bluuebunny/crossref_metadata_2025_split huggingface dataset:
Present and Future Capabilities of Acoustic Levitation and Positioning Devices
Authors: Rey Charles A. , Whymark Roy R. , Danley Thomas J. , Merkley Dennis R. 
Published: March 2011

ABSTRACTThe techniques of acoustic positioning without the use of resonant cavities have been explored and developed over a number of years and the currently available capabilities are reviewed. The performance and characteristics of these nonresonant acoustic systems are described in regard to containerless processing with emphasis on the low-g environment. This includes manipulation and mixing of liquid drops, super-cooling phenomena, heating to temperatures of 1600°C or higher, rapid cooling solidification, and surface shape control. Some possible applications are measurements of physical properties of substances at high temperatures or of highly reactive specimens, and the formation of unique glasses and alloys of new compositions.
Studies on Aqueous Two Phase Polymer Systems Useful for Partitioning of Biological Materials
Authors: Brooks Donald E. , Bamberger Stephan 
Published: March 2011

ABSTRACTThe two phase systems that result when aqueous solutions of dextran and poly(ethylene glycol) (PEG) are mixed above a critical concentration of a few percent provide a useful medium for the separation of biological cell subpopulations via partition between the top, PEG-rich phase and the liquid-liquid phase boundary. Interfacial tensions of such systems have been measured by the rotating drop technique and found to range between 10−1 and 102 μN m−1 . The tension was found to depend on the length of the tie line describing the system on a phase diagram, via a power law relationship which differed depending on the concentration of Na phosphate buffer present. The electrokinetic properties of drops of one phase suspended in the other were studied for a variety of systems. It was found that the droplet electrophoretic mobility increased monotonically with phosphate concentration and drop diameter but exhibited the opposite sign from that anticipated from phosphate partition measurements. It was possible to take advantage of these electrokinetic properties and dramatically enhance the speed of phase separation through application of relatively small electric fields.
Directional Solidification and Characterization of Hg1−xCdxTe Alloys
Authors: Lehoczky S. L. , Szofran F. R. 
Published: March 2011

ABSTRACTA series of Hg1−xCdxTe alloy crystals was grown by high-temperature-gradient directional solidification at furnace translation rates ranging from 0.068 to 1.12 μm/s. For several ingots, the measured longitudinal compositional profiles were fitted to theoretical profiles to estimate the magnitude of D, the liquid HgTe-CdTe interdiffusion coefficient. The best-fit value of D was about 5.5 × 105 cm2/s. The majority of the ingots showed significant radial compositional variations along the growth axis. These variations are attributed, at least in part, to fluid flows ahead of the growth interface. The results are discussed in terms of the heat transfer characteristics of the alloy/ampule/ furnace system and the effects of these characteristics on the shape and stability of the growth interface in a 1-g environment.
Growth of Single Crystals of Mercuric Iodide (HgI2) in Spacelab III1,2
Authors: Van Den Berg Lodewijk , Schnepple Wayne F. 
Published: March 2011

ABSTRACTContinued development of a system designed to grow crystals by physical vapor transport in the environment of Spacelab III will be described, with special emphasis on simulation of expected space conditions, adjustment of crystal growth parameters, and on board observation and control of the experiment by crew members and ground personnel.A critical factor in the use of mercuric iodide for semiconductor detectors of x-rays and gamma-rays is the crystalline quality of the material. The twofold purpose of the Spacelab III experiment is therefore to grow single crystals with superior electronic properties as an indirect result of the greatly reduced gravity field during the growth, and to obtain data which will lead to improved understanding of the vapor transport mechanismThe experiments planned to evaluate the space crystals, including gamma-ray diffractometry and measurements of stoichiometry, lattice dimensions, mechanical strength, luminescense, and detector performance will be discussed.
Studies of Liquid Metal Surfaces Using Auger Spectroscopy
Authors: Hardy Stephen , Fine Joseph 
Published: March 2011

ABSTRACTThe surface composition of liquid gallium-tin alloys has been studied in an Auger electron spectrometer (AES) as a function of bulk composition and temperature. The sessile drop samples were cleaned by argon ion bombardment sputtering of the liquid. This technique produced surfaces that were entirely free of impurities within the sensitivity of AES and remained so for many days. Tin was found to be strongly adsorbed at the liquid-vacuum interface. Surface concentrations based on Auger measurements are in reasonably good agreement with values calculated from surface tension measurements interpreted in terms of a monolayer depth distribution model for the adsorbed tin.
Ground Based Studies for the Space Processing of Lead-Tin-Telluride
Authors: Crouch Roger K. , Fripp A. L. , Debnam W. J. , Clark I. O. , Carlson F. M. 
Published: March 2011

