bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of Cooling Rate on the Tensile Yield Strength and Ductility Of B2 Compound in Nb-40at.% Ti-15at.%Al Alloy
Authors: Hou D.-H. , Fraser H.L. 
Published: March 2011

AbstractThe effect of cooling rate on the tensile properties of specimens of the Nb-40Ti-15A1 alloy (in at.%) subjected to various heat treatments has been studied. This alloy has the B2 crystal structure and an order-disorder transition temperature between 1020°C and 1100°C. Two heat treatments have been carried out; the first one involves an 1100°C/1hr heat treatment followed by furnace cooling, air cooling or water quenching. The second type of heat treatment involves re-heating the furnace-cooled and water-quenched specimens at 400°C for 10 minutes or 900°C for 30 minutes, followed by either furnace cooling or water quenching. Tensile properties, SEM fractographs and microstructures of these specimens have been assessed. It is shown that specimens furnace-cooled from 1100°C have higher strength and less ductility than the water quenched ones. An observed microstructural feature associated with cooling rates is the difference in anti-phase domain (APD) size. Discussions are focused on possible cooling rate related phenomena that could affect the tensile properties. It is proposed that the degree of long range ordering, not the APD size, is the dominant factor for the observed cooling rate effect on the tensile properties.
Refractory and Silicide Laves Phases
Authors: Livingston James D. 
Published: March 2011

AbstractPresent knowledge and understanding of deformation mechanisms, mechanical properties, and dislocations in Laves phases are reviewed. Although the amount of study applied to alloys containing these compounds has been relatively limited, several systems with promising high-temperature properties have been identified, including alloys hardened by binary chromides, ternary aluminides, and ternary silicides. Studies of model alloy systems have suggested possible approaches to increase the room-temperature ductility and toughness of Laves phases. Fundamental studies of the effects of stoichiometry, alloying, atom sizes, electronic structures, stacking fault energy, and other variables on dislocation mobility are needed.
Effect of Intermetallic Compounds on the Properties of Tantalum
Authors: Kumar P. , Mosheim C.E. , Michaluk C.A. 
Published: March 2011

While pure tantalum has excellent corrosion resistance and formability, its high temperature properties and thermal stability are marginal for some intended applications. Traditional approaches for improving these properties have been dispersion and solid solution strengthening. Modifications of properties via an intermetallic precipitation was not considered until recently.Results of an on-going investigation on the processing and evaluation of silicidestrengthened tantalum are presented. Yttrium silicide-containing Tantalum samples were produced via the P/M method. Evaluation consisted of microstructural, mechanical, chemical and functional tests. Results were compared with those of commercially available tantalum. Intermetallics precipitates were found to be very potent in altering these properties.While the preliminary results are encouraging, extensive functional testing is required to assure that there is no unexpected adverse effect.
Ternary MoSi2 Compounds for High Temperature Structural Applications
Authors: Chin S. , Anton D. L. , Giamei A. F. 
Published: March 2011

AbstractThe microstructure and phase composition of MoSi2 modified with Al, B, Ge, Hf, Nb, and Re have been investigated. B and Hf substitutions for Si and Mo, respectively, exhibited very low solubilities in MoSi2. Al and Nb substitutions for Si and Mo, respectively, changed the crystal structure from tetragonal C11b to hexagonal C40. Phase boundaries and solubility limits were determined for Al and Nb substitutions. Ge and Re substitutions for Si and Mo, respectively, exhibited complete solubility and maintained the tetragonal Cllb crystal structure. The mechanical properties evaluation as determined by four-point flexural testing indicate a ductile-to-brittle transition temperature (DBTT) of 1250-1350°C for all of the modifications evaluated. Isothermal oxidation testing at 1400°C indicates no significant debit in oxidation resistance of MoSi2 that can be attributed to alloying, however, alloys containing higher concentrations of the ternary elements may exhibit reduced oxidation resistances.
Identification of the 0.15 eV Donor Defect in Bulk GaAs
Authors: Fang Z-Q. , Hemsky J. W. , Look D. C. 
Published: March 2011

AbstractThe well-known 0.15-eV Hall-effect center appearing in bulk, n-type GaAs quenches under IR illumination and recovers via an Auger-like process at a rate similar to the Auger rate of EL2. On the other hand, the 0.15-eV VAs-related center produced by 1-MeV electron irradiation does not quench at all. Based on these data and a detailed theoretical analysis by Baraff and Schluter, we argue that the bulk 0.15-eV center is related to the AsGa-VAs defect or a related complex.
Effects of Processing and Prolonged High Temperature Exposure on the Microstructure of Nb-1Zr-C Sheet
Authors: Uz Mehmet , Titran R. H. 
Published: March 2011

