bluuebunny/crossref_metadata_2025 huggingface dataset:
Angular Dependent Critical Fields in NbTi-Ge Superlattices in the Weakly Localized Regime
Authors: Jin Ben Y. , Ketterson J. B. , Hilliard J. E. , McNiff E. J. , Foner S. , Schuller Ivan K.
Published: March 2011

The angular dependence of the upper critical fields, Hc(θ) for a set of NbTi-Ge superlattices were studied at various temperatures. The behavior of Hc(θ) at lower temperatures deviates from the Tinkham expression which is expected to be valid only in the Ginzberg-Landau regime close to Tc. We examine a model for calculating Hc(θ) involving the lowest eigenvalue of the gauge invariant diffusion equation (subject to boundary conditions appropriate to a slab) in the de Gennes expression for the upper critical field of a dirty superconductor at all temperatures. The disorder related localization and interaction effects as well, as the paramagnetic limiting effect, are also considered.
High Resolution Transmission Electron Microscopy of PbTe/Pb1-zEuxSeyTe1-v, Heterostructures.
Authors: Salamanca-Young L. , Partin D. L. , Heremans J. , Dresselhaus E. M.
Published: March 2011

High resolution transmission electron microscopy has been used to study the structure of PbTe/Pb1-zEuxSeyTe1-v semiconductor superlattices and heterojunctions grown on BaF2 substrates by molecular beam epitaxy. The objective of this study is to analyze the interface sharpness and the structural perfection of the samples at their interfaces. In the PbTe/Pb1-zEuxSeyTe1-v system, we have observed misfit dislocations and even amorphous regions for high Eu concentrations. We have also observed two directions of growth of the superlattice film. The interface appears to be sharp to approximately three monolayers. A model for the superlattice structure is suggested and used to obtain simulated images using computing methods. The simulated images are compared with those obtained experimentally.
Kinetics and Thermal Stability of Ni/Zr Multilayer Thin-Film Diffusion Couple during a Solid State Amorphization Reaction
Authors: Meng W. J. , Cotts E. J. , Johnson W. L. , Keck W. M.
Published: March 2011

Differential scanning calorimetry and X-ray diffraction have been utilized to monitor the solid state amorphization reaction in crystalline Ni/Zr multilayers. Enthalpy of mixing of amorphous NiZr alloys has been measured. Kinetics of amorphous phase formation and thermal stability have been discussed in some detail.
Orientations of Ultrathin NiSi2 Layers on Si
Authors: Tung R. T.
Published: March 2011

The reaction of monolayers of (metal) absorbâtes with clean (semiconductor) surfaces has long been studied by surface scientists using spectroscopie probes. [1] Recently it has been demonstrated that the knowledge acquired from these studies has led to new techniques for the fabrication of novel epitaxial structures which are not possible by any other means.[2] The orientation of NiSi2, as well as the layer uniformity, was found to be sensitive to slight variations in growth parameters. This discovery has led to the fabrication of single crystal NiSi2 layers of either type A or type B orientation on Si(111).[2] Type A NiSL has the same orientation as the silicon substrate. Type B NiSi2 shares the surface normal <111> axis with the Si, but is rotated 180δ about this axis with respect to the Si. The variation of NiSi2 orientation depends primarily on the deposited nickel thickness and is among the most intriguing phonomena in heteroepitaxial growth. Its significance became even more appreciated when it was discovered that the Schottky barrier height for type A NiSi2 differed significantly from that for type B NiSi2.[3] These results and the prospect of using thin epitaxial suicides in high speed devices have recently attracted a lot of attention as well as triggered investigations of other properties of this material system. Those who followed closely the experimental conditions as described in the original paper[2] have had no trouble in obtaining high quality suicide layers of pure orientation.[4] At the same time, many research groups have used slightly different conditions and, as a result, have not been able to grow single-orientation NiSi2 layers.
Picosecond Dynamics of Photoexcitations in Amorphous Multilayer Structures
Authors: Grahn H. T. , Vardeny Z. , Maris H. J. , Tauc J. , Abeles B.
Published: March 2011

We report on measurements of ultrafast relaxation processes in transmission and reflection in amorphous multilayer structures consisting of a-Si:H, a-SiNx:H, a-SiOx:H, and a-Ge:H. The decays recorded in transmission in the a-Si:H/a-SiNx:H and a-Si:H/a-SiOx:H multilayers depend strongly on the silicon sublayer thickness and are interpreted in terms of carrier transport to and trapping at interfacial defects. In the a-Si:H/a-Ge:H multilayers we observe oscillations in reflectivity due to standing acoustic waves with a frequency that depends on the repeat distance of the multilayer.
Two-Dimensional Excitons in A Strongly Localized Regime in CdTe/ZnTe Superlattices
Authors: Hefetz Y. , Lee D. , Nurmikko A. V. , Sivananthan S. , Chu X. , Faurie J.-P.
Published: March 2011

Time-resolved spectroscopy of the recombining exciton state in a highly strained II-VI semiconductor superlattice CdTe/ZnTe reveals strong localization effects at low lattice temperatures. Such phenomena originate naturally from small deviations in structural perfection on a monolayer scale in a strained superlattice with a small valence band offset. The quasi-2D aspect enhances the localization phenomena further.
Forkation and Oxidation of Titanium Silicide
Authors: Huang Tzuen-Luh , Lee Shuit-Tong
Published: March 2011

