bluuebunny/crossref_metadata_2025_split huggingface dataset:
Properties of an Array of Dislocations in a Strained Epitaxial Layer
Authors: Zhang Tong-Yi 
Published: March 2011

AbstractThe energy of a general array of dislocations in an epitaxial layer is formulated and expressed in terms of per unit area of interface. Several limiting cases are used to verify the solution and the results are compared to other independent treatments. The critical thickness required for the generation of an isolated dislocation is found by solving for the layer thickness which corresponds to a zero value of the formation energy. The critical dislocation density at a given thickness is also determined. An additional work required for sequential generation of dislocations in an epitaxial layer arises from dislocation-dislocation interaction and has to be expressed in terms of per unit length of dislocation line. The work hardening effect is found to increase sharply with decreasing distance between the fresh and the pre-existing dislocations once the distance falls below approximately twenty times the layer thickness. The additional work achieves the level of the self energy of an isolated dislocation when the distance between the fresh and the nearest pre-existing dislocation is comparable to twice the layer thickness.
Defect Reduction by Thermal Cyclic Growth in GaAs Grown on Si by Movpe
Authors: KÜrner W. , Dieter R. , Zieger K. , Goroncy F. , DÖrnen A. , Scholz F. 
Published: March 2011

AbstractThe growth of GaAs epilayers on Si should combine the advantages of both materials. The lattice mismatch and the difference in thermal expansion coefficients, however, result in the yet unsolved problems of high dislocation density and thermal stress in the GaAs layer. Recently, considerable improvements have been achieved by a ‘thermal cyclic growth’ (TCG) process. In this study we focus on the reduction of high defect concentration and dislocation density. The improvement of the epilayer quality is verified by DLTS, PL and DCXD. Results of TEM and DLTS measurements lead to the identification of a dislocation related defect.
Deep Levels Induced by SiCI4 Reactive Ion Etching in GaAs
Authors: Johnson N.P. , Foad M. A. , Murad S. , Holland M. C. , Wilkinson C. D. W. 
Published: March 2011

AbstractDeep Level Transient Spectroscopy (DLTS) is used to investigate the effect of SiC14 Reactive Ion Etching (RIE) on GaAs. At high power (150-80 W) with high DC self bias (380-240 V), five deep levels trapping electrons are observed at energies of 0.30, 0.42, 0.64, 0.86 and ∼0.8 eV below the conduction band edge. Depth profiling reveals an approximate exponential decay of the concentration of the deep levels. At low power the induced concentration falls, the small concentration of remaining deep levels is close to control (no etching) samples. The induced deep levels can account for reduced conductances in n+GaAs wires defined by RIE under similar experimental conditions.
Optical and Electronic Properties of GaAs/AlAs Random Superlattices
Authors: Wang E.G. , Xu J.H. , Su W.P. , Ting C.S. 
Published: March 2011

AbstractThe optical and electronic properties of three-dimensional (3D) random GaAs/AlAs superlattices (SLs) has been studied by using a tight-binding Hamiltonian with secondneighbor interactions. We calculate three completely disordered sequences with the probability of GaAs layers being 30%, 50%, and 70%. The higher the GaAs composition, the narrower the indirect gap. An energy-level crossing is found at the bottom of conduction band, which originates from the M-state splitting induced by layer disorder. The localized states over two - four monolayers play an important role in the absorption edge of random SL. The highest absorption intensity of the band-edge transitions in our random models is about eight times stronger than that of short period ordered GaAs/AlAs SL. Our results are in good agreement with some recent photoluminescence measurements.
Interaction Between Defects and Tunneling Effect in Heterostructures
Authors: Stievenard D. , Lannoo M. 
Published: March 2011

AbstractDue to the reduced size of quantum devices, defects play a dominant role in their electrical behaviour. We theoretically show that defects can change the electrical behaviour of a single barrier or a quantum well. For the barrier and the well, we have performed a quantum calculation of a defect assisted tunneling effect based on the WKB theory to describe the wave functions and on the Oppenheimer approach for the determination of the tunneling probability. The main effects are : appearance of a negative differential resistance (NDR) in the currentvoltage characteristics (I-V) of the single barrier and an apparent lowering of the band offset of the quantum well. In the latter case, we have experimentally measured this effect on an AlInAs-GaInAs-AlInAs well, using admittance spectroscopy. The apparent lowering is associated with a native defect located in the barrier, a defect studied using the DLTS technique.
Single-Source Precursors to Vanadium Nitride Thin Films
Authors: Winter Charles H. , Viejo Valerie C. , Proscia James W. 
Published: March 2011

