bluuebunny/crossref_metadata_2025_split huggingface dataset:
X-Ray Microprobe for the Microcharacterization of Materials
Authors: Sparks C. J. , Ice G. E. 
Published: March 2011

AbstractThe unique properties of X rays offer many advantages over those of electrons and other charged particles for the microcharacterization of materials. X rays are more efficient in exciting characteristic X-ray fluorescence and produce higher fluorescent signal-to-background ratios than obtained with electrons. Detectable limits for X rays are a few parts per billion which are 10−3 to 10−5 lower than for electrons. Energy deposition in the sample from X rays is 10–3 to 10–4 less than for electrons for the same detectable concentration. High-brightness storage rings, especially in the 7 GeV class with undulators, will have sources as brilliant as the most advanced electron probes. The highly collimated X-ray beams from undulators simplify the X-ray optics required to produce submicron X-ray probes with fluxes comparable to electron sources. Such X-ray microprobes will also produce unprecedentedly low levels of detection in diffraction, EXAFS, Auger, and photoelectron spectroscopies for structural and chemical characterization and elemental identification. These major improvements in microcharacterization capabilities will have wide-ranging ramifications not only in materials science but also in physics, chemistry, geochemistry, biology, and medicine.
Soft X-Ray Absorption Microscopy of Surfaces with Synchrotron Radiation
Authors: Harp G. R. , Tonner B. P. 
Published: March 2011

AbstractAs a spectroscopic technique, x-ray absorption near-edge structure (XANES) of core-levels using synchrotron radiation is in wide-spread use for the determination of the molecular composition of solid surfaces. A common detection method measures the yield of secondary electrons, which is proportional to the x-ray absorption coefficient for sufficiently high photon energy. In the experiments reported here, we show how the secondary electrons emitted as a result of photoabsorption can be used to generate a magnified image of the sample surface, with fundamental spatial limits determined by the deBroglie wavelength of the emitted electrons. Contrast in the secondary electron spatial distribution contains both topographical and chemical information about the sample surface. The use of tunable synchrotron radiation enables us to separate these contributions to the microscopic image, and to spatially resolve surface chemical composition as reflected in micro-XANES spectra.
The Argonne Advanced Photon Source
Authors: Moncton David E. 
Published: March 2011

AbstractArgonne National Laboratory is preparing to build a new synchrotron radiation source, the 7-GeV Advanced Photon Source (APS), that will provide the world's most brilliant x-ray beams for research. The APS will produce x-rays for materials research, condensed-matter physics, chemistry, and biological and medical studies by researchers from industry, universities, and national laboratories.
Bonding in Thin Epitaxial CoSi2 Films on Si(100)
Authors: Chambliss David D. , Rhodin T. N. , Rowe J. E. , Yalisove S. M. 
Published: March 2011

AbstractEpitaxy of CoSi2 layers on Si crystal surfaces can be strongly influenced by growing appropriate template layers. The electronic structure of thin (∼7Å) epitaxial CoSi2 films on Si(100) has been studied with angle-resolved photoemission to investigate atomic bonding in the layers and at their boundaries. Most Co atoms in the layers are in a CoSi2-like environment, including those Co atoms near the free surface. Cobalt atoms at the Si-CoSi 2 interface seem to have fewer Si neighbors.
Valence Band Electronic Structure of Cleaved Iron Oxide Single Crystals Studied by Resonant Photoemission
Authors: Lad Robert J. , Henrich Victor E. 
Published: March 2011

AbstractSynchrotron radiation has been used to perform resonant photoemission measurements across the 3p→3d photoabsorption threshold from cleaved FexO (x ≃0.945), Fe3O4, and α-Fe2O3 single crystal surfaces. The resonant enhancement of the Fe 3d photoelectrons allows the Fe 3d-derived final states in the valence band to be distinguished from the overlapping O 2p states. Using well-characterized single crystals, the distributions of Fe 3d-derived states associated with the ferrous (Fe2+) and ferric (Fe3+) cations have been identified. The Fe 3d-derived states are found to extend about 18 eV below the Fermi level in each oxide, which can be attributed to a significant amount of hybridization between the Fe 3d and O 2p orbitals.
Photoemission Exafs from InP(110) and Al/InP(110)
Authors: Choudhary K. M. , Mangat P. S. , Kilday D. , Margaritondo G. 
Published: March 2011