Refractory metal suicides have been used widely in VLSI fabrication, owing to their low resistivity, high-temperature compatibility, and oxidiz-ability. In this work, we have studied the titanium suicide formation, using a rapid thermal processor (RTP). Isothermal and isochronal sintering experiments were carried out to determine the appropriate process steps. The selective etch of the unreacted Ti was characterized. The sintered films were characterized by four-point probe, X-ray diffraction, and Auger electron spectroscopy. We also studied the oxidation at 800–1000°C of Ti suicide formed by sintering Ti and polycrystalline silicon using a RTP in N2 ambient. The oxidation results of Ti suicide formed using RTP in N2 ambient are compared with those formed using furnace sintering in vacuum/argon ambient and those deposited by cosputtering.
Coupled Two Dimensional Electron Gas Structures in the G1−xAlxAs/GaAs System
Authors: Christou A. , Hatsopoulos Z. , Bacalis N. , Papanicholaou N. , Ginoudi A.
Published: March 2011

Two 2-dimensional electron gas (DEG) regions coupled either by a superlattice, an undoped GaAs layer, or the combination of a tunneling barrier with a superlattice have been investigated by studying (a) non-ohmic conduction, (b) field effect characteristics parallel to the 2DEG channels and (c) negative differential resistance (NDR) for conduction perpendicular to the quantum wells. It is shown that coupling is optimized when the separation region is a superlattice. Tunneling through superlattice mini-bands can enhance field effect transistor transconductance.
Structural Studies of Nickel Films and their Interface with Sapphire Substrates
Authors: Sparks C. J. , Hasaka M. , Easton D. S. , Baik S. , Habenschuss T. , Ice G. E.
Published: March 2011

The perfection of epitaxial nickel films grown on the (00.ℓ) or basal plane of heated sapphire (A1203) single crystals were studied with X-ray diffraction techniques. Nickel films approximately 700 Å thick formed by vapor deposition increased in perfection as the temperature of the sapphire approached 1400°C. Although the nickel atom distances are 10.3% smaller than those of the closed-packed direction in sapphire, the strain was accommodated at the interface rather than being distributed through the thickness of the nickel film. Diffuse rods of X-ray scattering which are associated with diffraction from the interface gave information about the nature of the roughness at the interface.
Aluminum-Titanium Multilayer Interconnect With Titanium Diffusion Barrier
Authors: Tong-Lee S. , Huang Tzuen-Luh , Van Den Hove L. , Nichols D. N.
Published: March 2011

The metallurgical reaction at 450°C in forming gas ambient between the Ti diffusion barrier and Al, causing the contact degradation in the Al (1% Si)-Ti multilayer interconnects has been studied. The Ti-Al reaction is reduced by preheating the Ti layer in N2 using rapid thermal processing (RTP) at 2.500°C. The curtailed reaction is attributed to the thin surface titanium oxynitride layer. It was found that a 1000-Å Ti layer inserted between the multilayer and Si is effective as a sacrificial diffusion barrier against contact degradation, but 500-Å Ti is not. RTP of the thin Ti film rendered it effective as a diffusion barrier.
Epitaxial Film Growth of Single Crystal Ce/V Prepared by Molecular-Beam Epitaxy
Authors: Homma Hitoshi , Yang Kai-Y. , Schuller Ivan K.
Published: March 2011

The growth of epitaxial films of cerium (Ce)/vanadium (V)/on single crystal sapphires (α-A1203) was studied by in-situ reflection high energy electron diffraction and x-ray scattering. For the first time Ce(111) single crystal film was grown on V(110)/α-A12O3 (1120) in the Frank-van der Merwe mode. A new epitaxial orientation, different from the well known Nishiyama-Wasserman or Kurdjumov-Sachs orientations is found in the present study. Subsequent V(110) layers grow epitaxially with three equivalent domains.
Anneal Induced Changes in Amorphous Semiconductor Multilayers
Authors: Gonzalez-Hernandez J. , Allred D. D. , Nguyen O. V.
Published: March 2011

We have prepared, heat treated and characterized various amorphous semiconductor periodic multilayers and ultrathin films. These were prepared by several vapor deposition techniques at substrate temperatures ranging from 25°C to 300°C and possessed periodicities from 22 to 400Å. Films were subjected to isochronal thermal treatments at progressively higher temperatures. Two effects were observed: enhanced diffusion and retarded crystallization. Interdiffusion, at rates which are many orders of magnitude higher than those anticipated from crystalline data, was observed in a-Si/a-Ge multilayers. Crystallization of germanium, the more readily crystallized member of the couple, is retarded; the extent depends on the thickness of the layer. The thinner the layer, the greater the retardation. Where intermixing is thermodynamically unfavorable as in a-Si/a-SiNx or a-Ge/a-SiNx multilayers, and ultrathin germanium layers on SiO2, interdiffusion does not occur, however, crystallization of silicon or germanium is again substantially retarded.
Effect of Heating on the Structure of Au/GaAS Encapsulated with SiO2
Authors: Zeng X.-F. , Chung D. D. L. , Lakhani Amir
Published: March 2011

