bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical Characteristics and Device Applications of Zone-Melting-Recrystallized Si Films on SiO2
Authors: Tsaur B-Y. , Fan John C. C. , Geis M. W. , Chapman R. L. , Brueck S. R. J. , Silversmith D. J. , Mountain R. W.
Published: March 2011

Device-quality Si films have been prepared by using graphite strip heaters for zone melting poly-Si films deposited on SiO2-coated substrates. The electrical characteristics of these films have been studied by the fabrication and evaluation of thin-film resistors, Mosfets and MOS capacitors. High yields of functional transistor arrays and ring oscillators with promising speed performance have been obtained for CMOS test circuit chips fabricated in recrystallized Si films on 2-inch-diameter Si wafers. Dualgate Mosfets with a three-dimensional structure have been fabricated by using the zone-melting recrystallization technique.
Neutron Activation Measurements of As and Ga Loss During Transient Annealing of Gaas
Authors: Rose A. , Pollock J.T.A. , Scott M.D. , Adams F.M. , Williams J.S. , Lawson E.M.
Published: March 2011

Significant dissociation is normally detected under non-optimised transient annealing of GaAs. We have utilised neutron activation to measure As and Ga loss from virgin and implanted material annealed under various transient conditions. Complementary RBS data are reported. In particular, surface dissociation has been measured as a function of pulsed ruby laser power and for several combinations of time and surface temperature using an incoherent light source and a vitreous carbon strip heater.

The results indicate that neutron activation analysis offers a powerful tool to identify the conditions required to minimise GaAs dissociation during annealing. For examplq ruby laser pulses of energy 0.29–1.38 J cm−2 caused As loss of 4 – 90 × 10 cm−2.
Thermal Pulse Annealing of Hg1−xCdxTe
Authors: Dimiduk K. C. , Opyd W. G. , Greiner M. E. , Gibbons J. F. , Sigmon T. W.
Published: March 2011

Thermal pulse annealing has been used to modify the near surface of Hg1−xCdxTe. Using anneals of approximately 260°C for seven seconds, the crystal quality of epitaxial HgCdTe surfaces can be improved as observed by MeV He+ ion channeling. Similar anneals have also been used to repair the damage resulting from a 250 keV, 101511 B/cm2 implant into HgCdTe held at LN2. For higher temperatures and/or longer anneals, surface Hg loss is observed. Rutherford Backscattering measurements are used to measure this loss. The resulting loss rate data is described by No= A exp (−ΔE/kT) where A and ΔE depend on the material composition with A = 1029, ΔE = 1.8 eV and A = 1036, ΔE = 2.6 eV for x = 0.23 and 0.4, respectively.
Ion and Electron Spectroscopy During Pulsed Laser Irradiation of Silicon
Authors: Long J.P. , Williams R.T. , Royt T.R. , Rife J.C. , Kabler M.N.
Published: March 2011

Ion mass spectrometry, charged particle yields, and kinetic energy distributions of electrons and ions are used to characterize silicon wafers and vacuum-cleaved silicon surfaces under conditions related to laser annealing. We find that alkali metals dominate the positive ion emission from chemically-cleaned wafers, a mass-72 peak tentatively identified as Si2O+ comprises the main ion emission from the cleaved surface, and ion and electron temperatures can be derived from the energy distribution curves although the Si2O+ emission implies more than a simple thermal evaporation process.
Strain Relief by Tilting of Epitaxial GaAs Films on Si
Authors: Schowalter L. J. , Hall E. L. , Lewis N. , Hashimoto Shin
Published: March 2011

In this paper, a general formula is calculated relating the misalignment of a heteroepitaxial overlayer with respect to the substrate to the defects at the interface. High-resolution TEM studies are presented which show that the density of dislocations along the interface of GaAs grown on vicinal Si(100), with Burgers vector perpendicular to the interface, is consistent with the amount of tilt observed in ion-channeling studies. Arguments are also presented which demonstrate that the tilt observed is an effective form of strain relief but that this mechanism can only operate when the heteroepitaxial growth is nucleated by island growth. One significant conclusion is that the lower bound observed on the threading dislocation density in GaAs on Si is due to this mechanism of strain relief by tilting.
Onset of Misfit Dislocation Generation in As-Grown and Annealed Sil-XGex/Si Films
Authors: Scott M. P. , Laderman S. S. , Kamins T. I. , Rosner S. J. , Nauka K. , Noble D. B. , Hoyt J. L. , King C. A. , Gronet C. M. , Gibbons J. F.
Published: March 2011

X-ray topography and transmission electron microscopy were used to quantify misfit-dislocation spacings in as-grown Si1-xGex films formed by Limited Reaction Processing (LRP), which is a chemical vapor deposition technique. These analysis techniques were also used to study dislocation formation during annealing of material grown by both LRP and by molecular beam epitaxy (MBE). The thickness at which misfit dislocations first appear in as-grown material was similar for both growth techniques. The thermal stability of capped and uncapped films was also investigated after rapid thermal annealing in the range of 625 to 1000°C. Significantly fewer misfit dislocations were observed in samples containing an epitaxial silicon cap. Some differences in the number of misfit dislocation generated in CVD and MBE films were observed after annealing uncapped layers at temperatures between 625 and 825°C.
Thermal Stress-Induced Grain Boundary Voiding and Notching in Narrow Al-Based Metallizations
Authors: Li Che-Yu , Black R. D. , LaFontaine W. R.
Published: March 2011

