bluuebunny/crossref_metadata_2025_split huggingface dataset:
Silicon on Sapphire of Single Crystal Quality Obtained by Double Solid Phase Epitaxial Regrowth
Authors: Parker M. A. , Sinclair R. , Sigmon T. W. 
Published: March 2011

AbstractA dual-implantation and annealing procedure has been refined which results in silicon films of single crystal perfection on sapphire substrates. This double solid phase epitaxy (DPSE) procedure consists of two self-implantation steps that serve to amorphize the defect structure of the parent silicon film with subsequent annealing steps employed to recrystallize the amorphized structure. High resolution cross-section transmission electron microscopy (HRXTEM) and ion channeling have been employed to study the microstructure of the silicon films, the sapphire substrates, and the interface. The resulting perfection of the silicon layer is shown to be a sensitive function of the first self-implant energy, dose, and silicon film thickness. Also, a correlation has been established between microtwin density and dechanneling profiles. HRXTEM of microtwins in silicon on sapphire (SOS) starting material demonstrates contrast features identified as rotational Moire' fringes between the microtwins and the matrix by means of optical diffractometry. Best results are achieved for the first implant energy of 170 keV 28Si+. Thus, the DSPE process is shown to give optimal results in defect reduction.
Epitaxial Growth of SixGe1−x Films on Si by Solid Phase Epitaxy.
Authors: Pai C. S. , Lau S. S. 
Published: March 2011

AbstractIt has been demonstrated in the literature that amorphous Si (or Ge) can be transported across a metal layer and grown epitaxially on Si(Ge) single crystal substrates in the solid phase. The objective of this study is to investigate if amorphous SixGe1−x mixtures can be transported uniformly across a medium and grown epitaxially on single crystal substrates without phase separation. The samples were prepared by e-beam evaporation of thin Pd films onto Si<100> substrates, followed by co-evaporation of SixGe1−x alloyed films (0<x<1) without breaking vacuum. The samples were anneaie in vacuum at 300°C to form a Pd silicide-germanide layer at the interface, then at 500°C for transport of the alloyed layer across the Pd silicide-germanide layer and subsequent epitaxial growth on Si substrate. The samples were investigated by x-ray diffraction and by MeV ion backscattering and channeling. The results show the alloyed film transports uniformly with no phase separation detected. The channeling result shows the grown alloyed layer is epitaxial with some Pd trapped in the layer. This simple technique is potentially useful for forming lattice-matched non-alloyed ohmic contacts on III–V ternary and quaternary compounds.
Interdiffusion and Stability of Compositionally Modulated Films
Authors: Spaepen Frans 
Published: March 2011

AbstractThe thermodynamics and kinetics governing the stability of compositionally modulated materials are reviewed. Typical results of interdiffusion experiments on fcc and amorphous metals are discussed to demonstrate the sensitivity and special features of the technique. Two coarsening mechanisms, and the stability of orthogonal waves in phase separating systems are analyzed.
Strain and Damage Measurements in Ion Implanted AlxGa1−x As/GaAs Superlattices
Authors: Hamdi A. H. , Tandon J. L. , Vreeland T. , Nicolet M.-A. 
Published: March 2011

AbstractStrain measurements in AlxGa1−x As/GaAs superlattices have been carried out before and after Si ion implantation. For doses up to 5 × 1015 cm−2, no atomic intermixing of the sublayers is observed by backscattering spectrometry. However, with x-ray rocking curve measurements, significant changes in the strain profiles are detected for implantations with doses as low as 7 × 1012 cm−2. Interpretation of the rocking curves suggests that low-dose implantations release strain in the AlxGa1−x As sublayers. The strain profile recovery of the implanted samples, upon annealing at ∼ 420°C, implies that the damage caused by implantation is largely reversible.
Low Temperature Reordering of Implanted Amorphous Si with Al Surface Layers
Authors: Hung L. S. , Chen S. H. , Mayer J. W. 
Published: March 2011

AbstractIon backscattering and channeling techniques, transmission and scanning electron microscopy, and secondary ion mass spectroscopy were used to investigate the reordering characteristics of implanted amorphous Si in the presence of an Al surface layer. It was found that reordering takes place at the temperature of about 400°C and is associated with an interfacial migration between Al and Si. The regrowth behavior appears to be a function of the initial annealing temperature and annealing sequence. High density of twin faults and substantial concentration of Al are observed in the regrown layers. We believe that the low temperature reordering is due to processes analogous to solid epitaxial growth with transport media.
Epitaxial Growth of Refractory Silicides on Silicon
Authors: Chen L. J. , Cheng H. C. , Lin W. T. , Chou L. J. , Fung M. S. 
Published: March 2011