The structural effects of heating 1500 Å Au/GaAs (001) encapsulated with 2000 Å of SiO2 were examined by scanning electron microscopy and x-ray diffraction. It was observed that SiO2/Au/GaAs (capped) in vacuum up to 500°C remained shiny and gold in color, whereas similar heating of Au/GaAs (uncapped) caused a change of color from shiny gold to dull silver. Furthermore, mass spectroscopy showed that the amount of arsenic vapor evolved was much less for the capped sample. However, x-ray diffraction showed that Au7Ga2 formed abundantly in both types of samples after heating at 500°C, though the epitaxial relationship was AuyGa2 (001) // GaAs (001) for capped and Au7Ga2 (100) // GaAs (001) for uncapped. SEM revealed gold-rich aligned rectangular protrusions on the surfaces of SiO2/Au/GaAs as well as Au/GaAs after heating at 500°C, though the average length of these rectangles was 1.5 μm for the capped sample and 6.7 μm for the uncapped sample. Moreover, new morphological features absent in Au/GaAs were observed in SiO2/Au/GaAs. These features are a gold-rich maze with a line width of 6 Åm and gold-rich protruded lines with a line width of 9 Åm. The gold-rich protruded lines were formed by the growth and joining together of some gold-rich aligned rectangular protrusions. The gold-rich maze was observed in SiO2/Au/GaAs after heating in vacuum, but was not observed in SiO2/Au/GaAs after heating in nitrogen.
Chemical Vapor Deposition of Silicon Films Using Hexachlorodisilane
Authors: Taylor R. C. , Scott B. A. , Lin S.-T. , LeGoues F. , Tsang J. C.
Published: March 2011

The use of hexachlorodisilane (Si2Cl6) as an alternative to silane for growth of polycrystalline silicon films has been investigated. Films were grown at atmospheric pressure in both hydrogen and nitrogen carrier gases over a temperature range of 450–900°C. Deposition rate data indicate the existence of two growth regimes at high and low temperatures and in the presence or absence of hydrogen. The change from amorphous to polycrystalline growth takes place at 600–650°C. At 600°C deposited films are amorphous but crystallize during the growth process. The chlorine content of high-temperature films was found to be less than 0.01 at.%.
Cross-Section Transmission Electron Microscope Study of Ni/Au/Ge/Au Ohmic Contact to Gallium Arsenide
Authors: Kim Taeil , Chung D. D. L. , Mahajan S.
Published: March 2011

The interfacial structures resulting from the metallurgical reactions between a Ni/Au/Ge/Au film and (100) GaAs substrate were studied by cross-section TEM. Annealing at 300 – 350°C causes a complicated solid-solid phase reaction, resulting in the multilayer structure of Ni2Ge/Au7Ga2/NiAs/Au7Ga,/GaAs. The contact shows non-ohmic character, since most of the doping element Ge is trapped in the surface Ni2Ge layer When the contact is annealed at above 400°C. the layered structure is destroyed because one of the phases (Au-Ga) becomes liquid but other phases (Ni-Ge, Ni-As) remain solid Ge, which is captured in the surface layer, diffuses out of the Ni2Ge phase into the contact/GaAs interface through the Au-rich melt. Above this temperature, a Ge-doped n+ region is probably formed at the NiAs/GaAs interface and the contact becomes ohmic. With increasing annealing temperature, continuous grain growth of NiAs is found to occur and the NiAs/GaAs interface area increases. Thus the ohmic behavior of Au-Ge-Ni on n-GaAs can be explained by the low barrier height of the NiAs/GaAs interface and the formation of Ge-doped n+ region under the NiAs phase.
Liquid Phase Epitaxial Growth of Fe-Doped Semi-Insulating Inp and Ternary Alloys
Authors: Isozumi S. , Tanahashi T. , Kondo M. , Sugawara M. , Yamaguchi A. , Nakajima K.
Published: March 2011

Fe-doped semi-insul ati ng layers of InP, In0.48A10.52As,and In0.49Ga0.51P have been grown by liquid phase epitaxy for the first time. Behaviors of Fe doping in these materials have been well explained by the solubility of Fe in the growth solution and the temperature dependent distribution coefficients of Fe. It has been found that the distribution coefficients of Fe in the ternary alloys are much greater than those in InP.
Mechanical Property and Microstructure of TZP and TZP/Al2O3 Composites
Authors: Tsukuma Koji , Takahata Tsutomu
Published: March 2011

There are various types of microstructure in the TZP materials and their composite materials. The fine-grained microstructure is well-known as the basic microstructural type of TZP materials. Y-TZP and Ce-TZP belong to this group. The large-grained microstructure can exist in the TZP consisting of the tetragonal phase with low metastability, that is, Y-TZP doped with TiO2 and Ce-TZP containing a high CeO2 content. The composite material between Y-TZP and β-lanthanum alumina possessed a unique microstructure including elongated grains of β-Al2O3 type structure. This study provides a summary of the mechanical properties of these TZP and β-Al2O3 type structure composite materials, and points out how the mechanical behavior depends on the microstructural features.
Effect of Changes in Grain Boundary Toughness on the Strength of Alumina
Authors: Cook Robert F.
Published: March 2011

Indentation/strength data on a series of Ca-doped aluminas are presented, revealing considerable microstructural influence and increasing fracture resistance during crack propagation. The source of the increasing resistance is considered in terms of a restraining zone of grain-localized ligamentary bridges behind the crack tip. A simple fracture mechanics model is developed to characterize the effect of the restraining ligaments, which also allows the steady state toughness, applicable to large cracks, and the intrinsic strength, applicable to small cracks, to be predicted. The segregation of Ca to the grain boundaries is shown to correlate with decreases in grain boundary toughness and increases in toughness in the large crack limit. These latter two combined effects lead to decreases in intrinsic strength with increasing steady state toughness.
Comparison of Matrix Variation in Nicalon (Sic) Fiber Reinforced Composites
Authors: Johnson W. L. , Brasfield R. G.
Published: March 2011