Grain boundary voiding has been identified as a diffusional creep mechanism that produces failure of narrow Al-based metallizations during thermal aging. It is considered to be a reliability concern for sub-micron metallizations because the resulting failure rate has been observed to be strongly line width dependent. This paper presents a theoretical model for stress-induced grain boundary voiding. The proposed model is shown to account for the experimentally observed temperature and time dependence of thermal aging-induced line failure data reported in the literature.
Effect of Hydrogen on Thermal Stress in Layered Structure of Ti and Ti(Al) Thin Films.
Authors: Hu C.-K. , Ho P. S. , Gupta D.
Published: March 2011

The effect of hydrogen on stress in thin film structures has been investigated for Ti, Al, Ti(Al) and Al(Ti) films. The stress in the metal films was measured in-situ as a function of temperature and ambient (vacuum of 10-6Torr., forming gas and nitrogen) using a bending beam technique. The metal films were deposited on fused quartz or polyimide/fused quartz substrates using a dual e-gun evaporation method. The stress in pure Ti films was found to be strongly dependent on the annealing environment. Upon thermal cycling in a forming gas, an abrupt change of stress in the Ti film due to crack formation and delamination in the Ti film was observed. The possibility to eliminate the hydrogen effect by Al addition has been investigated. The hydrogen effect can be reduced by an addition of 5 at.% Al, but stress induced crack formation similar to the pure Ti film was still observed in this alloy film. An increase to 20 at.% Al in the alloy films eliminated the hydrogen effect, however, such an alloy film was brittle as cracks and delamination were observed after one thermal cycle from room temperature to 350 °C. A similar behavior in stress relaxation was observed in an Al-riched film with 20 at.% Ti.
Deformation in Thin Films Deposited on Rigid Substrates
Authors: Murakami Masanori
Published: March 2011

Stresses and strains are always present in thin films deposited on rigid substrates. They are introduced into the films during the deposition and/or subsequent heat and chemical treatments. Since the origins of the strains (stresses) in thin films and their shapes are different from those of bulk materials, the distribution of strains supported elastically by the films is different from that of the bulk materials. The present paper reviews deformation in thin films caused by elastic strains, using illustrative data of Pb and Nb films that were deposited on Si wafers. Also, x-ray diffraction techniques to detect such local deformation are briefly reviewed.
Thermally Induced Stresses and Strains in Laser Processing of Thin Films
Authors: Tuchman Judah A. , Welsh Lisa P. , Herman Irving P.
Published: March 2011

The stresses and strains induced in thermal laser processing of substrates and thin films on substrates, are obtained in terms of single integrals by solving the thermoelastic equations using a Gaussian profile laser as the heating source. This analysis is applied to silicon thin films on fused silica and sapphire substrates. In part, this study shows that defects can form in the films because the stresses induced during high temperature laser processing of silicon and similar materials can exceed the yield stress under certain experimental conditions.
Effects of Stress on the Adhesion of Metals to Polyimides
Authors: Seshan K. , Lacombe R. H. , Wagner J. B.
Published: March 2011

This paper describes the effects of ambient, thermal and mechanical stress on the adhesion of titanium (Ti) to polyimide (PI). Pull testing on the Ti/PI system shows that metal/polyimide bonding degrades when the composite is thermally cycled. A thermochemical mechanism is proposed that accounts for the interface degradation. We do not treat the adhesive interface as a discrete layer, but rather as a gradual “transition zone” between metal and polymer -- a zone that may grow, and/or change in composition and stress state, thus altering the adhesive properties. The mechanism predicts discontinuities that may develop in the transition zone. Through the use of finite element techniques, it is demonstrated that when loads and displacements are imposed on the composite containing interface discontinuities, large localized stresses develop. Such stresses could explain the experimentally observed low strength failures.
Characterization of Surface Mechanical Properties and Residual Stresses in Ion Implanted Nickel
Authors: Morrison D. J. , Jones J. W. , Was G. S. , Mashayekhi A. , Hoffman D. W.
Published: March 2011

In this study, we have measured changes in hardness and residual stress state in polycrystalline nickel samples which have undergone a variety of ion beam surface treatments including self-implantation, amorphization by ion beam mixing Ni-Al multilayers, and the formation of a two-phase microstructure by elevated temperature aluminum implantation. Hardness-depth profiles of the the near-surface regions were determined using an ultra-low load microindentation system, and residual stress states induced by the surface modifications were analyzed using optical interferometry. These property changes were correlated with the accumulation of surface fatigue damage.
Gas Phase and Surface Reactions in Mocvd of GaAs from Triethylgallium, Trimethylgallium, and Organometallic Arsenic Precursors
Authors: Omstead Thomas R. , Sickle Penny M. Van , Jensen Klavs F.
Published: March 2011

The growth of GaAs from triethylgallium (TEG) and trimethylgallium (TMG) with tertiarybutylarsine (tBAs), triethylarsenic (TEAs), and trimethylarsenic (TMAs), has been investigated by using a reactor equipped with a recording microbalance for in situ rate measurements. Rate data show that the growth with these precursors is dominated by the formation of adduct compounds in the gas lines, by adduct related parasitic gas phase reactions in the heated zone, and by the surface reactions. A model is proposed for the competition between deposition reactions and the parasitic gas phase reactions. Model predictions are in very good agreement with experimental data for all combinations of precursors except for TEG/TMAs where extensive gallium droplet formation is observed at low temperatures. Growth of reasonable quality GaAs with Hall mobilities of 7600 cm2/Vs at 77 K using TEG and tBAs is reported for the first time.
Application of X-Ray Scattering to the in Situ Study of Organometallic Vapor Phase Epitaxy
Authors: Fuoss P. H. , Kisker D. W. , Brennan S. , Kahn J. L.
Published: March 2011