AbstractEpitaxial refractory silicides were grown on silicon by solid phase epitaxy method. Transmission electron microscopy has been performed to study the microstructures of epitaxial layers and their orientation relationships with respect to substrate Si.Metal thin films, electron-gun deposited, or sputtered metal-silicon films were annealed in N2 ambient or in vacuum at 200°C-1100°C. Substrate heating, two step annealing and ion beam mixing were applied to induce the growth and improve the quality of epitaxial films. In this paper, formation and structures of epitaxial CrSi2, VSi2, ZrSi2, MoSi2 and WSi2 are presented. Preliminary results of the epitaxial growth of TiSi2, TaSi2 and NbSi2 are reported.
Transition From Single-Layer to Double-Layer Steps on GaAs(110) Prepared by Molecular Beam Epitaxy
Authors: Fuchs J. , Van Hove J. M. , Pukite P. R. , Whaley G. J. , Cohen P. I. 
Published: March 2011

AbstractEven though GaAs (110) is the only semiconductor whose surface structure is known with confidence, little is known about its microscopic growth mechanisms. We have used RHEED to study the role of steps in the MBE growth of GaAs on vicinal GaAs(11O) surfaces which were misoriented by less than 2 mrad. After thermally desorbing the initial oxide, 20 layers of GaAs deposited at 700K produced a surface with single atomic-layer steps having an average terrace length of a few hundred Angstroms. Upon annealing to 8OOK, a slow mass migration occurred producing a surface with one thousand Angstrom average terrace lengths and predominantly double layer step heights. The RHEED pattern was nearly instrument limited at in-phase angles of incidence, with little background intensity and bright Kikuchi lines. Subsequent deposition showed only weak oscillations in the RHEED intensity, in contrast to growth on the (001) surface. The period of the observed oscillations indicates that the layer-by-layer growth involves single-layer steps. Growth of as little as 5 atomic layers on a surface with double steps could not be annealed to give a RHEED intensity as great as the first annealed surface. These measurements reconcile previous LEED results with the oxygen adsorption measurements of Ranke. The results clearly show the dominance of steps in the formation of RHEED streaks.
A Critical Comparison of the Techniques used to Characterize the Crystallography of an Interface: Pd on mbe “Rown GaAs(100)
Authors: Delrue I. P. , Wittmer M. , Kuan T. S. , Ludeke R. 
Published: March 2011

AbstractIn situ Reflection High Energy Electron Diffraction and ex-situ Transmission Electron Diffraction and Ion Channeling have been applied to a reacted Pd-GaAs interface and the results obtained are critically compared. The investigation has been done on the stabilized c(2×8) surface obtained by MBE on GaAs(100) substrates. Smooth surface epitaxial growth has been observed by RHEED as soon as a few monolayers of Pd are deposited at a substrate temperature of about 325°C. TEM diffraction studies indicate the presence of an intermetallic hexagonal structure similar to the orthorhombic Pd5Ga2 but with slightly different lattice parameters due to the possible incorporation of As. A less abundant phase was also identified as an hexagonal structure similar to Pd8As2. Ion Channeling indicates pronounced reduction in scattering yield when the [100] axis of the substrate was aligned with the impinging beam, thus supporting the RHEED analysis. The three techniques listed above were found to be useful for the determination of the epitaxial relationship between the identified phases and the substrate.
Morphological Studies of Polysilicon Emitter Contacts
Authors: Bravman John C. , Patton Gary L. , Sinclair Robert , Plummer James D. 
Published: March 2011