The high-temperature behavior of NICALON fabric is discussed. Three fabric reinforced composites are described that use NICALON fabric to take advantage of its oxidation and erosion resistance. The matrix materials used were phenolic resin, pyrolytic carbon and beta-silicon carbide. Each composite was subjected to an erosive environment at 2755 K. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and laser Raman microprobe analysis (LRMA) were used to characterize the raw materials, the unfired composites, and the erosion tested composites. These analyses concentrated on the fiber/matrix interaction and the effect of erosion on each component of the composite.
Texture on Ground, Fractured, and Aged Y-TZP Surfaces
Authors: Reidinger Franz , Whalen Philip J.
Published: March 2011

The phase composition of Y-TZP surfaces has been shown to vary greatly depending on the thermo-mechanical history of the surface. The orientation of these different phases in the surface region is not always random. There is speculation that the alignment of the tetragonal phase before fracturing may play a part in increasing the toughness of these materials. This article deals with an X-ray diffraction analysis of various Y-TZP surfaces with special emphasis on the texture of the different phases. Surfaces which have been ground (and polished), fractured, and aged (200°C) have been examined. In all cases, the monoclinic component that was formed was strongly oriented. The tetragonal phase may or may not be oriented depending on surface treatment. Annealing above the monoclinic-tetragonal transition temperature had little effect on the tetragonal orientation in most cases. Samples fractured at 1000°C have no unusual orientation on the fracture faces.
Deflection-Toughened Corundum-Rutile Composites
Authors: Hori Saburo , Kaji Hisatsugu , Yoshimura Masahiro , Sōmiya Shigeyuki
Published: March 2011

Dense corundum-rutile composites containing plate-shaped corundum particles were prepared from the CVD Al2O3-TiO2 powders by adding a small amount of sodium and sintering below ˜1280°C. The fracture toughness increased up to 6.5 Mpa · ✓m and the increment of toughness was proportional to the volume % of plate-shaped corundum particles. The importance of tilt deflection and crack bowing rather than the twist deflection was suggested in this system.
Deformation Behavior of SiC Whisker Reinforced Si3N4
Authors: Nixon R. D. , Chevacharoenkul S. , Huckabee M. L. , Buljan S. T. , Davis R. F.
Published: March 2011

Constant compressive stress creep exp∼riments in jhe temperature and stress ranges of 1420K – 1570K and 50 MN/m2 –350 MN/m2 have been conducted on hot pressed unreinforced Si3N4 containing the densification aids of 6 wt% Y2O3 and 1.5 wt% Al2O3 and on a similarly prepared composite material reinforced with 20 vol% SiC whiskers. Steady-state creep data obtained on these materials in a N2 atmosphere gave stress exponent values of 1.2 – 1.6 and 0.4 – 1.6 for the unreinforced Si3N4 and the composite, respectively. A break in the steady-state creep rate vs. log stress observed only in the composite occurred at approximately 250 MN/m2 at the temperatures of 1520K and 1570K. This information coupled with the results of electron microscopy indicate that the temperature as well as the extensive crystallization (or lack of it) of the amorphous grain boundary phase are the principal factors controlling the deformation rate at a given stress within the limits of the small total strains achieved in this research.
Strength and Toughness of MG-PSZ and Y-TZP Materials at Cyrogenic Temperatures
Authors: Veitch S. , Marmach M. , Swain M. V.
Published: March 2011

The influence of temperature between R.T. and liquid nitrogen (−196°C) on the strength and toughness of three grades of Mg-PSZ and a 3 mol% Y-TZP material have been investigated. The toughness of the Mg-PSZ materials passes through a maximum at the Ms temperature, whereas the strength increases monotonically with decreasing temperature regardless of Ms. The Y-TZP material exhibits increasing toughness with decreasing temperature but the strength passes through a maximum at -80°C. The results are discussed in terms of transformation and R-curve limited strength of transformation toughened ceramics. For Mg-PSZ materials it is suggested that the critical stress to initiate a non reversible transformation on the tensile surface is responsible for microcracking and ensueing R-curve development.
Strengthening Mechanism in Consolidated Amorphous Alloys
Authors: Otooni M. A.
Published: March 2011

Several samples of consolidated amorphous alloys have been studied by using High Resolution Electron Microscopy (HREM), Differential Scanning Calorimetry (DSC), Microdiffraction (MD), and Energy Dispersive X-Ray Diffraction Analysis (EDXD). The phenomenon of plastic deformation at consolidated particulate interfaces has been examined. Two simultaneous processes have been identified occurring at these boundaries, namely, accelerated nucleation and growth of the deformed zone and the the formation of dislocation microstructures (dislocation networks). It has been observed that both type and the density of microstructures depend on the mode of consolidation. Post consolidation processing, annealing, affects density and the directional distribution of defects in the plastic zone. Microstructural examination of the consolidated mass has revealed two major factors important in the strengthening mechanism: (1) presence of a plastically deformed and pressureinduced nucleated zone; (2) presence of a system of dislocation networks in the compacted particulates. Based on these observations, it has been concluded that the stored strain energies in the plastically deformed zones provides the necessary activation energy for dislocation motions from one particulate to the next. These observations have been employed in developing a quasi-quantative model to explain the strengthening mechanism in consolidated amorphous alloys.
Effects of Microadditions of Cerium on Annealing Embrittlement in FeBSi Glasses
Authors: Kroeger D. M. , Mckamey C. G. , Scarbrough J. O.
Published: March 2011