Despite their importance, the detailed surface reactions and rearrangements which occur during chemical vapor deposition remain largely undetermined because of the lack of suitable experimental probes. In principle, x-ray scattering and spectroscopy techniques are well suited to studying these near atmospheric pressure processes but advances in this area have been limited both by the lack of suitable x-ray sources and by the difficulty of integrating the growth and measurement experiments. We have developed equipment and techniques to perform in situ x-ray scattering studies of the structure of surfaces during organometallic vapor phase epitaxial (OMVPE) growth using the extremely bright undulator radiation from the PEP electron storage ring. In this paper, we describe our initial experimental results studying cleaning and subsequent reconstruction of GaAs (001) surfaces in a flowing H2 ambient. These results demonstrate the excellent surface sensitivity, low background and high signal levels necessary to study the dynamic processes associated with semiconductor growth using OMVPE.
Studies of the Chemistry of Metal and Semiconductor Clusters
Authors: Jarrold M. F. , Bower J. E.
Published: March 2011

This article summarizes recent studies of the chemistry of aluminum and silicon cluster ions containing 3–27 atoms.
In-Situ Diagnostics of Diamond CVD
Authors: Butler J. E. , Celii F. G. , Pehrsson P. E. , Wang H. -t. , Nelson H. H.
Published: March 2011

The deposition of diamond, a metastable crystalline form of carbon, from low pressure gases poses intriguing questions about the mechanisms of growth. Tunable IR Diode Laser Absorption Spectroscopy, Laser Multi-Photon Ionization Spectroscopy, and Laser Induced Fluorescence were used to characterize the gaseous environment in the Chemical Vapor Deposition growth of diamond films. The quality of the deposited material was examined by optical and SEM microscopies, and Raman, Auger, and XPS spectroscopies. When a reactant mixture of 0.5% methane in hydrogen, was passed across a hot Tungsten filament (2000 C), C2H2, C2H4, H and CH3 were detected above the growing diamond surface, and concentration limits for undetected species were determined. These results are discussed in terms of simple models for species formation and consumption, as well as the implications for the diamond growth mechanism.
Chemical Reaction Pathways for the Deposition of Amorphous Silicon-Hydrogen Alloys by Remote Plasma Enhanced CVD
Authors: Parsons Gn , Tsu Dv , Lucovsky G
Published: March 2011

We have grown thin films of a-Si:H alloys by Remote Plasma Enhanced CVD (Remote PECVD) and have studied the deposition process by mass spectrometry. We find that the concentration of silane fragments (SiHx x=0 to 3) and higher silanes (e.g. disilane Si2H6) in the gas phase is below our detection limit of =0.5%. Bias experiments and a comparison of the a-Si:H deposition rate with the known concentration of silane in the gas phase suggest that in Remote PECVD, silane molecules, SiH4*, vibrationally excited in the gas phase or on the deposition surface may lead dirtectly to a-Si:H film deposition.
Chemical Kinetics of Silicon-Rich Oxide Growth in an LPCVD Reactor
Authors: Lam C. H. , Rose K.
Published: March 2011

The chemical kinetics of Silicon Rich Oxide (SRO) growth in a N2O-SiH4 LPCVD reactor has been studied at deposition temperatures from 610 to 680°C and pressures from 0.4 to 0.5 torr. We can produce SRO films with a wide spectrum of input reactant ratios γ = [N2O]/[SiH4] = 1 to 40. The dependence of film composition on γ changes dramatically in a region around γ = 2.

Growth for γ < 2 is consistent with the chemical kinetics of SIPOS growth. Growth for γ > 20 can be explained by oxidation of silicon in the bulk of the growing SRO film. We can explain growth from γ ≈ 4 to 20 by considering the chemical kinetics of possible binary surface reactions which may produce Si-Si or Si-O bonds. This allows us to accurately model the dependence of SRO growth rate in this region as a function of γ, pressure, and deposition temperature.
The Decomposition of Trimethylgallium and Trimethylaluminum on Si(100)
Authors: Lee F. , Gow T. R. , Lin R. , Backman A. L. , Lubben D. , Masel R. I.
Published: March 2011

The decomposition of trimethylgallium (TMG) and trimethylaluminum (TMA) on Si(100) is studied by TPD, XPS, and EELS. It is found that the decomposition of TMG is largely an intramolecular process. First one of the methyl groups in the TMG reacts with a hydrogen in another methyl group liberating methane. This leaves a CH2 group bound to the gallium which is seen clearly in EELS. Subsequently, another hydrogen reacts with a methyl group producing additional methane. This leaves a gallium atom and a CH group on the surface. Hydrogen desorbs, while carbon is incorporated into the growing film. Careful calibration of the peak areas in the TPD data indicates that 2.1 ± 0.3 moles of methane, 0.5 ± 0.03 moles of hydrogen, 1 mole of gallium, and 0.95 ± 0.1 moles of surface carbon are produced for every mole of TMG which decomposes. Since, the decomposition ratio is independent of the state of the surface, the surface orientation, and the level of impurities on the surface, it appears that the surface is not a direct participant in the reaction.