AbstractVanadium nitride films reflect infrared radiation and are candidates for solar control coatings for glass. Herein we report our efforts to prepare new precursors to vanadium nitride coatings. Treatment of vanadium tetrachloride with primary alkylamines in dichloromethane affords vanadium chloride amides of the empirical formula [VCI2(NHR)2(NH2R)2]. The characterization and properties of these compounds is presented. The complexes [VC12(NHR)2(NH2R)2] can be sublimed at ca. 100°C (0.1 mmHg) and serve as single-source precursors to vanadium carbonitride films. Films have been deposited in the temperature range of 400-600°C on glass and silicon substrates. The film properties and characterization will be overviewed.
Assessment of Carbon Contamination in Titanium Nitride Films Deposited from the Reaction of Titanium (IV) Ciiloride and Amines
Authors: Williams Keith B. , Stewart Ogie , Reck Gene P. , Proscia James W. 
Published: March 2011

AbstractThe reaction of titanium (IV) chloride and amines in an atmospheric pressure chemical vapor deposition (APCVD) has been previously shown to produce high quality titanium nitride films. These films were gold in appearance with high infrared reflectivity and resistivities as low as 80 microhm-cm. In the present study, the carbon content of the amines was systematically increased and the carbon levels in the films measured by XPS. For primary amines carbon contamination was not detected. Films deposited from secondary and tertiary amines had measurable carbon contamination. Correlation of carbon contamination with electrical resistivity and infrared reflectivity is discussed. Scanning electron micrographs and x-ray diffraction of the films are presented.
Performance of CVR Coatings for PBR Fuels
Authors: Adams Jay W. , Barletta R. E. , Svandrlik J. , Vanier P. E. 
Published: March 2011

AbstractAs a part of the component development process for the particle bed reactor (PBR), it is necessary to develop coatings for fuel particles which will be time and temperature stable. These coatings must not only protect the particle from attack by the hydrogen coolant, but must also help to maintain the bed in a coolable geometry and mitigate against fission product release. In order to develop these advanced coatings, a process to produce chemical vapor reaction (CVR) coatings on fuel for PBRs has been developed.The initial screening tests for these coatings consisted of testing in flowing hot hydrogen at one atmosphere. Surrogate fuel particles consisting of pyrolytic graphite coated graphite particles have been heated in flowing hydrogen at constant temperature. The carbon loss from these particles was measured as a function of time. Exposure temperatures ranging from 2500 to 3000 K were used and samples were exposed for up to 14 minutes in a cyclical fashion, cooling to room temperature between exposures. The rate of weight loss measured as a function of time is compared to that from other tests of coated materials under similar conditions. Microscopic examination of the coatings before and after exposure was also conducted and these results are presented.
Synthesis of New Nitrides Using Solid State Oxide Precursors
Authors: Houmes Joel D. , Bem David S. , Loye Hans-Conrad Zur 
Published: March 2011

AbstractSeveral novel transition metal nitrides were synthesized via ammonolysis of solid state oxide precursors at temperatures ranging from 700°C-900°C and reaction times ranging from 12 hours to 4 days. Both intermetallic nitrides, Fe3Mo3N and Co3Mo3N, and ionic/covalent nitrides, FeWN2, MnWN2, Ta5N6 and Nb5N6, were prepared by this method. The products were characterized by powder X-ray diffraction and their structures were determined by powder X-ray Rietveld refinement. The intermetallic nitrides were found to be isostructural with the eta-carbide structure, Fe3W3C, while the ionic/covalent nitrides have layered structures, with metals in octahedral and trigonal prismatic coordination environments. Two polymorphs of the MnWN2 composition, α-MnWN2 and β-MnWN2, were isolated after ammonolysis at 700°C and 800°C, respectively. While the alpha phase can be converted into the beta phase by heating to 800°C under ammonia, annealing the beta phase at 700°C did not result in a structural transformation. Magnetic measurements show that FeWN2 orders antiferromagnetically at 45K. The magnetic ordering temperature was confirmed by M6ssbauer spectroscopy. All the other nitrides were paramagnetic down to 5K. Conductivity measurements show that FeWN2 and MnWN2 are metallic.
Deposition of a-SiC:H Using Organosllanes in an Argon/;Hydrogen Plasma
Authors: Maya Leon 
Published: March 2011

