallium vapors under these conditions was demonstrated

Instability of Yb3+ and Pr3+ low-symmetry luminescence centers in gallium phosphide

International Nuclear Information System (INIS)

Kasatkin, V.A.

1985-01-01

The stability of γb 3+ and Pr 3+ low-symmetry luminescence centers formed in gallium phosphide during quenching were studied in the process of durable storage and annealing. Observation of the Yb 3+ and Pr 3+ centrer states was accomplished by the photoluminescence spectra at 18 K. It has been established that annealing in the dark under normal conditions results in a reduced integral luminescence intensity of all low-symmetry Yb 3+ and Pr 3+ centers. Annealing of quenched GaP and GaP saples at 400 K results in complete disappearance of intracenter luminescence of Pr 3+ and low-symmetry Yb 3+ centers. Decomposition during storage and low anealing temperature point to the instability of low-symmetry centers of Pr 3+ and Yb 3+ luminescence

Structural and electrooptical characteristics of quantum dots emitting at 1.3 μm on gallium arsenide

DEFF Research Database (Denmark)

Fiore, A.; Oesterle, U.; Stanley, R.P.

2001-01-01

We present a comprehensive study of the structural and emission properties of self-assembled InAs quantum dots emitting at 1.3 mum. The dots are grown by molecular beam epitaxy on gallium arsenide substrates. Room-temperature emission at 1.3 mum is obtained by embedding the dots in an InGaAs layer...

Indium gallium nitride/gallium nitride quantum wells grown on polar and nonpolar gallium nitride substrates

Science.gov (United States)

Lai, Kun-Yu

Nonpolar (m-plane or a-plane) gallium nitride (GaN) is predicted to be a potential substrate material to improve luminous efficiencies of nitride-based quantum wells (QWs). Numerical calculations indicated that the spontaneous emission rate in a single In0.15Ga0.85N/GaN QW could be improved by ˜2.2 times if the polarization-induced internal field was avoided by epitaxial deposition on nonpolar substrates. A challenge for nonpolar GaN is the limited size (less than 10x10 mm2) of substrates, which was addressed by expansion during the regrowth by Hydride Vapor Phase Epitaxy (HVPE). Subsurface damage in GaN substrates were reduced by annealing with NH3 and N2 at 950°C for 60 minutes. It was additionally found that the variation of m-plane QWs' emission properties was significantly increased when the substrate miscut toward a-axis was increased from 0° to 0.1°. InGaN/GaN QWs were grown by Metalorganic Chemical Vapor Deposition (MOCVD) on c-plane and m-plane GaN substrates. The QWs were studied by cathodoluminescence spectroscopy with different incident electron beam probe currents (0.1 nA ˜ 1000 nA). Lower emission intensities and longer peak wavelengths from c-plane QWs were attributed to the Quantum-confined Stark Effect (QCSE). The emission intensity ratios of m-plane QWs to c-plane QWs decreased from 3.04 at 1 nA to 1.53 at 1000 nA. This was identified as the stronger screening effects of QCSE at higher current densities in c-plane QWs. To further investigate these effects in a fabricated structure, biased photoluminescence measurements were performed on m-plane InGaN/GaN QWs. The purpose was to detect the possible internal fields induced by the dot-like structure in the InGaN layer through the response of these internal fields under externally applied fields. No energy shifts of the QWs were observed, which was attributed to strong surface leakage currents.

Measurements with an ultrafast scanning tunnelling microscope on photoexcited semiconductor layers

DEFF Research Database (Denmark)

Keil, Ulrich Dieter Felix; Jensen, Jacob Riis; Hvam, Jørn Märcher

1998-01-01

Summary form only given. We demonstrate the use of a ultrafast scanning tunnelling microscopes (USTM) for detecting laser-induced field transients on semiconductor layers. In principle, the instrument can detect transient field changes thus far observed as far-field THz radiation in the near......-field regime and resolve small signal sources. For photoexcited low temperature (LT) GaAs we can explain the signal by a diffusion current driven by the laser-induced carrier density gradient...

Superconductivity and structure of gallium under nanoconfinement

Energy Technology Data Exchange (ETDEWEB)

Charnaya, E V; Tien, Cheng; Lee, Min Kai [Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan (China); Kumzerov, Yu A [A F Ioffe Physico-Technical Institute RAS, St Petersburg, 194021 (Russian Federation)

2009-11-11

Superconductivity and crystalline structure were studied for two nanocomposites consisting of gallium loaded porous glasses with different pore sizes. The superconducting transition temperatures were found to differ from those in known bulk gallium modifications. The transition temperatures 7.1 and 6.7 K were ascribed to two new confined gallium structures, iota- and kappa-Ga, observed by synchrotron radiation x-ray powder diffraction. The evolution of superconductivity on decreasing the pore filling with gallium was also studied.

Low-relaxation spin waves in laser-molecular-beam epitaxy grown nanosized yttrium iron garnet films

Energy Technology Data Exchange (ETDEWEB)

Lutsev, L. V., E-mail: l-lutsev@mail.ru; Korovin, A. M.; Bursian, V. E.; Gastev, S. V.; Fedorov, V. V.; Suturin, S. M.; Sokolov, N. S. [Ioffe Physical-Technical Institute, Russian Academy of Sciences, 194021 St. Petersburg (Russian Federation)

2016-05-02

Synthesis of nanosized yttrium iron garnet (Y{sub 3}Fe{sub 5}O{sub 12}, YIG) films followed by the study of ferromagnetic resonance (FMR) and spin wave propagation in these films is reported. The YIG films were grown on gadolinium gallium garnet substrates by laser molecular beam epitaxy. It has been shown that spin waves propagating in YIG deposited at 700 °C have low damping. At the frequency of 3.29 GHz, the spin-wave damping parameter is less than 3.6 × 10{sup −5}. Magnetic inhomogeneities of the YIG films give the main contribution to the FMR linewidth. The contribution of the relaxation processes to the FMR linewidth is as low as 1.2%.

Optical properties of pure and Ce3+ doped gadolinium gallium garnet crystals and epitaxial layers

International Nuclear Information System (INIS)

Syvorotka, I.I.; Sugak, D.; Wierzbicka, A.; Wittlin, A.; Przybylińska, H.; Barzowska, J.; Barcz, A.; Berkowski, M.; Domagała, J.; Mahlik, S.; Grinberg, M.; Ma, Chong-Geng

2015-01-01

Results of X-ray diffraction and low temperature optical absorption measurements of cerium doped gadolinium gallium garnet single crystals and epitaxial layers are reported. In the region of intra-configurational 4f–4f transitions the spectra of the bulk crystals exhibit the signatures of several different Ce 3+ related centers. Apart from the dominant center, associated with Ce substituting gadolinium, at least three other centers are found, some of them attributed to the so-called antisite locations of rare-earth ions in the garnet host, i.e., in the Ga positions. X-ray diffraction data prove lattice expansion of bulk GGG crystals due to the presence of rare-earth antisites. The concentration of the additional Ce-related centers in epitaxial layers is much lower than in the bulk crystals. However, the Ce-doped layers incorporate a large amount of Pb from flux, which is the most probable source of nonradiative quenching of Ce luminescence, not observed in crystals grown by the Czochralski method. - Highlights: • Ce 3+ multicenters found in Gadolinium Gallium Garnet crystals and epitaxial layers. • High quality epitaxial layers of pure and Ce-doped GGG were grown. • Luminescence quenching of Ce 3+ by Pb ions from flux detected in GGG epitaxial layers. • X-ray diffraction allows measuring the amount of the rare-earth antisites in GGG

Optical and magneto-optical properties of zinc-oxide nanostructures grown by the low-temperature chemical route

Science.gov (United States)

Willander, M.; Alnoor, H.; Savoyant, A.; Adam, Rania E.; Nur, O.

2018-02-01

We demonstrate that the low temperature synthesis chemical route can be utilized to control the functionality of zinc oxide (ZnO) nanoparticles (NPs) and nanorods (NRs) for optical and magneto-optical performance. Different structural, optical, electro- and magneto-optical results will be displayed and analyzed. In the first part, we show how high quality ZnO NPs can be efficient for photodegradation using ultra-violet radiation. In the second part we will present our recent results on the control of the core defects in cobalt doped ZnO NR. Here and by using electron paramagnetic resonance (EPR) measurements, the substitution of Co2+ ions in the ZnO NRs crystal is shown. The relation between the incorporation and core defects concentration will be discussed. The findings give access to the magnetic anisotropy of ZnO NRs grown by the low temperature chemical route and can lead to demonstrate room temperature ferromagnetism in nanostructures with potential for different device applications.

Aluminum Gallium Nitride Alloys Grown via Metalorganic Vapor-Phase Epitaxy Using a Digital Growth Technique

Science.gov (United States)

Rodak, L. E.; Korakakis, D.

2011-04-01

This work investigates the use of a digital growth technique as a viable method for achieving high-quality aluminum gallium nitride (Al x Ga1- x N) films via metalorganic vapor-phase epitaxy. Digital alloys are superlattice structures with period thicknesses of a few monolayers. Alloys with an AlN mole fraction ranging from 0.1 to 0.9 were grown by adjusting the thickness of the AlN layer in the superlattice. High-resolution x-ray diffraction was used to determine the superlattice period and c-lattice parameter of the structure, while reciprocal-space mapping was used to determine the a-lattice parameter and evaluate growth coherency. A comparison of the measured lattice parameter with both the nominal value and also the underlying buffer layer is discussed.

Lattice Dynamics of Gallium Phosphide

International Nuclear Information System (INIS)

Yarnell, J.L.; Warren, J.L.; Wenzel, R.G.; Dean, P.J.

1968-01-01

Dispersion curves for phonons propagating in the [100], [110], and [111] directions in gallium phosphide have been measured using a triple-axis neutron diffraction spectrometer operating in the constant-Q mode. The sample was a pseudo-single crystal which was prepared by gluing together 36 single crystal plates of gallium phosphide 1 to 2.5 cm in diameter and ∼0.07 cm thick. The plates were grown epitaxially on substrates of gallium arsenide or gallium phosphide, and aligned individually by neutron diffraction. Rocking curves for eight reflections symmetrically distributed in the plane of the experiment had full widths at half maximum in the range 0.52° - 0.58° and were approximately Gaussian in shape. Gallium phosphide crystallizes in the zinc blende structure. A group theoretic analysis of the lattice dynamics of this structure and a shell model fit to the measured dispersion curves are presented. Various optical properties of gallium phosphide are discussed in terms of the phonon dispersion curves. In particular, the phonons which assist indirect electronic transitions are identified as those at the zone boundary in the [100] direction (symmetry point X) in agreement with theoretical and experimental indications that the extrema of the conduction and valence bands are at X and Γ (center of the zone), respectively. The LO branches lie above the TO branches throughout the Brillouin zone in contradiction to the predictions of Keyes and Mitra. The shell model fit indicates that the charge on the gallium atom is negative. (author)

Thermal Cycling and High Temperature Reverse Bias Testing of Control and Irradiated Gallium Nitride Power Transistors

Science.gov (United States)

Patterson, Richard L.; Boomer, Kristen T.; Scheick, Leif; Lauenstein, Jean-Marie; Casey, Megan; Hammoud, Ahmad

2014-01-01

The power systems for use in NASA space missions must work reliably under harsh conditions including radiation, thermal cycling, and exposure to extreme temperatures. Gallium nitride semiconductors show great promise, but information pertaining to their performance is scarce. Gallium nitride N-channel enhancement-mode field effect transistors made by EPC Corporation in a 2nd generation of manufacturing were exposed to radiation followed by long-term thermal cycling and testing under high temperature reverse bias conditions in order to address their reliability for use in space missions. Result of the experimental work are presented and discussed.

Urchin-like artificial gallium oxide nanowires grown by a novel MOCVD/CVD-based route for random laser application

Energy Technology Data Exchange (ETDEWEB)

Melo, Ronaldo P. de [Programa de Pós-Graduação em Ciências de Materiais, Universidade Federal de Pernambuco, Recife (Brazil); Colégio Militar do Recife, Exército Brasileiro, Recife PE 50730-120 (Brazil); Oliveira, Nathalia Talita C. [Programa de Pós-Graduação em Ciências de Materiais, Universidade Federal de Pernambuco, Recife (Brazil); Dominguez, Christian Tolentino; Gomes, Anderson S. L.; Araújo, Cid B. de [Departamento de Física, Universidade Federal de Pernambuco, 50670-901 Recife (Brazil); Falcão, Eduardo H. L.; Alves, Severino; Luz, Leonis L. da [Departamento de Química Fundamental, Universidade Federal de Pernambuco, 50670-901 Recife (Brazil); Chassagnon, Remi [Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 6303 CNRS-Université de Bourgogne, 9 Av. A. Savary, BP 47870, 21078 Dijon Cedex (France); Sacilotti, Marco [Departamento de Física, Universidade Federal de Pernambuco, 50670-901 Recife (Brazil); Nanoform Group, Laboratoire Interdisciplinaire Carnot de Bourgogne, Université de Bourgogne, Dijon (France)

2016-04-28

A novel procedure based on a two-step method was developed to obtain β-Ga{sub 2}O{sub 3} nanowires by the chemical vapor deposition (CVD) method. The first step consists in the gallium micro-spheres growth inside a metal-organic chemical vapor deposition environment, using an organometallic precursor. Nanoscale spheres covering the microspheres were obtained. The second step involves the CVD oxidization of the gallium micro-spheres, which allow the formation of β-Ga{sub 2}O{sub 3} nanowires on the micro-sphere surface, with the final result being a nanostructure mimicking nature's sea urchin morphology. The grown nanomaterial is characterized by several techniques, including X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray, transmission electron microscopy, and photoluminescence. A discussion about the growth mechanism and the optical properties of the β-Ga{sub 2}O{sub 3} material is presented considering its unknown true bandgap value (extending from 4.4 to 5.68 eV). As an application, the scattering properties of the nanomaterial are exploited to demonstrate random laser emission (around 570 nm) when it is permeated with a laser dye liquid solution.

Growth temperature and dopant species effects on deep levels in Si grown by low temperature molecular beam epitaxy

International Nuclear Information System (INIS)

Chung, Sung-Yong; Jin, Niu; Rice, Anthony T.; Berger, Paul R.; Yu, Ronghua; Fang, Z-Q.; Thompson, Phillip E.

2003-01-01

Deep-level transient spectroscopy measurements were performed in order to investigate the effects of substrate growth temperature and dopant species on deep levels in Si layers during low-temperature molecular beam epitaxial growth. The structures studied were n + -p junctions using B doping for the p layer and p + -n junctions using P doping for the n layer. While the density of hole traps H1 (0.38-0.41 eV) in the B-doped p layers showed a clear increase with decreasing growth temperature from 600 to 370 degree sign C, the electron trap density was relatively constant. Interestingly, the minority carrier electron traps E1 (0.42-0.45 eV) and E2 (0.257 eV), found in the B-doped p layers, are similar to the majority carrier electron traps E11 (0.48 eV) and E22 (0.269 eV) observed in P-doped n layers grown at 600 degree sign C. It is hypothesized that these dominating electron traps are associated with pure divacancy defects and are independent of the dopant species

Gallium interstitial contributions to diffusion in gallium arsenide

Science.gov (United States)

Schick, Joseph T.; Morgan, Caroline G.

2011-09-01

A new diffusion path is identified for gallium interstitials, which involves lower barriers than the barriers for previously identified diffusion paths [K. Levasseur-Smith and N. Mousseau, J. Appl. Phys. 103, 113502 (2008), P. A. Schultz and O. A. von Lilienfeld, Modelling and Simulation in Materials Science and Engineering 17, 084007 (2009)] for the charge states which dominate diffusion over most of the available range of Fermi energies. This path passes through the ⟨110⟩ gallium-gallium split interstitial configuration, and has a particularly low diffusion barrier of 0.35 eV for diffusion in the neutral charge state. As a part of this work, the character of the charge states for the gallium interstitials which are most important for diffusion is investigated, and it is shown that the last electron bound to the neutral interstitial occupies a shallow hydrogenic bound state composed of conduction band states for the hexagonal interstitial and both tetrahedral interstitials. How to properly account for the contributions of such interstitials is discussed for density-functional calculations with a k-point mesh not including the conduction band edge point. Diffusion barriers for gallium interstitials are calculated in all the charge states which can be important for a Fermi level anywhere in the gap, q = 0, +1, +2, and +3, for diffusion via the ⟨110⟩ gallium-gallium split interstitial configuration and via the hexagonal interstitial configuration. The lowest activation enthalpies over most of the available range of Fermi energies are found to correspond to diffusion in the neutral or singly positive state via the ⟨110⟩ gallium-gallium split interstitial configuration. It is shown that several different charge states and diffusion paths contribute significantly for Fermi levels within 0.2 eV above the valence band edge, which may help to explain some of the difficulties [H. Bracht and S. Brotzmann, Phys. Rev. B 71, 115216 (2005)] which have been

Effects of annealing on the recombination dynamics of low-temperature grown ZnO nanorods

Energy Technology Data Exchange (ETDEWEB)

Hilker, B.; Bekeny, C.; Voss, T.; Gutowski, J. [IFP, Universitaet Bremen, 28334 Bremen (Germany); Hauschild, R.; Kalt, H. [Universitaet Karlsruhe, 76128 Karlsruhe (Germany); Postels, B.; Bakin, Andrey; Waag, A. [IHT, TU Braunschweig, 38023 Braunschweig (Germany)

2007-07-01

We present systematic temperature and excitation density dependent time-resolved photoluminescence (TRPL) measurements of as-grown and annealed ZnO nanorods fabricated by an aqueous chemical growth (ACG) technique at {proportional_to}90 C. The as-grown nanorods show strong nearband-edge and rather weak deep-level emission indicating their already good optical quality. At 4K, we find a broad emission line at 3.36 eV (line width 30 meV) which we attribute to recombination from a donor band formed through the high donor concentration. After annealing in oxygen and nitrogen atmospheres at 600-800 C well-resolved and sharper excitonic transitions are observed. To understand the recombination dynamics in the nanorods we carried out TRPL measurements using a frequency-doubled femtosecond laser and a streak camera. The as-grown sample shows a very fast monoexponential decay time of {proportional_to}10ps independent of temperature and excitation density. In contrast, the annealed samples exhibit a biexponential decay. Each a fast {tau}1 and a slow {tau}2 time constant have been determined for all annealed samples both of them significantly varying depending on the annealing atmosphere and temperature. This will be discussed on the basis of a phenomenological rate-equation model.

Sensitivity of the crystal quality of SiGe layers grown at low temperatures by trisilane and germane

Energy Technology Data Exchange (ETDEWEB)

Abedin, A., E-mail: aabedin@kth.se; Moeen, M.; Cappetta, C.; Östling, M.; Radamson, H.H., E-mail: rad@kth.se

2016-08-31

This work investigates the crystal quality of SiGe layers grown at low temperatures using trisilane, and germane precursors. The crystal quality sensitivity was monitored for hydrogen chloride and/or minor oxygen amount during SiGe epitaxy or at the interface of SiGe/Si layers. The quality of the epi-layers was examined by quantifying noise parameter, K{sub 1/f} obtained from the power spectral density vs. 1/f curves. The results indicate that while it is difficult to detect small defect densities in SiGe layers by physical material characterization, the noise measurement could reveal the effects of oxygen contamination as low as 0.16 mPa inside and in the interface of the layers. - Highlights: • SiGe layers were grown using trisilane and germane. • Effect of HCl flow on Ge content and growth rate was investigated. • O{sub 2} partial pressures up to 4.3 mPa did not affect x-ray diffraction pattern. • O{sub 2} partial pressures as low as 0.16 mPa increased the noise level. • HCl increased metal contaminations of the layers and the noise level consequently.

Low Temperature Reactions for the Preparation of Group 13-15 Materials from Organo-gallium(I) and -indium(I) Compounds

National Research Council Canada - National Science Library

Beachley, O

1997-01-01

...) at 175 deg C and of neopentylgallium(I) Ga(CH2CMe3)n with P4 at 350- 400 deg C and with NH3 at 460-480 deg C in sealed tubes provide routes to indium phosphide, gallium phosphide and hexagonal gallium nitride, respectively...

Growth of 1.5 micron gallium indium nitrogen arsenic antimonide vertical cavity surface emitting lasers by molecular beam epitaxy

Science.gov (United States)

Wistey, Mark Allan

Fiber optics has revolutionized long distance communication and long haul networks, allowing unimaginable data speeds and noise-free telephone calls around the world for mere pennies per hour at the trunk level. But the high speeds of optical fiber generally do not extend to individual workstations or to the home, in large part because it has been difficult and expensive to produce lasers which emitted light at wavelengths which could take advantage of optical fiber. One of the most promising solutions to this problem is the development of a new class of semiconductors known as dilute nitrides. Dilute nitrides such as GaInNAs can be grown directly on gallium arsenide, which allows well-established processing techniques. More important, gallium arsenide allows the growth of vertical-cavity surface-emitting lasers (VCSELs), which can be grown in dense, 2D arrays on each wafer, providing tremendous economies of scale for manufacturing, testing, and packaging. Unfortunately, GaInNAs lasers have suffered from what has been dubbed the "nitrogen penalty," with high thresholds and low efficiency as the fraction of nitrogen in the semiconductor was increased. This thesis describes the steps taken to identify and essentially eliminate the nitrogen penalty. Protecting the wafer surface from plasma ignition, using an arsenic cap, greatly improved material quality. Using a Langmuir probe, we further found that the nitrogen plasma source produced a large number of ions which damaged the wafer during growth. The ions were dramatically reduced using deflection plates. Low voltage deflection plates were found to be preferable to high voltages, and simulations showed low voltages to be adequate for ion removal. The long wavelengths from dilute nitrides can be partly explained by wafer damage during growth. As a result of these studies, we demonstrated the first CW, room temperature lasers at wavelengths beyond 1.5mum on gallium arsenide, and the first GaInNAs(Sb) VCSELs beyond 1

Uniform GaN thin films grown on (100) silicon by remote plasma atomic layer deposition

International Nuclear Information System (INIS)

Shih, Huan-Yu; Chen, Miin-Jang; Lin, Ming-Chih; Chen, Liang-Yih

2015-01-01

The growth of uniform gallium nitride (GaN) thin films was reported on (100) Si substrate by remote plasma atomic layer deposition (RP-ALD) using triethylgallium (TEG) and NH 3 as the precursors. The self-limiting growth of GaN was manifested by the saturation of the deposition rate with the doses of TEG and NH 3 . The increase in the growth temperature leads to the rise of nitrogen content and improved crystallinity of GaN thin films, from amorphous at a low deposition temperature of 200 °C to polycrystalline hexagonal structures at a high growth temperature of 500 °C. No melting-back etching was observed at the GaN/Si interface. The excellent uniformity and almost atomic flat surface of the GaN thin films also infer the surface control mode of the GaN thin films grown by the RP-ALD technique. The GaN thin films grown by RP-ALD will be further applied in the light-emitting diodes and high electron mobility transistors on (100) Si substrate. (paper)

Post-annealing effects on pulsed laser deposition-grown GaN thin films

International Nuclear Information System (INIS)

Cheng, Yu-Wen; Wu, Hao-Yu; Lin, Yu-Zhong; Lee, Cheng-Che; Lin, Ching-Fuh

2015-01-01

In this work, the post-annealing effects on gallium nitride (GaN) thin films grown from pulsed laser deposition (PLD) are investigated. The as-deposited GaN thin films grown from PLD are annealed at different temperatures in nitrogen ambient. Significant changes of the GaN crystal properties are observed. Raman spectroscopy is used to observe the crystallinity, the change of residual stress, and the thermal decomposition of the annealed GaN thin films. X-ray diffraction is also applied to identify the crystal phase of GaN thin films, and the surface morphology of GaN thin films annealed at different temperatures is observed by scanning electron microscopy. Through the above analyses, the GaN thin films grown by PLD undergo three stages: phase transition, stress alteration, and thermal decomposition. At a low annealing temperature, the rock salt GaN in GaN films is transformed into wurtzite. The rock salt GaN diminishes with increasing annealing temperature. At a medium annealing temperature, the residual stress of the film changes significantly from compressive strain to tensile strain. As the annealing temperature further increases, the GaN undergoes thermal decomposition and the surface becomes granular. By investigating the annealing temperature effects and controlling the optimized annealing temperature of the GaN thin films, we are able to obtain highly crystalline and strain-free GaN thin films by PLD. - Highlights: • The GaN thin film is grown on sapphire by pulsed laser deposition. • The GaN film undergoes three stages with increasing annealing temperature. • In the first stage, the film transfers from rock salt to wurtzite phase. • In the second stage, the stress in film changes from compressive to tensile. • In the final stage, the film thermally decomposes and becomes granular

Effects of O2 plasma post-treatment on ZnO: Ga thin films grown by H2O-thermal ALD

Science.gov (United States)

Lee, Yueh-Lin; Chuang, Jia-Hao; Huang, Tzu-Hsuan; Ho, Chong-Long; Wu, Meng-Chyi

2013-03-01

Transparent conducting oxides have been widely employed in optoelectronic devices using the various deposition methods such as sputtering, thermal evaporator, and e-gun evaporator technologies.1-3 In this work, gallium doped zinc oxide (ZnO:Ga) thin films were grown on glass substrates via H2O-thermal atomic layer deposition (ALD) at different deposition temperatures. ALD-GZO thin films were constituted as a layer-by-layer structure by stacking zinc oxides and gallium oxides. Diethylzinc (DEZ), triethylgallium (TEG) and H2O were used as zinc, gallium precursors and oxygen source, respectively. Furthermore, we investigated the influences of O2 plasma post-treatment power on the surface morphology, electrical and optical property of ZnO:Ga films. As the result of O2 plasma post-treatment, the characteristics of ZnO:Ga films exhibit a smooth surface, low resistivity, high carrier concentration, and high optical transmittance in the visible spectrum. However, the transmittance decreases with O2 plasma power in the near- and mid-infrared regions.

TEM EDS analysis of epitaxially-grown self-assembled indium islands

Directory of Open Access Journals (Sweden)

Jasmine Sears

2017-05-01

Full Text Available Epitaxially-grown self-assembled indium nanostructures, or islands, show promise as nanoantennas. The elemental composition and internal structure of indium islands grown on gallium arsenide are explored using Transmission Electron Microscopy (TEM Energy Dispersive Spectroscopy (EDS. Several sizes of islands are examined, with larger islands exhibiting high (>94% average indium purity and smaller islands containing inhomogeneous gallium and arsenic contamination. These results enable more accurate predictions of indium nanoantenna behavior as a function of growth parameters.

Surface Roughness and Grain Size Characterization of Annealing Temperature Effect For Growth Gallium and Tantalum Doped Ba0.5 Sr0.5TiO3Thin Film

Directory of Open Access Journals (Sweden)

Irzaman

2009-01-01

Full Text Available Thin films 10 % gallium oxide doped barium strontium titanate (BGST and 10 % tantalum oxide doped barium strontium titanate (BTST were prepared on p-type Si (100 substrates using chemical solution deposition (CSD method with 1.00 M precursor. The films were deposited by spin coating method with spinning speed at 3000 rpm for 30 seconds. The post deposition annealing of the films were carried out in a furnace at 200oC, 240oC, 280oC (low temperature for 1 hour in oxygen gas atmosphere. The surface roughness and grain size analysis of the grown thin films are described by atomic force microscope (AFM method at 5000 nm x 5000 nm area. The rms surface roughness BGST thin films at 5000 nm x 5000 nm area are 0.632 nm, 0.564 nm, 0.487 nm for temperature 200oC, 240oC, 280oC, respectively, whereas the grain size (mean diameter are 238.4 nm, 219.0 nm, 185.1 nm for temperature 200oC, 240oC, 280oC, respectively. In fact, to increase annealing temperature from 200oC to 280oC would result in decreasing the rms roughness and grain size. Therefore, rms roughness and grain size would have the strong correlation annealing temperature.

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.

Role of low O 2 pressure and growth temperature on electrical transport of PLD grown ZnO thin films on Si substrates

Science.gov (United States)

Pandis, Ch.; Brilis, N.; Tsamakis, D.; Ali, H. A.; Krishnamoorthy, S.; Iliadis, A. A.

2006-06-01

Undoped ZnO thin films have been grown on (100) Si substrates by pulsed laser deposition. The effect of growth parameters such as temperature, O 2 partial pressure and laser fluence on the structural and electrical properties of the films has been investigated. It is shown that the well-known native n-type conductivity, attributed to the activation of hydrogenic donor states, exhibits a conversion from n-type to p-type when the O 2 partial pressure is reduced from 10 -4 to 10 -7 Torr at growth temperatures lower than 400 °C. The p-type conductivity could be attributed to the dominant role of the acceptor Zn vacancies for ZnO films grown at very low O 2 pressures.

Gallium-cladding compatibility testing plan. Phases 1 and 2: Test plan for gallium corrosion tests. Revision 2

International Nuclear Information System (INIS)

Wilson, D.F.; Morris, R.N.

1998-05-01

This test plan is a Level-2 document as defined in the Fissile Materials Disposition Program Light-Water-Reactor Mixed-Oxide Fuel Irradiation Test Project Plan. The plan summarizes and updates the projected Phases 1 and 2 Gallium-Cladding compatibility corrosion testing and the following post-test examination. This work will characterize the reactions and changes, if any, in mechanical properties that occur between Zircaloy clad and gallium or gallium oxide in the temperature range 30--700 C

Low-temperature fabrication of an HfO2 passivation layer for amorphous indium-gallium-zinc oxide thin film transistors using a solution process.

Science.gov (United States)

Hong, Seonghwan; Park, Sung Pyo; Kim, Yeong-Gyu; Kang, Byung Ha; Na, Jae Won; Kim, Hyun Jae

2017-11-24

We report low-temperature solution processing of hafnium oxide (HfO 2 ) passivation layers for amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs). At 150 °C, the hafnium chloride (HfCl 4 ) precursor readily hydrolyzed in deionized (DI) water and transformed into an HfO 2 film. The fabricated HfO 2 passivation layer prevented any interaction between the back surface of an a-IGZO TFT and ambient gas. Moreover, diffused Hf 4+ in the back-channel layer of the a-IGZO TFT reduced the oxygen vacancy, which is the origin of the electrical instability in a-IGZO TFTs. Consequently, the a-IGZO TFT with the HfO 2 passivation layer exhibited improved stability, showing a decrease in the threshold voltage shift from 4.83 to 1.68 V under a positive bias stress test conducted over 10,000 s.

Gallium-containing polymer brush film as efficient supported Lewis acid catalyst in a glass microreactor

Directory of Open Access Journals (Sweden)

Rajesh Munirathinam

2013-08-01

Full Text Available Polystyrene sulfonate polymer brushes, grown on the interior of the microchannels in a microreactor, have been used for the anchoring of gallium as a Lewis acid catalyst. Initially, gallium-containing polymer brushes were grown on a flat silicon oxide surface and were characterized by FTIR, ellipsometry, and X-ray photoelectron spectroscopy (XPS. XPS revealed the presence of one gallium per 2–3 styrene sulfonate groups of the polymer brushes. The catalytic activity of the Lewis acid-functionalized brushes in a microreactor was demonstrated for the dehydration of oximes, using cinnamaldehyde oxime as a model substrate, and for the formation of oxazoles by ring closure of ortho-hydroxy oximes. The catalytic activity of the microreactor could be maintained by periodic reactivation by treatment with GaCl3.

Spin filtering neutrons with a proton target dynamically polarized using photo-excited triplet states

International Nuclear Information System (INIS)

Haag, M.; Brandt, B. van den; Eichhorn, T.R.; Hautle, P.; Wenckebach, W.Th.

2012-01-01

In a test of principle a neutron spin filter has been built, which is based on dynamic nuclear polarization (DNP) using photo-excited triplet states. This DNP method has advantages over classical concepts as the requirements for cryogenic equipment and magnets are much relaxed: the spin filter is operated in a field of 0.3 T at a temperature of about 100 K and has performed reliably over periods of several weeks. The neutron beam was also used to analyze the polarization of the target employed as a spin filter. We obtained an independent measurement of the proton spin polarization of ∼0.13 in good agreement with the value determined with NMR. Moreover, the neutron beam was used to measure the proton spin polarization as a function of position in the naphthalene sample. The polarization was found to be homogeneous, even at low laser power, in contradiction to existing models describing the photo-excitation process.

Photoexcitation electron paramagnetic resonance studies on nickel-related defects in diamond

CERN Document Server

Pereira, R N; Neves, A J; Sobolev, N A

2003-01-01

Measurements of the electron paramagnetic resonance (EPR) upon photoexcitation are reported on Ni defects in diamonds grown with Ni-containing solvent/catalysts. The temperature dependence of the W8 EPR spectrum photoquenching shows that the relaxation of substitutional Ni sub s sup - upon electron ionization is very small, corroborating the interpretation that the previously reported photoinduced effects with thresholds at 2.5 and 3.0 eV correspond to two complementary photoionization transitions involving Ni sub s. Photoinduced behaviour of the NIRIM1 EPR centre favours the interstitial Ni sub i sup + model for this defect and suggests that the Ni sub i sup 0 sup / sup + level is located at 1.98 +- 0.03 eV below the conduction band. In N-doped diamond, Ni sub i is more likely to appear in the neutral state, undetectable by EPR, whereas at substitutional sites Ni sub s sup - is revealed. Observation of a strong AB2 EPR signal photoquenching and simultaneous detection of different spectral dependencies of the...

Role of many-body effects in the coherent dynamics of excitons in low-temperature-grown GaAs

Energy Technology Data Exchange (ETDEWEB)

Webber, D.; Hacquebard, L.; Hall, K. C. [Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia B3H 4R2 (Canada); Liu, X.; Dobrowolska, M.; Furdyna, J. K. [Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556 (United States)

2015-10-05

Femtosecond four-wave mixing experiments on low-temperature-grown (LT-) GaAs indicate a polarization-dependent nonlinear optical response at the exciton, which we attribute to Coulomb-mediated coupling between excitons and electron-hole pairs simultaneously excited by the broad-bandwidth laser pulses. Strong suppression of the exciton response through screening by carriers injected by a third pump pulse was observed, an effect that is transient due to rapid carrier trapping. Our findings highlight the need to account for the complex interplay of disorder and many-body effects in the design of ultrafast optoelectronic devices using this material.

Fabrication and properties of gallium metallic photonic crystals

International Nuclear Information System (INIS)

Kozhevnikov, V.F.; Diwekar, M.; Kamaev, V.P.; Shi, J.; Vardeny, Z.V.

2003-01-01

Gallium metallic photonic crystals with 100% filling factor have been fabricated via infiltration of liquid gallium into opals of 300-nm silica spheres using a novel high pressure-high temperature technique. The electrical resistance of the Ga-opal crystals was measured at temperatures from 10 to 280 K. The data obtained show that Ga-opal crystals are metallic network with slightly smaller temperature coefficient of resistivity than that for bulk gallium. Optical reflectivity of bulk gallium, plain opal and several Ga-opal crystals were measured at photon energies from 0.3 to 6 eV. A pronounced photonic stop band in the visible spectral range was found in both the plain and Ga infiltrated opals. The reflectivity spectra also show increase in reflectivity below 0.6 eV; which we interpret as a significantly lower effective plasma frequency of the metallic mesh in the infiltrated opal compare to the plasma frequency in the pure metal

Gallium

Science.gov (United States)

Foley, Nora K.; Jaskula, Brian W.; Kimball, Bryn E.; Schulte, Ruth F.; Schulz, Klaus J.; DeYoung,, John H.; Seal, Robert R.; Bradley, Dwight C.

2017-12-19

Gallium is a soft, silvery metallic element with an atomic number of 31 and the chemical symbol Ga. Gallium is used in a wide variety of products that have microelectronic components containing either gallium arsenide (GaAs) or gallium nitride (GaN). GaAs is able to change electricity directly into laser light and is used in the manufacture of optoelectronic devices (laser diodes, light-emitting diodes [LEDs], photo detectors, and solar cells), which are important for aerospace and telecommunications applications and industrial and medical equipment. GaAs is also used in the production of highly specialized integrated circuits, semiconductors, and transistors; these are necessary for defense applications and high-performance computers. For example, cell phones with advanced personal computer-like functionality (smartphones) use GaAs-rich semiconductor components. GaN is used principally in the manufacture of LEDs and laser diodes, power electronics, and radio-frequency electronics. Because GaN power transistors operate at higher voltages and with a higher power density than GaAs devices, the uses for advanced GaN-based products are expected to increase in the future. Gallium technologies also have large power-handling capabilities and are used for cable television transmission, commercial wireless infrastructure, power electronics, and satellites. Gallium is also used for such familiar applications as screen backlighting for computer notebooks, flat-screen televisions, and desktop computer monitors.Gallium is dispersed in small amounts in many minerals and rocks where it substitutes for elements of similar size and charge, such as aluminum and zinc. For example, gallium is found in small amounts (about 50 parts per million) in such aluminum-bearing minerals as diaspore-boehmite and gibbsite, which form bauxite deposits, and in the zinc-sulfide mineral sphalerite, which is found in many mineral deposits. At the present time, gallium metal is derived mainly as a

Transient transition from free carrier metallic state to exciton insulating state in GaAs by ultrafast photoexcitation

Science.gov (United States)

Nie, X. C.; Song, Hai-Ying; Zhang, Xiu; Gu, Peng; Liu, Shi-Bing; Li, Fan; Meng, Jian-Qiao; Duan, Yu-Xia; Liu, H. Y.

2018-03-01

We present systematic studies of the transient dynamics of GaAs by ultrafast time-resolved reflectivity. In photoexcited non-equilibrium states, we found a sign reverse in reflectivity change ΔR/R, from positive around room temperature to negative at cryogenic temperatures. The former corresponds to a free carrier metallic state, while the latter is attributed to an exciton insulating state, in which the transient electronic properties is mostly dominated by excitons, resulting in a transient metal–insulator transition (MIT). Two transition temperatures (T 1 and T 2) are well identified by analyzing the intensity change of the transient reflectivity. We found that photoexcited MIT starts emerging at T 1 as high as ∼ 230 K, in terms of a dip feature at 0.4 ps, and becomes stabilized below T 2 that is up to ∼ 180 K, associated with a negative constant after 40 ps. Our results address a phase diagram that provides a framework for the inducing of MIT through temperature and photoexcitation, and may shed light on the understanding of light-semiconductor interaction and exciton physics.

Gallium hole traps in irradiated KTiOPO{sub 4}:Ga crystals

Energy Technology Data Exchange (ETDEWEB)

Grachev, V.; Meyer, M.; Malovichko, G. [Physics Department, Montana State University, Bozeman, Montana 59717 (United States); Hunt, A. W. [Idaho Accelerator Center, Idaho State University, Pocatello, Idaho 83209 (United States)

2014-12-07

Nominally pure and gallium doped single crystals of potassium titanyl phosphate (KTiOPO{sub 4}) have been studied by Electron Paramagnetic Resonance at low temperatures before and after irradiation. Irradiation with 20 MeV electrons performed at room temperature and liquid nitrogen temperature caused an appearance of electrons and holes. Gallium impurities act as hole traps in KTiOPO{sub 4} creating Ga{sup 4+} centers. Two different Ga{sup 4+} centers were observed, Ga1 and Ga2. The Ga1 centers are dominant in Ga-doped samples. For the Ga1 center, a superhyperfine structure with one nucleus with nuclear spin ½ was registered and attributed to the interaction of gallium electrons with a phosphorus nucleus or proton in its surrounding. In both Ga1 and Ga2 centers, Ga{sup 4+} ions substitute for Ti{sup 4+} ions, but with a preference to one of two electrically distinct crystallographic positions (site selective substitution). The Ga doping eliminates one of the shortcomings of KTP crystals—ionic conductivity of bulk crystals. However, this does not improve significantly the resistance of the crystals to electron and γ-radiation.

Neutron detection using boron gallium nitride semiconductor material

Directory of Open Access Journals (Sweden)

Katsuhiro Atsumi

2014-03-01

Full Text Available In this study, we developed a new neutron-detection device using a boron gallium nitride (BGaN semiconductor in which the B atom acts as a neutron converter. BGaN and gallium nitride (GaN samples were grown by metal organic vapor phase epitaxy, and their radiation detection properties were evaluated. GaN exhibited good sensitivity to α-rays but poor sensitivity to γ-rays. Moreover, we confirmed that electrons were generated in the depletion layer under neutron irradiation. This resulted in a neutron-detection signal after α-rays were generated by the capture of neutrons by the B atoms. These results prove that BGaN is useful as a neutron-detecting semiconductor material.

Effect of growth temperature on defects in epitaxial GaN film grown by plasma assisted molecular beam epitaxy

Directory of Open Access Journals (Sweden)

S. S. Kushvaha

2014-02-01

Full Text Available We report the effect of growth temperature on defect states of GaN epitaxial layers grown on 3.5 μm thick GaN epi-layer on sapphire (0001 substrates using plasma assisted molecular beam epitaxy. The GaN samples grown at three different substrate temperatures at 730, 740 and 750 °C were characterized using atomic force microscopy and photoluminescence spectroscopy. The atomic force microscopy images of these samples show the presence of small surface and large hexagonal pits on the GaN film surfaces. The surface defect density of high temperature grown sample is smaller (4.0 × 108 cm−2 at 750 °C than that of the low temperature grown sample (1.1 × 109 cm−2 at 730 °C. A correlation between growth temperature and concentration of deep centre defect states from photoluminescence spectra is also presented. The GaN film grown at 750 °C exhibits the lowest defect concentration which confirms that the growth temperature strongly influences the surface morphology and affects the optical properties of the GaN epitaxial films.

Surface Passivation of CIGS Solar Cells Using Gallium Oxide

KAUST Repository

Garud, Siddhartha

2018-02-27

This work proposes gallium oxide grown by plasma-enhanced atomic layer deposition, as a surface passivation material at the CdS buffer interface of Cu(In,Ga)Se2 (CIGS) solar cells. In preliminary experiments, a metal-insulator-semiconductor (MIS) structure is used to compare aluminium oxide, gallium oxide, and hafnium oxide as passivation layers at the CIGS-CdS interface. The findings suggest that gallium oxide on CIGS may show a density of positive charges and qualitatively, the least interface trap density. Subsequent solar cell results with an estimated 0.5 nm passivation layer show an substantial absolute improvement of 56 mV in open-circuit voltage (VOC), 1 mA cm−2 in short-circuit current density (JSC), and 2.6% in overall efficiency as compared to a reference (with the reference showing 8.5% under AM 1.5G).

High purity liquid phase epitaxial gallium arsenide nuclear radiation detector

International Nuclear Information System (INIS)

Alexiev, D.; Butcher, K.S.A.

1991-11-01

Surface barrier radiation detector made from high purity liquid phase epitaxial gallium arsenide wafers have been operated as X- and γ-ray detectors at various operating temperatures. Low energy isotopes are resolved including 241 Am at 40 deg C. and the higher gamma energies of 235 U at -80 deg C. 15 refs., 1 tab., 6 figs

Ultrafast photocurrents and terahertz radiation in gallium arsenide and carbon based nanostructures

Energy Technology Data Exchange (ETDEWEB)

Prechtel, Hans Leonhard

2011-08-15

In this thesis we developed a measurement technique based on a common pump-probe scheme and coplanar stripline circuits that enables time-resolved photocurrent measurements of contacted nanosystems with a micrometer spatial and a picosecond time resolution. The measurement technique was applied to lowtemperature grown gallium arsenide (LT-GaAs), carbon nanotubes (CNTs), graphene, and p-doped gallium arsenide (GaAs) nanowires. The various mechanisms responsible for the generation of current pulses by pulsed laser excitation were reviewed. Furthermore the propagation of the resulting electromagnetic radiation along a coplanar stripline circuit was theoretically and numerically treated. The ultrafast photocurrent response of low-temperature grown GaAs was investigated. We found two photocurrent pulses in the time-resolved response. We showed that the first pulse is consistent with a displacement current pulse. We interpreted the second pulse to result from a transport current process. We further determined the velocity of the photo-generated charge carriers to exceed the drift, thermal and quantum velocities of single charge carriers. Hereby, we interpreted the transport current pulse to stem from an electron-hole plasma excitation. We demonstrated that the photocurrent response of CNTs comprises an ultrafast displacement current and a transport current. The data suggested that the photocurrent is finally terminated by the recombination lifetime of the charge carriers. To the best of our knowledge, we presented in this thesis the first recombination lifetime measurements of contacted, suspended, CVD grown CNT networks. In addition, we studied the ultrafast photocurrent dynamics of freely suspended graphene contacted by metal electrodes. At the graphene-metal interface, we demonstrated that built-in electric fields give rise to a photocurrent with a full-width-half-maximum of a few picoseconds and that a photo-thermoelectric effect generates a current with a decay time

Fundamental investigation of high temperature operation of field effect transistor devices

Science.gov (United States)

Chern, Jehn-Huar

In this dissertation copper germanium (CuGe)-based materials were investigated as potential ohmic contacts to n-type gallium arsenide (GaAs). The CuGe-based contacts to GaAs were found to not form any reaction products with GaAs and to have low contact resistance comparable to that of nickel gold germanium (NiAuGe) ohmic contacts to GaAs. The potential for high temperature applications using CuGe ohmic contacts was investigated. A guideline for further reduction of the contact resistance has been achieved after investigating the detailed mechanism of the formation of binary CuGe contacts over a wide range of Ge concentrations. The thermal stability of CuGe contacts was significantly enhanced and improved by introducing a diffusion barrier, titanium tungsten nitride (TiWNx), and a gold (Au) overlayer for high temperature applications. Novel approaches such as epitaxial thulium phosphide (TmP) Schottky contacts and the utilization of low temperature (LT)-aluminum gallium arsenide (AlGaAs) were also investigated in this dissertation and likely will be the standard technologies for a new generation of high-temperature electronics. Inserting a layer of aluminum arsenide (AlAs) underneath the channel of a GaAs-based MESFET was found to reduce substrate leakage currents by a factor of 30 compared with the same MESFET directly fabricated on a semi-insulating GaAs substrate. In addition to AlAs, and AlxGa1-xAs materials, new materials grown at low temperatures such as LT-AlGaAs were used in heterojunction FET structures as a back wall barrier. Low drain leakage currents were achieved using AlAs and LT-AlGaAs as the back wall barriers. Some fundamental properties regarding these materials are of great interest and in need of further characterization. Part of the work in this dissertation was devoted to the characterization of device performance for different structure designs at elevated temperatures. The suitability of GaAs-based and gallium arsenide (GaN)-based MESFET

Photo-excited states in germanium at liquid-helium temperatures

International Nuclear Information System (INIS)

Culbertson, J.C.

1982-12-01

A wide variety of experimental work dealing with the basic properties of photoexcited states in Ge at liquid helium temperatures is presented. The primary emphasis is on the electron-hole liquid (EHL) and the free exciton (FE). The EHL is composed of two interpenetrating Fermi liquids, one of electrons and one of holes, each with its own Fermi level. The FE dealt with here is a mobile, loosely bound state of an electron and a hole. We report the first absolute measurement of the density dependence of the enhancement factor g/sub eh/(0) for the EHL in Ge. This factor g/sub eh/(0) is a measure of the electron-hole spatial correlation function, and provides a valuable and sensitive test for the predictions of various many-body-theory approximations. An EHL droplet - FE gas system confined to a strain induced potential well was used. The measurement approach relied on only a few simple and verifiable assumptions. A byproduct of this work was the measurement as a function of stress of: the electron and hole Fermi levels E/sub F//sup e/ and E/sub F//sup h/, the EHL density n/sub l/, the condensation energy phi of a FE relative to the EHL, and the binding energy of a FE (E/sub x/) relative to free carriers (FC). The decay of a FE-FC system confined to a strain induced potential well is studied. The first direct measurement of the FE diffusivity D/sub x/ is reported. The evolution in time of spatial profiles of FE luminescence were measured. From these FE density profiles, D/sub x/(4.2K) approx. = to 300 cm 2 s - 1 , the surface recombination velocity S approx. = 3000 cm s - 1 , and the FE lifetime tau/sub x/ = 27 μs with surface effects excluded were determined

Carbon and nitrogen metabolism in arbuscular mycorrhizal maize plants under low-temperature stress

DEFF Research Database (Denmark)

Zhu, Xian-Can; Song, Feng-Bin; Liu, Fulai

2015-01-01

Effects of the arbuscular mycorrhizal (AM) fungus Glomus tortuosum on carbon (C) and nitrogen (N) metabolism of Zea mays L. grown under low-temperature stress was investigated. Maize plants inoculated or not inoculated with AM fungus were grown in a growth chamber at 258C for 4 weeks...... temperature regimes. AM symbiosis modulated C metabolic enzymes, thereby inducing an accumulation of soluble sugars, which may have contributed to an increased tolerance to low temperature, and therefore higher Pn in maize plants....

Toxicity of indium arsenide, gallium arsenide, and aluminium gallium arsenide

International Nuclear Information System (INIS)

Tanaka, Akiyo

2004-01-01

Gallium arsenide (GaAs), indium arsenide (InAs), and aluminium gallium arsenide (AlGaAs) are semiconductor applications. Although the increased use of these materials has raised concerns about occupational exposure to them, there is little information regarding the adverse health effects to workers arising from exposure to these particles. However, available data indicate these semiconductor materials can be toxic in animals. Although acute and chronic toxicity of the lung, reproductive organs, and kidney are associated with exposure to these semiconductor materials, in particular, chronic toxicity should pay much attention owing to low solubility of these materials. Between InAs, GaAs, and AlGaAs, InAs was the most toxic material to the lung followed by GaAs and AlGaAs when given intratracheally. This was probably due to difference in the toxicity of the counter-element of arsenic in semiconductor materials, such as indium, gallium, or aluminium, and not arsenic itself. It appeared that indium, gallium, or aluminium was toxic when released from the particles, though the physical character of the particles also contributes to toxic effect. Although there is no evidence of the carcinogenicity of InAs or AlGaAs, GaAs and InP, which are semiconductor materials, showed the clear evidence of carcinogenic potential. It is necessary to pay much greater attention to the human exposure of semiconductor materials

Low temperature transport in p-doped InAs nanowires

DEFF Research Database (Denmark)

Upadhyay, Shivendra; Jespersen, Thomas Sand; Madsen, Morten Hannibal

2013-01-01

We present low temperature electrical measurements of p-type Indium Arsenide nanowires grown via molecular beam epitaxy using Beryllium as a dopant. Growth of p-type wires without stacking faults is demonstrated. Devices in field-effect geometries exhibit ambipolar behavior, and the temperature...

Theory of Primary Photoexcitations in Donor-Acceptor Copolymers

OpenAIRE

Aryanpour, Karan; Dutta, Tirthankar; Huynh, Uyen N. V.; Vardeny, Zeev Valy; Mazumdar, Sumit

2015-01-01

We present a generic theory of primary photoexcitations in low band gap donor-acceptor conjugated copolymers. Because of the combined effects of strong electron correlations and broken symmetry, there is considerable mixing between a charge-transfer exciton and an energetically proximate triplet-triplet state with an overall spin singlet. The triplet-triplet state, optically forbidden in homopolymers, is allowed in donor-acceptor copolymers. For an intermediate difference in electron affiniti...