TMA adsorbs as dimers. However, the dimers decompose upon heating to 400 K. Thereafter, the chemistry of TMA decomposition is similar to that for TMG. Nonetheless, the product ratio varies with the TMA coverage, the state of the surface, and the aluminum coverage. Also, silicon-carbon bonds are evident at 600 K in EELS. It is suggested, therefore, that the decomposition of TMA is similar to that of TMG, except that methyl groups in TMA have a tendency to migrate to the support. In both TMA and TMG, carbon incorporation is an intrinsic part of the decomposition process. This suggests that TMA and TMG would not be appropriate source gases when one needs to produce films with very low carbon levels.
Valence Hole Localization in Molecular Auger Decay
Authors: Lapiano-Smith D. A. , Ma C. I. , Wu K. T. , Hanson D. M.
Published: March 2011

Studies of the unimolecular decay, following the excitation of core electrons of the carbon and fluorine atoms in carbon tetrafluoride and silicon and fluorine in silicon tetrafluoride by monochromatic, synchrotron radiation, provided evidence for a “valence bond depopulation” fragmentation mechanism. The fragmentation processes were examined using time-of flight mass spectroscopy. The mass spectra show the distribution of ions collected in coincidence with low and high energy electrons. Distinct changes in the mass spectra with atomic site of excitation and photon energy are observed. The observation of F2+ ions in the time-of-flight mass spectra following excitation of a fluorine is electron in SiF4 is significant because it provides direct evidence for the formation of a localized, two-hole, final valence state that persists on the time scale of fragmentation. In contrast, the lack of F2+ ions from CF4, indicates that the fragmentation occurs through a delocalized two-hole state.
Mechanisms in the Ion-Assisted Etching of TiSi2
Authors: O'Brien W. L. , Rhodin T. N. , Rathbun L. C.
Published: March 2011

A detailed investigation into the mechanisms of the ion-assisted etching of TiSi2 using 1000 eV argon ions and chlorine gas is reported. X-ray photoelectron spectroscopy (XPS) was used to investigate surface product distributions and modulated ion beam mass spectroscopy (MIBMS) was used to investigate gas phase product distributions. Identical experiments were performed on silicon and titanium single crystal substrates. Information on chemical mechanisms during ion-assisted etching was obtained by comparing the product distributions of the three substrates. For each substrate, the di and tetrachlorides were the major gas phase products. These products were emitted with high thermal velocities following a surface residence process. TiCl and TiCl2 products were found on the titanium surface after simultaneous exposure to chlorine and argon ions, but not on the TiSi2 surface. These observations are discussed in terms of specific chemical mechanisms which are critical during ion-assisted etching.
Spin-on Silicon Oxide (SOX): Physical Properties of the Sol
Authors: Ryan Vivian , Smolinsky Gerald
Published: March 2011

This paper describes an analysis of the physical properties of the sol using several complementary light scattering techniques. Polymerization and aggregation kinetics were followed through time-dependent changes in the size, shape, and density of the sol particles. The sot growth rate was controlled by choice of solvent and silicon concentration. Changes in viscosity and pH were small during the reaction period. Three different particle-growth regimes exist in which either the particle density increased, decreased, or remained the same. The addition of boron, hydrofluoric acid, or water accelerated the reaction. The sol experimental data correlate with the density and wet-etching rate of the cured films. After curing, high-density films were obtained from sols with three common characteristics: an average particle diameter >450 Å, a relatively high polydispersity, and a low particle density. These criteria were generally satisfied by solutions one to two days old.
Effects of the Selenium Precursor on the Growth of ZnSe by Metalorganic Chemical Vapor Deposition
Authors: Giapis Konstantinos P. , Da-Cheng Lu , Jensen Klavs F.
Published: March 2011

The growth of ZnSe on GaAs substrates by metalorganic chemical vapor deposition was investigated in a specially designed vertical downflow reactor. Dimethylzinc was used as the Zn source while different Se source compounds (hydrogen selenide (H2Se), diethylselenide and methylallylselenide) were employed to determine the effect of different source combinations on morphology, thickness uniformity, growth rate, electrical properties and photoluminescence (PL) characteristics of the grown ZnSe films. The H2Se was produced in situ by reaction of H2 and Se followed by distillation to control the amount of H2Se entering the reaction zone. H2Se produced very high mobility films with good PL spectra but poor surface morphology. Diethylselenide led to layers of good morphology and PL characteristics but the films were highly resistive. Unusual surface features were observed for methylallylselenide.
Microstructure and Magneto-Optical Properties of TbFeCo Films Prepared by Facing Targets Sputtering
Authors: Ito H. , Hirata T. , Naoe M.
Published: March 2011

The microstructure of TbFeCo amorphous films deposited by a facing targets type of sputtering (FTS) method varied with the change of deposition rate Rd. The films deposited at Rd of about 100–200 nm/min did not present any distinguishable columnar structure while the ones at Rd of about 50 nm/min revealed obvious columnar structure. The films with columnless structure exhibited Kerr rotation angle θk of 0.37 deg. of which the value was higher than that of the films with columnar structure over the wide range of Th content. The torque measurement implied that the presence of columnar structure was not mainly necessary for the occurrence of large perpendicular magnetic anisotropy. Under satisfactory confinement of plasma during sputtering, the dense, uniform and columnless TbFeCo films can be obtained on plasma-free substrate even at Rd as high as 200 nm/min, without destroying the excellent magnetic properties and magneto-optical characteristics.
On the Coercivity of Granular Fe-SiO2 Films
Authors: Liou S. H. , Chen C. H. , Chen H. S. , Kortan A. R. , Chien C. L.
Published: March 2011