AbstractSelected organosilanes were examined as precursors for the deposition of amorphous hydrogenated silicon carbide in an argon/hydrogen plasma. The effect of process variables on the quality of the films was established by means of FTIR, Auger spectroscopy, XPS, XRD, chemical analysis, and weight losses upon pyrolysis. For a give power level there is a limiting feeding rate of the precursor under which operation of the system is dominated by thermodynamics and leads to high quality silicon carbide films that are nearly stoichiometric and low in hydrogen. Beyond that limit, carbosilane polymer formation and excessive hydrogen incorporation takes place. The hydrogen content of the plasma affects the deposition rate and the hydrogen content of the film. In the thermodynamically dominated regime the nature of the precursor has no effect on the quality of the film, it affects only the relative utilization efficiency.
Synthesis and Stabilization of Hexagonal Boron Nitride Materials
Authors: David Patrick , Mathiot Alain , Lulewicz Jean-Daniel , Narcy Bruno 
Published: March 2011

AbstractBoron nitride presents many interesting properties for high temperature applications: high specific modulus, high electrical resistivity, electromagnetic transparency and strong chemical stability. However synthesis and densification by liquid or gas phase reactions (CVD, CVI or plasma processes) required for high technology applications (thermal shield, protective coating, microwave windows) are difficult to bring into play because material characteristics are strongly dependent on elaboration conditions. Boron nitride ultrafine powder synthesized by gas phase reaction in RF plasma (using NH3 and BCh3 at 800-1400°C) and composites obtained using a rapid densification process (vapor phase infiltration using trichloroborazole compound as precursor) have been studied. In both cases post synthesis heat treatment had to be performed in order to get stabilization of the material, and to avoid its hydrolysis. The stability has been related to the physical characteristics of the material. Thermodynamical studies using Gibbs energy minimization calculations were helpful to determine synthesis and heat treatment conditions.
Enhancement of Oxidation Resistance of Silicon Carbide by High-Dose and Multi-Energy Aluminum Implantation
Authors: Yang Zunde , Du Honghua , Libera Matthew , Withrow Stephen P. , Casas Luis M. , Lareau Richard T. 
Published: March 2011

AbstractHigh-dose and multi-energy aluminum implantation of α-SiC (0001) was carried out to achieve a broad aluminum distribution extending from the sample surface to a depth of approximately 350 nm. Oxidation resistance of the implanted crystals was studied in 1 atm flowing oxygen at 1300°C. Aluminum implantation resulted in a 45% improvement in the oxidation resistance of α-SiC as compared with unimplanted crystals due to the formation of structurally dense mullite (3A12O3.2SiO2) in the oxidation scale.
One-Step Synthesis of Dithiocarbamates from Metal Powders
Authors: Hepp Aloysius F. , Hehemann David G. , Duraj Stan A. , Clark Eric B. , Eckles William E. , Fanwick Phillip E. 
Published: March 2011

AbstractNeutral metal dithiocarbamate complexes (M(NR2CS2)x) are well-known precursors to metal sulfides, a class of materials with numerous technological applications. We are involved in a research effort to prepare new precursors to metal sulfides using simple, reproducible synthetic procedures. We describe the results of our synthetic and characterization studies for M = Fe, Co, Ni, Cu, and In. For example, treatment of metallic indium with tetramethylthiuramdisulfide (tmtd) in 4-methylpyridine (4-Mepy) at 25°C produces a new homoleptic indium (III) dithiocarbamate, In(N(CH3)2CS2)3 (I), in yields of over 60%. The indium (III) dithiocarbamate was characterized by X-ray crystallography; (I) exists in the solid state as discrete distorted-octahedral molecules. Compound (I) crystallizes in the Plbar (No. 2) space group with lattice parameters: a = 9.282(1) A, b = 10.08 1(1) Å, c = 12.502 Å, ∝ = 73.9 1(1)°, β = 70.21(1)°, γ = 85.84(1)°, and Z = 2. X-ray diffraction and mass spectral data were used to characterize the products of the analogous reactions with Fe, Co, Ni, and Cu. We discuss both use of dithiocarbamates as precursors and our approach to their preparation.
Processable, Chemical Routes to Binary Metal Sulfides
Authors: Rees William S. , Krauter Gertrud 
Published: March 2011