Photo-excitation of carotenoids causes cytotoxicity via singlet oxygen production

International Nuclear Information System (INIS)

Yoshii, Hiroshi; Yoshii, Yukie; Asai, Tatsuya; Furukawa, Takako; Takaichi, Shinichi; Fujibayashi, Yasuhisa

2012-01-01

Highlights: ► Some photo-excited carotenoids have photosensitizing ability. ► They are able to produce ROS. ► Photo-excited fucoxanthin can produce singlet oxygen through energy transfer. -- Abstract: Carotenoids, natural pigments widely distributed in algae and plants, have a conjugated double bond system. Their excitation energies are correlated with conjugation length. We hypothesized that carotenoids whose energy states are above the singlet excited state of oxygen (singlet oxygen) would possess photosensitizing properties. Here, we demonstrated that human skin melanoma (A375) cells are damaged through the photo-excitation of several carotenoids (neoxanthin, fucoxanthin and siphonaxanthin). In contrast, photo-excitation of carotenoids that possess energy states below that of singlet oxygen, such as β-carotene, lutein, loroxanthin and violaxanthin, did not enhance cell death. Production of reactive oxygen species (ROS) by photo-excited fucoxanthin or neoxanthin was confirmed using a reporter assay for ROS production with HeLa Hyper cells, which express a fluorescent indicator protein for intracellular ROS. Fucoxanthin and neoxanthin also showed high cellular penetration and retention. Electron spin resonance spectra using 2,2,6,6-tetramethil-4-piperidone as a singlet oxygen trapping agent demonstrated that singlet oxygen was produced via energy transfer from photo-excited fucoxanthin to oxygen molecules. These results suggest that carotenoids such as fucoxanthin, which are capable of singlet oxygen production through photo-excitation and show good penetration and retention in target cells, are useful as photosensitizers in photodynamic therapy for skin disease.

Atmospheric pressure chemical vapor deposition (APCVD) grown bi-layer graphene transistor characteristics at high temperature

KAUST Repository

Qaisi, Ramy M.; Smith, Casey; Hussain, Muhammad Mustafa

2014-01-01

We report the characteristics of atmospheric chemical vapor deposition grown bilayer graphene transistors fabricated on ultra-scaled (10 nm) high-κ dielectric aluminum oxide (Al2O3) at elevated temperatures. We observed that the drive current increased by >400% as temperature increased from room temperature to 250 °C. Low gate leakage was maintained for prolonged exposure at 100 °C but increased significantly at temperatures >200 °C. These results provide important insights for considering chemical vapor deposition graphene on aluminum oxide for high temperature applications where low power and high frequency operation are required. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Atmospheric pressure chemical vapor deposition (APCVD) grown bi-layer graphene transistor characteristics at high temperature

KAUST Repository

Qaisi, Ramy M.

2014-05-15

We report the characteristics of atmospheric chemical vapor deposition grown bilayer graphene transistors fabricated on ultra-scaled (10 nm) high-κ dielectric aluminum oxide (Al2O3) at elevated temperatures. We observed that the drive current increased by >400% as temperature increased from room temperature to 250 °C. Low gate leakage was maintained for prolonged exposure at 100 °C but increased significantly at temperatures >200 °C. These results provide important insights for considering chemical vapor deposition graphene on aluminum oxide for high temperature applications where low power and high frequency operation are required. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Low-frequency noise properties in Pt-indium gallium zinc oxide Schottky diodes

Energy Technology Data Exchange (ETDEWEB)

Zhang, Jiawei; Zhang, Linqing; Ma, Xiaochen; Wilson, Joshua [School of Electrical and Electronic Engineering, University of Manchester, Manchester M13 9PL (United Kingdom); Jin, Jidong [Department of Electrical Engineering and Electronics, University of Liverpool, Liverpool L69 3GJ (United Kingdom); Du, Lulu; Xin, Qian [School of Physics, Shandong University, Jinan 250100 (China); Song, Aimin, E-mail: A.Song@manchester.ac.uk [School of Electrical and Electronic Engineering, University of Manchester, Manchester M13 9PL (United Kingdom); School of Physics, Shandong University, Jinan 250100 (China)

2015-08-31

The low-frequency noise properties of Pt-indium gallium zinc oxide (IGZO) Schottky diodes at different forward biases are investigated. The IGZO layer and Pt contact were deposited by RF sputtering at room temperature. The diode showed an ideality factor of 1.2 and a barrier height of 0.94 eV. The current noise spectral density exhibited 1/f behavior at low frequencies. The analysis of the current dependency of the noise spectral density revealed that for the as-deposited diode, the noise followed Luo's mobility and diffusivity fluctuation model in the thermionic-emission-limited region and Hooge's empirical theory in the series-resistance-limited region. A low Hooge's constant of 1.4 × 10{sup −9} was found in the space-charge region. In the series-resistance-limited region, the Hooge's constant was 2.2 × 10{sup −5}. After annealing, the diode showed degradation in the electrical performance. The interface-trap-induced noise dominated the noise spectrum. By using the random walk model, the interface-trap density was obtained to be 3.6 × 10{sup 15 }eV{sup −1 }cm{sup −2}. This work provides a quantitative approach to analyze the properties of Pt-IGZO interfacial layers. These low noise properties are a prerequisite to the use of IGZO Schottky diodes in switch elements in memory devices, photosensors, and mixer diodes.

On the nature of gallium species in gallium-modified mordenite and MFI zeolites. A comparative DRIFT study of carbon monoxide adsorption and hydrogen dissociation.

Science.gov (United States)

Serykh, Alexander I; Kolesnikov, Stanislav P

2011-04-21

The results of a DRIFT study of carbon monoxide molecular adsorption and hydrogen dissociative adsorption on gallium-modified mordenite and MFI (ZSM-5) zeolites are presented. It was found that in the reduced gallium-modified mordenite (Ga-MOR) both Ga(3+) and Ga(+) exchanged cations are present and can be detected by CO adsorption. Ga(3+) cations in Ga-MOR dissociatively adsorb molecular hydrogen at elevated temperatures, resulting in the formation of gallium hydride species and acidic hydroxyl groups. In the reduced Ga-MFI evacuated at 823 K under medium vacuum conditions only Ga(+) exchanged intrazeolite cations were detected. It was found, however, that Ga(3+) intrazeolite exchanged cations which form upon high-temperature disproportionation of Ga(+) cations in the reduced Ga-MFI and Ga-MOR can be stabilized by high-temperature oxidation of these zeolites.

Vapor-solid-solid grown Ge nanowires at integrated circuit compatible temperature by molecular beam epitaxy

Science.gov (United States)

Zhu, Zhongyunshen; Song, Yuxin; Zhang, Zhenpu; Sun, Hao; Han, Yi; Li, Yaoyao; Zhang, Liyao; Xue, Zhongying; Di, Zengfeng; Wang, Shumin

2017-09-01

We demonstrate Au-assisted vapor-solid-solid (VSS) growth of Ge nanowires (NWs) by molecular beam epitaxy at the substrate temperature of ˜180 °C, which is compatible with the temperature window for Si-based integrated circuit. Low temperature grown Ge NWs hold a smaller size, similar uniformity, and better fit with Au tips in diameter, in contrast to Ge NWs grown at around or above the eutectic temperature of Au-Ge alloy in the vapor-liquid-solid (VLS) growth. Six ⟨110⟩ growth orientations were observed on Ge (110) by the VSS growth at ˜180 °C, differing from only one vertical growth direction of Ge NWs by the VLS growth at a high temperature. The evolution of NWs dimension and morphology from the VLS growth to the VSS growth is qualitatively explained by analyzing the mechanism of the two growth modes.

Accelerated carrier recombination by grain boundary/edge defects in MBE grown transition metal dichalcogenides

Science.gov (United States)

Chen, Ke; Roy, Anupam; Rai, Amritesh; Movva, Hema C. P.; Meng, Xianghai; He, Feng; Banerjee, Sanjay K.; Wang, Yaguo

2018-05-01

Defect-carrier interaction in transition metal dichalcogenides (TMDs) plays important roles in carrier relaxation dynamics and carrier transport, which determines the performance of electronic devices. With femtosecond laser time-resolved spectroscopy, we investigated the effect of grain boundary/edge defects on the ultrafast dynamics of photoexcited carrier in molecular beam epitaxy (MBE)-grown MoTe2 and MoSe2. We found that, comparing with exfoliated samples, the carrier recombination rate in MBE-grown samples accelerates by about 50 times. We attribute this striking difference to the existence of abundant grain boundary/edge defects in MBE-grown samples, which can serve as effective recombination centers for the photoexcited carriers. We also observed coherent acoustic phonons in both exfoliated and MBE-grown MoTe2, indicating strong electron-phonon coupling in this materials. Our measured sound velocity agrees well with the previously reported result of theoretical calculation. Our findings provide a useful reference for the fundamental parameters: carrier lifetime and sound velocity and reveal the undiscovered carrier recombination effect of grain boundary/edge defects, both of which will facilitate the defect engineering in TMD materials for high speed opto-electronics.

Accelerated carrier recombination by grain boundary/edge defects in MBE grown transition metal dichalcogenides

Directory of Open Access Journals (Sweden)

Ke Chen

2018-05-01

Full Text Available Defect-carrier interaction in transition metal dichalcogenides (TMDs plays important roles in carrier relaxation dynamics and carrier transport, which determines the performance of electronic devices. With femtosecond laser time-resolved spectroscopy, we investigated the effect of grain boundary/edge defects on the ultrafast dynamics of photoexcited carrier in molecular beam epitaxy (MBE-grown MoTe2 and MoSe2. We found that, comparing with exfoliated samples, the carrier recombination rate in MBE-grown samples accelerates by about 50 times. We attribute this striking difference to the existence of abundant grain boundary/edge defects in MBE-grown samples, which can serve as effective recombination centers for the photoexcited carriers. We also observed coherent acoustic phonons in both exfoliated and MBE-grown MoTe2, indicating strong electron-phonon coupling in this materials. Our measured sound velocity agrees well with the previously reported result of theoretical calculation. Our findings provide a useful reference for the fundamental parameters: carrier lifetime and sound velocity and reveal the undiscovered carrier recombination effect of grain boundary/edge defects, both of which will facilitate the defect engineering in TMD materials for high speed opto-electronics.

The Knight shift in liquid gallium confined within porous glasses and opals

International Nuclear Information System (INIS)

Charnaya, E V; Michel, D; Tien, C; Kumzerov, Yu A; Yaskov, D

2003-01-01

71 Ga nuclear magnetic resonance studies were carried out for liquid gallium embedded into porous glasses with different pore sizes and into artificial opals within the temperature range from about 320 K to complete confined gallium freezing. A general decrease in the Knight shift compared to the bulk melt depending on pore sizes was observed in contrast to theoretical predictions. Correlations between alterations in the Knight shift and pore sizes were established for particular pore geometry. It was also observed that confined geometry affects the temperature dependence of the Knight shift in liquid gallium

Hilar accumulation of gallium-67 in patients with normal chest radiographs

International Nuclear Information System (INIS)

Hoshi, Hiroaki; Yamada, Hiroki; Kawahira, Kozaburo; Watanabe, Katsushi

1982-01-01

Gallium-67 scintigraphy is a useful screening test to detect malignant or inflammatory lesions. However, the accumulations of Gallium-67 in the normal pulmonary hilum are found in some cases. So, 277 cases with Gallium-67 scintigraphy were discussed. The hilar accumulation of Gallium-67 was classified into four grades, namely Grade 0: no Gallium-67 uptake, Grade I: low Gallium-67 uptake, Grade II: moderate Gallium-67 uptake, and Grade III: high Gallium-67 uptake. Gallium-67 uptake was found in 38 of 277 cases (14%). Thirty cases of these were estimated as Grade I (79%). Cases with Grade II were 20.3%, and only two cases were Grade III (0.7%). Gallium-67 accumulation, was bilateral in 28 cases out of 38 and cases with Gallium-67 accumulation increased with age. Twenty five of the 38 cases with Gallium-67 accumulation had such findings as suggesting old pulmonary inflammation though they had no symptoms of respiratory diseases. This study suggests that hilar Gallium-67 accumulation has no correlation with the active inflammation of the lymphnodes. (author)

β-Ga2O3 versus ε-Ga2O3: Control of the crystal phase composition of gallium oxide thin film prepared by metal-organic chemical vapor deposition

Science.gov (United States)

Zhuo, Yi; Chen, Zimin; Tu, Wenbin; Ma, Xuejin; Pei, Yanli; Wang, Gang

2017-10-01

Gallium oxide thin films of β and ε phase were grown on c-plane sapphire using metal-organic chemical vapor deposition and the phase compositions were analyzed using X-ray diffraction. The epitaxial phase diagram was constructed as a function of the growth temperature and VI/III ratio. A low growth temperature and low VI/III ratio were beneficial for the formation of hexagonal-type ε-Ga2O3. Further structure analysis revealed that the epitaxial relationship between ε-Ga2O3 and c-plane sapphire is ε-Ga2O3 (0001) || Al2O3 (0001) and ε-Ga2O3 || Al2O3 . The structural evolution of the mixed-phase sample during film thickening was investigated. By reducing the growth rate, the film evolved from a mixed phase to the energetically favored ε phase. Based on these results, a Ga2O3 thin film with a phase-pure ε-Ga2O3 upper layer was successfully obtained.

Gallium-67 activity in bronchoalveolar lavage fluid in sarcoidosis

International Nuclear Information System (INIS)

Trauth, H.A.; Heimes, K.; Schubotz, R.; von Wichert, P.

1986-01-01

Roentgenograms and gallium-67 scans and gallium-67 counts of BAL fluid samples, together with differential cell counts, have proved to be useful in assessing activity and lung involvement in sarcoidosis. In active pulmonary sarcoidosis gallium-67 scans are usually positive. Quantitation of gallium-67 uptake in lung scans, however, may be difficult. Because gallium-67 uptake and cell counts in BAL fluid may be correlated, we set out to investigate gallium-67 activity in BAL fluid recovered from patient of different groups. Sixteen patients with recently diagnosed and untreated sarcoidosis, nine patients with healthy lungs, and five patients with CFA were studied. Gallium-67 uptake of the lung, gallium-67 activity in the lavage fluid, SACE and LACE levels, and alpha 1-AT activity were measured. Significantly more gallium-67 activity was found in BAL fluid from sarcoidosis patients than in that from CFA patients (alpha = .001) or patients with healthy lungs (alpha = .001). Gallium-67 activity in BAL fluid could be well correlated with the number of lymphocytes in BAL fluid, but poorly with the number of macrophages. Subjects with increased levels of SACE or serum alpha 1-AT showed higher lavage gallium-67 activity than did normals, but no correlation could be established. High gallium-67 activity in lavage fluid may be correlated with acute sarcoidosis or physiological deterioration; low activity denotes change for the better. The results show that gallium-67 counts in BAL fluid reflects the intensity of gallium-67 uptake and thus of activity of pulmonary sarcoidosis

Modeling non-adiabatic photoexcited reaction dynamics in condensed phases

International Nuclear Information System (INIS)

Coker, D.F.

2003-01-01

Reactions of photoexcited molecules, ions, and radicals in condensed phase environments involve non-adiabatic dynamics over coupled electronic surfaces. We focus on how local environmental symmetries can effect non-adiabatic coupling between excited electronic states and thus influence, in a possibly controllable way, the outcome of photo-excited reactions. Semi-classical and mixed quantum-classical non-adiabatic molecular dynamics methods, together with semi-empirical excited state potentials are used to probe the dynamical mixing of electronic states in different environments from molecular clusters, to simple liquids and solids, and photo-excited reactions in complex reaction environments such as zeolites

ODMR of shallow donors in Zn-doped LEC-grown InP

International Nuclear Information System (INIS)

Trombetta, J.M.; Kennedy, T.A.

1990-01-01

ODMR spectra observed while monitoring the shallow donor-shallow acceptor pair emission in Zn-doped LEC-grown InP display strong features in the region near the conduction electron value of g = 1.20. In addition to a previously observed narrow line, the authors observe a much broader resonance which dominates at low photoexcitation intensity. This broader line is interpreted as the unresolved exchange split resonances of electrons bound to residual shallow donors. The exchange broadening arises from interaction with nearby paramagnetic centers. Both resonances result in a decrease in the shallow-donor-to shallow-acceptor radiative recombination and give evidence for pair recombination processes which compete with this emission

Extrinsic photoresponse enhancement under additional intrinsic photoexcitation in organic semiconductors

Energy Technology Data Exchange (ETDEWEB)

Kounavis, P., E-mail: pkounavis@upatras.gr [Department of Electrical and Computer Engineering, School of Engineering, University of Patras, 26504 Patras (Greece)

2016-06-28

Dual light beam photoresponse experiments are employed to explore the photoresponse under simultaneous extrinsic and intrinsic photoexcitation of organic semiconductors. The photoresponse of a red modulated light extrinsic photoexcitation is found that can be significantly enhanced under an additional blue bias-light intrinsic photoexcitation in two terminal pentacene films on glass substrates. From the frequency resolved photoresponse, it is deduced that the phenomenon of photoresponse enhancement can be attributed to an increase in the extrinsic photogeneration rate of the red modulated light and/or an improvement of the drift velocity of carriers under an additional blue light intrinsic photoexcitation. The possible predominant extrinsic photogeneration mechanism, which can be compatible with the observed dependence of the photoresponse enhancement on the frequency and on the light intensities of the red and blue light excitation, is the singlet exciton dissociation through electron transfer to acceptor-like traps. Moreover, an improvement in the drift velocity of carriers traversing grain boundaries with potential energy barriers, which may be reduced by trapping of minority carriers created from the intrinsic photoexcitation, may partly contribute to the photoresponse enhancement.

Extrinsic photoresponse enhancement under additional intrinsic photoexcitation in organic semiconductors

International Nuclear Information System (INIS)

Kounavis, P.

2016-01-01

Dual light beam photoresponse experiments are employed to explore the photoresponse under simultaneous extrinsic and intrinsic photoexcitation of organic semiconductors. The photoresponse of a red modulated light extrinsic photoexcitation is found that can be significantly enhanced under an additional blue bias-light intrinsic photoexcitation in two terminal pentacene films on glass substrates. From the frequency resolved photoresponse, it is deduced that the phenomenon of photoresponse enhancement can be attributed to an increase in the extrinsic photogeneration rate of the red modulated light and/or an improvement of the drift velocity of carriers under an additional blue light intrinsic photoexcitation. The possible predominant extrinsic photogeneration mechanism, which can be compatible with the observed dependence of the photoresponse enhancement on the frequency and on the light intensities of the red and blue light excitation, is the singlet exciton dissociation through electron transfer to acceptor-like traps. Moreover, an improvement in the drift velocity of carriers traversing grain boundaries with potential energy barriers, which may be reduced by trapping of minority carriers created from the intrinsic photoexcitation, may partly contribute to the photoresponse enhancement.

Optical and Micro-Structural Characterization of MBE Grown Indium Gallium Nitride Polar Quantum Dots

KAUST Repository

El Afandy, Rami

2011-01-01

Gallium nitride and related materials have ushered in scientific and technological breakthrough for lighting, mass data storage and high power electronic applications. These III-nitride materials have found their niche in blue light emitting diodes

Dose dependent disposition of gallium-67 in rats

International Nuclear Information System (INIS)

Gautam, S.R.

1982-01-01

Radioactive gallium-67 has been employed as a diagnostic and follow-up agent for cancer therapy. Currently gallium nitrate is undergoing Phase I clinical studies. A million fold increase in the concentration of the carrier gallium citrate over the range of carrier-free gallium-67 (pgm) to 1.0 μg caused no significant alteration in the disposition of gallium-67 in rats.Gallium-67 was eliminated from blood with a biological t1/2 of 4.1 days. A linear tissue binding profile was observed for gallium-67 over this concentration range. A multi-compartment pharmacokinetic model was developed in which all the tissues studied were treated as separate compartments. At 1.0 mg dose level, significant alteration in the disposition of gallium-67 was observed in rats, > 95% of the initial radioactivity was characteristic reappearance of the radioactivity in the blood approximately 4 hours after dosing leading to a ''hump'' in the blood concentration-time profiles. Following the 1.0 mg dose low tissue levels were observed, except for the kidneys, which contained about 8% of the administered dose per gram of the tissue one-half hour after dosing. A non-linear tissue binding profile was observed to be associated with gallium at high doses. It was hypothesized that the rapid loss of gallium-67 from the vascular system following the high doses of gallium citrate was due to the accumulation of the drug in the kidneys where it was eventually eliminated via urine. The kidneys thus would act as a temporary storage site for gallium. It was concluded that the dose-related renal toxicity associated with gallium therapy may be attributed to the kidney's role as a temporary storage site following high doses

Some properties of Ga-As-Alsub(x)Gasub(1-x)As heterojunction grown by low temperature liquid phase epitaxy

International Nuclear Information System (INIS)

Yu Lisheng; Liu Hongxun; Zhang Bei; Wang Shumin

1986-03-01

GaAs-Alsub(x)Gasub(1-x)As heterojunction was grown by liquid phase epitaxy at low growth temperature 650-700 deg. C. The series resistance of heterojunction with DH laser structure was measured. Doping properties of Mg in GaAs and Alsub(x)Gasub(1-x)As were investigated. It is found that impurity concentration of Mg as high as 10 18 cm -3 can be doped easily. The Shubnikov-de-Haas oscillation was observed in GaAs-N Alsub(0.35)Gasub(0.65)As heterointerface. It is demonstrated that in these heterointerfaces there exists 2DEG with some contribution from 3D electron of N-AlGaAs layer. (author)

Feasibility of flooding the reactor cavity with liquid gallium coolant for IVR-ERVC strategy

International Nuclear Information System (INIS)

Park, Seong Dae; Bang, In Cheol

2013-01-01

Highlights: ► We investigate the feasibility of gallium liquid metal application for IVR-ERVC. ► We consider overall concerns to apply the liquid metal. ► Decay heat can be removed by flooding the reactor cavity with gallium liquid metal. -- Abstract: In this paper, a new approach replacing the ERVC coolant by a liquid metal instead of water is studied to avoid the heat removal limit of CHF during boiling of water. As the flooding material, gallium is used in terms of the melting and boiling points. Gallium has the enough low melting point of ∼29.7 °C to ensure to maintain liquid state within the containment building. A gallium storage tank for the new flooding system of the ERVC is located in higher position than one of the reactor cavity to make a passive system using the gravity for the event of a station blackout (SBO). While the decay heat from the reactor vessel is removed by gallium, the borated water which is coming out from the reactor system plays a role as the ultimate heat sink in this ERVC system. In the system, two configurations of gallium and borated water are devised depending on whether the direct contact between them occurs. In the first configuration, two fluids are separated by the block structure. The decay heat is transported from molten corium to gallium through the vessel wall. Then the heat is ultimately dissipated by boiling of water in the block structure surface facing the borated water. In the second configuration, the cavity is flooded with both borated water and gallium in the same reactor cavity space. As the result, two layers of the fluids are naturally formed by the density difference. Like the first configuration, finally the heat removal is achieved by boiling of water via gallium. The CFD analysis shows that the maximum temperature of gallium is much lower than its boiling point while the natural circulation is stably formed in two types of the configurations without any serious risk of thermal limit

Compatibility of ITER candidate structural materials with static gallium

International Nuclear Information System (INIS)

Luebbers, P.R.; Michaud, W.F.; Chopra, O.K.

1993-12-01

Tests were conducted on the compatibility of gallium with candidate structural materials for the International Thermonuclear Experimental Reactor, e.g., Type 316 SS, Inconel 625, and Nb-5 Mo-1 Zr alloy, as well as Armco iron, Nickel 270, and pure chromium. Type 316 stainless steel is least resistant to corrosion in static gallium and Nb-5 Mo-1 Zr alloy is most resistant. At 400 degrees C, corrosion rates are ∼4.0, 0.5, and 0.03 mm/yr for type 316 SS, Inconel 625, and Nb-5 Mo- 1 Zr alloy, respectively. The pure metals react rapidly with gallium. In contrast to findings in earlier studies, pure iron shows greater corrosion than nickel. The corrosion rates at 400 degrees C are ≥88 and 18 mm/yr, respectively, for Armco iron and Nickel 270. The results indicate that at temperatures up to 400 degrees C, corrosion occurs primarily by dissolution and is accompanied by formation of metal/gallium intermetallic compounds. The solubility data for pure metals and oxygen in gallium are reviewed. The physical, chemical, and radioactive properties of gallium are also presented. The supply and availability of gallium, as well as price predictions through the year 2020, are summarized

Radiochemical neutron activation analysis based multi-elemental analysis of high purity gallium

International Nuclear Information System (INIS)

Tashimova, F.A.; Sadikov, I.I; Salimov, M.I.; Zinov'ev, V.G.

2006-01-01

Full text: Gallium is one of the widely used materials in semiconductor and optoelectronics industry. Gallium is used to produce infrared detectors, piezoelectric sensors, high- and low-temperature transistors for space and defense technology. One of the most important requirements for semiconductor materials of gallium compounds is an excessive high purity for layers and films. Information on impurities (type of an impurity, concentration, character of distribution) is important as for better understanding of the physical and chemical processes taking place in formed semiconductor structures and for the 'know-how' of devices on their basis. The object of this work is to develop radiochemical neutron activation technique for analysis of high purity gallium. Irradiation of 0.1 g of gallium sample in neutron flux of 5·10 13 cm -2 s -1 for 5 hours will result in induced activity of more than 10 8 Bq, due to 72 Ga radionuclide, half-life of which is 14.1 hours. Therefore to perform instrumental NAA of gallium long period (10 day) cooling is required, and high sensitive determination of elements producing short- and long-lived radionuclides (T 1/2 72 Ga. We have studied the behavior of gallium in extraction-chromatographic system 'TBP-HCl'. The experiments have shown that higher factor of distribution (D) and capacity on gallium can be achieved when 'TBP-4M HCl' system is used. However more than 10 trace elements have high D and thus they cannot be separated from 72 Ga. To resolve the problem and increase the number of separated trace elements we have used preliminary satisfaction of chromatographic column with tellurium, which has D higher than the most of elements in 'TBP-4M HCl' system and thus suppresses extraction of elements. Distribution profile of gallium along the column and elution curve of 25 trace elements have been measured. Chemical yields of separated elements measured by using radiotracers are more than 93%. On the basis of the carried out researches

Liquid gallium jet-plasma interaction studies in ISTTOK tokamak

International Nuclear Information System (INIS)

Gomes, R.B.; Fernandes, H.; Silva, C.; Sarakovskis, A.; Pereira, T.; Figueiredo, J.; Carvalho, B.; Soares, A.; Duarte, P.; Varandas, C.; Lielausis, O.; Klyukin, A.; Platacis, E.; Tale, I.; Alekseyv, A.

2009-01-01

Liquid metals have been pointed out as a suitable solution to solve problems related to the use of solid walls submitted to high power loads allowing, simultaneously, an efficient heat exhaustion process from fusion devices. The most promising candidate materials are lithium and gallium. However, lithium has a short liquid state temperature range when compared with gallium. To explore further this property, ISTTOK tokamak is being used to test the interaction of a free flying liquid gallium jet with the plasma. ISTTOK has been successfully operated with this jet without noticeable discharge degradation and no severe effect on the main plasma parameters or a significant plasma contamination by liquid metal. Additionally the response of an infrared sensor, intended to measure the jet surface temperature increase during its interaction with the plasma, has been studied. The jet power extraction capability is extrapolated from the heat flux profiles measured in ISTTOK plasmas.

Eutectic Gallium-Indium (EGaIn) : A Liquid Metal Alloy for the Formation of Stable Structures in Microchannels at Room Temperature

NARCIS (Netherlands)

Dickey, Michael D.; Chiechi, Ryan C.; Larsen, Ryan J.; Weiss, Emily A.; Weitz, David A.; Whitesides, George M.

2008-01-01

This paper describes the rheological behavior of the liquid metal eutectic gallium-indium (EGaIn) as it is injected into microfluidic channels to form stable microstructures of liquid metal. EGaIn is well-suited for this application because of its rheological properties at room temperature: it

Compatibility of candidate structural materials with static gallium

International Nuclear Information System (INIS)

Luebbers, P.R.; Michaud, W.F.; Chopra, O.K.

1993-01-01

Scoping tests were conducted on compatibility of gallium with candidate structural materials, e.g., Type 316 SS, Inconel 625, and Nb-5 Mo-1 Zr alloy, as well as Armco iron, Nickel 270, and pure chronimum. Type 316 stainless steel is least resistant and Nb-5 Mo-1 Zr alloy is most resistant to corrosion in static gallium. At 400 degrees C, corrosion rates are ∼4.0, 0.5, and 0.03 mm/y for Type 316 SS, Inconel 625, and Nb-5 Mo-1 Zr alloy, respectively. The pure metals react rapidly with gallium. In contrast to findings in earlier studies, pure iron shows greater corrosion than does nickel. The corrosion rates at 400 degrees C are ≥90 and 17 mm/y, respectively, for Armco iron and Nickel 270. The results indicate that at temperatures up to 400 degrees C, corrosion occurs primarily by dissolution accompanied by formation of metal/gallium intermetallic compounds

Thermodynamic and transport properties of liquid gallium

International Nuclear Information System (INIS)

Park, H.Y.; Jhon, M.S.

1982-01-01

The significant structure theory of liquids has been successfully applied to liquid gallium. In this work, we have assumed that two structures exist simultaneously in liquid gallium. One is considerec as loosely close packed β-Ga-like structure and the other is remainder of solid α-Ga or α-Ga-like structure. This two structural model is introduced to construct the liquid partition function. Using the partition function, the thermodynamic and transport properties are calculated ever a wide temperature range. The calculated results are quite satisfactory when compared with the experimental results. (Author)

Thermal Plasma Synthesis of Crystalline Gallium Nitride Nanopowder from Gallium Nitrate Hydrate and Melamine

Directory of Open Access Journals (Sweden)

Tae-Hee Kim

2016-02-01

Full Text Available Gallium nitride (GaN nanopowder used as a blue fluorescent material was synthesized by using a direct current (DC non-transferred arc plasma. Gallium nitrate hydrate (Ga(NO33∙xH2O was used as a raw material and NH3 gas was used as a nitridation source. Additionally, melamine (C3H6N6 powder was injected into the plasma flame to prevent the oxidation of gallium to gallium oxide (Ga2O3. Argon thermal plasma was applied to synthesize GaN nanopowder. The synthesized GaN nanopowder by thermal plasma has low crystallinity and purity. It was improved to relatively high crystallinity and purity by annealing. The crystallinity is enhanced by the thermal treatment and the purity was increased by the elimination of residual C3H6N6. The combined process of thermal plasma and annealing was appropriate for synthesizing crystalline GaN nanopowder. The annealing process after the plasma synthesis of GaN nanopowder eliminated residual contamination and enhanced the crystallinity of GaN nanopowder. As a result, crystalline GaN nanopowder which has an average particle size of 30 nm was synthesized by the combination of thermal plasma treatment and annealing.

Low temperature grown ZnO@TiO{sub 2} core shell nanorod arrays for dye sensitized solar cell application

Energy Technology Data Exchange (ETDEWEB)

Goh, Gregory Kia Liang [Institute of Materials Research and Engineering, A*STAR (Agency for Science, Technology, and Research), 3 Research Link, 117602 Singapore (Singapore); Le, Hong Quang, E-mail: lehq@imre.a-star.edu.sg [Institute of Materials Research and Engineering, A*STAR (Agency for Science, Technology, and Research), 3 Research Link, 117602 Singapore (Singapore); Huang, Tang Jiao; Hui, Benjamin Tan Tiong [Department of Materials Science and Engineering (DMSE), Faculty of Engineering National University of Singapore (NUS) BLK E3A, #04-10, 7 Engineering Drive 1, Singapore 117574 (Singapore)

2014-06-01

High aspect ratio ZnO nanorod arrays were synthesized on fluorine-doped tin oxide glasses via a low temperature solution method. By adjusting the growth condition and adding polyethylenimine, ZnO nanorod arrays with tunable length were successfully achieved. The ZnO@TiO{sub 2} core shells structures were realized by a fast growth method of immersion into a (NH{sub 4}){sub 2}·TiF{sub 6} solution. Transmission electron microscopy, X-ray Diffraction and energy dispersive X-ray measurements all confirmed the existence of a titania shell uniformly covering the ZnO nanorod's surface. Results of solar cell testing showed that addition of a TiO{sub 2} shell to the ZnO nanorod significantly increased short circuit current (from 4.2 to 5.2 mA/cm{sup 2}), open circuit voltage (from 0.6 V to 0.8 V) and fill factor (from 42.8% to 73.02%). The overall cell efficiency jumped from 1.1% for bare ZnO nanorod to 3.03% for a ZnO@TiO{sub 2} core shell structured solar cell with a 18–22 nm shell thickness, a nearly threefold increase. - Graphical abstract: The synthesis process of coating TiO{sub 2} shell onto ZnO nanorod core is shown schematically. A thin, uniform, and conformal shell had been grown on the surface of the ZnO core after immersing in the (NH{sub 4}){sub 2}·TiF{sub 6} solution for 5–15 min. - Highlights: • ZnO@TiO{sub 2} core shell nanorod has been grown on FTO substrate using low temperature solution method. • TEM, XRD, EDX results confirmed the existing of titana shell, uniformly covered rod's surface. • TiO{sub 2} shell suppressed recombination, demonstrated significant enhancement in cell's efficiency. • Core shell DSSC's efficiency achieved as high as 3.03%, 3 times higher than that of ZnO nanorods.

Acclimation of Saccharomyces cerevisiae to low temperature: a chemostat-based transcriptome analysis.

Science.gov (United States)

Tai, Siew Leng; Daran-Lapujade, Pascale; Walsh, Michael C; Pronk, Jack T; Daran, Jean-Marc

2007-12-01

Effects of suboptimal temperatures on transcriptional regulation in yeast have been extensively studied in batch cultures. To eliminate indirect effects of specific growth rates that are inherent to batch-cultivation studies, genome-wide transcriptional responses to low temperatures were analyzed in steady-state chemostats, grown at a fixed specific growth rate (0.03 h(-1)). Although in vivo metabolic fluxes were essentially the same in cultures grown at 12 and at 30 degrees C, concentrations of the growth-limiting nutrients (glucose or ammonia) were higher at 12 degrees C. This difference was reflected by transcript levels of genes that encode transporters for the growth-limiting nutrients. Several transcriptional responses to low temperature occurred under both nutrient-limitation regimes. Increased transcription of ribosome-biogenesis genes emphasized the importance of adapting protein-synthesis capacity to low temperature. In contrast to observations in cold-shock and batch-culture studies, transcript levels of environmental stress response genes were reduced at 12 degrees C. Transcription of trehalose-biosynthesis genes and intracellular trehalose levels indicated that, in contrast to its role in cold-shock adaptation, trehalose is not involved in steady-state low-temperature adaptation. Comparison of the chemostat-based transcriptome data with literature data revealed large differences between transcriptional reprogramming during long-term low-temperature acclimation and the transcriptional responses to a rapid transition to low temperature.

Thermodynamics properties of plutonium in NaCl-KCl and CaCl2 at 1073 K and in liquid gallium

International Nuclear Information System (INIS)

Lambertin, D.; Ched'homme, S.; Bourges, G.; Pescayre, L.; Sanchez, S.; Picard, G.

2004-01-01

Cadmium and bismuth metal are mostly used as solvent in nuclear pyrochemical processes and especially in actinides/lanthanides separations. Gallium metal has been chosen because no literature values are available with plutonium and its regeneration by refining at low temperature is possible. Electrochemical window of gallium metal and activity coefficient of plutonium in gallium have been determined by using potentiometric method. Secondly, the electrochemical properties of plutonium have been studied in molten equimolar NaCl/KCl and CaCl 2 at 1073 K by cyclic voltammetry. The standard potentials of Pu(III)/Pu redox couple, respectively, -2,54 V and -2,51 V, led to the calculation of the activity coefficients of Pu(III). In CaCl 2 the complexation of Pu(III) ions is lower and the voltage gap between Pu(III)/Pu couple and the solvent limit is higher. The new data on plutonium electrochemistry in molten chlorides and liquid gallium media combined with literature data on lanthanides suggest that gallium can be a good solvent metal for pyro-chemistry separation. (authors)

Complete Stokes polarimetry of magneto-optical Faraday effect in a terbium gallium garnet crystal at cryogenic temperatures.

Science.gov (United States)

Majeed, Hassaan; Shaheen, Amrozia; Anwar, Muhammad Sabieh

2013-10-21

We report the complete determination of the polarization changes caused in linearly polarized incident light due to propagation in a magneto-optically active terbium gallium garnet (TGG) single crystal, at temperatures ranging from 6.3 to 300 K. A 28-fold increase in the Verdet constant of the TGG crystal is seen as its temperature decreases to 6.3 K. In contrast with polarimetry of light emerging from a Faraday material at room temperature, polarimetry at cryogenic temperatures cannot be carried out using the conventional fixed polarizer-analyzer technique because the assumption that ellipticity is negligible becomes increasingly invalid as temperature is lowered. It is shown that complete determination of light polarization in such a case requires the determination of its Stokes parameters, otherwise inaccurate measurements will result with negative implications for practical devices.

Effects of radiation and temperature on gallium nitride (GaN) metal-semiconductor-metal ultraviolet photodetectors

Science.gov (United States)

Chiamori, Heather C.; Angadi, Chetan; Suria, Ateeq; Shankar, Ashwin; Hou, Minmin; Bhattacharya, Sharmila; Senesky, Debbie G.

2014-06-01

The development of radiation-hardened, temperature-tolerant materials, sensors and electronics will enable lightweight space sub-systems (reduced packaging requirements) with increased operation lifetimes in extreme harsh environments such as those encountered during space exploration. Gallium nitride (GaN) is a ceramic, semiconductor material stable within high-radiation, high-temperature and chemically corrosive environments due to its wide bandgap (3.4 eV). These material properties can be leveraged for ultraviolet (UV) wavelength photodetection. In this paper, current results of GaN metal-semiconductor-metal (MSM) UV photodetectors behavior after irradiation up to 50 krad and temperatures of 15°C to 150°C is presented. These initial results indicate that GaN-based sensors can provide robust operation within extreme harsh environments. Future directions for GaN-based photodetector technology for down-hole, automotive and space exploration applications are also discussed.

Point defects in gallium arsenide characterized by positron annihilation spectroscopy and deep level transient spectroscopy

International Nuclear Information System (INIS)

Mih, R.; Gronsky, R.; Sterne, P.A.

1995-01-01

Positron annihilation lifetime spectroscopy (PALS) is a unique technique for detection of vacancy related defects in both as-grown and irradiated materials. The authors present a systematic study of vacancy defects in stoichiometrically controlled p-type Gallium Arsenide grown by the Hot-Wall Czochralski method. Microstructural information based on PALS, was correlated to crystallographic data and electrical measurements. Vacancies were detected and compared to electrical levels detected by deep level transient spectroscopy and stoichiometry based on crystallographic data

EDXRF and TXRF determination of gallium in gallium-uranium matrix

International Nuclear Information System (INIS)

Misra, N.L.; Sanjay Kumar, S.; Dhara, Sangita; Aggarwal, S.K.; Venugopal, V.

2009-01-01

Energy Dispersive X-Ray Fluorescence (EDXRF) and Total Reflection X-ray Fluorescence (TXRF) methods for determination of Gallium in Gallium-Uranium matrix have been developed. For EDXRF determinations, 200 μL of standards/samples mixed with internal standard copper were dispersed on 30 mm diameter absorbent sheet so that it behaves like a thin film of the sample. The Gallium amounts in samples were determined from their EDXRF spectra using a calibration plot. For TXRF determinations, samples were taken on flat polished quartz sample supports and Gallium was determined in conventional way. For EDXRF and TXRF determinations, the average precision and accuracy obtained for Ga determinations was better than 3% (1σ). (author)

High-quality AlGaN/GaN grown on sapphire by gas-source molecular beam epitaxy using a thin low-temperature AlN layer

Energy Technology Data Exchange (ETDEWEB)

Jurkovic, M.J.; Li, L.K.; Turk, B.; Wang, W.I.; Syed, S.; Simonian, D.; Stormer, H.L.

2000-07-01

Growth of high-quality AlGaN/GaN heterostructures on sapphire by ammonia gas-source molecular beam epitaxy is reported. Incorporation of a thin AlN layer grown at low temperature within the GaN buffer is shown to result in enhanced electrical and structural characteristics for subsequently grown heterostructures. AlGaN/GaN structures exhibiting reduced background doping and enhanced Hall mobilities (2100, 10310 and 12200 cm{sup 2}/Vs with carrier sheet densities of 6.1 x 10{sup 12} cm{sup {minus}2}, and 5.8 x 10{sup 12} cm{sup {minus}2} at 300 K, 77 K, and 0.3 K, respectively) correlate with dislocation filtering in the thin AlN layer. Magnetotransport measurements at 0.3 K reveal well-resolved Shubnikov-de Haas oscillations starting at 3 T.

Exploration of a mechanism for the production of highly unsaturated fatty acids in Scenedesmus sp. at low temperature grown on oil crop residue based medium.

Science.gov (United States)

Lu, Qian; Li, Jun; Wang, Jinghan; Li, Kun; Li, Jingjing; Han, Pei; Chen, Paul; Zhou, Wenguang

2017-11-01

The ability of algae to produce lipids comprising of unsaturated fatty acids varies with strains and culture conditions. This study investigates the effect of temperature on the production of unsaturated fatty acids in Scenedesmus sp. grown on oil crop residue based medium. At low temperature (10°C), synthesis of lipids compromising of high contents of unsaturated fatty acids took place primarily in the early stage while protein accumulation mainly occurred in the late stage. This stepwise lipid-protein synthesis process was found to be associated with the contents of acetyl-CoA and α-KG in the algal cells. A mechanism was proposed and tested through simulation experiments which quantified the carbon flux allocation in algal cells at different cultivation stages. It is concluded that low culture temperature such as 10°C is suitable for the production of lipids comprising of unsaturated fatty acids. Copyright © 2017 Elsevier Ltd. All rights reserved.

Diode behavior in ultra-thin low temperature ALD grown zinc-oxide on silicon

Directory of Open Access Journals (Sweden)

Nazek El-Atab

2013-10-01

Full Text Available A thin-film ZnO(n/Si(p+ heterojunction diode is demonstrated. The thin film ZnO layer is deposited by Atomic Layer Deposition (ALD at different temperatures on a p-type silicon substrate. Atomic force microscopy (AFM AC-in-Air method in addition to conductive AFM (CAFM were used for the characterization of ZnO layer and to measure the current-voltage characteristics. Forward and reverse bias n-p diode behavior with good rectification properties is achieved. The diode with ZnO grown at 80°C exhibited the highest on/off ratio with a turn-on voltage (VON ∼3.5 V. The measured breakdown voltage (VBR and electric field (EBR for this diode are 5.4 V and 3.86 MV/cm, respectively.

Single layer porous gold films grown at different temperatures

International Nuclear Information System (INIS)

Zhang Renyun; Hummelgard, Magnus; Olin, Hakan

2010-01-01

Large area porous gold films can be used in several areas including electrochemical electrodes, as an essential component in sensors, or as a conducting material in electronics. Here, we report on evaporation induced crystal growth of large area porous gold films at 20, 40 and 60 deg. C. The gold films were grown on liquid surface at 20 deg. C, while the films were grown on the wall of beakers when temperature increased to 40 and 60 deg. C. The porous gold films consisted of a dense network of gold nanowires as characterized by TEM and SEM. TEM diffraction results indicated that higher temperature formed larger crystallites of gold wires. An in situ TEM imaging of the coalescence of gold nanoparticles mimicked the process of the growth of these porous films, and a plotting of the coalescence time and the neck radius showed a diffusion process. The densities of these gold films were also characterized by transmittance, and the results showed film grown at 20 deg. C had the highest density, while the film grown at 60 deg. C had the lowest consistent with SEM and TEM characterization. Electrical measurements of these gold films showed that the most conductive films were the ones grown at 40 deg. C. The conductivities of the gold films were related to the amount of contamination, density and the diameter of the gold nanowires in the films. In addition, a gold film/gold nanoparticle hybrid was made, which showed a 10% decrease in transmittance during hybridization, pointing to applications as chemical and biological sensors.

Amorphous indium gallium zinc oxide thin film grown by pulse laser deposition technique

Energy Technology Data Exchange (ETDEWEB)

Mistry, Bhaumik V., E-mail: bhaumik-phy@yahoo.co.in; Joshi, U. S. [Department of Physics, University School of Sciences, Gujarat University, Ahmedabad-380 009 (India)

2016-05-23

Highly electrically conducting and transparent in visible light IGZO thin film were grown on glass substrate at substrate temperature of 400 C by a pulse laser deposition techniques. Structural, surface, electrical, and optical properties of IGZO thin films were investigated at room temperature. Smooth surface morphology and amorphous nature of the film has been confirmed from the AFM and GIXRD analysis. A resistivity down to 7.7×10{sup −3} V cm was reproducibly obtained while maintaining optical transmission exceeding 70% at wavelengths from 340 to 780 nm. The carrier densities of the film was obtain to the value 1.9×10{sup 18} cm{sup 3}, while the Hall mobility of the IGZO thin film was 16 cm{sup 2} V{sup −1}S{sup −1}.

Thermodynamics properties of plutonium in NaCl-KCl and CaCl{sub 2} at 1073 K and in liquid gallium

Energy Technology Data Exchange (ETDEWEB)

Lambertin, D.; Ched' homme, S.; Bourges, G.; Pescayre, L.; Sanchez, S.; Picard, G

2004-07-01

Cadmium and bismuth metal are mostly used as solvent in nuclear pyrochemical processes and especially in actinides/lanthanides separations. Gallium metal has been chosen because no literature values are available with plutonium and its regeneration by refining at low temperature is possible. Electrochemical window of gallium metal and activity coefficient of plutonium in gallium have been determined by using potentiometric method. Secondly, the electrochemical properties of plutonium have been studied in molten equimolar NaCl/KCl and CaCl{sub 2} at 1073 K by cyclic voltammetry. The standard potentials of Pu(III)/Pu redox couple, respectively, -2,54 V and -2,51 V, led to the calculation of the activity coefficients of Pu(III). In CaCl{sub 2} the complexation of Pu(III) ions is lower and the voltage gap between Pu(III)/Pu couple and the solvent limit is higher. The new data on plutonium electrochemistry in molten chlorides and liquid gallium media combined with literature data on lanthanides suggest that gallium can be a good solvent metal for pyro-chemistry separation. (authors)

Optimization of growth parameters for MOVPE-grown GaSb and Ga1−xInxSb

International Nuclear Information System (INIS)

Miya, S.S.; Wagener, V.; Botha, J.R.

2012-01-01

The triethylgallium/trimethylantimony (TEGa/TMSb) precursor combination was used for the metal-organic vapour phase epitaxial growth of GaSb at a growth temperature of 520 °C at atmospheric pressure. Trimethylindium was added in the case of Ga 1−x In x Sb growth. The effects of group V flux to group III flux ratio (V/III ratio) on the crystallinity and optical properties of GaSb layers are reported. It has been observed from the crystalline quality and optical properties that nominal V/III ratios of values greater than unity are required for GaSb epitaxial layers grown at this temperature. It has also been shown that Ga 1−x In x Sb can be grown using TEGa as a source of gallium species at atmospheric pressure. The relationship between Ga 1−x In x Sb vapour composition and solid composition has been studied at a V/III ratio of 0.78.

Probing Microenvironment in Ionic Liquids by Time-Resolved EPR of Photoexcited Triplets.

Science.gov (United States)

Ivanov, M Yu; Veber, S L; Prikhod'ko, S A; Adonin, N Yu; Bagryanskaya, E G; Fedin, M V

2015-10-22

Unusual physicochemical properties of ionic liquids (ILs) open vistas for a variety of new applications. Herewith, we investigate the influence of microviscosity and nanostructuring of ILs on spin dynamics of the dissolved photoexcited molecules. We use two most common ILs [Bmim]PF6 and [Bmim]BF4 (with its close analogue [C10mim]BF4) as solvents and photoexcited Zn tetraphenylporphyrin (ZnTPP) as a probe. Time-resolved electron paramagnetic resonance (TR EPR) is employed to investigate spectra and kinetics of spin-polarized triplet ZnTPP in the temperature range 100-270 K. TR EPR data clearly indicate the presence of two microenvironments of ZnTPP in frozen ILs at 100-200 K, being manifested in different spectral shapes and different spin relaxation rates. For one of these microenvironments TR EPR data is quite similar to those obtained in common frozen organic solvents (toluene, glycerol, N-methyl-2-pyrrolidone). However, the second one favors the remarkably slow relaxation of spin polarization, being much longer than in the case of common solvents. Additional experiments using continuous wave EPR and stable nitroxide as a probe confirmed the formation of heterogeneities upon freezing of ILs and complemented TR EPR results. Thus, TR EPR of photoexcited triplets can be effectively used for probing heterogeneities and nanostructuring in frozen ILs. In addition, the increase of polarization lifetime in frozen ILs is an interesting finding that might allow investigation of short-lived intermediates inaccessible otherwise.

Structural and electronic properties of InN nanowire network grown by vapor-liquid-solid method

Science.gov (United States)

Barick, B. K.; Rodríguez-Fernández, Carlos; Cantarero, Andres; Dhar, S.

2015-05-01

Growth of InN nanowires have been carried out on quartz substrates at different temperatures by vapor-liquid-solid (VLS) technique using different thicknesses of Au catalyst layer. It has been found that a narrow window of Au layer thickness and growth temperature leads to multi-nucleation, in which each site acts as the origin of several nanowires. In this multi-nucleation regime, several tens of micrometer long wires with diameter as small as 20 nm are found to grow along [ 11 2 ¯ 0 ] direction (a-plane) to form a dense network. Structural and electronic properties of these wires are studied. As grown nanowires show degenerate n-type behavior. Furthermore, x-ray photoemission study reveals an accumulation of electrons on the surface of these nanowires. Interestingly, the wire network shows persistence of photoconductivity for several hours after switching off the photoexcitation.

Structural and electronic properties of InN nanowire network grown by vapor-liquid-solid method

Energy Technology Data Exchange (ETDEWEB)

Barick, B. K., E-mail: bkbarick@gmail.com, E-mail: subho-dh@yahoo.co.in; Dhar, S., E-mail: bkbarick@gmail.com, E-mail: subho-dh@yahoo.co.in [Department of Physics, Indian Institute of Technology, Bombay, Mumbai-400076 (India); Rodríguez-Fernández, Carlos; Cantarero, Andres [Materials Science Institute, University of Valencia, PO Box 22085, 46071 Valencia (Spain)

2015-05-15

Growth of InN nanowires have been carried out on quartz substrates at different temperatures by vapor-liquid-solid (VLS) technique using different thicknesses of Au catalyst layer. It has been found that a narrow window of Au layer thickness and growth temperature leads to multi-nucleation, in which each site acts as the origin of several nanowires. In this multi-nucleation regime, several tens of micrometer long wires with diameter as small as 20 nm are found to grow along [112{sup -}0] direction (a-plane) to form a dense network. Structural and electronic properties of these wires are studied. As grown nanowires show degenerate n-type behavior. Furthermore, x-ray photoemission study reveals an accumulation of electrons on the surface of these nanowires. Interestingly, the wire network shows persistence of photoconductivity for several hours after switching off the photoexcitation.

Density-dependent electron scattering in photoexcited GaAs in strongly diffusive regime

DEFF Research Database (Denmark)

Mics, Zoltán; D’Angio, Andrea; Jensen, Søren A.

2013-01-01

In a series of systematic optical pump–terahertz probe experiments, we study the density-dependent electron scattering rate in photoexcited GaAs in the regime of strong carrier diffusion. The terahertz frequency-resolved transient sheet conductivity spectra are perfectly described by the Drude...... model, directly yielding the electron scattering rates. A diffusion model is applied to determine the spatial extent of the photoexcited electron-hole gas at each moment after photoexcitation, yielding the time-dependent electron density, and hence the density-dependent electron scattering time. We find...

