bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis of Sulfated Pt/ZrO2 Catalysts Using Different Precipitants for n-Hexane Hydroisomerization
Authors: Yu Guo-Xian , Panl Wei , Zhou Xiao-Long , Chen Li-Fang , Wang Jin-An 
Published: April 2011

AbstractAmmonia (AOH), dimethylamine (DME) and triethanolamine (TEA) as precipitants were used to prepare Pt-SO42-/ZrO2 catalysts, and the crystalline structures, textural structures and surface acid properties of the catalyst samples were characterized and n-hexane hydroisomerization activity over the samples were investigated. DME and TEA as the precipitants would delay the crystallization process. The organic amines were difficult to remove during the washing process, leading to the rinsing times increase, which probably decreased the catalyst BET area. Super Lewis acid sites in SZ catalysts would play very important roles in catalytic hydroisomerization activity.
Utilization of Solar Energy and Atmospheric Oxygen in the Photodregradation of Diesel in Water by Cu/TiO2 Catalysts
Authors: Manriquez Ma. , Corro Grisel , Hernandez J. Gonzalo 
Published: April 2011

AbstractPhotocatalytic destruction of the water soluble diesel fraction (WSF) was performed using Cu/TiO2 catalysts. Inexpensive and clean solar light and atmospheric oxygen were used as the energy source and oxidant, respectively. We investigated the effect of Cu species on the formation of a doping energy level between the conduction and valence band in TiO2. Photocatalytic reactions were investigated by monitoring the evolution of WSF as a function oftime of solar irradiation by UV-vis and FTIR spectroscopic techniques. The photocatalytic process in the presence of 5%Cu/TiO2 catalyst, is shown to be quantitatively efficient in the destruction of the water-soluble diesel fraction. The total destruction of water-soluble compounds originating from diesel residues indicates that photocatalysis can be employed for WSF treatment.
Hydrogen Production by Steam Reforming of Methanol over New Ag-Au(1-D)-CeO2 Catalyst
Authors: Pérez-Hernández R. , Gutiérrez-Martínez A. , Gutiérrez-Wing C. 
Published: April 2011

AbstractA Ag-Au(1-D)-CeO2 catalyst was prepared by precipitation method using Ag-Au nanowires and Ce(NO3)3·6H2O as precursors. The catalytic activity of the catalysts was evaluated in a steam reforming of methanol (SRM) reaction from 250 to 475 °C. 100 % of methanol conversion was observed at 450 °C together with high H2 selectivity. This study evidenced that the use of 1-D metallic nanostructures could be used as an active phase on a CeO2 matrix for steam reforming of methanol for H2 generation to be used as fuel.
Synthesis of Acetone and Acetaldehyde from Propane-Butane Mixture
Authors: Dossumov Kusman. , Tungatarova Svetlana. A. 
Published: April 2011

AbstractSupported polyoxide catalysts on the base of Mo and W, as well as natural Kazakhstan's clays were tested in the process of oxidative conversion of propane and propane-butane mixture. The influence of reaction temperature, contact time, composition and percentage of the active component of catalyst were determined. The important petrochemical products - acetone (500-550°) and acetaldehyde (300-350°) were the main liquid products of reaction on natural Kazakhstan's clays and also on clays modified by Mo, Bi, Cr and Ga ions.
HgCdTe Surface Cleanup and Etch Using a Remote Hydrogen Plasma
Authors: Smith Patricia B. 
Published: April 2011

AbstractDry passivation of HgCdTe with ZnS or CdTe using physical or chemical vapor deposition can be improved by incorporating an in situ plasma cleanup of the HgCdTe surface prior to the deposition. Contamination at the HgCdTe/ dielectric interface from ambient oxide and hydrocarbon residues may lead to fixed charge in capacitor or diode device structures. In addition, the oxides of HgCdTe are known to be thermally unstable. Removal of the surface contamination layer is advantageous for producing a consistent and electrically reliable interface. We describe the interaction of a remotely generated H2 or H2/Ar plasma (2.45 GHz, 600W) with HgCdTe, using ex-situ and in-situ ellipsometry, and atomic force microscopy. This work represents the first effort to characterize a low damage HgCdTe surface cleanup process which is compatible with vacuum in-situ passivation.
The Growth Of High-Quality MCT Films by MBE Using in Situ Ellipsometry
Authors: Svitashev K.K. , Dvorwetsky S.A. , Shvets V.A. , Mardezhov A.S. , Sidoroy YU.G. , Nis I.E. , Varavin V.S. , Liberman V. , Remesnik V. G. 
Published: April 2011