AbstractPhotoemission EXAFS (PEXAFS) studies of InP(110), InP(110) + 1 Å Al and InP(110) + 3 Å Al are presented. In each case, photoemission from the P 2p core-level was monitored using a cylindrical mirror analyzer by a two-point CIS (constant-initial-state spectroscopy) method in 150–280 eV photon energy range. The data were analyzed by conventional Fourier analysis procedures using the theoretical phase function of McKale et al. plus absorber phase function of Teo and Lee. No diffraction effect other than EXAFS is observed. For the clean InP(110) surface, the PEXAFS results show relaxation (contraction) of the surface in excellent agreement with the LEED results. But a small contraction in the P-P bond length (surface unit mesh parameter, a0) has also been measured, which was not reported in the LEED studies. For the InP(110) surface covered with 1 Å Al, metal (cluster)-induced surface structural changes in the substrate are determined which include removal of relaxation of the surface unit mesh in combination with change in the P-In bond length within the surface unit mesh. At the 3 Å Al-coverage on the InP(110) surface, the interface resembles AlP.
Bond Selective Chemistry with Photon-Stimulated Desorption
Authors: Yarmoff J. A. , Joyce S. A. 
Published: March 2011

AbstractPhoton stimulated desorption of fluorine ions from silicon surfaces was studied via excitation of the Si 2p core level with synchrotron radiation. These results showed that the process is chemically selective in that the removal of a fluorine ion from a silicon species in a given oxidation state can be enhanced by tuning the photon energy to the excitation wavelength corresponding to a transition from the 2p core level of the bonding atom to the conduction band minimum. This process was studied as a possible means for the production of surfaces with selected compositions of species. The results of selective exposures of fluorinated surfaces to monochromatized radiation indicated that secondary desorption processes and the inherent chemistry of the surface reactions can override the effects of selective desorption. Other possibilities for selective surface reactions via core-level excitations are discussed.
Polarized X-Ray Absorption Studies of Oxide Superconductors
Authors: Alp E. Ercan , Mini S. M. , Ramanathan M. , Veal B. W. , Soderholm L. , Goodman G. L. , Dabrowski B. , Shenoy G. K. , Guo J. , Ellis D. E. , Bommanavar A. , Hyun O. B. 
Published: March 2011

AbstractPolarized X-ray absorption studies have been carried out at the Cu K-edge to study the effect of Sr doping in La2CuO4 and oxygen doping in YBa2Cu3O6+x. These measurements help to elucidate the transitions giving rise to the absorption edges. We offer an explanation of the polarization shifts of features in terms of the results of our embedded cluster calculations of electronic structure.
Photoluminescence measurement of sidewall damage in etched InGaAsP/lnP and GaAs/AIGaAs microstructures
Authors: Grabbe P. , Scherer A. , Kash K. , Bhat R. , Harbison J. , Florez L. , Koza M. 
Published: March 2011

ABSTRACTWe report the first investigation of the effect of dry etching parameters on the sidewall carrier recombination rate of GaAs/AIGaAs and lnPilnGaAsP microstructures. Surface recombination was measured as a function of ion voltage and etching time. The increase in recombination rate due to etching can be reversed by subsequent chemical removal of the immediate sidewall layer. By monitoring the recovery in recombination rate as a function of the amount of sidewall layer removed, the effective damage depth is inferred.
Comprehensive Investigation of Traps in GaAs/A1GaAs Heterostructures and Superlattices by DLTS
Authors: Papaioannou G. , Kiriakidis G. , Georgakilas A. , Christou A. 
Published: March 2011

ABSTRACTThe electron traps of GaAs/AlGaAs heterostructures or superlattices (S.L.) have been investigated in a series of device structures which ranged from simple Schottky diodes to high electron mobility transistors. For the S.L. structure traps investigated, emission into the El miniband as well as A1GaAs trapping was considered. In simple heterostructures such as HEMTs, DLTS investigation of electron trapping from the 2DEG channel revealed a number of new traps, which were previously undetected with CTS (Current Transient Spectroscopy) investigations of the 2DEG. Interface traps in GaAs/AIGaAs heterojunctions were also investigated and distinguished from previously reported traps.
Molecular Beam Epitaxial Growth and Characterization of GaAs on Sapphire and Silicon-on-Sapphire Substrates
Authors: Humphreys T. P. , Miner C. J. , Parikh N. R. , Das K. , Summerville M. K. , Posthill J. B. , Nemanich R. J. , Sukow C. A. 
Published: March 2011