Microadditions of cerium retard annealing embrittlement in some but not all metallic glass compositions in the FeBSi system. Effects on embrittlement of doping with both cerium and oxygen have been determined for a series of compositions, FexB13 Si87-x. For X > 80, cerium retards annealing embrittlement and oxygen promotes it, suggesting that the beneficial effect of cerium additions results from gettering of impurities. The results indicate that for those compositions in the FeBSi system with the highest values of the saturation magnetization, Ms, microadditions of cerium can prevent annealing embrittlement until the onset of crystallization.
High-Performance Light-Weight Allovs by Rapid Solidification Processing
Authors: Kim Nack J. , Das S. K.
Published: March 2011

There exists a great need for the development of high-performance light-weight alloys for aerospace application. Application of rapid solidification processing (RSP) has shown a strong potential for the improvement of properties of existing alloys and also for the development of novel alloy systems with superior properties. The present paper reviews the Allied-Signal's activities in the development of high-performance lightweight alloys by RSP. Examples include (i) high temperature aluminum alloys, (ii) aluminum-lithium alloys and (iii) corrosion resistant magnesium alloys.
The Effect of Solidification Rate on the Formability of Nickel Aluinide Containing Iron and Boron
Authors: Carro G. , Flanagan W. F.
Published: March 2011

It has been repcrted that rapid solidification insproves the ductility of certain nickel aluminides. This work. was devised to test whether it gives addittinal improvement in a nickel aluminide containing both Fe and B. Small samples were solidified in free-fall or splat-quenced after free-fall. Their uicrostructure has been characterized, and the results of preliminary tests, which give a quantitative measure of mechanical properties, are discussed.
Microstructure in Rapidly Quenched Al-Ti,Al-B and Al-Ti-B Alloys
Authors: Majumdar A. , Mair R. H. , Muddle B. C.
Published: March 2011

Rapidly quenched ribbons (˜50m thickness) of Al-5wt.%Ti, Al-lwt.%B and a range of Al-Ti-B alloys have been produced by melt spinning under He atmosphere and the microstructures of the ribbons, following solidification and post-solidification heat treatment, characterized using analytical electron microscopy. In the Al-5Ti alloy, the coarse equilibrium primary phase (b.c.t. Al3 Ti) that is observed following conventional casting is replaced by fine (0.1–0. 2μm), cuboidal particles of a metastable cubic (Ll2) Al3Ti in melt-spun ribbon. These metastable particles form directly from the melt and act as nucleation sites for the solid solution which subsequently forms. A refined microstructure with an average grain size of 1–2μm results. A supersaturation of Ti is retained in matrix solid solution following solidification and a variety of solid state precipitate forms, including fine dispersions of coherent, metastable Al3 Ti particles, is observed to emerge during post-solidification heat treatment. For the Al-1B alloy, the coarse distribution of primary AlB2 particles in a chill-cast ingot is replaced by a fine, uniform dispersion of the metastable boride, α-AlB12, in the melt-spun ribbon. Attempts to induce a refined boride dispersion in melt-spun Al-Ti-B alloys have proved largely unsuccessful.
Microstructure and Properties of Rapidly Solidified Complex Titanium Alloys
Authors: Munroe P. R. , Woodfield A. P. , Loretto M. H.
Published: March 2011

Rapidly solidified titanium alloys containing carbon and erbium have been examined microstructurally in the as-quenched and aged conditions. Studies show that cubic erbia forms initially, but prolonged aging results in the formation of trigonal erbia. The formation of this phase is enhanced by the presence of carbon.
Amorphous Transition Metal-Rare Earth Alloy Films for Magneto-Optic Recording
Authors: Luborsky Fred E.
Published: March 2011

This paper reviews the history of the development of films for use in magneto-optic recording. A discussion of why these early attempts with films of MnBi and Europium compounds were abandoned is given. The current work on amorphous transition metal-rare earth alloys is then reviewed. The origins of the necessary perpendicular magnetic anisotropy are discussed. The ideal combination of properties desired are: a high room temperature coercivity, a large temperature coefficient of coercivity, a large perpendicular anisotropy constant, large Ms, thermal and environmental stability, and, depending on whether a reflection or absorption mode of operation will be used, a large Kerr rotation with large reflectivity or a large Faraday rotation with a small specific absorption. These factors, their control, bow they influence the recording performance and the limits on performance of these amorphous films are discussed.
Dynamics of Rapid Solidification in Silicon
Authors: Peercy P. S. , Thompson Michael O. , Tsao J. Y.
Published: March 2011

Real-time techniques were used to study rapid melt and solidification dynamics in silicon. In crystalline Si, the interface response function was characterized and found to be asymmetric for large deviations from the melting temperature, which will require reevaluation of conventional transition state treatments of melt and solidification. In amorphous Si, the mechanism of explosive crystallization was studied. The explosive transformation is mediated by a buried liquid layer, and detailed measurements have led to the suggestion that polycrystalline Si nucleates at the moving liquid-amorphous interface. For certain conditions, this process could yield fine-grained polycrystalline Si; for other conditions it permits epitaxial regrowth from the underlying crystalline Si for maximum melt thickness much less than the original amorphous layer thickness.
Deposition, Characterization, and Magneto-Optical Properties of Amorphous TbFe Alloys
Authors: Chakravartty D. , Mansuripur M. , Ruane M. F.
Published: March 2011

Amorphous films of TbxFe1-x are prepared by simultaneous RF bias sputtering onto various substrates and the hysteresis loops of the resulting samples are obtained both by magneto-optical and VSM loop tracers. The coercivities of the samples deposited in the same run but onto different substrates are observed to be somewhat different and these differences are discussed in light of the current understanding of the deposition process.
Interdiffusion in Amorphous Compositionally Modulated Ni-Zr Thin Films
Authors: Atzmon M. , Spaepen F.
Published: March 2011

