bluuebunny/crossref_metadata_2025_split huggingface dataset:
Low Gravity Solidification Structures in the TIN-15WT %Lead and TIN-3WT%Bismuth Alloys
Authors: Johnston Mary H. , Parr Richard A. 
Published: March 2011

ABSTRACTThe tin-15wt%lead and tin-3wt%bismuth alloys have been solidified in the low-gravity environment provided by the Space Processing Applications Rocket (SPAR), on the KC–135 airplane, and at high “g” levels in a centrifuge furnace. In each case the resultant cast structure was significantly different from that obtained in ground based experiments. Earlier low-gravity studies with the metal-model system NH4Cl-H2O presaged these results. This paper presents and discusses the influence of changes in the gravity force on the grain structure of these materials.
Review of The European Microgravity Activities
Authors: Malmejac Yves , Huth Ulrich 
Published: March 2011

ABSTRACTA few months ago, european activities in the field of microgravity research appeared as being an addition of single programmatic elements without enough logics, coordination and scientific background. Under the active pressure and guidance of many european scientists who became more and more aware of the basic interest of materials research in the microgravity environment, and due to the efforts of the ESA executive, the situation could evolve in a significant way, succeeding now in getting the official recognition of the necessity and content of a coherent european microgravity programme by both the ESA Council and the community of classical Space scientists. This presentation will deal with the scientific motivations of this new-born Programme through both the initial status and the most rational ambitions for future. The poirts of emphasis of the necessary multidisciplinary cooperative exertion together with the possible involvement of these scientists who could not derive benefit from any of the existing national programmes will then be stressed. At last the resulting priority objectives will be briefly reviewed before discussing the needed coordination with other european and non-european microgravity activities.
Structural Studies of Hydrogenated Amorphous Carbon Infrared Coatings
Authors: Robinson C. J. , Samant M. G. , Stohr J. , Speriosu V. S. , Guarnieri C. R. , Cuomo J. J. 
Published: March 2011

ABSTRACTHydrogenated amorphous carbon thin films are well known for their mechanical hardness and optical properties which make them useful for applications in infrared device coatings. In this work films have been prepared by plasma. decomposition of methane using an RF diode reactor operating under conditions of high self bias potential (Vb = 1 KeV). The resulting ion bombardment during film growth leads to the formation of hard, insulating carbon coatings which have a band gap of ≃1.1 eV and are transparent in the IR. Nuclear reaction analysis has been used to quantify the atomic concentration of hydrogen incorporated in the films and extended x-ray absorption fine structure (EXAFS) has been used to determine local site geometry. Only first and second nearest neighbor bond lengths are observed with no evidence of further long range order or microcrystallinity. A model for atomic structure is proposed which includes both sp2 and sp3 bond configurations and direct comparisons are made with data obtained from sputtered carbon films, graphite and diamond.
Materials Requirements for IR Detectors and Imagers
Authors: Kinch M. A. 
Published: March 2011

ABSTRACTThe requirements of infrared systems have increased significantly over the years, from the simple linear, low resolution, photoconductive array to the present-day, large area, high-density, photodiode (MIS and metalurgical) arrays, with on-focal-plane signal processing of considerable complexity. The success that has been achieved in meeting the performance goals appropriate for these systems has been due, to a large degree, to significant advances in the relevant materials technologies. The technologies of importance over the last twenty years are briefly reviewed, and the current state of the art, with its dominance by intrinsic alloy materials, is addressed in detail. The limitations of current bulk and epitaxial intrinsic materials technologies are considerable, both from a performance and a producibility point of view, when compared to the quality and quantity of material required by future infrared systems. These limitations are considered together with possible ways to overcome them.
Subsurface Micro-Lattice Strain Mapping
Authors: Ananthanarayanan T. S. , Rosemeier R. G. , Mayo W. E. , Becla P. 
Published: March 2011

SYNOPSISDefect morphology and distribution up to depths of 20um have been shown to be critical to device performance in micro-electronic applications. A unique and novel x-ray diffraction method called DARC (Digital Automated Rocking Curve) topography has been effectively utilized to map crystalline micro-lattice strains in various substrates and epitaxial films. The spatial resolution of this technique is in the the order of 100um and the analysis time for a 2cm2 area is about 10 secs. DARC topography incorporates state-ofthe- art 1-dimensional and 2-dimensional X-ray detectors to modify a conventional Double Crystal Diffractometer to obtain color x-ray rocking curve topographs.This technique, being non-destructive and non-intrusive in nature, is an invaluable tool in materials’ quality control for IR detector fabrication. The DARC topographs clearly delineate areas of microplastic strain inhomogeniety. Materials analyzed using this technique include HgMnTe, HgCdTe, BaF2, PbSe, PbS both substrates and epitaxial films. By varying the incident x-ray beam wavelength the depth of penetration can be adjusted from a 1–2 micron up to 15–20um. This can easily be achieved in a synchrotron.
Characterization of Ultra High Purity Silicon Epitaxy Using Photoluminscence Spectroscopy
Authors: Huffman J. E. , Thewalt M. L. W. , Steele A. G. 
Published: March 2011