AbstractUsing high resolution lattice imaging techniques, the morphology of thepolycrystalline silicon - single crystal silicon interface has been correlated to (1) the surface treatment used prior to polysilicon deposition, (2) the polysilicon implant dose, and (3) high temperature annealing. Specimens which were chemically oxidized prior to deposition exhibited a continuous layer of amorphous oxide ≈1.5nm thick. High temperature annealing produces small discontinuities in this oxide which allow the polysilicon to make direct contact with, and become epitaxially aligned to, the substrate. Specimens which were etched in HF prior to deposition were characterized by nearly oxide-free interfaces, which, following implantation and annealing, exhibited regions of epitaxial realignment significantly larger than those found in the chemically oxidized films. Heavily implanted films annealed at high temperature displayed almost complete epitaxial realignment.
Amorphous Phase Formation in Solid State Reactions of Layered Nickel Zirconium Films
Authors: Clemens Bruce M. , Buchholz Jeffrey C. 
Published: March 2011

AbstractFormation of an amorphous zirconium-nickel phase by solid state reaction of a layered crystalline structure has been studied by in-situ resistivity, x-ray diffraction, and Auger depth profiling. The reaction was studied as a function of layer thickness and reaction temperature.Samples with a layer thickness of less than 4 atomic planes had x-ray diffraction spectra with one broad maximum characteristic of amorphous material. As the layer thickness increased, the maximum broadened and separated into two resolved peaks corresponding to crystalline nickel and zirconium. These structures were transformed to an amorphous nickel-zirconium alloy by an anneal at temperatures below the crystallization temperature of the amorphous phase. The reaction occured by a layer growth process, where the thickness of the layer evolved linearly with the square root of time.
Amorphous and Crystalline Phase Formation by Ion-Mixing of Ru-Zr and Ru-Ti
Authors: Cheng Y-T. , Johnson W. L. , Nicolet M-A. 
Published: March 2011

AbstractIon mixing of multilayered Ru-Zr and Ru-Ti at different compositions and substrate temperatures produced various metastable phases. The applicability of previously proposed rules regarding amorphous phase formation are examined. Effects of point defect in amorphous phase formation by ion mixing are discussed.
Metal Rich Silicide Formation Between Thin Films of Vanadium and Amorphous Silicon
Authors: Psaras P. A. , Eizenbergt M. , Tu K. N. 
Published: March 2011

Extended AbstractThe formation of silicides via a solid state reaction of silicon and transition metal thin film is characterized by the sequential appearance of the various compounds rather than the simultaneous formation of all possible compounds [1]. Thin films of refractory metals will form disilicides on a single crystal silicon substrate (unlimited supply of silicon) and since they are stable with silicon, no other silicides will form. This situation is illustrated in Fig. la) by the formation of VSi2 in the case of vanadium on silicon. On the other hand, which silicide will form in the case where there is an excess amount of refractory metal is unknown. The objective of this work was to study this case utilizing the vanadium silicon binary system [2].
Phase Transitions in Gold Contacts to Gallium Arsenide
Authors: Beam Edward , Chung D. D. L. 
Published: March 2011

AbstractX-ray diffraction was used in situ to study the phase transitions which occurred in 1500 Å Au/GaAs(100) upon heating and cooling. The reaction between Au and GaAs took the form Au + Ga → α Au-Ga. Upon heating, α Au-Ga completely dissolved in liquid Au-Ga. Upon subsequent cooling, β Au-Ga (or Au7Ga2) formed. In 1 atm of nitrogen, phase transitions were observed reversibly at 525 ± 25°C (due to the complete dissolution of α Au-Ga upon heating) and 415 ± 5°C (due to the peritectic transformation of β Au-Ga to α Au-Ga and liquid Au-Ga upon heating). In a vacuum of 425 μ (0.031 Kg/2m) similar phase transitions were observed at 425 ± 25°C and 387 ± 13°C, respectively.
Microstructures in Rapidly Solidified Ll2-TYPE Ni-Al-Cr Alloys
Authors: Huang S. C. , Chang K. M. , Hall E. L. , Laforce R. F. 
Published: March 2011

ABSTRACTA microstructural study of the melt spun alloys Ni75 Al25. Ni72.5 Al22.5Cr5. and Ni67.5A120Cr12.5 was carried out. Variations in grain morpfology; phase separation and ordering structure were observed. The results are discussed in terms of alloy stoichiometry, Cr effect on phase reaction, microsegregation of Al and the cooling rate.
Resistivity of Short-Range and Long-Range Order Changes in Ni4Mo
Authors: Lei T. S. , Vasudevan K. , Stansbury E. E. 
Published: March 2011