We report measurements of interdiffusion in compositionally modulated amorphous Ni-Zr films. We show the dependence of the diffusion coefficient on the modulation wavelength and correlate it with the thermodynamic properties of the Ni-Zr system. A bulk interdiffusion coefficient is extrapolated from the data. Our values for the interdiffusivity in Ni55Zr45 are about three orders of magnitude lower than those obtained by other authors for similar alloys. Possible explanations are suggested.
The Structural and Mechanical Properties of a Cu60 Zr40 (at %) Alloy Processed by High Velocity Injection (HVT)
Authors: Hays C. C. , Naugle D. G.
Published: March 2011

In the HVI process, alloys are arc-melted in a watercooled copper crucible and injected (at high velocities) into a circular channel by a gas/vacuum coupled pressure gradient. The molten jet rapidly solidifies, as it is in good thermal contact with the circular walls of the copper channel. This process (melting and injection) is carried out in the inert protective atmospheres (helium). The samples produced are in the form of cylindrical rods with large length to diameter ratios (40:1). The samples exhibit a good surface finish and are of high density. Results presented in this paper show that amorphous samples can be produced using the HVI process.
On the Formation of Rapidly Quenched Ti-Pd and Pd-Si Alloys: A Comparison with Mechanically Alloyed Materials
Authors: Politis C. , Thompson J. R.
Published: March 2011

We have investigated the formation of amorphous and microcrystalline alloys of Pd-Si and Ti-Pd. In order to allow comparison of the two methods, both liquid quenching (LQ) for rapid solidification and mechanical alloying (MA) techniques were employed. Characterization of the materials was obtained through X-ray diffraction and differential thermal analysis (DTA).

Both the LQ and MA syntheses yielded amorphous Pd80Si20alloys, with very similar X-ray line widths and crystallization temperaiures. However, the MA alloys contained as minority component a second phase, indexed to Pd3Si.

Quite different results were obtained for the Ti-Pd alloys. LQ splats containing 42, 66, and 80 at % Ti were not amorphous but microcrystalline, as might be expected from the very similar atomic radii of Ti and Pd. In contrast, a broad range of amorphicity, from approximately 42 to 85 at % Ti, was found in the MA synthesized materials. Overall, these results show that the two methods, LQ and MA, differ in the mechanisms of amorphization. This conclusion is further supported by additional MA and LQ experiments on ternary Ti-Pd-Cu alloys.
Annealing of Cold Worked Hypostoichiometric Ni3Al Alloys Using Positron Lifetime Spectroscopy
Authors: Usmar S. G. , Lynn K. G.
Published: March 2011

Hypostoichiometric Ni3Al alloys of composition 76.2 Ni:23.8 Al containing impurity levels of boron and hafnium (supplied by Oak Ridge National Laboratory) were either cold rolled or pressed. Rolled and pressed samples were deformed by 20% and 10% thickness reductions, respectively. Samples were annealed isochronally at approximately 50ºC intervals up to 1050ºC. Two major annealing stages were apparent in all three alloys studied. These could be attributed to vacancy migration to sinks and annealingof dislocations and(or) recrystallization. The onset of vacancy migration occurred at approximately 200ºC in all three alloys. Annealing of dislocations started at 650ºC to 700ºC and was complete at 1000ºC for alloys which contained boron and or hafnium impurities. In the pure alloy the onset of dislocation annealing occurred at 800ºC and was incomplete at the highest (1050ºC) annealing temperatures reached.
Microstructures of Rapidly Solidified Ti-15Al-11Mo Alloy
Authors: Jackson A. G. , Teal K. , Froes F. H.
Published: March 2011

The microstructural development in a Ti3Al alloy modified with an addition ofil w/o Mo has been studied. Under equilibrium conditions (arcmelted) a two phase ordered hexagonal and ordered bcc structure is present. Evidence of omega phase was alsoobserved. By rapid solidification the hexagonal structure is suppressed, which contrastswith the behavior of a Ti3Al alloy modified with a similar amount of Nb. The mechanism by which the phases present form is discussed in terms of the atomic movements required.
Lattice Location of Ta in Ni3Ai by Ion Channeling and Nuclear Reaction Analysis
Authors: Lin H. , Sehberling L. E. , Lyman P. F. , Pope D. P.
Published: March 2011

We have investigated the lattice location of Ta in Ni3Al using Rutherford backscattering with channeling, and nuclear reaction analysis. An 8 MeV 4He ion beam was directed along the < 100> crystallographic axis of the Ni75Al24Ta single crystal. A silicon surface barrier detector was used to analyze 4He ions backscattered from Ni and Ta atoms. Neutrons generated from Al by the 27Al(4He,n)30P reaction were detected by a large volume liquid scintillator placed outside of the scattering chamber. Essentially all of the Ta atoms were found to be substitutional, as determined by the Ta channeling minimum yield. A comparison of the width of the channeling angular scan for Al, Ni and Ta indicated that the Ta atoms are predominantly distributed on the Ni sites. This result is in conflict with expectations based on the ternary phase diagram.
Effects of Fe and Mn Additions on the Ductility and Fracture of Ni3Al
Authors: Dimiduk Dennis M. , Weddington Vicky L. , Lipsitt Harry A.
Published: March 2011