ABSTRACTHigh purity epitaxial silicon samples, grown on indium doped and on ultrahigh resistivity silicon substrates, were analyzed for impurity content using photoluminescence spectroscopy (PL) and spreading resistance analysis (SRA). Calibrated SRA indicated typical net carrier concentrations of < 3×1012cm-3 in the epitaxial layers, and about 7×1011 cm-3 in the substrates. Impurities were identified by collecting highly resolved, very clean no-phonon and TO-phonon replica PL spectra at liquid helium temperatures. Spectra were taken on the substrate material alone and on substrates with epitaxy. Ga, As, A1, B and P contamination was evident in the epitaxy. Correlation of SRA and PL results on samples with various levels of contamination at the epitaxy substrate interface identified Al as the main
interfacial impurity.
On the Auger Recombination Process in P-Type Lpe HgCdTe
Authors: Chen J. S. , Bajaj J. , Tennant W. E. , Lo D. S. , Brown M. , Bostrup G. 
Published: March 2011

ABSTRACTMinority carrier lifetime measurements at 77K were carried out in ptype liquid phase epitaxial (LPE) Hg 1-xCdx Te/CdTe (x = 0.22) using the photoconductive decay technique. Lifetimes of 20 to 7000 ns were obtained in samples with hole concentrations, p, in the range 1014 to 1016 cm-3. The hole concentrations were determineg by analyzing the Hall data using a double-layer model. It was found that the minority carrier lifetime is inversely proportional to p01.86. This result demonstrates that the Auger mechanism may be the dominant recombination process in p-type LPE Hg0.78 Cd0.22Te/CdTe. The temperature dependence of minority carrier lifetime was also measured between 10 and 200K for several samples.
Characterization of HgCdTe Epilayers and HgTe-CdTe Superlattice Structures Grown by Molecular Beam Epitaxy
Authors: Myers T. H. , Yanka R. W. , Karins J. P. , Harris K. A. , Cook J. W. , Schetzina J. F. 
Published: March 2011

ABSTRACTThe results of an in-depth study of HgCdTe epilayers and HgTe-CdTe superlattice structures are summarized. In particular, both spectral and transient photoconductance measurements have been made on samples which were also characterized by x-ray diffraction, Hall, IR transmission, IR photoluminescence, and transmission electron microscopy measurements. Selected HgCdTe samples grown at General Electric during this investigation exhibit some of the best structural and electrical properties reported to date for MBE-grown HgCdTe. Sharp photoconductance spectra have been obtained for HgTe-CdTe superlattice structures grown at North Carolina State University. This study is part of an on-going collaborative effort between General Electric's Electronics Laboratory and North Carolina State University.
A Study of the MBE HgTe Growth Process
Authors: Koestner Roland J. , Schaake H. F. 
Published: March 2011

ABSTRACTThe MBE growth of HgTe on CdTe is examined over a hundred-fold range in Hg/Te2 flux ratio and over four separate substrate surface orientations [(111)Te, (111)Te-4 degrees, (112)Te and (001)]. The 77K Hall mobility of the (112)Te and (001) oriented HgTe layers approaches the best bulk values reported to date, although our (111)Te and (111)Te-4 deg oriented HgTe films yield much lower values. The growth process is shown to be very far from thermodynamic equilibrium at our optimal substrate temperature and calculated equivalent Hg beam pressure. Important clues to help understand the kinetics governing the HgTe growth process are uncovered by studying the defects that form under Hg- or Te-rich conditions with cross-sectional transmission electron microscopy (XTEM). Since multilayered structures are an important application for MBE growth of Hg-based semiconductors, we have also examined the interfacial roughness present in HgTe-CdTe superlattices (SL) as a function of growth orientation.
InSb: A Key Material for IR Detector Applications
Authors: Jost S. R. , Meikleham V. F. , Myers T. H. 
Published: March 2011