ABSTRACTEpitaxial GaAs layers have been grown by molecular beam epitaxy on (1012) sapphire and silicon-on-sapphire substrates. The grown layers were characterized by optical and transmission electron microscopy; Rutherford backscattering/channeling of 2.1 MeV He+ ions; Raman spectroscopy; Hall mobility measurements; photoluminescence spectroscopy and current-voltage measurements from metal-semiconductor contacts. The extensive microstructural, electrical and optical analysis of the GaAs layers indicates that the films deposited on silicon-on-sapphire are superior to those grown directly on (1012) sapphire substrates.
Mechanisms of Self-Diffusion and of Doping-Enhancement of Superlattice Disordering in GaAs and AlAs Compounds
Authors: Tan T.Y. , Gösele U. 
Published: March 2011

ABSTRACTAn understanding of the mechanisms of self-diffusion and of interdiffusion in the compound materials GaAs and AlAs may be arrived at byt noting the effects of (i) charge, (ii) As pressure, and (iii) point defect supersaturation, on the doping enhanced superlattice disordering phenomena. The Ga self-diffusion (and hence Ga-Al interdiffusion) is dominated by the triply-negatively-charged Ga (or Al) vacancy, , under intrinsic and n-doping conditions. Under p-doping, a positively charged Ga self-interstitial , with m not known, contributes to the Ga(AI) diffusion process. Less is known for the group V element diffusion, but the As vacancy (VAs) should be contributing under intrinsic and n-doping conditions while the As selfinterstitial (LAs) may be contributing under p-doping. The contribution of a defect pair may also be involved under p-doping.
Studies of In0.53Ga0.47As/InP Superlattice Mixing and Conversion
Authors: Schwarz S.A. , Mei P. , Hwang D.M. , Schwartz C.L. , Venkatesan T. , Palmstrøm C.J. , Stoffel N.G. , Bhat R. 
Published: March 2011

ABSTRACTSealed ampoule Zn diffusions into an unstrained In0.53Ga0.47As/InP superlattice are observed to preferentially induce cation (In, Ga) interdiffusion. The extent of interdiffusion is monitored in these studies by SIMS (secondary ion mass spectrometry). In some cases, Zn entirely displaces In in the InP layers forming an In1−xGaxAs/Zn3P2 superlattice. Under still more stringent conditions, all In and Ga is replaced, resulting in a Zn3As2/Zn3P2 superlattice. These structures are capable of supporting considerable strain due to the absence of grown-in defects. TEM (transmission electron microscopy) micrographs of several samples reveal defect free highly strained layers with thicknesses exceeding the predicted critical values. A high dose Zn implant was examined in which mixing proceeded until the Zn concentration dropped below a threshold concentration of approximately 1020 cm−3 during the anneal. These results, in total, strongly support a kickout mechanism for Zn induced mixing. Si diffusion was observed, in one case, to induce comparable cation and anion interdiffusion, thereby reducing the layer bandgap disparity, as opposed to Zn which increases the difference in layer bandgaps. Almost no interdiffusion was induced by Si diffusion from MBE (molecular beam epitaxy) polycrystalline Si films, due either to the very high resultant Si concentrations or to the capping effect of the film. The data suggest that both anion and cation site defects play a role in the Si induced mixing process.
Doping Study of Se into AlGaAs Layers Grown by MBE, and their Application to HEMT Structures
Authors: Maed T. , Ishikawa T. , Kondo K. 
Published: March 2011

ABSTRACTWe studied doping Se into AlGaAs layers using PbSe as a dopant source for molecular beam epitaxy (MBE). Good controllability and abruptness equivalent to that of Si-doping were obtained. Se-doping was successfully applied to HEMT structures with reduced DX center concentrations. The two dimensional electron gas (2DEG) characteristics of these structures were comparable to those of Si-doped structures.
On the Origin of the New Electron Traps Induced By Rapid Thermal Annealing in GaAs Using Capping Proximity Technique.
Authors: Marrakchi G. , Chaussemy G. , Laugier A. , Guillot. G. 
Published: March 2011

ABSTRACTRapid Thermal Annealing (RTA) effects on generation or annihilation of deep levels in GaAs have been investigated by Deep Level Transient Spectroscopy (DLTS). Capping proximity technique using three annealing configurations are employed to anneal Liquid Encapsulated Czochralski (LEC) and Bridgman (B) substrates, or Vapor Phase Epitaxy (VPE) and Liquid Phase Epitaxy (LPE) layers. The RTA treatment is performed from 800 to 950°C for two annealing times ( 3 and 10s).The DLTS data show that the evolution of the native defects depends on the GaAs growth method and also the annealing configuration. We observe the appearance of two new electron traps named RL1 and RL2 induced by the RTA process which depend on the kind of substrate: RL1 and RL2 are created in LEC material while only RL1 is detected in B material. A general comparison of our results with others reported in the literature show that these new electron traps are related to the change of stoichiometry at the GaAs surface and also depend on the existence of specific native defects in the starting GaAs material. It is proposed that the creation of RL1 is related to the EL6 native defect and discuss a possible physical origin for this level. We also propose that RL2 and EL5 originate from the same defect and suggest the divacancy VGaVAs as a possible origin for this trap.
Transient Thermal Analysis for Rapid Thermal Processing of GaAs
Authors: Yang F. K. , Pien S. J. , Kwor R. 
Published: March 2011