AbstractHigh temperature stability of the microstructure of Nb-lZr sheet containing 0.1 and 0.06 wt.%C was studied as affected by processing and prolonged 1350-K exposure with and without applied stress. Sheets were fabricated by cold rolling bars that were single-, double- or triple-extruded at 1900 K. Creep samples were double-annealed (1 h @ 1755 K + 2 h @ 1475 K) prior to testing at 1350 K for 10,000 - 34,500 h. The microstructures of the as-cast, extruded, rolled, DA and crept samples were characterized using various metallographic and analytical methods. The precipitates were rather coarse Nb2C initially, but transformed to finer (≤1 µm) carbides of (Zr,Nb)C with each subsequent high temperature process. The grain size, and the relative amount and morphology of (Zr,Nb)C were found to be affected by the number of extrusions and to some extent by C-content. However, the microstructures of all the crept samples were similar with (Zr,Nb)C distributed throughout the matrix indicating that prolonged exposure to 1350 K gave rise to complete transformation of Nb2 C to (Zr,Nb)C regardless of the processing history. These and other observations are presented with the emphasis on the correlation between processing, microstructure and creep properties.
Tensile and Stress-Rupture Behavior of Hafnium Carbide Dispersed Molybdenum and Tungsten Base Alloy Wires
Authors: Yun H.M. , Titran R.H. 
Published: March 2011

AbstractThe tensile strain rate sensitivity and the stress-rupture strength of Mo-base and W-base alloy wires, 380 µm in diameter, were determined over the temperature range from 1200 to 1600 K. Three molybdenum alloy wires; Mo + 1.1 wt% hafnium carbide (MoHfC), Mo + 25 wt% W + 1.1 wt% hafnium carbide (MoHfC+25W) and Mo + 45 wt% W + 1.1 wt% hafnium carbide (MoHfC+45W), and a W + 0.4 wt% hafnium carbide (WHfC) tungsten alloy wire were evaluated.The tensile strength of all wires studied was found to have a positive strain rate sensitivity. The strain rate dependency increased with increasing temperature and is associated with grain broadening of the initial fibrous structures. The hafnium carbide dispersed W-base and Mo-base alloys have superior tensile and stress-rupture properties than those without HfC. On a density compensated basis the MoHfC wires exhibit superior tensile and stress-rupture strengths to the WHfC wires up to approximately 1400 K. Addition of tungsten in the Mo-alloy wires was found to increase the long-term stress-rupture strength at temperatures above 1400 K.
Microstructural Evolution and Densification Kinetics During Sintering of Oxide-Dispersed Tungsten Alloys
Authors: Chen Li-Chyong , Bewlay Bernard P. 
Published: March 2011

AbstractThe present paper discusses the role of ceria and hafnia dispersions in tungsten alloys on the microstructural evolution and densification kinetics during sintering. Densification kinetics were measured using dilatometry, and microstructural changes were examined using scanning electron microscopy and Auger electron spectroscopy. Activation energies for sintering were obtained by analyzing the shift of the iso-density points as a function of linear heating rate. Sintering of both tungsten and ceria-dispersed tungsten were found to be controlled by grain boundary diffusion, with apparent activation energies of 318±21 and 385±15 kJ/mole, respectively. However, densification of hafnia-dispersed tungsten is not controlled by a single mechanism. Under different conditions hafnia can enhance or retard densification; the mechanisms associated with this behavior are discussed. In particular, the relationships between sintering behavior and the tungsten-ceria and tungsten-hafnia interfaces are examined. Comparison with conventional oxide dispersoids, such as thoria, will also be made.
C11b-C40 Transformation-Induced 1/4<111> Faults in Mosi2
Authors: Kad B.K. , Vecchio K.S. , Bewlay B.P. , Asaro R.J. 
Published: March 2011

AbstractPrevious experimental evidence for the transformation of MoSi2 from the high temperature C40 structure to the low temperature C11b structure has been re-examined such that the fault character and the existence of the C40 structure is now questioned. New observations of faults in single crystals prepared over a range of growth rates from 1cm/hr to 30cm/hr are presented. Transformation-induced stacking faults, which were previously described as 1/4<111> lying on {110), have been re-identified as 1/6[001] condensation faults on (001). These faults were probably produced by silicon loss during crystal growth. The contribution that these faults may make to macroscopic strain under the action of diffusion-assisted mechanisms at elevated temperatures is discussed.
Microstructures and Mechanical Behavior of Nb-Ti Base Beta + Silicide Alloys
Authors: Subramanian P. R. , Mendiratta M. G. , Dimiduk D. M. 
Published: March 2011

