bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ground and Excited Electronic Energy Surfaces of the MnS4 Cluster in ZnS:Mn2+
Authors: Richardson J. W. , Janssen G. J. H. 
Published: March 2011

AbstractGaussian-based Self Consistent Field (SCF) MOs are obtained at various nuclear geometries for the MnS4 cluster in the external potential of cubic ZnS. Electronic relaxation and d-shell electron correlation effects are then included. For Td symmetry, quartet d-d excitation energies calculated as functions of R(Mn-S) qualitatively resemble the simple CF diagram. While separations between successive quartet levels agree closely with experiment, the threshold is about 0.5 eV high; much of this discrepancy is removed by including additional correlation effects from charge-transfer states. Large Jahn-Teller (JT) splittings of 4T1 and 4T2 levels are found with D2d distortion. Difficulty in accurately evaluating force constants interferes with predicting the corresponding deformations and stabilization energies. Estimates, encorporating the observed Stokes'; shift and JT stabilization energy, are that R(Mn-S) decreases by ∼0.1 Å and the S-Mn-S dihedral angle increases by 7sim;8°, in the lowest quartet level.
DC- and FIR-Magneto-Transport in Zn(1−x)Mn(x)Se
Authors: Erhardt W. , von Ortenberg M. , Twardowski A. , Demianiuk M. 
Published: March 2011

AbstractDC- and FIR-magneto-transport measurements on Zn(1−x)Mn(x)Se for x<0.05 are interpreted in terms of nonresonant spin-flip hopping and resonant spin-flip conductivity. In combination with magnetization data the exchange-matrix element of the conduction band is determined to α = 0.32 eV.
Synthesis of the Dilute Magnetic Semiconductor CdMnTe by Ion Implantation of Mn into CdTe
Authors: Braunstein G. H. , Heiman D. , Withrow S. P. , Dresselhaus G. 
Published: March 2011

AbstractThe dilute magnetic semiconductor CdMnTe has been synthesized by ion implantation of Mn into CdTe. Samples of CdTe have been implanted with Mn ions of 60 keV energy to fluences in the range 1 × 1013 cm−2 to 2×1016 cm−2 and subsequently annealed, using rapid thermal annealing, for 10–15 sec at temperatures 300 ≤ TA ≤ 730°C. The successful formation of a near surface layer of CdMnTe is demonstrated by studies of the structural, electronic and magnetic properties of the ion implanted and annealed sampies; Rutherford backscattering-channeling analysis of the radiation-induced damage indicates complete recovery of lattice order after annealing at 700°C. Photoluminescence measurements, performed at 2K, reveal an increase in the energy band gap of the ion implanted alloy with respect to CdTe. Application of magnetic fields, up to 8T, produce both the characteristic energy shift of the excitonic recombination peak and polarization of the emitted radiation (in the Faraday configuration) previously observed in bulk–grown CdMnTe material.
Submicron Heterostructures of Diluted Magnetic Semiconductors
Authors: Gunshor R. L. , Kolodziejski L. A. , Otsuka N. , Datta S. , Nurmikko A. V. 
Published: March 2011

AbstractThe successful thin film growth of diluted magnetic semiconductors (DMS) by molecular beam epitaxy has “nucleated” a new field of research in which the DMS material is incorporated in a variety of novel superlattice and quantum well structures. The observation of reflection high energy electron diffraction intensity oscillations in ZnSe and MnSe has enabled the fabrication of ultrathin layered structures involving the “hypothetical” zincblende magnetic semiconductor MnSe. The expected antiferromagnetic ordering of MnSe is increasingly inhibited as the MnSe layer thickness is reduced from ten monolayers to the quasi-2D limit of one monolayer. Further developments include new observations of the epitaxial growth and nucleation of ZnSe, utilizing GaAs epilayers as the substrate material.
Optical Properties of Doped Cd1−xMnxTe
Authors: Lansari Y. , Giles N. C. , Schetzina J. F. , Becia P. , Kaiser D. 
Published: March 2011

AbstractThe introduction of phosphorus and arsenic dopants into bulk Cd1−xMnx Te crystals grown by the Bridgman-Stockbarger technique has been studieA-with respect to the resulting optical properties. Samples with a Mn composition in the range 0.10 < x < 0.30, both as-grown and annealed, were investigated. A combination of room temperature transmittance and reflectance measurements over the spectral range from the ultraviolet to the far infrared has been used to gain information concerning the structural quality of the samples. Low temperature photoluminescence measurements (1.6−5 K) were used to determine optical quality and excitonic energies.
Raman Scattering by Magnetic Excitations in Diluted Magnetic Semiconductors
Authors: Ramdas A. K. , Rodriguez S. 
Published: March 2011