Zno Micro/Nanostructures Grown on Sapphire Substrates Using Low-Temperature Vapor-Trapped Thermal Chemical Vapor Deposition: Structural and Optical Properties

Directory of Open Access Journals (Sweden)

Po-Sheng Hu

2017-12-01

Full Text Available In this research, the Zn(C5H7O22·xH2O-based growth of ZnO micro/nanostructures in a low temperature, vapor-trapped chemical vapor deposition system was attempted to optimize structural and optical properties for potential biomedical applications. By trapping in-flow gas molecules and Zinc vapor inside a chamber tube by partially obstructing a chamber outlet, a high pressure condition can be achieved, and this experimental setup has the advantages of ease of synthesis, being a low temperature process, and cost effectiveness. Empirically, the growth process proceeded under a chamber condition of an atmospheric pressure of 730 torr, a controlled volume flow rate of input gas, N2/O2, of 500/500 Standard Cubic Centimeters per Minute (SCCM, and a designated oven temperature of 500 °C. Specifically, the dependence of structural and optical properties of the structures on growth duration and spatially dependent temperature were investigated utilizing scanning electron microscopy, X-ray diffraction (XRD, photoluminescence (PL, and ultraviolet-visible transmission spectroscopy. The experimental results indicate that the grown thin film observed with hexagonal structures and higher structural uniformity enables more prominent structural and optical signatures. XRD spectra present the dominant peaks along crystal planes of (002 and (101 as the main direction of crystallization. In addition, while the structures excited with laser wavelength of 325 nm emit a signature radiation around 380 nm, an ultraviolet lamp with a wavelength of 254 nm revealed distinctive photoluminescence peaks at 363.96 nm and 403.52 nm, elucidating different degrees of structural correlation as functions of growth duration and the spatial gradient of temperature. Transmittance spectra of the structures illustrate typical variation in the wavelength range of 200 nm to 400 nm, and its structural correlation is less significant when compared with PL.

Model of ultrafast demagnetization driven by spin-orbit coupling in a photoexcited antiferromagnetic insulator Cr2O3

Science.gov (United States)

Guo, Feng; Zhang, Na; Jin, Wei; Chang, Jun

2017-06-01

We theoretically study the dynamic time evolution following laser pulse pumping in an antiferromagnetic insulator Cr2O3. From the photoexcited high-spin quartet states to the long-lived low-spin doublet states, the ultrafast demagnetization processes are investigated by solving the dissipative Schrödinger equation. We find that the demagnetization times are of the order of hundreds of femtoseconds, in good agreement with recent experiments. The switching times could be strongly reduced by properly tuning the energy gaps between the multiplet energy levels of Cr3+. Furthermore, the relaxation times also depend on the hybridization of atomic orbitals in the first photoexcited state. Our results suggest that the selective manipulation of the electronic structure by engineering stress-strain or chemical substitution allows effective control of the magnetic state switching in photoexcited insulating transition-metal oxides.

Challenges for critical raw material recovery from WEEE - The case study of gallium.

Science.gov (United States)

Ueberschaar, Maximilian; Otto, Sarah Julie; Rotter, Vera Susanne

2017-02-01

Gallium and gallium compounds are more frequently used in future oriented technologies such as photovoltaics, light diodes and semiconductor technology. In the long term the supply risk is estimated to be critical. Germany is one of the major primary gallium producer, recycler of gallium from new scrap and GaAs wafer producer. Therefore, new concepts for a resource saving handling of gallium and appropriate recycling strategies have to be designed. This study focus on options for a possible recycling of gallium from waste electric and electronic equipment. To identify first starting points, a substance flow analysis was carried out for gallium applied in integrated circuits applied on printed circuit boards and for LEDs used for background lighting in Germany in 2012. Moreover, integrated circuits (radio amplifier chips) were investigated in detail to deduce first approaches for a recycling of such components. An analysis of recycling barriers was carried out in order to investigate general opportunities and risks for the recycling of gallium from chips and LEDs. Results show, that significant gallium losses arose in primary production and in waste management. 93±11%, equivalent to 43,000±4700kg of the total gallium potential was lost over the whole primary production process until applied in electronic goods. The largest share of 14,000±2300kggallium was lost in the production process of primary raw materials. The subsequent refining process was related to additional 6900±3700kg and the chip and wafer production to 21,700±3200kg lost gallium. Results for the waste management revealed only low collection rates for related end-of-life devices. Not collected devices held 300 ± 200 kg gallium. Due to the fact, that current waste management processes do not recover gallium, further 80 ± 10 kg gallium were lost. A thermal pre-treatment of the chips, followed by a manual separation allowed an isolation of gallium rich fractions, with gallium mass fractions up to

Sputter deposited gallium doped ZnO for TCO applications

Energy Technology Data Exchange (ETDEWEB)

Dietrich, Marc; Kronenberger, Achim; Polity, Angelika; Meyer, Bruno [I. Physikalisches Institut, Justus Liebig Universitaet Giessen (Germany); Blaesing, Juergen; Krost, Alois [FNW/IEP/AHE, Otto-von-Guericke Universitaet Magdeburg (Germany)

2010-07-01

Transparent conducting oxides to be used for flat panel or display applications should exhibit low electrical resistivity in line with a high optical transmission in the visible spectral range. Today indium-tin-oxide is the material which meets these requirements best. However, the limited availability of indium makes it useful to search for alternatives and ZnO doped with group III elements are promising candidates. While the Al doping in high concentrations causes problems due to the formation of insulating Al-oxides, Gallium related oxides are typically n-type conducting wide band gap semiconductors. Therefore we deposited Gallium doped ZnO thin films on quartz and sapphire substrates by radio frequency magnetron sputtering with a ZnO/Ga{sub 2}O{sub 3}(3at%) composite target. The substrate temperature and the oxygen flow during the sputtering process were varied to optimise the layer properties. Introducing oxygen to the sputtering gas allowed to vary the resistivity of the films by three orders of magnitude from about 1 {omega}cm down to less than 1 m{omega}cm.

Peculiarities of electrooptical characteristics of gallium phosphide light-emitting diodes in high injection level conditions

Directory of Open Access Journals (Sweden)

O. M. Hontaruk

2015-04-01

Full Text Available Electroluminescence of green N-doped gallium phosphide light-emitting diodes was studied. The negative differential resistance region in the current-voltage characteristics was found at low temperature (Т ≤ 90 К. Possible reason of this phenomenon is the redistribution of recombinational flows between annihilation channels on isolated nitrogen atoms and annihilation channel on the NN1 pairs.

Gallium Nitride Schottky betavoltaic nuclear batteries

International Nuclear Information System (INIS)

Lu Min; Zhang Guoguang; Fu Kai; Yu Guohao; Su Dan; Hu Jifeng

2011-01-01

Research highlights: → Gallium Nitride nuclear batteries with Ni-63 are demonstrated for the first time. → Open circuit voltage of 0.1 V and conversion efficiency of 0.32% have been obtained. → The limited performance is due to thin effective energy deposition layer. → The output power is expected to greatly increase with growing thick GaN films. -- Abstract: Gallium Nitride (GaN) Schottky betavoltaic nuclear batteries (GNBB) are demonstrated in our work for the first time. GaN films are grown on sapphire substrates by metalorganic chemical vapor deposition (MOCVD), and then GaN Schottky diodes are fabricated by normal micro-fabrication process. Nickel with mass number of 63 ( 63 Ni), which emits β particles, is loaded on the GaN Schottky diodes to achieve GNBB. X-ray diffraction (XRD) and photoluminescence (PL) are carried out to investigate the crystal quality for the GaN films as grown. Current-voltage (I-V) characteristics shows that the GaN Schottky diodes are not jet broken down at -200 V due to consummate fabrication processes, and the open circuit voltage of the GNBB is 0.1 V and the short circuit current density is 1.2 nA cm -2 . The limited performance of the GNBB is due to thin effective energy deposition layer, which is only 206 nm to absorb very small partial energy of the β particles because of the relatively high dislocation density and carrier concentration. However, the conversion efficiency of 0.32% and charge collection efficiency (CCE) of 29% for the GNBB have been obtained. Therefore, the output power of the GNBB are expected to greatly increase with growing high quality thick GaN films.

Absence of low temperature phase transitions and enhancement of ferroelectric transition temperature in highly strained BaTiO{sub 3} epitaxial films grown on MgO Substrates

Energy Technology Data Exchange (ETDEWEB)

Kumar, Satish; Kumar, Dhirendra; Sathe, V. G., E-mail: vasant@csr.res.in [UGC-DAE Consortium for Scientific Research, University Campus, Khandwa Road, Indore 452001 (India); Kumar, Ravi; Sharma, T. K. [Semiconductor Physics and Devices Lab, Raja Ramanna Centre for Advanced Technology, Indore 452013 (India)

2015-04-07

Recently, a large enhancement in the ferroelectric transition temperature of several oxides is reported by growing the respective thin films on appropriate substrates. This phenomenon is correlated with high residual strain in thin films often leading to large increase in the tetragonality of their crystal structure. However, such an enhancement of transition temperature is usually limited to very thin films of ∼10 nm thickness. Here, we report growth of fully strained epitaxial thin films of BaTiO{sub 3} of 400 nm thickness, which are coherently grown on MgO substrates by pulsed laser deposition technique. Conventional high resolution x-ray diffraction and also the reciprocal space map measurements confirm that the film is fully strained with in-plane tensile strain of 5.5% that dramatically increases the tetragonality to 1.05. Raman measurements reveal that the tetragonal to cubic structural phase transition is observed at 583 K, which results in an enhancement of ∼200 K. Furthermore, temperature dependent Raman studies on these films corroborate absence of all the low temperature phase transitions. Numerical calculations based on thermodynamical model predict a value of the transition temperature that is greater than 1500 °C. Our experimental results are therefore in clear deviation from the existing strain dependent phase diagrams.

Composition control of low-volatile solids through chemical vapor transport reactions. III. The example of gallium monoselenide: Control of the polytypic structure, non-stoichiometry and properties

International Nuclear Information System (INIS)

Zavrazhnov, A.; Naumov, A.; Sidey, V.; Pervov, V.

2012-01-01

Highlights: ► This work is devoted to the composition control of solids with selective CVT method. ► Phase identity and non-stoichiometry of solids (GaSe, etc.) depend on CVT-temperatures. ► The interrelation between the properties of GaSe and CVT conditions is also found. ► For iodide transporting system the diagram of phase stability of solids is adjusted. ► High temperatures and Se-rich non-stoichiometry are necessary for γ-GaSe stability. - Abstract: By means of particular examples, the present work demonstrates the possibility of directed delicate non-destructive control of structure, composition and properties of inorganic solids using the method of selective chemical vapor transport (SCVT). Gallium monoselenide GaSe is the main model object. Additional, though less detailed, explanation is given by the example of gallium monosulfide GaS. Experimental evidences on the possibility of the control of polytypic structure, non-stoichiometry and properties of gallium monoselenide were obtained in non-isothermal variant of selective chemical vapor transport which has non-destructive character. Diagnostics of the phase (polytypic) composition and non-stoichiometry of GaSe was performed with the use of X-ray diffractometry as well as with the use of cathode luminescence spectra. It was experimentally found that there exists a connection of non-stoichiometry and the properties of gallium selenides with the determining conditions of selective chemical vapor transport: temperature of controlled sample (T 2 ) and the difference of temperatures between the hot and cold zones (ΔT). It is shown that the phase diagram of Ga–Se system needs to be partially revised near the composition of Ga 1 Se 1 . The reason for such revision is the fact that two polytypes (ε-GaSe and γ-GaSe) exist on this phase diagram as independent phases.

Directional phonon-assisted cascading of photoexcited carriers in stepped Inx(Al0.17Ga0.83)1-xAs/Al0.17Ga0.83As multiple quantum wells

DEFF Research Database (Denmark)

Machida, S.; Matsuo, M.; Fujiwara, K.

2002-01-01

Perpendicular motion of photoexcited electron and hole pairs assisted by phononscattering is investigated in a novel step-graded staircase heterostructure consisting of strained In-1(Al0.17Ga0.83)(1-x). As multiple quantum wells (QWs) with similar widths but five different x values by cw and time...... amplitude in the inter-mediate temperature range, These variations reveal that the photoexcited carriers directionally move from shallower to deeper QWs via phonon-assisted activation above the barrier hand edge state. The PL dynamics directly indicate the perpendicular flowing of photoexcited carriers...

Optimization of growth parameters for MOVPE-grown GaSb and Ga{sub 1-x}In{sub x}Sb

Energy Technology Data Exchange (ETDEWEB)

Miya, S.S.; Wagener, V. [Department of Physics, Private Bag X 77000, Nelson Mandela Metropolitan University, Port Elizabeth 6001 (South Africa); Botha, J.R., E-mail: reinhardt.botha@nmmu.ac.za [Department of Physics, Private Bag X 77000, Nelson Mandela Metropolitan University, Port Elizabeth 6001 (South Africa)

2012-05-15

The triethylgallium/trimethylantimony (TEGa/TMSb) precursor combination was used for the metal-organic vapour phase epitaxial growth of GaSb at a growth temperature of 520 Degree-Sign C at atmospheric pressure. Trimethylindium was added in the case of Ga{sub 1-x}In{sub x}Sb growth. The effects of group V flux to group III flux ratio (V/III ratio) on the crystallinity and optical properties of GaSb layers are reported. It has been observed from the crystalline quality and optical properties that nominal V/III ratios of values greater than unity are required for GaSb epitaxial layers grown at this temperature. It has also been shown that Ga{sub 1-x}In{sub x}Sb can be grown using TEGa as a source of gallium species at atmospheric pressure. The relationship between Ga{sub 1-x}In{sub x}Sb vapour composition and solid composition has been studied at a V/III ratio of 0.78.

Structural and electronic properties of InN nanowire network grown by vapor-liquid-solid method

Directory of Open Access Journals (Sweden)

B. K. Barick

2015-05-01

Full Text Available Growth of InN nanowires have been carried out on quartz substrates at different temperatures by vapor-liquid-solid (VLS technique using different thicknesses of Au catalyst layer. It has been found that a narrow window of Au layer thickness and growth temperature leads to multi-nucleation, in which each site acts as the origin of several nanowires. In this multi-nucleation regime, several tens of micrometer long wires with diameter as small as 20 nm are found to grow along [ 11 2 ̄ 0 ] direction (a-plane to form a dense network. Structural and electronic properties of these wires are studied. As grown nanowires show degenerate n-type behavior. Furthermore, x-ray photoemission study reveals an accumulation of electrons on the surface of these nanowires. Interestingly, the wire network shows persistence of photoconductivity for several hours after switching off the photoexcitation.

Molecular Beam Epitaxy-Grown InGaN Nanowires and Nanomushrooms for Solid State Lighting

KAUST Repository

Gasim, Anwar A.

2012-05-01

InGaN is a promising semiconductor for solid state lighting thanks to its bandgap which spans the entire visible regime of the electromagnetic spectrum. InGaN is grown heteroepitaxially due to the absence of a native substrate; however, this results in a strained film and a high dislocation density—two effects that have been associated with efficiency droop, which is the disastrous drop in efficiency of a light-emitting diode (LED) as the input current increases. Heteroepitaxially grown nanowires have recently attracted great interest due to their property of eliminating the detrimental effects of the lattice mismatch and the corollary efficiency droop. In this study, InGaN nanowires were grown on a low-cost Si (111) substrate via molecular beam epitaxy. Unique nanostructures, taking the form of mushrooms, have been observed in localized regions on the samples. These nanomushrooms consist of a nanowire body with a wide cap on top. Photoluminescence characterization revealed that the nanowires emit violet-blue, whilst the nanomushrooms emit a broad yellow-orange-red luminescence. The simultaneous emission from the nanowires and nanomushrooms forms white light. Structural characterization of a single nanomushroom via transmission electron microscopy revealed a simultaneous increase in indium and decrease in gallium at the interface between the body and the cap. Furthermore, the cap itself was found to be indium-rich, confirming it as the source of the longer wavelength yellow-orange-red luminescence. It is believed that the nanomushroom cap formed as a consequence of the saturation of growth on the c-plane of the nanowire. It is proposed that the formation of an indium droplet on the tip of the nanowire saturated growth on the c-plane, forcing the indium and gallium adatoms to incorporate on the sidewall m-planes instead, but only at the nanowire tip. This resulted in the formation of a mushroom-like cap on the tip. How and why the indium droplets formed is not

Pulsed laser deposition of epitaxial yttrium iron garnet films with low Gilbert damping and bulk-like magnetization

Directory of Open Access Journals (Sweden)

M. C. Onbasli

2014-10-01

Full Text Available Yttrium iron garnet (YIG, Y 3Fe5O12 films have been epitaxially grown on Gadolinium Gallium Garnet (GGG, Gd3Ga5O12 substrates with (100 orientation using pulsed laser deposition. The films were single-phase, epitaxial with the GGG substrate, and the root-mean-square surface roughness varied between 0.14 nm and 0.2 nm. Films with thicknesses ranging from 17 to 200 nm exhibited low coercivity (<2 Oe, near-bulk room temperature saturation moments (∼135 emu cm−3, in-plane easy axis, and damping parameters as low as 2.2 × 10−4. These high quality YIG thin films are useful in the investigation of the origins of novel magnetic phenomena and magnetization dynamics.

Crystalline-like temperature dependence of the electrical characteristics in amorphous Indium-Gallium-Zinc-Oxide thin film transistors

Science.gov (United States)

Estrada, M.; Hernandez-Barrios, Y.; Cerdeira, A.; Ávila-Herrera, F.; Tinoco, J.; Moldovan, O.; Lime, F.; Iñiguez, B.

2017-09-01

A crystalline-like temperature dependence of the electrical characteristics of amorphous Indium-Gallium-Zinc-Oxide (a-IGZO) thin film transistors (TFTs) is reported, in which the drain current reduces as the temperature is increased. This behavior appears for values of drain and gate voltages above which a change in the predominant conduction mechanism occurs. After studying the possible conduction mechanisms, it was determined that, for gate and drain voltages below these values, hopping is the predominant mechanism with the current increasing with temperature, while for values above, the predominant conduction mechanism becomes percolation in the conduction band or band conduction and IDS reduces as the temperature increases. It was determined that this behavior appears, when the effect of trapping is reduced, either by varying the density of states, their characteristic energy or both. Simulations were used to further confirm the causes of the observed behavior.

Photo-induced valence change of the sulfur atom in an L-cysteine thin film grown on a silver metal substrate in a saliva-emulated aqueous solution

Energy Technology Data Exchange (ETDEWEB)

Tsujibayashi, Toru [Department of Physics, Osaka Dental University, 8-1 Kuzuha-hanazono, Hirakata, Osaka 573-1121 (Japan); Azuma, Junpei; Yamamoto, Isamu; Takahashi, Kazutoshi; Kamada, Masao [Synchrotron Light Application Center, Saga University, 1 Honjo, Saga, Saga 840-8502 (Japan)

2015-04-27

A thin film of L-cysteine (HSCH{sub 2}CH(NH{sub 2})COOH) is grown on a silver substrate in saliva-emulated aqueous solution. X-ray photoemission spectroscopic measurements have revealed that the sulfur atom shows valence change under IR laser irradiation at 825 nm. The valence change maintains for about a minute at room temperature and more than an hour between 110 and 250 K after stopping the laser irradiation. It is not observed at all at temperatures lower than 110 K. This temperature-dependent behavior indicates that the photo-excited electronic change should be accompanied by a conformational change in the L-cysteine molecule. It is strongly suggested that the reversible valence change of the sulfur atom is applicable to a memory used around room temperature.

Growth of Gold-assisted Gallium Arsenide Nanowires on Silicon Substrates via Molecular Beam Epitaxy

Directory of Open Access Journals (Sweden)

Ramon M. delos Santos

2008-06-01

Full Text Available Gallium arsenide nanowires were grown on silicon (100 substrates by what is called the vapor-liquid-solid (VLS growth mechanism using a molecular beam epitaxy (MBE system. Good quality nanowires with surface density of approximately 108 nanowires per square centimeter were produced by utilizing gold nanoparticles, with density of 1011 nanoparticles per square centimeter, as catalysts for nanowire growth. X-ray diffraction measurements, scanning electron microscopy, transmission electron microscopy and Raman spectroscopy revealed that the nanowires are epitaxially grown on the silicon substrates, are oriented along the [111] direction and have cubic zincblende structure.

Photoexcited carrier trapping and recombination at Fe centers in GaN

International Nuclear Information System (INIS)

Uždavinys, T. K.; Marcinkevičius, S.; Leach, J. H.; Evans, K. R.; Look, D. C.

2016-01-01

Fe doped GaN was studied by time-resolved photoluminescence (PL) spectroscopy. The shape of PL transients at different temperatures and excitation powers allowed discrimination between electron and hole capture to Fe"3"+ and Fe"2"+ centers, respectively. Analysis of the internal structure of Fe ions and intra-ion relaxation rates suggests that for high repetition rates of photoexciting laser pulses the electron and hole trapping takes place in the excited state rather than the ground state of Fe ions. Hence, the estimated electron and hole capture coefficients of 5.5 × 10"−"8 cm"3/s and 1.8 × 10"−"8 cm"3/s should be attributed to excited Fe"3"+ and Fe"2"+ states. The difference in electron capture rates determined for high (MHz) and low (Hz) (Fang et al., Appl. Phys. Lett. 107, 051901 (2015)) pulse repetition rates may be assigned to the different Fe states participating in the carrier capture. A weak temperature dependence of the electron trapping rate shows that the potential barrier for the multiphonon electron capture is small. A spectral feature observed at ∼420 nm is assigned to the radiative recombination of an electron in the ground Fe"2"+ state and a bound hole.

Medical Applications and Toxicities of Gallium Compounds

Directory of Open Access Journals (Sweden)

Christopher R. Chitambar

2010-05-01

Full Text Available Over the past two to three decades, gallium compounds have gained importance in the fields of medicine and electronics. In clinical medicine, radioactive gallium and stable gallium nitrate are used as diagnostic and therapeutic agents in cancer and disorders of calcium and bone metabolism. In addition, gallium compounds have displayed anti-inflammatory and immunosuppressive activity in animal models of human disease while more recent studies have shown that gallium compounds may function as antimicrobial agents against certain pathogens. In a totally different realm, the chemical properties of gallium arsenide have led to its use in the semiconductor industry. Gallium compounds, whether used medically or in the electronics field, have toxicities. Patients receiving gallium nitrate for the treatment of various diseases may benefit from such therapy, but knowledge of the therapeutic index of this drug is necessary to avoid clinical toxicities. Animals exposed to gallium arsenide display toxicities in certain organ systems suggesting that environmental risks may exist for individuals exposed to this compound in the workplace. Although the arsenic moiety of gallium arsenide appears to be mainly responsible for its pulmonary toxicity, gallium may contribute to some of the detrimental effects in other organs. The use of older and newer gallium compounds in clinical medicine may be advanced by a better understanding of their mechanisms of action, drug resistance, pharmacology, and side-effects. This review will discuss the medical applications of gallium and its mechanisms of action, the newer gallium compounds and future directions for development, and the toxicities of gallium compounds in current use.

Aluminium, gallium, indium and thallium

International Nuclear Information System (INIS)

Brown, Paul L.; Ekberg, Christian

2016-01-01

Aluminium can exist in a number of oxyhydroxide mineral phases including corundum, diaspore, boehmite and gibbsite. The stability constants at zero ionic strength reported for Al(OH) 3 (aq) vary linearly with respect to the inverse of absolute temperature. A full suite of thermodynamic parameters is available for all aluminium phases and hydrolysis species. Gallium hydrolyses to a greater extent than aluminium, with the onset of hydrolysis reactions occurring just above a pHof 1. In fact, even though aluminium has the smallest ionic radius of this series of metals, it has the weakest hydrolysis species and oxide/hydroxide phases.This is due to the presence of stabilising d-orbitals in the heavier metals, gallium, indium and thallium(III). There are few available data for the stability constants of indium(III) hydrolysis species. Of those that are available, the range in the proposed stability constants covers many orders of magnitude.

Low-Temperature, Chemically Grown Titanium Oxide Thin Films with a High Hole Tunneling Rate for Si Solar Cells

Directory of Open Access Journals (Sweden)

Yu-Tsu Lee

2016-05-01

Full Text Available In this paper, we propose a chemically grown titanium oxide (TiO2 on Si to form a heterojunction for photovoltaic devices. The chemically grown TiO2 does not block hole transport. Ultraviolet photoemission spectroscopy was used to study the band alignment. A substantial band offset at the TiO2/Si interface was observed. X-ray photoemission spectroscopy (XPS revealed that the chemically grown TiO2 is oxygen-deficient and contains numerous gap states. A multiple-trap-assisted tunneling (TAT model was used to explain the high hole injection rate. According to this model, the tunneling rate can be 105 orders of magnitude higher for holes passing through TiO2 than for flow through SiO2. With 24-nm-thick TiO2, a Si solar cell achieves a 33.2 mA/cm2 photocurrent on a planar substrate, with a 9.4% power conversion efficiency. Plan-view scanning electron microscopy images indicate that a moth-eye-like structure formed during TiO2 deposition. This structure enables light harvesting for a high photocurrent. The high photocurrent and ease of production of chemically grown TiO2 imply that it is a suitable candidate for future low-cost, high-efficiency solar cell applications.

Prospects for recovering gallium from extracted coal

Energy Technology Data Exchange (ETDEWEB)

Ratynskiy, V M; Reznik, A M; Zekel, L A; Zharov, Yu N

1979-01-01

The authors conducted research in order to establish the physical-chemical mechanisms governing the behavior of rare and dispersed elements within the thermal treatment processes used to treat coal and enrichment waste. New means are proposed for obtaining concentrations of gallium. These methods are under consideration primarily for the isolation of gallium as a by-product during the production of aggloporite from coal waste. The authors examine in detail the results of research dealing with the transfer of gallium compounds in a solution, the extraction of gallium from solutions, the separation of impurities from gallium, and the isolation of gallium from extract. Utilizing research results, the authors determine the expenditure coefficient and costs for additives used to extract gallium from waste by-products. The realization of this gallium extraction process from those products having the best prospects for gallium content resulted in economic savings.

First results from the Soviet-American Gallium Experiment

International Nuclear Information System (INIS)

Abazov, A.I.; Abdurashitov, D.N.; Anosov, O.L.; Eroshkina, L.A.; Faizov, E.L.; Gavrin, V.N.; Kalikhov, A.V.; Knodel, T.V.; Knyshenko, I.I.; Kornoukhov, V.N.; Mezentseva, S.A.; Mirmov, I.N.; Ostrinsky, A.I.; Petukhov, V.V.; Pshukov, A.M.; Revzin, N.Y.; Shikhin, A.A.; Timofeyev, P.V.; Veretenkin, E.P.; Vermul, V.M.; Zakharov, Y.; Zatsepin, G.T.; Zhandarov, V.I.; Davis, R. Jr.; Lande, K.; Cherry, M.L.; Kouzes, R.T.

1990-01-01

The Soviet-American Gallium Experiment is the first experiment able to measure the dominant flux of low energy p-p solar neutrinos. Four extractions made during January to May 1990 from 30 tons of gallium have been counted and indicate that the flux is consistent with 0 SNU and is less than 72 SNU (68% CL) and less than 138 SNU (95% CL). This is to be compared with the flux of 132 SNU predicted by the Standard Solar Model. 10 refs., 4 figs., 1 tab

Leaching of gallium from gaiter granite, eastern desert, Egypt

International Nuclear Information System (INIS)

Zahran, M.A.; Mahmoud, KH.F.; Mahdy, M.A.; Abd El-Hamid, A.M.

2006-01-01

Preliminary leaching tests of gallium from some Egyptian granite rocks such as those of Gabal Gattar area was investigated by using 8 M HCl acid and sodium perchlorate as oxidant. To achieve the optimum leaching conditions, the factors affecting the leaching efficiency as the acid type and concentration, oxidant type and amount, leaching temperature, agitation time, solid / liquid ratio and the effect of grain size were studied. The complete chemical analysis of the collected samples was firstly carried out to determine the chemical features of the Gattarian granite. More than 97% of gallium content was leached when applying these optimum leaching conditions

Effect of post-growth annealing on secondary phase formation in low-temperature-grown Mn-doped GaAs

DEFF Research Database (Denmark)

Kovács, A.; Sadowski, J.; Kasama, Takeshi

2013-01-01

The microstructures of annealed GaAs layers containing 0.1%, 0.5% and 2% Mn are studied using aberration-corrected transmission electron microscopy (TEM). The layers were grown by molecular beam epitaxy at 270 °C. After heat treatment at 400, 560 and 630 °C, they are found to contain precipitate...... in annealed GaMnAs layers doped with low Mn concentrations is proposed....

Long-chain amine-templated synthesis of gallium sulfide and gallium selenide nanotubes

Science.gov (United States)

Seral-Ascaso, A.; Metel, S.; Pokle, A.; Backes, C.; Zhang, C. J.; Nerl, H. C.; Rode, K.; Berner, N. C.; Downing, C.; McEvoy, N.; Muñoz, E.; Harvey, A.; Gholamvand, Z.; Duesberg, G. S.; Coleman, J. N.; Nicolosi, V.

2016-06-01

We describe the soft chemistry synthesis of amine-templated gallium chalcogenide nanotubes through the reaction of gallium(iii) acetylacetonate and the chalcogen (sulfur, selenium) using a mixture of long-chain amines (hexadecylamine and dodecylamine) as a solvent. Beyond their role as solvent, the amines also act as a template, directing the growth of discrete units with a one-dimensional multilayer tubular nanostructure. These new materials, which broaden the family of amine-stabilized gallium chalcogenides, can be tentatively classified as direct large band gap semiconductors. Their preliminary performance as active material for electrodes in lithium ion batteries has also been tested, demonstrating great potential in energy storage field even without optimization.We describe the soft chemistry synthesis of amine-templated gallium chalcogenide nanotubes through the reaction of gallium(iii) acetylacetonate and the chalcogen (sulfur, selenium) using a mixture of long-chain amines (hexadecylamine and dodecylamine) as a solvent. Beyond their role as solvent, the amines also act as a template, directing the growth of discrete units with a one-dimensional multilayer tubular nanostructure. These new materials, which broaden the family of amine-stabilized gallium chalcogenides, can be tentatively classified as direct large band gap semiconductors. Their preliminary performance as active material for electrodes in lithium ion batteries has also been tested, demonstrating great potential in energy storage field even without optimization. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr01663d

Magnetic refrigeration cycle analysis using selected thermodynamic property characterizations for gadolinium gallium garnet

International Nuclear Information System (INIS)

Murphy, R.W.

1992-01-01

Magneto-thermodynamic property characterizations were selected, adapted, and compared to material property data for gadolinium gallium garnet in the temperature range 4--40 K and magnetic field range 0--6 T. The most appropriate formulations were incorporated into a model in which methods similar to those previously developed for other materials and temperature ranges were used to make limitation and relative performance assessments of Carnot, ideal regenerative, and pseudo-constant field regenerative cycles. Analysis showed that although Carnot cycle limitations on available temperature lift for gadolinium gallium garnet are not as severe as those for materials previously examined, substantial improvements in cooling capacity/temperature lift combinations can be achieved using regenerative cycles within specified fields limits if significant loss mechanisms are mitigated

Theory of Primary Photoexcitations in Donor-Acceptor Copolymers.

Science.gov (United States)

Aryanpour, Karan; Dutta, Tirthankar; Huynh, Uyen N V; Vardeny, Zeev Valy; Mazumdar, Sumit

2015-12-31

We present a generic theory of primary photoexcitations in low band gap donor-acceptor conjugated copolymers. Because of the combined effects of strong electron correlations and broken symmetry, there is considerable mixing between a charge-transfer exciton and an energetically proximate triplet-triplet state with an overall spin singlet. The triplet-triplet state, optically forbidden in homopolymers, is allowed in donor-acceptor copolymers. For an intermediate difference in electron affinities of the donor and the acceptor, the triplet-triplet state can have a stronger oscillator strength than the charge-transfer exciton. We discuss the possibility of intramolecular singlet fission from the triplet-triplet state, and how such fission can be detected experimentally.

Selective growth of gallium nitride nanowires by femtosecond laser patterning

International Nuclear Information System (INIS)

Ng, D.K.T.; Hong, M.H.; Tan, L.S.; Zhou, Y.; Chen, G.X.

2008-01-01

We report on gallium nitride (GaN) nanowires grown using pulsed laser ablation, adopting the vapor-liquid-solid (VLS) growth mechanism. The GaN nanowires are obtained based on the principle that a catalyst is required to initiate the nanowires growth. Locations of the GaN nanowires are patterned using femtosecond laser and focused ion beam. Scanning electron microscopy (SEM) is used to characterize the nanowires. This patterning of GaN nanowires will enable selective growth of nanowires and bottom-up assembly of integrated electronic and photonic devices

Selective growth of gallium nitride nanowires by femtosecond laser patterning

Energy Technology Data Exchange (ETDEWEB)

Ng, D.K.T. [Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Data Storage Institute, Agency for Science, Technology and Research, DSI Building, 5 Engineering Drive 1, Singapore 117608 (Singapore); Hong, M.H. [Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Data Storage Institute, Agency for Science, Technology and Research, DSI Building, 5 Engineering Drive 1, Singapore 117608 (Singapore)], E-mail: HONG_Minghui@dsi.a-star.edu.sg; Tan, L.S. [Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Zhou, Y. [Data Storage Institute, Agency for Science, Technology and Research, DSI Building, 5 Engineering Drive 1, Singapore 117608 (Singapore); Department of Mechanical Engineering, National University of Singapore, 2 Engineering Drive 3, Singapore 117576 (Singapore); Chen, G.X. [Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore)

2008-01-31

We report on gallium nitride (GaN) nanowires grown using pulsed laser ablation, adopting the vapor-liquid-solid (VLS) growth mechanism. The GaN nanowires are obtained based on the principle that a catalyst is required to initiate the nanowires growth. Locations of the GaN nanowires are patterned using femtosecond laser and focused ion beam. Scanning electron microscopy (SEM) is used to characterize the nanowires. This patterning of GaN nanowires will enable selective growth of nanowires and bottom-up assembly of integrated electronic and photonic devices.

Structural and elastoplastic properties of β -Ga2O3 films grown on hybrid SiC/Si substrates

Science.gov (United States)

Osipov, A. V.; Grashchenko, A. S.; Kukushkin, S. A.; Nikolaev, V. I.; Osipova, E. V.; Pechnikov, A. I.; Soshnikov, I. P.

2018-04-01

Structural and mechanical properties of gallium oxide films grown on (001), (011) and (111) silicon substrates with a buffer layer of silicon carbide are studied. The buffer layer was fabricated by the atom substitution method, i.e., one silicon atom per unit cell in the substrate was substituted by a carbon atom by chemical reaction with carbon monoxide. The surface and bulk structure properties of gallium oxide films have been studied by atomic-force microscopy and scanning electron microscopy. The nanoindentation method was used to investigate the elastoplastic characteristics of gallium oxide, and also to determine the elastic recovery parameter of the films under study. The ultimate tensile strength, hardness, elastic stiffness constants, elastic compliance constants, Young's modulus, linear compressibility, shear modulus, Poisson's ratio and other characteristics of gallium oxide have been calculated by quantum chemistry methods based on the PBESOL functional. It is shown that all these properties of gallium oxide are essentially anisotropic. The calculated values are compared with experimental data. We conclude that a change in the silicon orientation leads to a significant reorientation of gallium oxide.

Effect of Different Arbuscular Mycorrhizal Fungi on Growth and Physiology of Maize at Ambient and Low Temperature Regimes

Directory of Open Access Journals (Sweden)

Xiaoying Chen

2014-01-01

Full Text Available The effect of four different arbuscular mycorrhizal fungi (AMF on the growth and lipid peroxidation, soluble sugar, proline contents, and antioxidant enzymes activities of Zea mays L. was studied in pot culture subjected to two temperature regimes. Maize plants were grown in pots filled with a mixture of sandy and black soil for 5 weeks, and then half of the plants were exposed to low temperature for 1 week while the rest of the plants were grown under ambient temperature and severed as control. Different AMF resulted in different root colonization and low temperature significantly decreased AM colonization. Low temperature remarkably decreased plant height and total dry weight but increased root dry weight and root-shoot ratio. The AM plants had higher proline content compared with the non-AM plants. The maize plants inoculated with Glomus etunicatum and G. intraradices had higher malondialdehyde and soluble sugar contents under low temperature condition. The activities of catalase (CAT and peroxidase of AM inoculated maize were higher than those of non-AM ones. Low temperature noticeably decreased the activities of CAT. The results suggest that low temperature adversely affects maize physiology and AM symbiosis can improve maize seedlings tolerance to low temperature stress.

Collector for recovering gallium from weapons plutonium

International Nuclear Information System (INIS)

Philip, C.V.; Anthony, R.G.; Chokkaram, S.

1998-09-01

Currently, the separation of gallium from weapons plutonium involves the use of aqueous processing using either solvent extraction of ion exchange. However, this process generates significant quantities of liquid radioactive wastes. A Thermally Induced Gallium Removal process, or TIGR, developed by researchers at Los Alamos National Laboratories, is a simpler alternative to aqueous processing. This research examined this process, and the behavior of gallium suboxide, a vapor that is swept away by passing hydrogen/argon over gallium trioxide/plutonium oxide heated at 1100 C during the TIGR process. Through experimental procedures, efforts were made to prevent the deposition of corrosive gallium onto furnace and vent surfaces. Experimental procedures included three options for gallium removal and collection: (1) collection of gallium suboxide through use of a cold finger; (2) collection by in situ air oxidation; and (3) collection of gallium on copper. Results conclude all three collection mechanisms are feasible. In addition, gallium trioxide exists in three crystalline forms, and each form was encountered during each experiment, and that each form will have a different reactivity

Sucrose Phosphate Synthase and Sucrose Accumulation at Low Temperature 1

Science.gov (United States)

Guy, Charles L.; Huber, Joan L. A.; Huber, Steven C.

1992-01-01

The influence of growth temperature on the free sugar and sucrose phosphate synthase content and activity of spinach (Spinacia oleracea) leaf tissue was studied. When plants were grown at 25°C for 3 weeks and then transferred to a constant 5°C, sucrose, glucose, and fructose accumulated to high levels during a 14-d period. Predawn sugar levels increased from 14- to 20-fold over the levels present at the outset of the low-temperature treatment. Sucrose was the most abundant free sugar before, during, and after exposure to 5°C. Leaf sucrose phosphate synthase activity was significantly increased by the low-temperature treatment, whereas sucrose synthase and invertases were not. Synthesis of the sucrose phosphate synthase subunit was increased during and after low-temperature exposure and paralleled an increase in the steady-state level of the subunit. The increases in sucrose and its primary biosynthetic enzyme, sucrose phosphate synthase, are discussed in relation to adjustment of metabolism to low nonfreezing temperature and freezing stress tolerance. Images Figure 1 Figure 2 Figure 3 PMID:16652990

Gallium and copper radiopharmaceutical chemistry

International Nuclear Information System (INIS)

Green, M.A.

1991-01-01

Gallium and copper radionuclides have a long history of use in nuclear medicine. Table 1 presents the nuclear properties of several gallium and copper isotopes that either are used in the routine practice of clinical nuclear medicine or exhibit particular characteristics that might make them useful in diagnostic or therapeutic medicine. This paper will provide some historic perspective along with an overview of some current research directions in gallium and copper radiopharmaceutical chemistry. A more extensive review of gallium radiopharmaceutical chemistry has recently appeared and can be consulted for a more in-depth treatment of this topic

Dynamics of photoexcited quasiparticles in heavy electron compounds

International Nuclear Information System (INIS)

Demsar, Jure; Sarrao, John L; Taylor, Antoinette J

2006-01-01

Femtosecond real-time spectroscopy is an emerging new tool for studying low energy electronic structure in correlated electron systems. Motivated by recent advances in understanding the nature of relaxation phenomena in various correlated electron systems (superconductors, density wave systems) the technique has been applied to heavy electron compounds in comparison with their non-magnetic counterparts. While the dynamics in their non-magnetic analogues are similar to the dynamics observed in noble metals (only weak temperature dependences are observed) and can be treated with a simple two-temperature model, the photoexcited carrier dynamics in heavy electron systems show dramatic changes as a function of temperature and excitation level. In particular, below some characteristic temperature the relaxation rate starts to decrease, dropping by more than two orders of magnitude upon cooling down to liquid He temperatures. This behaviour has been consistently observed in various heavy fermion metals as well as Kondo insulators, and is believed to be quite general. In order to account for the experimental observations, two theoretical models have been proposed. The first treats the heavy electron systems as simple metals with very flat electron dispersion near the Fermi level. An electron-phonon thermalization scenario can account for the observed slowing down of the relaxation provided that there exists a mechanism for suppression of electron-phonon scattering when both the initial and final electronic states lie in the region of flat dispersion. An alternative scenario argues that the relaxation dynamics in heavy electron systems are governed by the Rothwarf-Taylor bottleneck, where the dynamics are governed by the presence of a narrow gap in the density of states near the Fermi level. The so-called hybridization gap results from hybridization between localized moments and the conduction electron background. Remarkable agreement with the model suggests that carrier

High Quality, Low Cost Bulk Gallium Nitride Substrates Grown by the Electrochemical Solution Growth Method

Energy Technology Data Exchange (ETDEWEB)

Seacrist, Michael [SunEdison Inc., St. Peters, MO (United States)

2017-08-15

The objective of this project was to develop the Electrochemical Solution Growth (ESG) method conceived / patented at Sandia National Laboratory into a commercially viable bulk gallium nitride (GaN) growth process that can be scaled to low cost, high quality, and large area GaN wafer substrate manufacturing. The goal was to advance the ESG growth technology by demonstrating rotating seed growth at the lab scale and then transitioning process to prototype commercial system, while validating the GaN material and electronic / optical device quality. The desired outcome of the project is a prototype commercial process for US-based manufacturing of high quality, large area, and lower cost GaN substrates that can drive widespread deployment of energy efficient GaN-based power electronic and optical devices. In year 1 of the project (Sept 2012 – Dec 2013) the overall objective was to demonstrate crystalline GaN growth > 100um on a GaN seed crystal. The development plan included tasks to demonstrate and implement a method for purifying reagent grade salts, develop the reactor 1 process for rotating seed Electrochemical Solution Growth (ESG) of GaN, grow and characterize ESG GaN films, develop a fluid flow and reaction chemistry model for GaN film growth, and design / build an improved growth reactor capable of scaling to 50mm seed diameter. The first year’s project objectives were met in some task areas including salt purification, film characterization, modeling, and reactor 2 design / fabrication. However, the key project objective of the growth of a crystalline GaN film on the seed template was not achieved. Amorphous film growth on the order of a few tenths of a micron has been detected with a film composition including Ga and N, plus several other impurities originating from the process solution and hardware. The presence of these impurities, particularly the oxygen, has inhibited the demonstration of crystalline GaN film growth on the seed template. However, the

Ohmic contact formation process on low n-type gallium arsenide (GaAs) using indium gallium zinc oxide (IGZO)

Energy Technology Data Exchange (ETDEWEB)

Yang, Seong-Uk [Samsung-SKKU Graphene Center and School of Electronics and Electrical Engineering, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of); Product and Test Engineering Team, System LSI Division, Samsung Electronics Co., Ltd, Yongin 446-711 (Korea, Republic of); Jung, Woo-Shik [Department of Electrical Engineering, Stanford University, Stanford, CA 94305 (United States); Lee, In-Yeal; Jung, Hyun-Wook; Kim, Gil-Ho [Samsung-SKKU Graphene Center and School of Electronics and Electrical Engineering, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of); Park, Jin-Hong, E-mail: jhpark9@skku.edu [Samsung-SKKU Graphene Center and School of Electronics and Electrical Engineering, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of)

2014-02-01

Highlights: • We propose a method to fabricate non-gold Ohmic contact on low n-type GaAs with IGZO. • 0.15 A/cm{sup 2} on-current and 1.5 on/off-current ratio are achieved in the junction. • InAs and InGaAs formed by this process decrease an electron barrier height. • Traps generated by diffused O atoms also induce a trap-assisted tunneling phenomenon. - Abstract: Here, an excellent non-gold Ohmic contact on low n-type GaAs is demonstrated by using indium gallium zinc oxide and investigating through time of flight-secondary ion mass spectrometry, X-ray photoelectron spectroscopy, transmission electron microscopy, J–V measurement, and H [enthalpy], S [entropy], Cp [heat capacity] chemistry simulation. In is diffused through GaAs during annealing and reacts with As, forming InAs and InGaAs phases with lower energy bandgap. As a result, it decreases the electron barrier height, eventually increasing the reverse current. In addition, traps generated by diffused O atoms induce a trap-assisted tunneling phenomenon, increasing generation current and subsequently the reverse current. Therefore, an excellent Ohmic contact with 0.15 A/cm{sup 2} on-current density and 1.5 on/off-current ratio is achieved on n-type GaAs.

Molecular Structure, Vibrational Spectra, Quantum Chemical Calculations and Photochemistry of Picolinamide and Isonicotinamide Isolated in Cryogenic Inert Matrixes and in the Neat Low-Temperature Solid Phases

OpenAIRE

Borba, Ana; Gómez-Zavaglia, Andrea; Fausto, R.

2007-01-01

Picolinamide (PA) and isonicotinamide (INA), two structural isomers of pyridinecarboxamide, have been investigated by matrix isolation and low-temperature solid-state infrared spectroscopy, combined with UV (λ > 235 nm) photoexcitation and density functional theory and ab initio (MP2) theoretical studies. In consonance with the theoretical data, both PA and INA were found to exist in a single conformation in cryogenic rare gas matrixes. Comparison between the experimental spectra of the matri...

Luminescent properties of Cr-doped gallium garnet crystals grown by the micro-pulling-down method

Czech Academy of Sciences Publication Activity Database

Kurosawa, S.; Suzuki, A.; Yamaji, A.; Kamada, K.; Pejchal, Jan; Ohashi, Y.; Yokota, Y.; Chani, V.I.; Yoshikawa, A.

2016-01-01

Roč. 452, Oct (2016), s. 95-100 ISSN 0022-0248. [American Conference on Crystal Growth and Epitaxy /20./ (ACCGE) / 17th Biennial Workshop on Organometallic Vapor Phase Epitaxy (OMVPE) / 2nd 2D Electronic Materials Symposium. Big Sky, MT, 02.08.2015-07.08.2015] Institutional support: RVO:68378271 Keywords : scintillator materials * single crystal growth * gallium compounds Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.751, year: 2016

Design and Evaluation of Large-Aperture Gallium Fixed-Point Blackbody

Science.gov (United States)

Khromchenko, V. B.; Mekhontsev, S. N.; Hanssen, L. M.

2009-02-01

To complement existing water bath blackbodies that now serve as NIST primary standard sources in the temperature range from 15 °C to 75 °C, a gallium fixed-point blackbody has been recently built. The main objectives of the project included creating an extended-area radiation source with a target emissivity of 0.9999 capable of operating either inside a cryo-vacuum chamber or in a standard laboratory environment. A minimum aperture diameter of 45 mm is necessary for the calibration of radiometers with a collimated input geometry or large spot size. This article describes the design and performance evaluation of the gallium fixed-point blackbody, including the calculation and measurements of directional effective emissivity, estimates of uncertainty due to the temperature drop across the interface between the pure metal and radiating surfaces, as well as the radiometrically obtained spatial uniformity of the radiance temperature and the melting plateau stability. Another important test is the measurement of the cavity reflectance, which was achieved by using total integrated scatter measurements at a laser wavelength of 10.6 μm. The result allows one to predict the performance under the low-background conditions of a cryo-chamber. Finally, results of the spectral radiance comparison with the NIST water-bath blackbody are provided. The experimental results are in good agreement with predicted values and demonstrate the potential of our approach. It is anticipated that, after completion of the characterization, a similar source operating at the water triple point will be constructed.

Cr2O3 thin films grown at room temperature by low pressure laser chemical vapour deposition

International Nuclear Information System (INIS)

Sousa, P.M.; Silvestre, A.J.; Conde, O.

2011-01-01

Chromia (Cr 2 O 3 ) has been extensively explored for the purpose of developing widespread industrial applications, owing to the convergence of a variety of mechanical, physical and chemical properties in one single oxide material. Various methods have been used for large area synthesis of Cr 2 O 3 films. However, for selective area growth and growth on thermally sensitive materials, laser-assisted chemical vapour deposition (LCVD) can be applied advantageously. Here we report on the growth of single layers of pure Cr 2 O 3 onto sapphire substrates at room temperature by low pressure photolytic LCVD, using UV laser radiation and Cr(CO) 6 as chromium precursor. The feasibility of the LCVD technique to access selective area deposition of chromia thin films is demonstrated. Best results were obtained for a laser fluence of 120 mJ cm -2 and a partial pressure ratio of O 2 to Cr(CO) 6 of 1.0. Samples grown with these experimental parameters are polycrystalline and their microstructure is characterised by a high density of particles whose size follows a lognormal distribution. Deposition rates of 0.1 nm s -1 and mean particle sizes of 1.85 μm were measured for these films.

Gallium nitrate: effects on cartilage during limb regeneration in the axolotl, Ambystoma mexicanum.

Science.gov (United States)

Tassava, Roy A; Mendenhall, Luciara; Apseloff, Glen; Gerber, Nicholas

2002-09-01

Gallium nitrate, a drug shown to have efficacy in Paget's disease of bone, hypercalcemia of malignancy, and a variety of experimental autoimmune diseases, also inhibits the growth of some types of cancer. We examined dose and timing of administration of gallium nitrate on limb regeneration in the Mexican axolotl, Ambystoma mexicanum. Administered by intraperitoneal injection, gallium nitrate inhibited limb regeneration in a dose-dependent manner. Gallium nitrate initially suppressed epithelial wound healing and subsequently distorted both anterior-posterior and proximo-distal chondrogenic patterns. Gallium nitrate given at three days after amputation severely inhibited regeneration at high doses (6.25 mg/axolotl) and altered the normal patterning of the regenerates at low doses (3.75 mg/axolotl). Administration of 6.25 mg of gallium nitrate at four or 14 days prior to amputation also inhibited regeneration. In amputated limbs of gallium-treated axolotls, the chondrocytes were lost from inside the radius/ulna. Limbs that regenerated after gallium treatment was terminated showed blastema formation preferentially over the ulna. New cartilage of the regenerate often attached to the sides of the existing radius/ulna proximally into the stump and less so to the distal cut ends. J. Exp. Zool. 293:384-394, 2002. Copyright 2002 Wiley-Liss, Inc.

Gallium-67 citrate scan in extrapulmonary tuberculosis

Energy Technology Data Exchange (ETDEWEB)

Lin Wanyu [Taichung Veterans General Hospital (Taiwan). Dept. of Nuclear Medicine; Hsieh Jihfang [Chi-Mei Foundation Hospital, Tainan (Taiwan)

1999-07-01

Aim: Whole-body gallium scan was performed to evaluate the usefulness of gallium scan for detecting extrapulmonary tuberculosis (TB) lesions. Methods: Thirty-seven patients with extrapulmonary TB were included in this study. Four patients were found to have two lesions. Totally, 41 lesions were identified, including 19 TB arthritis, 8 spinal TB, 5 TB meningitis, 3 TB lymphadenopathy, 2 TB pericarditis, 1 TB peritonitis, 1 intestinal TB, 1 skin TB and 1 renal TB. Results: Of the 41 extrapulmonary TB lesions, gallium scan detected 32 lesions with a sensitivity of 78%. All the patients with TB meningitis showed negative gallium scan. When the five cases of TB meningitis were excluded, the detection sensitivity of gallium scan increased to 88.9% (32/36). Conclusion: Our data revealed that gallium scan is a convenient and useful method for evaluating extrapulmonary TB lesions other than TB-meningitis. We suggest that gallium scan be included in the clinical routine for patients with suspected extrapulmonary TB. (orig.) [German] Ziel: Es wurden Ganzkoerper-Gallium-Szintigramme angefertigt, um den Nutzen der Gallium-Szintigraphie zur Erfassung von extrapulmonalen Tuberkuloseherden (TB) zu erfassen. Methoden: 37 Patienten mit extrapulmonaler TB wurden eingeschlossen. 4 Patienten hatten 2 Laesionen. Insgesamt wurden 41 Laesionen identifiziert, hierunter 19 TB-Arthritis, 8 spinale TB, 5 TB-Meningitis, 3 TB-Lymphadenopathie, 2 TB-Perikarditis, 1 TB-Peritonitis, 1 intestinale TB, 1 Haut-TB und eine Nieren-TB. Ergebnisse: Von den 41 extrapulmonalen TB-Herden erfasste die Gallium-Szintigraphie 32 Herde mit einer Sensitivitaet von 78%. Alle Patienten mit TB-Meningitis zeigten einen negativen Gallium-Scan. Wenn die 5 Faelle mit TB-Meningitis ausgeschlossen wurden, stieg die Sensitivititaet der Gallium-Szintigraphie auf 88,9% (32/36). Schlussfolgerung: Die Daten zeigen, dass die Gallium-Szintigraphie eine einfache und nuetzliche Methode zur Erfassung extrapulmonaler TB-Herde ist

Gallium scintigraphy in AIDS

International Nuclear Information System (INIS)

Van der Wall, Hans; Provan, I.; Murray, C.; Dwyer, M.; Jones, P.D.