AbstractStudies on Nb/Nb5Si3 based in-situ composites have demonstrated an acceptable balance of low-temperature damage tolerance and high-temperature strength/creep resistance. However, catastrophic oxidation and embrittlement of these materials limit their usefulness in structural applications. Alloying studies were initiated at Wright Laboratory with the aim of obtaining incremental improvement in the overall oxidation response of the Nb/Nb5Si3 system, while seeking microstructurally similar systems. The results showed that reduced metal recession rates and oxygen embrittlement can be obtained by Ti and Al additions to Nb-Si base alloys. This paper focuses on the effect of Ti and Al alloying additions to Nb-Si base alloys on phase equilibria, microstructures, temperature dependence of strength, low-temperature toughness, and environmental resistance.
Vacuum Plasma Spray Forming of High Temperature Silicides
Authors: Sampath S. , Herman H. 
Published: March 2011

AbstractMolybdenum disilicide and its composites have been fabricated by a number of researchers in recent years through vacuum plasma spray (VPS) forming. VPS is capable of producing dense, fine grained deposits of these high temperature intermetallics and is a promising technique for near-net-shape manufacturing. Reviewed here is VPS forming of high temperature silicide intermetallics, principally Mosi2 and its composites. A discussion will be given of the processing-structure-properties relationship of the spray formed silicide.
Recrystallization Kinetics During Fast Thermal Annealing of Pfn+ Implanted Silicon+
Authors: Adekova W. O. , Muller J. C. , Siffert P. , Pedulli L. 
Published: March 2011

ABSTRACTThe damage recovery and electrical activation of PFn+ (1 ≤n ⩽,5) implanted silicon layers during fast thermal annealing has been investigated. The <100> oriented wafers were implanted by glow discharge with 30 keV PFn+ ions at a dose of 2.5–3.1015 ions/cm2 and subsequently annealed using incoherent light pulses in the temperature range 600–1100°C with irradiation times of 1–15 secs.Our results show that the maximum electrical activity is obtained by about 750°C, 15 sec and the same activity is reached for shorter annealing
times and higher temperatures (typically 820°/ 5 sec; 950°C / 1 sec). These values and Rutherford Backscattering analysis reveal that the velocity of regrowth of the PFn+-implantation amorphized layer is lower than in the case of P+ implantation and that the former requires a higher activation energync≃3.4 eV.TEM analysis reveals precipitates in 820°C/4 s annealed samples with the appearance of dislocation loops at 980°C/4 s annealing. Finally two characterizable defect levels (ETT = EV + 180 meV, ET2 = EV + 542 meV) are seen to remain in the PFn+ implanted samples examined by DLTS, even after annealing at 1100°C.
Regrowth Rates of Amorphous Layers in Silicon-on-Sapphire Films
Authors: Timans P. J. , McMahon R. A. , Ahmed H. 
Published: March 2011

ABSTRACTThe rate and direction of regrowth of amorphous layers, created by self-implantation, in silicon-on-sapphire (SOS) have been studied using time
resolved reflectivity (TRR) experiments performed simultaneously at two wavelengths. Regrowth of an amorphous layer towards the surface was observed in specimens implanted with 3.1015Si+/cm2 at 50keV and regrowth of a buried amorphous layer, from a surface seed towards the sapphire, was observed in specimens implanted with 1.1015Si+/cm2 at 175keV. Rapid isothermal heating to regrow the layers was performed in an electron beam annealing system. The combination of 514.5nm and 632.8nm wavelengths was found to be particularly useful for TRR studies since the high absorption in amorphous silicon, at the shorter wavelength, means that the TRR trace is not complicated by reflection from the silicon-sapphire interface until regrowth is nearly complete. The dual wavelength method removes ambiguity about the position of the amorphous to crystalline interface and the direction of regrowth. The temperature dependence of the refractive index of silicon leads to large changes in the reflectivity of SOS films as they are heated. The combination of regrowth rate observations and reflectivity measurements during heating has been used to characterize the isothermal heating cycle, avoiding the difficulties of using pyrometers operating at the useful near infra-red wavelengths, where sapphire is transparent.
Metastable Activation in Rapid Thermal Annealed Arsenic Implanted Silicon
Authors: Kamgar Avid , Baiocchi F. A. 
Published: March 2011