AbstractRaman scattering provides significant information on the nature of the magnetic excitations of diluted magnetic semiconductors (DMS). Transitions involving an exchange of a quantum of angular momentum between the system and the radiation field result in Raman lines with shifts equal to the energy of the magnetic excitations in which the total spin of the crystal changes by ħ. Such transitions have a one-to-one correspondence with those seen in magnetic resonance but observed in the optical rather than in the microwave region of the electromagnetic spectrum. In the Mn-based II-VI DMS a variety of magnetic excitations have been observed in their Raman spectra. Microscopic models underlying these phenomena provide powerful insights into the nature of the magnetism of DMS.
Magnetic Contribution to the Energy Gap of Zn1−xMnxTe
Authors: Gaj J. A. , Golnik A. , Lascaray J. P. , Coquillat D. , Dejardins-Deruelle M. C. 
Published: March 2011

AbstractSystematic masurements of energy gap and magnetic susceptibility of Zn1−xMnxTe in a composition range from 0 to 0.703 Mn mole fraction were performed as a function of temperature. The results show that the magnetic contribution to the energy gap variation is proportional to a product of temperature and susceptibility.
Ion - Carrier Exchange Interaction in Cd1−xMnxS
Authors: Nawrocki M. , Lascaray J. P. , Coquillat D. , Demianiuk M. 
Published: March 2011

AbstractMagnetoreflectivity measurements in Faraday and Voigt geometry in the free exciton region (A, B and C excitons are visible) were performed on Cd0.07Mn0.13S at T=1.6 K for magnetic field up to 5.5 T. An analysis of the results in terms of a mean field model for wurtzite type crystal enabled to determine band parameters Δ1, Δ2, Δ3 and exchange integral for valence band N0ß = -1.8 ± 0.08 eV
Time-Resolved Photoluminescence of CD(1-x)MN(x)SE and CD(1-x)MN(x)TE as a Function of Temperature
Authors: zayhowski J. J. , Kershaw R. N. , Ridgley D. , Dwight K. , Wold A. , Galazka R. R. , Giriat W. 
Published: March 2011

AbstractThe characteristics of the photoluminescence of Cd(1-x)Mn(x)Se (x = 0.05, 0.10, 0.20, 0.30) and Cd(1-x)Mn(x)Te (x = 0.20, 0.30, 0.45) change considerably as the sample temperature is reduced below the exciton-magnetic polaron (EMP) threshold temperature. At low temperatures the formation of magnetic polarons has large effects on the luminescence energy, the radiative lifetime, the radiative efficiency, and the spectral half-width of the luminescence. It is also observed that the formation time of the EMP increases almost linearly with temperature. All of these effects are explained with a simple model for the EMP.
Effects of Exchange Interaction in Diluted Magnetic Semiconductor Quantum Wells
Authors: Kossut Jacek , Furdyna Jacek K. 
Published: March 2011

AbstractThe presence of transition metal ions (typically Mn2+) in diluted magnetic semiconductors (DMS) results in a strong spin-spin coupling between localized magnetic moments and band electrons. This leads to considerable modifications of the semiconductor band structure in the presence of strong magnetic fields, e.g., to large spin-dependent shifts of the electronic states at the band edge. This feature is of particular interest in the context of quantum wells involving DMS. Starting with the original idea of a “spin-superlattice”, we concentrate on various opportunities which arise due to the tunability of the depth of the quantum wells by the magnetic field and/or temperature associated with the aforementioned spindependent effects. Thus, we discuss boil-off and freeze-out of electrons to and from quantum wells, selective spin tunneling across the barriers, tunable infrared emitters, enhancement of electronic g-factors in shallow non-magnetic wells surrounded by DMS barriers, the possibility of transition from a type-1 to a type-il superlattice induced by the magnetic field, and quantum oscillations anomalies in DMS quantum wells.
Steady Thermocapillary Flows and Their Stability
Authors: Sen A. K. , Smith M. K. , Davis S. H. , Homsy G. M. 
Published: March 2011