The coercivity of granular Fe embedded inside an SiO2 matrix was as high as 3 kOe at 6K, and 1.1 kOe at 300K. In this study, we observed a linear temperature (T) dependence of the coercivity for the samples prepared at a high substrate temperature (773K), and a T1/2 dependence of the coercivity for the sample prepared at a low substrate temperature (473K). This indicates that the microstructures of films prepared at different substrate temperatures are not the same. This phenomenon can be explained if we assume that there are interconnections between particles for the sample prepared at a high substrate temperature. We looked for evidence of interconnections between particles with transmission electron microscopy (TEM).
Microstructure of an Al2O3/Metal Composite Containing an Al2O3 Filler Material
Authors: Breval E. , Nagelberg A. S.
Published: March 2011

A ceramic matrix composite consisting of 100–200 μm Al2O3 grains (90 grit) embedded an Al2O3/metal matrix was examine. The matrix was produced by the directed oxidation of a molten Al alloy. The microstructure was studied by optical methods, x-ray diffraction and transmission electron microscopy (TEM) in conjunction with energy dispersive spectrometry (EDS). The matrix A12O3 was interconnected and present as ∼50–500 nm grains in ∼ 10–50 μm regions. Within these regions, the Al2O3 was separated by low angle. Al2O3/Al2O3 grain boundaries. The boundaries between regions consisted either of high angle Al2O3/Al2O3 boundaries with no grain boundary phase or of tortuous metal channels from 50 nm up to 1 μm in width. The metallic constituent within the regions was only partly interconnected, consisting of similar channels or isolated spheres of 1–500 nm. The metal consisted of Al and Si. Large fractions of the filler Al2O3 surface (∼50%) were directly bonded to the matrix Al2O3.
Microsegregation to Antiphase Boundaries in Monolithic γ′ Phase with Ternary Additions
Authors: Wu Y. P. , Sanchez J. M. , Tien J. K.
Published: March 2011

The microsegregation to (111) anti-phase boundaries of the constituents and of the ternary atoms in monolithic γ′ phase is modeled using the tetrahedron approximation of the Cluster Variation Method. Similar to the binary case, alloy stoichiometry and temperature play an important role in determining the type and degree of atomic segregation to anti-phase boundaries. For a given composition, the segregation phenomenon is also found to be dependent on the site preference of the ternary additions. The results of our calculations are also used in order to assess the contribution of anti-phase boundary dislocation dragging to the strength of γ′ intermetallics.
Theoretical Studies of Ni3Al and Nial with Impurities
Authors: Chen S. P. , Voter A. F. , Boring A. M. , Albers R. C. , Hay P. J.
Published: March 2011

Intermetallic compounds have been extensively studied because of their superior strength, low creep rate, and high melting point [1,2]. However, room temperature ductility for the L12 and B2 phases are a continuing problem. Both L12 Ni3Al [3,4] and B2 NiAl [5,6] exhibit an intergranular fracture mode. Understanding grain boundaries in these materials is of particular importance since intergranular fracture limits the applicability of these otherwise promising materials. In an effort to understand the fracture mechanism, we have used embedded atom potentials [7] to study the properties of Ni 3Al [8,9,10] and NiAl [11]. We also consider the effect of boron, sulfur, and nickel segregation on the strength of grain boundaries in Ni3Al and NiAl. Many of the results presented here appear in literature elsewhere [8,9,10,11].
Surface Energy Anisotropy of Diffusion-Induced Ni3A1 Crystals
Authors: Chou T. C. , Chou Y. T.
Published: March 2011

Faceted crystals with well-defined {100}, {110}, and {1111 surfaces were observed in the interdiffusion zone during chemical interdiffusion of Ni/Ni 3 Al diffusion couple in the temperature range of 800°−1200°C. Composition of the diffusion-induced crystals was determined to be 87.6Ni-12.4A1 (wt%) by electron microprobe.

The shape of Ni3Al crystals showed a 26-sided polyhedron (rhombicuboctahedron) with a m3m point group symmetry at low temperature range (800° to 1000°C). At high temperatures, for example at 1212°C, the crystal shape changes to a 14-sided polyhedral form (tetrakaidecahedron) with the same point group symmetry.

Based on the crystal geometry, equations describing the surface energy anisotropy, γ{111}/γ{100}, and γ{100}/γ{100}, were obtained. The surface-energy anisotropy was then calculated from the crystal dimension. For the equilibrium crystals with tetrakaidecahedral form, the inequality γ{110} > γ{110} > γ{111} holds. On the other hand, for crystals of rhombicuboctahedral form, the inequality becomes γ{110} > γ{111} > γ{100}. The experimental values were consistent with theoretical calculations based on the broken-bond model.
Compression Deformation Structures of Single Crystal TiAl
Authors: Huang B. Y. , Oliver B. F. , Oliver W. C.
Published: March 2011

The compression deformation behavior of single crystalline TiAl was examined by transmission electron microscopy (T.E.M.). The relatively pure Ti–56 a/o Al crystal was containerless processed in ultrapure hydrogen. The crystal growth direction is 18° off (011) and 60° off [111] in the [011]– [111]-[010] unit triangle. At low stresses, a/2 [110] type dislocations were observed. a/2 [110] dislocations appeared at slightly higher stresses. Additional plastic deformation initiates twinning. Twinning plays an important role at higher stresses. Diffraction results indicate that most of the twins have the (111) mirror plane.