AbstractThe ellipsometry and RHEED study of MCT grown on (112) CdTe and GaAs by MBE was carried out. The dependence of ellipsometric parameter on composition is evaluated. As shown we can measure the growth rate, the roughness changing, initial temperature and composition by ellipsometry in situ. We investigated the evolution of roughness of film surface. We observed the appearance of surface roughness at initial stage of MCT growth under various composition (XcdTe0÷0.4). The following growth in optimal growth condition (including constancy of substrate temperature) gives us the smoothing of the surface and supplies us the high-quality MCT films. It is found that under constant temperature of substrate heater we can not grow the thick, perfect film of MCT. The concentration, mobility and life time of carriers in MCT films were respectively: n=1.8*1014 ÷8.2*1015cm−3, μn=44000÷370000cm2 V−1 s−1, τ=40÷220ns;p=1.8*1015÷8.4*1015 cm−3, μp=215÷284 cm2V−1 s−1 τ=12÷20ns.
Differentially Strained P-Doped Quantum well Infrared Photodetector
Authors: Kuroda R.T. , Garmire E. 
Published: April 2011

AbstractIn this paper, we discuss a differentially strained p-doped quantum well infrared photodetector that achieves high performance specifications. We examine key device specifications for a 9 and 18 μm infrared detector. We calculate that through differential strain, these novel detectors have improved gain and substantially reduced dark current over previous quantum well infrared photodetectors, while being able to detect normal incident light.
Progress in Cd1−xZnxTe (CZT) Radiation Detectors
Authors: Butler J. F. , Doty F. P. , Apotovsky B. , Friesenhahn S. J. , Lingren C. 
Published: April 2011

AbstractResults of a program to improve the performance of Cd1−xZnxTe detectors by adjusting growth parameters to achieve low-strain, high purity low defect crystals, investigating surface effect phenomena and contacting methods, and establishing reproducible manufacturing methods are reviewed and discussed. Processing and fabrication methods were developed which are applicable throughout the composition range. Energy spectra for room temperature Cd1−xZnxTe detectors exhibit resolutions (FWHM) from 2.16 keV at 14 keV to 6.9 keV at 122 keV. An energy resolution of 910 eV at 5.9 keV was achieved at −25 C. Stable ohmic contacts and gamma ray detection for ZnTe are reported for the first time. Applications of Cd1−xZnxTe to nuclear medicine and X-ray fluorescence are discussed. New gamma ray imagers using Cd1-−ZnxTe detector arrays are described, and imaging data for a 32 × 32 monolithic array of 1 mm2 elements on a 42mm × 42mm substrate are presented.
Characterization of Doped GexSi1−x Multiple Quantum well Structures for far- IR Detectors
Authors: Greve D. W. , Misra R. , Strong R. , Schlesinger T.E. 
Published: April 2011

AbstractDoped GexSi1−x/Si multiple quantum well structures have been grown by UHV/CVD and characterized by various techniques. SIMS and X- ray confirm the intended modulation of germanium and boron concentrations, and photoluminescence has been used to assess material quality. Strong free- carrier absorption has been observed at normal incidence in some samples. The results suggest that doping intermediate between 4 × 1018 cm−3 and 4 × 1019 cm−3 is necessary for useful detectors.
Undoped Lec GaAs as an Infrared Bolometer Detector
Authors: Estill S , Brozel M. R. 
Published: April 2011

AbstractUndoped LEC GaAs grown with very low residual acceptor concentration is often low resistivity with an activation energy for conduction of 0.43 eV. We demonstrate that this material can form a very sensitive bolometer element and show how large two dimensional bolometer arrays might be fabricated from this material.
Growth of MBE-Codeposited IrSi3 on Si(111) and Si(100)
Authors: Gibson Gary A. , Lange Davis A. , Falco Charles M. 
Published: April 2011

AbstractWe have used Molecular Beam Epitaxy (MBE) to successfully grow films that are predominantly IrSi3 on both Si(111) and Si(100) substrates by codeposition of Si and Ir in a 3:1 ratio. Bragg-Brentano and Seemann-Bohlin x-ray diffraction reveal that polycrystalline IrSi3 films form as low as 450 °C. This is the lowest temperature yet reported for growth of this iridium silicide phase. These x-ray diffraction techniques, along with Transmission Electron Microscope (TEM) diffraction and in situ Low Energy Electron Diffraction (LEED), show that at higher deposition temperatures codeposition can form IrSi3 films on Si(111) that consist predominantly of a single epitaxial growth orientation. Ion beam channeling and x-ray rocking curves show that the epitaxial quality of IrSi3 films deposited on Si(111) is superior to that of IrSi3 films deposited on Si(100). We also present evidence for several new epitaxial IrSi3 growth modes on Si(111) and Si(100).
Low Temperature Pl Characterization of Lpee Grown GaSb and GaInAsSb Epilayers
Authors: Iyer S. , Hegde S. , Bajaj K.K. , Abul-Fadl Ali , Mitchel W. 
Published: April 2011

