Using high reactor pressures (>1 bar) and a unique rate control mechanism, three fibers were recently obtained by laser assisted chemical vapor deposition (LCVD) having elemental (i.e., boron, carbon, and silicon) compositions, small diameters (>9 μm), and surprisingly high growth rates (0.3–1.1 mm/s). By reacting silane and ammonia at high pressures (>1 bar) near the focus of a Nd-YAG laser beam, we have now obtained the first LCVD fibers with binary (i.e., silicon-nitrogen and silicon nitride) compositions having small diameters and high growth rates (0.34–0.74 mm/s). These fibers were amorphous.

Surface modification is achieved by coating the aluminum surface with a powder mix of {Si + flux + a metal (Me)} and heating at ∼600 °C for a time interval of the order of 1 min. During heating, the flux melts and dissolves the native surface oxide film on aluminum, thus allowing Si to react with the substrate to form a film of liquid Al-Si alloy of near-eutectic composition. The component Me of the powder coating then reacts with the molten metal layer to modify the metallurgical properties of the surface after solidification.

High energy ball milling has been used to produce nanocrystalline Y1Ba2Cu3O7-δ powders. These powders are being used as starting materials for manufacturing superconducting textured wires by a solid state recrystallization process. Magnetic and microstructural characterizations were performed as a function of milling time. The milling reduces the average crystal size and creates low and high-angle grain boundaries which increase the granularity of the superconductor. As a result, the long-range order on the oxygen sublattice and on the yttrium and barium sites is destroyed. A transition from orthorhombic to tetragonal and finally to a cubic metastable phase is observed. Total loss of superconductivity occurs after about 1 h of milling. Prior to this time, superconductivity can partially be restored by room-temperature aging. High-temperature heat treatment of the nanocrystalline phase produces a tetragonal structure with c = 3a.

Dense polycrystalline Bi2Sr2Cu2Ox (2201), Bi2Sr2CaCu2Ox (2212), and (Bi, Pb)2Sr2Ca2Cu3Ox (2223) specimens were compressed in air at 730–835 °C. All of the materials exhibited an apparent steady-state creep response. Strain rate was proportional to stress to the 3.1–3.8 power. Apparent activation energies for the deformation processes were 520 ± 50 kJ/mole for the 2201, 630 ± 210 kJ/mole for the 2212, and 960 ± 210 kJ/mole for the 2223. Transmission electron microscopy revealed substantial generation and propagation of basal-plane dislocations during deformation. Few nonbasal-plane dislocations were observed. Intergranular fracture was evident in all deformed samples, and intragianular fracture was evident along the basal planes of some grains. It is suggested that the kinetics of fracture were determined by dislocation motion within the grains.

Using molecular dynamics computer simulations and interatomic potentials derived partly by Voter and Chen1 and Rifkin et al.,2 we studied the surface reconstruction taking place on free surfaces of arrays of RuAl. Surface reconstruction appears to be very important on {111} and {110} types of planes and almost nonexistent on {100} type of planes. Cracks oriented so that their crack planes were either {111} types or {110} types exhibit on their internal free surface important surface reconstruction. It is believed that this effect may have some contribution in the brittle versus ductile behavior of the crack.

Dislocation dissociations in Al3Ti alloys modified with Mn to stabilize the L12 cubic structure have been studied with transmission electron microscopy and computer simulation of images. Dissociations of a〈110〉 superdislocations into pairs of a/2〈110〉 partials bounding APB's were observed at all temperatures from room temperature to 700 °C. Asymmetrical image contrast, in which one of the a/2〈110〉 partials gives a much more intense image than the other, was observed at small separations of the partials. Although some investigators have taken such asymmetry to suggest SISF-type dissociations in similar alloys, the current work demonstrates that the asymmetry is fully consistent with APB-type dissociation. Further, the degree of image asymmetry decreases as the spacing of the partials increases. It is concluded that identification of the partial dislocations with “near-invisibility criteria” for fractional values of g · b is unreliable, and that computer simulation of images is useful for identification of the partials. However, as expected, the ability to distinguish simulated bright-field images of APB- and SISF-type dissociations also becomes difficult as the separation of the partials becomes very small. Under these conditions, both weak-beam imaging and simulations are necessary to identify the dissociations. Weak-beam simulations have shown that fringe contrast must be present under certain imaging conditions for SISF dissociations, and this contrast has never been observed in this study or in previously published studies of dissociated single superdislocations in cubic Al3Ti alloys. Finally, APB contrast formed with superlattice reflection imaging has been observed between partials on both {111} and {100} after deformation at 700 °C.