1990-01-01

Gallium-67 scanning, indicated either for the elucidation of symptoms or for the assessment of appropriate therapy, was performed in 56 AIDS patients who underwent a total of 77 scans from 1986 to 1988. The age range of the patients was 13-66 years with an average age of 39 years. The majority of patients (95%) were male homosexuals. Gallium scanning has been applied to a wide spectrum of malignancies and to the detection of occult infections. Several mechanisms of uptake have been postulated for the localization of gallium. In general, gallium-67 acts as an analogue of the ferric ion, binding to transferrin soon after intravenous injection. It is believed that it is bound to transferrin receptors on the surface of tumour cells with subsequent intracellular transport. In infection, the association is probably with lactoferrin elaborated by polymorphonuclear cells and siderophores elaborated by bacteria. Gallium-67 is normally distributed to bone and bone marrow, liver, spleen, breast and bowel. In particular, the concentration in the ascending and transverse colon necessitates adequate bowel preparation. Lacrimal, nasopharyngeal and genital activity may also be seen. 11 refs., 2 tabs., 6 figs

Negative permittivity of ZnO thin films prepared from aluminum and gallium doped ceramics via pulsed-laser deposition

DEFF Research Database (Denmark)

Bodea, M. A.; Sbarcea, G.; Naik, G. V.

2013-01-01

Aluminum and gallium doped zinc oxide thin films with negative dielectric permittivity in the near infrared spectral range are grown by pulsed laser deposition. Composite ceramics comprising ZnO and secondary phase Al2O3 or Ga2O3 are employed as targets for laser ablation. Films deposited on glass...

Potential effects of gallium on cladding materials

International Nuclear Information System (INIS)

Wilson, D.F.; Beahm, E.C.; Besmann, T.M.; DeVan, J.H.; DiStefano, J.R.; Gat, U.; Greene, S.R.; Rittenhouse, P.L.; Worley, B.A.

1997-10-01

This paper identifies and examines issues concerning the incorporation of gallium in weapons derived plutonium in light water reactor (LWR) MOX fuels. Particular attention is given to the more likely effects of the gallium on the behavior of the cladding material. The chemistry of weapons grade (WG) MOX, including possible consequences of gallium within plutonium agglomerates, was assessed. Based on the calculated oxidation potentials of MOX fuel, the effect that gallium may have on reactions involving fission products and possible impact on cladding performance were postulated. Gallium transport mechanisms are discussed. With an understanding of oxidation potentials and assumptions of mechanisms for gallium transport, possible effects of gallium on corrosion of cladding were evaluated. Potential and unresolved issues and suggested research and development (R and D) required to provide missing information are presented

Hydrogen inventory in gallium

International Nuclear Information System (INIS)

Mazayev, S.N.; Prokofiev, Yu.G.

1994-01-01

Investigations of hydrogen inventory in gallium (99.9%) were carried out after saturation both from molecular phase and from glow discharge plasma at room temperature, 370 and 520 K. Saturation took place during 3000 s under hydrogen pressure of 20 Pa, and ion flux was about 1x10 15 ions/cm 2 s with an energy about 400 eV during discharge. Hydrogen concentration in Ga at room temperature and that for 370 K by the saturation from gaseous phase was (2-3)x10 14 cm -3 Pa -1/2 . Hydrogen concentration at temperature 520 K increased by five times. Inventory at room temperature for irradiation from discharge was 7x10 16 cm -3 at the dose about 3x10 18 ions/cm 2 . It was more than inventory at temperature 520 K by four times and more than maximum inventory from gaseous phase at 520 K by a factor of 10. Inventory increased when temperature decreased. Diffusion coefficient D=0.003 exp(-2300/RT) cm 2 /s, was estimated from temperature dependence. ((orig.))

Solvothermal synthesis of gallium-indium-zinc-oxide nanoparticles for electrolyte-gated transistors.

Science.gov (United States)

Santos, Lídia; Nunes, Daniela; Calmeiro, Tomás; Branquinho, Rita; Salgueiro, Daniela; Barquinha, Pedro; Pereira, Luís; Martins, Rodrigo; Fortunato, Elvira

2015-01-14

Solution-processed field-effect transistors are strategic building blocks when considering low-cost sustainable flexible electronics. Nevertheless, some challenges (e.g., processing temperature, reliability, reproducibility in large areas, and cost effectiveness) are requirements that must be surpassed in order to achieve high-performance transistors. The present work reports electrolyte-gated transistors using as channel layer gallium-indium-zinc-oxide nanoparticles produced by solvothermal synthesis combined with a solid-state electrolyte based on aqueous dispersions of vinyl acetate stabilized with cellulose derivatives, acrylic acid ester in styrene and lithium perchlorate. The devices fabricated using this approach display a ION/IOFF up to 1 × 10(6), threshold voltage (VTh) of 0.3-1.9 V, and mobility up to 1 cm(2)/(V s), as a function of gallium-indium-zinc-oxide ink formulation and two different annealing temperatures. These results validates the usage of electrolyte-gated transistors as a viable and promising alternative for nanoparticle based semiconductor devices as the electrolyte improves the interface and promotes a more efficient step coverage of the channel layer, reducing the operating voltage when compared with conventional dielectrics gating. Moreover, it is shown that by controlling the applied gate potential, the operation mechanism of the electrolyte-gated transistors can be modified from electric double layer to electrochemical doping.

Influence of seed layer treatment on low temperature grown ZnO nanotubes: Performances in dye sensitized solar cells

Energy Technology Data Exchange (ETDEWEB)

Ameen, Sadia [Energy Materials and Surface Science Laboratory, Solar Energy Research Center, School of Chemical Engineering, Chonbuk National University, Jeonju 561-756 (Korea, Republic of); Akhtar, M. Shaheer [School of Semiconductor and Chemical Engineering and Solar Energy Research Center, Chonbuk National University, Jeonju 561-756 (Korea, Republic of); New and Renewable Energy Material Development Center (NewREC), Chonbuk National University, Buan-gun, Jeonbuk (Korea, Republic of); Kim, Young Soon [Energy Materials and Surface Science Laboratory, Solar Energy Research Center, School of Chemical Engineering, Chonbuk National University, Jeonju 561-756 (Korea, Republic of); Yang, O-Bong [School of Semiconductor and Chemical Engineering and Solar Energy Research Center, Chonbuk National University, Jeonju 561-756 (Korea, Republic of); Shin, Hyung-Shik, E-mail: hsshin@jbnu.ac.k [Energy Materials and Surface Science Laboratory, Solar Energy Research Center, School of Chemical Engineering, Chonbuk National University, Jeonju 561-756 (Korea, Republic of)

2011-01-01

Non-aligned and highly densely aligned ZnO nanotube (NTs), synthesized by low temperature solution method were applied as photoanode materials for the fabrication of efficient dye-sensitized solar cells (DSSCs). The crystalline and the morphological analysis revealed that the grown aligned ZnO NTs possessed a typical hexagonal crystal structure of outer and inner diameter {approx}250 nm and {approx}100 nm, respectively. ZnO seeding on FTO substrates is an essential step to achieve the aligned ZnO NTs. A DSSC fabricated with aligned ZnO NTs photoanode achieved high solar-to-electricity conversion efficiency of {approx}2.2% with short circuit current (J{sub SC}) of 5.5 mA/cm{sup 2}, open circuit voltage (V{sub OC}) of 0.65 V and fill factor (FF) of 0.61. Significantly, the aligned ZnO NTs photoanode showed three times improved solar-to-electricity conversion efficiency than DSSC fabricated with non-aligned ZnO NTs. The enhanced performances were credited to the aligned morphology of ZnO NTs which executed the high charge collection and the transfer of electrons at the interfaces of ZnO NTs and electrolyte layer.

The role of gallium-67 in Hodgkin's disease

International Nuclear Information System (INIS)

Bogart, Jeffrey A.; Chung, T. Chung; Mariados, Neil F.

1996-01-01

Purpose/Objective: Although widely used, the value of gallium imaging in managing Hodgkin's lymphoma remains unclear. Methods: Retrospective review of gallium and treatment data in patients with Hodgkin's disease between January 1990 and July 1995. Results: Eighty-six of 101 patients had Ga-67 imaging. Stage was as follows: 1A-11 patients, 1B - 2, 2A - 27, 2B - 22, 3A - 10, 3B - 5, 4A - 3 and 4B - 6. Sixty-two patients had staging gallium scans and 15% of tumors were not gallium avid. Two patients were upstaged based on gallium scan. Five patients had positive laparotomy and all had negative abdominal gallium exams. Three studies had false positive lesions. Initial therapy was assessed with gallium in 61 patients and 45 had complete response. Tumor recurred in 36% ((10(28))) of patients gallium negative after 3-6 cycles of chemotherapy, with no recurrences in 17 patients gallium negative after radiotherapy or chemo radiation. Six of 7 patients with focal gallium uptake after chemotherapy received radiotherapy and all remain disease free. Seven patients had persistent or progressive gallium-avid tumor after chemotherapy correlating with clinical disease. Two patients had false positive exams after radiotherapy. Twenty-two patients had gallium scans at recurrence. One scan was (false) negative and in two cases, gallium imaging was the initial evidence of recurrent tumor. Conclusion: Ga-67 imaging may help confirm the presence of active Hodgkin's disease, but was unreliable in defining disease remission after chemotherapy in this study population. Prospective studies may help define the role of gallium scans

Germanium MOS capacitors grown on Silicon using low temperature RF-PECVD

Science.gov (United States)

Dushaq, Ghada; Rasras, Mahmoud; Nayfeh, Ammar

2017-10-01

In this paper, Ge metal-oxide-semiconductor capacitors (MOSCAPs) are fabricated on Si using a low temperature two-step deposition technique by radio frequency plasma enhanced chemical vapor deposition. The MOSCAP gate stack consists of atomic layer deposition of Al2O3 as the gate oxide and a Ti/Al metal gate electrode. The electrical characteristics of 9 nm Al2O3/i-Ge/Si MOSCAPs exhibit an n-type (p-channel) behavior and normal high frequency C-V responses. In addition to CV measurements, the gate leakage versus the applied voltage is measured and discussed. Moreover, the electrical behavior is discussed in terms of the material and interface quality. The Ge/high-k interface trap density versus the surface potential is extracted using the most commonly used methods in detemining the interface traps based on the capacitance-voltage (C-V) curves. The discussion included the Dit calculation from the conductance method, the high-low frequency (Castagné-Vapaille) method, and the Terman (high-frequency) method. Furthermore, the origins of the discrepancies in the interface trap densities determined from the different methods are discussed. The study of the post annealed Ge layers at different temperatures in H2 and N2 gas ambient revealed an improved electrical and transport properties of the films treated at T  Ge/Si demonstrates a great potential for p-channel transistor applications in a monolithically integrated CMOS platform.

A model for arsenic anti-site incorporation in GaAs grown by hydride vapor phase epitaxy

Energy Technology Data Exchange (ETDEWEB)

Schulte, K. L.; Kuech, T. F. [Department of Chemical and Biological Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)

2014-12-28

GaAs growth by hydride vapor phase epitaxy (HVPE) has regained interest as a potential route to low cost, high efficiency thin film photovoltaics. In order to attain the highest efficiencies, deep level defect incorporation in these materials must be understood and controlled. The arsenic anti-site defect, As{sub Ga} or EL2, is the predominant deep level defect in HVPE-grown GaAs. In the present study, the relationships between HVPE growth conditions and incorporation of EL2 in GaAs epilayers were determined. Epitaxial n-GaAs layers were grown under a wide range of deposition temperatures (T{sub D}) and gallium chloride partial pressures (P{sub GaCl}), and the EL2 concentration, [EL2], was determined by deep level transient spectroscopy. [EL2] agreed with equilibrium thermodynamic predictions in layers grown under conditions in which the growth rate, R{sub G}, was controlled by conditions near thermodynamic equilibrium. [EL2] fell below equilibrium levels when R{sub G} was controlled by surface kinetic processes, with the disparity increasing as R{sub G} decreased. The surface chemical composition during growth was determined to have a strong influence on EL2 incorporation. Under thermodynamically limited growth conditions, e.g., high T{sub D} and/or low P{sub GaCl}, the surface vacancy concentration was high and the bulk crystal was close to equilibrium with the vapor phase. Under kinetically limited growth conditions, e.g., low T{sub D} and/or high P{sub GaCl}, the surface attained a high GaCl coverage, blocking As adsorption. This competitive adsorption process reduced the growth rate and also limited the amount of arsenic that incorporated as As{sub Ga}. A defect incorporation model which accounted for the surface concentration of arsenic as a function of the growth conditions, was developed. This model was used to identify optimal growth parameters for the growth of thin films for photovoltaics, conditions in which a high growth rate and low [EL2] could be

Spectral and luminescence properties of Cr(3+) ad Nd(3+) ions in gallium garnet crystals

Science.gov (United States)

Denisov, A. L.; Ostroumov, V. G.; Saidov, Z. S.; Smirnov, V. A.; Shcherbakov, I. A.

1986-01-01

The effective peak stimulated-emission cross section of chromium-doped gadolinium-scandium-gallium garnets (GSGG) has been determined to be 8.5 x 10 to the -21st sq cm at room temperature. The values of the energy-gap Delta E(2E-4T2) chromim fluorescence lifetime and the chromium to neodymium energy-transfer parameter C(DA) (Cr-Nd) are determined for several gallium garnets. Temperature-dependent absorption and luminescence spectra of neodymium-doped GGG and GSGG are reported and discussed in the context of their use as laser materials.

Development of III-nitride semiconductors by molecular beam epitaxy and cluster beam epitaxy and fabrication of LEDs based on indium gallium nitride MQWs

Science.gov (United States)

Chen, Tai-Chou Papo

The family of III-Nitrides (the binaries InN, GaN, AIN, and their alloys) is one of the most important classes of semiconductor materials. Of the three, Indium Nitride (InN) and Aluminum Nitride (AIN) have been investigated much less than Gallium Nitride (GaN). However, both of these materials are important for optoelectronic infrared and ultraviolet devices. In particular, since InN was found recently to be a narrow gap semiconductor (Eg=0.7eV), its development should extend the applications of nitride semiconductors to the spectral region appropriate to fiber optics communication and photovoltaic applications. Similarly, the development of AIN should lead to deep UV light emitting diodes (LEDs). The first part of this work addresses the evaluation of structural, optical and transport properties of InN films grown by two different deposition methods. In one method, active nitrogen was produced in the form of nitrogen radicals by a radio frequency (RF) plasma-assisted source. In an alternative method, active nitrogen was produced in the form of clusters containing approximately 2000 nitrogen molecules. These clusters were produced by adiabatic expansion from high stagnation pressure through a narrow nozzle into vacuum. The clusters were singly or doubly ionized with positive charge by electron impact and accelerated up to approximately 20 to 25 KV prior to their disintegration on the substrate. Due to the high local temperature produced during the impact of clusters with the substrate, this method is suitable for the deposition of InN at very low temperatures. The films are auto-doped n-type with carrier concentrations varying from 3 x 1018 to 1020 cm-3 and the electron effective mass of these films was determined to be 0.09m0. The majority of the AIN films was grown by the cluster beam epitaxy method and was doped n- and p- type by incorporating silicon (Si) and magnesium (Mg) during the film deposition. All films were grown under Al-rich conditions at relatively

Early diagnosis of disc-space infection using gallium-67

International Nuclear Information System (INIS)

Norris, S.; Ehrlich, M.G.; Keim, D.E.; Guiterman, H.; McKusick, K.A.

1978-01-01

A 4-year-old boy had had progressive central lumbar pain and hamstring spasm. He had a normal lumbar-spine x-ray except for minimal L-5, S1 spondylolysis, but gave an abnormal gallium-67 scan in the region of the low lumbar spine. Eight weeks following intensive antibiotic therapy, confirmation of the diagnosis of disc-space infection was established by roentgenographic studies that demonstrated narrowing of the L 4 to 5 intervertebral disc space. A technetium-99m diphosphonate bone scan, performed concurrently with the gallium-67 study, was normal

Low-temperature synthesis of 2D MoS2 on a plastic substrate for a flexible gas sensor.

Science.gov (United States)

Zhao, Yuxi; Song, Jeong-Gyu; Ryu, Gyeong Hee; Ko, Kyung Yong; Woo, Whang Je; Kim, Youngjun; Kim, Donghyun; Lim, Jun Hyung; Lee, Sunhee; Lee, Zonghoon; Park, Jusang; Kim, Hyungjun

2018-05-08

The efficient synthesis of two-dimensional molybdenum disulfide (2D MoS2) at low temperatures is essential for use in flexible devices. In this study, 2D MoS2 was grown directly at a low temperature of 200 °C on both hard (SiO2) and soft substrates (polyimide (PI)) using chemical vapor deposition (CVD) with Mo(CO)6 and H2S. We investigated the effect of the growth temperature and Mo concentration on the layered growth by Raman spectroscopy and microscopy. 2D MoS2 was grown by using low Mo concentration at a low temperature. Through optical microscopy, Raman spectroscopy, X-ray photoemission spectroscopy, photoluminescence, and transmission electron microscopy measurements, MoS2 produced by low-temperature CVD was determined to possess a layered structure with good uniformity, stoichiometry, and a controllable number of layers. Furthermore, we demonstrated the realization of a 2D MoS2-based flexible gas sensor on a PI substrate without any transfer processes, with competitive sensor performance and mechanical durability at room temperature. This fabrication process has potential for burgeoning flexible and wearable nanotechnology applications.

Gallium-67 citrate scan in extrapulmonary tuberculosis

International Nuclear Information System (INIS)

Lin Wanyu

1999-01-01

Aim: Whole-body gallium scan was performed to evaluate the usefulness of gallium scan for detecting extrapulmonary tuberculosis (TB) lesions. Methods: Thirty-seven patients with extrapulmonary TB were included in this study. Four patients were found to have two lesions. Totally, 41 lesions were identified, including 19 TB arthritis, 8 spinal TB, 5 TB meningitis, 3 TB lymphadenopathy, 2 TB pericarditis, 1 TB peritonitis, 1 intestinal TB, 1 skin TB and 1 renal TB. Results: Of the 41 extrapulmonary TB lesions, gallium scan detected 32 lesions with a sensitivity of 78%. All the patients with TB meningitis showed negative gallium scan. When the five cases of TB meningitis were excluded, the detection sensitivity of gallium scan increased to 88.9% (32/36). Conclusion: Our data revealed that gallium scan is a convenient and useful method for evaluating extrapulmonary TB lesions other than TB-meningitis. We suggest that gallium scan be included in the clinical routine for patients with suspected extrapulmonary TB. (orig.) [de

Co2FeAl Heusler thin films grown on Si and MgO substrates: Annealing temperature effect

International Nuclear Information System (INIS)

Belmeguenai, M.; Tuzcuoglu, H.; Zighem, F.; Chérif, S. M.; Moch, P.; Gabor, M. S.; Petrisor, T.; Tiusan, C.

2014-01-01

10 nm and 50 nm Co 2 FeAl (CFA) thin films have been deposited on MgO(001) and Si(001) substrates by magnetron sputtering and annealed at different temperatures. X-rays diffraction revealed polycrystalline or epitaxial growth (according to CFA(001)[110]//MgO(001)[100] epitaxial relation) for CFA films grown on a Si and on a MgO substrate, respectively. For these later, the chemical order varies from the A2 phase to the B2 phase when increasing the annealing temperature (T a ), while only the A2 disorder type has been observed for CFA grown on Si. Microstrip ferromagnetic resonance (MS-FMR) measurements revealed that the in-plane anisotropy results from the superposition of a uniaxial and a fourfold symmetry term for CFA grown on MgO substrates. This fourfold anisotropy, which disappears completely for samples grown on Si, is in accord with the crystal structure of the samples. The fourfold anisotropy field decreases when increasing T a , while the uniaxial anisotropy field is nearly unaffected by T a within the investigated range. The MS-FMR data also allow for concluding that the gyromagnetic factor remains constant and that the exchange stiffness constant increases with T a . Finally, the FMR linewidth decreases when increasing T a , due to the enhancement of the chemical order. We derive a very low intrinsic damping parameter (1.1×10 −3 and 1.3×10 −3 for films of 50 nm thickness annealed at 615 °C grown on MgO and on Si, respectively)

Enhanced low-temperature thermoelectrical properties of BiTeCl grown by topotactic method

International Nuclear Information System (INIS)

Jacimovic, J.; Mettan, X.; Pisoni, A.; Gaal, R.; Katrych, S.; Demko, L.; Akrap, A.; Forro, L.; Berger, H.; Bugnon, P.; Magrez, A.

2014-01-01

We developed a topotactic strategy to grow BiTeCl single crystals. Structural characterization by means of X-ray diffraction was performed, and the high crystallinity of the material was proven. Measurements of the thermoelectrical coefficients electrical resistivity, thermoelectric power and thermal conductivity show an enhanced room temperature power factor of 20 μW cm −1 K −2 . The high value of the figure of merit (ZT = 0.17) confirms that BiTeCl is a promising material for engineering in thermoelectric applications at low temperature

WO{sub 3} nanorods prepared by low-temperature seeded growth hydrothermal reaction

Energy Technology Data Exchange (ETDEWEB)

Ng, Chai Yan [School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang (Malaysia); Abdul Razak, Khairunisak, E-mail: khairunisak@eng.usm.my [School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang (Malaysia); NanoBiotechnology Research and Innovation (NanoBRI), Institute for Research in Molecular Medicine (INFORMM), Universiti Sains Malaysia, 11800 USM, Penang (Malaysia); Lockman, Zainovia, E-mail: zainovia@eng.usm.my [School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang (Malaysia)

2014-03-05

Highlights: • WO{sub 3} nanorods with 5–10 nm diameter were grown directly on seeded tungsten foil. • WO{sub 3} nanorods were successfully grown at low temperature of 80 °C. • WO{sub 3} nanorods were grown on the entire surface of the seed layer after 24 h. • Annealed nanorods showed better electrochromic properties than as-made nanorods. -- Abstract: This work describes the first tungsten oxide (WO{sub 3}) nanorods hydrothermally grown on W foil. WO{sub 3} nanorods were successfully grown at low hydrothermal temperature of 80 °C by seeded growth hydrothermal reaction. The seed layer was prepared by thermally oxidized the W foil at 400 °C for 0.5 h. This work discusses the effect of hydrothermal reaction and annealing period on the morphological, structural, and electrochromic properties of WO{sub 3} nanorods. Various hydrothermal reaction periods (8–24 h) were studied. Monoclinic WO{sub 3} nanorods with 5–10 nm diameter were obtained after hydrothermal reaction for 24 h. These 24 h WO{sub 3} nanorods were also annealed at 400 °C with varying dwelling periods (0.5–4 h). Electrochromic properties of WO{sub 3} nanorods in an acidic electrolyte were analyzed using cyclic voltammetry and UV–vis spectrophotometry. WO{sub 3} nanorods annealed at 400 °C for 1 h showed the highest charge capacity and the largest optical contrast among the 24 h WO{sub 3} films. The sample also showed good cycling stability without significant degradation. Based on the results, the reaction mechanism of WO{sub 3} nanorod formation on W foil was proposed.

Variation of crystallinity and stoichiometry in films of gallium oxide, gallium nitride and barium zirconate prepared by means of PLD

International Nuclear Information System (INIS)

Brendt, Jochen

2011-01-01

Pulsed Laser Deposition (PLD) is an ablation technique for thin film preparation of many materials. The film properties can be well controlled by the process parameters. Therefore, in many cases a given material can be deposited with different properties by changing one or more process parameters. In this thesis thin films of gallium oxide, gallium nitride and barium zirconate were deposited with a large variation in structure and stoichiometry by means of Pulsed Laser Deposition. The characterization of the film crystallinity, phase purity and short range structural order was completed by means of X-ray diffraction and X-ray absorption spectroscopy. The stoichiometry was investigated using electron probe microanalysis. For analyzing the correlation between the structure and stoichiometry with the optical and electrical properties, optical absorption and electrical conductivity measurements were carried out. The investigation of all three material systems showed that very unique properties can be realized when combining an amorphous structure and a non-stoichiometric composition. For example, in amorphous and oxygen deficient gallium oxide an insulator-metal-transition can be induced by partial crystallization of the as prepared phase accomplished by annealing at about 400 C in argon atmosphere (as shown in literature). Furthermore, amorphous and highly non-stoichiometric barium zirconate has the ability to split water molecules to hydrogen and oxygen at room temperature. A detailed analysis of both phenomena has been performed by means of photoemission and transmission electron microscopy in the case of gallium oxide and via X-ray absorption spectroscopy and gas chromatography in the case of barium zirconate.

Thermal, spectroscopic and laser properties of Nd3+ in gadolinium scandium gallium garnet crystal produced by optical floating zone method

Science.gov (United States)

Tian, Li; Wang, Shuxian; Wu, Kui; Wang, Baolin; Yu, Haohai; Zhang, Huaijin; Cai, Huaqiang; Huang, Hui

2013-12-01

A neodymium-doped gadolinium scandium gallium garnet (Nd:GSGG) single crystal with dimensions of Φ 5 × 20 mm2 has been grown by means of optical floating zone (OFZ). X-ray powder diffraction (XRPD) result shows that the as-grown Nd:GSGG crystal possesses a cubic structure with space group Ia3d and a cell parameter of a = 1.2561 nm. Effective elemental segregation coefficients of the Nd:GSGG as-grown crystal were calculated by using X-ray fluorescence (XRF). The thermal properties of the Nd:GSGG crystal were systematically studied by measuring the specific heat, thermal expansion and thermal diffusion coefficient, and the thermal conductivity of this crystal was calculated. The absorption and luminescence spectra of Nd:GSGG were measured at room temperature (RT). By using the Judd-Ofelt (J-O) theory, the theoretical radiative lifetime was calculated and compared with the experimental result. Continuous wave (CW) laser performance was achieved with the Nd:GSGG at the wavelength of 1062 nm when it was pumped by a laser diode (LD). A maximum output power of 0.792 W at 1062 nm was obtained with a slope efficiency of 11.89% under a pump power of 7.36 W, and an optical-optical conversion efficiency of 11.72%.

Low temperature growth and properties of ZnO nanorod arrays

International Nuclear Information System (INIS)

Wu, Xiang; Zheng, Yufeng; Chen, Huibo; Gong, Lihong; Qu, Fengyu

2011-01-01

In this paper, well aligned ZnO nanorod arrays were synthesized by a simple hydrothermal route at a low temperature. The diameters of the as-synthesized products were 20–60 nm and the lengths were as much as several micrometers. The surfaces and tops of the nanorods were smooth. The as-grown nanorod arrays were investigated by x-ray powder diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), photoluminescence (PL) spectroscopy and contact angle (CA) analysis. The as-grown nanorods were single crystalline structures with a wurtzite phase, and grew along the [0001] direction. The PL spectrum with only one strong peak at 383 nm shows good intrinsic emission

Electrical transport properties of graphene nanowalls grown at low temperature using plasma enhanced chemical vapor deposition

Science.gov (United States)

Zhao, Rong; Ahktar, Meysam; Alruqi, Adel; Dharmasena, Ruchira; Jasinski, Jacek B.; Thantirige, Rukshan M.; Sumanasekera, Gamini U.

2017-05-01

In this work, we report the electrical transport properties of uniform and vertically oriented graphene (graphene nanowalls) directly synthesized on multiple substrates including glass, Si/SiO2 wafers, and copper foils using radio-frequency plasma enhanced chemical vapor deposition (PECVD) with methane (CH4) as the precursor at relatively low temperatures. The temperature for optimum growth was established with the aid of transmission electron microscopy, scanning electron microscopy, and Raman spectroscopy. This approach offers means for low-cost graphene nanowalls growth on an arbitrary substrate with the added advantage of transfer-free device fabrication. The temperature dependence of the electrical transport properties (resistivity and thermopower) were studied in the temperature range, 30-300 K and analyzed with a combination of 2D-variable range hopping (VRH) and thermally activated (TA) conduction mechanisms. An anomalous temperature dependence of the thermopower was observed for all the samples and explained with a combination of a diffusion term having a linear temperature dependence plus a term with an inverse temperature dependence.

Simple Hydrogen Plasma Doping Process of Amorphous Indium Gallium Zinc Oxide-Based Phototransistors for Visible Light Detection.

Science.gov (United States)

Kang, Byung Ha; Kim, Won-Gi; Chung, Jusung; Lee, Jin Hyeok; Kim, Hyun Jae

2018-02-28

A homojunction-structured amorphous indium gallium zinc oxide (a-IGZO) phototransistor that can detect visible light is reported. The key element of this technology is an absorption layer composed of hydrogen-doped a-IGZO. This absorption layer is fabricated by simple hydrogen plasma doping, and subgap states are induced by increasing the amount of hydrogen impurities. These subgap states, which lead to a higher number of photoexcited carriers and aggravate the instability under negative bias illumination stress, enabled the detection of a wide range of visible light (400-700 nm). The optimal condition of the hydrogen-doped absorption layer (HAL) is fabricated at a hydrogen partial pressure ratio of 2%. As a result, the optimized a-IGZO phototransistor with the HAL exhibits a high photoresponsivity of 1932.6 A/W, a photosensitivity of 3.85 × 10 6 , and a detectivity of 6.93 × 10 11 Jones under 635 nm light illumination.

67Gallium lung scans in progressive systemic sclerosis

International Nuclear Information System (INIS)

Baron, M.; Feiglin, D.; Hyland, R.; Urowitz, M.B.; Shiff, B.

1983-01-01

67 Gallium lung scans were performed in 19 patients with progressive systemic sclerosis (scleroderma). Results were expressed quantitatively as the 67 Gallium Uptake Index. The mean total pulmonary 67 Gallium Uptake Index in patients was significantly higher than that in controls (41 versus 25), and 4 patients (21%) fell outside the normal range. There were no clinical or laboratory variables that correlated with the 56 Gallium uptake. Increased pulmonary 67 Gallium uptake in scleroderma may prove useful as an index of pulmonary disease activity

Impacts of electronically photo-excited NO2 on air pollution in the South Coast Air Basin of California

Directory of Open Access Journals (Sweden)

D. Dabdub

2010-02-01

Full Text Available A new path for hydroxyl radical formation via photo-excitation of nitrogen dioxide (NO2 and the reaction of photo-excited NO2 with water is evaluated using the UCI-CIT model for the South Coast Air Basin of California (SoCAB. Two separate studies predict different reaction rates, which differ by nearly an order of magnitude, for the reaction of photo-excited NO2 with water. Impacts of this new chemical mechanism on ozone and particulate matter formation, while utilizing both reaction rates, are quantified by simulating two summer episodes. First, sensitivity simulations are conducted to evaluate the uncertainty in the rate of reaction of photo-excited NO2 with water reported in the literature. Results indicate that the addition of photo-excited NO2 chemistry increases peak 8-h average ozone and particulate matter concentrations. The importance of this new chemistry is then evaluated in the context of pollution control strategies. A series of simulations are conducted to generate isopleths for ozone and particulate matter concentrations, varying baseline nitrogen oxides (NOx and volatile organic compounds (VOC emissions. Isopleths are obtained using 1987 emissions, to represent past conditions, and 2005, to represent current conditions in the SoCAB. Results show that the sensitivity of modeled pollutant control strategies due to photoexcitation decreases with the decrease in baseline emissions from 1987 to 2005. Results show that including NO2 photo-excitation, increases the sensitivity of ozone concentration with respect to changes in NOx emissions for both years. In particular, decreasing NOx emissions in 2005 when NO2 photo-excitation is included, while utilizing the higher reaction rate, leads to ozone relative reduction factors that are 15% lower than in a case without photo-excited NO2. This implies that photoexcitation increases the effectiveness in reducing ozone through NOx emissions reductions alone, which has implications for the

Co{sub 2}FeAl Heusler thin films grown on Si and MgO substrates: Annealing temperature effect

Energy Technology Data Exchange (ETDEWEB)

Belmeguenai, M., E-mail: belmeguenai.mohamed@univ-paris13.fr; Tuzcuoglu, H.; Zighem, F.; Chérif, S. M.; Moch, P. [LSPM (CNRS-UPR 3407), 99 avenue Jean-Baptiste Clément, Université Paris 13, 93430 Villetaneuse (France); Gabor, M. S., E-mail: mihai.gabor@phys.utcluj.ro; Petrisor, T. [Center for Superconductivity, Spintronics and Surface Science, Technical University of Cluj-Napoca, Str. Memorandumului No. 28 RO-400114 Cluj-Napoca (Romania); Tiusan, C. [Center for Superconductivity, Spintronics and Surface Science, Technical University of Cluj-Napoca, Str. Memorandumului No. 28 RO-400114 Cluj-Napoca (Romania); Institut Jean Lamour, CNRS, Université de Nancy, BP 70239, F–54506 Vandoeuvre (France)

2014-01-28

10 nm and 50 nm Co{sub 2}FeAl (CFA) thin films have been deposited on MgO(001) and Si(001) substrates by magnetron sputtering and annealed at different temperatures. X-rays diffraction revealed polycrystalline or epitaxial growth (according to CFA(001)[110]//MgO(001)[100] epitaxial relation) for CFA films grown on a Si and on a MgO substrate, respectively. For these later, the chemical order varies from the A2 phase to the B2 phase when increasing the annealing temperature (T{sub a}), while only the A2 disorder type has been observed for CFA grown on Si. Microstrip ferromagnetic resonance (MS-FMR) measurements revealed that the in-plane anisotropy results from the superposition of a uniaxial and a fourfold symmetry term for CFA grown on MgO substrates. This fourfold anisotropy, which disappears completely for samples grown on Si, is in accord with the crystal structure of the samples. The fourfold anisotropy field decreases when increasing T{sub a}, while the uniaxial anisotropy field is nearly unaffected by T{sub a} within the investigated range. The MS-FMR data also allow for concluding that the gyromagnetic factor remains constant and that the exchange stiffness constant increases with T{sub a}. Finally, the FMR linewidth decreases when increasing T{sub a}, due to the enhancement of the chemical order. We derive a very low intrinsic damping parameter (1.1×10{sup −3} and 1.3×10{sup −3} for films of 50 nm thickness annealed at 615 °C grown on MgO and on Si, respectively)

Photoexcited quantum dots for killing multidrug-resistant bacteria

Science.gov (United States)

Courtney, Colleen M.; Goodman, Samuel M.; McDaniel, Jessica A.; Madinger, Nancy E.; Chatterjee, Anushree; Nagpal, Prashant

2016-05-01

Multidrug-resistant bacterial infections are an ever-growing threat because of the shrinking arsenal of efficacious antibiotics. Metal nanoparticles can induce cell death, yet the toxicity effect is typically nonspecific. Here, we show that photoexcited quantum dots (QDs) can kill a wide range of multidrug-resistant bacterial clinical isolates, including methicillin-resistant Staphylococcus aureus, carbapenem-resistant Escherichia coli, and extended-spectrum β-lactamase-producing Klebsiella pneumoniae and Salmonella typhimurium. The killing effect is independent of material and controlled by the redox potentials of the photogenerated charge carriers, which selectively alter the cellular redox state. We also show that the QDs can be tailored to kill 92% of bacterial cells in a monoculture, and in a co-culture of E. coli and HEK 293T cells, while leaving the mammalian cells intact, or to increase bacterial proliferation. Photoexcited QDs could be used in the study of the effect of redox states on living systems, and lead to clinical phototherapy for the treatment of infections.

Thermodynamics of gallium arsenide electrodeposition

International Nuclear Information System (INIS)

Perrault, G.G.

1986-01-01

Gallium Arsenide is well known as a very interesting compound for photoelectrical devices. Up to now, it has been prepared mostly by high temperature technology, and the authors considered that it might be of interest to set up an electrodeposition technique suitable to prepare thin layers of this compound. A reaction sequence similar to the one observed for Cadmium Sulfide or Cadmium Telluride could be considered. In these cases, the metal chalcogenide is obtained from the precipitation of the metal ions dissolved in the solutions by the reduction product of the metalloidic compound

Gallium-67 scintigraphy and the Heart

International Nuclear Information System (INIS)

Garayt, D.

1987-01-01

Although gallium-67 was initially used for tumor imaging, clinical studies suggested its potential use as a method of detecting occult inflammatory lesions. The demonstration of diffuse myocardial uptake of gallium-67 during Lyme disease myocarditis is consistent with a pattern of diffuse myocarditis as seen in sarcoid myocarditis. Two cases are presented. A critical review of the various applications of gallium-67 scintigraphy to myocardium investigation is carried out [fr

Low-temperature transport in ultra-thin tungsten films

Energy Technology Data Exchange (ETDEWEB)

Chiatti, Olivio [Neue Materialien, Institut fuer Physik, Humboldt-Univ. Berlin (Germany); London Centre for Nanotechnology, University College London (United Kingdom); Nash, Christopher; Warburton, Paul [London Centre for Nanotechnology, University College London (United Kingdom)

2012-07-01

Tungsten-containing films, fabricated by focused-ion-beam-induced chemical vapour deposition, are known to have an enhanced superconducting transition temperature compared to bulk tungsten, and have been investigated previously for film thickness down to 25 nm. In this work, by using ion-beam doses below 50 pC/{mu}m{sup 2} on a substrate of amorphous silicon, we have grown continuous films with thickness below 20 nm. The electron transport properties were investigated at temperatures down to 350 mK and in magnetic fields up to 3 T, parallel and perpendicular to the films. The films in this work are closer to the limit of two-dimensional systems and are superconducting at low temperatures. Magnetoresistance measurements yield upper critical fields of the order of 1 T, and the resulting coherence length is smaller than the film thickness.

Gallium Electromagnetic (GEM) Thrustor Concept and Design

Science.gov (United States)

Polzin, Kurt A.; Markusic, Thomas E.

2006-01-01

We describe the design of a new type of two-stage pulsed electromagnetic accelerator, the gallium electromagnetic (GEM) thruster. A schematic illustration of the GEM thruster concept is given in Fig. 1. In this concept, liquid gallium propellant is pumped into the first stage through a porous metal electrode using an electromagneticpump[l]. At a designated time, a pulsed discharge (approx.10-50 J) is initiated in the first stage, ablating the liquid gallium from the porous electrode surface and ejecting a dense thermal gallium plasma into the second state. The presence of the gallium plasma in the second stage serves to trigger the high-energy (approx.500 I), send-stage puke which provides the primary electromagnetic (j x B) acceleration.

Low temperature synthesis of graphene on arbitrary substrates and its transport properties

Science.gov (United States)

Zhao, Rong; Akhtar, Meysam; Alruqi, Adel; Jasinski, Jacek; Sumanasekera, Gamini; Department of Physics; Astronomy, University of Louisville Collaboration; Conn CenterRenewable Energy, University of Louisville Collaboration

Here we report the direct synthesis of uniform and vertically oriented graphene films on multiple substrates including glass, Si/SiO2, and copper foil by radio-frequency plasma enhanced chemical vapor deposition (PECVD) using methane as the carbon precursor at relatively low temperatures. Raman spectra of all the samples show characteristic Raman peaks of graphene. The temperature dependence of electrical transport properties such as 4-probe resistance, thermo electrical power and hall mobility were measured for graphene grown on glass substrates at varying temperature from 500 ° C to 700 ° C. The morphological and surface characteristics were also studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). This work demonstrates the potential of low temperature and transfer-free graphene growth for future graphene-based electronic applications.

The frequency-domain relaxation response of gallium doped Cd{sub 1-x}Mn{sub x}Te

Energy Technology Data Exchange (ETDEWEB)

Trzmiel, Justyna; Weron, Karina [Institute of Physics, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw (Poland); Jurlewicz, Agnieszka [Hugo Steinhaus Center, Institute of Mathematics and Computer Science, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw (Poland)

2010-03-10

In this paper the complex dielectric permittivity of gallium doped Cd{sub 0.99}Mn{sub 0.01}Te mixed crystals is studied at different temperatures. We observe a two-power-law relaxation pattern with m and n, the low- and high-frequency power-law exponents respectively, satisfying the relation m < 1 - n. To interpret the empirical result we propose a correlated-cluster relaxation mechanism. This approach allows us to find origins of both power-law exponents, m and n.

Measurement of solar proton-proton fusion neutrinos with a Soviet-American gallium experiment: Technical progress report

International Nuclear Information System (INIS)

Cherry, M.L.

1989-06-01

A gallium solar neutrino detector is sensitive to low-energy proton-proton fusion neutrinos. A flux of 70 SNU is expected in a gallium detector from the p-p reaction independent of solar model calculations. If, however, neutrino oscillations in the solar interior are responsible for the suppressed 8 B flux measured by the Homestake 37 Cl experiment, then a comparison of the gallium and chlorine results may make possible a determination of the neutrino mass difference and mixing angle. A 60-ton gallium detector is currently being constructed in the Baksan Laboratory in the Soviet Union, and should be taking data by the end of 1989

InGaN compositional patterning by ultraviolet photoexcitation during NH3-based MOMBE - A pathway to 3D epitaxy

International Nuclear Information System (INIS)

Pritchett, D.; Henderson, W.; Billingsley, D.; Doolittle, W.A.

2008-01-01

Lateral compositional patterning of InGaN during NH 3 -based MOMBE by digital micromirror patterning of UV photoexcitation is demonstrated. Preferential desorption of In/In-methyl species during InGaN surface exposure to an elliptically focused 5 kW Hg-Xe arc lamp (λ=365 nm) limits the incorporation of indium during growth. Localized photoexcitation results in the preferential In/In-methyl desorption, resulting in indium mole fractions of 0.10 in unexposed regions to as low as 0 in fully exposed regions. The technique demonstrates promise for integration of micromirrors for dynamic and maskless selective epitaxy towards the realization of complex, 3D device structures. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Micro-Scale Gallium Nitride Pressure Sensors for Advanced Harsh Environment Space Technology

Data.gov (United States)

National Aeronautics and Space Administration — The goal of this research is to study the high-temperature response of the 2-dimesional electron gas (2DEG) that occurs at the interface of aluminum gallium nitride...

Electron transfer and energy transfer reactions in photoexcited a-nonathiophene/C60 films and solutions

NARCIS (Netherlands)

Janssen, R.A.J.; Moses, D.; Sariciftci, N.S.; Heeger, A.J.

1994-01-01

Photoexcitation of a nonathiophene in film or solution across the p-p* energy gap produces a metastable triplet state. In the presence of C60, on the other hand, an ultra fast electron transfer from the photoexcited nonathiophene onto C60 is observed in films, whereas in solution C60 is involved in

The roles of the temperature on the structural and electronic properties of deep-level V{sub As}V{sub Ga} defects in gallium arsenide

Energy Technology Data Exchange (ETDEWEB)

Ma, Deming, E-mail: xautmdm@163.com; Chen, Xi; Qiao, Hongbo; Shi, Wei; Li, Enling

2015-07-15

Highlights: • The energy gap of the Ga{sub As}As{sub Ga}V{sub As}V{sub Ga} is 0.82 eV. • Proves that the Ga{sub As}As{sub Ga}V{sub As}V{sub Ga} belongs to EL2 deep-level defect in GaAs. • Proves that EL2 and EL6 deep-level defects can transform into each other. • Temperature has an important effect on the microstructure of deep-level defects. - Abstract: The roles of temperature on the structural and electronic properties of V{sub As}V{sub Ga} defects in gallium arsenide have been studied by using ab-initio molecular dynamic (MD) simulation. Our calculated results show that the relatively stable quaternary complex defect of Ga{sub As}As{sub Ga}V{sub As}V{sub Ga} can be converted from the V{sub As}V{sub Ga} complex clusters defect between 300 K and 1173 K; however, from 1173 K to 1373 K, the decomposition of the complex defect Ga{sub As}As{sub Ga}V{sub As}V{sub Ga} occurs, turning into a deep-level V{sub As}V{sub Ga} cluster defect and an isolated As{sub Ga} antisite defect, and relevant defect of Ga{sub As} is recovered. The properties of Ga{sub As}As{sub Ga}V{sub As}V{sub Ga} defect has been studied by first-principles calculations based on hybrid density functional theory. Our calculated results show that the Ga{sub As}As{sub Ga}V{sub As}V{sub Ga} belongs to EL2 deep-level defect in GaAs. Thus, we reveal that the temperature has an important effect on the microstructure of deep-level defects and defect energy level in gallium arsenide that EL2 and EL6 deep-level defects have a certain correlation, which means they could transform into each other. Controlling temperature in the growth process of GaAs could change the microstructure of deep-level defects and defect energy levels in gallium arsenide materials, whereby affects the electron transport properties of materials.

Low moisture availability inhibits the enhancing effect of increased soil temperature on net photosynthesis of white birch (Betula papyrifera) seedlings grown under ambient and elevated carbon dioxide concentrations.

Science.gov (United States)

Ambebe, Titus F; Dang, Qing-Lai

2009-11-01

White birch (Betula papyrifera Marsh.) seedlings were grown under two carbon dioxide concentrations (ambient: 360 micromol mol(-1) and elevated: 720 micromol mol(-1)), three soil temperatures (5, 15 and 25 degrees C initially, increased to 7, 17 and 27 degrees C, respectively, 1 month later) and three moisture regimes (low: 30-40%; intermediate: 45-55% and high: 60-70% field water capacity) in greenhouses. In situ gas exchange and chlorophyll fluorescence were measured after 2 months of treatments. Net photosynthetic rate (A(n)) of seedlings grown under the intermediate and high moisture regimes increased from low to intermediate T(soil) and then decreased to high T(soil). There were no significant differences between the low and high T(soil), with the exception that A(n) was significantly higher under high than low T(soil) at the high moisture regime. No significant T(soil) effect on A(n) was observed at the low moisture regime. The intermediate T(soil) increased stomatal conductance (g(s)) only at intermediate and high but not at low moisture regime, whereas there were no significant differences between the low and high T(soil) treatments. Furthermore, the difference in g(s) between the intermediate and high T(soil) at high moisture regime was not statistically significant. The low moisture regime significantly reduced the internal to ambient CO2 concentration ratio at all T(soil). There were no significant individual or interactive effects of treatment on maximum carboxylation rate of Rubisco, light-saturated electron transport rate, triose phosphate utilization or potential photochemical efficiency of photosystem II. The results of this study suggest that soil moisture condition should be taken into account when predicting the responses of white birch to soil warming.

Density-dependent electron scattering in photoexcited GaAs

DEFF Research Database (Denmark)

Mics, Zoltán; D'’Angio, Andrea; Jensen, Søren A.

2013-01-01

—In a series of systematic optical pump - terahertz probe experiments we study the density-dependent electron scattering rate in photoexcited GaAs in a large range of carrier densities. The electron scattering time decreases by as much as a factor of 4, from 320 to 60 fs, as the electron density...

Cr{sub 2}O{sub 3} thin films grown at room temperature by low pressure laser chemical vapour deposition

Energy Technology Data Exchange (ETDEWEB)

Sousa, P.M. [Universidade de Lisboa, Faculdade de Ciencias, Departamento de Fisica and ICEMS, Campo Grande, Ed. C8, 1749-016 Lisboa (Portugal); Silvestre, A.J., E-mail: asilvestre@deq.isel.ipl.p [Instituto Superior de Engenharia de Lisboa and ICEMS, R. Conselheiro Emidio Navarro 1, 1959-007 Lisboa (Portugal); Conde, O. [Universidade de Lisboa, Faculdade de Ciencias, Departamento de Fisica and ICEMS, Campo Grande, Ed. C8, 1749-016 Lisboa (Portugal)

2011-03-31

Chromia (Cr{sub 2}O{sub 3}) has been extensively explored for the purpose of developing widespread industrial applications, owing to the convergence of a variety of mechanical, physical and chemical properties in one single oxide material. Various methods have been used for large area synthesis of Cr{sub 2}O{sub 3} films. However, for selective area growth and growth on thermally sensitive materials, laser-assisted chemical vapour deposition (LCVD) can be applied advantageously. Here we report on the growth of single layers of pure Cr{sub 2}O{sub 3} onto sapphire substrates at room temperature by low pressure photolytic LCVD, using UV laser radiation and Cr(CO){sub 6} as chromium precursor. The feasibility of the LCVD technique to access selective area deposition of chromia thin films is demonstrated. Best results were obtained for a laser fluence of 120 mJ cm{sup -2} and a partial pressure ratio of O{sub 2} to Cr(CO){sub 6} of 1.0. Samples grown with these experimental parameters are polycrystalline and their microstructure is characterised by a high density of particles whose size follows a lognormal distribution. Deposition rates of 0.1 nm s{sup -1} and mean particle sizes of 1.85 {mu}m were measured for these films.

The mobility of indium and gallium in groundwater systems: constraining the role of sorption in sand column experiments

Science.gov (United States)

Dror, I.; Ringering, K.; Yecheskel, Y.; Berkowitz, B.

2017-12-01

The mobility of indium and gallium in groundwater environments was studied via laboratory experiments using quartz sand as a porous medium. Indium and gallium are metals of very low abundance in the Earth's crust and, correspondingly, the biosphere is only adapted to very small concentrations of these elements. However, in modern semiconductor industries, both elements play a central role and are incorporated in devices of mass production such as smartphones and digital cameras. The resulting considerable increase in production, use and discharge of indium and gallium throughout the last two decades, with a continuous and fast increase in the near future, raises questions regarding the fate of both elements in the environment. However, the transport behavior of these two metals in soils and groundwater systems remains poorly understood to date. Because of the low solubility of both elements in aqueous solutions, trisodium citrate was used as a complexation agent to stabilize the solutions, enabling investigation of the transport of these metals at neutral pH. Column experiments showed different binding capacities for indium and gallium, where gallium is much more mobile compared to indium and both metals are substantially retarded in the column. Different affinities were also confirmed by examining sorption isotherms of indium and gallium in equilibrium batch systems. The effect of natural organic matter on the mobility of indium and gallium was also studied, by addition of humic acid. For both metals, the presence of humic acid affects the sorption dynamics: for indium, sorption is strongly inhibited leading to much higher mobility, whereas gallium showed a slightly higher sorption affinity and very similar mobility compared to the same setup without humic acid addition. However, in all cases, the binding capacity of gallium to quartz is much weaker than that of indium. These results are consistent with the assumption that indium and gallium form different types

Far-infrared cw difference-frequency generation using vertically integrated and planar low temperature grown GaAs photomixers: application to H2S rotational spectrum up to 3 THz

Science.gov (United States)

Mouret, G.; Matton, S.; Bocquet, R.; Hindle, F.; Peytavit, E.; Lampin, J. F.; Lippens, D.

2004-10-01

The generation of continuous coherent THz radiation by mixing two cw Ti:Sa laser beams with a well-controlled frequency separation for a new scheme of vertically integrated low temperature grown GaAs (LTG-GaAs) spiral photomixer is reported. For this new photomixer device used in THz emission, the LTG-GaAs active layer is sandwiched between the two parallel metal plates of a high-speed photodetector loaded by a broadband spiral antenna. We have exploited the advantage of a higher delivered power in the low part of the spectrum (<2000 GHz), while a low RC time constant planar interdigitated detector was used at the upper frequency. The performances of the spectroscopic setup in terms of spectral resolution (5 MHz), tunability and frequency capability are assessed by measurements of the pure rotational spectra of hydrogen sulfide (H2S) up to 3000 GHz.

The influence of electron irradiation at the various temperatures and annealing on carriers mobility at the low temperatures in neutron transmutation doped gallium arsenide

International Nuclear Information System (INIS)

Korshunov, F.P.; Kurilovich, N.F.; Prokhorenko, T.A.; Troshchinskii, V.T.; Shesholko, V.K.