ABSTRACTLow temperature (600–800&C) thermal treatment subsequent to high temperature short time anneal of As implanted Si has resulted in significant clustering of As atoms in Si. Si wafers implanted with As at a variety of doses and energies were subjected to single and multiple thermal anneals using incoherent tungsten radiation. Sheet resistance (R▩ ), and Rutherford backscattering (RBS) and channeling measurements were carried out on the wafers. The metastable behavior observed in the activation of As was attributed to electrical deactivation of As atoms caused by clustering. From the temperature dependence of the rate of increase in R▩ we extracted a value of 1.1 eV for the activation energy of electronic deactivation of As atoms in agreement with the value obtained earlier for the activation of As clustering. We also report, for the first time, observation of a structure in the Si RBS spectrum which represents a defective layer in Si caused by the clustering As atoms.
Rapic Thermal Annealing of W-TI Bilayers on Silicon
Authors: Wei C. S. , Van der Spiegel J. , Setton M. , Santiago J. , Tanielian M. , Blackstone S. 
Published: March 2011

ABSTRACTW-Ti bilayers on Si have been processed by fast thermal annealing in air, in N2/H2 (5%), and vacuum (1 E-3 and 1 E-6 Torr). The results indicate that the W layer on top of Ti acts as an effective protection barrier against oxidation of Ti in all atmospheres except air. Titanium-rich silicides are formed after 500 °C, while TiSi2 is completed at about 600 °C. At 700 °C a bilayer of WSi2/TiSi2 is found. Silicon is found to be the diffusing specie during the formation of WSi2. Finally, a ternary silicide, Ti0.6W0.4Si2, starts to form after 780 °C. The final ternary silicide phase has'an Mlectrical resistivity of about 60 μΩ-cm.
Material and Electrical Properties of Gate Dielectrics Grown by Rapid Thermal Processing
Authors: Nulman J. , Krusius J. P. , Renteln P. 
Published: March 2011

ABSTRACTThe material and electrical characteristics of silicon dielectric films prepared via Rapid Thermal Processing (RTP) are described. A commercial RTP system with heat provided by tungsten-halogen lamps was used. Silicon dioxide films were grown in pure oxygen and in oxygen with 4% hydrogen chloride ambients. As grown films were either annealed in a nitrogen ambient or nitrided in an ammonia ambient. Film thickness ranges from 4 to 70 nm for RTP times from 0 to 300 s at 1150 C. Current-voltage and capacitance-voltage methods were used for electrical characteristics. Ellipsometry, Auger and TEM were used for material characterization.
Rapid Optical Annealing for Improved GaAs Fet Uniformity
Authors: Kazior Thomas E. , Tabatabaie-Alavi Kamal 
Published: March 2011

ABSTRACTAn Eaton Nova Rapid Optical Annealer (ROA 400) has been used to activate n and n+ Si implants for use in power and low noise FET structures for GaAs MMIC's. PECVD SiN capped 3" SI GaAs wafers were annealed at temperatures ranging from 800 to 970 °C for times ranging from 0 (transient light pulse) to 20 sec. Doping profiles were determined using a Polaron concentration profiler; FATFET's were used for measuring drift mobility; and short gate (l.0μm gate length) FET's were fabricated to establish activation uniformity and to determine d.c. and r.f. performance. Results have indicated peak implant activation as high as 90% and electron mobilities of up to 4700cm2/V-sec for carrier concentrations of 1.3×1017/cm3 – results comparable to conventional furnace annealing. The most significant improvement of optical annealing comes in device uniformity. Saturated current uniformities of < ±3% have been achieved over 3" wafers with excellent reproducibility from wafer to wafer. Power FET structures with zero bias gm of 120mS/mm with uniformities of <±5mS/mm have been measured. R.f. measurements on these devices yielded output powers of >500mW/mm with power added efficiencies as high as 35%.
The Annealing of Phosphorus-Ion-Implanted Copper Indium Disulfide by A Pulsed Electron Beam
Authors: Lin J. L. , Lue J. T. , Leng H. Y. , Yang M. H. , Hwang H. L. 
Published: March 2011

ABSTRACTPulsed Electron beam annealing of phosphorus implanted CuInS2 has been found to be an efficient method in p-type doping of CuInS2. A sheet resistance as low as 10.1 Ω/‮, a sheet carrier concentration as high as l.0 ×1016 cm−2, and a hole mobility as high as 499 cm2 /V.s have been obtained. The irradiation energy density for the best doping condition was determined to be in the ranges between 11–13 J/cm2. Using Van der Pauw/Hall technique in conjunction with a chemical etching technique, the effective carrier concentration profiles have been determined with a maximum carrier concentration of ∼9×1019cm−3. Excellent p-n CuInS2 homojunctions have been fabricated by electron-beam pulse annealing with anideality factor of 1.75.
METALLIC EPITAXY OF TRANSITION METALS ON SEMICONDUCTORS
Authors: Prinz G.A. 
Published: March 2011