ABSTRACTInSb has served as an important mid-wave IR (λ=3−5μm) detector material for several decades. In this presentation, we will briefly review General Electric's InSb Charge Injection Device technology. Emphasis will be placed on device performance as a function of material parameters. A new InSb materials technology utilizing liquid phase epitaxy will be described. This epitaxial growth technology improves InSb material parameters and increases minority carrier lifetimes by more than two orders of magnitude to near the Auger limit. Comparisons will be made between available bulk material parameters and that of the epitaxial material.
Dual Ion Beam Sputter Deposition of Cdte, Hgte and Hgcdte Films
Authors: Krishnaswamy S. V. , Rieger J. H. , Doyle N. J. , Francombe M. H. 
Published: March 2011

ABSTRACTExperiments have been performed to assess the feasibility of using ionbeam sputter deposition for the growth of CdTe, HgTe and HgCdTe films. Some simple cryogenically cooled dual-target configurations have been employed in an investigation of epitaxial growth on CdTe substrates. Good-quality epitaxy was achieved for CdTe at temperatures down to 140°C, and for HgTe and HgCdTe at temperatures extending to below 50° C.Based upon compositional and phase analyses, and upon IR absorption measurements, we conclude that, using an excess Hg flux, stoichiometric transfer of the HgCdTe target composition to the substrate is approximately obtained. However, some departure from stoichiometry is produced at higher substrate temperatures (> 150”C) due to thermal re-evaporation of Hg, and under high sputtered Hg fluxes due to selective re-sputtering of HgTe. The good structural quality and excellent compositional uniformity of the films indicate that ion-beam sputter deposition may be suitable for low-temperature processing of IR detector structures.
Issues in the Growth of Bulk Crystals of Infrared Materials
Authors: Bachmann K. J. , Goslowsky H. 
Published: March 2011

ABSTRACTSelected issues in the growth of bulk single crystals for applications in infrared optoelectronics are reviewed including an overview over materials choices, bulk III-V crystal growth, and the growth of II-VI, IV-VI and I-III-VI2 compounds and alloys. The most important issues are the control of purity, perfection, stoichiometry, and uniformity during crystal growth and the control of the surface properties in wafer fabrication. Specific examples are given to illustrate problems related to these issues and to discuss approaches to their solution.
Real Time Observation of Periodic Step Arrays During Silicon Vapour Phase Homoepitaxy
Authors: Robbins D. J. , Young I. M. , Pidduck A. J. , Pickering C. , Glasper J. L. , Gasson D. B. 
Published: March 2011

ABSTRACTLight scattering has been used to characterise the periodic surface topography which develops on (001) Si epitaxial layers growing by a step flow mechanism. The periodicity provides a measure of the average kink density along the misorientation steps which develop a sawtooth form during growth. The diffracting properties of the layers have been determined after growth by angle-resolved scattering measurements. In-situ light scattering at fixed angle has been used to fol low the build-up of the periodic step arrays. The periodic structure is a metastable state of the surface maintained by the supersaturation during growth, and it decays on switching off the silane source gas or when the temperature is reduced below the point at which surface diffusion will support the sawtooth step shape.
Microscopic Model for the Epitaxy of CaF2 ON Si(111)
Authors: Himpsel F. J. , Karlsson U. O. , Morar J. F. , Rieger D. , Yarmoff J. A. 
Published: March 2011

ABSTRACTThe epitaxy of CaF2 on Si(111) is characterized on an atomic scale using various photoelectron spectroscopy techniques. We find both F and Ca bonding to Si with Ca forming most of the interface bonds. The bonding orbital is found at 1.5 eV below the valence band maximum of Si. It consists of the Si3p-like dangling bond orbital and the 4s electron of Ca1+. Ca has changed its oxidation state at the interface from Ca2+ to Ca1+, which is demonstrated by the multiplet structure of the Ca 2p absorption edge. The electronic properties of the CaF2 interface layer are altered dramatically relative to bulk material, with the band gap shrinking from 12 eV to about 2 eV. Such strong effects raise prospects for creating new materials in the vicinity of an interface.
A Photoemission Study of the Epitaxial Growth of Si on Gap(110)
Authors: Niles David W. , Tang Ming , Höchst Hartmut 
Published: March 2011