Recent studies suggested that additions of either Fe or Mn to polycrystalline Ni3Al without boron, result in a ductile alloy. In the present study the effects of Fe and Mn additions on the strength and ductility of Ni3Al were investigated at 25°C, 600°C in air and at 600°C in vacuum. Metallographic examination showed that with 4 at.% solute a single phase structure existed but at higher solute levels the alloys were two phase. Single phase materials tested in bending showed virtually no plastic strain and low bend strengths at all temperatures. The two phase materials tested at 25°C and 600°C in vacuum showed marked ductility. However, the same alloys tested at 600°C in air exhibited brittle failure. These results suggest that Fe and Mn have no effect on the high temperature dynamic environmental embrittlement known to occur in Ni3Al.
Creep Deformation of Ta Modified Gamma Prime Single Crystals
Authors: Anton D.L. , Pearson D.D. , Snow D.B.
Published: March 2011

The role of substitutional element alloying of single phase γ' has become of primary interest to alloy designers who would like to exploit its low density and excellent oxidation resistance. Current γ' alloys have not shown sufficient strength to be useful in a creep limited environment. In order to maximize the potential of single phase γ' alloys and to more fully understand the creep strengthening mechanisms in two phase Ni-base superalloys, it has become necessary to clarify the role of Al-substitution elements. Ta is a potent strengthening element in γ' as well as imparting beneficial surface stability to superalloys; its effect on the creep properties of Ni3Al is the subject of this paper. The 1300°C isotherm of the Ni-Al-Ta system was determined in order to establish the γ' single phase field. Comrpositions were fabricated having chemistries which systematically varied both the Al:Ta ratio at Ni=75% and Ni:(AI+Ta) ratio at Ta=6%. Creep tests were conducted on <001> oriented single crystals at 760, 871 and 982°C. Electron microscopy was used to characterize the nature of slip deformation, confirm phase purity and to determine the existence of tetragonal distortions in these crystals. In this manner the strengthening due to Ta was examined in the absence of grain boundary effects. These γ' mono—crystals did not display classical creep response. Incubation creep was observed in all of the specimens tested. Surprisingly, the maximum incubation time was found to occur in the high ratio Ni:(Al+Ta) compounds, where less than 0.5% creep strain was obtained after 200 hours at stress. After incubation, either tertiary creep leading to failure, or apparently classic primary, secondary and tertiary creep ensued. In addition extremely long elongations, to 85%, were measured.
Effects of Mo and Ti Additions on The High Temperature Compressive Properties of Iron Aluminides Near Fe3Al
Authors: Diehm R. S. , Mikkola D. E.
Published: March 2011

Hot compression testing has been used to examine the effects of Mo and Ti additions on the yield strength and rate of work hardening for cast alloys near Fe3Al. A few powder processed materials have also been studied. Significant improvements in high temperature compressive properties on alloying have been related to increases in the DO3→B2 transition temperature and the associated changes in the nature of the dislocations involved in the deformation processes.
Evaluation of Multicomponent Nickel Base LI2 and Other Intermetallic Alloys as High Temperature Structural Materials
Authors: Shah D. M. , Duhl D. N.
Published: March 2011

Multicomponent nickel base intermetallics with the L12 structure were evaluated as high temperature structural materials. The compounds were based on the γ' composition of PWA 1480, a high strength single crystal nickel base superalloy. The best balance of properties in the compound was achieved with <111> oriented single crystals but no significant advantage could be demonstrated over the precipitation hardened superalloys. Insufficient impact resistance was a major deficiency of the L12 compounds. Other nickel base intermetallics were also evaluated but showed little advantage over superalloys.
Reaction Chemistry and Thermodynamics of the Ni-Al and Fe-Al Systems
Authors: Santandrea Robert P. , Behrens Robert G. , King Mary A.
Published: March 2011

The reaction chemistry of the Fe-Al and Ni-Al systems was studied using differential scanning calorimetry (DSC). Experimentally measured heats of reaction and compositions of reaction products were characterized in terms of sample heating rates, reaction temperature, shape and size of aluminum powder, and sample preparation. Standard enthalpies of formation were derived from DSC results. Reaction products were identified by x-ray powder diffraction techniques.
Rapidly Solidified Binary Tial Alloys
Authors: Huang S. C. , Hall E. L. , Gigliotti M. F. X.
Published: March 2011

Melt spinning has been carried out on binary TiAl alloys at three Ti/Al ratios. Antiphase domains were observed in one ribbon specimen, but no significant disordering was induced by the rapid solidification as indicated by X-ray and electron diffraction analyses. Bending tests of both the ribbons and the consolidated counterparts showed a decrease in ductility with increasing Al concentration. This compositional effect can be correlated with the TiAl tetragonality (the c/a ratio) as well as the grain structure.
Order—Disorder Behavior of Grain Boundaries in a two Dimensional Mcdel Ordered Alloy
Authors: Farkas Diana , Jang Ho
Published: March 2011

The order-disorder behavior of a Σ = 5 grain boundary was investigated using a two dimensional latice gas model and the cluster variation method. It is found that a disordered layer forms in the grain boundary region at temperatures significantly below theorder—disorder temperature for the bulk. Under certain assumptions for the pair interaction energies the model predicts grain boundary compositions different from the bulk.
On the use of Positron Annihilation Spectroscopy in the Study of a Nonuniform Spatial Distribution of Metallurgical Defects
Authors: Schaffer James P.
Published: March 2011

Most of the Interpretation of positron annihilation results to date have been done within the context of the simple trapping model which assumes a uniform spatial distribution of defects within the specimen examined. While this assumption is often justifiable there are numerous metallurgical defect configurations which are markedly nonuniform. In this work some of the appropriate trapping models which have previously appeared in the literature will be briefly reviewed. Additional models which are currently being developed will be presented and the series of experiments which are being used to test the trapping models will be described.
Charging Microscopy of Semi-Insulating Gallium Arsenide
Authors: Sheu T.C. , Myhajlenko S. , Edwards J.L. , Roedel R.J. , Krause S.J.
Published: March 2011