AbstractAlthough epitaxial growth of single crystal metal films was reported at least five decades ago, the availability of modern ultra high vacuum technology and sensitive characterization of thin film properties has opened many new directions in this area of materials research. Of considerable interest is the utilization of the interfacial forces associated with epitaxial growth to stabilize structures which may exist in a metastable minimumenergy configuration. The problem of metastable structural phases of elemental metals will be discussed with particular emphasis upon the 3-d transition metals. In these materials the magnetic properties both depend dramatically upon the structural phase and contribute toward determining the stable minimum energy configuration.
GROWTH AND CHARACTERIZATION OF EPITAXIAL Si/CoSi2 AND Si/CoSi2/Si HETEROSTRUCTURES
Authors: HUNT B.D. , LEWIS N. , HALL E.L. , JTURNER L.G. , SCHOWALTER L.J. , OLANOTO MASAKO , HASHIMOTO SHIN 
Published: March 2011

AbstractThin (<200Å), epitaxial CoSi2 films have been grown on (111) Siwafers in a UHV system using a variety of growth techniques including solid phase epitaxy (SPE), reactive deposition epitaxy (RDE), and molecular beam epitaxy (MBE). SEN and TEN studies reveal significant variations in the epitaxial silicide surface morphology as a function of the sillciqd formation method. Pinhole densities are generally greater than 107 cm-2, although some reduction can be achieved by utilizing proper growth techniques. Si epilayers were deposited over the CoSi2 films inthe temperature range from 550ºC to 800ºC, and the reesuulttinng structures have been characterized using SEM, cross—sectional TEN, and ion channeling measurements. These measurements show that the Si epitaxial quality increases with growth temperature, although the average Si surface roughness and the CoSi2 pinhole density also increase as the growth temperature is raised.
ELECTRONIC AND CRYSTALLOGRAPHIC STRUCTURE OF IRON FILMS EPITAXIALLY GROWN ON Cu SINGLE CRYSTALS
Authors: MONTANO P.A. , LEE Y.C. , MARCANO J. , MIN H. 
Published: March 2011

AbstractThe crystallographic and electronic structure of iron films epitaxially grown on Cu single crystals was investigated by LEED, AS, EELS and UPS. The Cu(l00), Cu(ll0) and Cu(lll)faces were used as substrates for the growth of the iron films. In our study emphasis was placed on the modification of surface properties due to the Fe/Cu interface. Significant variation with respect to α—Fe was observed in the electronic structure of fcc iron formed on the various crystal faces.
STRAIN IN MAGNETIC EuS/SrS SUPERLATTICES INVESTIGATED BY He ION CHANNELING
Authors: MANTL S. , BUCHAL CH. , STRITZKER B. , SAFTIC B. 
Published: March 2011

AbstractHe ion channeling experiments indicate that molecular beam grown epitaxial multilayers of EuS/SrS on (111) Si are under strain. Angular scans of the normalized He backscattering yields showed that inclined [100] directions vary by 0.28 ± 0.05º between the first two 30 nm thick layers due to tetragonal distortion of the EuS and SrS lattices. Comparison of theoretical estimated kink angles and experimental results indicated cormplete elastic accommodation of the 0.9 % lattice mismatch between EuS and SrS in the superlattice. In contrast, thin EuS layers on (111) Si are epitaxial but incommensurate because of the large 10 % lattice mismatch.
X-RAY AND TRANSPORT STUDIES OF RUTHENIUM-IRIDIUM BICRYSTAL SUPERLATTICES
Authors: CLARKE ROY , LAMELAS F. , UHER C. , CUNNINGHAM J.E. , FLYNN C.P. 
Published: March 2011

AbstractThe stacking structure and epitaxial ordering are studied in MBE-grown Ru-Ir superlattices of wavelengths λ = 41\ and 62\. These samples span the fcc-hcp crossover previously found to occur when the Ir component is thinner than about 10 monolayers. Evidence for a new stacking sequence of period 3λ is found in the λ=41\ sample, possibly resulting from stacking faults in the Ir layers. The superconducting transition temperature is significantly higher in the 41\ sample (Tc=0.19K) than in the 62\ sample (Tc=0.15K).