ABSTRACTWe have used angular resolved ultraviolet photoemission spectroscopy to study the epitaxial growth of Si on GaP(110). Surface state emission obscures the top of the valence band (TVB). The Fermi level for the clean GaP(110) surface is 1.20±0.05eV above the TVB. 1ML (monolayer) of Si pins the Fermi level position at 1.40±0.05eV above the TVB. Further deposition of Si leads to a valence band discontinuity ΔEv=1.07 ±0.10eV.
Angle-Resolved X-Ray Photoelectron Spectroscopy for the Characterization of GaAs(001) and Inp(001) Surfaces
Authors: Alnot Patrick , Olivier J. , Wyczisk F. 
Published: March 2011

ABSTRACTElectron scattering and diffraction in X-ray photoemission spectroscopy (XPS) have been used to characterize GaAs(001) and InP(001) chemically etched surfaces. 6a(3d),As(3d), In(4d) and P(2p) photoelectrons have been observed as a function of polar angles for the two [1–10] and [110] azimuths For kinetic energy range of these photoelectrons the experimental results have been correctly predicted by the single-scattering cluster model with spherical-wave corrections.The problems of quantitative measurements in XPS have been discussed in relation with the diffraction phenomena.
Structure Analysis of the Al-Inp (100) Interface
Authors: d'Anterroches C. , Houzay F. , Bensoussan M. 
Published: March 2011

ABSTRACTHigh Resolution Electron Microscopy (HREM) images of the Al/InP interface were obtained from as-deposited films. The high purity Al films were deposited onto a clean (100) InP surface in a Molecular Beam Epitaxy (MBE) chamber. The in situ Reflection High Energy Electron Diffraction (RHEED) and Ultra-Violet Photoemission Spectroscopy (UPS) analyses showed a transformation of the InP surface during the Al deposition. The UPS data are interpreted as a strong exchange reaction between incoming Al and substrate In atoms. The In atoms are released and recover metallic behavior while Al atoms are involved in covalent bonds. At high coverages the RHEED analysis shows an epitaxial relationship in between Al and InP such as (110)Al//(100)InP with the two variants: [001]Al//[011]InP and [001]Al//[0–11]InP. The HREM images show that the interface AI/InP is perturbed and an intermediate layer is found. This layer appears to have the same crystal structure as InP indicated by extension of atomic planes from InP to the layer. However, the observed intensity, which corresponds to the mean potential of the forming atoms, is lighter than that of InP. Hence,out of these HREM and UPS results it is derived that an AlP or AlxIn1−xP compound is located at the Al/InP interface.
Surface Diffusion and Nucleation Processes in Thin Film Formation: The Case of Ag/Si(111)
Authors: Venables J. A. , Doust T. , Kariotis R. 
Published: March 2011

ABSTRACTSurface diffusion and crystal growth processes have been studied in the Stranski-Krastanov growth system Ag/Si(111), using several UHV-SEM techniques. By depositing Ag at various rates 0.2 ≤ R ≤ 1.4 ML-min−1 through a mask of holes, surface diffusion of Ag over the intermediate layer has been observed, in competition with re-evaporation at high, and nucleation at low substrate temperatures, in the range 620 < T < 850K. The Si(111) √3Ag intermediate layer has been visualized using biassed secondary electron imaging. The surface diffusion and nucleation processes observed have been analyzed in terms of kinetic models. Comparison with experiment yields values for the adsorption, diffusion and binding (Ea′ Ed and Eb) energies of Ag on the intermediate layer. These values are approximately Ea = 2.45 ± 0.1 eV, Ed 0.35 ± 0.05 eV and Eb = 0.10 ± 0.03 eV, where the uncertainties result at least as much from lack of knowledge of pre-exponential factors in the models as in the accuracy of the experiments.
The Effect of Surface Structure on the Epitaxial Growth of Si on CoSi2(111)
Authors: Tung R. T. , Hellman F. 
Published: March 2011

ABSTRACTTwo distinctively different structures were found on CoSi2(111), the CoSi2-C and the CoSi2-S, which correspond to, respectively, an essentially bulk-terminated surface and one which consists of an additional Si double layer. Details of the two structures suggest new growth techniques for Si epitaxy. Single crystal Si layers with either identical orientation as the silicide or a 180°-rotated orientation can be fabricated by use of carefully designed Si templates.
Molecular Dynamics Studies of the Adatom Induced Rearrangement of the Silicon {100} Surface
Authors: Brenner Donald W. , Garrison Barbara J. 
Published: March 2011