A small amount of (111) twins were also observed. Superdislocations of the a<011> type were not observed to contribute to the plastic deformation in this crystal. The results indicate that plastic deformation by twinning follows the low density of ordinary dislocations.
Effect of Preoxidation and Grain Size on Ductility of a Boron-Doped Ni3Al at Elevated Temperatures
Authors: Takeyama M. , Liu C. T.
Published: March 2011

The ductility of preoxidized Ni3Al (Ni-23Al-0.5Hf-0.2B, at.%) specimens with various grain sizes (17∼193 μm) was evaluated by means of tensile tests at 600 and 760°C in vacuum. It was found that the preoxidation does not affect the ductility of the finest-grained material at either temperature, whereas it causes severe embrittlement in the largest-grained material, especially at 760°C. A continuous, thin Al-rich oxide layer, which forms on the fine-grained samples, protects the underlying alloy from oxygen penetration, preventing any loss of ductility, whereas the nickel-rich oxide which forms on the large-grained samples allows oxygen to penetrate along grain boundaries, causing severe embrittlement. The grain boundaries act as short-circuit paths for rapid diffusion of aluminum atoms from the bulk to the surfaces, and this is responsible for the difference in oxidation behavior between fine- and large-grained materials. The embrittlement of large-grained samples can be eliminated through control of oxide formation on Ni3Al surfaces.
Room Temperature Tensile Ductility in Polycrystalline B2 NiAl
Authors: Vedula K. , Hahn K. H. , Boulogne B.
Published: March 2011

Binary polycrystalline alloys of B2 NiAl, ranging from 47 to 51.5 at% Al, were prepared by casting and extrusion. These were tested in tension at temperatures ranging from 300 K to 873 K. Significant tensile ductility is observed in the near-stoichiometric alloy at room temperature as well as at 473 K in spite of the presence of only <100> dislocations. This anomaly appears to be related to the recrystallized texture, to the lower yield strength and to the presence of residual dislocations at grain boundaries in this alloy.
The Development of Alloys Based on Ni3Si
Authors: Oliver W. C.
Published: March 2011

Alloys with large volume fractions of the intermetallic phase Ni3Si have unique aqueous corrosion resistance that provides the driving force for an alloy design program to improve their generally poor room temperature mechanical properties. The target of the alloy design program at Oak Ridge National Laboratory was to produce wrought alloys with at least 10% room temperature ductility while retaining good aqueous corrosion resistance. In this paper several important findings will be discussed. These include macro and micro alloying (B, C, Be) to produce superplastic wrought alloys with high strength and high room-temperature ductility. Some of the alloys developed are strong enough to be competitive with medium temperature structural alloys such as Inconel® 718.
Structural and Chemical Composition of Ni-Al Powders
Authors: Maurer R. , Galinski G. , Laag R. , Kaysser W. A.
Published: March 2011

Ni3Al and NiAl pre-alloyed powders produced by argon gas atomization are investigated by light and transmission electron microscopy concerning their structure, chemical and phase composition. For example, Ni3Al powder consists of a L12 matrix (γ′ -phase) with precipitates whose Al content is 6% higher than in the matrix. Selected single powder particles were isothermally deformed in a modified high resolution dilatometer to investigate the creep behavior. From these experiments HIP parameters are predicted and compared with HIP experiments at different pressures and temperatures. HIP diagrams were calculated according to Ashby's model.
On APB Dragging and APB Energy Anisotropy in Binary Ni3Al
Authors: Dimiduk Dennis M. , Williams J. C. , Thompson A. W.
Published: March 2011

Recent weak-beam electron microscopic studies of Ni3Al provided evidence indicating that glide of Kear-Wilsdorf locked dislocation segments may occur on {111} planes, accompanied by APB dragging, during deformation at high temperature. A direct implication of those studies is that a mechanism other than the onset of {010} slip may be important in controlling the peak in yield strength in Ni3Al. The present weak-beam investigations of Ni3Al have centered on the possibility that such configurations result from thermally induced dislocation kink and jog activity rather than the APB dragging mechanism. previously proposed.
Dynamic Compaction and Hot-Isostatic-Pressing of Nickelaluminides
Authors: Arkens O. , Delaey L. , de Tavernier J. , Huybrechts B. , Buekenhout L. , Libouton J. C.
Published: March 2011

Explosive compaction and HIPping of stoichiometric mixtures of Ni and Al (and B) powder is optimized in order to obtain fine grained NiAl− and Ni3Al(+B) intermetallics.

Starting from an appropriate mixture of pure fine Ni− and fine Al− (and B) powders fine nickel-aluminides are produced due to a selfpropagation high temperature synthesis during processing. HIPping experiments are done also on spherical Ni-coated Al-powders. The specimens are characterized by metallography and the homogeneity of the final product is controlled by microanalytical methods.
Notch Effects on Room Temperature Tensile and Bend Properties of Ni3Al and Ni3Al+B
Authors: Khadkikar P. S. , Rigney J. D. , Lewandowski J. J. , Vedula K.
Published: March 2011

The notched mechanical properties of Ni3AI and Ni3Al+B prepared by powder metallurgy techniques have been determined in both tension and bending at room temperature. Ten- sile tests performed using double notched specimens containing relatively blunt notches produced intergranular fracture in both Ni3Al and Ni3AI+B, with evidence of fracture initiating in an intergranular manner ahead of the blunt notch in both cases. Estimates of notched fracture toughness from bend tests and of local grain boundary fracture stress from the notched tensile tests suggest an increase in these values with boron addition.
Processing and Microstructure of Melt Spun Niai Alloys
Authors: Locci I. E. , Noebe R. D. , Moser J. A. , Lee D. S. , Nathal M.
Published: March 2011