AbstractMetal thiolates of the general formula M(SR)2(M = Pb, Zn, Cd) and Cl-Hg-SR (R = alkyl) have been prepared and characterized by spectroscopic techniques, TGA and, in selected cases, single crystal X-ray diffraction. The metalbis(thiolate) compounds can be converted into the related metal sulfides by thermolyses. The solid state materials have been characterized by XRPD, SEM and, in selected cases, by particle size determination. The volatile pyrolytic co-products have been isolated and characterized by GC/MS. The decomposition pathways of mercury chlorothiolates are more complicated and depend on the nature of the organic group present in Cl-Hg-SR.
The Crowdion Spreading and Radiation Stability Possibility of Non-Oxides
Authors: Koshkin Vladimir M. , Dmitriev Yuri N. 
Published: March 2011

AbstractThe paper suggests a criterion for selection of radiation stable semiconductors and dielectrics.The search for materials with great radiation stability (RS) is one of the basic problems in materials science. The absolute RS of crystals could be provided only in case when all elementary radiation defects (Frenkel pairs) are unstable, and annihilated immediately at any low temperatures in the places whete they were born. The presence of an instability zone (IZ) of point defects vacancy (v) - interstitial atom (i) is a necessary condition for RS [1,2]. The characteristic radius r0 of IZ at v-i Coulomb interaction is on the order of 10-30 Å [3]. The important parameter is a mean distance x between stopping point of atom i, knocked out from its site, and the v born at this site. Without taking into account the periodic structure, the analytical expression for x was obtained[4]. The value of x appears to be not large. For example, if the knocked out atom has the energy of 10 keV, the mean distance between v and i is 10 Å in iron, and only 3 Å in copper (x < r0). So, the greatest part of i's seem to remain in IZ, and therefore must recombine with “their” own v's. This would result in RS being greater than what was really observed in majority of nonmetal crystals.
Chemical Bond Distribution and Short Range Order in Non-Oxide Ciialcogenide Glasses. Results from NMR Spectroscopy
Authors: Tepe Thomas , Lyda Carri , Tullius Michael , Lathrop David , Leone Jason , Eckert Hellmut 
Published: March 2011

AbstractSolid-state 31p MAS-NMR provides powerful insights into the local order of phosphorus selenide based glasses. Specifically, it allows a quantitative characterization of the melt equilibrium PSe3/2 + Se -> Se=PSe3/2 describing the stability of four-coordinate P atoms. Using this technique, the effect of isovalent substitution by As, and Te, and of other glass constituents Ge and TI on this equilibrium and on the quantitative phosphorus speciation is studied in detail.
Scanning Probe Microscopy Study of Layered Dichalcogenide ReS2
Authors: Kelty Stephen P. , Ruppert Albert F. , Chianelli Russell R. , Ren Jingqing , Whangbo Myung-Hwan 
Published: March 2011

AbstractSingle crystal ReS2 was characterized using atomic force microscopy (AFM) and scanning tunneling microscopy (STM). The observed atomic-resolution AFM and STM images were interpreted by calculating the total, p(r0), and partial electron density distribution, p(r0, ef), respectively, of a single ReS2 layer. The experimental and theoretical results indicate that the basal plane surface state density is dominated by contributions from the sulfur layer This is in contrast to bulk band structure calculations which would predict that the major contribution to the STM images should be from the Re atoms. Furthermore, the surface-to-tip STM images are found to be quite different from tip-to-surface images. By interpreting STM and AFM data from p(r0) and p(r0, ef) calculations, it is shown that site specific structural and electronic details of the surface can be elucidated.
The Synthesis of Polycrystalline Chalcopyrite Semiconductors by Microwave Irradiation
Authors: Landry Christopher C. , Barron Andrew R. 
Published: March 2011

AbstractPolycrystalline samples of the chalcopyrites CuInS2, CuInSe2, AgInS2, and AgInSe2 have been prepared from stoichiometric mixtures of the pure elements using microwave irradiation. The reactions were performed in sealed quartz tubes in as few as three minutes. The products were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, and X-ray photoelectron spectroscopy (XPS). The surface morphology and shape of the particles produced by this method suggests that the products are formed from liquid melts.
Strategies for Crystal Engineering of Polar Solids
Authors: Zaworotko Mike , Subramanian S. , Macgillivray L. R. 
Published: March 2011