The electromigration boundary value problem is investigated for the three physically reasonable boundary conditions, assuming a perfectly blocking boundary on one side. The solution to this problem is believed to be that for nucleation dominated electromigration lifetime. The three boundary conditions investigated are the semi-infinite constant vacancy source of Shatzkes and Lloyd,9 the closed system of De Groot13 and Kirchheim and Käber,19 and the heretofore unsolved constant vacancy source at a finite distance from the blocking boundary. It is argued that the first is unrealistic in that there is no length effect possible, which has been repeatedly observed experimentally. The second is argued to be too restrictive to account for failure, leaving the last as the most physically reasonable under most circumstances. The deceptively simple appearance of the boundary conditions belies a complex, double infinite series solution arrived at by a unique approach to inverting the Laplace transform of the solution. The solution correctly predicts the experimental observations of a length effect and, combined with the understanding provided by the solutions under the other two boundary conditions, the effect of a thick passivation layer on electromigration lifetime.

Co/Cu superlattices with total thicknesses ranging from 10 nm to 60 nm and with periodicities of 1.6–8.5 nm were sputtered on single-crystalline sapphire (1120)-substrates. Sputtering with low rates at room temperature yields samples of high epitaxial and crystalline quality. By careful choice of the sputtering parameters, either the fee [100] or the fcc [111] orientation can be selected as growth direction on one and the same substrate orientation. The preference for a particular film orientation appears to be kinetically driven. In all cases, the average lattice spacings d and the appearance of satellite reflections in x-ray Bragg-scans point to coherent growth up to thicknesses of 30 nm. X-ray small angle reflectivity measurements reveal clear oscillations and satellites indicative for smooth interfaces. Scanning electron microscope (SEM) and transmission electron microscope (TEM) observations supplement the characterization of the films.

The reconstructions of high-angle twist grain boundaries on the four densest atomic planes in fcc copper, as described by a Lennard-Jones potential, and gold, as described by an embedded-atom-method potential, are investigated using the recently developed method of grand-canonical simulated quenching. It is found that the grain boundaries on the widely spaced (111) and (100) planes do not reconstruct, while those on the less widely spaced (110) and (113) planes do reconstruct. The effect that reconstruction can have on the physical properties of an interfacial system is illustrated by comparing the elastic properties and ideal cleavage energies of reconstructed grain boundaries with those of corresponding unreconstructed grain boundaries.

Observations of various metastable crystalline and amorphous polymorphs of Ll2-type intermetallics Zr3Al and Ni3Al are summarized. The difference in the tendency of these two alloys to become amorphous is obvious. Regardless of the nonequilibrium routes employed for synthesis and processing, amorphous Zr3Al is obtained easily, while amorphization of Ni3Al is rare. An analysis of thermodynamic and kinetic factors responsible for the observed polymorph selection and amorphization behavior is presented. The inadequacy of a simplified model proposed earlier is also discussed.