AbstractWe have investigated the low temperature (4.5 K) photoluminescence (PL) spectra of GaSb and GaInAsSb layers. The layers were grown by liquid phase electro-epitaxial (LPEE) technique. Several bound excitomc transitions were observed both in GaSb and GaInAsSb layers. Shift in the PL peak energy corresponding to the band to band transition with temperature was determined. The linear part of the shift above 100K, exhibited a slope of -0.3 meV/K.
The Burstein-Moss Shift in Quantum Confined Infrared Materials
Authors: Ghatak Kamakeya P. , De Badal 
Published: April 2011

AbstractIn this paper we have investigated the Burstein-Moss shift in quantum wires and dots of III-V and II-VI materials on the basis of Kane and Hopfield models for the appropriate carrier dispersion laws. It is found taking Hg1−xCdxTe, In1−xGax AsyP1−y lattice matched to InP and CdS as examples that the Burstein-Moss shift exhibits oscillatory dependences for quantum wires and dots of the said materials with respect to doping and film thickness respectively. Besides, the numerical value of the same shift is greatest in quantum dots and least in quantum wires. In addition, the theoretical analysis is in agreement with the experimental datas as given elsewhere.
Extending HgCdTe Photovoltaic Detector Technology to Cutoff Wavelengths of 17 μm
Authors: Krueger E. E. , Pultz G. N. , Maschhoff K. R. , Tobin S. P. , Norton P. W. , Rutter J. H. , Reine M. B. 
Published: April 2011

AbstractWe are developing two-layer LPE P-on-n HgCdTe photovoltaic detector arrays with cutoff wavelengths out to 17 μm for a NASA spaceborne infrared radiometer. These bilinear multiplexed arrays will operate at 60 K, and must achieve sensitivities approaching the background limit for a background photon flux of 2×1015 photons/cm2-sec. The detectors must operate at reverse bias voltage to interface with silicon CMOS multiplexer circuits, and must exhibit low 1/f noise.This paper reviews progress toward these demanding requirements. The limiting junction current mechanisms for HgCdTe photodiodes at these very long cutoff wavelengths are reviewed. Data are presented for both CdTe-passivated and ZnS-passivated arrays at 60 K with cutoff wavelengths of 15.4−16.9 μm. Average R0A products of 13 ohm-cm2 and quantum efficiencies of 89% have been achieved for cutoff wavelengths of 15.4 μm at 60 K. These array data demonstrate the potential for VLWIR PV HgCdTe to meet the requirements for advanced NASA applications.
Cyclic CVD for Preparation of Silicon Films of Adjustable Structure
Authors: Koynov Svetoslav , Grebner Stefan , Fischer Thomas , Schwarz Reinhard 
Published: April 2011

ABSTRACTTwo versions of a deposition method referred to as CYCLIC-CVD are presented. Both are based on the repetition of cycles involving two steps: a) a thin a-Si:H layer deposition and b) a hydrogen plasma treatment. In the first version the cycles consist of a thermal CVD deposition step at 500–550 °C followed by a hydrogen plasma step. Device quality a-Si:H films of less than 3 at.% hydrogen content have been prepared. In the second version, which we call Closed Chamber CVD (CC-CVD) the deposition step is done by conventional PE CVD. However, the hydrogenation step is performed with closed reactor chamber. The latter step provides conservation of silicon mass at an equilibrium between H-etching and redeposition. As a result, μc-Si films of high crystallinity are produced with a high overall deposition rate.
Optimization of a Dual-Mode RF / Microwave Plasma for Amorphous thin film Deposition
Authors: Etemadi R. , Leroy O. , Drevillon B. , Godet C. 
Published: April 2011

ABSTRACTA new dual-plasma (surface wave-coupled microwave and capacitively-coupled radiofrequency) PECVD reactor for high growth rate of Amorphous insulating alloys is being developped. A high flexibility for thin film materials synthesis is expected, because the energy of the ion bombardment can be monitored independently from the microwave plasma chemistry. In situ diagnostics (Optical EMission Spectroscopy and Spectroscopie Ellipsometry) are used for the optimization of the dual-Mode plasma deposition of hydrogenated Amorphous silicon a-Si:H and silicon oxides a-SiOx:H (with 0 ≤ × ≤ 2). The growth of stoichiometric oxide at 3.3 nm / s has been achieved.
A Unified Description of the Density of States for Hydrogen and Electrons in Amorphous Silicon
Authors: Deane S.C. , Powell M.J. 
Published: April 2011