ABSTRACTA thermal analysis is performed to simulate the rapid heating process for ion implanted GaAs with consideration of the doping effect. The results are for cases with various concentrations and thicknesses of doping layer. Also studied are the heating processes for silicon dioxide capped GaAs. The effects of the thickness of the oxide layer are discussed. The magnitude of the temperature differences across the wafer is addressed. The present analysis considers xenon-arc lamps and tungsten-halogen lamps as the light sources.
Behaviour of Implanted Hydrogen in Gallium Phosphide Single Crystals
Authors: Zavada J. M. , Wilson R. G. , Novak S. W. , Pearton S. J. , Von Neida A. R. 
Published: March 2011

ABSTRACTIn this paper we report on the depth distributions of implanted hydrogen in GaP crystals and the subsequent changes produced by post- implantation furnace annealing. A sulfur doped n+ GaP wafer has been implanted with 333 keV protons to a fluence of 5E15/cm+2. A similar wafer was implanted with 350 keV deuterons to the same fluence. Portions of each wafer have been furnace annealed at temperatures up to 500°C. The implanted hydrogen and the dopant S atoms were then depth profiled using secondary ion mass spectrometry (SIMS). The measurements show that the redistribution of hydrogen begins with annealing at about 300°C and proceeds both towards the surface and deeper into the substrate. The overall behavior is similar to that found previously for hydrogen in GaAs. However, in GaP crystals this redistribution begins at a higher temperature and proceeds more slowly in the implanted region. Based on the SIMS profiles, diffusion coefficients for hydrogen migrating into substrate are obtained.
Rapid Thermal Techniques for Zinc Diffusion and Metal/Gallium Arsenide Alloying to Produce Low Resistance Ohmic Contacts
Authors: Rajeswaran G. , Lawrence D. J. , Lee S.-Tong , Kahen K. B. 
Published: March 2011

ABSTRACTRapid thermal processing has been utilized to diffuse Zn into GaAs from a thin film zinc silicate source prepared by atmospheric pressure chemical vapor deposition (CVD). The zinc source was capped with ∼500 Å of silicon dioxide (SiO2 ). At 750°C for 20 sec, the diffusion of Zn reached a depth of 0.8 μm. For these diffusions, the diffusion constant is concentration dependent and is proportional to the square of the Zn concentration. Above 7500 C, anomalous secondary diffusion fronts were observed in the Zn diffusion profiles. A new model is proposed that explains the diffusion profiles at all temperatures. Ohmic contacts have been made to the above Zn-diffused surfaces using Cr/AuZn/Au metallizations. A typical value of the specific contact resistance is 8.0 × 10−7 ohm-cm2.
Fabrication and Electrical Properties of MBE Grown Metal-Gallium and Metal-Arsenic Compounds on Ga1-xAlxAs
Authors: Palmstrøm C.J. , Garrison K.C. , Fimland B.-O. , Sands T. , Bartynski R.A. 
Published: March 2011

ABSTRACTFilms of CoGa and CoAs have been deposited on Ga1-xAlxAs surfaces. CoAs films were found to be highly textured, but not single crystal. For CoGa films, however, single crystal growth was observed. The crystalline quality of the (100) oriented CoGa was good as determined by Rutherford backscattering with channeling measurements (χmin ∼7%) and cross-sectional transmission electron microscopy. Schottky barrier diodes fabricated from (100)CoGa/Ga1-xAlxAs and CoAs/Ga1-xAlxAs showed good characteristics with low ideality factors, n<1.15. Good Schottky barrier behavior was also found for (100)ErAs/GaAs structures.
Ion Damage Studies in GaAs-Algaas Ultra-Narrow Wires
Authors: Cheeks T. L. , Roukes M. L. , Scherer A. , Van Der Gaag B. P. , Craighead H. G. 
Published: March 2011