The thermodynamic parameters of all stable phases in the Ni-Zr system are reported in this paper. The available experimental data are taken into account in deriving the interaction parameters of various phases. The Ni7Zr2, Ni21Zr8, Ni11Zr9, NiZr, and NiZr2 phases are treated as stoichiometric. The solid solubility of the Ni5Zr, Ni3Zr, and Ni10Zr7 phases are described using a two sublattice model. The calculated thermodynamic properties and the phase diagram are in good agreement with the experimental ones. The thermodynamic parameters, along with the classical nucleation and crystal growth theory, have been used to explain the formation of metastable noncrystalline and crystalline phases upon rapid quenching of the liquid alloys. It has been demonstrated that even without any prior knowledge of the physical property, such as glass transition or crystallization temperature and thermodynamic property, such as the enthalpy of amorphous → crystal transformation of the amorphous alloy, it is possible to make a reasonably good “first order prediction” of the glass-forming range in a binary system. The experimentally determined glass-forming range in the Ni-Zr system is found to be in good agreement with the predicted one.

Improvement of copper to graphite adhesion by thin interfacial films of titanium and chromium was investigated. Graphite fibers and highly oriented pyrolytic graphite flats were sputter-coated first with 10 nm of titanium or chromium and then with 50 nm of copper. After annealing to 970 °C in argon/5%-hydrogen at atmospheric pressure for 5 min, copper without an interfacial bond layer agglomerated into nearly spherical particles, copper with the chromium bond layer agglomerated into particles with a contact angle less than 90°, indicating improvement in adhesion, and copper with the titanium bond layer exhibited a continuous metal film. In the latter case, most of the interfacial titanium was observed to have migrated into the copper and to the free surface, where the titanium reacted with contaminants in the annealing ambient.

An oxy-acetylene flame, impinging vertically upward on an Si(001) substrate, is systematically examined for morphological variations in the resulting diamond deposits. The flame is operated under near neutral (O2/C2H2 ratio near 1.0) conditions in the unconfined, open atmosphere. Singly twinned crystal morphologies in addition to the usual (001) faceted structures are observed and reported for the first time. Similar morphological variations are observed along the radial as well as the axial (vertical) coordinate directions in the flame. Large changes in morphology are observed for changes in vertical position as small as 50 μm.

Six CVD diamond thin films were examined by magic angle spinning (MAS) 13C nuclear magnetic resonance (NMR), Raman, and electron spin resonance spectroscopy. The use of film samples cut to the diameter of the magic-angle spinning rotor provided ease of spinning and the opportunity to obtain good signal-to-noise spectra in 4 to 16 h. MAS NMR linewidths exhibit a linear correlation with Raman linewidths and reflect the optical quality of the material. Residual MAS NMR linewidths most likely arise from a combination of crystal defect sites and paramagnetic effects.

Diamond deposition was attempted on polyacrylonitrile (PAN) fiber and vapor grown carbon fiber (VGCF). PAN fibers were severely etched in a microwave plasma, whereas diamond was successfully deposited on VGCF. A diamond growth rate of 0.1 μm/h on VGCF was determined at a gas mixture of 99.9 sccm H2/0.1 sccm CH4 and a pressure of 30 Torr. It is proposed that diamond formation on VGCF occurs on not only the prism planes, but also the basal planes owing to the unique structure of VGCF. An explanation is proposed to explain diamond nucleation on the basal planes.

Different properties of the mixtures of polyethylene with carbon black modified by the implantation of Sb+ ions were studied. Chemical changes of polymer were examined by IR- and UV-visible spectroscopy. Sheet resistivity as a function of sample temperature was studied. Depth profiles of implanted Sb atoms and incorporated oxygen were determined by the Rutherford backscattering technique. The percolation threshold of unimplanted mixtures is found at 4.5 and 5 wt. % of carbon black. As a result of ion implantation, the polymer is oxidized and conjugated double bonds are produced. The mixtures with carbon black concentration above percolation threshold exhibit metal-like conductivity. For the mixtures below percolation threshold, the measurements of resistivity versus temperature dependence indicate semiconductor type conductivity and charge transport via a variable range-hopping mechanism.