ABSTRACTShort-range order (SRO) and long-range order (LRO) reactions in Ni Mo as a function of room temperature deformation ahd thermal treatments betwean −269 and 1300°C are Reported. Resistivity results show that SRO is dispersed by heating near 1300°C and by cold working to 68% reduction of area (RA). The resistivity decreases to a minimum at 68% RA after which an increase is attributed to an increase in defect density.The resistivity as a function of variations in the time-temperature history is reported. Cooling at 60°C/min; results in the maximum “frozen in” SRO with resistivity of 144 μohm cm at 25°C; th8 resistivity of the LRO state obtained on slow cooling is 48 μohm cm. At −269°C, the resistivities are 139 and 8 μohm cm for the SRO and LRO states respectively. Correlations relate kinetics and microstructures to resistivity changes during heating, cooling and isothermal SRO-LRO transformations. Preliminary results of reheating fully ordered samples to near 868°C and quenching are reported. Results are discussed with relevance to existing theories.
γ/γ′: The Key to Superalloy Behavior
Authors: Giamei A. F. , Pearson D. D. , Anton D. L. 
Published: March 2011

ABSTRACTGamma prime (Ni3Al), with its unusual temperature dependence of yield strength, is the strengthening phase in Ni-base superalloys. Many facets of γ/γ′ coherent precipitation strengthening have been well studied: coarsening kinetics, volume fraction vs. strength, yield strength vs. temperature, dislocation dynamics, etc.This contribution deals with several important aspects of two phase behavior in coherent systems (for high temperature application) which are either relatively new or have received inadequate attention. The most desirable γ/γ′ misfit, in sense and magnitude, is dependent on the temperature of application. It must be recognized that the sense and size of misfit are not only a function of alloying, but temperature as well. Sufficient data are presented for various alloying additions to γ and γ′ to allow one to roughly compute the misfit at room temperature or 1000C. The evolution and significance of the ′′ morphology are discussed. Stability of particle size and shape are related to misfit, temperature and stress. It is demonstrated that for high temperature creep resistance, a fine rafted structure is the most desirable. Finally, some data are presented which demonstrate the dependence of γ′ strength on stoichiometry as well-as temperature.A portion of this work was sponsored by AFOSR, with A. Rosenstein as contract monitor.
The Effect of Surface Oxide Films on the Mechanical Behavior of NiAl
Authors: Noebe R. D. , Gibala R. 
Published: March 2011

ABSTRACTThin surface films have been shown to enhance the ductility and decrease the flow stress of several body-centered cubic metals at temperatures T < 0.2 Tm. The origin of this effect lies in the large difference in the intrinsic mobilities of edge and screw dislocations in body-centered cubic crystals. B2 ordered intermetallic alloys, although simple cubic in structure, are based on the body-centered cubic structure and have dislocation core structures, dislocation mobilities and temperature and orientation dependent deformation qualitatively similar to that of bcc metals. This investigation was initiated to examine possible effects of surface films on the mechanical behavior of B2 ordered intermetallic alloys, using oxidized NiAl as the initial material for investigation. Experiments were performed on an impure non-stoichiometric (47.1 at.% Al) single crystal material with an axial orientation near [123]. Surface film softening was observed at room temperature in compression at a strain rate of 2 x 10-4 s-1. Flow stresses of the oxide coated crystals were as much as 20% lower than those of identically prepared uncoated crystals. The strains to fracture of coated specimens were larger than those of uncoated specimens and in a few instances the ductility enhancement was as much as four times. Of the several oxides examined, the largest softening effects were found for a thermally deposited delta-A1203 film formed at 1000 °C for 1 hour. The current results for NiAl are compared to results previously obtained for bcc metals. Experiments which could further enhance the film softening effects observed in B2 ordered intermetallic alloys are suggested.
creep Behaviour of the Ordered Intermetallic (FE, NI)Al Phase
Authors: Rudy M. , Sauthoff G. 
Published: March 2011

ABSTRACTThe deformation behaviour of the ordered intermetallic (Fe, Ni)Al phase with B2 structure is studied as a function of composition and temperature with stress strain tests and creep tests.The alloy composition has been varied with respect to stoichiometry and the Fe/Ni ratio. The creep resistivity depends on the alloy composition in a complex manner: a deviation from the stoichiometric compositions leads to a reduction of the creep resistance, and there is a maximum of the creep resistance for the ternary alloys with about 10% Fe.
The B2 Aluminides As Alternative Materials
Authors: Stephens Joseph R. 
Published: March 2011