ABSTRACTThis paper summarizes the results of a series of studies dealing with crystal growth from the melt and in particular, the growth of the narrow bandgap semiconductor PbSnTe by the Bridgman technique. Theoretical calculations have shown that for low Prandtl number fluids such as semiconductors, convection has no effect on the temperature field in the melt but has a significant effect on the compositional field. They also show that convective flow will exist in a Bridgman growth system on Earth, even in the “thermally stable” configuration. Measurements of the specific heat have been made up to temperatures of 722° C. The thermal diffusivity has been measured up to 1010° C which includes values for the melt. The interdiffusion coefficients for PbTe and SnTe in the melt have been determined. A technique has been developed and tested which provides a vacuum tight quartz ampoule with electrical feedthroughs for interface demarcation studies during the Bridgman growth. Analysis of crystals grown has indicated that the PbSnTe system is solutally unstable and the distribution of SnTe in the crystal, after an anomalous first to freeze region, follows that predicted by Pfann for convection controlled growth. Studies of the amount of supercooling in PbSnTe indicates that this may explain an anomalous composition distribution in the first to freeze region of an unseeded growth.
Brazing Under Microgravity in a Resistance Heated Furnace
Authors: Key Frieler , Roland Stickler , Eberhard Siegfried 
Published: March 2011

ABSTRACTVacuum brazing under 1-g and microgravity (carried out on TEXUS II in preparation of an experiment for FSLP) conditions revealed the effect of various parameters (e.g. thermal history, hydrostatic pressure, buoyancy forces) on the microstructure of the joint and the gap filling phenomena.The following results will be presented:(a) Design of brazing specimens(b) Variations of microstructure depending on gap width, gravity, and thermal history(c) Flow patterns of molten braze as revealed by radioactive tracer experiments(d) Evaluation of Plateau-type simulation experiments
Solidification Studies of Nb-Ge Alloys at Large Degrees of Supercooling
Authors: Lacy L. L. , Robinson M.B. , Rathz T.J. , Evans N. D. , Bayuzick R. J. 
Published: March 2011

ABSTRACTA 32 meter evacuated drop tube has been used to investigate the solidification of Nb-Ge alloys after deep undercooling. Samples have been supercooled as much as 500°K below the liquidus by using free-fall conditions to eliminate crucible induced nucleation. Final microstructures are dependent on the quenching rates at the bottom of the drop tube with a striking extension of the β phase solubility limit at the higher quenching rates.
Application of Microgravity and Containerless Environments to the Investigation of Fusion Target Fabrication Technology
Authors: Lee Mark C. , Kendall James M. , Elleman Daniel D. , Rhim Won-Kyu , Helizon Roger S. , Youngberg Charles L. , Feng I-An , Wang Taylor G. 
Published: March 2011

ABSTRACTDuring the past few years we have been studying several of the physical processes relevant to the production of spherical shells for inertial confinement fusion targets, both in a microgravity environment and in a containerless environment. The work has led to the development of several experimental facilities. Those which are most unique are described here, and fall into three categories as follows: 1. Ones which provide an induced low- or microgravity containerless environment, such as a vertical drag-free wind tunnel, two differing low-pressure and/or high-temperature drop towers for processing metallic or metallic-glass specimens, and a neutral buoyancy tank, 2. Ones providing containerless processing capability, such as a focusing radiator and an electrostatic levitator and 3. Ones providing extended microgravity and containerless capabilities, such as the KC-135 aircraft and the Space Processing Application Rockets. The physical processes which we have been studying include, but are not limited to, those which establish the shell sphericity, concentricity, surface topology, material properties, coatings, heating and cooling requirements and the effects of gravity on fusion pellet fabrication processes.
High Quality CdTe Growth by Gradient Freeze Method
Authors: Tanaka A. , Masa Y. , Seto S. , Kawasaki T. 
Published: March 2011