Thermally induced solid-state reactions between a 70 nm Pt film and a single-crystal (001) β-SiC substrate at temperatures from 300 °C to 1000 °C for various time durations are investigated by 2 MeV He backscattering spectrometry, x-ray diffraction, secondary ion mass spectrometry, scanning electron microscopy, and cross-sectional transmission electron microscopy. Backscattering spectrometry shows that Pt reacts with SiC at 500 °C. The product phase identified by x-ray diffraction is Pt3Si. At 600–900 °C, the main reaction product is Pt2Si, but the depth distribution of the Pt atoms changes with annealing temperature. When the sample is annealed at 1000 °C, the surface morphology deteriorates with the formation of some dendrite-like hillocks; both Pt2Si and PtSi are detected by x-ray diffraction. Samples annealed at 500–900 °C have a double-layer structure with a silicide surface layer and a carbon-silicide mixed layer below in contact with the substrate. The SiC—Pt interaction is resolved at an atomic scale with high-resolution electron microscopy. It is found that the grains of the sputtered Pt film first align themselves preferentially along an orientation of {111}Pt//{001}SiC without reaction between Pt and SiC. A thin amorphous interlayer then forms at 400 °C. At 450 °C, a new crystalline phase nucleates discretely at the Pt-interlayer interface and projects into or across the amorphous interlayer toward the SiC, while the undisturbed amorphous interlayer between the newly formed crystallites maintains its thickness. These nuclei grow extensively down into the substrate region at 500 °C, and the rest of the Pt film is converted to Pt3Si. Comparison between the thermal reaction of SiC-Pt and that of Si–Pt is discussed.

CuInSe2 thin film solar cells with an efficiency of about 10% were studied with a cross-sectional high resolution transmission electron microscope (HRTEM). The growth defects such as twins, stacking faults, and intergrowth phase in the CuInSe2 thin films were studied in detail. Polycrystalline CuInSe2 films were deposited on a Mo-coated glass substrate by using the three source evaporation system. The CuInSe2 film contains fivefold multiply twinned crystallites as well as a high density of twins in the {112} plane. The CuInSe2 film also contains intergrowth phase with a long range of periodicities of 10 Å parallel to the [112] direction of the chalcopyrite structure. The intergrowth phase composition is similar to the chalcopyrite phase. The structural model of the intergrowth phase is proposed on the basis of the high resolution electron micrograph.

The saturated vapor pressure and pyrolytic properties of di-n-butyltin(IV) diacetate have been investigated with and without oxygen in order to understand the orientational growth of SnO2 thin films by spray pyrolysis. The dependence of the saturated vapor pressure on temperature was determined: log P(evap.)Torr = −2.827 × 103/T + 7.687. It has been found that the pyrolysis of this compound consisted of two stages: elimination of the n-butyl groups in a temperature range between about 280°and 310 °C, and of the acetoxy groups above 320 °C. Such decompositions were shifted toward lower temperatures under oxygen. It was also found that oxygen in air in addition to intramolecular oxygen contributed to the formation of SnO2 crystal phase. Moreover, it was suggested that pyrolized chemical species preserving the Sn-O bond probably related the orientational growth of the (200) plane of sprayed SnO2 thin films.

ZnO/PrCoOx and ZnO/PrCoOx/ZnO junctions have been fabricated by sputtering as a model of a single grain boundary in a ceramic ZnO varistor. The relations between barrier parameters and varistor characteristics were investigated using voltage-current (V-I) capacitance-voltage (C-V), and deep-level transient spectroscopy (DLTS) measurements. The varistor voltage of the junctions increases as the donor density (ND) of the ZnO film decreases. The interface states vary according to the method of ZnO sputtering. A clear correlation has been established between the α value and the interface states. The highest α value is obtained when ND is ≃ 1018 cm−3, the interface level is 0.70 eV, and the breakdown voltage is 3–4 V. Oxygen is effective on control of ND in ZnO and the interface states. Al added as a dopant is also effective in terms of its ability to increase ND in ZnO. However, Al doping was found to degrade the interface states and increase the leakage current.