ABSTRACTWe derive the hydrogen density of states for hydrogenated Amorphous silicon (a-Si:H), which is completely consistent with the electronic density of states for the defect pool model. If silicon dangling bond energies are distributed in energy, as in a defect pool model, then the hydrogen density of states becomes quite complex, with the hydrogen binding energy dependent on the Fermi level and dangling bond transition energy. We demonstrate that the electronic density of states for dangling bonds is almost identical to our previous defect pool model, while the hydrogen density of states can account for the results of hydrogenation-dehydrogenation experiments. The effective hydrogen correlation energy is variable, being negative for most hydrogen binding sites, but positive for most defect sites.
Molecular Dynamics Studies of Diamondlike Amorphous Carbon
Authors: Fedders P. A. , Drabold D. A. 
Published: April 2011

ABSTRACTFirst principles molecular dynamics methods are used to construct supercells for diamondlike Amorphous carbon, to study its properties, and to compare and contrast it with a-Si. As with recent lab fabricated material, these supercells contain no hydrogen. Several structural models are introduced and the topological, electronic, and vibrational properties are discussed. In particular, in spite of the presence of 3-fold coordinated sites and no hydrogenation, we have obtained a supercell sample that has a gap of about 2.5 eV containing no defect states. To our knowledge, ours is the only theoretical work that agrees with recent experiments in this respect. We explore the nature of defects in the Amorphous network and, in particular, the atomistic origin of the clean gap in unhydrogenated C but not in unhydrogenated Si.
Fabrication of Highly Stable a-Si:H from Chlorinated Precursors
Authors: Azuma M. , Yokoi T. , Shimizu I. 
Published: April 2011

ABSTRACTHigh quality a-Si:H was fabricated from SiH2Cl2 by ECR hydrogen plasma at high growth rate (>15 A/s). After sticking the precursors, SiHnClm (n+m≤3), stable Si-network was formed by chemical reactions enhanced on the heated substrate due to strong interaction between Cl and H bonded with Si. The defect densities of 3×1015 and 3×1016 cm3 were obtained for the films in the as-grown and the saturated states after light soaking, respectively. In these stable films, a surprisingly large amount of voids (2–10 vol%) was found by the simulation of the spectra of pseudo-dielectric constant measured by spectral ellipsometry.
Metastable Defect Kinetics in Hydrogen Passivated Polycrystalline Silicon
Authors: Nickel N. H. , Street R. A. , Jackson W. B. , Johnson N. M. 
Published: April 2011

ABSTRACTThe temperature dependence of the dark conductivity, σD, of unhydrogenated and hydrogen passivated polycrystalline silicon (poly-Si) films was Measured. While σD of unhydrogenated poly-Si did not exhibit any influence of thermal treatment prior to the measurement, striking effects were observed in hydrogenated poly-Si films. Below 268 K a cooling-rate dependent metastable change of σD is observed. The dark conductivity increases by more than 8 orders of magnitude. This frozen-in state is metastable: Annealing and a slow cool restore the temperature dependence of the relaxed state. The time and temperature dependence of the relaxation reveal that this process is thermally activated with 0.74 eV. The lack of the quenching metastability in unhydrogenated poly-Si is direct evidence that the metastable changes in σD are due to the formation and dissociation of an electrically active hydrogen complex, in the grain-boundary regions.
New Model for Local H-Atom Bonding Re-Arrangements Associated with the Staebler-Wronski Effect in a-Si:H and a-Si:H-Based Alloys
Authors: Lucovsky G. , Williams M.J. , Cho S.M. , Jing Z. , Whitten J.L. 
Published: April 2011

ABSTRACTMany photoelectronic properties of a-Si,N:H alloys prepared by remote PECVD (RPECVD) from two N-atom source gases - N2 and NH3 - are the same; however, the photo-induced changes in the electrical properties in alloys with -2.1 eV bandgaps are ∼3 to 5 times greater in alloys deposited from NH3, which display Si-NH, as well as SiH bonding. Based on this result, we show that bonding groups important in the Staebler-Wronski effect include (i) ≡SiH, and nearest-neighbor (ii) ≡Si-NH-Sis and/or ≡Si-O-Sis in which the respective N and O-atoms make H-bonds with the sSiH group. The model, based on ab-initio calculations, includes a H-exchange reaction in which trapping of photo-generated holes promotes a transfer of the H-atom from the ^SiH group to a nearest-neighbor ≡Si-NH-Si≡ creating (i) a Si-dangling bond (Si*) and (ii) a Metastable (≡Si-NH2-Si≡) + group. Calculations indicate that neutral (≡Si-NH2≡Sis) ° is unstable, so that relaxation of (≡Si-NH2-Si≡) + groups can occur by trapping of a thermally-released (trapped) electron during a post-light-soaking thermal-anneal. The same type of model is developed for hole/electron trapping-induced H-atom transfer between ≡SiH and ≡Si-0-Si≡ groups in other a-Si:H Materials.
Relationship Between Plasma Chemistry and Electron Trapping rate in Plasma-Deposited Silicon Nitride
Authors: Smith Donald L 
Published: April 2011