ABSTRACTLow energy ion damage effects have been investigated in GaAs-A1GaAs two dimensional electron gas (2DEG) materials. The effect of ion mass (He, Ar, Xe) and adsorbed C12 on the charge carrier density and mobility has been studied for ion bombarded 2DEG systems. The 2DEG mobility was significantly reduced by ion damage with the effect becoming more dramatic with smaller ion mass. For the same treatment, the two dimensional carrier density was relatively unaffected. The results of He ion exposure showed serious degradation of the 2DEG with moderate ion dose. Electrical measurements were performed to determine the conducting widths of narrow patterned wires. For the same structural widths (mask width) He defined wires showed smaller electrical widths than Ar milling in the presence of chlorine. Serious limitations to patterning small structures may be imposed using beam processes that include He or other light mass species.
Models and Mechanisms of III-V Compound Semiconductor Growth by Movpe
Authors: Jensen Klavs F. , Mountziaris Triantafillos J. , Fotiadis Dimitrios I. 
Published: March 2011

AbstractA kinetic model for metalorganic vapor phase epitaxy (MOVPE) of GaAs from trimethylgallium and arsine is imbedded into two-dimensional transport phenomena descriptions of horizontal and vertical MOVPE reactors. The mechanism involves 15 gas-phase species, 17 gas-phase reactions, 9 surface species and 26 surface reactions. The surface reactions take into account different crystallographic orientations of the GaAs substrate. Carbon incorporation is predicted to occur via carbene containing species. A sensitivity analysis shows that only a few reactions are needed to simulate observed growth rates while the full mechanism is important in computing carbon levels in GaAs. The model predictions are in good agreement with data for trimethylgallium decomposition in hot isothermal tubes, with GaAs growth in horizontal reactors, and with carbon incorporation in vertical reactors. The transport-reaction model demonstrates that both gas-phase and surface reactions as well as transport phenomena are important in predicting MOVPE reactor performance.
Purity and Uv Absorption Cross Sections of TMA, TMG, and TMAs
Authors: Okabe Hideo , Emadi-Babaki M.K. 
Published: March 2011

AbstractVapor pressures of commercial electronic grade TMA,.TMG and TMAs samples have been measured at various temperatures and compared with those of known pure samples. Only TMA showed the presence of impurities. The UV absorption spectrum of impure TMA shows toluene to be an impurity. The UV absorption cross sections of TMA, TMG and TMAs have been measured and tabulated at several wavelengths.
Quantum-Confined Optical Interband Transitions in 5-Doped Doping Superlattices
Authors: Schubert E. F. , Harris T. D. , Cunningham J. E. 
Published: March 2011

AbstractOptical absorption and photoluminescence experiments are performed on GaAs doping superlattices, which have a δ-function-like doping profile of alternating n-type and p-type dopant sheets. Absorption and emission spectra reveal for the first time the clear signature of quantum-confined interband transitions. The peaks of the experimental absorption and luminescence spectra are assigned to calculated energies of quantum-confined transitions with very good agreement. It is shown that the employment of the δ-doping technique results in improved optical properties of doping superlattices.
Molecular Beam Epitaxical Growth of AlxGa1-xAs on non- Planar Patterned GaAs (100)
Authors: Guha S. , Madhukar A. , Kaviani K. , Chen Li , Kuchibhotla R. , Kapre R. , Hyugachi M. , Xie Z. 
Published: March 2011

AbstractWe have examined some aspects of inter-facet migration during molecular beam epitaxical(MBE) growth of AlxGal-xAs on patterned GaAs (100) substrates. Scanning and cross-sectional transmission electron microscopy are employed to examine the evolution of the growth front profile. We observe significant inter facet migration from (3111/1411) facets which originate from the terrace edges to the flat terrace region. The migration length of cations on these facets is at least 0.9 μm for GaAs growth while for A10.5Ga0.5As it is less than 0.3 μm. We also observe a decreasing inter- facet migration rate with increasing growth. This interfacet migration is exploited for in situ, growth kinetics controlled, creation of laterally confined quantum well structures on the top terrace region and photoluminescence results for these structures are presented.
Heteroepitaxy of III-V Compounds on Si Substrates for Solar Cells and Led
Authors: Yamaguchi Masafumi , Kondo Susumu 
Published: March 2011

AbstractHeteroepitaxial growth of GaAs, InP, GaP and InGaP on Si substrates is studied using MOCVD (Metal-Organic Chemical Vapor Deposition). High qgaliti GaAs films on Si, with a dislocation density of about 106 cm−2, are obtained by combining strained- layer superlattice insertion and thermal cycle annealing. Reduction of dislocation density in the III-V compounds on Si is discussed based on a simple model, where dislocation annihilation is assumed to be caused by dislocation movement under thermal and misfit stress. As a result of dislocation density reduction, high-efficiency GaAs-on-Si solar cells with total-area efficiencies of 18.3% (AMO) and 20% (AM1.5), and red and yellow emissions from InGaP-on-Si light-emitting diodes (LEDs) have been realized.