1999-01-01

The influence of electron irradiation at the various temperatures and annealing on measured at T=100 K carriers mobility in neutron transmutation doped GaAs have been investigated. It was detected that rate of mobility decreasing with irradiation dose increasing decreases when irradiation temperature increases. It was shown that at the same time it take place the radiation defects creating and their particular or full annealing (in the dependence on irradiation temperature). Radiation stimulated annealing (annealing that take place during irradiation at the elevated temperatures) is more effective than the annealing at the same temperatures that take place after crystals are irradiated at room temperature. It means that any defects annealing during irradiation at elevated temperatures take place at more low temperatures than that during annealing after irradiation at room temperature

Experimental investigation of aluminum complexing with sodium ion and of gallium and iron (III) speciation in natural solutions

International Nuclear Information System (INIS)

Diakonov, Igor

1995-01-01

The aim of this work is to acquire thermodynamic data on the aqueous complexes forming between sodium and aluminum, gallium and hydroxide, and iron (III) and hydroxide. These data will provide for a better understanding of the transport and distribution of these elements in surface and hydrothermal fluids. Stability constants of the sodium-aluminate complex (Na Al(OH) 4 deg.) were obtained from boehmite solubility measurements at temperatures from 125 to 350 deg. C in alkaline solutions containing from 0.1 to 1 mol/L sodium. Complementary potentiometric measurements were performed with a sodium selective electrode, between 75 and 200 deg C (the potentiometric study was carried out by Gleb Pokrovski). Analyses of these data within the framework of the revised Helgeson-Kirkham-Flowers (HKF) model allowed determination of the HKF parameters for Na Al(OH) 4 deg. and calculation of its thermodynamic properties to 800 deg. C and 5 kb. The results of this work show that Na Al(OH) 4 deg. complex formation increases significantly the solubility of aluminum-bearing minerals and consequently aluminum mobility in hydrothermal fluids. Gallium speciation in surface and hydrothermal fluids is dominated by the negatively charged species, Ga(OH) 4 - . The thermodynamic properties of this species were determined from of OEGaOOH solubility measurements as a function of pH and temperature from 25 to 250 deg. C. In general, the variation of gallium aqueous speciation with pH is similar to that of aluminum other than at temperatures less than 200 deg. C over the pH range 3 - 6. This difference can account for the independent behavior of gallium versus aluminum in numerous low temperature natural systems. The thermodynamic properties of Fe(OH) 3 deg. which dominates the speciation of Fe(III) in surface waters and Fe(OH) 4 - were determined from hematite solubility measurements as a function of pH, oxygen pressure and temperature from 110 to 300 deg. C. The available thermodynamic data on

On the photon annealing of silicon-implanted gallium-nitride layers

International Nuclear Information System (INIS)

Seleznev, B. I.; Moskalev, G. Ya.; Fedorov, D. G.

2016-01-01

The conditions for the formation of ion-doped layers in gallium nitride upon the incorporation of silicon ions followed by photon annealing in the presence of silicon dioxide and nitride coatings are analyzed. The conditions of the formation of ion-doped layers with a high degree of impurity activation are established. The temperature dependences of the surface concentration and mobility of charge carriers in ion-doped GaN layers annealed at different temperatures are studied.

Positron emission tomography changes management, improves prognostic stratification and is superior to gallium scintigraphy in patients with low-grade lymphoma: results of a multicentre prospective study

International Nuclear Information System (INIS)

Scott, Andrew M.; Gunawardana, Dishan H.; Wong, Joseph; Kirkwood, Ian; Hicks, Rodney J.; Ho Shon, Ivan; Ramshaw, Jayne E.; Robins, Peter

2009-01-01

Positron emission tomography (PET) was evaluated in low-grade non-Hodgkin lymphoma (NHL) to determine its impact on staging and management and to compare PET and gallium scans. PET resulted in management plan changes in 74 patients with untreated low-grade NHL stages I to III. Patient outcomes to 12 months were documented. PET identified additional lesions in 50% of patients, led to a change in stage in 32%, and had a significant impact on management in 34%. Inferior progression-free survival was noted in patients with additional lesions detected by PET (p=0.001) and in the 28% of patients upstaged by PET to stage III or IV (p=0.024). In a subset of 16 patients undergoing both PET and gallium scans, PET was found to be superior. PET has a major role in the management of low-grade NHL in addition to its proven role in aggressive lymphoma. (orig.)

InGaN compositional patterning by ultraviolet photoexcitation during NH{sub 3}-based MOMBE - A pathway to 3D epitaxy

Energy Technology Data Exchange (ETDEWEB)

Pritchett, D.; Henderson, W.; Billingsley, D.; Doolittle, W.A. [School of Electrical and Computer Engineering, Georgia Institute of Technology, 777 Atlantic Dr., Atlanta, GA 30332 (United States)

2008-07-01

Lateral compositional patterning of InGaN during NH{sub 3}-based MOMBE by digital micromirror patterning of UV photoexcitation is demonstrated. Preferential desorption of In/In-methyl species during InGaN surface exposure to an elliptically focused 5 kW Hg-Xe arc lamp ({lambda}=365 nm) limits the incorporation of indium during growth. Localized photoexcitation results in the preferential In/In-methyl desorption, resulting in indium mole fractions of 0.10 in unexposed regions to as low as 0 in fully exposed regions. The technique demonstrates promise for integration of micromirrors for dynamic and maskless selective epitaxy towards the realization of complex, 3D device structures. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Photoconduction efficiencies and dynamics in GaN nanowires grown by chemical vapor deposition and molecular beam epitaxy: A comparison study

International Nuclear Information System (INIS)

Chen, R. S.; Tsai, H. Y.; Huang, Y. S.; Chen, Y. T.; Chen, L. C.; Chen, K. H.

2012-01-01

The normalized gains, which determines the intrinsic photoconduction (PC) efficiencies, have been defined and compared for the gallium nitride (GaN) nanowires (NWs) grown by chemical vapor deposition (CVD) and molecular beam epitaxy (MBE). By excluding the contributions of experimental parameters and under the same light intensity, the CVD-grown GaN NWs exhibit the normalized gain which is near two orders of magnitude higher than that of the MBE-ones. The temperature-dependent time-resolved photocurrent measurement further indicates that the higher photoconduction efficiency in the CVD-GaN NWs is originated from the longer carrier lifetime induced by the higher barrier height (φ B = 160 ± 30 mV) of surface band bending. In addition, the experimentally estimated barrier height at 20 ± 2 mV for the MBE-GaN NWs, which is much lower than the theoretical value, is inferred to be resulted from the lower density of charged surface states on the non-polar side walls.

NIM Realization of the Gallium Triple Point

Science.gov (United States)

Xiaoke, Yan; Ping, Qiu; Yuning, Duan; Yongmei, Qu

2003-09-01

In the last three years (1999 to 2001), the gallium triple-point cell has been successfully developed, and much corresponding research has been carried out at the National Institute of Metrology (NIM), Beijing, China. This paper presents the cell design, apparatus and procedure for realizing the gallium triple point, and presents studies on the different freezing methods. The reproducibility is 0.03 mK, and the expanded uncertainty of realization of the gallium triple point is evaluated to be 0.17 mK (p=0.99, k=2.9). Also, the reproducibility of the gallium triple point was compared with that of the triple point of water.

Incidental diagnosis of pregnancy on bone and gallium scintigraphy

International Nuclear Information System (INIS)

Palestro, C.J.; Malat, J.; Collica, C.J.; Richman, A.H.

1986-01-01

Bone and gallium scintigraphy were performed as part of the diagnostic workup of a 21-yr-old woman who presented at our institution with a history of progressively worsening low back pain over a 1-wk period of time. The angiographic phase of the bone scan demonstrated a well-defined radionuclide blush within the pelvis just cephalad to the urinary bladder with persistent hyperemia noted in the blood-pool image. We attribute these findings to a uterine blush secondary to the pronounced uterine muscular hyperplasia, hyperemia, and edema that accompany pregnancy. Gallium scintigraphy demonstrated intense bilateral breast accumulation of the imaging agent in a typical doughnut pattern which is commonly found in the prelactating and lactating breast. Also demonstrated was apparent gallium accumulation in the placenta. This case is presented to emphasize the radionuclide findings that occur during pregnancy, particularly the incidental finding of radionuclide blush during the angiographic phase of a radionuclide scintigraphy which should alert the nuclear physician to the possibility of pregnancy in a woman of childbearing age

Weak antilocalization and low-temperature characterization of sputtered polycrystalline bismuth selenide

Science.gov (United States)

Sahu, Protyush; Chen, Jun-Yang; Myers, Jason C.; Wang, Jian-Ping

2018-03-01

We report a thorough crystal and transport characterization of sputtered polycrystalline BixSe1 -x (20 nm), grown on a thermally oxidized silicon substrate. The crystal and grain structures of the sample are characterized by transmission electron microscopy. Selected-area electron diffraction shows a highly polycrystalline structure. Transport measurements suggest semiconducting behavior of the BixSe1 -x film with a very high carrier concentration (˜1020 cm3) and low mobility [˜8 cm2/(V s)]. High-field magnetoresistance measurements reveal weak antilocalization, to which both the low mobility and the angular dependence suggest an impurity-dominated contribution. Fitting parameters are obtained from 2D magnetoconductivity using the Hikami-Larkin-Nagaoka equation. The variation of the phase coherence length with temperature suggests electron-electron scattering for phase decoherence. Electron-electron interaction theory is used to analyze the low-temperature conductivity.

Fluorimetric analysis of gallium in bauxite, by-products, products from gallium processing and its control solutions

International Nuclear Information System (INIS)

Ferreira, C.A.M.; Medeiros, V.

1987-01-01

The gallium processing since raw material analysis until end-products analysis is studied. Gallium presence in by-products and products, as well as the fluorimetric method is analyzed. Equipments and materials used in laboratory, reagents and chemical solutions are described. (M.J.C.) [pt

Fluorine-enhanced low-temperature wafer bonding of native-oxide covered Si wafers

Science.gov (United States)

Tong, Q.-Y.; Gan, Q.; Fountain, G.; Enquist, P.; Scholz, R.; Gösele, U.

2004-10-01

The bonding energy of bonded native-oxide-covered silicon wafers treated in the HNO3/H2O/HF or the HNO3/HF solution prior to room-temperature contact is significantly higher than bonded standard RCA1 cleaned wafer pairs after low-temperature annealing. The bonding energy reaches over 2000mJ/m2 after annealing at 100 °C. The very slight etching and fluorine in the chemically grown oxide are believed to be the main contributors to the enhanced bonding energy. Transmission-electron-microscopic images have shown that the chemically formed native oxide at bonding interface is embedded with many flake-like cavities. The cavities can absorb the by-products of the interfacial reactions that result in covalent bond formation at low temperatures allowing the strong bond to be retained.

Water-Mediated Photochemical Treatments for Low-Temperature Passivation of Metal-Oxide Thin-Film Transistors.

Science.gov (United States)

Heo, Jae Sang; Jo, Jeong-Wan; Kang, Jingu; Jeong, Chan-Yong; Jeong, Hu Young; Kim, Sung Kyu; Kim, Kwanpyo; Kwon, Hyuck-In; Kim, Jaekyun; Kim, Yong-Hoon; Kim, Myung-Gil; Park, Sung Kyu

2016-04-27

The low-temperature electrical passivation of an amorphous oxide semiconductor (AOS) thin-film transistor (TFT) is achieved by a deep ultraviolet (DUV) light irradiation-water treatment-DUV irradiation (DWD) method. The water treatment of the first DUV-annealed amorphous indium-gallium-zinc-oxide (a-IGZO) thin film is likely to induce the preferred adsorption of water molecules at the oxygen vacancies and leads to subsequent hydroxide formation in the bulk a-IGZO films. Although the water treatment initially degraded the electrical performance of the a-IGZO TFTs, the second DUV irradiation on the water-treated devices may enable a more complete metal-oxygen-metal lattice formation while maintaining low oxygen vacancies in the oxide films. Overall, the stable and dense metal-oxygen-metal (M-O-M) network formation could be easily achieved at low temperatures (below 150 °C). The successful passivation of structural imperfections in the a-IGZO TFTs, such as hydroxyl group (OH-) and oxygen vacancies, mainly results in the enhanced electrical performances of the DWD-processed a-IGZO TFTs (on/off current ratio of 8.65 × 10(9), subthreshold slope of 0.16 V/decade, an average mobility of >6.94 cm(2) V(-1) s(-1), and a bias stability of ΔVTH IGZO TFTs.

Liquid gallium cooling of silicon crystals in high intensity photon beams

International Nuclear Information System (INIS)

Smither, R.K.; Forster, G.A.; Bilderback, D.H.; Bedzyk, M.; Finkelstein, K.; Henderson, C.; White, J.; Berman, L.E.; Stefan, P.; Oversluizen, T.

1989-01-01

The high-brilliance, insertion-device-based photon beams of the next generation of synchrotron sources (Argonne's APS and Grenoble's ESRF) will deliver large thermal loads (1--10 kW) to the first optical elements. Considering the problems that present synchrotron users are experiencing with beams from recently installed insertion devices, new and improved methods of cooling these first optical elements, particularly when they are diffraction crystals, are clearly needed. A series of finite element calculations were performed to test the efficiency of new cooling geometries and various cooling fluids. The best results were obtained with liquid Ga metal flowing in channels just below the surface of the crystal. Ga was selected because of its good thermal conductivity and thermal capacity, low melting point, high boiling point, low kinetic viscosity, and very low vapor pressure. Its very low vapor pressure, even at elevated temperatures, makes it especially attractive in UHV conditions. A series of experiments were conducted at CHESS in February of 1988 that compared liquid gallium-cooled silicon diffraction crystals with water-cooled crystals. A six-pole wiggler beam was used to perform these tests on three different Si crystals, two with new cooling geometries and the one presently in use. A special high-pressure electromagnetic induction pump, recently developed at Argonne, was used to circulate the liquid gallium through the silicon crystals. In all experiments, the specially cooled crystal was used as the first crystal in a two crystal monochromator. An infrared camera was used to monitor the thermal profiles and correlated them with rocking curve measurements. A second set of cooling experiments were conducted in June of 1988 that used the intense, highly collimated beam from the newly installed ANL/CHESS undulator

Layer-by-layer composition and structure of silicon subjected to combined gallium and nitrogen ion implantation for the ion synthesis of gallium nitride

Energy Technology Data Exchange (ETDEWEB)

Korolev, D. S.; Mikhaylov, A. N.; Belov, A. I.; Vasiliev, V. K.; Guseinov, D. V.; Okulich, E. V. [Nizhny Novgorod State University (Russian Federation); Shemukhin, A. A. [Moscow State University, Skobeltsyn Institute of Nuclear Physics (Russian Federation); Surodin, S. I.; Nikolitchev, D. E.; Nezhdanov, A. V.; Pirogov, A. V.; Pavlov, D. A.; Tetelbaum, D. I., E-mail: tetelbaum@phys.unn.ru [Nizhny Novgorod State University (Russian Federation)

2016-02-15

The composition and structure of silicon surface layers subjected to combined gallium and nitrogen ion implantation with subsequent annealing have been studied by the X-ray photoelectron spectroscopy, Rutherford backscattering, electron spin resonance, Raman spectroscopy, and transmission electron microscopy techniques. A slight redistribution of the implanted atoms before annealing and their substantial migration towards the surface during annealing depending on the sequence of implantations are observed. It is found that about 2% of atoms of the implanted layer are replaced with gallium bonded to nitrogen; however, it is impossible to detect the gallium-nitride phase. At the same time, gallium-enriched inclusions containing ∼25 at % of gallium are detected as candidates for the further synthesis of gallium-nitride inclusions.

Study of the possibility of growing germanium single crystals under low temperature gradients

Science.gov (United States)

Moskovskih, V. A.; Kasimkin, P. V.; Shlegel, V. N.; Vasiliev, Y. V.; Gridchin, V. A.; Podkopaev, O. I.; Zhdankov, V. N.

2014-03-01

The possibility of growing germanium single crystals under low temperature gradients in order to produce a dislocation-free material has been studied. Germanium crystals with a dislocation density of about 100-200 cm-2 have been grown in a system with a weight control of crystal growth at maximum axial gradients of about 1.5 K/cm.

State and prospects of Russian and world gallium market

Directory of Open Access Journals (Sweden)

F. D. Larichkin

2017-12-01

Full Text Available The authors consider the state of Russian and world mineral and raw materials base of gallium, the main spheres of application in various branches and industries of the national economy. The article presents the generalization and analysis of trends in world and Russian production, consumption of rare metal and its compounds, the world trade and global market of gallium and products based on it, consuming it in new science-intensive innovative industries, including the production of military equipment. The unique chemical properties of gallium remained unclaimed for a long time. Only after the discovery of the semiconductor properties of gallium compounds has the situation radically changed: the rate of growth in production and consumption of metallic gallium at the end of the twentieth and beginning of the 21st century amounted to an average of more than 8% per year. The largest area of consumption of gallium is the production of semiconductor materials – gallium arsenide (GaAs and gallium nitride (GaN. The areas of application of gallium not related to the semiconductor industry are very small. Industry structure of consumption of GaAs and GaN: in integrated circuits is 66%; optoelectronic devices (light-emitting diodes, laser diodes, photodetectors and solar batteries – 20%; the remaining 14% – scientific research, special alloys, etc. Optoelectronic devices are used in aerospace industry, consumer goods, industrial and medical equipment and telecommunications. Integral circuits are used in the military industry, high-power computers and electronic communications. The most significant growing sectors of the market are LEDs, electronics based on gallium nitride and solar cells. Solar energy has become the fastest growing branch of the world economy. The volumes of gallium production in Russia do not correspond to its raw material, scientific and technological potential as the country and require the development activation based on state

Low-temperature electrical transport in B-doped ultrananocrystalline diamond film

International Nuclear Information System (INIS)

Li, Lin; Zhao, Jing; Hu, Zhaosheng; Quan, Baogang; Li, Junjie; Gu, Changzhi

2014-01-01

B-doped ultrananocrystalline diamond (UNCD) films are grown using hot-filament chemical vapor deposition method, and their electrical transport properties varying with temperature are investigated. When the B-doped concentration of UNCD film is low, a step-like increase feature of the resistance is observed with decreasing temperature, reflecting at least three temperature-modified electronic state densities at the Fermi level according to three-dimensional Mott's variable range hopping transport mechanism, which is very different from that of reported B-doped nanodiamond. With increasing B-doped concentration, a superconductive transformation occurs in the UNCD film and the highest transformation temperature of 5.3 K is observed, which is higher than that reported for superconducting nanodiamond films. In addition, the superconducting coherence length is about 0.63 nm, which breaks a reported theoretical and experimental prediction about ultra-nanoscale diamond's superconductivity

Specific heat studies of pure Nb3Sn single crystals at low temperature

International Nuclear Information System (INIS)

Escudero, R; Morales, F; Bernes, S

2009-01-01

Specific heat measurements performed on high purity vapor-grown Nb 3 Sn crystals show clear features related to both the martensitic and superconducting transitions. Our measurements indicate that the martensitic anomaly does not display hysteresis, meaning that the martensitic transition could be a weak first-order or a second-order thermodynamic transition. Careful measurements of the two transition temperatures display an inverse correlation between them. At low temperature, specific heat measurements show the existence of a single superconducting energy gap feature.

Influence of growth temperature on electrical, optical, and plasmonic properties of aluminum:zinc oxide films grown by radio frequency magnetron sputtering

Energy Technology Data Exchange (ETDEWEB)

Dondapati, Hareesh; Santiago, Kevin; Pradhan, A. K. [Center for Materials Research, Norfolk State University, 700 Park Avenue, Norfolk, Virginia 23504 (United States)

2013-10-14

We have investigated the responsible mechanism for the observation of metallic conductivity at room temperature and metal-semiconductor transition (MST) at lower temperatures for aluminum-doped zinc oxide (AZO) films. AZO films were grown on glass substrates by radio-frequency magnetron sputtering with varying substrate temperatures (T{sub s}). The films were found to be crystalline with the electrical resistivity close to 1.1 × 10{sup −3} Ω cm and transmittance more than 85% in the visible region. The saturated optical band gap of 3.76 eV was observed for the sample grown at T{sub s} of 400 °C, however, a slight decrease in the bandgap was noticed above 400 °C, which can be explained by Burstein–Moss effect. Temperature dependent resistivity measurements of these highly conducting and transparent films showed a MST at ∼110 K. The observed metal-like and metal-semiconductor transitions are explained by taking into account the Mott phase transition and localization effects due to defects. All AZO films demonstrate crossover in permittivity from positive to negative and low loss in the near-infrared region, illustrating its applications for plasmonic metamaterials, including waveguides for near infrared telecommunication region. Based on the results presented in this study, the low electrical resistivity and high optical transmittance of AZO films suggested a possibility for the application in the flexible electronic devices, such as transparent conducting oxide film on LEDs, solar cells, and touch panels.

High quality TmIG films with perpendicular magnetic anisotropy grown by sputtering

Science.gov (United States)

Wu, C. N.; Tseng, C. C.; Yeh, S. L.; Lin, K. Y.; Cheng, C. K.; Fanchiang, Y. T.; Hong, M.; Kwo, J.

Ferrimagnetic thulium iron garnet (TmIG) films grown on gadolinium gallium garnet substrates recently showed stress-induced perpendicular magnetic anisotropy (PMA), attractive for realization of quantum anomalous Hall effect (QAHE) of topological insulator (TI) films via the proximity effect. Moreover, current induced magnetization switching of Pt/TmIG has been demonstrated for the development of room temperature (RT) spintronic devices. In this work, high quality TmIG films (about 25nm) were grown by sputtering at RT followed by post-annealing. We showed that the film composition is tunable by varying the growth parameters. The XRD results showed excellent crystallinity of stoichiometric TmIG films with an out-of-plane lattice constant of 1.2322nm, a narrow film rocking curve of 0.017 degree, and a film roughness of 0.2 nm. The stoichiometric films exhibited PMA and the saturation magnetization at RT was 109 emu/cm3 (RT bulk value 110 emu/cm3) with a coercive field of 2.7 Oe. In contrast, TmIG films of Fe deficiency showed in-plane magnetic anisotropy. The high quality sputtered TmIG films will be applied to heterostructures with TIs or metals with strong spin-orbit coupling for novel spintronics.

The global anthropogenic gallium system: determinants of demand, supply and efficiency improvements.

Science.gov (United States)

Løvik, Amund N; Restrepo, Eliette; Müller, Daniel B

2015-05-05

Gallium has been labeled as a critical metal due to rapidly growing consumption, importance for low-carbon technologies such as solid state lighting and photovoltaics, and being produced only as a byproduct of other metals (mainly aluminum). The global system of primary production, manufacturing, use and recycling has not yet been described or quantified in the literature. This prevents predictions of future demand, supply and possibilities for efficiency improvements on a system level. We present a description of the global anthropogenic gallium system and quantify the system using a combination of statistical data and technical parameters. We estimated that gallium was produced from 8 to 21% of alumina plants in 2011. The most important applications of gallium are NdFeB permanent magnets, integrated circuits and GaAs/GaP-based light-emitting diodes, demanding 22-37%, 16-27%, and 11-21% of primary metal production, respectively. GaN-based light-emitting diodes and photovoltaics are less important, both with 2-6%. We estimated that 120-170 tons, corresponding to 40-60% of primary production, ended up in production wastes that were either disposed of or stored. While demand for gallium is expected to rise in the future, our results indicated that it is possible to increase primary production substantially with conventional technology, as well as improve the system-wide material efficiency.

Photoexcitation dynamics in organic solar cell donor/acceptor system

Energy Technology Data Exchange (ETDEWEB)

Aarnio, H.

2012-07-01

In this work, photoinduced absorption techniques have been used in a number of ways to clarify the charge generation and recombination processes in two polymers used in organic solar cells, namely APFO3 and P3HT. Emphasis has been on identifying photoexcitations, modeling their dynamics and determining their lifetimes.

Gallium uptake in myositis ossificans. Potential pitfalls in diagnosis

International Nuclear Information System (INIS)

Salzman, L.; Lee, V.W.; Grant, P.

1987-01-01

Seven cases of gallium uptake in myositis ossificans are described. Gallium scans are done frequently in paraplegics, quadriplegics, and comatose patients to look for occult infection. It is important to be aware of possible gallium uptake in myositis ossificans, particularly in the extremities, which is frequent in these patients. Gallium uptake may be present prior to any abnormalities seen on plain films or CT scans. It is important to correlate roentgenograms with abnormal gallium scans, particularly in the extremities, to avoid potential pitfalls in diagnosis and prevent unnecessary antibiotic treatment. A bone scan should be obtained whenever possible, particularly when roentgenograms are negative, to confirm the diagnosis

Liquid gallium cooling of silicon crystals in high intensity photon beam

International Nuclear Information System (INIS)

Smither, R.K.; Forster, G.A.; Bilderback, D.H.

1988-11-01

The high-brilliance, insertion-device-based, photon beams of the next generation of synchrotron sources will deliver large thermal loads (1 kW to 10 kW) to the first optical elements. Considering the problems that present synchrotron users are experiencing with beams from recently installed insertion devices, new and improved methods of cooling these first optical elements, particularly when they are diffraction crystals, are clearly needed. A series of finite element calculations were performed to test the efficiency of new cooling geometries and new cooling fluids. The best results were obtained with liquid Ga metal flowing in channels just below the surface of the crystal. Ga was selected because of its good thermal conductivity and thermal capacity, low melting point, high boiling point, low kinetic viscosity, and very low vapor pressure. Its very low vapor pressure, even at elevated temperatures, makes it especially attractive in uhv conditions. A series of experiments were conducted at CHESS in February of 1988 that compared liquid gallium cooled silicon diffraction crystals with water cooled crystals. 2 refs., 16 figs., 1 tab

Evaluation of Low Pressure Fogging System for Improving Crop Yield of Tomato (Lycopersicon esculentum Mill.: Grown under Heat Stress Conditions

Directory of Open Access Journals (Sweden)

Kobi Shilo

2013-06-01

Full Text Available In Mediterranean regions, many tomato plants are grown throughout the hot summer period (May–September in sheltered cultivation, mainly for plant protection reasons. Most of the shelters that are used are low cost net houses covered with 50 mesh insect proof net. In most cases these net houses have a flat roof and no ventilation or climate control measures. This insufficient ventilation during the hot summer leads to above optimal air temperatures and causes moderate heat stress inside the shelters, which leads to yield reduction. The aim of this study was to evaluate the ability of a simple and inexpensive low pressure fogging system installed in a naturally ventilated net house to lower temperatures and improve the yield during the summer. The study showed that in areas where relative air humidity (RH during the daytime is less than 60%, tomato plants improved their performance when grown through the summer in net houses under moderate heat stress. Under fogging conditions pollen grain viability and fruit set were significantly improved. This improvement influenced the yield picked during September (104–136 DAP. However, total seasonal yield was not affected by the fogging treatment.

Growth and Low Temperature Transport Measurements of Pure and Doped Bismuth Selenide

DEFF Research Database (Denmark)

Mlack, Jerome Thomas

Se3, which is a strong spin orbit material and a topological insulator. I describe a synthesis technique and low-temperature transport measurements of nanostructures of Bi2Se3, that when annealed with palladium show evidence of superconductivity. The growth method is a catalyst-free atmospheric...... with palladium via annealing, the transport properties of the samples can be altered to exhibit superconductivity. Thin films of palladium are deposited on prefabricated Bi2Se3 nanodevices and annealed at temperatures in excess of 100 Celsius. We find that Bi2Se3 absorbs Pd under these conditions...... pressure vapor-solid growth. The growth method yields a variety of nanostructures, and materials analysis shows ordered structures of bismuth selenide in all cases. Low-temperature measurements of as-grown nanostructures indicate tunable carrier density in all samples. By doping the nanostructures...

Ultra-low damping in lift-off structured yttrium iron garnet thin films

Science.gov (United States)

Krysztofik, A.; Coy, L. E.; Kuświk, P.; Załeski, K.; Głowiński, H.; Dubowik, J.

2017-11-01

We show that using maskless photolithography and the lift-off technique, patterned yttrium iron garnet thin films possessing ultra-low Gilbert damping can be accomplished. The films of 70 nm thickness were grown on (001)-oriented gadolinium gallium garnet by means of pulsed laser deposition, and they exhibit high crystalline quality, low surface roughness, and the effective magnetization of 127 emu/cm3. The Gilbert damping parameter is as low as 5 ×10-4. The obtained structures have well-defined sharp edges which along with good structural and magnetic film properties pave a path in the fabrication of high-quality magnonic circuits and oxide-based spintronic devices.

ASSESSMENT OF GALLIUM OXIDE TECHNOLOGY

Science.gov (United States)

2017-08-01

AFRL-RY-WP-TR-2017-0167 ASSESSMENT OF GALLIUM OXIDE TECHNOLOGY Burhan Bayraktaroglu Devices for Sensing Branch Aerospace...TITLE AND SUBTITLE ASSESSMENT OF GALLIUM OXIDE TECHNOLOGY 5a. CONTRACT NUMBER In-house 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER N/A 6...report summarizes the current status of the Ga2O3 technology based on published results on theoretical electronic structure, materials growth, and

Polarization dependent femtosecond laser modification of MBE-grown III-V nanostructures on silicon

OpenAIRE

Zandbergen, Sander R.; Gibson, Ricky; Amirsolaimani, Babak; Mehravar, Soroush; Keiffer, Patrick; Azarm, Ali; Kieu, Khanh

2017-01-01

We report a novel, polarization dependent, femtosecond laser-induced modification of surface nanostructures of indium, gallium, and arsenic grown on silicon via molecular beam epitaxy, yielding shape control from linear and circular polarization of laser excitation. Linear polarization causes an elongation effect, beyond the dimensions of the unexposed nanostructures, ranging from 88 nm to over 1 um, and circular polarization causes the nanostructures to flatten out or form loops of material,...

Effect of low NH3 flux towards high quality semi-polar (11-22) GaN on m-plane sapphire via MOCVD

Science.gov (United States)

Omar, Al-Zuhairi; Shuhaimi Bin Abu Bakar, Ahmad; Makinudin, Abdullah Haaziq Ahmad; Khudus, Muhammad Imran Mustafa Abdul; Azman, Adreen; Kamarundzaman, Anas; Supangat, Azzuliani

2018-05-01

The effect of ammonia flux towards the quality of the semi-polar (11-22) gallium nitride thin film on m-plane (10-10) sapphire is presented. Semi-polar (11-22) gallium nitride epi-layers were obtained using a two-step growth method, consisting of high temperature aluminum nitride followed by gallium nitride via metal organic chemical vapor deposition. The surface morphology analysis via field emission scanning electron microscopy and atomic force microscopy of the semi-polar (11-22) gallium nitride has shown that low ammonia flux promotes two-dimensional growth with low surface roughness of 4.08 nm. A dominant diffraction peak of (11-22) gallium nitride was also observed via X-ray diffraction upon utilizing low ammonia flux. The on- and off-axis X-ray rocking curve measurements illustrate the enhancement of the crystal quality, which might result from the reduction of the basal stacking faults and perfect dislocation. The full width half maximum values were reduced by at least 15% for both on- and off-axis measurements.

Horizontal Assembly of Single Nanowire Diode Fabricated by p-n Junction GaN NW Grown by MOCVD

Directory of Open Access Journals (Sweden)

Ji-Hyeon Park

2014-01-01

Full Text Available Uniaxially p-n junction gallium nitride nanowires have been synthesized via metal-organic chemical vapor deposition method. Nanowires prepared on Si(111 substrates were found to grow perpendicular to the substrate, and the transmission electron microscopy studies demonstrated that the nanowires had singlecrystalline structures with a growth axis. The parallel assembly of the p-n junction nanowire was prepared on a Si substrate with a thermally grown SiO2 layer. The transport studies of horizontal gallium nitride nanowire structures assembled from p- and n-type materials show that these junctions correspond to well-defined p-n junction diodes. The p-n junction devices based on GaN nanowires suspended over the electrodes were fabricated and their electrical properties were investigated. The horizontally assembled gallium nitride nanowire diodes suspended over the electrodes exhibited a substantial increase in conductance under UV light exposure. Apart from the selectivity to different light wavelengths, high responsivity and extremely short response time have also been obtained.

Gallium scintigraphy in Hansen's disease

International Nuclear Information System (INIS)

Braga, F.J.H.N.; Sao Paulo Univ., SP; Araejo, E.B.; Camargo, E.E.; Tedesco-Marchesi, L.C.M.; Rivitti, M.C.M.; Bouladour, H.; Galle, P.

1991-01-01

Gallium 67 imaging was used in 12 patients with documented Hansen's disease undergoing treatment or not in an attempt to determine the pattern of the disease. Diagnosis was confirmed by histopathology in all patients. The Mitsuda reaction was seen in all patients. Specific nuclear studies were performed when needed to evaluate particular organs better. Gallium 67 images show homogeneous, diffuse and moderate accumulation over the entire skin surface (except for the face) of untreated patients with multibacillary disease. The face skin in these cases presented homogeneous, diffuse but very marked uptake of gallium. Internal organ involvement was variable. There was a very good correlation among clinical, scintigraphical, immunological and histopathological data. The pattern of the body skin ('skin outlining') and face skin ('beard distribution') may be distinct for untreated patients with multibacillary leprosy. (orig.)

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.

Relationships Between Temperature, pH, and Crusting on Mg/Ca Ratios in Laboratory-Grown Neogloboquadrina Foraminifera

Science.gov (United States)

Davis, Catherine V.; Fehrenbacher, Jennifer S.; Hill, Tessa M.; Russell, Ann D.; Spero, Howard J.

2017-11-01

Mg/Ca ratio paleothermometry in foraminifera is an important tool for the reconstruction and interpretation of past environments. However, existing Mg/Ca:temperature relationships for planktic species inhabiting middle- and high-latitude environments are limited by a lack of information about the development and impact of low-Mg/Ca ratio "crusts" and the influence of the carbonate system on Mg/Ca ratios in these groups. To address this, we cultured individual specimens of Neogloboquadrina incompta and Neogloboquadrina pachyderma in seawater across a range of temperature (6°-12°C) and pH (7.4-8.2). We found by laser ablation inductively couple mass spectrometry analyses of shells that culture-grown crust calcite in N. incompta had a lower Mg/Ca ratio than ontogenetic calcite formed at the same temperature, suggesting that temperature is not responsible for the low-Mg/Ca ratio of neogloboquadrinid crusts. The Mg/Ca:temperature relationship for ontogenetic calcite in N. incompta was consistent with the previously published culture-based relationship, and no significant relationship was found between Mg/Ca ratios and pH in this species. However, the Mg/Ca ratio in laboratory-cultured N. pachyderma was much higher than that reported in previous core top and sediment trap samples, due to lack of crust formation in culture. Application of our ontogenetic calcite-specific Mg/Ca:temperature relationships to fossil N. pachyderma and N. incompta from five intervals in cores from the Santa Barbara Basin and the Bering Sea shows that excluding crust calcite in fossil specimens may improve Mg/Ca-based temperature estimates.

Zero Temperature Hope Calculations

International Nuclear Information System (INIS)

Rozsnyai, B. F.

2002-01-01

The primary purpose of the HOPE code is to calculate opacities over a wide temperature and density range. It can also produce equation of state (EOS) data. Since the experimental data at the high temperature region are scarce, comparisons of predictions with the ample zero temperature data provide a valuable physics check of the code. In this report we show a selected few examples across the periodic table. Below we give a brief general information about the physics of the HOPE code. The HOPE code is an ''average atom'' (AA) Dirac-Slater self-consistent code. The AA label in the case of finite temperature means that the one-electron levels are populated according to the Fermi statistics, at zero temperature it means that the ''aufbau'' principle works, i.e. no a priory electronic configuration is set, although it can be done. As such, it is a one-particle model (any Hartree-Fock model is a one particle model). The code is an ''ion-sphere'' model, meaning that the atom under investigation is neutral within the ion-sphere radius. Furthermore, the boundary conditions for the bound states are also set at the ion-sphere radius, which distinguishes the code from the INFERNO, OPAL and STA codes. Once the self-consistent AA state is obtained, the code proceeds to generate many-electron configurations and proceeds to calculate photoabsorption in the ''detailed configuration accounting'' (DCA) scheme. However, this last feature is meaningless at zero temperature. There is one important feature in the HOPE code which should be noted; any self-consistent model is self-consistent in the space of the occupied orbitals. The unoccupied orbitals, where electrons are lifted via photoexcitation, are unphysical. The rigorous way to deal with that problem is to carry out complete self-consistent calculations both in the initial and final states connecting photoexcitations, an enormous computational task. The Amaldi correction is an attempt to address this problem by distorting the

Superconductivity and low temperature electrical transport in B-doped CVD nanocrystalline diamond

Directory of Open Access Journals (Sweden)

Milos Nesladek, Jiri J. Mares, Dominique Tromson, Christine Mer, Philippe Bergonzo, Pavel Hubik and Jozef Kristofik

2006-01-01

Full Text Available In this work, we report on superconductivity (SC found in thin B-doped nanocrystalline diamond films, prepared by the PE-CVD technique. The thickness of the films varies from about 100 to 400 nm, the films are grown on low-alkaline glass at substrate temperatures of about 500–700 °C. The SIMS measurements show that films can be heavily doped with boron in concentrations in the range of 3×1021 cm−3. The Raman spectra show Fano resonances, confirming the substitutional B-incorporation. The low temperature magnetotransport measurements reveal a positive magnetoresistance. The SC transition is observed at about Tc=1.66 K. A simple theory exploiting the concept of weak localization accounting for this transition is proposed.

High-quality graphene grown on polycrystalline PtRh{sub 20} alloy foils by low pressure chemical vapor deposition and its electrical transport properties

Energy Technology Data Exchange (ETDEWEB)

Yang, He; Shen, Chengmin, E-mail: cmshen@iphy.ac.cn; Tian, Yuan; Bao, Lihong; Chen, Peng; Yang, Rong; Yang, Tianzhong; Li, Junjie; Gu, Changzhi; Gao, Hong-Jun [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China)

2016-02-08

High-quality continuous uniform monolayer graphene was grown on polycrystalline PtRh{sub 20} alloy foils by low pressure chemical vapor deposition. The morphology of graphene was investigated by Raman spectroscopy, scanning electron microscopy, and atomic force microscopy. Analysis results confirm that high quality single-layer graphene was fabricated on PtRh{sub 20} foil at 1050 °C using a lower flux of methane under low pressure. Graphene films were transferred onto the SiO{sub 2}/Si substrate by the bubbling transfer method. The mobility of a test field effect transistor made of the graphene grown on PtRh{sub 20} was measured and reckoned at room temperature, showing that the carrier mobility was about 4000 cm{sup 2} V{sup −1} s{sup −1}. The results indicate that desired quality of single-layer graphene grown on PtRh{sub 20} foils can be obtained by tuning reaction conditions.

Gallium-containing hydroxyapatite for potential use in orthopedics

International Nuclear Information System (INIS)

Melnikov, P.; Teixeira, A.R.; Malzac, A.; Coelho, M. de B.

2009-01-01

A novel material that may be recommended for grafts and implants stimulating bone growth has been obtained by introducing gallium ions (up to 11.0 mass%) into crystalline lattice of hydroxyapatite. The doping was carried out using gallium nitrate and sodium gallate solutions. In both cases, lattice parameters of gallium-doped hydroxyapatite are identical to those of pure synthetic hydroxyapatite. Gallium does not replace calcium as a result of heterovalent substitution and consequently produces no distortions in the framework of hydroxyapatite matrix. It remains strongly fixed in the form of solid solution of intercalation. According to scanning electron microscopy images gallium insertion does not cause any morphological alterations in hydroxyapatite structure and the product developed meets physico-chemical criteria for biomaterial to be employed in orthopedic practice and local handling of traumatic injuries. Its future usage opens the opportunity to enhance osteosynthesis and calcium retention in loco.

The anomalous low temperature resistivity of thermally evaporated α-Mn thin film

International Nuclear Information System (INIS)

Ampong, F.K.; Boakye, F.; Nkum, R.K.

2010-01-01

Electrical resistivity measurements have been carried out on thermally evaporated α-Mn thin film between 300 and 1.4 K using the van der Pauw four probe technique. The film was grown on a glass substrate held at a temperature of 373 K, in an ambient pressure of 5x10 -6 Torr. The results show a resistance minimum, a notable characteristic of α-Mn but at a (rather high) temperature of 194±1 K. Below the resistivity maximum which corresponds to 70 K, the resistivity drops by only 0.02 μΩm indicating a rather short range magnetic ordering. The low temperature results show a tendency towards saturation of the resistivity as the temperature approaches zero suggesting a Kondo scattering.

The anomalous low temperature resistivity of thermally evaporated alpha-Mn thin film

Energy Technology Data Exchange (ETDEWEB)

Ampong, F.K., E-mail: kampxx@yahoo.co [Department of Physics, Kwame Nkrumah University of Science and Technology, Kumasi (Ghana); Boakye, F.; Nkum, R.K. [Department of Physics, Kwame Nkrumah University of Science and Technology, Kumasi (Ghana)

2010-08-15

Electrical resistivity measurements have been carried out on thermally evaporated alpha-Mn thin film between 300 and 1.4 K using the van der Pauw four probe technique. The film was grown on a glass substrate held at a temperature of 373 K, in an ambient pressure of 5x10{sup -6} Torr. The results show a resistance minimum, a notable characteristic of alpha-Mn but at a (rather high) temperature of 194+-1 K. Below the resistivity maximum which corresponds to 70 K, the resistivity drops by only 0.02 muOMEGAm indicating a rather short range magnetic ordering. The low temperature results show a tendency towards saturation of the resistivity as the temperature approaches zero suggesting a Kondo scattering.

Formation of gallium nitride templates and freestanding substrates by hydride vapor phase epitaxy for homoepitaxial growth of III-nitride devices

Science.gov (United States)

Williams, Adrian Daniel

Gallium nitride (GaN) is a direct wide band gap semiconductor currently under heavy development worldwide due to interest in its applications in ultra-violet optoelectronics, power electronics, devices operating in harsh environments (high temperature or corrorsive), etc. While a number of devices have been demonstrated with this material and its related alloys, the unavailability of GaN substrates is seen as one of the current major bottlenecks to both material quality and device performance. This dissertation is concerned with the synthesis of high quality GaN substrates by the hydride vapor phase epitaxy method (HVPE). In this work, the flow of growth precursors in a home-built HVPE reactor was modeled by the Navier-Stokes equation and solved by finite element analysis to promote uniformity of GaN on 2'' sapphire substrates. Kinetics of growth was studied and various regimes of growth were identified to establish a methodology for HVPE GaN growth, independent of reactor geometry. GaN templates as well as bulk substrates were fabricated in this work. Realization of freestanding GaN substrates was achieved through discovery of a natural stress-induced method of separating bulk GaN from sapphire via mechanical failure of a low-temperature GaN buffer layer. Such a process eliminates the need for pre- or post-processing of sapphire substrates, as is currently the standard. Stress in GaN-on-sapphire is discussed, with the dominant contributor identified as thermal stress due to thermal expansion coefficient mismatch between the two materials. This thermal stress is analyzed using Stoney's equation and conditions for crack-free growth of thick GaN substrates were identified. An etch-back process for planarizing GaN templates was also developed and successfully applied to rough GaN templates. The planarization of GaN has been mainly addressed by chemo-mechanical polishing (CMP) methods in the literature, with notable shortcomings including the inability to effectively

Gallium-67 scintigraphy in borderline lepromatous leprosy

International Nuclear Information System (INIS)

Mouratidis, B.; Lomas, F.E.

1993-01-01

A middle aged woman with a pyrexia of unknown origin was shown to have borderline lepromatous leprosy. Early gallium-67 scintigraphy demonstrated increased uptake in the subcutaneous tissues of the face and thighs. As a result of these findings skin biopsy was obtained from the right thigh which gave a diagnosis of borderline lepromatous leprosy. The authors have been unable to find other reports of gallium-67 scintigraphy in leprosy but the pattern of gallium-67 distribution should suggest the diagnosis. 5 refs., 1 fig

Shock initiation experiments on ratchet grown PBX 9502

Energy Technology Data Exchange (ETDEWEB)

Gustavsen, Richard L [Los Alamos National Laboratory; Thompson, Darla G [Los Alamos National Laboratory; Olinger, Barton W [Los Alamos National Laboratory; Deluca, Racci [Los Alamos National Laboratory; Bartram, Brian D [Los Alamos National Laboratory; Pierce, Timothy H [Los Alamos National Laboratory; Sanchez, Nathaniel J [Los Alamos National Laboratory

2010-01-01

This study compares the shock initiation behavior of PBX 9502 pressed to less than nominal density (nominal density is 1.890 {+-} 0.005 g/cm{sup 3}) with PBX 9502 pressed to nominal density and then ''ratchet grown'' to low density. PBX 9502 is an insensitive plastic bonded explosive consisting of 95 weight % dry-aminated tri-amino-tri-nitro-benzene (TATB) and 5 weight % Kel-F 800 plastic binder. ''Ratchet growth'' - an irreversible increase in specific volume - occurs when an explosive based on TATB is temperature cycled. The design of our study is as follows: PBX 9502, all from the same lot, received the following four treatments. Samples in the first group were pressed to less than nominal density. These were not ratchet grown and used as a baseline. Samples in the second group were pressed to nominal density and then ratchet grown by temperature cycling 30 times between -54 C and +80 C. Samples in the final group were pressed to nominal density and cut into 100 mm by 25.4 mm diameter cylinders. During thermal cycling the cylinders were axially constrained by a 100 psi load. Samples for shock initiation experiments were cut perpendicular (disks) and parallel (slabs) to the axial load. The four sample groups can be summarized with the terms pressed low, ratchet grown/no load, axial load/disks, and axial load/slabs. All samples were shock initiated with nearly identical inputs in plate impact experiments carried out on a gas gun. Wave profiles were measured after propagation through 3, 4, 5, and 6 mm of explosive. Side by side comparison of wave profiles from different samples is used as a measure of relative sensitivity. All reduced density samples were more shock sensitive than nominal density PBX 9502. Differences in shock sensitivity between ratchet grown and pressed to low density PBX 9502 were small, but the low density pressings are slightly more sensitive than the ratchet grown samples.

Proof-of-Concept Experiments on a Gallium-Based Ignitron for Pulsed Power Applications

Science.gov (United States)

Ali, H. K.; Hanson, V. S.; Polzin, K. A.; Pearson, J. B.

2015-01-01

ignitron designs have used mercury as the liquid metal cathode, owing to its presence as a liquid at room temperatures and a vapor pressure of 10 Pa (75 mtorr) at room temperature. While these are favorable properties, there are obvious environmental and personal safety concerns with the storage, handling, and use of mercury and its compounds. The purpose of the present work was to fabricate and test an ignitron that used as its cathode an alternate liquid metal that was safe to handle and store. To that end, an ignitron test article that used liquid gallium as the cathode material was developed and tested. Gallium is a metal that has a melting temperature of 29.76 C, which is slightly above room temperature, and a boiling point of over 2,300 C at atmospheric pressure. This property makes gallium the element with the largest relative difference between melting and boiling points. Gallium has a limited role in biology, and when ingested, it will be subsequently processed by the body and expelled rather than accumulating to toxic levels. The next section of this Technical Memorandum (TM) provides background information on the development of mercury-based ignitrons, which serves as the starting point for the development of the gallium-based variant. Afterwards, the experimental hardware and setup used in proof-of-concept testing of a basic gallium ignitron are presented. Experimental data, consisting of discharge voltage and current waveforms as well as high-speed imaging of the gallium arc discharge in the gallium ignitron test article, are presented to demonstrate the efficacy of the concept. Discussion of the data and suggestions on improvements for future iterations of the design are presented in the final two sections of this TM.

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

International Nuclear Information System (INIS)

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

2008-01-01

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

Growth and Etch Rate Study of Low Temperature Anodic Silicon Dioxide Thin Films

Directory of Open Access Journals (Sweden)

Akarapu Ashok

2014-01-01

Full Text Available Silicon dioxide (SiO2 thin films are most commonly used insulating films in the fabrication of silicon-based integrated circuits (ICs and microelectromechanical systems (MEMS. Several techniques with different processing environments have been investigated to deposit silicon dioxide films at temperatures down to room temperature. Anodic oxidation of silicon is one of the low temperature processes to grow oxide films even below room temperature. In the present work, uniform silicon dioxide thin films are grown at room temperature by using anodic oxidation technique. Oxide films are synthesized in potentiostatic and potentiodynamic regimes at large applied voltages in order to investigate the effect of voltage, mechanical stirring of electrolyte, current density and the water percentage on growth rate, and the different properties of as-grown oxide films. Ellipsometry, FTIR, and SEM are employed to investigate various properties of the oxide films. A 5.25 Å/V growth rate is achieved in potentiostatic mode. In the case of potentiodynamic mode, 160 nm thickness is attained at 300 V. The oxide films developed in both modes are slightly silicon rich, uniform, and less porous. The present study is intended to inspect various properties which are considered for applications in MEMS and Microelectronics.

Novel ethylenediamine-gallium phosphate containing 6-fold coordinated gallium atoms with unusual four equatorial Ga–N bonds

Energy Technology Data Exchange (ETDEWEB)

Torre-Fernández, Laura [Departamentos de Química Física y Analítica y Química Orgánica e Inorgánica, Universidad de Oviedo-CINN, 33006 Oviedo (Spain); Espina, Aránzazu; Khainakov, Sergei A.; Amghouz, Zakariae [Servicios Científico Técnicos, Universidad de Oviedo, 33006 Oviedo (Spain); García, José R. [Departamentos de Química Física y Analítica y Química Orgánica e Inorgánica, Universidad de Oviedo-CINN, 33006 Oviedo (Spain); García-Granda, Santiago, E-mail: sgg@uniovi.es [Departamentos de Química Física y Analítica y Química Orgánica e Inorgánica, Universidad de Oviedo-CINN, 33006 Oviedo (Spain)

2014-07-01

A novel ethylenediamine-gallium phosphate, formulated as Ga(H{sub 2}NCH{sub 2}CH{sub 2}NH{sub 2}){sub 2}PO{sub 4}·2H{sub 2}O, was synthesized under hydrothermal conditions. The crystal structure, including hydrogen positions, was determined using single-crystal X-ray diffraction data (monoclinic, a=9.4886(3) Å, b=6.0374(2) Å, c=10.2874(3) Å, and β=104.226(3)°, space group Pc) and the bulk was characterized by chemical (Ga–P–C–H–N) and thermal analysis (TG–MS and DSC), including activation energy data of its thermo-oxidative degradation, powder X-ray diffraction (PXRD), solid-state nuclear magnetic resonance (SS-NMR) measurements, and transmission electron microscopy (TEM, SAED/NBD, and STEM BF-EDX). The crystal structure is built up of infinite zig-zag chains running along the c-axis, formed by vertex-shared (PO{sub 4}) and (GaO{sub 2}N{sub 4}) polyhedra. The new compound is characterized by unusual four equatorial Ga–N bonds coming from two nonequivalent ethylenediamine molecules and exhibits strong blue emission at 430 nm (λ{sub ex}=350 nm) in the solid state at room temperature. - Graphical abstract: Single crystals of a new ethylenediamine-gallium phosphate, Ga(H{sub 2}NCH{sub 2}CH{sub 2}NH{sub 2}){sub 2}PO{sub 4}·2H{sub 2}O, were obtained and the structural features presented. This structure is one of the scarce examples of GaPO with Ga–N bonds reported. - Highlights: • A novel ethylenediamine-gallium phosphate was hydrothermally synthesized. • The new compound is characterized by unusual four equatorial Ga–N bonds. • Void-volume analysis shows cages and channels with sizes ideally suited to accommodate small molecules. • The new compound exhibits strong blue emission.