ABSTRACTAs part of NASA's Conservation of Strategic Aerospace Materials (COSAM) Program, a research effort is underway to explore the potential of the B2 aluminides as structural material alternatives for the strategic element containing superalloys currently used in gas turbine engines. Emphasis is being place on the equiatomic Fe and Ni aluminides. Although Co is a strategic material, the equiatomic Co aluminide is also being studied to gain a more complete understanding of these fourth period intermetallics. The research effort is a cooperative program involving in-house research at NASA Lewis plus several university grant programs. Research focuses on initial processing techniques such as ingot melting, powder metallurgy, and rapid solidification with and without additional thermomechanical processing; high temperature deformation - primarily compressive creep; compositional effects within the binary B2 aluminides; third-element alloying addition effects on high temperature strength and oxidation resistance; and near room temperature ductility as influenced by processing, alloying, and grain size. This paper will review the various programs now underway and present some of the highlights of research results.
A review of Rapid Solidification Studies of Intermetallic Compounds
Authors: Koch C. C. 
Published: March 2011

ABSTRACTA review of rapid solidification studies of high temperature ordered intermetallic compounds is presented. Emphasis is on the nickel - and iron - aluminides which are of potential interest as structural materials. The nickel-base aluminides which have been rapidly solidified exhibit changes in grain size, compositional segregation, and degree of long range order (as reflected in APB size and distribution) which markedly affect mechanical properties. Some experiments indicate the formation of a metastable L12 phase in rapidly solidified Fe-(Ni, Mn)-Al-C alloys, while other work observes only a metastable fcc phase in the same composition range. The metastable phases and/or microstructures in both nickel and iron aluminides are destroyed by annealing at temperatures >750K, with subsequent degradation of mechanical properties. Rapid solidification studies of several other intermetallic compounds are briefly noted.
Ni-base Intermetallics for High Temperature Alloy Design
Authors: Nash P. 
Published: March 2011

ABSTRACTFurther development of Ni-base superalloys based on γ–γ′ structures offers little hope of substantial improvements in properties for gas turbine applications. However because of the substantial technology base which exists for nickel base alloys there are considerable advantages, in research time and money, in developing new nickel base alloys. Interest in the 1970's in directionally solidified composites indicated some possible new systems to replace γ–γ′ alloys. More recently there has been renewed interest in aluminides such as FeAl, CoAl and NiAl. These materials exhibit melting points which are substantially greater than for current γ–γ′ alloys. Problems of lack of ductility for these alloys may be resolved by alloying and novel processing routes such as rapid solidification.In addition to NiAl there are a number of other nickel intermetallics which from limited experimental data are worth considering at least as second phases. Some of these compounds are Ni7Hf2, Ni7Zr2, Ni5Zr, Ni6A1Ta and Heusler alloys of the type NiAlx where x is a transition element. The solubilities and phase relationships and where available the mechanical property data in a number of nickel ternary systems will be reviewed in terms of their potential for development of new high temperature alloys.
Silicon-Nickel Compounds by Ion Implantation
Authors: Mayer S. G. B. , Milillo F. F. , Potter D. I. 
Published: March 2011

ABSTRACTCompounds of silicon and nickel have been formed by implanting silicon ions into nickel at various fluences and temperatures. Temperature during implantation is a major factor controlling implanted ion concentrations and phase developments. The ordered phase Ni3Si, which forms during implantation at 600°C, is replaced by Ni5Si2 during implantation at 400°C or below. In contrast to aluminum implantation of nickel, crystalline phases form even at high fluences (>1 × 1018 ions/cm2) and at low temperatures (<200°C) in silicon implanted nickel.
Switchable Microcrystallization Near Threshold in Laser Annealing of GeSe2 Glass and Evaporated Films
Authors: Phillips J. C. 
Published: March 2011

ABSTRACTJust below threshold for irreversible macrocrystallization there may exist a narrow energy (or power) density region where microcrystallites are formed. In the case of Si and GaAs this region lies just above the threshold for melting and the microcrystallites are formed irreversibly. In the case of GeSe2 when Urbach tail laser energy is used just below the macrocrystallization threshold the photons selectively replace like-atom bonds with chemically ordered bonds, and microcrystallization can be thermally reversed in melt-quenched glass at temperatures as low as Tg/2.