ABSTRACTA molecular dynamics simulation of the silicon adatom induced rearrangement of the silicon {100} symmetric dimer reconstructed surface has been performed. Surface diffusion is proposed to play a critical role in the reordering of this surface which leads to good epitaxy while it plays much less of a role in the reordering induced by an amorphous overlayer. These results are used to provide atomic-scale models which are consistent with high-energy ion channeling/blocking and LEED studies by Gossman and Feldman of the initial stages of silicon growth on this surface.
Role of Surface Reconstruction and External Ion Beam in the Growth Kinetics of III-V Molecular Beam Epitaxy
Authors: Ogale S. B. , Thomsen M. , Madhukar A. 
Published: March 2011

ABSTRACTComputer simulations of III-V molecular beam epitaxy (MBE) show that surface reconstruction induced modulation of kinetic rates could give rise to ordering in alloys. Results are also presented for the possible influence of an external ion beam in achieving low temperature epitaxy as well as smoother growth front under usual conditions.
Method for the Reduction of Photothermal Deflection Spectroscopy Data Taken on Amorphous Silicon (a-Si:H)
Authors: Wiedeman S. , Bennett M. S. , Newton J. L. 
Published: March 2011

AbstractPhotothermal deflection spectroscopy (PDS) is a sensitive method used to measure weak optical absorption of sub-bandgap radiation. A method utilizing Fourier transformation is presented which allows removal of optical interference effects and noise which is typically present in PDS data taken on a-Si:H, yet leaves the underlying PDS spectra undistorted. The method greatly facilitates comparison of PDS spectra taken on different samples, and simplifies further analysis. Examples using a-Si samples produced under different deposition conditions are presented to demonstrate the utility of the method.
Porous Morphology and Oxidation Kinetics in a-Si:H RF Sputtered by He/H2
Authors: Shinar J. , Shinar R. , Mitra S. , Albers M. L. , Shanks H. R. , Moustakas T. D. 
Published: March 2011

Abstracta-Si:H films rf sputtered in 10 mT He and 0.5 mT H2, in contrast to those prepared in Ar/H2 or Xe/H2, exhibit port depositional oxidation when sputtered at power levels of 0.55 – 3.3 W/cm2 (100 – 600W). SEM measurements show that the morphology of the films evolves from a cracked, microcrystalline, glassy one at higher rf power levels to a porous one at low power levels. This trend is also correlated with a sharply increasing density of Si-H2 dihydride bonds at decreasing rf levels. Auger depth profiles of the oxygen concentration in the films agree with a diffusion controlled process of a source solute of O2 molecules into a semi-infinite solid solvent. Yet IR absorption measurements indicate that the oxygen is confined to the internal surfaces of the microvoids. The diffusion constant is a very sensitive functi n of the sputtering conditions. At low rf power levels, it is as low as 10−16 – 10−1 cm2 /sec at room temperature, but increases to ∼10−13 at 250 – 350°C.These results are discussed in terms of a porous network of microvoids, through which the O2 “squeezes” into the film.
Identification of Chemical Growth Mechanisms in Amorphous Semiconductors
Authors: Reimer Jeffrey A. , Mccarthy Michael J. , Gleason Karen K. , Morrison Philip W. 
Published: March 2011

AbstractExperimental and computational results for three classes of experiments are reported. NMR measurements of phosphorus in amorphous hydrogenated silicon indicate that bonding rearrangements in bulk films are possible. Monte Carlo simulations of film growth demonstrate that surface diffusion is the dominant physical phenomenon responsible for the bulk hydrogen content of a-Si:H films. Finally, the gas phase chemistry of silane, as elucidated by our new “diesel” reactor, is considerably more complicated than many authors assume in models for thin films grown from silane.
Growth of Amorphous and Crystalline Silicon by HR-CVD (Hydrogen Radical Enhanced CVD)
Authors: Shibata N. , Fukuda K. , Ohtoshi H. , Hanna J. , Oda S. , Shimizu I. 
Published: March 2011

AbstractSystematic studies have been made on preparation of Si thin films from SiF4 under control over the flow of atomic hydrogens. The gas phase reactions taking place in the mixture of fragments (SiFn) resulting from plasma-induced dissociation and atomic hydrogens were widely investigated by a mass spectroscopy. Chemically active species,i.e., SiF2H and SiH2F were found as those related to the growth of films. The growth in the vicinity of substrates involves either endothermic or radical-enhanced reaction for the propagation of the three dimensional Si networks, accompaning release of terminators such as H and F. Accordingly, Si thin films with structures from amorphous to crystalline were obtained by controlling the flow of atomic hydrogen. A marked improvement in the hole-transport was established in the Si films containing hydrogen less than 5–6 at % due to the reduction in the tail states near the valence band.