ABSTRACTCrystal engineering has been invoked to design structural analogues of two prototypal SHG active solids, p-nitroaniline (pNA) and potassium dihydrogenphosphate (KDP). pNA exists as linear polar strands because of head-to-tail hydrogen bonding between adjacent molecules whereas KDP is a self-assembled hydrogen bonded diamondoid network that becomes polar when the hydrogen bonds align. We detail preparation and crystallographic characterization of two classes of multicomponent solid, organic cation hydrogen sulfates and cocrystals of the cubane cluster [M (CO)3(μ3-OH)]4, which structurally mimic pNA and KDP, respectively. Several of the Multi-component solids are polar and they represent a generic approach to designing new polar materials since one component can be changed without altering the basic architecture within the crystal.
Molecular-Level Control in The Deposition of Ultrathin Films of Highly Conductive, In-Situ Polymerized P-Doped Conjugated Polymers
Authors: Fou A. C. , Ellis D. L. , Rubner M. F. 
Published: March 2011

ABSTRACTA novel thin film processing technique has been developed for the fabrication of ultrathin films of conducting polymers with angstrom-level control over thickness and multilayer architecture. Molecular self-assembly of in-situ polymerized conjugated polymers consists of a layer-by-layer process in which a substrate is alternately dipped into a solution of a p-doped conducting polymer (e.g. polypyrrole, polyaniline) and a solution of a polyanion. In-situ oxidative polymerization produces the more highly conductive, underivatized form of the conjugated polymer, which is deposited in a single layer of precisely controlled thickness (30 to 60 Å). The thickness of each layer can be fine-tuned by adjusting the dipping time and the solution chemistry. The surface chemistry of the substrate (e.g. hydrophobic, charged, etc.) also strongly influences the deposition, thereby making it possible to selectively deposit conducting polypyrrole onto well defined regions of the substrates. Typical multilayer films exhibit conductivities in the range of 20–50 S/cm, but samples with conductivities as high as 300 S/cm have been realized. There is no limit to the number of layers that can be built up nor to the complexity of the multilayer architecture of the film; achieved simply by alternating the sequence of dips into solutions of various polycations and polyanions. This new self-assembly process opens up vast possibilities in applications which require large area, ultrathin films of conducting polymers and, more importantly, in applications that can take advantage of the unique interactions achievable in the complex, supermolecular architectures of multilayer films.
Conducting Polymers: Past, Present and Future…
Authors: MacDiarmid Alan G. , Epstein Arthur J. 
Published: March 2011

ABSTRACTSince their discovery 16 years ago, the field of intrinsically conducing polymers — “synthetic Metals” — has developed at an unexpectedly rapid rate. The concept of “doping” is the unifying theme which distinguishes this class of organic polymers — “conducting polymers” — from all others. Doping results in dramatic electronic and magnetic changes with a concomitant increase in conductivity to, or approaching, the metallic regime. Doping phenomena and the chief types of dopable organic polymers are described with particular emphasis on polyaniline, which is now probably the most actively-studied conducting polymer. It has been commercialized on a relatively large scale and presently appears to be the leading conducting polymer for technology. It shows considerable promise for electromagnetic interference (EMI) shielding and as a gas separation Membrane, and is currently used in commercial rechargeable batteries. Polypyrrole is used commercially in capacitors and as an electrically conductive coating on conventional fabrics. Additional potential uses of conducting polymers such as light-emitting diodes, electrochromic windows, chemical sensors, etc. are also described briefly.
Solubility and Dispersion Characteristics of Polyaniline
Authors: Shacklette L. W. , Han C. C. 
Published: March 2011

ABSTRACTWe have demonstrated that the solubility characteristics of undoped polyaniline can be understood from the point of view of standard solubility parameters which measure the propensity for the polymer and the solvent to engage in dispersive, polar, and hydrogen bonding interactions. By empirical measures and group additive calculations, emeraldine base has been shown to be characterized by solvent interaction parameters: δd = 17.4 MPa1/2, δp = 8.1 MPa1/2, and δh = 10.7 MPa1/2, which together are equivalent to a total solubility parameter: δ = 22.2 MPa1/2. In the case of doped polyanilines, the solubility parameters can influence or even dominate the interactions of the doped polymer. Without the modifying influence of the dopant anion, the doped polyaniline compositions are more strongly polar and hydrogen bonding than the undoped polymer.