The influence of various melt spinning parameters and the effect of consolidation on the microstructure of melt spun NiAl and NiAl + W alloys have been examined by optical and electron microscopy techniques. It was found that the addition of 0.5 at.% W to NiAl results in a fine dispersion of W particles after melt spinning which effectively controls grain growth during annealing treatments or consolidation at temperatures between 1523 and 1723 K. Increased wheel speeds are effective at reducing both ribbon thickness and grain size, such that proper choice of both composition and casting parameters can produce structures with grain sizes as small as 2 μ m. Finally, fabrication of continuous fiber reinforced composites which used pulverized ribbon as the matrix material was demonstrated.
Phase and Microstructure of Fe Modified A13 Ti
Authors: Porter W. D. , Hisatsune K. , Sparks C. J. , Oliver W. C. , Oliver W. C.
Published: March 2011

Alloys of Al75-xFexTi25, where x = 0 to 12 at. % Fe, were fabricated by splat cooling and examined primarily with X-ray diffraction to determine the crystallographic phases present, their composition, volume fraction, lattice parameters, and sublattice occupation. The tetragonal DO22 structure of Al3Ti dissolved 0.8 ± 0.4 at. % Fe, with additional iron partitioned to the Ll2 structure containing 6.2 ± 0.4 at. % Fe, and completed the transformation to the Ll2 structure with the addition of about 6 at. % Fe. The lattice parameters of both phases were independent of iron concentration up to about 6 at. %. At 8 at. % Fe, the iron was found to be predominantly distributed on the nominal aluminum sublattice which also contained about 5 at. % Ti. The Al3 Ti composition was similarly found to contain about 5 at. % Ti on the aluminum sublattice. All compositions, including a single crystal of Al67Fe8 Ti25, were found to be brittle.
The mechanisms of plastic deformation of rapidly solidified Al3Ti and Al67Ni8Ti25 intermetallic compounds.
Authors: Vasudevan Vijay K. , Wheeler Robert , Fraser Hamish L.
Published: March 2011

The dislocation structures in rapidly solidified Al3Ti with the DO22 structure and the ternary Al-25Ti-8Ni (at.%) alloy with the L12 structure deformed in compression in the temperature range of 25 to 800°C have been studied by transmission electron microscopy. The room temperature deformation microstructure of the Al3Ti compound is characterized by the presence of stacking faults/order twins on {111} planes bounded by partial dislocations with Burgers vector b=1/6<112], as reported by others. At intermediate temperatures, besides the stacking faults, slip is also observed as bands on the {001] plane delineated by dislocations with b=1/2<110] which bound APB's. At 600°C, the reported increase in ductility is associated here with additional slip on the {001)<110], {001)[100] and {001)[010] systems. Dislocations with b=<110] exist as pairs of partial dislocations with b=1/2<110] connected by APB's. The mean separation between the partials was measured to be 30 nm, corresponding to an APB energy of ≍32 mJ.m-2 on the (001) plane. Observations also indicate that the APB energy is anisotropic, i.e., is considerably higher on the {111} planes compared to the {001) plane. The deformation microstructure of the Al-25Ti-8Ni L12 alloy is characterized by slip of dislocations with b=<110> gliding on {111} planes, a major fraction of which exist as dipoles. Following deformation at 300°C, there is essentially no evidence of dissociation of these dislocations, although some dissociated dislocations on (001) having b=l/2<110> are also observed. With an increase in temperature, there is a considerable increase in dislocation activity and strong evidence for 1/2<110> dissociated dislocations is present.
Microstructure/Processing Relationships in High-Energy High-Rate Consolidated Powder Composites of Nb-Stabilized Ti3Al + TiAl
Authors: Persad C. , Lee B.-H. , Hou C.-J. , Eliezer Z. , Marcus H. L.
Published: March 2011

A new approach to powder processing is employed in forming titanium aluminide composites. The processing consists of internal heating of a customized powder blend by a fast electrical discharge of a homopolar generator. The high-energy high-rate “1MJ in 1s” pulse permits rapid heating of an electrically conducting powder mixture in a cold wall die. This short time at temperature approach offers the opportunity to control phase transformations and the degree of microstructural coarsening not readily possible with standard powder processing approaches. This paper describes the consolidation results of titanium aluminide-based powder composite materials. The focus of this study was the definition of microstructure/processing relationships for each of the composite constituents, first as monoliths and then in composite forms. Non-equilibrium phases present in rapidly solidified TiAl powders are transformed to metastable intermediates en route to the equilibrium gamma phase. The initial single phase beta in Nb-stabilized Ti3Al is transformed to alpha two with an intermediate beta two phase. In composite blends of TiAl powders mixed with Nb-stabilized Ti3Al powders a 10 μm thick interfacial layer is formed on the dispersed TiAl. Limited control of post-pulse heat extraction prevents full retention of the rapidly solidified powder microstructures.
Synthesis of Ladder Polymers Via Soluble Precursor Polymers
Authors: Dalton Larry R. , Yu Luping
Published: March 2011