ABSTRACTThe vertical Bridgman method, a gradient freeze technique, is feasible for the growth of high quality, large CdTe crystals. The equi-composition contour of Zn in doped crystals has been used to reveal the solid-liquid interface shape in the growth process. A slow cooling rate is necessary to obtain a convex interface shape. A low temperature gradient at the solid-liquid interface, down to 2 °C/cm, and Zn doping are found to be effective to reduce the etch pit density to 5×103/cm2 (minimum) to 104/cm2 (average). The crystallographic quality has been evaluated by means of X-ray diffraction, X-ray topography, etch pit delineation with the Nakagawa etchant, infrared measurements, photoluminescence and Hall effect measurements. CdTe crystals are found to be free from subgrain structure, Te precipitates and deep levels, and have high electron mobility.
Controtle Substitutional Doping of Cdte Thin Films and Cd 1-xMn xTe-CdTe Superlattices
Authors: Bicknell R. N. , Giles N. C. , Schetzina J. F. 
Published: March 2011

ABSTRACTWe report the successful substitutional doping of CdTe epilayers grown by a new technique: photoassisted molecular beam epitaxy, in which the substrate is illuminated during the film deposition process. This new technique was found to produce dramatic changes in the electrical transport properties of the epilayers. In particular, highly conducting n-type and p-type CdTe films have been grown using In and Sb as n-type and p-type dopants,respectively. Photoassisted MBE has also recently been employed to produce for the first time highly conducting CdMnTe epilayers and Cd 1-xMnxTe-CdTe superlattices.
Tailored Microstructures for Infrared Detection
Authors: Chen Quark Y. , Bates C. W. 
Published: March 2011

ABSTRACTUsing the effective medium approximation[1–4] and the theory of photoemission from small particles,[5] we look into the design-rules of infrared materials based upon the metalsemiconductor random heterostructures with Ag particles embedded in the semiconductor. It is found that semiconductor host matrices with higher dielectric constants show better optical absorption in the infrared and that optical properties are closely related to microstructural parameters such as volume fraction of metal particles, percentage of aggregation and particle size. Cu, Ag and Au particles all show similar characteristics. We synthesized materials with small silver particles embedded in Si. Their microstructures are analysized using X-ray diffraction, electron microscopy and sputter Auger profiling. Finally, we present the optical properties of these materials and make comparisons with our theoretical results.
Laser Annealing of Narrow Gap HgTe-Based Alloys
Authors: Kremer R. E. , Moore F. G. , Tamjidi M. R. , Tang Y. 
Published: March 2011

ABSTRACTWe have used a cw CO2 laser to study the effects of rapidly annealing HgTe-based alloys. Both as-grown and thermally annealed samples of HgCdTe, HgMnTe, HgZnTe, and HgMgTe have been examined for mercury loss and surface damage using energy-dispersive x-ray analysis and optical reflectivity measurements. Small, but systematic differences were found between the asgrown and the thermally annealed samples and among the various materials studied. No degradation of the material at all was observed when the samples were cooled to 77 K and exposed to the laser.
Study of HgTe-cdTe Multilayer Structures by Transmission Electron Microscopy
Authors: Otsuka N. , Ihm Y. E. , Harris K. A. , Cook J. W. , Schetzina J. F. 
Published: March 2011

ABSTRACTA transmission electron microscope study of HqTe-CdTe multilayer structures grown by molecular beam epitaxy (MBE) on (100) Cd Zn Te is presented. Both cross-sectional and plain-view observations show highly reaular structures of superlattices and tunnel structures. Dislocation densities estimated by Plan-view observations are of the order of 104 cm−2 in these multilayer structures. A quantitative characterization of interface sharpness of superlattices has been carried out by intensity analysis of satellite spots in electron diffraction patterns. It is shown that interfaces in these superlattices are hichly abrupt with a width of one or two monolayers. These observations suggest the effectiveness of the use of lattice-matched substrates to qrow high quality HgTe-CdTe multilayer structures.
Hgl−xCdxTe Near Surface Characterization using Computer Aided Rutherford Backscattering Spectrometry
Authors: Kao T.-M. , Sigmon T. W. 
Published: March 2011

ABSTRACTIn this work, we report the use of Rutherford backscattering(RBS) measurements and computer simulations to provide accurate stoichiometry information and semi-quantitative defect densities for the near surface region of Hg1−xCdxTe (MCT). The accuracy of the Hg1−xCdx Te x-values determined by our method is found to be comparable to other commonly used methods, such as FTIR or the electron microprobe. The data obtained as structural defects from RBS channeling measurements are in basic agreement with other techniques, such as chemical etching. The sensitivity of the channeling measurement to uniformly distributed dislocations is found to be about 107−108 cm−2, however, for dislocations forming subgrains, the detectable level of dislocation comes to 105 – 106 cm−2. The depth profiles of lattice disorder resulting from ion implantation into MCT are also extracted from RBS channeling measurements using these simulation programs. These profiles are found to closely match the calculated profiles for the displaced atoms calculated using an implantation modeling program (TRIM). We also report on the use of channeling-in-grazing-angle-out technique for evaluating the stoichiometry of the first few monolayers of the MCT surface.
Interdiffused Multilayer Processing (IMP) in Alloy Growth
Authors: Mullin J B , Giess J , Irvine S J C , Gough J S , Royle A 
Published: March 2011