The recent demonstration of “charging microscopy” to reveal resistivity variations in semi-insulating GaAs has generated interest in using the scanning electron microscope (SEM) as a contactless characterization technique for GaAs wafers. Resistivity variations give rise to a surface potential and secondary electron (SE) contrast, or “charging microscopy”, when viewing a wafer in the SEM. In this work we have shown that operating conditions may play a significant role in the SE image. Varying accelerating voltage from 5 to 35 keV gave rise to minor changes in the SE image, but varying beam current from 2×10−11A to 2×10−6A resulted in dramatic changes in the SE image, with two image contrast reversals occurring. The explanation for these changes in the SE image are unclear, but factors that are involved include surface and bulk conductivity, beam induced dielctric relaxation, and the sample-detector geometry.
Periodic {001} Walls of Defects in Proton-Irradiated Cu and Ni
Authors: Ehrhart P. , Jäger W. , Schilling W. , Dworschak F. , Gadalla Afaf A. , Tsukuda N.
Published: March 2011

The evolution of the defect structure in 3 MeV-proton irradiated Cu and Ni has been investigated by transmission electron microscopy and by differential dilatometry. The proton irradiations were performed at T≦100°C up to irradiation doses of 2 dpa. An efficient loss of selfinterstitial atoms at dislocations and a consequently high average concentration of vacancies in clusters is observed starting from rather low fluences. In addition an ordering of the defects in the form of periodic {001} walls with a typical periodicity length of ≈ 60 nm is observed for all equivalent {001} planes. The walls consist of high local concentrations of dislocations, dislocation loops and stacking-fault tetrahedra. The observed formation of periodic arraysof defect walls is considered as an example for a possibly general microstructural phenomenon in metals under irradiation.
A Positron Annihilation Lifetime Study of Poly(Bisphenol-a Carbonate)
Authors: Jones P. L. , Hill A. J. , Pearsall G. W. , Lind J. H.
Published: March 2011

Positron annihilation lifetime spectroscopy has proven to be sensitive to glass transitions and other free volume dependent phase transitions in amorphous and semicrystalline polymers. The thermal dependence of the lifetime spectra of positrons in compression-molded poly(bisphenol-A carbonate) has been measured from 253K to 323K, then modelled using a three component fit. The longest-lived component lifetime τ3 was found to vary linearly with increasing temperature independent of thermal history. The corresponding component intensity I3 was found to vary in a non-linear fashion with increasing temperature, exhibiting a significant dependence on thermal history. The observed thermal response of τ3 and I3 is discussed in terms of both molecular relaxation and the ductile-to-brittle transition behavior of poly(bisphenol-A carbonate).
Correlation of Electrical Properties with Structure Imaging of Semiconductor Interfaces
Authors: Batstone J.L. , Gibson J.M. , Tung R.T. , Levi A.F.J. , Outten C.A.
Published: March 2011

High resolution electron microscopy (HREM) is recognised as a powerful technique for thedetermination of atomic structures at crystal defects and interfaces. The application ofHREM to the study of insulator/semiconductor and metal/semiconductor interfaces is of particular technological interest. Correlation of electrical properties withinterface structure has been performed, taking advantage of the resolution available in the JEOL 4000EX. Images are usually obtained in a <110> projection, however in the JEOL 4000EX (point-to point resolution <1.7A). we have imaged semiconductor interfaces in the <100=direction using the (220) planes of 1.92Å spacing revealing all atomic columns in silicon, permitting “structure images” of interfaces to be obtained. Two types of interface have been studied at <1.9Å resolution. The roughness of the important crystalline Si/amorphousSiO2interface observed in implanted buried oxide layers and after wet and dry oxidation of silicon is relevant for the correlation of carrier mobilities with interface structure. Analysis of both the NiSi2/Si(100) and AI/AIGaAs(100) crystal/crystal interfaces where a periodic structure is observed in the plane of the interface allows the use of rigid shift measurements and multislice image calculations to determine an atomistic model. The influence of the NiSi2/Si interface structure on the Schottky barrier height is discussed.
Structural Studies of Nucleation and the Initial Stages of Growth of Epitaxial Gaas on Si(100) Substrates
Authors: Hull R. , Fischer-Colbrie A. , Rosner S.J. , Koch S.M. , Harris J.S.
Published: March 2011

Nucleation and growth of GaAs fIlms deposited by Molecular Beam Epitaxy upon Si(l00) substrates are studied by transmission electron microscopy. The initial nucleation of GaAs consists of approximately hemispherical islands associated with steps upon the substratesurface and coherently strained to the substrate lattice. As the island size increases, crystalline defects relax the strain between epilayer and substrate. Island coalescence is a secondary defect generation mechanism. Subsequent growth of the epitaxial GaAs layer reveals a progressive deterioration of the GaAs/Si interface planarity and the growth and eventual dissolution of amorphous or misoriented crystalline regions at the GaAs/Si interface.
Tem Study of the Accidental Modulation of Mbe Grown AlxGal-x As
Authors: Britton E.G. , Stobbs W.M.
Published: March 2011

Composition modulations with a wavelength of -1-3 nm have been observed by transmission electron microscopy in nominally uniform AlxGa1-x As grown by molecular beam epitaxy. We describe the characterisation of this phenomenon and discuss its possible origins, in the light of the reported existence of a long range ordered structure.