Although ladder polymers have been known for some time, poor solubility and low molecular weights have prevented processing and have discouraged consideration of these materials for structural and electronic applications. Poor solubility can be associated with strong Van der Waals interactions between delocalized π-electron clouds on adjacent chains. The optimum orbital overlap along the polymer backbone existent for ladder polymers has motivated reexamination of these systems for electronic applications. We have pursued alternatives to the tradiational acid-catalyzed polycondensation of underivatized monomers at elevated temperatures by reacting derivatized (e.g., with alkyl or vinylamine substituents) monomers at reduced temperature in organic solvents (e.g., DMF) to produce open-chain precursors to ladder polymers. These are converted to fully-fused ladder polymers by thermal processing either in solution or as solid state (e.g., thin film) materials. The preparation of precursors of improved solubility greatly enhances processing options and has permitted the utilization of both Langmuir-Blodgett methods and the perparation of optical quality films by casting (including spin casting). By control of thermal processing conditions, both derivatized and underivatized ladder polymers have been prepared. Our approach offers obvious advantages for the investigation of the effect of conformation and of substituents upon electronic properties. The preparation of copolymers with rigid rod and flexible chain segments incorporated in the polymer backbone has also been investigated. For such materials, polymers with fully fused ladder segments can exhibit improved solubility in DMF relative to polymers with open chain segments due to the absence of favorable hydrogen bonding stuctures in the former. Finally, we are investigating the effect of electrochemical polymerization of Langmuir-Blodgett films prepared with derivatized diaminobenzene. Such an approach clearly takes advantage of improved solubility of the derivatized monomer and improved molecular order which can be realized with the Langmuir-Blodgett method. Free radical polymerization may facilitate the realization of improved molecular weight distributions.
Synthesis and Dilute Solution Characterization of Extended Chain Poly(Benzazoles)
Authors: Chow Andrea W. , Bitler Steven P. , Penwell Paul E. , Wolfe James F.
Published: March 2011

This paper reports the synthesis method for polymerizaing poly(2,6-benzothiazole) (ABPBT) and poly(2,5-benzoxazole) (ABPBO), and their dilute solution properties using low angle light scattering and viscometry. Our data indicate that the Mark-Houwink-Sakurada exponents for these extended-chain polymers are near unity, suggesting a semi-rigid conformation in dilute solutions. The solution properties agree well with the Yamakawa-Fujii worm-like chain model when persistence lengths of 130 Å and 90 Å are assumed for ABPBT and ABPBO, respectively. These values of persistence length are also in good agreement with those predicted by Flory's virtual bond model using information on the molecular geometries taken from x-ray crystallographic data on oriented fibers of ABPBT and ABPBO.
Gelation of Rodlike Polymers
Authors: Russo Paul S. , Chowdhury Aslam H. , Mustafa Mazidah
Published: March 2011

Some opportunities for utilizing gelation of rodlike polymers such as poly(p-phenylenebenzobisthiazole) for the production of new materials are described. Morphological studies concerning gels of poly(γ–benzyl–α,L–glutamate) in the solvents toluene, N,N-dimethylformamide and N,N-dimethylformamide/water are reviewed, newly interpreted and extended. A provisional diagram which maps out the gelling behavior in four distinct regions of concentration and temperature concludes the article.
A Model for Nematic Phases in a Reversibly Assembling System of Hard Rods and Plates
Authors: Taylort Mark P. , Berger Alan E. , Herzfeld Judith
Published: March 2011

: Liquid crystalline behavior is exhibited by many amphiphilic solutions as a result of the reversible formation of anisotropic aggregates. We model such a system by combining a phenomenological description of aggregation with a lattice statistics calculation of the configurational entropy of a polydisperse collection of hard rods and plates. In this model, nematic liquid crystalline phases of axial, planar and biaxial symmetry are possible. We present a calculated phase diagram, and corresponding particle size distributions, for the case when rod and plate growth are equally favored. Regions of stability are found for axial and planar phases, but not for biaxial phases.
Liquid Crystal-Like Phase Separation in Systems of Macroscopic Rods
Authors: Chick Larry A. , Viney Christopher , Aksay Ilhan A.
Published: March 2011

Experiments with monolayers of macroscopic rods indicate separation into isotropic and aligned phases at greater-than-critical concentrations. This behavior is qualitatively similar to that of rodlike liquid crystalline polymers, which in turn has been modelled successfully in threedimensions by Flory and Ronca. We have adapted their approach to predict the ordering of rods in two dimensions. A preliminary phase diagram is presented. The critical rod concentration at which an aligned phase can appear first is a decreasing function of rod axial ratio. Rods of a given axial ratio will phase separate at lower overall concentrations in two dimensions than in three.
Evolved Gas Analysis of Rigid-Rod Polymers
Authors: Jones E. Grant , Pedrick Donald L.
Published: March 2011

The rigid-rod polymer system poly(phenylenebenzobisthiazole), designated as PBZT, has considerable potential in materials engineering. The vacuum thermal behavior of this system and various substituted analogues, including methyl-, phenyl-, and benzothiazolyl-substituted members, has been studied using the combined techniques of thermogravimetry and mass spectroscopy (TG-MS).

Primary volatile products identified from the PBZT series include H2S, HCN, CS2, NH3, C6H5CN, C6H4(CN)2, and HSCN. The presence of pendant groups such as methyl, phenyl, or benzothiazolyl results in the evolution of methane, benzene, or benzothiazole in low-temperature degradation processes. The relative abundance and temporal sequence of these gases which are evolved during slow heating in vacuum provide valuable information concerning thermal stability.

The implications of the identification and study of evolved gases toward the understanding of the mechanisms of heat treating of rigid-rod polymer systems will be discussed.