ABSTRACTThermocapillarity can drive steady flows in float-zone configurations. These flows can become unstable and exhibit time-periodic oscillations. In order to obtain insight into such phenomena, studies are made of a simplified system consisting of liquid in a two-dimensional slot. Steady flows and their instabilities are examined.
Measurement of Surface Rheological Effects on a Rotating Flow
Authors: Gans Roger F. , Singler Timothy J. 
Published: March 2011

ABSTRACTWe report measurement of azimuthal velocity as a function of radius near the boundary between a liquid annulus and (a) a rigid freely floating cylinder and (b) an air core contained in a rapidly rotating horizontal cylindrical container. Case (a) agrees with previous theoretical calculations and verifies the method. Case (b) demonstrates (1) that the interface can support stress and (2) that there is a distinct difference in the scale of radial variation in the bulk liquid from that observed in case (a).
Flow Structure in Continuous Flow Electrophoresis Chambers
Authors: DEIBER J. A. , Saville D. A. 
Published: March 2011

ABSTRACTThere are at least two ways that hydrodynamic processes can limit continuous flow electrophoresis. One arises from the sensitivity of the flow to small temperature gradients, especially at low flow rates and power levels. This sensitivity can be suppressed, at least in principle, by providing a carefully tailored, stabilizing temperature gradient in the cooling system that surrounds the flow channel. At higher power levels another limitation arises due to a restructuring of the main flow. This restructuring is caused by buoyancy, which is in turn affected by the electro-osmotic crossflow. Approximate solutions to appropriate partial differential equations have been computed by finite difference methods. One set of results is described here to illustrate the strong coupling between the structure of the main (axial) flow and the electro-osmotic flow.
The Effect of Small Temperature Gradients on Flow in a Continuous Flow Electrophoresis Chamber
Authors: Rhodes Percy H. , Snyder Robert S. 
Published: March 2011

ABSTRACTContinuous flow electrophoresis employs an electric field to separate biological cells suspended in a flowing liquid buffer solution. Good separations based on differences in electrophoretic mobility are obtained only when a unidirectional flow is maintained. The desired flow has a parabolic structure in the narrow dimension of the chamber and is uniform across the width, except near the edges where the no-slip condition prevails. However, because of buoyancy, very small lateral or axial temperature gradients deform the flow significantly. The results of experiments conducted with a specially instrumented chamber show the origin and structure of the buoyancy-driven perturbations. It is found that very small temperature gradients can disturb the flow significantly, as was predicted by earlier theoretical work.
A Theory of Electrophoresis of Emulsion Drops in Aqueous Two-Phase Polymer Systems
Authors: Levine Samuel 
Published: March 2011

ABSTRACTTwo immiscible liquid phases form when an aqueous mixture of the electrically neutral polymers dextran and polyethylene glycol are equilibrated at sufficient concentrations. Certain supporting electrolytes which contain sulphate, phosphate or citrate ions partition unequally between the phases, and in their presence, electrophoresis of a drop of one phase suspended in the other is observed, with large mobilities. These mobilities depend linearly on the radius of the drop and the direction of the drop's motion is reversed when the disperse phase and the continuous phase are interchanged. When those ions which produce electrophoresis are present the potential Implied by the direction of electrophoresis is opposite to the Donnan potential observed between the two phases. To explain these results, we postulate an electric dipole layer associated with a mixture of oriented polymer molecules at the surface of a drop. In addition, a potential difference between the interiors of the two phases results from the unequal ion distribution. For the idealised model of a surface layer of point dipoles the inner and outer diffuse layers carry net charges equal in magnitude but opposite in sign. The classical theory of electrophoresis due to Henry, Overbeek and Booth is adapted to the motion of an emulsion drop under an electric field when diffuse ionic layers are present inside and outside the drop. Relaxation effects are treated for the case where the two diffuse layer thicknesses are small compared with the drop radius. An expression is obtained for the electrophoretic mobility of a drop which depends linearly on radius and also shows an increase with increase in salt concentration. The theory presented here is related to the work of Levich.
Thermocapillary Motion of Bubbles Inside Drops
Authors: Shankar N. , Cole Robert , Shankar Subramanian R. 
Published: March 2011