ABSTRACTThe Interdiffused Multilayer Processing (IMP) technique has been developed as a way of growing uniform layers of cadmium mercury telluride (CMT). The principle of the technique is discussed in the context of an interdiffusion coefficient so as to assess the potential applicability of the technique to the growth of other II–VI or III–V alloys. The development of IMP for the growth of CMT layers, together with the properties of the layers and their suitability for use in the fabrication of IR detectors, are reviewed.
Molecular Beam Epitaxial Growth of Cdl-xznxTe Matched to HgCdTe Alloys
Authors: Magnea N. , Dal'bo F. , Pautrat J. L. , Million A. , Cioccio L. Di , Feuillet G. 
Published: March 2011

ABSTRACTCD1−xZnxTe alloys of various composition have been grown by the Molecular Beam Epitaxy Technique and characterized by Transmission Electron Microscopy. C(V) measurements and photoluminescence spectroscopy techniques. The quality of the thick layers is comparable to that of bulk material. Thin strained layers have also been grown whose interfaces are structurally good. The recombination within a CdTe well confined between Cd1−xZnxTe barriers is dominated by intrinsic processes.
CdTe Films Grown on InSb Substrates by Organometallic Epitaxy
Authors: Bhat I. B. , Taskar N. R. , Ayers J. , Patel K. , Ghandhi S. K. 
Published: March 2011

ABSTRACTCadmium telluride layers were grown on InSb substrates by organometallic vapor phase epitaxy and examined using secondary ion mass spectrometry (SIMS), photoluminescence (Pb) and double crystal x-ray diffraction (DCD). The substrate temperature and the nature of the surface prior to growth are shown to be the most important parameters which influence the quality of CdTe layers. Growth on diethyltelluride (DETe) stabilized InSb substrates resulted in CdTe growth with a misorientation of about 4 minutes of arc with respect to the substrates. On the other hand, the grown layers followed the orientation of the substrates when a dimethylcadmium (DMCd) stabilized InSb was used. Growth at 350°C resulted in the smallest x-ray rocking curve (DCRC) full width at half maximum (FWHM) of about 20 arc seconds.
Plasma-Assisted Epitaxial Growth of Compound Semiconductors for Infrared Application
Authors: Matsushita K. , Hariu T. , Fang S. F. , Shida K. , Gao Q. Z. 
Published: March 2011

ABSTRACTGaSb, InSb and InAs epitaxial layers with mirror surface were grown on GaSb, GaAs, InP, Si and sapphire substrates at relatively low temperatures by plasma-assisted epitaxy (PAE) in hydrogen plasma. Carrier concentrations and Hall mobilities of undoped PAE layers at room temperature are p=6×O16 cm−3; μp=750cm2/Vs, n=1×1016cm−3; μn=39,000cm2/Vs and n=7×1017 cm−3; μn=21,000cm2/Vs for GaSb on GaAs, InSb on GaAs and InAs on InP, respectively. As the first application of PAE layers to optoelectronic devices, p-GaSb/n-GaAs heterojunction photodiodes have been demonstrated to result in remarkable reduction of dark current with photoresponse in the wavelength region between 0.85 and 1.7μm for the light incident from GaAs.
Defects in Mg-Doped InP and GaInAs Grown by Omvpe
Authors: Bacher Fred R. , Cholan H. , Leigh Wallace B. 
Published: March 2011