Fabrication of magnetic nano liquid metal fluid through loading of Ni nanoparticles into gallium or its alloy

Energy Technology Data Exchange (ETDEWEB)

Xiong, Mingfeng; Gao, Yunxia [Key Lab of Cryogenics and Beijing Key Lab of CryoBiomedical Engineering, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190 (China); Liu, Jing, E-mail: jliu@mail.ipc.ac.cn [Key Lab of Cryogenics and Beijing Key Lab of CryoBiomedical Engineering, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190 (China); Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing 100084 (China)

2014-03-15

In this study, Ni nanoparticles were loaded into the partially oxidized gallium and its alloys to fabricate desired magnetic nanofluid. It was disclosed that the Ni nanoparticles sharply increased the freezing temperature and latent heat of the obtained magnetic nano liquid metal fluid, while the melting process was less affected. For the gallium sample added with 10 vol% coated Ni particles, a hysteresis loop was observed and the magnetization intensity decreased with the increase of the temperature. The slope for the magnetization-temperature curve within 10–30 K was about 20 times of that from 40 K to 400 K. Further, the dynamic impact experiments of striking magnetic liquid metal droplets on the magnet revealed that the regurgitating of the leading edge of the liquid disk and the subsequent wave that often occurred in the gallium-indium droplets would disappear for the magnetic fluids case due to attraction force of the magnet. - Graphical abstract: High speed videos for the impact of striking GaIn{sub 24.5} based magnetic liquid metal droplets on a magnet plate. - Highlights: • A feasible way to fabricate magnetic nano liquid metal fluid was presented. • Ni nanoparticles sharply increased freezing temperature and latent heat of magnetic nanofluid. • A hysteresis loop phenomenon was observed for the magnetic nanofluid. • Temperature dependent magnetization spanning from 10 K to 400 K was measured. • Impact phenomena of striking magnetic droplets on magnet were disclosed.

Surface characterization of low-temperature grown yttrium oxide

Science.gov (United States)

Krawczyk, Mirosław; Lisowski, Wojciech; Pisarek, Marcin; Nikiforow, Kostiantyn; Jablonski, Aleksander

2018-04-01

The step-by-step growth of yttrium oxide layer was controlled in situ using X-ray photoelectron spectroscopy (XPS). The O/Y atomic concentration (AC) ratio in the surface layer of finally oxidized Y substrate was found to be equal to 1.48. The as-grown yttrium oxide layers were then analyzed ex situ using combination of Auger electron spectroscopy (AES), elastic-peak electron spectroscopy (EPES) and scanning electron microscopy (SEM) in order to characterize their surface chemical composition, electron transport phenomena and surface morphology. Prior to EPES measurements, the Y oxide surface was pre-sputtered by 3 kV argon ions, and the resulting AES-derived composition was found to be Y0.383O0.465C0.152 (O/Y AC ratio of 1.21). The SEM images revealed different surface morphology of sample before and after Ar sputtering. The oxide precipitates were observed on the top of un-sputtered Y oxide layer, whereas the oxide growth at the Ar ion-sputtered surface proceeded along defects lines normal to the layer plane. The inelastic mean free path (IMFP) characterizing electron transport was evaluated as a function of energy in the range of 0.5-2 keV from the EPES method. Two reference materials (Ni and Au) were used in these measurements. Experimental IMFPs determined for the Y0.383O0.465C0.152 and Y2O3 surface compositions, λ, were uncorrected for surface excitations and approximated by the simple function λ = kEp at electron energies E between 500 eV and 2000 eV, where k and p were fitted parameters. These values were also compared with IMFPs resulting from the TPP-2 M predictive equation for both oxide compositions. The fitted functions were found to be reasonably consistent with the measured and predicted IMFPs. In both cases, the average value of the mean percentage deviation from the fits varied between 5% and 37%. The IMFPs measured for Y0.383O0.465C0.152 surface composition were found to be similar to the IMFPs for Y2O3.

Gallium 67 uptake in thymic rebound

International Nuclear Information System (INIS)

Hurst, R.; Sabio, H.; Teates, C.D.

1988-01-01

We have reported a case of localized thymic enlargement and uptake of gallium 67 in a child who had received antineoplastic chemotherapy. The enlarged thymus showed normal histology, a picture consistent with thymic rebound after nonspecific stress. This case further demonstrates the need to consider thymic rebound as a cause of gallium 67 uptake in children with neoplastic diseases

Study of breakdown voltage of indium-gallium-zinc-oxide-based Schottky diode

Energy Technology Data Exchange (ETDEWEB)

Xin, Qian; Yan, Linlong; Luo, Yi [School of Physics, Shandong University, Jinan 250100 (China); Song, Aimin, E-mail: A.Song@manchester.ac.uk [School of Physics, Shandong University, Jinan 250100 (China); School of Electrical and Electronic Engineering, University of Manchester, Manchester M13 9PL (United Kingdom)

2015-03-16

In contrast to the intensive studies on thin-film transistors based on indium gallium zinc oxide (IGZO), the research on IGZO-based diodes is still very limited, particularly on their behavior and stability under high bias voltages. Our experiments reveal a sensitive dependence of the breakdown voltage of IGZO Schottky diodes on the anode metal and the IGZO film thickness. Devices with an Au anode are found to breakdown easily at a reverse bias as low as −2.5 V, while the devices with a Pd anode and a 200-nm, fully depleted IGZO layer have survived up to −15 V. All diodes are fabricated by radio-frequency magnetron sputtering at room temperature without any thermal treatment, yet showing an ideality factor as low as 1.14, showing the possibility of achieving high-performance Schottky diodes on flexible plastic substrate.

Study of breakdown voltage of indium-gallium-zinc-oxide-based Schottky diode

International Nuclear Information System (INIS)

Xin, Qian; Yan, Linlong; Luo, Yi; Song, Aimin

2015-01-01

In contrast to the intensive studies on thin-film transistors based on indium gallium zinc oxide (IGZO), the research on IGZO-based diodes is still very limited, particularly on their behavior and stability under high bias voltages. Our experiments reveal a sensitive dependence of the breakdown voltage of IGZO Schottky diodes on the anode metal and the IGZO film thickness. Devices with an Au anode are found to breakdown easily at a reverse bias as low as −2.5 V, while the devices with a Pd anode and a 200-nm, fully depleted IGZO layer have survived up to −15 V. All diodes are fabricated by radio-frequency magnetron sputtering at room temperature without any thermal treatment, yet showing an ideality factor as low as 1.14, showing the possibility of achieving high-performance Schottky diodes on flexible plastic substrate

Application of extraction of gallium molybdotungstate HPA for their investigation in solutions and gallium determination

International Nuclear Information System (INIS)

Kol'tsova, E.G.; Vakulich, A.N.; Tsyganok, L.P.

2001-01-01

Extraction of gallium molybdotungstate heteropolyacids and their associates with a row of triphenylmethane dyes, use of extraction for study of complexing in Mo 6 -W 6 -Ga 3+ -H 3 O + system are investigated. Research of optimal analytical states and development of extraction spectrophotometric methods of gallium determination are done. It is shown that increase of Mo 6 part in heteropolyanion improves solvation interaction of heteropolyacids with organic solvents elevating extraction properties of polyanion [ru

Temperature dependence of the electrical conductivity of vapor grown carbon nanofiber/epoxy composites with different filler dispersion levels

International Nuclear Information System (INIS)

Cardoso, P.; Silva, J.; Agostinho Moreira, J.; Klosterman, D.; Hattum, F.W.J. van; Simoes, R.; Lanceros-Mendez, S.

2012-01-01

The influence of the dispersion of vapor grown carbon nanofibers (VGCNF) on the electrical properties of VGCNF/epoxy composites has been studied. A homogeneous dispersion of the VGCNF does not imply better electrical properties. The presence of well distributed clusters appears to be a key factor for increasing composite conductivity. It is also shown that the main conduction mechanism has an ionic nature for concentrations below the percolation threshold, while above the percolation threshold it is dominated by hopping between the fillers. Finally, using the granular system theory it is possible to explain the origin of conduction at low temperatures. -- Highlights: ► The influence of dispersion of carbon nanofibers on epoxy is investigated. ► A homogeneous dispersion does not imply better electrical properties. ► The conduction mechanism has an ionic nature below the percolation threshold. ► Above the percolation threshold it is dominated by hopping between the fillers. ► The granular system theory allows explaining conduction at low temperatures.

Temperature dependence of the electrical conductivity of vapor grown carbon nanofiber/epoxy composites with different filler dispersion levels

Energy Technology Data Exchange (ETDEWEB)

Cardoso, P. [Center of Physics, University of Minho, Campus de Gualtar, 4710-057 Braga (Portugal); Silva, J. [Center of Physics, University of Minho, Campus de Gualtar, 4710-057 Braga (Portugal); Institute for Polymers and Composites IPC/I3N, University of Minho, Campus de Azurém, 4800-058 Guimares (Portugal); Agostinho Moreira, J. [IFIMUP and IN—Institute of Nanoscience and Nanotechnology, Department of Physics and Astronomy, Faculty of Science, University of Porto, Rua do Campo Alegre, 687, 4169-007 Porto (Portugal); Klosterman, D. [Chemical and Materials Engineering, University of Dayton, 300 College Park, Dayton, OH 45469-0246 (United States); Hattum, F.W.J. van [Institute for Polymers and Composites IPC/I3N, University of Minho, Campus de Azurém, 4800-058 Guimares (Portugal); Simoes, R. [Institute for Polymers and Composites IPC/I3N, University of Minho, Campus de Azurém, 4800-058 Guimares (Portugal); School of Technology, Polytechnic Institute of Cávado and Ave, Campus do IPCA, 4750-810 Barcelos (Portugal); Lanceros-Mendez, S., E-mail: lanceros@fisica.uminho.pt [Center of Physics, University of Minho, Campus de Gualtar, 4710-057 Braga (Portugal); INL—International Iberian Nanotechnology Laboratory, 4715-330 Braga (Portugal)

2012-10-01

The influence of the dispersion of vapor grown carbon nanofibers (VGCNF) on the electrical properties of VGCNF/epoxy composites has been studied. A homogeneous dispersion of the VGCNF does not imply better electrical properties. The presence of well distributed clusters appears to be a key factor for increasing composite conductivity. It is also shown that the main conduction mechanism has an ionic nature for concentrations below the percolation threshold, while above the percolation threshold it is dominated by hopping between the fillers. Finally, using the granular system theory it is possible to explain the origin of conduction at low temperatures. -- Highlights: ► The influence of dispersion of carbon nanofibers on epoxy is investigated. ► A homogeneous dispersion does not imply better electrical properties. ► The conduction mechanism has an ionic nature below the percolation threshold. ► Above the percolation threshold it is dominated by hopping between the fillers. ► The granular system theory allows explaining conduction at low temperatures.

Low Temperature CVD Grown Graphene for Highly Selective Gas Sensors Working under Ambient Conditions

NARCIS (Netherlands)

Ricciardella, F.; Vollebregt, S.; Polichetti, T.; Alfano, B.; Massera, E.; Sarro, P.M.

2017-01-01

In this paper we report on gas sensors based on graphene grown by Chemical Vapor Deposition at 850 °C. Mo was used as catalyst for graphene nucleation. Resistors were directly designed on pre-patterned Mo using the transfer-free process we recently developed, thus avoiding films damage during the

Gallium Safety in the Laboratory

International Nuclear Information System (INIS)

Cadwallader, L.C.

2003-01-01

A university laboratory experiment for the US Department of Energy magnetic fusion research program required a simulant for liquid lithium. The simulant choices were narrowed to liquid gallium and galinstan (Ga-In-Sn) alloy. Safety information on liquid gallium and galinstan were compiled, and the choice was made to use galinstan. A laboratory safety walkthrough was performed in the fall of 2002 to support the galinstan experiment. The experiment has been operating successfully since early 2002

Electrophoretic Deposition of Gallium with High Deposition Rate

Directory of Open Access Journals (Sweden)

Hanfei Zhang

2014-12-01

Full Text Available In this work, electrophoretic deposition (EPD is reported to form gallium thin film with high deposition rate and low cost while avoiding the highly toxic chemicals typically used in electroplating. A maximum deposition rate of ~0.6 μm/min, almost one order of magnitude higher than the typical value reported for electroplating, is obtained when employing a set of proper deposition parameters. The thickness of the film is shown to increase with deposition time when sequential deposition is employed. The concentration of Mg(NO32, the charging salt, is also found to be a critical factor to control the deposition rate. Various gallium micropatterns are obtained by masking the substrate during the process, demonstrating process compatibility with microfabrication. The reported novel approach can potentially be employed in a broad range of applications with Ga as a raw material, including microelectronics, photovoltaic cells, and flexible liquid metal microelectrodes.

Fabrication of Aluminum Gallium Nitride/Gallium Nitride MESFET And It's Applications in Biosensing

Science.gov (United States)

Alur, Siddharth

Gallium Nitride has been researched extensively for the past three decades for its application in Light Emitting Diodes (LED's), power devices and UV photodetectors. With the recent developments in crystal growth technology and the ability to control the doping there has been an increased interest in heterostructures formed between Gallium nitride and it's alloy Aluminium Gallium Nitride. These heterostructures due to the combined effect of spontaneous and piezoelectric effect can form a high density and a high mobility electron gas channel without any intentional doping. This high density electron gas makes these heterostructures ideal to be used as sensors. Gallium Nitride is also chemically very stable. Detection of biomolecules in a fast and reliable manner is very important in the areas of food safety and medical research. For biomolecular detection it is paramount to have a robust binding of the probes on the sensor surface. Therefore, in this dissertation, the fabrication and application of the AlGaN/GaN heterostructures as biological sensors for the detection of DNA and Organophosphate hydrolase enzyme is discussed. In order to use these AlGaN/GaN heterostructures as biological sensors capable of working in a liquid environment photodefinable polydimethyl-siloxane is used as an encapsulant. The immobilization conditions for a robust binding of thiolated DNA and the catalytic receptor enzyme organophosphate hydrolase on gold surfaces is developed with the help of X-ray photoelectron spectroscopy. DNA and OPH are detected by measuring the change in the drain current of the device as a function of time.

Microstructure and initial growth characteristics of the low temperature microcrystalline silicon films on silicon nitride surface

International Nuclear Information System (INIS)

Park, Young-Bae; Rhee, Shi-Woo

2001-01-01

Microstructure and initial growth characteristics of the hydrogenated microcrystalline Si (μc-Si:H) films grown on hydrogenated amorphous silicon nitride (a-SiN x :H) surface at low temperature were investigated using high resolution transmission electron microscope and micro-Raman spectroscopy. With increasing the Si and Si - H contents in the SiN x :H surfaces, μc-Si crystallites, a few nanometers in size, were directly grown on amorphous nitride surfaces. It is believed that the crystallites were grown through the nucleation and phase transition from amorphous to crystal in a hydrogen-rich ambient of gas phase and growing surface. The crystallite growth characteristics on the dielectric surface were dependent on the stoichiometric (x=N/Si) ratio corresponding hydrogen bond configuration of the SiN x :H surface. Surface facetting and anisotropic growth of the Si crystallites resulted from the different growth rate on the different lattice planes of Si. No twins and stacking faults were observed in the (111) lattice planes of the Si crystallites surrounding the a-Si matrix. This atomic-scale structure was considered to be the characteristic of the low temperature crystallization of the μc-Si:H by the strain relaxation of crystallites in the a-Si:H matrix. [copyright] 2001 American Institute of Physics

Bandgap modulation in photoexcited topological insulator Bi{sub 2}Te{sub 3} via atomic displacements

Energy Technology Data Exchange (ETDEWEB)

Hada, Masaki, E-mail: hadamasaki@okayama-u.ac.jp [Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530 (Japan); Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503 (Japan); PRESTO, Japan Science and Technology Agency, Kawaguchi 332-0012 (Japan); Norimatsu, Katsura; Tsuruta, Tetsuya; Igarashi, Kyushiro; Kayanuma, Yosuke; Sasagawa, Takao; Nakamura, Kazutaka G. [Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503 (Japan); Tanaka, Sei' ichi; Ishikawa, Tadahiko; Koshihara, Shin-ya [Department of Chemistry and Materials Science, Tokyo Institute of Technology, Tokyo 152-8551 (Japan); Keskin, Sercan [The Max Planck Institute for the Structure and Dynamics of Matter, The Hamburg Centre for Ultrafast Imaging, University of Hamburg, Hamburg 22761 (Germany); Miller, R. J. Dwayne [The Max Planck Institute for the Structure and Dynamics of Matter, The Hamburg Centre for Ultrafast Imaging, University of Hamburg, Hamburg 22761 (Germany); Departments of Chemistry and Physics, University of Toronto, Toronto M5S 3H6 (Canada); Onda, Ken [PRESTO, Japan Science and Technology Agency, Kawaguchi 332-0012 (Japan); Graduate School of Science and Engineering, Tokyo Institute of Technology, Yokohama 226-8502 (Japan)

2016-07-14

The atomic and electronic dynamics in the topological insulator (TI) Bi{sub 2}Te{sub 3} under strong photoexcitation were characterized with time-resolved electron diffraction and time-resolved mid-infrared spectroscopy. Three-dimensional TIs characterized as bulk insulators with an electronic conduction surface band have shown a variety of exotic responses in terms of electronic transport when observed under conditions of applied pressure, magnetic field, or circularly polarized light. However, the atomic motions and their correlation between electronic systems in TIs under strong photoexcitation have not been explored. The artificial and transient modification of the electronic structures in TIs via photoinduced atomic motions represents a novel mechanism for providing a comparable level of bandgap control. The results of time-domain crystallography indicate that photoexcitation induces two-step atomic motions: first bismuth and then tellurium center-symmetric displacements. These atomic motions in Bi{sub 2}Te{sub 3} trigger 10% bulk bandgap narrowing, which is consistent with the time-resolved mid-infrared spectroscopy results.

Gallium oxide nanorods as novel, safe and durable anode material for Li- and Na-ion batteries

International Nuclear Information System (INIS)

Meligrana, Giuseppina; Lueangchaichaweng, Warunee; Colò, Francesca; Destro, Matteo; Fiorilli, Sonia; Pescarmona, Paolo P.; Gerbaldi, Claudio

2017-01-01

Highlights: • Gallium oxide nanorods applied for the first time as anode material for Li-/Na-ion batteries. • Durable ambient temperature cycling (400 cycles) was observed in Li-based cells. • Stable reversible cycling (> 200 mAh g"−"1) was achieved for the first time in Na-based cells. - Abstract: Gallium oxide nanorods prepared by template-free synthesis are reported for the first time as safe and durable anode material for lithium- and sodium-ion batteries. The ambient temperature electrochemical response of the nanorods, tested by cyclic voltammetry and constant-current reversible cycling, is highly satisfying in terms of remarkable stability and capacity retention upon long-term operation (400 cycles), even at high current densities. The newly proposed application of gallium oxide nanorods as electrode material is notable also because this material can preserve the electrical pathway without the need of any “buffer matrix” to compensate for the expansion upon lithium or sodium reversible storage. The highly promising electrochemical performance is attributed to the high aspect ratio and high surface area that stem from the nanorod morphology and which can lead to short diffusion path and fast kinetics of both cations (Li"+ or Na"+) and electrons.

Trialkylphosphine-stabilized copper(I) gallium(III) phenylchalcogenolate complexes: crystal structures and generation of ternary semiconductors by thermolysis.

Science.gov (United States)

Kluge, Oliver; Krautscheid, Harald

2012-06-18

A series of organometallic trialkylphosphine-stabilized copper gallium phenylchalcogenolate complexes [(R(3)P)(m)Cu(n)Me(2-x)Ga(EPh)(n+x+1)] (R = Me, Et, (i)Pr, (t)Bu; E = S, Se, Te; x = 0, 1) has been prepared and structurally characterized by X-ray diffraction. From their molecular structures three groups of compounds can be distinguished: ionic compounds, ring systems, and cage structures. All these complexes contain one gallium atom bound to one or two methyl groups, whereas the number of copper atoms, and therefore the nuclearity of the complexes, is variable and depends mainly on size and amount of phosphine ligand used in synthesis. The Ga-E bonds are relatively rigid, in contrast to flexible Cu-E bonds. The lengths of the latter are controlled by the coordination number and steric influences. The Ga-E bond lengths depend systematically on the number of methyl groups bound to the gallium atom, with somewhat shorter bonds in monomethyl compounds compared to dimethyl compounds. Quantum chemical computations reproduce this trend and show furthermore that the rotation of one phenyl group around the Ga-E bond is a low energy process with two distinct minima, corresponding to two different conformations found experimentally. Mixtures of different types of chalcogen atoms on molecular scale are possible, and then ligand exchange reactions in solution lead to mixed site occupation. In thermogravimetric studies the complexes were converted into the ternary semiconductors CuGaE(2). The thermolysis reaction is completed at temperatures between 250 and 400 °C, typically with lower temperatures for the heavier chalcogens. Because of significant release of Me(3)Ga during the thermolysis process, and especially in case of copper excess in the precursor complexes, binary copper chalcogenides are obtained as additional thermolysis products. Quaternary semiconductors can be obtained from mixed chalcogen precursors.

System for illuminating a region for isotopically selective photoexcitation

International Nuclear Information System (INIS)

Debaryshe, P.G.; Janes, G.S.; Levy, R.H.; Lindenmeier, C.W.

1979-01-01

A method is described to improve laser beam utilization in isotope separation techniques (using laser induced isotopically selective photoexcitation) by increasing the probability of photon absorption without extreme beam propagation lengths. For this purpose an optical reflection system has been designed for illuminating substantially all of three-dimensional space of a transversely flowing vapor with multiple traversals of a beam of radiation. (UK)

Stimulated emission of photoexcited polarized electrons from GaAs

International Nuclear Information System (INIS)

Derbenev, Ya.S.; Melikyan, R.A.

1986-01-01

The influence of electric field on the emission of photoexcited polarized electrons is investigated. The thermalization of excited electrons is shown to be prevented at the field intensity in semiconductor of about 3 kV/cm. As a consequence the quantum yield grows up to unity. With the increase of the output energy of electrons the effective operation time of photocathode also increases

Czochralski growth of gallium indium antimonide alloy crystals

Energy Technology Data Exchange (ETDEWEB)

Tsaur, S.C.

1998-02-01

Attempts were made to grow alloy crystals of Ga{sub 1{minus}x}In{sub x}Sb by the conventional Czochralski process. A transparent furnace was used, with hydrogen purging through the chamber during crystal growth. Single crystal seeds up to about 2 to 5 mole% InSb were grown from seeds of 1 to 2 mole% InSb, which were grown from essentially pure GaSb seeds of the [111] direction. Single crystals were grown with InSb rising from about 2 to 6 mole% at the seed ends to about 14 to 23 mole% InSb at the finish ends. A floating-crucible technique that had been effective in reducing segregation in doped crystals, was used to reduce segregation in Czochralski growth of alloy crystals of Ga{sub 1{minus}x}In{sub x}Sb. Crystals close to the targeted composition of 1 mole% InSb were grown. However, difficulties were encountered in reaching higher targeted InSb concentrations. Crystals about 2 mole% were grown when 4 mole% was targeted. It was observed that mixing occurred between the melts rendering the compositions of the melts; and, hence, the resultant crystal unpredictable. The higher density of the growth melt than that of the replenishing melt could have triggered thermosolutal convection to cause such mixing. It was also observed that the floating crucible stuck to the outer crucible when the liquidus temperature of the replenishing melt was significantly higher than that of the growth melt. The homogeneous Ga{sub 1{minus}x}In{sub x}Sb single crystals were grown successfully by a pressure-differential technique. By separating a quartz tube into an upper chamber for crystal growth and a lower chamber for replenishing. The melts were connected by a capillary tube to suppress mixing between them. A constant pressure differential was maintained between the chambers to keep the growth melt up in the growth chamber. The method was first tested with a low temperature alloy Bi{sub 1{minus}x}Sb{sub x}. Single crystals of Ga{sub 1{minus}x}In{sub x}Sb were grown with uniform

Element-specific and site-specific ion desorption from adsorbed molecules by deep core-level photoexcitation at the K-edges

CERN Document Server

Baba, Y H

2003-01-01

This article reviews our recent works on the ion desorption from adsorbed and condensed molecules at low temperature following the core-level photoexcitations using synchrotron soft x-rays. The systems investigated here are adsorbed molecules with relatively heavy molecular weight containing third-row elements such as Si, P, S, and Cl. Compared with molecules composed of second-row elements, the highly element-specific and site-specific fragment-ion desorption were observed when we tune the photon energy at the dipole-allowed 1s -> sigma sup * (3p sup *) resonance. On the basis of the resonance Auger decay spectra around the 1s ionization thresholds, the observed highly specific ion desorption is interpreted by the localization of the excited electrons (here we call as 'spectator electrons') in the antibonding sigma sup * orbital. In order to separate the direct photo-induced process from the indirect processes triggered by the secondary electrons, the photon-stimulated ion desorption was also investigated in...

Inflammatory pseudotumor: A gallium-avid mobile mesenteric mass

International Nuclear Information System (INIS)

Auringer, S.T.; Scott, M.D.; Sumner, T.E.

1991-01-01

An 8-yr-old boy with a 1-mo history of culture-negative fever and anemia underwent gallium, ultrasound, and computed tomography studies as part of the evaluation of a fever of unknown origin. These studies revealed a mobile gallium-avid solid abdominal mass subsequently proven to be an inflammatory pseudotumor of the mesentery, a rare benign mass. This report documents the gallium-avid nature of this rare lesion and discusses associated characteristic clinical, pathologic, and radiographic features

Implantation activation annealing of Si-implanted gallium nitride at temperatures > 1,100 C

International Nuclear Information System (INIS)

Zolper, J.C.; Han, J.; Biefeld, R.M.

1997-01-01

The activation annealing of Si-implanted GaN is reported for temperatures from 1,100 to 1,400 C. Although previous work has shown that Si-implanted GaN can be activated by a rapid thermal annealing at ∼1,100 C, it was also shown that significant damage remained in the crystal. Therefore, both AlN-encapsulated and uncapped Si-implanted GaN samples were annealed in a metal organic chemical vapor deposition system in a N 2 /NH 3 ambient to further assess the annealing process. Electrical Hall characterization shows increases in carrier density and mobility for annealing up to 1,300 C before degrading at 1,400 C due to decomposition of the GaN epilayer. Rutherford backscattering spectra show that the high annealing temperatures reduce the implantation induced damage profile but do not completely restore the as-grown crystallinity

Low temperature synthesis of coiled carbon nanotubes and their magnetic properties

Science.gov (United States)

Krishna, Vemula Mohana; Somanathan, T.; Manikandan, E.

2018-04-01

In this paper, coiled like structure of carbon nanotubes (c-CNTs) have been effectively grown on bi-metal substituted α-alumina nanoparticles catalyst by chemical vapor deposition (CVD) system. Highly graphitized and dense bundles of carbon product were attained at a low temperature of 550 °C. The coiled carbon nanostructures in very longer lengths were noticed by field emission scanning electron microscope (FESEM) observation. Furthermore, high purity material was achieved, which correlates the energy dispersive x-ray spectroscopy (EDX) analysis. High resolution transmission electron microscope (HRTEM) revealed the diameter and graphitization of coiled structures. The superparamagnetic like behavior was observed at room temperature for the as-synthesized product, which was found by VSM investigation.

Determination of gallium in flint clay by neutron activation analysis

International Nuclear Information System (INIS)

Padova, A.; Even, O.

1975-01-01

Neutron activation analysis was applied to determine gallium traces in different flint clay samples found in Israel. The principal 835 KeV gamma ray of gallium-72 was measured with a 60 cm 2 Ge(Li) spectrometer in conjunction with a Packard 4000 channel analyzer and Wang table computer, model 720 C. Samples were weighed into polyethylene vials, sealed and inserted into polyethylene rabbit. Gallium metal and gallium oxide used as standards were similarly prepared for irradiation for 10 minutes in the I.R.R.I., at a thermal flux of 3.5x10 12 n/cm 2 sec. Careful calibration of the spectrometer and judicious choice of cooling time eliminate the influence of such elements as europium-152, and sodium-24 and make possible the determination of gallium without prior chemical separation. Representative Israel flint clay samples contain about 55 ppm gallium. (B.G.)

Low-temperature annealing of radiation defects in electron-irradiated gallium phosphide

International Nuclear Information System (INIS)

Kolb, A.A.; Megela, I.G.; Buturlakin, A.P.; Goyer, D.B.

1990-01-01

The isochronal annealing of radiation defects in high-energy electron irradiated n-GaP monocrystals within the 77 to 300 K range has been investigated by optical and electrical techniques. The changes in conductance and charge carrier mobility as functions of annealing temperature as well as the variation of optical absorption spectra of GaP under irradiation and annealing provide evidence that most of radiation defects are likely secondary complexes of defects

Optical characteristics of a gallium laser plasma

International Nuclear Information System (INIS)

Shuaibov, A.K.; Shimon, L.L.; Dashchenko, A.I.; Shevera, I.V.; Chuchman, M.P.

2001-01-01

Results are presented from studies of the emission from an erosion gallium laser plasma at a moderate intensity (W = (1-5) x 10 8 W/cm 2 ) of a 1.06-μm laser radiation. It is shown that, under these conditions, the lower excited states of gallium atoms are populated most efficiently. Among the ions, only the most intense GaII lines are observed in the emission spectrum. The populations of GaI and GaII excited states are not related to direct electron excitation, but are determined by the recombination of gallium ions with slow electrons. The recombination times of GaIII and GaII ions in the core of the plasma jet are determined from the waveforms of emission in the GaII and GaI spectral lines and are equal to 10 and 140 ns, respectively. The results obtained are of interest for spectroscopic diagnostics of an erosion plasma produced from gallium-containing layered crystals during the laser deposition of thin films

Low-Temperature Processed Ga-Doped ZnO Coatings from Colloidal Inks

KAUST Repository

Della Gaspera, Enrico; Bersani, Marco; Cittadini, Michela; Guglielmi, Massimo; Pagani, Diego; Noriega, Rodrigo; Mehra, Saahil; Salleo, Alberto; Martucci, Alessandro

2013-01-01

We present a new colloidal synthesis of gallium-doped zinc oxide nanocrystals that are transparent in the visible and absorb in the near-infrared. Thermal decomposition of zinc stearate and gallium nitrate after hot injection of the precursors in a

Advanced processing of gallium nitride and gallium nitride-based devices: Ultra-high temperature annealing and implantation incorporation

Science.gov (United States)

Yu, Haijiang

This dissertation is focused on three fields: ultra-high temperature annealing of GaN, activation of implanted GaN and the implantation incorporation into AlGaN/GaN HEMT processing, with an aim to increase the performance, manufacturability and reliability of AlGaN/GaN HEMTs. First, the ultra high temperature (around 1500°C) annealing of MOCVD grown GaN on sapphire has been studied, and a thermally induced threading dislocation (TD) motion and reaction are reported. Using a rapid thermal annealing (RTA) approach capable of heating 2 inch wafers to around 1500°C with 100 bar N2 over-pressure, evidence of dislocation motion was first observed in transmission electron microscopy (TEM) micrographs of both planar and patterned GaN films protected by an AIN capping layer. An associated decrease in x-ray rocking curve (XRC) full-width-half-maximum (FWHM) was also observed for both the symmetric and asymmetric scans. After annealing, the AIN capping layer remained intact, and optical measurements showed no degradation of the opto-electronic properties of the films. Then activation annealing of Si implants in MOCVD grown GaN has been studied for use in ohmic contacts. Si was implanted in semi-insulating GaN at 100 keV with doses from 5 x 1014 cm-2 to 1.5 x 1016 cm-2. Rapid thermal annealing at 1500°C with 100 bar N2 over-pressure was used for dopant activation, resulting in a minimum sheet resistance of 13.9 O/square for a dose of 7 x 1015 cm-2. Secondary ion mass spectroscopy measurements showed a post-activation broadening of the dopant concentration peak by 20 nm (at half the maximum), while X-Ray triple axis o-2theta scans indicated nearly complete implant damage recovery. Transfer length method measurements of the resistance of Ti/Al/Ni/Au contacts to activated GaN:Si (5 x 1015 cm-2 at 100 keV) indicated lowest contact resistances of 0.07 Omm and 0.02 Omm for as-deposited and subsequently annealed contacts, respectively. Finally, the incorporation of Si implantation

Computer-assisted sequential quantitative analysis of gallium scans in pulmonary sarcoidosis

International Nuclear Information System (INIS)

Rohatgi, P.K.; Bates, H.R.; Noss, R.W.

1985-01-01

Fifty-one sequential gallium citrate scans were performed in 22 patients with biopsy-proven sarcoidosis. A computer-assisted quantitative analysis of these scans was performed to obtain a gallium score. The changes in gallium score were correlated with changes in serum angiotensin converting enzyme (SACE) activity and objective changes in clinical status. There was a good concordance between changes in gallium score, SACE activity and clinical assessment in patients with sarcoidosis, and changes in gallium index were slightly superior to SACE index in assessing activity of sarcoidosis. (author)

Uptake of gallium-67 citrate in clean surgical incisions after colorectal surgery

International Nuclear Information System (INIS)

Lin Wanyu; Wang Shyhjen; Tsai Shihchuan; Chao Tehsin

2001-01-01

Non-specific accumulation of gallium-67 citrate (gallium) in uncomplicated surgical incisions is not uncommon. It is important to know the normal pattern of gallium uptake at surgical incision sites in order to properly interpret the gallium scan when investigating possible wound infection in patients who have undergone abdominal surgery. We studied 42 patients without wound infection after colorectal surgery and performed gallium scans within 40 days after surgery. Patients were divided into three groups according to the interval between the operation and the scan. In group A (26 patients) gallium scan was performed within 7 days after surgery, in group B (8 patients) between 8 and 14 days after surgery, and in group C (8 patients) between 15 and 40 days after surgery. Our data showed that in group A, 61.5% had gallium accumulation at the surgical incision site. In group B, 50% had accumulation of gallium at the surgical incision site, while in group C only one patient (12.5%) showed gallium uptake. It is concluded that the incidence of increased gallium uptake at clean surgical incision sites is high after colorectal surgery. Nuclear medicine physicians should bear in mind the high incidence of non-specific gallium uptake at such sites during the interpretation of possible wound infection in patients after colorectal surgery. (orig.)

Self-assembled InAs quantum dots formed by molecular beam epitaxy at low temperature and postgrowth annealing

NARCIS (Netherlands)

Zhan, H.H.; Nötzel, R.; Hamhuis, G.J.; Eijkemans, T.J.; Wolter, J.H.

2003-01-01

Self-assembled InAs quantum dots are grown at low temperature (LT) by molecular beam epitaxy (MBE) on GaAs substrates. The growth is in situ monitored by reflection high-energy electron diffraction, and ex situ evaluated by atomic force microscopy for the morphological properties, and by

Effective photoexcitation cross section of 115In(γ,γ′115mIn from photoactivation data

Directory of Open Access Journals (Sweden)

Versteegen M.

2016-01-01

Full Text Available Photoexcitation yields of the 115mIn metastable state were measured with Bremsstrahlung γ beams over a range of endpoint energies between 4.5 and 18 MeV. An effective cross section of the 115In(γ,γ′115mIn photoexcitation cross section was determinedto reproduce the data. This cross section is built from a cross section calculated with the TALYS code, to which an enhancement is added at about 8.5 MeV.

Gallium-67 uptake by the thyroid associated with progressive systemic sclerosis

International Nuclear Information System (INIS)

Sjoberg, R.J.; Blue, P.W.; Kidd, G.S.

1989-01-01

Although thyroidal uptake of gallium-67 has been described in several thyroid disorders, gallium-67 scanning is not commonly used in the evaluation of thyroid disease. Thyroidal gallium-67 uptake has been reported to occur frequently with subacute thyroiditis, anaplastic thyroid carcinoma, and thyroid lymphoma, and occasionally with Hashimoto's thyroiditis and follicular thyroid carcinoma. A patient is described with progressive systemic sclerosis who, while being scanned for possible active pulmonary involvement, was found incidentally to have abnormal gallium-67 uptake only in the thyroid gland. Fine needle aspiration cytology of the thyroid revealed Hashimoto's thyroiditis. Although Hashimoto's thyroiditis occurs with increased frequency in patients with progressive systemic sclerosis, thyroidal uptake of gallium-67 associated with progressive systemic sclerosis has not, to our knowledge, been previously described. Since aggressive thyroid malignancies frequently are imaged by gallium-67 scintigraphy, fine needle aspiration cytology of the thyroid often is essential in the evaluation of thyroidal gallium-67 uptake

Gallium-67 uptake by the thyroid associated with progressive systemic sclerosis

Energy Technology Data Exchange (ETDEWEB)

Sjoberg, R.J.; Blue, P.W.; Kidd, G.S.

1989-01-01

Although thyroidal uptake of gallium-67 has been described in several thyroid disorders, gallium-67 scanning is not commonly used in the evaluation of thyroid disease. Thyroidal gallium-67 uptake has been reported to occur frequently with subacute thyroiditis, anaplastic thyroid carcinoma, and thyroid lymphoma, and occasionally with Hashimoto's thyroiditis and follicular thyroid carcinoma. A patient is described with progressive systemic sclerosis who, while being scanned for possible active pulmonary involvement, was found incidentally to have abnormal gallium-67 uptake only in the thyroid gland. Fine needle aspiration cytology of the thyroid revealed Hashimoto's thyroiditis. Although Hashimoto's thyroiditis occurs with increased frequency in patients with progressive systemic sclerosis, thyroidal uptake of gallium-67 associated with progressive systemic sclerosis has not, to our knowledge, been previously described. Since aggressive thyroid malignancies frequently are imaged by gallium-67 scintigraphy, fine needle aspiration cytology of the thyroid often is essential in the evaluation of thyroidal gallium-67 uptake.

On the pathway of photoexcited electrons: probing photon-to-electron and photon-to-phonon conversions in silicon by ATR-IR

DEFF Research Database (Denmark)

Karabudak, Engin; Yüce, Emre; Schlautmann, Stefan

2012-01-01

Photoexcitation and charge carrier thermalization inside semiconductor photocatalysts are two important steps in solar fuel production. Here, photoexcitation and charge carrier thermalization in a silicon wafer are for the first time probed by a novel, yet simple and user-friendly Attenuated Tota...

Novel low-temperature growth of SnO2 nanowires and their gas-sensing properties

International Nuclear Information System (INIS)

Kumar, R. Rakesh; Parmar, Mitesh; Narasimha Rao, K.; Rajanna, K.; Phani, A.R.

2013-01-01

Graphical abstract: -- A simple thermal evaporation method is presented for the growth of crystalline SnO 2 nanowires at a low substrate temperature of 450 °C via an gold-assisted vapor–liquid–solid mechanism. The as-grown nanowires were characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffraction, and were also tested for methanol vapor sensing. Transmission electron microscopy studies revealed the single-crystalline nature of the each nanowire. The fabricated sensor shows good response to methanol vapor at an operating temperature of 450 °C.

Analysis of Low Temperature Organic Rankine Cycles for Solar Applications

Science.gov (United States)

Li, Yunfei

The present work focuses on Organic Rankine Cycle (ORC) systems and their application to low temperature waste heat recovery, combined heat and power as well as off-grid solar power generation applications. As CO_2 issues come to the fore front and fossil fuels become more expensive, interest in low grade heat recovery has grown dramatically in the past few years. Solar energy, as a clean, renewable, pollution-free and sustainable energy has great potential for the use of ORC systems. Several ORC solutions have been proposed to generate electricity from low temperature sources. The ORC systems discussed here can be applied to fields such as solar thermal, biological waste heat, engine exhaust gases, small-scale cogeneration, domestic boilers, etc. The current work presents a thermodynamic and economic analysis for the use of ORC systems to convert solar energy or low exergy energy to generate electrical power. The organic working fluids investigated here were selected to investigate the effect of the fluid saturation temperature on the performance of ORCs. The working fluids under investigation are R113, R245fa, R123, with boiling points between 40°C and 200°C at pressures from 10 kPa to 10 MPa. Ambient temperature air at 20oC to 30oC is utilized as cooling resource, and allowing for a temperature difference 10°C for effective heat transfer. Consequently, the working fluids are condensed at 40°C. A combined first- and second-law analysis is performed by varying some system independent parameters at various reference temperatures. The present work shows that ORC systems can be viable and economical for the applications such as waste heat use and off-grid power generation even though they are likely to be more expensive than grid power.

Electrical and thermal conductivity of low temperature CVD graphene: the effect of disorder

International Nuclear Information System (INIS)

Vlassiouk, Ivan; Datskos, Panos; Smirnov, Sergei; Ivanov, Ilia; Hensley, Dale; Lavrik, Nickolay V; Fulvio, Pasquale F; Dai Sheng; Meyer, Harry; Chi Miaofang

2011-01-01

In this paper we present a study of graphene produced by chemical vapor deposition (CVD) under different conditions with the main emphasis on correlating the thermal and electrical properties with the degree of disorder. Graphene grown by CVD on Cu and Ni catalysts demonstrates the increasing extent of disorder at low deposition temperatures as revealed by the Raman peak ratio, I G /I D . We relate this ratio to the characteristic domain size, L a , and investigate the electrical and thermal conductivity of graphene as a function of L a . The electrical resistivity, ρ, measured on graphene samples transferred onto SiO 2 /Si substrates shows linear correlation with L a -1 . The thermal conductivity, K, measured on the same graphene samples suspended on silicon pillars, on the other hand, appears to have a much weaker dependence on L a , close to K ∼ L a 1/3 . It results in an apparent ρ ∼ K 3 correlation between them. Despite the progressively increasing structural disorder in graphene grown at lower temperatures, it shows remarkably high thermal conductivity (10 2 -10 3 W K -1 m -1 ) and low electrical (10 3 -3 x 10 5 Ω) resistivities suitable for various applications.

Low-threshold stimulated emission at 249 nm and 256 nm from AlGaN-based multiple-quantum-well lasers grown on sapphire substrates

Energy Technology Data Exchange (ETDEWEB)

Li, Xiao-Hang; Detchprohm, Theeradetch; Kao, Tsung-Ting; Satter, Md. Mahbub; Shen, Shyh-Chiang; Douglas Yoder, P.; Dupuis, Russell D., E-mail: dupuis@gatech.edu [Center for Compound Semiconductors and School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0250 (United States); Wang, Shuo; Wei, Yong O.; Xie, Hongen; Fischer, Alec M.; Ponce, Fernando A. [Department of Physics, Arizona State University, Tempe, Arizona 85287-1504 (United States); Wernicke, Tim; Reich, Christoph; Martens, Martin; Kneissl, Michael [Technical University of Berlin, Institute for Solid State Physics, Berlin D-10623 (Germany)

2014-10-06

Optically pumped deep-ultraviolet (DUV) lasing with low threshold was demonstrated from AlGaN-based multiple-quantum-well (MQW) heterostructures grown on sapphire substrates. The epitaxial layers were grown pseudomorphically by metalorganic chemical vapor deposition on (0001) sapphire substrates. Stimulated emission was observed at wavelengths of 256 nm and 249 nm with thresholds of 61 kW/cm{sup 2} and 95 kW/cm{sup 2} at room temperature, respectively. The thresholds are comparable to the reported state-of-the-art AlGaN-based MQW DUV lasers grown on bulk AlN substrates emitting at 266 nm. These low thresholds are attributed to the optimization of active region and waveguide layer as well as the use of high-quality AlN/sapphire templates. The stimulated emission above threshold was dominated by transverse-electric polarization. This work demonstrates the potential candidacy of sapphire substrates for DUV diode lasers.

Low-threshold stimulated emission at 249 nm and 256 nm from AlGaN-based multiple-quantum-well lasers grown on sapphire substrates

International Nuclear Information System (INIS)

Li, Xiao-Hang; Detchprohm, Theeradetch; Kao, Tsung-Ting; Satter, Md. Mahbub; Shen, Shyh-Chiang; Douglas Yoder, P.; Dupuis, Russell D.; Wang, Shuo; Wei, Yong O.; Xie, Hongen; Fischer, Alec M.; Ponce, Fernando A.; Wernicke, Tim; Reich, Christoph; Martens, Martin; Kneissl, Michael

2014-01-01

Optically pumped deep-ultraviolet (DUV) lasing with low threshold was demonstrated from AlGaN-based multiple-quantum-well (MQW) heterostructures grown on sapphire substrates. The epitaxial layers were grown pseudomorphically by metalorganic chemical vapor deposition on (0001) sapphire substrates. Stimulated emission was observed at wavelengths of 256 nm and 249 nm with thresholds of 61 kW/cm 2 and 95 kW/cm 2 at room temperature, respectively. The thresholds are comparable to the reported state-of-the-art AlGaN-based MQW DUV lasers grown on bulk AlN substrates emitting at 266 nm. These low thresholds are attributed to the optimization of active region and waveguide layer as well as the use of high-quality AlN/sapphire templates. The stimulated emission above threshold was dominated by transverse-electric polarization. This work demonstrates the potential candidacy of sapphire substrates for DUV diode lasers.

Low resistive edge contacts to CVD-grown graphene using a CMOS compatible metal

Energy Technology Data Exchange (ETDEWEB)

Shaygan, Mehrdad; Otto, Martin; Sagade, Abhay A.; Neumaier, Daniel [Advanced Microelectronic Center Aachen, AMO GmbH, Aachen (Germany); Chavarin, Carlos A. [Lehrstuhl Werkstoffe der Elektrotechnik, Duisburg-Essen Univ., Duisburg (Germany); Innovations for High Performance Microelectronics, IHP GmbH, Frankfurt (Oder) (Germany); Bacher, Gerd; Mertin, Wolfgang [Lehrstuhl Werkstoffe der Elektrotechnik, Duisburg-Essen Univ., Duisburg (Germany)

2017-11-15

The exploitation of the excellent intrinsic electronic properties of graphene for device applications is hampered by a large contact resistance between the metal and graphene. The formation of edge contacts rather than top contacts is one of the most promising solutions for realizing low ohmic contacts. In this paper the fabrication and characterization of edge contacts to large area CVD-grown monolayer graphene by means of optical lithography using CMOS compatible metals, i.e. Nickel and Aluminum is reported. Extraction of the contact resistance by Transfer Line Method (TLM) as well as the direct measurement using Kelvin Probe Force Microscopy demonstrates a very low width specific contact resistance down to 130 Ωμm. The contact resistance is found to be stable for annealing temperatures up to 150 C enabling further device processing. Using this contact scheme for edge contacts, a field effect transistor based on CVD graphene with a high transconductance of 0.63 mS/μm at 1 V bias voltage is fabricated. (copyright 2017 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Low temperature {sup 57}Fe Moessbauer study of cucumber root

Energy Technology Data Exchange (ETDEWEB)

Kovacs, K; Kuzmann, E; Homonnay, Z; Vertes, A [Institute of Chemistry, Eoetvoes Lorand University, PO Box 32, 1512 Budapest (Hungary); Fodor, F [Department of Plant Physiology and Molecular Plant Biology, Eoetvoes Lorand University, PO Box 32, 1512 Budapest (Hungary); Machala, L, E-mail: kkriszti@chem.elte.h [Centre for Nanomaterial Research, Palacky University, Svobody 26, Olomouc 771 46 (Czech Republic)

2010-03-01

Iron uptake and distribution in cucumber root were studied with the help of {sup 57}Fe Moessbauer spectroscopy at low temperature applying external magnetic field. Cucumber was grown in iron sufficient modified Hoagland nutrient solution. Moessbauer spectra of the frozen roots taken at 4.2 and 1.5 K, at 5 T external magnetic field support the identification of the main iron species (Fe{sup III}-carboxylates, hydrous ferric oxides, Fe{sup III}-sulfate-hydroxide) suggested according to its Moessbauer spectra taken between 35-200 K [1]. The magnetic ordering temperature of the hydrous ferric oxide and Fe{sup III}-sulfate-hydroxide was found to be in the range of 4.2-1.5 K, which suggests the incorporation of H{sub 3}O{sup +}, PO{sub 4}{sup 3-} and citrate into these minerals.

Nuclear microprobe imaging of gallium nitrate in cancer cells

Science.gov (United States)

Ortega, Richard; Suda, Asami; Devès, Guillaume

2003-09-01

Gallium nitrate is used in clinical oncology as treatment for hypercalcemia and for cancer that has spread to the bone. Its mechanism of antitumor action has not been fully elucidated yet. The knowledge of the intracellular distribution of anticancer drugs is of particular interest in oncology to better understand their cellular pharmacology. In addition, most metal-based anticancer compounds interact with endogenous trace elements in cells, altering their metabolism. The purpose of this experiment was to examine, by use of nuclear microprobe analysis, the cellular distribution of gallium and endogenous trace elements within cancer cells exposed to gallium nitrate. In a majority of cellular analyses, gallium was found homogeneously distributed in cells following the distribution of carbon. In a smaller number of cells, however, gallium appeared concentrated together with P, Ca and Fe within round structures of about 2-5 μm diameter located in the perinuclear region. These intracellular structures are typical of lysosomial material.

Nuclear microprobe imaging of gallium nitrate in cancer cells

International Nuclear Information System (INIS)

Ortega, Richard; Suda, Asami; Deves, Guillaume

2003-01-01

Gallium nitrate is used in clinical oncology as treatment for hypercalcemia and for cancer that has spread to the bone. Its mechanism of antitumor action has not been fully elucidated yet. The knowledge of the intracellular distribution of anticancer drugs is of particular interest in oncology to better understand their cellular pharmacology. In addition, most metal-based anticancer compounds interact with endogenous trace elements in cells, altering their metabolism. The purpose of this experiment was to examine, by use of nuclear microprobe analysis, the cellular distribution of gallium and endogenous trace elements within cancer cells exposed to gallium nitrate. In a majority of cellular analyses, gallium was found homogeneously distributed in cells following the distribution of carbon. In a smaller number of cells, however, gallium appeared concentrated together with P, Ca and Fe within round structures of about 2-5 μm diameter located in the perinuclear region. These intracellular structures are typical of lysosomial material

The role of gallium-67 scanning in febrile patients

International Nuclear Information System (INIS)

Mouratidis, B.; Lomas, F.

1994-01-01

The source of sepsis in febrile patients can be a difficult diagnostic problem. Gallium-67 has been utilized as a diagnostic tool in the evaluation of these patients. A retrospective review was done of 47 patients who presented with pyrexia of unknown origin (27 patients), postoperative fever (11 patients), septicaemia (4 patients) and miscellaneous sepsis (5 patients). Whole body imaging with Gallium-67 gave an overall sensitivity and specificity of 86 and 77%, respectively, which compares favourably with previous studies. The sensitivity and specificity was similar in all patient subgroups. Gallium-67 allowed for more effective and directed use of organ-specific imaging modalities, such as computed tomography, ultrasound and guided intervention, in localizing and defining the source of sepsis. Where more than one possible source of fever was present, Gallium-67 scanning correctly identified the activity of the different foci. Gallium-67 scanning should be used early in the evaluation of patients presenting with fever of uncertain origin. 9 refs., 5 tabs., 2 figs

Rutile TiO2 thin films grown by reactive high power impulse magnetron sputtering

International Nuclear Information System (INIS)

Agnarsson, B.; Magnus, F.; Tryggvason, T.K.; Ingason, A.S.; Leosson, K.; Olafsson, S.; Gudmundsson, J.T.

2013-01-01

Thin TiO 2 films were grown on Si(001) substrates by reactive dc magnetron sputtering (dcMS) and high power impulse magnetron sputtering (HiPIMS) at temperatures ranging from 300 to 700 °C. Optical and structural properties of films were compared both before and after post-annealing using scanning electron microscopy, low angle X-ray reflection (XRR), grazing incidence X-ray diffractometry and spectroscopic ellipsometry. Both dcMS- and HiPIMS-grown films reveal polycrystalline rutile TiO 2 , even prior to post-annealing. The HiPIMS-grown films exhibit significantly larger grains compared to that of dcMC-grown films, approaching 100% of the film thickness for films grown at 700 °C. In addition, the XRR surface roughness of HiPIMS-grown films was significantly lower than that of dcMS-grown films over the whole temperature range 300–700 °C. Dispersion curves could only be obtained for the HiPIMS-grown films, which were shown to have a refractive index in the range of 2.7–2.85 at 500 nm. The results show that thin, rutile TiO 2 films, with high refractive index, can be obtained by HiPIMS at relatively low growth temperatures, without post-annealing. Furthermore, these films are smoother and show better optical characteristics than their dcMS-grown counterparts. - Highlights: • We demonstrate growth of rutile TiO 2 on Si (111) by high power impulse magnetron sputtering. • The films exhibit significantly larger grains than dc magnetron sputtered films • TiO 2 films with high refractive index are obtained without post-growth annealing

Survey of the market, supply and availability of gallium

Energy Technology Data Exchange (ETDEWEB)

Rosi, F.D.