ABSTRACTThe quasi-static thermocapillary migration of a bubble located inside a drop in free fall is considered for arbitrary axisymmetric temperature fields prescribed on the drop surface. Some results are presented, and an approximation based on the superposition of simpler solutions is discussed.
Experimental Observation of the Thermocapillary Driven Motion of Bubbles in a Molten Glass Under Low Gravity Conditions
Authors: Smith H. D. , Mattox D. M. , Wilcox W. R. , Subramanian R. S. , Meyyappan M. 
Published: March 2011

ABSTRACTTheory and ground based studies of bubble behavior in a fluid in the presence of a temperature gradient strongly indicate the action of a thermocapillary force which causes the bubbles to move. This'phenomenon been considered in the traditional treatments of glass fining. To demonstrate that the observed motion conformed to theoretical prediction it was necessary to perform the experiment under low gravity conditions. NASA's SPAR program provided an excellent opportunity to do this.A sodium borate melt containing a specific bubble array was subjected to a well defined temperature gradient for more than 4 minutes. The sample was contained in a platinum/ fused-silica cell which permitted photographic coverage of the experiment. Photographs were taken at one second intervals during the course of the experiment. They clearly show that the bubbles move toward the hot spot on the platinum heater strip. The observed motion is consistent with the theoretical predictions for the temperature gradients parallel and perpendicular to the heater strip.
Materials Science in Space
Authors: Carruthers John R. 
Published: March 2011

ABSTRACTThe preparation of solid materials involves the control and manipulation of fluids in ways that are sensitive to gravitational influences. Although these effects are pervasive, surprisingly little is understood about phenomena such as natural convection and containerless processes under boundary conditions of interest to materials processing. Recent emphasis has focused on process fundamentals involving areas such as fluid dynamics, heat flow, and thermophysical property measurement as can be seen in this Symposium. Such a knowledge base is essential to any sensible evolution of the space environment as a capability for studying materials processing and preparing limited quantities of materials under quiescent or containerless conditions for subsequent assessment on earth. A brief overview of current work will be presented, together with possible future directions.
Preliminary Study of the Effects of a Reversible Chemical Reaction on Gas Bubble Dissolution
Authors: Weinberg Michael C. 
Published: March 2011

ABSTRACTA preliminary investigation of the effects of a reversible chemical reaction upon the dissolution of an isolated, stationary gas bubble in a glassmelt is presented. The exact governing equations, for the model system, are formulated and discussed. The approximate quasi-steady state version of these equations are solved analytically and bubble dissolution rates are computed. These results are compared with numerical solutions obtained from the finite difference form of the exact governing equations.
Anomalous Phase Separation Behavior of Gel-Derived soda-silica Glasses
Authors: Neilson George F. , Weinberg Michael C. 
Published: March 2011

ABSTRACTThe effects of retained bound hydroxyl groups on amorphous immiscibility behavior and on the kinetics of phase separation were studied in glasses containing from 10 to 19 percent sodium oxide prepared by the gel process. Differences in behavior as functions of preliminary thermal treatment of the gel precursor and of melting conditions were studied, employing IR spectroscopy, SAXS and WAXD to monitor the variation in glass microstructure. Both the initial gel treatment and the OH concentration in the prepared glasses were found to affect the immiscibility temperatures, and the magnitude of the maximum temperature increase was also a function of the sodium oxide concentration. It is suggested that the variation in thermodynamic behavior may be caused by the structural arrangement attained by the OH groups during the gel condensation process, which in turn affects the extent of hydrogen bonding to nonbridging oxygen ions.
Chemical Vapor Transport, Crystal Growth, Thermodynamic and Fluid Dynamic Analysis of the Hgl−xCdxTe System
Authors: Wiedemeier Heribert , Chandra Dipankar 
Published: March 2011

EXTENDED ABSTRACTThe chemical vapor transport and crystal growth properties of the Hgl−xCdxTe iodine system (x=0.2, 0.5 and 0.7) are investigated as a function of transport agent pressure and orientation of the density gradient with respect to the gravity vector to understand the effects of convection on mass transfer and crystal morphology. A thermodynamic analysis of the solid-gas phase system yielded the composition of the vapor and the partial pressures of the gaseous species as a function of temperature and total pressure to assist in the elucidation of the dominant transport mode. Optical and scanning electron microscopy, electron microprobe, chemical etching, X-ray diffraction and energy dispersive spectroscopy techniques were employed to examine the surface and bulk morphology and compositional homogeneity of single crystals obtained under different conditions.
Response of Mnbi-Bi Eutectic to Freezing Rate Changes
Authors: Nair M. , Fu T-W. , Wilcox W. R. , Doddi K. , Ravishankar P. S. , Larson D. 
Published: March 2011