ABSTRACTWe report on the defects present in doped InP and GaInAs grown by organometallic vapor phase epitaxy (OMVPE). The material was grown in an atmospheric pressure system using group III trimethyl sources, arsine and phosphine. Bis(cyclopentadienyl) magnesium (Cp2Mg) was present as a p-type source of magnesium. Defects in as-grown material were characterized using photoluminescence (PL), Hall-effect, and deep level transient spectroscopy (DLTS). Various levels of Mg doping were investigated, ranging from 5 × 1015 to 1 × 1019 cm−3. Radiative defects were observed at 77 K corresponding to PL emission from conduction band/shallow donor to acceptor levels including emission at 1.37 eV identified as the shallow hydrogenic acceptor, and emission lines at 1.3 eV and 1.0 eV in heavily doped material. Corresponding hole traps in InP:Mg were observed by DLTS having thermal activation energies of 0.20 and 0.40 eV, the 0.40 eV trap being the dominant defect in p-type InP. In GaInAs grown near lattice-matched to InP, radiative emission is also observed from deep centers 100 meV from band edge emission. This emission is observed to be related to lattice-mismatch of the ternary with the InP, and is found to be accentuated and broadened in GaInAs doped with Mg.
Epitaxy in the Presence of Very Large Misfit: High Resolution TEM Study of Al/Si, Ag/Si, Al/CaF2/Si and Ag/CaF2/Si
Authors: LeGoues F. K , Liehr M. , Renier M. 
Published: March 2011

ABSTRACTWe summarize high resolution transmission electron microscopy studies of interfaces with 33% misfit. We explain the existence of epitaxial interfaces for this systems by a geometrical argument similar to the 0-lattice models used to study high angle grain boundaries. Differences between systems very similar in structures are explained. We use the thus found epitaxial interfaces to build multilayered structures of the type metal/insulator/semiconductor.
The Initial Stages of Silicide Epitaxy - Nucleation and Morphology
Authors: Nemanich R. J. , Doland C. M. , Ponce F. A. 
Published: March 2011

ABSTRACTThe initial stages of epitaxial silicide formation are described in terms of the nucleation properties. The reaction process is divided into the stages of interdiffusion, nucleation, and growth and coalescence. The aspects of the nucleation from the interdiffused regions are described. Results are presented for Pd and Pt deposited on clean Si surfaces. The initial thickness where silicide compound formation is observed is related to he critical cluster size of the nucleation model. The epitaxial morphology can be strongly influenced by heterogeneous nucleation involving the substrate interface, and this effect is demonstrated by reaction with metal overlayers less than the critical thickness.
Study of Epitaxial Growth of Au on Ni(110) by Scanning Tunneling Microscopy
Authors: Kuk Y. , Silverman P. J. , Buck T. M. 
Published: March 2011

ABSTRACTThe structure of the Au segregated Ni(110)-0.8%Au surface has been studied by scanning tunneling microscopy. The segregated Au layer forms a (7×4) structure with a c(2×4) subunit. At various coverages of Au overlayer, commensurate and incommensurate Au structures were observed. At a coverage of I monolayer, islands and facets assciated with incommensurate Au atoms were observed.
Photoemission Studies of the Initial Adsorption and Growth of Ag on Ge(111)
Authors: Wachs A. L. , Miller T. , Shapiro A. P. , Chiang T. -C. 
Published: March 2011

ABSTRACTWe present electron diffraction, and high-resolution angle-resolved and angle-integrated photoemission studies of the initial phases of adsorption and growth of Ag on Ge(111). The results provide information on the structural properties of the Ge(111)-c(2×8) substrate surface, show Ag grows upon it almost laminarly at room temperature, and unambiguously demonstrate the presence of a small amount of Ge segregating on top of the growing Ag overlayer. The origins and behavior of these segregated atoms are discussed. Ag films more than a few monolayers thick exhibit quantum well states which are observed to evolve as a function of film thickness.
Nucleation of Gaas on Vicinal Si(100) Surfaces
Authors: Hull R. , Fischer-Colbrie A. , Rosner S. J. , Koch S. M. , Harris J. S. 
Published: March 2011

ABSTRACTWe investigate the nucleation of epitaxial GaAs grown on vicinal Si(100) surfaces by Molecular Beam Epitaxy. We find that the vicinal surface structure is highly sensitive to the surface cleaning process, and that in-situ desorption of a volatile surface oxide at 900°C appears to result in significant step mobility, resulting in the formation of low angle surface facets. Nucleation of GaAs then occurs on these facets, raising the possibilty of influencing the heteroepitaxial nucleation and growth processes by influencing the substrate surface “template” at the surface cleaning stage.
Gas Phase Reactions in Horizontal MOCVD Reactors
Authors: Tanaka Hitoshi , Komeno J. 
Published: March 2011

ABSTRACTWe have applied kinetic simulation to MOCVD chemistry in a horizontal MOCVD reactor. Both chemical reactions and material diffusion are considered. For trimethylgallium decomposition, concentrations of chemical species reach their steady state values which differ largely from the equilibrium values.