1980-07-01

The objective of this study was to assess the present consumption and supply of gallium, its potential availability in the satellite power system (SPS) implementation time frame, and commercial and new processing methods for increasing the production of gallium. Findings are reported in detail. The findings strongly suggest that with proper long range planning adequate gallium would be available from free-enterprise world supplies of bauxite for SPS implementation.

Catalytic behavior of gallium-containing mesoporous silicas

Directory of Open Access Journals (Sweden)

K. Bachari

2017-02-01

Full Text Available The vapor phase tert-butylation of anisole with tert-butanol reaction has been inspected over a series of Ga-FSM-16 with different Si/Ga ratios = 75, 35, 5 synthesized by intercalating kanemite using cetyltrimethylammonium bromide (CTMABr and gallium nitrate. The resulting samples were characterized by means of inductively coupled plasma (ICP technique, BET, BJH, XRD and a temperature–programed–desorption (TPD of pyridine. In addition, the influence of molar ratio, influence of temperature, weight hourly space velocity (WHSV and time on stream on the selectivity of products was investigated and the results are discussed.

[Oil degradation by basidiomycetes in soil and peat at low temperatures].

Science.gov (United States)

Kulikova, N A; Klein, O I; Pivchenko, D V; Landesman, E O; Pozdnyakova, N N; Turkovskaya, O V; Zaichik, B Ts; Ruzhitskii, A O; Koroleva, O V

2016-01-01

A total of 17 basidiomycete strains causing white rot and growing on oil-contaminated substrates have been screened. Three strains with high (Steccherinum murashkinskyi), average (Trametes maxima), and low (Pleurotus ostreatus) capacities for the colonization of oil-contaminated substrates have been selected. The potential for degrading crude oil hydrocarbons has been assessed with the use of fungi grown on nonsterile soil and peat at low temperatures. Candida sp. and Rhodococcus sp. commercial strains have been used as reference organisms with oil-degrading ability. All microorganisms introduced in oil-contaminated soil have proved to be ineffective, whereas the inoculation of peat with basidiomycetes and oil-degrading microorganisms accelerated the destruction of oil hydrocarbons. The greatest degradation potential of oil-aliphatic hydrocarbons has been found in S. murashlinskyi. T. maxima turned out to be the most successful in degrading aromatic hydrocarbons. It has been suggested that aboriginal microflora contributes importantly to the effectiveness of oil-destructing microorganisms. T. maxima and S. murashkinskyi strains are promising for further study as oil-oxidizing agents during bioremediation of oil-contaminated peat soil under conditions of low temperatures.

67Gallium • the D,etection and Localization

African Journals Online (AJOL)

1971-12-11

Dec 11, 1971 ... gallium and its compounds was first aroused when it was noted that this element is contained .... MATERIALS AND METHODS. ;;'Gallium citrate was .... another in a patient with a pathological fracture of the right humerus that ...

Photoluminescence characteristics of low indium composition InGaN thin films grown on sapphire by metalorganic chemical vapor deposition

International Nuclear Information System (INIS)

Feng, Z.C.; Liu, W.; Chua, S.J.; Yu, J.W.; Yang, C.C.; Yang, T.R.; Zhao, J.

2006-01-01

The wavelength shifts in the photoluminescence (PL) from low indium composition (∼ 3%) InGaN epitaxial thin films, grown on sapphire substrates by metalorganic chemical vapour deposition, has been studied by a combination of experiment and theory. As temperature increases from 6 K, the PL peak energy red-shifts very slightly first, then blue-shifts to reach a maximum at near 100 K, and red-shifts again till room temperature. This unique PL behaviour, indicating the existence of the phase separation, is interpreted qualitatively from the spatial variation of band structure due to the In-compositional fluctuation. Theoretical calculation, based upon a model involving the band-tail states in the radiative recombination, explains the experimental data successfully

Investigations on low temperature thermoluminescence centres in quartz

International Nuclear Information System (INIS)

Bernhardt, H.

1984-01-01

The present paper will help to understand the often investigated process of thermoluminescence of quartz which is of high complexity. A lot of traps exist in quartz crystals which compete with each other with respect to the trapping of charge carriers during the X-ray treatment. That is why a variety of processes takes place after X-irradiation at liquid nitrogen temperature (LNT) of quartz which complicate the phenomenology of low temperature thermoluminescence. This competition in the trapping process leads to the so-called 'sensibilization' or 'desensibilization' effects of thermoluminescence, respectively, which are described in this paper for the first time. This effect means the dependence of the LNT thermoluminescence intensity on a pre-irradiation dose applied at room temperature (RT). The influence of this pre-irradiation is understood assuming the saturation of competitive traps. This favours an enhanced trapping of charge carriers at LNT-(shallow) traps instead of the preferential trapping on the deep traps in the case of X-ray treatment of the as-grown crystal at LNT. To get the afore mentioned model we take into account not only thermoluminescence but also coloration, ir- and vuv-absorption measurements. (author)

Effects of substrate temperature, substrate orientation, and energetic atomic collisions on the structure of GaN films grown by reactive sputtering

Energy Technology Data Exchange (ETDEWEB)

Schiaber, Ziani S.; Lisboa-Filho, Paulo N.; Silva, José H. D. da [Universidade Estadual Paulista, UNESP, Bauru, São Paulo 17033-360 (Brazil); Leite, Douglas M. G. [Universidade Federal de Itajubá, UNIFEI, Itajubá, Minas Gerais 37500-903 (Brazil); Bortoleto, José R. R. [Universidade Estadual Paulista, UNESP, Sorocaba, São Paulo 18087-180 (Brazil)

2013-11-14

The combined effects of substrate temperature, substrate orientation, and energetic particle impingement on the structure of GaN films grown by reactive radio-frequency magnetron sputtering are investigated. Monte-Carlo based simulations are employed to analyze the energies of the species generated in the plasma and colliding with the growing surface. Polycrystalline films grown at temperatures ranging from 500 to 1000 °C clearly showed a dependence of orientation texture and surface morphology on substrate orientation (c- and a-plane sapphire) in which the (0001) GaN planes were parallel to the substrate surface. A large increase in interplanar spacing associated with the increase in both a- and c-parameters of the hexagonal lattice and a redshift of the optical bandgap were observed at substrate temperatures higher than 600 °C. The results showed that the tensile stresses produced during the film's growth in high-temperature deposition ranges were much larger than the expected compressive stresses caused by the difference in the thermal expansion coefficients of the film and substrate in the cool-down process after the film growth. The best films were deposited at 500 °C, 30 W and 600 °C, 45 W, which corresponds to conditions where the out diffusion from the film is low. Under these conditions the benefits of the temperature increase because of the decrease in defect density are greater than the problems caused by the strongly strained lattice that occurr at higher temperatures. The results are useful to the analysis of the growth conditions of GaN films by reactive sputtering.

Interface Study on Amorphous Indium Gallium Zinc Oxide Thin Film Transistors Using High-k Gate Dielectric Materials

Directory of Open Access Journals (Sweden)

Yu-Hsien Lin

2015-01-01

Full Text Available We investigated amorphous indium gallium zinc oxide (a-IGZO thin film transistors (TFTs using different high-k gate dielectric materials such as silicon nitride (Si3N4 and aluminum oxide (Al2O3 at low temperature process (<300°C and compared them with low temperature silicon dioxide (SiO2. The IGZO device with high-k gate dielectric material will expect to get high gate capacitance density to induce large amount of channel carrier and generate the higher drive current. In addition, for the integrating process of integrating IGZO device, postannealing treatment is an essential process for completing the process. The chemical reaction of the high-k/IGZO interface due to heat formation in high-k/IGZO materials results in reliability issue. We also used the voltage stress for testing the reliability for the device with different high-k gate dielectric materials and explained the interface effect by charge band diagram.

Interface Study on Amorphous Indium Gallium Zinc Oxide Thin Film Transistors Using High-k Gate Dielectric Materials

International Nuclear Information System (INIS)

Lin, Y. H.; Chou, J. C.

2015-01-01

We investigated amorphous indium gallium zinc oxide (a-IGZO) thin film transistors (TFT_s) using different high-Κ gate dielectric materials such as silicon nitride (Si_3N_4) and aluminum oxide (Al_2O_3) at low temperature process (<300 degree) and compared them with low temperature silicon dioxide (SiO_2). The IGZO device with high-Κ gate dielectric material will expect to get high gate capacitance density to induce large amount of channel carrier and generate the higher drive current. In addition, for the integrating process of integrating IGZO device, post annealing treatment is an essential process for completing the process. The chemical reaction of the high-κ/IGZO interface due to heat formation in high-Κ/IGZO materials results in reliability issue. We also used the voltage stress for testing the reliability for the device with different high-Κ gate dielectric materials and explained the interface effect by charge band diagram.

Electrical and mechanical stability of aluminum-doped ZnO films grown on flexible substrates by atomic layer deposition

International Nuclear Information System (INIS)

Luka, G.; Witkowski, B.S.; Wachnicki, L.; Jakiela, R.; Virt, I.S.; Andrzejczuk, M.; Lewandowska, M.; Godlewski, M.

2014-01-01

Highlights: • Transparent and conductive ZnO:Al films were grown by atomic layer deposition. • The films were grown on flexible substrates at low growth temperatures (110–140 °C). • So-obtained films have low resistivities, of the order of 10 −3 Ω cm. • Bending tests indicated a critical bending radius of ≈1.2 cm. • Possible sources of the film resistivity changes upon bending are proposed. - Abstract: Aluminum-doped zinc oxide (AZO) films were grown on polyethylene terephthalate (PET) substrates by atomic layer deposition (ALD) at low deposition temperatures (110–140 °C). The films have low resistivities, ∼10 −3 Ω cm, and high transparency (∼90%) in the visible range. Bending tests indicated a critical bending radius of ≈1.2 cm, below which the resistivity changes became irreversible. The films deposited on PET with additional buffer layer are more stable upon bending and temperature changes

Study of current instabilities in high resistivity gallium arsenide

International Nuclear Information System (INIS)

Barraud, A.

1968-01-01

We have shown the existence and made a study of the current oscillations produced in high-resistivity gallium arsenide by a strong electric field. The oscillations are associated with the slow travelling of a region of high electrical field across the whole sample. An experimental study of the properties of these instabilities has made it possible for us to distinguish this phenomenon from the Gunn effect, from acoustic-electric effects and from contact effects. In order to account for this type of instability, a differential trapping mechanism involving repulsive impurities is proposed; this mechanism can reduce the concentration of charge carriers in the conduction band at strong electrical fields and can lead to the production of a high-field domain. By developing this model qualitatively we have been able to account for all the properties of high-resistance gallium arsenide crystals subjected to a strong electrical field: increase of the Hall constant, existence of a voltage threshold for these oscillations, production of domains of high field, low rate of propagation of these domains, and finally the possibility of inverting the direction of the propagation of the domain without destroying the latter. A quantitative development of the model makes it possible to calculate the various characteristic parameters of these instabilities. Comparison with experiment shows that there is a good agreement, the small deviations coming especially from the lack of knowledge concerning transport properties in gallium arsenide subjected to high fields. From a study of this model, it appears that the instability phenomenon can occur over a wide range of repulsive centre concentrations, and also for a large range of resistivities. This is the reason why it appears systematically in gallium arsenide of medium and high resistivity. (authors) [fr

Indium oxide thin-film transistors processed at low temperature via ultrasonic spray pyrolysis

KAUST Repository

Faber, Hendrik

2015-01-14

The use of ultrasonic spray pyrolysis is demonstrated for the growth of polycrystalline, highly uniform indium oxide films at temperatures in the range of 200-300 °C in air using an aqueous In(NO3)3 precursor solution. Electrical characterization of as-deposited films by field-effect measurements reveals a strong dependence of the electron mobility on deposition temperature. Transistors fabricated at ∼250 °C exhibit optimum performance with maximum electron mobility values in the range of 15-20 cm2 V -1 s-1 and current on/off ratio in excess of 106. Structural and compositional analysis of as-grown films by means of X-ray diffraction, diffuse scattering, and X-ray photoelectron spectroscopy reveal that layers deposited at 250 °C are denser and contain a reduced amount of hydroxyl groups as compared to films grown at either lower or higher temperatures. Microstructural analysis of semiconducting films deposited at 250 °C by high resolution cross-sectional transmission electron microscopy reveals that as-grown layers are extremely thin (∼7 nm) and composed of laterally large (30-60 nm) highly crystalline In2O3 domains. These unique characteristics of the In2O3 films are believed to be responsible for the high electron mobilities obtained from transistors fabricated at 250 °C. Our work demonstrates the ability to grow high quality low-dimensional In2O3 films and devices via ultrasonic spray pyrolysis over large area substrates while at the same time it provides guidelines for further material and device improvements.

Gallium accumulation in early pulmonary Pneumocystis carinii infection

International Nuclear Information System (INIS)

Stevens, D.A.; Allegra, J.C.

1986-01-01

The accumulation of gallium 67 citrate in pulmonary Pneumocystis carinii is well known. The sensitivity of gallium uptake in detecting early inflammatory processes, even when conventional roentgenograms are normal, would seem to make it possible in immunocompromised patients to make a presumptive diagnosis of this serious infection early in its course without using invasive techniques to demonstrate the organism. However, the presence of gallium uptake in radiation pneumonitis, pulmonary drug toxicity, and other processes that also occur in this group limit its usefulness. In our two patients--a young woman with Hodgkin's disease and an elderly woman with small cell lung cancer--this technique proved helpful. Although the latter patient was successfully treated empirically, such empiric treatment should be reserved for patients unable or unwilling to undergo invasive tests. Pulmonary gallium uptake in patients with respiratory symptoms, even with a normal chest film, should prompt attempts to directly demonstrate the organism

iTRAQ-based proteome profiling of Saccharomyces cerevisiae and cryotolerant species Saccharomyces uvarum and Saccharomyces kudriavzevii during low-temperature wine fermentation.

Science.gov (United States)

García-Ríos, Estéfani; Querol, Amparo; Guillamón, José Manuel

2016-09-02

Temperature is one of the most important parameters to affect the duration and rate of alcoholic fermentation and final wine quality. Some species of the Saccharomyces genus have shown better adaptation at low temperature than Saccharomyces cerevisiae, which was the case of cryotolerant yeasts Saccharomyces uvarum and Saccharomyces kudriavzevii. In an attempt to detect inter-specific metabolic differences, we characterized the proteomic landscape of these cryotolerant species grown at 12°C and 28°C, which we compared with the proteome of S. cerevisiae (poorly adapted at low temperature). Our results showed that the main differences among the proteomic profiling of the three Saccharomyces strains grown at 12°C and 28°C lay in translation, glycolysis and amino acid metabolism. Our data corroborate previous transcriptomic results, which suggest that S. kudriavzevii is better adapted to grow at low temperature as a result of enhanced more efficient translation. Fitter amino acid biosynthetic pathways can also be mechanisms that better explain biomass yield in cryotolerant strains. Yet even at low temperature, S. cerevisiae is the most fermentative competitive species. A higher concentration of glycolytic and alcoholic fermentation enzymes in the S. cerevisiae strain might explain such greater fermentation activity. Temperature is one of the main relevant environmental variables that microorganisms have to cope with and it is also a key factor in some industrial processes that involve microorganisms. However, we are still far from understanding the molecular and physiological mechanisms of adaptation at low temperatures. The results obtained in this study provided a global atlas of the proteome changes triggered by temperature in three different species of the genus Saccharomyces with different degree of cryotolerance. These results would facilitate a better understanding of mechanisms for how yeast could adapt at the low temperature of growth. Copyright © 2016

Characterization of ZnO film grown on polycarbonate by atomic layer deposition at low temperature

Energy Technology Data Exchange (ETDEWEB)

Lee, Gyeong Beom; Han, Gwon Deok; Shim, Joon Hyung; Choi, Byoung-Ho, E-mail: bhchoi@korea.ac.kr [School of Mechanical Engineering, Korea University, Seoul 136-707 (Korea, Republic of)

2015-01-15

ZnO is an attractive material for use in various technological products such as phosphors, gas sensors, and transparent conductors. Recently, aluminum-doped zinc oxide has received attention as a potential replacement for indium tin oxide, which is one of the transparent conductive oxides used in flat panel displays, organic light-emitting diodes, and organic solar cells. In this study, the characteristics of ZnO films deposited on polycarbonate (PC) substrates by atomic layer deposition (ALD) are investigated for various process temperatures. The growth mechanism of these films was investigated at low process temperatures using x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS). XRD and XPS were used to determine the preferred orientation and chemical composition of the films, respectively. Furthermore, the difference of the deposition mechanisms on an amorphous organic material, i.e., PC substrate and an inorganic material such as silicon was discussed from the viewpoint of the diffusion and deposition of precursors. The structure of the films was also investigated by chemical analysis in order to determine the effect of growth temperature on the films deposited by ALD.

Psoas abscess localization by gallium scan in aplastic anemia

International Nuclear Information System (INIS)

Oster, M.W.; Gelrud, L.G.; Lotz, M.J.; Herzig, G.P.; Johnston, G.S.

1975-01-01

Gallium 67 scanning is an effective method of detecting inflammatory lesions, especially abscesses. A 10-year-old boy with aplastic anemia and severe leukopenia and granulocytopenia had a psoas abscess diagnosed by gallium scan. The patient died with Candida sepsis 18 days after bone marrow transplantation. At autopsy, a chronic psoas abscess with Candida was found. The gallium scan offers a clinically effective and noninvasive means of evaluating suspected infection in the granulocytopenia patient. (U.S.)

Study of current instabilities in high resistivity gallium arsenide; Etude des instabilites de courant dans l'arseniure de gallium de haute resistivite

Energy Technology Data Exchange (ETDEWEB)

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

1968-07-01

We have shown the existence and made a study of the current oscillations produced in high-resistivity gallium arsenide by a strong electric field. The oscillations are associated with the slow travelling of a region of high electrical field across the whole sample. An experimental study of the properties of these instabilities has made it possible for us to distinguish this phenomenon from the Gunn effect, from acoustic-electric effects and from contact effects. In order to account for this type of instability, a differential trapping mechanism involving repulsive impurities is proposed; this mechanism can reduce the concentration of charge carriers in the conduction band at strong electrical fields and can lead to the production of a high-field domain. By developing this model qualitatively we have been able to account for all the properties of high-resistance gallium arsenide crystals subjected to a strong electrical field: increase of the Hall constant, existence of a voltage threshold for these oscillations, production of domains of high field, low rate of propagation of these domains, and finally the possibility of inverting the direction of the propagation of the domain without destroying the latter. A quantitative development of the model makes it possible to calculate the various characteristic parameters of these instabilities. Comparison with experiment shows that there is a good agreement, the small deviations coming especially from the lack of knowledge concerning transport properties in gallium arsenide subjected to high fields. From a study of this model, it appears that the instability phenomenon can occur over a wide range of repulsive centre concentrations, and also for a large range of resistivities. This is the reason why it appears systematically in gallium arsenide of medium and high resistivity. (authors) [French] Nous avons mis en evidence et etudie des oscillations de courant qui se produisent a champ electrique eleve dans l'arseniure de

Characterization of high temperature-tolerant rhizobia isolated from Prosopis juliflora grown in alkaline soil.

Science.gov (United States)

Kulkarni, Suneeta; Nautiyal, Chandra Shekhar

1999-10-01

A method was developed for the fast screening and selection of high-temperature tolerant rhizobial strains from root nodules of Prosopis juliflora growing in alkaline soils. The high-temperature tolerant rhizobia were selected from 2,500 Rhizobium isolates with similar growth patterns on yeast mannitol agar plates after 72 h incubation at 30 and 45 degrees C, followed by a second screening at 47.5 degrees C. Seventeen high-temperature tolerant rhizobial strains having distinguishable protein band patterns were finally selected for further screening by subjecting them to temperature stress up to 60 degrees C in yeast mannitol broth for 6 h. The high-temperature tolerant strains were NBRI12, NBRI329, NBRI330, NBRI332, and NBRI133. Using this procedure, a large number of rhizobia from root nodules of P. juliflora were screened for high-temperature tolerance. The assimilation of several carbon sources, tolerance to high pH and salt stress, and ability to nodulate P. juliflora growing in a glasshouse and nursery of the strains were studied. All five isolates had higher plant dry weight in the range of 29.9 to 88.6% in comparison with uninoculated nursery-grown plants. It was demonstrated that it is possible to screen in nature for superior rhizobia exemplified by the isolation of temperature-tolerant strains, which established effective symbiosis with nursery-grown P. juliflora. These findings indicate a correlation between strain performance under in vitro stress in pure culture and strain behavior under symbiotic conditions. Pure culture evaluation may be a useful tool in search for Rhizobium strains better suited for soil environments where high temperature, pH, and salt stress constitutes a limitation for symbiotic biological nitrogen fixation.

Recovery of gallium from coal fly ash by a dual reactive extraction process

Energy Technology Data Exchange (ETDEWEB)

Gutierrez, B.; Pazos, C.; Coca, J. [University of Oviedo, Oviedo (Spain). Dept. of Chemical Engineering and Environmental Technology

1997-08-01

This paper describes the extraction of gallium from coal fly ash by leaching and extraction with commercial extractants Amerlite LA-2 and LIX-54N dissolved in kerosene. Leaching of gallium and other metals from the fly ash was carried out with 6 M hydrochloric acid. The leaching liquor is first contacted with Amerlite LA-2 which extracts the gallium and iron. The iron is then precipitated with sodium hydroxide, while gallium remains in solution. Gallium is extracted selectively from the base solution with LIX 54; the resulting stripped solution contains 83% of the gallium present in the leaching liquor.

Daphnia fed algal food grown at elevated temperature have reduced fitness

Directory of Open Access Journals (Sweden)

Anna B. Sikora

2014-05-01

Full Text Available Lake water temperature is negatively correlated with fatty acids content and P:C ratio in green algae. Hence, elevated temperature may indirectly reduce the fitness of Daphnia due to induced decrease in algal food quality. The aim of this study was to test the hypotheses that quality of algal food decreases with increasing temperature of its culture and that large-bodied Daphnia are more vulnerable to the temperature-related deterioration of algal food quality than small-bodied ones. Laboratory life-table experiments were performed at 20°C with large-bodied D. pulicaria and small-bodied D. cucullata fed with the green alga Scenedesmus obliquus, that had been grown at temperatures of 16, 24 or 32°C. The somatic growth rates of both species decreased significantly with increasing algal culture temperature and this effect was more pronounced in D. pulicaria than in D. cucullata. In the former species, age at first reproduction significantly increased and clutch size significantly decreased with increasing temperature of algae growth, while no significant changes in these two parameters were observed in the latter species. The proportion of egg-bearing females decreased with increasing algal culture temperature in both species. The results of this study support the notion that the quality of algal food decreases with increasing water temperature and also suggest that small-bodied Daphnia species might be less vulnerable to temperature-related decreases in algal food quality than large-bodied ones.

Sclerotial formation of Polyporus umbellatus by low temperature treatment under artificial conditions.

Science.gov (United States)

Xing, Yong-Mei; Zhang, Li-Chun; Liang, Han-Qiao; Lv, Jing; Song, Chao; Guo, Shun-Xing; Wang, Chun-Lan; Lee, Tae-Soo; Lee, Min-Woong

2013-01-01

Polyporus umbellatus sclerotia have been used as a diuretic agent in China for over two thousand years. A shortage of the natural P. umbellatus has prompted researchers to induce sclerotial formation in the laboratory. P. umbellatus cultivation in a sawdust-based substrate was investigated to evaluate the effect of low temperature conditions on sclerotial formation. A phenol-sulfuric acid method was employed to determine the polysaccharide content of wild P. umbellatus sclerotia and mycelia and sclerotia grown in low-temperature treatments. In addition, reactive oxygen species (ROS) content, expressed as the fluorescence intensity of mycelia during sclerotial differentiation was determined. Analysis of ROS generation and sclerotial formation in mycelia after treatment with the antioxidants such as diphenyleneiodonium chloride (DPI), apocynin (Apo), or vitamin C were studied. Furthermore, macroscopic and microscopic characteristics of sclerotial differentiation were observed. Sclerotia were not induced by continuous cultivation at 25°C. The polysaccharide content of the artificial sclerotia is 78% of that of wild sclerotia. In the low-temperature treatment group, the fluorescent intensity of ROS was higher than that of the room temperature (25°C) group which did not induce sclerotial formation all through the cultivation. The antioxidants DPI and Apo reduced ROS levels and did not induce sclerotial formation. Although the concentration-dependent effects of vitamin C (5-15 mg mL(-1)) also reduced ROS generation and inhibited sclerotial formation, using a low concentration of vitamin C (1 mg mL(-1)) successfully induced sclerotial differentiation and increased ROS production. Exposure to low temperatures induced P. umbellatus sclerotial morphogenesis during cultivation. Low temperature treatment enhanced ROS in mycelia, which may be important in triggering sclerotial differentiation in P. umbellatus. Moreover, the application of antioxidants impaired ROS generation

A noise thermometry investigation of the melting point of gallium at the NIM

Science.gov (United States)

Zhang, J. T.; Xue, S.

2006-06-01

This paper describes a study of the melting point of gallium with the new NIM Johnson noise thermometer (JNT). The new thermometer adopts the structure of switching correlator and commutator with the reference resistor maintained at the triple point of water. The electronic system of the new thermometer is basically the same as the current JNT, but the preamplifiers have been improved slightly. This study demonstrates that examining the characteristics of the noise signals in the frequency domain is of critical importance in constructing an improved new thermometer, where a power spectral analysis is found to be critical in establishing appropriate grounding for the new thermometer. The new JNT is tested on measurements of the thermodynamic temperature of the melting point of gallium, which give the thermodynamic temperature of 302.9160 K, with an overall integration time of 190 h and a combined standard uncertainty of 9.4 mK. The uncertainty analysis indicates that a standard combined uncertainty of 3 mK could be achieved with the new thermometer over an integration period of 1750 h.

Sodium Flux Growth of Bulk Gallium Nitride

Science.gov (United States)

Von Dollen, Paul Martin

This dissertation focused on development of a novel apparatus and techniques for crystal growth of bulk gallium nitride (GaN) using the sodium flux method. Though several methods exist to produce bulk GaN, none have been commercialized on an industrial scale. The sodium flux method offers potentially lower cost production due to relatively mild process conditions while maintaining high crystal quality. But the current equipment and methods for sodium flux growth of bulk GaN are generally not amenable to large-scale crystal growth or in situ investigation of growth processes, which has hampered progress. A key task was to prevent sodium loss or migration from the sodium-gallium growth melt while permitting N2 gas to access the growing crystal, which was accomplished by implementing a reflux condensing stem along with a reusable sealed capsule. The reflux condensing stem also enabled direct monitoring and control of the melt temperature, which has not been previously reported for the sodium flux method. Molybdenum-based materials were identified from a corrosion study as candidates for direct containment of the corrosive sodium-gallium melt. Successful introduction of these materials allowed implementation of a crucible-free containment system, which improved process control and can potentially reduce crystal impurity levels. Using the new growth system, the (0001) Ga face (+c plane) growth rate was >50 mum/hr, which is the highest bulk GaN growth rate reported for the sodium flux method. Omega X-ray rocking curve (?-XRC) measurements indicated the presence of multiple grains, though full width at half maximum (FWHM) values for individual peaks were 1020 atoms/cm3, possibly due to reactor cleaning and handling procedures. This dissertation also introduced an in situ technique to correlate changes in N2 pressure with dissolution of nitrogen and precipitation of GaN from the sodium-gallium melt. Different stages of N2 pressure decay were identified and linked to

Self-assembled GaN nano-column grown on Si(111) substrate using Au+Ga alloy seeding method by metalorganic chemical vapor deposition

International Nuclear Information System (INIS)

Shim, Byung-Young; Ko, Eun-A; Song, Jae-Chul; Kang, Dong-Hun; Kim, Dong-Wook; Lee, In-Hwan; Kannappan, Santhakumar; Lee, Cheul-Ro

2007-01-01

Single-crystal GaN nano-column arrays were grown on Au-coated silicon (111) substrate by Au-Ga alloy seeding method using metalorganic chemical vapor deposition (MOCVD). The nano-column arrays were studied as a function of growth parameters and Au thin film thickness. The diameter and length of the as-grown nano-column vary from 100 to 500 nm and 4 to 6 μm, respectively. The surface morphology and optical properties of the nano-columns were investigated using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), cathodoluminescence (CL) and photoluminescence (PL). The Au+Ga alloy droplets were found to be uniformly distributed on silicon surface. Further, SEM image reveals a vertical growth and cylindrical in shape GaN nano-column. The chemical composition of the nano-column, which composed of gallium and nitrogen ions, was estimated by EDX. CL reveals a strong band edge emission from the GaN nano-column. PL spectra show a peak at 365.7 nm with a full-width half maximum (FWHM) of 65 meV which indicates good optical quality GaN nano-column with low dislocation density. Our results suggest that single crystal GaN nano-column can be grown on Au+Ga alloy on silicon substrate with a low dislocation density for better device performances. (author)

Conversion of n-Butane to iso-Butene on Gallium/HZSM-5 Catalysts

Directory of Open Access Journals (Sweden)

S.M. Gheno

2002-07-01

Full Text Available The conversion of n-butane to iso-butene on gallium/HZSM-5 catalysts at 350ºC and WHSV=2.5h8-1 was studied. The catalysts were prepared by ion exchange from a Ga(NO32 solution and further submitted to calcination in air at 530ºC. TEM analysis with an EDAX detector and TPR-H2 data showed that after calcination the Ga species were present mainly as Ga2O3, which are reduced to Ga2O at temperatures near 610ºC. The specific acid activity (SAA of the catalysts increased with the increase in aluminum content in the zeolite, and for a fixed Si/Al ratio, the SAA increased with Ga content. Values for specific hydro/dehydrogenation activity (SH/DHA were significantly higher than those for SAA, indicating that the catalytic process is controlled by the kinetics on acid sites. Moreover, the production of iso-butene with a selectivity higher than 25% was a evidence that in gallium/HZSM-5-based catalysts the rate of the hydrogenation reaction is lower than that of the dehydrogenation reaction; this behavior confirmed the dehydrogenation nature of gallium species, thereby showing great promise for iso-butene production.

Characterization of Tolypocladium cylindrosporum (Hypocreales: Ophiocordycipitacea) and its impact against Aedes aegypti and Aedes albopictus eggs at low temperature

Science.gov (United States)

We examined the growth characteristics of Tolypocladium cylindrosporum IBT 41712 and its potential to infect eggs of Aedes aegypti Linnaeus and Aedes albopictus (Skuse) mosquitoes at low temperature (15 deg C). When grown on sabouraud dextrose agar supplemented with yeast extract, IBT 41712 formed w...

Angiotensin-I-converting enzyme and gallium scan in noninvasive evaluation of sarcoidosis

Energy Technology Data Exchange (ETDEWEB)

Nosal, A. (Harbor General Hospital, Torrance, CA); Schleissner, L.A.; Mishkin, F.S.; Lieberman, J.

1979-03-01

Angiotensin-converting enzyme assays and gallium-scan results were obtained from 27 patients with biopsy-proven, clinically active sarcoidosis. Twenty-three of these patients had elevated converting enzyme levels, and 22 had positive gallium-scan results. Three of four patients with normal or borderline-elevated levels of angiotensin-converting enzyme also had positive gallium-scan results. Of 156 nonsarcoid patients (pulmonary and other diseases), 27 were found to have elevated serum converting enzyme levels, and 25 of these had negative gallium-scan results. These results indicate that the combination of an assay of angiotensin-converting enzyme and gallium scan increases diagnostic specificity from 83% to 99% without sacrificing sensitivity. It was concluded that the concurrent use of angiotensin-converting enzyme assay and gallium scan is of value in the diagnosis of sarcoidosis.

Angiotensin-I-converting enzyme and gallium scan in noninvasive evaluation of sarcoidosis

International Nuclear Information System (INIS)

Nosal, A.; Schleissner, L.A.; Mishkin, F.S.; Lieberman, J.

1979-01-01

Angiotensin-converting enzyme assays and gallium-scan results were obtained from 27 patients with biopsy-proven, clinically active sarcoidosis. Twenty-three of these patients had elevated converting enzyme levels, and 22 had positive gallium-scan results. Three of four patients with normal or borderline-elevated levels of angiotensin-converting enzyme also had positive gallium-scan results. Of 156 nonsarcoid patients (pulmonary and other diseases), 27 were found to have elevated serum converting enzyme levels, and 25 of these had negative gallium-scan results. These results indicate that the combination of an assay of angiotensin-converting enzyme and gallium scan increases diagnostic specificity from 83% to 99% without sacrificing sensitivity. It was concluded that the concurrent use of angiotensin-converting enzyme assay and gallium scan is of value in the diagnosis of sarcoidosis

Processing and electrical properties of gallium-substituted lead zirconate titanate ceramics

Science.gov (United States)

Hajra, Sugato; Sharma, Pulkit; Sahoo, Sushrisangita; Rout, P. K.; Choudhary, R. N. P.

2017-12-01

In the present paper, the effect of gallium (Ga) substitution on structural, microstructural, electrical conductivity of Pb(ZrTi)O3 (PZT) in the morphotropic phase boundary (MPB) region (i.e., Pb0.96Ga0.04(Zr0.48Ti0.52)0.99O3 (PGaZT-4)) was investigated. Increased grain density increases the resistivity of the Ga-modified PZT system. Preliminary structural analysis using X-ray diffraction pattern and data showed the existence of two phases [major tetragonal (T) and minor monoclinic (M)]. Field emission scanning electron micrograph (FESEM) showed the distribution of spherical as well as platelet type grains with small pores. The behavior of dielectric constant with temperature of PGaZT-4 exhibited the suppression of the ferroelectric phase transition [i.e., disappearance of Curie temperature ( T c)]. The complex impedance spectroscopy (CIS) technique helped to investigate the impedance parameters of PGaZT-4 in MPB region in a wide range of temperature (250-500 °C) and frequency (1-1000 kHz) region. The impedance parameters of the material are found to be strongly dependent on frequency of AC electric field and temperature. The substitution of gallium at the Pb site of PZT generally enhances the dielectric constant and decreases loss tangent. The AC conductivity vs frequency ( f = ω2 π) in the region of dispersion follows the universal response of Jonscher's equation. Enhanced resistive characteristics were observed for Ga-substituted PZT in comparison to the pure PZT, which was well ensured from the studies of electrical parameters, such as impedance and AC conductivity.

Two-Dimensional Modeling of Aluminum Gallium Nitride/Gallium Nitride High Electron Mobility Transistor

National Research Council Canada - National Science Library

Holmes, Kenneth

2002-01-01

Gallium Nitride (GaN) High Electron Mobility Transistors (HEMT's) are microwave power devices that have the performance characteristics to improve the capabilities of current and future Navy radar and communication systems...

Proportional counter response calculations for gallium solar neutrino detectors

International Nuclear Information System (INIS)

Kouzes, R.T.; Reynolds, D.

1989-01-01

Gallium bases solar neutrino detectors are sensitive to the primary pp reaction in the sun. Two experiments using gallium, SAGE in the Soviet Union and GALLEX in Europe, are under construction and will produce data by 1989. The radioactive /sup 71/Ge produced by neutrinos interacting with the gallium detector material, is chemically extracted and counted in miniature proportional counters. A number of calculations have been carried out to simulate the response of these counters to the decay of /sup 71/Ge and to background events

Synthesis of ZnO Nanostructures for Low Temperature CO and UV Sensing

Directory of Open Access Journals (Sweden)

Nazar Abbas Shah

2012-10-01

Full Text Available In this paper, synthesis and results of the low temperature sensing of carbon monoxide (CO gas and room temperature UV sensors using one dimensional (1-D ZnO nanostructures are presented. Comb-like structures, belts and rods, and needle-shaped nanobelts were synthesized by varying synthesis temperature using a vapor transport method. Needle-like ZnO nanobelts are unique as, according to our knowledge, there is no evidence of such morphology in previous literature. The structural, morphological and optical characterization was carried out using X-ray diffraction, scanning electron microscopy and diffused reflectance spectroscopy techniques. It was observed that the sensing response of comb-like structures for UV light was greater as compared to the other grown structures. Comb-like structure based gas sensors successfully detect CO at 75 °C while other structures did not show any response.

Semi-quantitative evaluation of gallium-67 scintigraphy in lupus nephritis

International Nuclear Information System (INIS)

Lin Wanyu; Hsieh Jihfang; Tsai Shihchuan; Lan Joungliang; Cheng Kaiyuan; Wang Shyhjen

2000-01-01

Within nuclear medicine there is a trend towards quantitative analysis. Gallium renal scan has been reported to be useful in monitoring the disease activity of lupus nephritis. However, only visual interpretation using a four-grade scale has been performed in previous studies, and this method is not sensitive enough for follow-up. In this study, we developed a semi-quantitative method for gallium renal scintigraphy to find a potential parameter for the evaluation of lupus nephritis. Forty-eight patients with lupus nephritis underwent renal biopsy to determine World Health Organization classification, activity index (AI) and chronicity index (CI). A delayed 48-h gallium scan was also performed and interpreted by visual and semi-quantitative methods. For semi-quantitative analysis of the gallium uptake in both kidneys, regions of interest (ROIs) were drawn over both kidneys, the right forearm and the adjacent spine. The uptake ratios between these ROIs were calculated and expressed as the ''kidney/spine ratio (K/S ratio)'' or the ''kidney/arm ratio (K/A ratio)''. Spearman's rank correlation test and Mann-Whitney U test were used for statistical analysis. Our data showed a good correlation between the semi-quantitative gallium scan and the results of visual interpretation. K/S ratios showed a better correlation with AI than did K/A ratios. Furthermore, the left K/S ratio displayed a better correlation with AI than did the right K/S ratio. In contrast, CI did not correlate well with the results of semi-quantitative gallium scan. In conclusion, semi-quantitative gallium renal scan is easy to perform and shows a good correlation with the results of visual interpretation and renal biopsy. The left K/S ratio from semi-quantitative renal gallium scintigraphy displays the best correlation with AI and is a useful parameter in evaluating the disease activity in lupus nephritis. (orig.)

Two years of on-orbit gallium arsenide performance from the LIPS solar cell panel experiment

Science.gov (United States)

Francis, R. W.; Betz, F. E.

1985-01-01

The LIPS on-orbit performance of the gallium arsenide panel experiment was analyzed from flight operation telemetry data. Algorithms were developed to calculate the daily maximum power and associated solar array parameters by two independent methods. The first technique utilizes a least mean square polynomial fit to the power curve obtained with intensity and temperature corrected currents and voltages; whereas, the second incorporates an empirical expression for fill factor based on an open circuit voltage and the calculated series resistance. Maximum power, fill factor, open circuit voltage, short circuit current and series resistance of the solar cell array are examined as a function of flight time. Trends are analyzed with respect to possible mechanisms which may affect successive periods of output power during 2 years of flight operation. Degradation factors responsible for the on-orbit performance characteristics of gallium arsenide are discussed in relation to the calculated solar cell parameters. Performance trends and the potential degradation mechanisms are correlated with existing laboratory and flight data on both gallium arsenide and silicon solar cells for similar environments.

First heats of cerium solution in liquid aluminium, gallium, indium, tin, lead and bismuth

International Nuclear Information System (INIS)

Yamshchikov, L.F.; Lebedev, V.A.; Nichkov, I.F.; Raspopin, S.P.; Shein, V.G.

1983-01-01

Cerium solution heats in liquid alluminium, gallium, indium, tin, lead and bismuth are determined in high temperature mixing calorimeter with an isothermal shell. The statistical analysis carried out proves that values of cerium solution heat in fusible metals obtained by the methods of electric motive forces and calorimety give a satisfactory agreement

Skirting terahertz waves in a photo-excited nanoslit structure

Energy Technology Data Exchange (ETDEWEB)

Shalaby, Mostafa, E-mail: mostafa.shalaby@psi.ch, E-mail: thomas.feurer@iap.unibe.ch [INRS-EMT, Varennes, Quebec J3X 1S2 (Canada); SwissFEL, Paul Scherrer Institut, Villigen 5232 (Switzerland); Fabiańska, Justyna; Feurer, Thomas, E-mail: mostafa.shalaby@psi.ch, E-mail: thomas.feurer@iap.unibe.ch [Institute of Applied Physics, University of Bern, Sidlerstrasse 5, CH-3012 Bern (Switzerland); Peccianti, Marco [INRS-EMT, Varennes, Quebec J3X 1S2 (Canada); Department of Physics and Astronomy, University of Sussex, Pevensey Building II, 3A8, Falmer, Brighton BN1 9QH (United Kingdom); Ozturk, Yavuz; Vidal, Francois; Morandotti, Roberto [INRS-EMT, Varennes, Quebec J3X 1S2 (Canada); Sigg, Hans [LMN, Paul Scherrer Institut, Villigen 5232 (Switzerland)

2014-04-28

Terahertz fields can be dramatically enhanced as they propagate through nanometer-sized slits. The enhancement is mediated by a significant accumulation of the induced surface charges on the surrounding metal. This enhancement is shown here to be dynamically modulated while the nanoslits are gradually shunted using a copropagating optical beam. The terahertz fields are found to skirt the nanoscale photo-excited region underneath the slits, scattering to the far field and rigorously mapping the near field.

Low-Temperature Crystalline Titanium Dioxide by Atomic Layer Deposition for Dye-Sensitized Solar Cells

KAUST Repository

Chandiran, Aravind Kumar

2013-04-24

Low-temperature processing of dye-sensitized solar cells (DSCs) is crucial to enable commercialization with low-cost, plastic substrates. Prior studies have focused on mechanical compression of premade particles on plastic or glass substrates; however, this did not yield sufficient interconnections for good carrier transport. Furthermore, such compression can lead to more heterogeneous porosity. To circumvent these problems, we have developed a low-temperature processing route for photoanodes where crystalline TiO2 is deposited onto well-defined, mesoporous templates. The TiO2 is grown by atomic layer deposition (ALD), and the crystalline films are achieved at a growth temperature of 200 C. The ALD TiO2 thickness was systematically studied in terms of charge transport and performance to lead to optimized photovoltaic performance. We found that a 15 nm TiO2 overlayer on an 8 μm thick SiO2 film leads to a high power conversion efficiency of 7.1% with the state-of-the-art zinc porphyrin sensitizer and cobalt bipyridine redox mediator. © 2013 American Chemical Society.

Inhalation developmental toxicology studies: Gallium arsenide in mice and rats

Energy Technology Data Exchange (ETDEWEB)

Mast, T.J.; Greenspan, B.J.; Dill, J.A.; Stoney, K.H.; Evanoff, J.J.; Rommereim, R.L.

1990-12-01

Gallium arsenide is a crystalline compound used extensively in the semiconductor industry. Workers preparing solar cells and gallium arsenide ingots and wafers are potentially at risk from the inhalation of gallium arsenide dust. The potential for gallium arsenide to cause developmental toxicity was assessed in Sprague- Dawley rats and CD-1 (Swiss) mice exposed to 0, 10, 37, or 75 mg/m{sup 3} gallium arsenide, 6 h/day, 7 days/week. Each of the four treatment groups consisted of 10 virgin females (for comparison), and {approx}30 positively mated rats or {approx}24 positively mated mice. Mice were exposed on 4--17 days of gestation (dg), and rats on 4--19 dg. The day of plug or sperm detection was designated as 0 dg. Body weights were obtained throughout the study period, and uterine and fetal body weights were obtained at sacrifice (rats, 20 dg; mice, 18 dg). Implants were enumerated and their status recorded. Live fetuses were sexed and examined for gross, visceral, skeletal, and soft-tissue craniofacial defects. Gallium and arsenic concentrations were determined in the maternal blood and uterine contents of the rats (3/group) at 7, 14, and 20 dg. 37 refs., 11 figs., 30 tabs.

Role of Gallium and labeled leukocyte scintigraphy in AIDS patient

International Nuclear Information System (INIS)

Palestro, C.J.; Goldsmith, S.J.

1995-01-01

Because AIDS patients frequently present with minimal symptomatology, radionuclide imaging with its ability to survey the entire body, is especially valuable. Gallium-67 citrate, the most commonly performed radionuclide study for localizing infection in these patients, is most useful for detecting opportunistic infections, especially in the thorax. A negative gallium scan, particularly when the chest X-ray is unremarkable, rules strongly against pulmonary disease. A negative gallium scan in a patient with an abnormal chest X-ray and Kaposi's sarcoma, suggests that the patient's respiratory distress is related to the neoplasm. Diffuse pulmonary parenchymal uptake of gallium in the HIV (+) patient is most often associated with PCP. While there are other causes of diffuse pulmonary uptake, the more intense or heterogeneous the uptake, the more likely the patient is to have PCP. Focal pulmonary uptake is usually associated with bacterial pneumonia although PCP may occasionally present in this fashion. Lymph node uptake of gallium is usually associated with Mycob acterium avium complex, tuberculosis, or Iymphoma. When corresponding abnormalities are present on thallium scintigraphy lymphoma is likely. Gallium positive, thallium negative, studies suggest mycobacterial disease. Labeled leukocyte imaging is not useful for detecting opportunistic infections probably because of the inflammatory response incited by these organisms. Leukocyte imaging is, however, more sensitive for detecting bacterial pneumonia. In the abdomen, gallium imaging is most useful for identifying lymphadenopathy, while labeled leukocyte imaging is superior for detecting AlDS-associated colitides. In summary, radionuclide studies are valuable diagnostic modalities in AIDS. Their success can be maximized by tailoring the study to the individual's needs

Low temperature carrier transport study of monolayer MoS{sub 2} field effect transistors prepared by chemical vapor deposition under an atmospheric pressure

Energy Technology Data Exchange (ETDEWEB)

Liu, Xinke, E-mail: xkliu@szu.edu.cn, E-mail: wujing026@gmail.com; He, Jiazhu; Tang, Dan; Lu, Youming; Zhu, Deliang; Liu, Wenjun; Cao, Peijiang; Han, Sun [College of Materials Science and Engineering, Shenzhen Engineering Laboratory for Advanced Technology of Ceramics, Nanshan District Key Lab for Biopolymer and Safety Evaluation, Shenzhen University, 3688 Nanhai Ave, Shenzhen 518060 (China); Liu, Qiang; Wen, Jiao; Yu, Wenjie [State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, CAS, 865 Chang Ning Road, Shanghai 200050 (China); Liu, Wenjun [State Key Laboratory of ASIC and System, Department of Microelectronics, Fudan University, 220 Handan Road, Shanghai 200433 (China); Wu, Jing, E-mail: xkliu@szu.edu.cn, E-mail: wujing026@gmail.com [Department of Physics, National University of Singapore, 21 Lower Kent Ridge Road, 117576 Singapore (Singapore); He, Zhubing [Department of Materials Science and Engineering, South University of Science and Technology of China, 1088 Xueyuan Road, Shenzhen 518055 (China); Ang, Kah-Wee [Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, 117583 Singapore (Singapore)

2015-09-28

Large size monolayer Molybdenum disulphide (MoS{sub 2}) was successfully grown by chemical vapor deposition method under an atmospheric pressure. The electrical transport properties of the fabricated back-gate monolayer MoS{sub 2} field effect transistors (FETs) were investigated under low temperatures; a peak field effect mobility of 59 cm{sup 2}V{sup −1}s{sup −1} was achieved. With the assist of Raman measurement under low temperature, this work identified the mobility limiting factor for the monolayer MoS{sub 2} FETs: homopolar phonon scattering under low temperature and electron-polar optical phonon scattering at room temperature.

The Russian-American Gallium solar neutrino Experiment (SAGE)

International Nuclear Information System (INIS)

Bowles, T.J.

1994-01-01

The Russian-American Gallium Experiment (SAGE) began measurements of the integral flux of solar neutrinos using 30 tons of metallic gallium as the target in January 1990. The mass of the gallium was increased to 57 tons in September 1991 and SAGE began to count the decay of 71 Ge using both the K and L peaks in September 1992. The results indicate a deficit of about 40% of the flux predicted by the Standard Solar Model. The chemical extraction and counting techniques used by SAGE are presented, with particular attention on backgrounds. The present status, results, and future plans of SAGE are presented, along with a discussion of the possible physics implications

Neutron diffraction study at 0.3 K of the magnetic properties of rare-earth aluminium or gallium garnets; Etude par diffraction des neutrons a 0,3 K des proprietes magnetiques de grenats de terre rare et d'aluminium ou de gallium

Energy Technology Data Exchange (ETDEWEB)

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

1969-03-01

In order to study ordered magnetic states below 1.5 deg. K by neutron diffraction measurements, a helium-3 cryostat has been realised in which the thermalization of a great quantity of powdered sample is performed by a helium-4 superfluid film, and which leaves the possibility of applying an external magnetic field. We thus studied essentially the magnetic phase transitions of rare-earth aluminium or gallium garnets. First we determined the antiferromagnetic structures of the erbium gallium garnet (T{sub N} = 0.79 deg. K) and of the neodymium gallium garnet (T{sub N} = 0.516 deg. K). The metamagnetic behavior of the erbium gallium garnet has been observed and compared to that of the dysprosium aluminium garnet. Second we considered the 'non-Kramers' ions Tb{sup 3+} and Ho{sup 3+} in the aluminium garnets. In this case, only two single ground states (well isolated from upper levels) have to be considered. A molecular field model with purely magnetic dipolar interactions, leads then to the existence of magnetic phase transition with antiferromagnetic ordering. This has been observed for the terbium-aluminium garnet below T{sub N} 1.35 deg. K and for the holmium-aluminium garnet below T{sub N} {approx} 0.98 deg. K. (author) [French] Afin d'acceder a l'etude par diffraction des neutrons des etats magnetiques ordonnes en-dessous de 1,5 deg. K, nous avons realise un cryostat a helium-3 qui assure la mise en temperature de la quantite importante d'echantillon en poudre a l'aide d'un film d'helium-4-superfluide, et qui laisse la possibilite d'application d'un champ magnetique exterieur. Nous avons essentiellement etudie avec cette technique les transitions de phase magnetique de grenats de terre rare et d'aluminium ou de gallium. C'est ainsi qu'on a determine l'ordre antiferromagnetique dans les grenats de gallium-erbium (T{sub N} = 0,79 deg. K) et de gallium-neodyme (T{sub N} = 0,516 deg. K). Le comportement metamagnetique du grenat de gallium-erbium a ete mis en evidence

Low temperature and self catalytic growth of ultrafine ITO nanowires by electron beam evaporation method and their optical and electrical properties

International Nuclear Information System (INIS)

Kumar, R. Rakesh; Rao, K. Narasimha; Rajanna, K.; Phani, A.R.