ABSTRACTSilicon nitride deposited by plasma-enhanced chemical vapor deposition (PECVD) from SiH4 and NH3 is not crystalline Si3N4 with a specific stoichiometric ratio, but rather SiNxHy, an Amorphous network in which the N/Si ratio can vary from zero in Amorphous Si (a-Si) to almost two. The rate at which injected electrons are trapped in SiNxHy decreases by over 103 when N/Si is increased from 4/3 to the N saturation point, and the trapping centers are therefore likely to be Si dangling bonds. Trapping is undesirable in semiconductor devices except in memory applications, because it shifts the device's flat-band voltage, although in a-Si thin-film transistors (TFT's) the nitride trapping rate can easily be made Much smaller than the rate of electron trapping in deep states of the a-Si. When deposition plasma chemistry is driven to the N-saturation point, SiNxHy has a trapping rate lower than that of the best PECVDSiO2, although this is still 104 above that of thermal oxide grown on single-crystal Si. N-saturated deposition requires not only a high NH3/'SiH4 feed ratio, but also sufficient plasma power to activate the NH3 so that it will completely consume the SiH4 in formation of the tetra-aminosilane [Si (NH2) 4] precursor molecule. Then, the Si in the Amorphous network becomes entirely bonded to N rather than to both H and N, and NH groups act like O does in SiO2 to lower the coordination of the network and thus avoid dangling bonds.
Effects of Intermittent Deposition on the Defect Density in a-Si:H
Authors: Kamei Toshihiro , Hata Nobuhiro , Matsuda Akihisa 
Published: April 2011

ABSTRACTEffects of intermittent deposition on the defect density in hydrogenated Amorphous silicon (a-Si:H) are investigated at various substrate temperatures by using a mechanical shutter, while maintaining the discharge continuously. The intermittent deposition experiments, where monolayer growth and intermission (waiting time) are repeated in cycles, enable us to study surface dangling bond (DB) recombination and thermal hydrogen desorption separately from other reactions on the growth surface. The defect density in films prepared at lower substrate temperatures decreases with the waiting time, while that deposited at higher substrate temperatures increases with the waiting time.
The Interpretation of the Constant Photocurrent Method in Terms of Deep Defect Density of States in A-SI.H
Authors: Siebke Frank , Stiebig Helmut 
Published: April 2011

ABSTRACTThe constant photocurrent Method (CPM) is often used to measure the sub-bandgap absorption for the determination of the defect density. However, the absolute value of the derived defect density depends on the method of data analysis and the calibration factor. Normally the calibration factor is obtained from electron spin resonance (ESR) but the defect pool model gives rise to doubt whether ESR detects the same defects as CPm. Therefore, we propose combined total-yield photoelectron spectroscopy (TYPES) and CPM Measurements on n-type a-Si:H to determine the calibration factor. Furthermore, we calculate CPM spectra by extending an approach to simulate photoconductivity, taking into account the full set of optical transitions, and compare the results with standard evaluation Methods.
Structural, Optical and Electrical Properties of <P> μc-Si:H Very Thin Films Deposited by the VHF-GD Technique
Authors: Flückiger Roger , Meier J. , Shah A. , Catana A. , Brunel M. , Nguyen H. V. , Collins R. W. , Carius R. 
Published: April 2011

ABSTRACTIn this paper we present new results for very thin <p> μc-Si:H films (< 350 Å) deposited at low temperature (170 C) by the Very High Frequency - Glow Discharge technique (VHF-GD) at 70 MHz. First, the effect of boron doping on the growth and electrical properties of μc-Si:H very thin films is investigated, leading to an optimised value of about 0.6 % (B2H6/SiH4). Structural properties of an optimised thickness series ranging from 100 to 350 Å are studied using TEM, Raman, grazing angle X-ray diffraction/reflection and spectroscopie ellipsometry. Further, a columnar structure growth model for these very thin <p>-type μc-Si:H films will be proposed.