ABSTRACTPreviously we reported on a theoretical treatment of the influence on freezing rate of sudden changes in translation rate in the Bridgman-Stockbarger technique [11]. This has now been extended to consideration of a linear ramped translation rate and an oscillatory freezing rate. Oscillations above a few hertz are found to be highly damped in smalldiameter apparatus.An experimental test was made of the theoretical predictions for a sudden change of translation rate. MnBi-Bi eutectic was solidified with current induced interface demarcation.The experimental results correspond reasonably well with theory if the silica ampoule wall is assumed either (1) to contribute only a resistance to heat exchange of sample with the furnace wall, or (2) to transmit heat effectively in the axial direction by radiation.In an attempt to explain the fact that a finer microstructure is obtained in space, MnBi-Bi microstructure is being determined when the freezing rate is rapidly increased or decreased. Preliminary results indicate that fiber branching does not occur as readily as does fiber termination.
Directional Solidification of Alloys in Systems Containing a Liquid Miscibility Gap
Authors: Grugel R. N. , Lograsso T. A. , Hellawell A. 
Published: March 2011

ABSTRACTThe problem considered is the unidirectional growth of alloys close to monotectic composition and within the miscibility gap when the direction of gravity is down the temperature gradient (solidification upwards) or up the temperature gradient (solidification downwards). The systems Al-In and Al-Bi are taken as examples. With solidification upwards it is shown that bulk liquid composition adjusts to that of the monotectic while in the reverse situation, the bulk liquid gradually rises. In the former case it is possible to grow aligned fibrous structures of monotectic composition but in the latter the microstructures are irregular and globular.
A Qualitative Model for Predicting Alkyl Stability and its Relevance to Organometallic Growth of HgCdTe and GaAlAs
Authors: Hoke William E. 
Published: March 2011

ABSTRACTA qualitative stability model established for hydrocarbon molecules and extended to organometallic compounds is applied to alkyl organometallic compounds used in thin film growth. For hydrocarbon molecules the strength of a carbon-hydrogen bond is reduced by neighboring alkyl groups, The mechanism for this effect is delocalization of the unpaired electronic charge in the resultant free radical by neighboring alkyl groups. The delocalization effect is present in organometallic compounds and is illustrated here for several alkyl organometallic systems. Two applications of the delocalization effect in thin film growth are discussed. First the thermal stability of organotellurium compounds is substantially reduced in branched compounds which permits significantly lower HgCdTe metalorganic growth temperatures. Also carbon incorporation in GaAs and GaAlAs is reduced with ethyl instead of methyl organometallic compounds. An important factor contributing to this result is the weaker carbon-metal bonds in the ethyl compounds.
MBE Growth of Mercury Cadmium Telluride: Issues and Practical Solutions
Authors: Cook J. W. , Harris K. A. , Schetzina J. F. 
Published: March 2011

ABSTRACTThe growth of thin films of mercury-based materials by molecular beam epitaxy (MBE) presents significant experimental problems which must be overcome in order to successfully grow infrared detector materials such as mercury cadmium telluride (MCT). Many of the problems associated with the use of Hg in MBE arise from its high room temperature vapor pressure (2 mTorr) and its low sticking coefficient. The MBE system must be designed for Hg usage by considering such things as the ultra high vacuum pumping system, the Hg source, Hg containment, and Hg removal. In addition, Hg is a toxic heavy metal and must be handled appropriately. Other problems involved with the growth of MCT are associated with the design of the MBE furnaces which are used to evaporate cadmium telluride and tellurium.
Bulk Crystal Growth of Hg1−xCdxTe for Avalanche Photodiode Applications
Authors: Duy T. Nguyen , Durand A. , Lyot J. L. 
Published: March 2011

ABSTRACTHigh gap Hg1−xCdxTe (MCT) crystal is grown by a solvent method using a travelling heater zone. The use of the solvent zone permits a low temperature and low mercury pressure growth of MCT in a large composition range. In the Cadmium rich alloy range the MCT material exhibits a large spin orbit coupling leading to a resonance at Eg = ΔO. Due to this particular resonance effect the ionization coefficient of hole is higher than that of the electron, resulting in a low exess noise factor in the avalanche photodiodes whose bandgap energy is close to the spin orbit splitting ΔO.