2014-01-01

Highlights: • ITO nanowires were grown by e-beam evaporation method. • ITO nanowires growth done at low substrate temperature of 350 °C. • Nanowires growth was carried out without use of catalyst and reactive oxygen gas. • Nanowires growth proceeds via self catalytic VLS growth. • Grown nanowires have diameter 10–20 nm and length 1–4 μm long. • ITO nanowire films have shown good antireflection property. - Abstract: We report the self catalytic growth of Sn-doped indium oxide (ITO) nanowires (NWs) over a large area glass and silicon substrates by electron beam evaporation method at low substrate temperatures of 250–400 °C. The ITO NWs growth was carried out without using an additional reactive oxygen gas and a metal catalyst particle. Ultrafine diameter (∼10–15 nm) and micron long ITO NWs growth was observed in a temperature window of 300–400 °C. Transmission electron microscope studies confirmed single crystalline nature of the NWs and energy dispersive spectroscopy studies on the NWs confirmed that the NWs growth proceeds via self catalytic vapor-liquid-solid (VLS) growth mechanism. ITO nanowire films grown on glass substrates at a substrate temperature of 300–400 °C have shown ∼2–6% reflection and ∼70–85% transmission in the visible region. Effect of deposition parameters was systematically investigated. The large area growth of ITO nanowire films would find potential applications in the optoelectronic devices

Structural investigations of homoepitaxial Si films grown at low temperature by pulsed magnetron sputtering on Si(111) substrates

Energy Technology Data Exchange (ETDEWEB)

Fenske, F. [Hahn-Meitner-Institut Berlin, Abt. Silizium-Photovoltaik, Kekulestr. 5, D-12485 Berlin (Germany)], E-mail: fenske@hmi.de; Schulze, S.; Hietschold, M. [Technische Universitaet Chemnitz, Analytik an Festkoerperoberflaechen, Reichenhainer Str. 70, D-09107 Chemnitz (Germany); Schmidbauer, M. [Institut fuer Kristallzuechtung Berlin, Max-Born-Str.2, D-12489 Berlin (Germany)

2008-06-02

Using pulsed magnetron sputtering at low substrate temperature (T{sub s} = 580 {sup o}C) the homoepitaxial growth on Si(111) was studied. The films were comprehensively characterized by cross-section transmission electron microscopy and various diffraction methods. Up to a film thickness of 1240 nm no breakdown of the epitaxial growth was observed. The surface microstructure, characterized by electron backscatter diffraction, exhibits exclusively crystalline structure with (111) orientation. Careful analysis of selected area electron diffraction patterns and high-resolution X-ray diffraction data clearly proves the existence of twinning/stacking faults in the {l_brace}111{r_brace} planes. Besides these defects - which are typical for low-temperature epitaxy - no additional significant defects related to the energetic particle bombardment by the sputter deposition method are observed.

Structural investigations of homoepitaxial Si films grown at low temperature by pulsed magnetron sputtering on Si(111) substrates

International Nuclear Information System (INIS)

Fenske, F.; Schulze, S.; Hietschold, M.; Schmidbauer, M.

2008-01-01

Using pulsed magnetron sputtering at low substrate temperature (T s = 580 o C) the homoepitaxial growth on Si(111) was studied. The films were comprehensively characterized by cross-section transmission electron microscopy and various diffraction methods. Up to a film thickness of 1240 nm no breakdown of the epitaxial growth was observed. The surface microstructure, characterized by electron backscatter diffraction, exhibits exclusively crystalline structure with (111) orientation. Careful analysis of selected area electron diffraction patterns and high-resolution X-ray diffraction data clearly proves the existence of twinning/stacking faults in the {111} planes. Besides these defects - which are typical for low-temperature epitaxy - no additional significant defects related to the energetic particle bombardment by the sputter deposition method are observed

Gallium nitride at the millennial transition

International Nuclear Information System (INIS)

Pankovo, J.I.

2000-01-01

The properties of gallium nitride were uncovered in the early years of exploratory research and endowed with negative electron affinity that could be used to make efficient cold cathodes and even dynodes for electron multipliers. GaN has another property i.e. polar nature of the crystal which makes this material piezo-electric and has non-linear optical properties. The piezo-electric properties led to new piezo electric effect may cause interfacial charge. The non-uniform distribution of acceptors, there is also presence of threading and other dislocation in GaN. Defects reappear where two adjacent overgrowth merge, but the good lateral overgrow region is large enough to make lasers. Injection lasers benefit from strong electrical and optical environment. This was achieved by using quantum wells of InGaN in GaN and this can be doped with rare earth elements to exploit the atomic transition between core levels in these elements. The emission efficiency of electrically excited Er in GaN is nearly temperature incentive from 80K to room temperature. An other application of GaN is as a heterojunction emitter for a bi-polar transistor (HBT) that can operate at high temperatures. (A.B.)

Identification of quenchers of photoexcited States as novel agents for skin photoprotection.

Science.gov (United States)

Wondrak, Georg T; Jacobson, Myron K; Jacobson, Elaine L

2005-02-01

Photooxidative stress is a key mechanism in UVA-induced skin photodamage. Photoexcited states of endogenous UVA chromophores such as porphyrins, melanin precursors, and cross-link-fluorophores of skin collagen exert skin photodamage by direct reaction with substrate molecules (type I photosensitization) or molecular oxygen (type II), leading to formation of reactive oxygen species. Based on our previous research on the role of photoexcited states of endogenous skin chromophores as sensitizers of photooxidative stress, we describe here the identification of a novel class of chemopreventive agents for topical skin photoprotection: quenchers of photoexcited states (QPES). QPES compounds antagonize the harmful excited state chemistry of endogenous sensitizers by physical quenching, facilitating the harmless return of the sensitizer excited state to the electronic ground state by energy dissipation. To identify QPES compounds suitable for development, we designed a primary screening assay based on QPES suppression of photosensitized plasmid cleavage using conditions that exclude antioxidants. This screen is followed with a screen to test for nonsacrificial quenching of dye-sensitized singlet oxygen ((1)O(2)) formation by electron paramagnetic resonance detection of 2,2,6,6-tetramethyl-piperidine-1-oxyl, a stable free radical indicative of (1)O(2) formation. These initial screens identified a pyrrolidine pharmacophore with pronounced QPES activity, and l-proline and other noncytotoxic proline derivatives containing this pharmacophore were then screened for efficacy in cellular models of sensitized photodamage. These compounds showed QPES protection against dye-sensitized and psoralen-UVA-induced apoptosis and suppression of proliferation in cultured human skin keratinocytes and fibroblasts. Furthermore, QPES photoprotection of reconstructed full thickness human skin exposed to solar simulated light has been demonstrated.

Acoustic emission during low temperature phase transformations in plutonium

International Nuclear Information System (INIS)

Khejpl, K.; Karpenter, S.

1988-01-01

To study the nature of phase transformations in plutonium and plutonium-gallium alloys (0.3 and 0.57% Ga) the measurement of acoustic emission is conducted. The presence of acoustic emission testifies to martensitic character of transformation, related to sharp local changes in the volume, which cause elastic waves. It is detected that during α reversible β transformations in non-alloyed plutonium acoustic emission is absent, and that testifies to nonmartensitic nature of the transformations. σ reversible α transformation in plutonium-gallium alloys is accompanied by the appearance of acoustic emission, i.e. it is of martensitic origin

Temperature-dependent Hall effect studies of ZnO thin films grown by metalorganic chemical vapour deposition

International Nuclear Information System (INIS)

Roro, K T; Dangbegnon, J K; Sivaraya, S; Westraadt, J E; Neethling, J H; Leitch, A W R; Botha, J R; Kassier, G H

2008-01-01

The electrical properties of zinc oxide (ZnO) thin films of various thicknesses (0.3–4.4 µm) grown by metalorganic chemical vapour deposition on glass substrates have been studied by using temperature-dependent Hall-effect (TDH) measurements in the 18–300 K range. The high quality of the layers has been confirmed with x-ray diffraction, transmission electron microscopy, scanning electron microscopy and photoluminescence techniques. TDH measurements indicate the presence of a degenerate layer which significantly influences the low-temperature data. It is found that the measured mobility generally increases with increasing layer thickness, reaching a value of 120 cm 2 V −1 s −1 at room temperature for the 4.4 µm thick sample. The lateral grain size of the layers is also found to increase with thickness indicating a clear correlation between the size of the surface grains and the electrical properties of corresponding films. Theoretical fits to the Hall data suggest that the bulk conduction of the layers is dominated by a weakly compensated donor with activation energy in the 33–41 meV range and concentration of the order of 10 17 cm −3 , as well as a total acceptor concentration of mid-10 15 cm −3 . Grain boundary scattering is found to be an important limiting factor of the mobility throughout the temperature range considered

Substrate temperature dependence of ZnTe epilayers grown on GaAs(0 0 1) by molecular beam epitaxy

Science.gov (United States)

Zhao, Jie; Zeng, Yiping; Liu, Chao; Li, Yanbo

2010-04-01

ZnTe thin films have been grown on GaAs(0 0 1) substrates at different temperatures with constant Zn and Te beam equivalent pressures (BEPs) by molecular beam epitaxy (MBE). In situ reflection high-energy electron diffraction (RHEED) observation indicates that two-dimensional (2D) growth mode can be established after around one-minute three-dimensional (3D) nucleation by increasing the substrate temperature to 340 °C. We found that Zn desorption from the ZnTe surface is much greater than that of Te at higher temperatures, and estimated the Zn sticking coefficient by the evolution of growth rate. The Zn sticking coefficient decreases from 0.93 to 0.58 as the temperature is elevated from 320 to 400 °C. The ZnTe epilayer grown at 360 °C displays the narrowest full-width at half-maximum (FWHM) of 660 arcsec from (0 0 4) reflection in double-crystal X-ray rocking curve (DCXRC) measurements. The surface morphology of ZnTe epilayers is strongly dependent on the substrate temperature, and the root-mean-square (RMS) roughness diminishes drastically with the increase in temperature.

Effect of etching stop layer on characteristics of amorphous IGZO thin film transistor fabricated at low temperature

Directory of Open Access Journals (Sweden)

Xifeng Li

2013-03-01

Full Text Available Transparent bottom-gate amorphous Indium-Gallium-Zinc Oxide (a-IGZO thin-film transistors (TFTs had been successfully fabricated at relative low temperature. The influence of reaction gas ratio of N2O and SiH4 during the growth of etching stop layer (SiOx on the characteristics of a-IGZO TFTs was investigated. The transfer characteristics of the TFTs were changed markedly because active layer of a-IGZO films was modified by plasma in the growth process of SiOx. By optimizing the deposition parameters of etching stop layer process, a-IGZO TFTs were manufactured and exhibited good performance with a field-effect mobility of 8.5 cm2V-1s-1, a threshold voltage of 1.3 V, and good stability under gate bias stress of 20 V for 10000 s.

Influence of deposition temperature on the structural and morphological properties of Be3N2 thin films grown by reactive laser ablation

International Nuclear Information System (INIS)

Chale-Lara, F.; Farias, M.H.; De la Cruz, W.; Zapata-Torres, M.

2010-01-01

Be 3 N 2 thin films have been grown on Si(1 1 1) substrates using the pulsed laser deposition method at different substrate temperatures: room temperature (RT), 200 deg. C, 400 deg. C, 600 deg. C and 700 deg. C. Additionally, two samples were deposited at RT and were annealed after deposition in situ at 600 deg. C and 700 deg. C. In order to obtain the stoichiometry of the samples, they have been characterized in situ by X-ray photoelectron (XPS) and reflection electron energy loss spectroscopy (REELS). The influence of the substrate temperature on the morphological and structural properties of the films was investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD). The results show that all prepared films presented the Be 3 N 2 stoichiometry. Formation of whiskers with diameters of 100-200 nm appears at the surface of the films prepared with a substrate temperature of 600 deg. C or 700 deg. C. However, the samples grown at RT and annealed at 600 deg. C or 700 deg. C do not show whiskers on the surface. The average root mean square (RMS) roughness and the average grain size of the samples grown with respect the substrate temperature is presented. The films grown with a substrate temperature between the room temperature to 400 deg. C, and the sample annealed in situ at 600 deg. C were amorphous; while the αBe 3 N 2 phase was presented on the samples with a substrate temperature of 600 deg. C, 700 deg. C and that deposited with the substrate at RT and annealed in situ at 700 deg. C.

Window structure for passivating solar cells based on gallium arsenide

Science.gov (United States)

Barnett, Allen M. (Inventor)

1985-01-01

Passivated gallium arsenide solar photovoltaic cells with high resistance to moisture and oxygen are provided by means of a gallium arsenide phosphide window graded through its thickness from arsenic rich to phosphorus rich.

Semi-quantitative evaluation of gallium-67 scintigraphy in lupus nephritis

Energy Technology Data Exchange (ETDEWEB)

Lin Wanyu [Dept. of Nuclear Medicine, Taichung Veterans General Hospital, Taichung (Taiwan); Dept. of Radiological Technology, Chung-Tai College of Medical Technology, Taichung (Taiwan); Hsieh Jihfang [Section of Nuclear Medicine, Chi-Mei Foundation Hospital, Yunk Kang City, Tainan (Taiwan); Tsai Shihchuan [Dept. of Nuclear Medicine, Show Chwan Memorial Hospital, Changhua (Taiwan); Lan Joungliang [Dept. of Internal Medicine, Taichung Veterans General Hospital, Taichung (Taiwan); Cheng Kaiyuan [Dept. of Radiological Technology, Chung-Tai College of Medical Technology, Taichung (Taiwan); Wang Shyhjen [Dept. of Nuclear Medicine, Taichung Veterans General Hospital, Taichung (Taiwan)

2000-11-01

Within nuclear medicine there is a trend towards quantitative analysis. Gallium renal scan has been reported to be useful in monitoring the disease activity of lupus nephritis. However, only visual interpretation using a four-grade scale has been performed in previous studies, and this method is not sensitive enough for follow-up. In this study, we developed a semi-quantitative method for gallium renal scintigraphy to find a potential parameter for the evaluation of lupus nephritis. Forty-eight patients with lupus nephritis underwent renal biopsy to determine World Health Organization classification, activity index (AI) and chronicity index (CI). A delayed 48-h gallium scan was also performed and interpreted by visual and semi-quantitative methods. For semi-quantitative analysis of the gallium uptake in both kidneys, regions of interest (ROIs) were drawn over both kidneys, the right forearm and the adjacent spine. The uptake ratios between these ROIs were calculated and expressed as the ''kidney/spine ratio (K/S ratio)'' or the ''kidney/arm ratio (K/A ratio)''. Spearman's rank correlation test and Mann-Whitney U test were used for statistical analysis. Our data showed a good correlation between the semi-quantitative gallium scan and the results of visual interpretation. K/S ratios showed a better correlation with AI than did K/A ratios. Furthermore, the left K/S ratio displayed a better correlation with AI than did the right K/S ratio. In contrast, CI did not correlate well with the results of semi-quantitative gallium scan. In conclusion, semi-quantitative gallium renal scan is easy to perform and shows a good correlation with the results of visual interpretation and renal biopsy. The left K/S ratio from semi-quantitative renal gallium scintigraphy displays the best correlation with AI and is a useful parameter in evaluating the disease activity in lupus nephritis. (orig.)

Gallium and copper radiopharmaceutical chemistry

International Nuclear Information System (INIS)

Green, M.A.; John, E.K.; Barnhart, A.J.

1990-01-01

Several isotopes of gallium and copper exhibit nuclear properties that make them attractive for applications in nuclear medicine, most notably Ga-67, Ga-68, Cu-67 and Cu-62. Of these, gamma-emitting Ga-67 has historically found the greatest clinical use, based on the observation that tracer gallium(III) citrate rapidly produces Ga-67 transferrin upon intravenous injection and then slowly affords selective Ga-67 localization in sites of abscess and certain tumors. Copper-67 has received attention as a potential label for tissue-selective monoclonal antibodies, since its associated γ-photons can be used for external imaging and its β - -emissions could be used for radiation therapy. Positron-emitting gallium-68 and copper-62, being available from parent/daughter generator systems, have attracted interest as potential labels for radiopharmaceuticals used in positron emission tomography (PET) because they could reduce the dependence of this imaging technology on hospital-based cyclotrons. The 10 min. half-life of Cu-62 is particularly well-suited to the time frame of PET studies of tissue perfusion, an application for which Cu(II)-bis(thiosemicarbazone) derivatives appear promising. The 68 min. half-life of Ga-68 makes it appropriate for PET studies over longer imaging time spans

Processing and electrical properties of gallium-substituted lead zirconate titanate ceramics

Energy Technology Data Exchange (ETDEWEB)

Hajra, Sugato; Sharma, Pulkit; Rout, P.K. [Siksha O Anusandhan University, Department of Electrical and Electronics Engineering, Bhubaneswar (India); Sahoo, Sushrisangita; Choudhary, R.N.P. [Siksha O Anusandhan University, Department of Physics, Bhubaneswar (India)

2017-12-15

In the present paper, the effect of gallium (Ga) substitution on structural, microstructural, electrical conductivity of Pb(ZrTi)O{sub 3} (PZT) in the morphotropic phase boundary (MPB) region (i.e., Pb{sub 0.96}Ga{sub 0.04}(Zr{sub 0.48}Ti{sub 0.52}){sub 0.99}O{sub 3} (PGaZT-4)) was investigated. Increased grain density increases the resistivity of the Ga-modified PZT system. Preliminary structural analysis using X-ray diffraction pattern and data showed the existence of two phases [major tetragonal (T) and minor monoclinic (M)]. Field emission scanning electron micrograph (FESEM) showed the distribution of spherical as well as platelet type grains with small pores. The behavior of dielectric constant with temperature of PGaZT-4 exhibited the suppression of the ferroelectric phase transition [i.e., disappearance of Curie temperature (T{sub c})]. The complex impedance spectroscopy (CIS) technique helped to investigate the impedance parameters of PGaZT-4 in MPB region in a wide range of temperature (250-500 C) and frequency (1-1000 kHz) region. The impedance parameters of the material are found to be strongly dependent on frequency of AC electric field and temperature. The substitution of gallium at the Pb site of PZT generally enhances the dielectric constant and decreases loss tangent. The AC conductivity vs frequency (f = ω2π) in the region of dispersion follows the universal response of Jonscher's equation. Enhanced resistive characteristics were observed for Ga-substituted PZT in comparison to the pure PZT, which was well ensured from the studies of electrical parameters, such as impedance and AC conductivity. (orig.)

Growth characteristics of (100)HgCdTe layers in low-temperature MOVPE with ditertiarybutyltelluride

Science.gov (United States)

Yasuda, K.; Hatano, H.; Ferid, T.; Minamide, M.; Maejima, T.; Kawamoto, K.

1996-09-01

Low-temperature growth of (100)HgCdTe (MCT) layers in MOVPE has been studied using ditertiarybutyltelluride (DtBTe), dimethylcadmium (DMCd), and elementary mercury as precursors. MCT layers were grown at 275°C on (100)GaAs substrates. Growths were carried out in a vertical growth cell which has a narrow spacing between the substrate and cell ceiling. Using the growth cell, the Cd-composition ( x) of MCT layers was controlled over a wide range from 0 to 0.98 by the DMCd flow. The growth rate of the MCT layers was constant at 5 μm h -1 for the increased DMCd flow. Preferential Cd-incorporation into MCT layers and an increase of the growth rate were observed in the presence of mercury vapor. The growth characteristics were considered to be due to the alkyl-exchange reaction between DMCd and mercury. The electrical properties and crystallinity of grown layers were also evaluated, which showed that layers with high quality can be grown at 275°C.

Sorption of trace amounts of gallium (III) on iron (III) oxide

International Nuclear Information System (INIS)

Music, S.; Gessner, M.; Wolf, R.H.H.

1979-01-01

The sorption of trace amounts of gallium(III) on iron(III) oxide has been studied as a function of pH. Optimum conditions have been found for the preconcentration of traces of gallium(III) by iron(III) oxide. The influence of surface active substances and of complexing agents on the sorption of trace amounts of gallium(III) on iron(III) oxide has been also studied. (orig.) [de

Sorption of trace amounts of gallium (III) on iron (III) oxide

Energy Technology Data Exchange (ETDEWEB)

Music, S; Gessner, M; Wolf, R H.H. [Institut Rudjer Boskovic, Zagreb (Yugoslavia)

1979-01-01

The sorption of trace amounts of gallium(III) on iron(III) oxide has been studied as a function of pH. Optimum conditions have been found for the preconcentration of traces of gallium(III) by iron(III) oxide. The influence of surface active substances and of complexing agents on the sorption of trace amounts of gallium(III) on iron(III) oxide has been also studied.

Multiple scaling power in liquid gallium under pressure conditions

Energy Technology Data Exchange (ETDEWEB)

Li, Renfeng; Wang, Luhong; Li, Liangliang; Yu, Tony; Zhao, Haiyan; Chapman, Karena W.; Rivers, Mark L.; Chupas, Peter J.; Mao, Ho-kwang; Liu, Haozhe

2017-06-01

Generally, a single scaling exponent, Df, can characterize the fractal structures of metallic glasses according to the scaling power law. However, when the scaling power law is applied to liquid gallium upon compression, the results show multiple scaling exponents and the values are beyond 3 within the first four coordination spheres in real space, indicating that the power law fails to describe the fractal feature in liquid gallium. The increase in the first coordination number with pressure leads to the fact that first coordination spheres at different pressures are not similar to each other in a geometrical sense. This multiple scaling power behavior is confined within a correlation length of ξ ≈ 14–15 Å at applied pressure according to decay of G(r) in liquid gallium. Beyond this length the liquid gallium system could roughly be viewed as homogeneous, as indicated by the scaling exponent, Ds, which is close to 3 beyond the first four coordination spheres.

Spray deposited gallium doped tin oxide thinfilm for acetone sensor application

Science.gov (United States)

Preethi, M. S.; Bharath, S. P.; Bangera, Kasturi V.

2018-04-01

Undoped and gallium doped (1 at.%, 2 at.% and 3 at.%) tin oxide thin films were prepared using spray pyrolysis technique by optimising the deposition conditions such as precursor concentration, substrate temperature and spraying rate. X-ray diffraction analysis revealed formation of tetragonally structured polycrystalline films. The SEM micrographs of Ga doped films showed microstructures. The electrical resistivity of the doped films was found to be more than that of the undoped films. The Ga-doped tin oxide thin films were characterised for gas sensors. 1 at.% Ga doped thin films were found to be better acetone gas sensor, showed 68% sensitivity at 350°C temperature.

Low-cost growth of magnesium doped gallium nitride thin films by sol-gel spin coating method

Science.gov (United States)

Amin, N. Mohd; Ng, S. S.

2018-01-01

Low-cost sol-gel spin coating growth of magnesium (Mg) doped gallium nitride (GaN) thin films with different concentrations of Mg was reported. The effects of the Mg concentration on the structural, surface morphology, elemental compositions, lattice vibrational, and electrical properties of the deposited films were investigated. X-ray diffraction results show that the Mg-doped samples have wurtzite structure with preferred orientation of GaN(002). The crystallite size decreases and the surface of the films with pits/pores were formed, while the crystalline quality of the films degraded as the Mg concentration increases from 2% to 6. %. All the Raman active phonon modes of the wurtzite GaN were observed while a broad peak attributed to the Mg-related lattice vibrational mode was detected at 669 cm-1. Hall effect results show that the resistivity of the thin films decreases while the hole concentration and hall mobility of thin films increases as the concentration of the Mg increases.

DETERMINATION OF VICKERS MICROHARDNESS IN β-Ga2O3 SINGLE CRYSTALS GROWN FROM THEIR OWN MELT

Directory of Open Access Journals (Sweden)

L. I. Guzilova

2015-05-01

Full Text Available The results of microhardness measurements of β-Ga2O3 single crystals for (001 crystallographic face are reported. The crystals were grown by the free crystallization with the "Garnet-2M" equipment. Microhardness values ​​ were determined by the Vickers method at varying loads. A four-sided diamond pyramid was used as an indenter. The average value of gallium oxide microhardness was equal to 8.91 GPa. We have carried out comparison of the values ​​obtained with the microhardness for the other wide bandgap semiconductors - epitaxial GaN layers grown on 6H-SiC and GaP layers grown on GaP:S. The findings are usable for machining process development of β-Ga2O3 single crystal substrates. In particular, silicon carbide and electrocorundum may be recommended for β-Ga2O3 machine processing.

Low to moderate temperature nanolaminate heater

Science.gov (United States)

Eckels, J Del [Livermore, CA; Nunes, Peter J [Danville, CA; Simpson, Randall L [Livermore, CA; Hau-Riege, Stefan [Fremont, CA; Walton, Chris [Oakland, CA; Carter, J Chance [Livermore, CA; Reynolds, John G [San Ramon, CA

2011-01-11

A low to moderate temperature heat source comprising a high temperature energy source modified to output low to moderate temperatures wherein the high temperature energy source modified to output low to moderate temperatures is positioned between two thin pieces to form a close contact sheath. In one embodiment the high temperature energy source modified to output low to moderate temperatures is a nanolaminate multilayer foil of reactive materials that produces a heating level of less than 200.degree. C.

Wave fronts, pulses and wave trains in photoexcited superlattices behaving as excitable or oscillatory media

International Nuclear Information System (INIS)

Arana, J I; Bonilla, L L; Grahn, H T

2011-01-01

Undoped and strongly photoexcited semiconductor superlattices with field-dependent recombination behave as excitable or oscillatory media with spatially discrete nonlinear convection and diffusion. Infinitely long, dc-current-biased superlattices behaving as excitable media exhibit wave fronts with increasing or decreasing profiles, whose velocities can be calculated by means of asymptotic methods. These superlattices can also support pulses of the electric field. Pulses moving downstream with the flux of electrons can be constructed from their component wave fronts, whereas pulses advancing upstream do so slowly and experience saltatory motion: they change slowly in long intervals of time separated by fast transitions during which the pulses jump to the previous superlattice period. Photoexcited superlattices can also behave as oscillatory media and exhibit wave trains. (paper)

Gallium scintigraphy in a case of septic cavernous sinus thrombosis

International Nuclear Information System (INIS)

Palestro, C.J.; Malat, J.; Gladstone, A.G.; Richman, A.H.

1986-01-01

Septic cavernous sinus thrombosis, a relatively uncommon disease entity, frequently can be fatal. Early diagnosis is imperative in order that appropriate treatment be instituted. A 59-year-old woman who was admitted to our institution with complaints of diplopia, blurred vision and fevers that developed following a tooth extraction is presented. Initial CT and lumbar puncture on the day of admission were totally normal. A repeat CT performed 48 hours after admission, on the same day as gallium imaging, demonstrated findings consistent with cavernous sinus thrombosis. Gallium imaging demonstrated intense uptake in the left cavernous sinus and left orbit as well as moderately increased activity in the right cavernous sinus and orbit, confirming infection. The patient was treated with antibiotics, and repeat CT and gallium imaging were performed ten days later, both of which demonstrated near total resolution of the disease process. Conceivably, if gallium imaging had been initiated on the day of admission it may have been the first study to demonstrate an infectious process in the cavernous sinus. Gallium imaging should be considered as a diagnostic tool in the noninvasive workup of this entity

Electron-phonon relaxation and excited electron distribution in gallium nitride

Energy Technology Data Exchange (ETDEWEB)

Zhukov, V. P. [Institute of Solid State Chemistry, Urals Branch of the Russian Academy of Sciences, Pervomayskaya st. 91, Yekaterinburg (Russian Federation); Donostia International Physics Center (DIPC), P. Manuel de Lardizabal 4, 20018 San Sebastian (Spain); Tyuterev, V. G., E-mail: valtyut00@mail.ru [Donostia International Physics Center (DIPC), P. Manuel de Lardizabal 4, 20018 San Sebastian (Spain); Tomsk State Pedagogical University, Kievskaya st. 60, Tomsk (Russian Federation); Tomsk State University, Lenin st. 36, Tomsk (Russian Federation); Chulkov, E. V. [Donostia International Physics Center (DIPC), P. Manuel de Lardizabal 4, 20018 San Sebastian (Spain); Tomsk State University, Lenin st. 36, Tomsk (Russian Federation); Departamento de Fisica de Materiales, Facultad de Ciencias Qumicas, UPV/EHU and Centro de Fisica de Materiales CFM-MPC and Centro Mixto CSIC-UPV/EHU, Apdo. 1072, 20080 San Sebastian (Spain); Echenique, P. M. [Donostia International Physics Center (DIPC), P. Manuel de Lardizabal 4, 20018 San Sebastian (Spain); Departamento de Fisica de Materiales, Facultad de Ciencias Qumicas, UPV/EHU and Centro de Fisica de Materiales CFM-MPC and Centro Mixto CSIC-UPV/EHU, Apdo. 1072, 20080 San Sebastian (Spain)

2016-08-28

We develop a theory of energy relaxation in semiconductors and insulators highly excited by the long-acting external irradiation. We derive the equation for the non-equilibrium distribution function of excited electrons. The solution for this function breaks up into the sum of two contributions. The low-energy contribution is concentrated in a narrow range near the bottom of the conduction band. It has the typical form of a Fermi distribution with an effective temperature and chemical potential. The effective temperature and chemical potential in this low-energy term are determined by the intensity of carriers' generation, the speed of electron-phonon relaxation, rates of inter-band recombination, and electron capture on the defects. In addition, there is a substantial high-energy correction. This high-energy “tail” largely covers the conduction band. The shape of the high-energy “tail” strongly depends on the rate of electron-phonon relaxation but does not depend on the rates of recombination and trapping. We apply the theory to the calculation of a non-equilibrium distribution of electrons in an irradiated GaN. Probabilities of optical excitations from the valence to conduction band and electron-phonon coupling probabilities in GaN were calculated by the density functional perturbation theory. Our calculation of both parts of distribution function in gallium nitride shows that when the speed of the electron-phonon scattering is comparable with the rate of recombination and trapping then the contribution of the non-Fermi “tail” is comparable with that of the low-energy Fermi-like component. So the high-energy contribution can essentially affect the charge transport in the irradiated and highly doped semiconductors.

Realization of the Gallium Triple Point at NMIJ/AIST

Science.gov (United States)

Nakano, T.; Tamura, O.; Sakurai, H.

2008-02-01

The triple point of gallium has been realized by a calorimetric method using capsule-type standard platinum resistance thermometers (CSPRTs) and a small glass cell containing about 97 mmol (6.8 g) of gallium with a nominal purity of 99.99999%. The melting curve shows a very flat and relatively linear dependence on 1/ F in the region from 1/ F = 1 to 1/ F = 20 with a narrow width of the melting curve within 0.1 mK. Also, a large gallium triple-point cell was fabricated for the calibration of client-owned CSPRTs. The gallium triple-point cell consists of a PTFE crucible and a PTFE cap with a re-entrant well and a small vent. The PTFE cell contains 780 g of gallium from the same source as used for the small glass cell. The PTFE cell is completely covered by a stainless-steel jacket with a valve to enable evacuation of the cell. The melting curve of the large cell shows a flat plateau that remains within 0.03 mK over 10 days and that is reproducible within 0.05 mK over 8 months. The calibrated value of a CSPRT obtained using the large cell agrees with that obtained using the small glass cell within the uncertainties of the calibrations.

Photodetectors based on carbon nanotubes deposited by using a spray technique on semi-insulating gallium arsenide

Directory of Open Access Journals (Sweden)

Domenico Melisi

2014-11-01

Full Text Available In this paper, a spray technique is used to perform low temperature deposition of multi-wall carbon nanotubes on semi-insulating gallium arsenide in order to obtain photodectors. A dispersion of nanotube powder in non-polar 1,2-dichloroethane is used as starting material. The morphological properties of the deposited films has been analysed by means of electron microscopy, in scanning and transmission mode. Detectors with different layouts have been prepared and current–voltage characteristics have been recorded in the dark and under irradiation with light in the range from ultraviolet to near infrared. The device spectral efficiency obtained from the electrical characterization is finally reported and an improvement of the photodetector behavior due to the nanotubes is presented and discussed.

Organometallic model complexes elucidate the active gallium species in alkane dehydrogenation catalysts based on ligand effects in Ga K-edge XANES

Energy Technology Data Exchange (ETDEWEB)

Getsoian, Andrew “Bean”; Das, Ujjal; Camacho-Bunquin, Jeffrey; Zhang, Guanghui; Gallagher, James R.; Hu, Bo; Cheah, Singfoong; Schaidle, Joshua A.; Ruddy, Daniel A.; Hensley, Jesse E.; Krause, Theodore R.; Curtiss, Larry A.; Miller, Jeffrey T.; Hock, Adam S.

2016-01-01

Gallium-modified zeolites are known catalysts for the dehydrogenation of alkanes, reactivity that finds industrial application in the aromatization of light alkanes by Ga-ZSM5. While the role of gallium cations in alkane activation is well known, the oxidation state and coordination environment of gallium under reaction conditions has been the subject of debate. Edge shifts in Ga K-edge XANES spectra acquired under reaction conditions have long been interpreted as evidence for reduction of Ga(III) to Ga(I). However, a change in oxidation state is not the only factor that can give rise to a change in the XANES spectrum. In order to better understand the XANES spectra of working catalysts, we have synthesized a series of molecular model compounds and grafted surface organometallic Ga species and compared their XANES spectra to those of gallium-based catalysts acquired under reducing conditions. We demonstrate that changes in the identity and number of gallium nearest neighbors can give rise to changes in XANES spectra similar to those attributed in literature to changes in oxidation state. Specifically, spectral features previously attributed to Ga(I) may be equally well interpreted as evidence for low-coordinate Ga(III) alkyl or hydride species. These findings apply both to gallium-impregnated zeolite catalysts and to silica-supported single site gallium catalysts, the latter of which is found to be active and selective for dehydrogenation of propane and hydrogenation of propylene.

Gallium scan in recurrent Hodgkin's disease in children

International Nuclear Information System (INIS)

Yeh, S.D.; Benua, R.S.; Tan, C.T.

1979-01-01

In 18 of 88 children with biopsy proven and previously untreated Hodgkin's disease, recurrence developed during a period from four to 53 months after therapy (median period, 22 months). In 16 patients in whom gallium scans were performed, 21 positive gallium scans were obtained during 26 episodes of recurrence. Abnormalities were noted in half of them during a period from one to 10 months prior to physical, laboratory, radiographic or histologic confirmation of recurrence (median period about 5 months). We have concluded that the gallium scan is very useful in initial workup and is sensitive in detecting early recurrence in children with Hodgkin's disease. Such scans are indicated when there is clinical suspicion of recurrence, when other modalities are unavailable or when the results of other studies are equivocal

Cutaneous gallium uptake in patients with AIDS with mycobacterium avium-intracellulare septicemia

International Nuclear Information System (INIS)

Allwright, S.J.; Chapman, P.R.; Antico, V.F.; Gruenewald, S.M.

1988-01-01

Gallium imaging is increasingly being used for the early detection of complications in patients with AIDS. A 26-year-old homosexual man who was HIV antibody positive underwent gallium imaging for investigation of possible Pneumocystis carinii pneumonia. Widespread cutaneous focal uptake was seen, which was subsequently shown to be due to mycobacterium avium-intracellulare (MAI) septicemia. This case demonstrates the importance of whole body imaging rather than imaging target areas only, the utility of gallium imaging in aiding the early detection of clinically unsuspected disease, and shows a new pattern of gallium uptake in disseminated MAI infection

Dynamic correlation of photo-excited electrons: Anomalous levels induced by light–matter coupling

Energy Technology Data Exchange (ETDEWEB)

Jiang, Xiankai [Shanghai Institute of Applied Physics, Chinese Academy of Sciences, P.O. Box 800-204, Shanghai 201800 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Huai, Ping, E-mail: huaiping@sinap.ac.cn [Shanghai Institute of Applied Physics, Chinese Academy of Sciences, P.O. Box 800-204, Shanghai 201800 (China); Song, Bo, E-mail: bosong@sinap.ac.cn [Shanghai Institute of Applied Physics, Chinese Academy of Sciences, P.O. Box 800-204, Shanghai 201800 (China)

2014-04-01

Nonlinear light–matter coupling plays an important role in many aspects of modern physics, such as spectroscopy, photo-induced phase transition, light-based devices, light-harvesting systems, light-directed reactions and bio-detection. However, excited states of electrons are still unclear for nano-structures and molecules in a light field. Our studies unexpectedly present that light can induce anomalous levels in the electronic structure of a donor–acceptor nanostructure with the help of the photo-excited electrons transferring dynamically between the donor and the acceptor. Furthermore, the physics underlying is revealed to be the photo-induced dynamical spin–flip correlation among electrons. These anomalous levels can significantly enhance the electron current through the nanostructure. These findings are expected to contribute greatly to the understanding of the photo-excited electrons with dynamic correlations, which provides a push to the development and application of techniques based on photosensitive molecules and nanostructures, such as light-triggered molecular devices, spectroscopic analysis, bio-molecule detection, and systems for solar energy conversion.

Taking snapshots of photoexcited molecules in disordered media using pulsed synchrotron x-rays

International Nuclear Information System (INIS)

Chen, L.X.

2004-01-01

Photoexcited molecules are quintessential reactants in photochemistry. Structures of these photoexcited molecules in disordered media in which a majority of photochemical reactions take place remained elusive for decades owing to a lack of suitable X-ray sources, despite their importance in understanding fundamental aspects in photochemistry. As new pulsed X-ray sources become available, short-lived excited-state molecular structures in disordered media can now be captured by using laser-pulse pump, X-ray pulse-probe techniques of third-generation synchrotron sources with time resolutions of 30-100 ps, as demonstrated by examples in this review. These studies provide unprecedented information on structural origins of molecular properties in the excited states. By using other ultrafast X-ray facilities that will be completed in the near future, time-resolution for the excited-state structure measurements should reach the femtosecond timescales, which will make 'molecular movies' of bond breaking or formation, and vibrational relaxation, a reality.

Mechanisms of thermal induced gallium removal (TIGR) from plutonium dioxide. Revision 1

International Nuclear Information System (INIS)

DeMuth, S.F.

1998-01-01

This study was initiated in order to determine the advantages of using a mixed-bed rather than a fixed-bed reactor (i.e. furnace) for separation of gallium from PuO 2 by the Thermal Induced Gallium Removal (TIGR) process. The TIGR process is based upon vaporization of gallium suboxide (Ga 2 O). from essentially nonvolatile PuO 2 . The gallium suboxide is formed by passing a reducing gas (i.e. hydrogen) over the PuO 2 particles. Several mechanisms are involved in the reduction and convective vaporization of the gallium suboxide. If the mass transfer of the gallium suboxide across the solid to gas interface significantly affects the processing time, it may be advantageous to use a mixed-bed reactor rather than a fixed-bed reactor. However, due to the difficulty of handling PuO 2 powder, a mixed-bed reactor should be used only if significant advantages can be demonstrated. Based on available data, the results of this study provide strong evidence that a mixed-bed reactor (i.e. furnace) would provide little advantage over a fixed-bed reactor. This is due to the conclusion that the mechanism of internal gallium diffusion within the particle has the predominant affect on the processing time. This is an important conclusion since the use of a mixed-bed would require development of more complex hardware than for a fixed-bed

Electrical and optoelectronic properties of gallium nitride

International Nuclear Information System (INIS)

Flannery, Lorraine Barbara

2002-01-01

This thesis describes novel research carried out on two related topics, the electrical properties of n and p-type GaN and the use of GaN in the fabrication of UV photodetectors. The electrical properties of GaN were assessed mainly by Hall effect measurements, which play a crucial role in the determination of the concentration of shallow electrically active impurities and defects. Most of the Hall effect measurements were carried out on Si and unintentionally doped GaN layers grown on sapphire substrates using a Varian Modular Gen II MBE machine equipped with an Oxford Applied Research CARS25 RF or HD25 RF nitrogen source to supply the active nitrogen. It was necessary to consider parallel conduction in two channels to interpret the temperature dependent Hall effect characteristics of the highest purity layers. Parallel conduction was found to influence the transport properties of these layers even at room temperature and give rise to an increased compensation ratio. The impurity band was found to be located at 23 ± 7 meV below the conduction band in layers containing impurity densities less than 3.8 x 10 18 cm -3 but was found to broaden with increasing impurity content, reducing the activation energy to 5 ± 3 meV in layers containing impurity densities greater than ∼4.5 x 10 18 cm -3 . Doping studies were conducted on Mg doped GaN layers grown on sapphire substrates using the MBE and MOVPE growth techniques. The effect of the growth parameters on Mg incorporation was determined using SIMS and Hall effect measurements for the MBE samples sets. P-type conductivity was successfully demonstrated in Mg doped layers grown under nitrogen rich conditions with layer thickness greater than 0.9 μm using the CARS25 RF source. The highest hole density, p H and mobility, μ H of 9.6 x 10 17 cm -3 and 5.4 cm 2 V -1 s -1 respectively were recorded in the thickest layer grown (1.56 μm). P-type doping studies were also carried out on Mg doped GaN layers grown on GaAs (111)B

Evolution of low-temperature phases in a low-temperature structural transition of a La cuprate

International Nuclear Information System (INIS)

Inoue, Y.; Horibe, Y.; Koyama, Y.

1997-01-01

The microstructure produced by a low-temperature structural phase transition in La 1.5 Nd 0.4 Sr 0.1 CuO 4 has been examined by transmission electron microscopy with the help of imaging plates. The low-temperature transition was found to be proceeded not only by the growth of the Pccn/low-temperature-tetragonal phases nucleated along the twin boundary but also by the nucleation and growth of the phases in the interior of the low-temperature-orthorhombic domain. In addition, because the map of the octahedron tilt as an order parameter is not identical to that of the spontaneous strain accompanied by the transition, the microstructure below the transition is understood to be a very complex mixture of the low-temperature phases. copyright 1997 The American Physical Society

VLS-grown diffusion doped ZnO nanowires and their luminescence properties

International Nuclear Information System (INIS)

Roy, Pushan Guha; Dutta, Amartya; Das, Arpita; Bhattacharyya, Anirban; Sen, Sayantani; Pramanik, Pallabi

2015-01-01

Zinc Oxide (ZnO) nanowires were deposited by vapor–liquid–solid (VLS) method on to aluminum doped ZnO (AZO) thin films grown by sol-gel technique. For various device applications, current injection into such nanowires is critical. This is expected to be more efficient for ZnO nanowires deposited on to AZO compared to those deposited on to a foreign substrate such as silicon. In this work we compare the morphological and optical properties of nanowires grown on AZO with those grown under similar conditions on silicon (Si) wafers. For nanowires grown on silicon, diameters around 44 nm with heights around 2.2 μm were obtained. For the growth on to AZO, the diameters were around 90 nm while the heights were around 520 nm. Room temperature photoluminescence (RT-PL) measurements show improved near band-edge emission for nanowires grown on to AZO, indicating higher material quality. This is further established by low temperature photoluminescence (LT-PL) measurements where excitonic transitions with width as small as 14 meV have been obtained at 4 K for such structures. Electron energy loss spectroscopy (EELS) studies indicate the presence of Al in the nanowires, indicating a new technique for introduction of dopants into these structures. These results indicate that ZnO nanowires on sol-gel grown AZO thin films show promise in the development of various optoelectronic devices. (paper)

Targeting Gallium to Cancer Cells through the Folate Receptor

Directory of Open Access Journals (Sweden)

Nerissa Viola-Villegas

2008-01-01

Full Text Available The development of gallium(III compounds as anti-cancer agents for both treatment and diagnosis is a rapidly developing field of research. Problems remain in exploring the full potential of gallium(III as a safe and successful therapeutic agent or as an imaging agent. One of the major issues is that gallium(III compounds have little tropism for cancer cells. We have combined the targeting properties of folic acid (FA with long chain liquid polymer poly(ethylene glycol (PEG 'spacers’. This FA-PEG unit has been coupled to the gallium coordination complex of 1,4,7,10-tetraazacyclo-dodecane-N, N′, N′, N′′-tetraacetic acid (DOTA through amide linkages for delivery into target cells overexpressing the folate receptor (FR. In vitro cytotoxicity assays were conducted against a multi-drug resistant ovarian cell line (A2780/AD that overexpresses the FR and contrasted against a FR free Chinese hamster ovary (CHO cell line. Results are rationalized taking into account stability studies conducted in RPMI 1640 media and HEPES buffer at pH 7.4.

Targeting Gallium to Cancer Cells through the Folate Receptor

Directory of Open Access Journals (Sweden)

Nerissa Viola-Villegas

2008-01-01

Full Text Available The development of gallium(III compounds as anti-cancer agents for both treatment and diagnosis is a rapidly developing field of research. Problems remain in exploring the full potential of gallium(III as a safe and successful therapeutic agent or as an imaging agent. One of the major issues is that gallium(III compounds have little tropism for cancer cells. We have combined the targeting properties of folic acid (FA with long chain liquid polymer poly(ethylene glycol (PEG ‘spacers’. This FA-PEG unit has been coupled to the gallium coordination complex of 1,4,7,10-tetraazacyclo-dodecane-N,N′,N′′,N′′′-tetraacetic acid (DOTA through amide linkages for delivery into target cells overexpressing the folate receptor (FR. In vitro cytotoxicity assays were conducted against a multi-drug resistant ovarian cell line (A2780/AD that overexpresses the FR and contrasted against a FR free Chinese hamster ovary (CHO cell line. Results are rationalized taking into account stability studies conducted in RPMI 1640 media and HEPES buffer at pH 7.4.

F-doped SnO2 thin films grown on flexible substrates at low temperatures by pulsed laser deposition

International Nuclear Information System (INIS)

Kim, H.; Auyeung, R.C.Y.; Pique, A.

2011-01-01

Fluorine-doped tin oxide (SnO 2 :F) films were deposited on polyethersulfone plastic substrates by pulsed laser deposition. The electrical and optical properties of the SnO 2 :F films were investigated as a function of deposition conditions such as substrate temperature and oxygen partial pressure during deposition. High quality SnO 2 :F films were achieved under an optimum oxygen pressure range (7.4-8 Pa) at relatively low growth temperatures (25-150 deg. C). As-deposited films exhibited low electrical resistivities of 1-7 mΩ-cm, high optical transmittance of 80-90% in the visible range, and optical band-gap energies of 3.87-3.96 eV. Atomic force microscopy measurements revealed a reduced root mean square surface roughness of the SnO 2 :F films compared to that of the bare substrates indicating planarization of the underlying substrate.

Elastic properties of crystalline and liquid gallium at high pressures

Science.gov (United States)

Lyapin, A. G.; Gromnitskaya, E. L.; Yagafarov, O. F.; Stal'Gorova, O. V.; Brazhkin, V. V.

2008-11-01

isobaric dependences G( T) with increasing temperature, are revealed in the vicinity of the melting curve. The bulk modulus of liquid gallium near the melting curve proves to be rather close to the corresponding values for the normal metal Ga II.

Elastic properties of crystalline and liquid gallium at high pressures

International Nuclear Information System (INIS)

Lyapin, A. G.; Gromnitskaya, E. L.; Yagafarov, O. F.; Stal'gorova, O. V.; Brazhkin, V. V.

2008-01-01

dependences G(T) with increasing temperature, are revealed in the vicinity of the melting curve. The bulk modulus of liquid gallium near the melting curve proves to be rather close to the corresponding values for the normal metal Ga II

Low-temperature epitaxy of silicon by electron beam evaporation

Energy Technology Data Exchange (ETDEWEB)

Gorka, B. [Hahn-Meitner-Institut Berlin, Kekulestr. 5, 12489 Berlin (Germany); Dogan, P. [Hahn-Meitner-Institut Berlin, Kekulestr. 5, 12489 Berlin (Germany)], E-mail: pinar.dogan@hmi.de; Sieber, I.; Fenske, F.; Gall, S. [Hahn-Meitner-Institut Berlin, Kekulestr. 5, 12489 Berlin (Germany)

2007-07-16

In this paper we report on homoepitaxial growth of thin Si films at substrate temperatures T{sub s} = 500-650 deg. C under non-ultra-high vacuum conditions by using electron beam evaporation. Si films were grown at high deposition rates on monocrystalline Si wafers with (100), (110) and (111) orientations. The ultra-violet visible reflectance spectra of the films show a dependence on T{sub s} and on the substrate orientation. To determine the structural quality of the films in more detail Secco etch experiments were carried out. No etch pits were found on the films grown on (100) oriented wafers. However, on films grown on (110) and (111) oriented wafers different types of etch pits could be detected. Films were also grown on polycrystalline silicon (poly-Si) seed layers prepared by an Aluminum-Induced Crystallisation (AIC) process on glass substrates. Electron Backscattering Diffraction (EBSD) shows that the film growth proceeds epitaxially on the grains of the seed layer. But a considerably higher density of extended defects is revealed by Secco etch experiments.

Comparative PL study of individual ZnO nanorods, grown by APMOCVD and CBD techniques

Energy Technology Data Exchange (ETDEWEB)

Khranovskyy, Volodymyr, E-mail: volkh@ifm.liu.se [Department of Physics, Chemistry and Biology (IFM), Linkoeping University, 58183 Linkoeping (Sweden); Yakimova, Rositza; Karlsson, Fredrik; Syed, Abdul S.; Holtz, Per-Olof [Department of Physics, Chemistry and Biology (IFM), Linkoeping University, 58183 Linkoeping (Sweden); Nigussa Urgessa, Zelalem [Department of Physics, P.O Box 77000, Nelson Mandela Metropolitan University, Port Elizabeth 6031 (South Africa); Samuel Oluwafemi, Oluwatobi [Department of Chemistry and Chemical Technology, Walter Sisulu University, Mthatha Campus, Private Bag XI 5117 (South Africa); Reinhardt Botha, Johannes [Department of Physics, P.O Box 77000, Nelson Mandela Metropolitan University, Port Elizabeth 6031 (South Africa)

2012-05-15

The photoluminescence properties of individual ZnO nanorods, grown by atmospheric pressure metalorganic chemical vapor deposition (APMOCV) and chemical bath deposition (CBD) are investigated by means of temperature dependent micro-PL. It was found that the low temperature PL spectra are driven by neutral donor bound exciton emission D{sup 0}X, peaked at 3.359 and 3.363 eV for APMOCVD and CBD ZnO nanorods, respectively. The temperature increase causes a red energy shift of the peaks and enhancement of the free excitonic emission (FX). The FX was found to dominate after 150 K for both samples. It was observed that while APMOCVD ZnO nanorods possess a constant low signal of visible deep level emission with temperature, the ZnO nanorods grown by CBD revealed the thermal activation of deep level emission (DLE) after 130 K. The resulting room temperature DLE was a wide band located at 420-550 nm. The PL properties of individual ZnO nanorods can be of importance for their forthcoming application in future optoelectronics and photonics.

Comparative PL study of individual ZnO nanorods, grown by APMOCVD and CBD techniques

International Nuclear Information System (INIS)

Khranovskyy, Volodymyr; Yakimova, Rositza; Karlsson, Fredrik; Syed, Abdul S.; Holtz, Per-Olof; Nigussa Urgessa, Zelalem; Samuel Oluwafemi, Oluwatobi; Reinhardt Botha, Johannes

2012-01-01

The photoluminescence properties of individual ZnO nanorods, grown by atmospheric pressure metalorganic chemical vapor deposition (APMOCV) and chemical bath deposition (CBD) are investigated by means of temperature dependent micro-PL. It was found that the low temperature PL spectra are driven by neutral donor bound exciton emission D 0 X, peaked at 3.359 and 3.363 eV for APMOCVD and CBD ZnO nanorods, respectively. The temperature increase causes a red energy shift of the peaks and enhancement of the free excitonic emission (FX). The FX was found to dominate after 150 K for both samples. It was observed that while APMOCVD ZnO nanorods possess a constant low signal of visible deep level emission with temperature, the ZnO nanorods grown by CBD revealed the thermal activation of deep level emission (DLE) after 130 K. The resulting room temperature DLE was a wide band located at 420–550 nm. The PL properties of individual ZnO nanorods can be of importance for their forthcoming application in future optoelectronics and photonics.

Low-temperature liquid-phase epitaxy and optical waveguiding of rare-earth-ion-doped KY(WO4)2 thin layers

NARCIS (Netherlands)

Romanyuk, Y.E.; Utke, I.; Ehrentraut, D.; Apostolopoulos, V.; Pollnau, Markus; Garcia-Revilla, S.; Valiente, B.

2004-01-01

Crystalline $KY(WO_{4})_{2}$ thin layers doped with different rare-earth ions were grown on b-oriented, undoped $KY(WO_{4})_{2}$ substrates by liquid-phase epitaxy employing a low-temperature flux. The ternary chloride mixture of NaCl, KCl, and CsCl with a melting point of 480°C was used as a