Alumina films, 160 nm thick, were deposited on (100) -oriented silicon single-crystal substrates by pyrohydrolysis of aluminum chloride. Such films are candidate gate materials for an improved pH ion-sensitive field-effect transistor (pH-ISFET) for industrial and medical pH measurements. The current-voltage (I–V) characteristics of films annealed for 30 min at temperatures of 850, 1000, and 1175 °C were determined, Annealing at 850 °C produced the optimum I–V behavior for the aluminum oxide pH-sensitive films as evidenced by minimum leakage current and maximum breakdown voltage. The structures of the annealed films were examined using transmission electron microscopy. The anneals at 1000 and 1175 °C caused partial and complete transformation, respectively, of the as-deposited α-alumina to the α-alumina phase. Associated with a-alumina formation was the creation of voids along the grain boundaries and in the grain interiors that provided paths of increased electrical conduction through the alumina films and degraded their dielectric behavior.

Ab initio molecular orbital calculations of oxygen 2p hole states of small CuO clusters representing the chains and planes in YBa2Cu3O7−x are reported. The results suggest that the absorption observed at 0.37 eV in reflectivity studies of YBa2Cu3O7−x may be due to excitation of these holes between inequivalent oxygen sites.

Cubic boron nitride (C–BN)' powders admixed with graphite-structured boron nitride powder (g-DN), silicon carbide whisker (SCW), or silicon nitride whisker (SNW) were shock compacted to pressures up to 22 GPa. Unlike previous work with diamond and graphite [D. K. Potter and T. J. Ahrens, J. Appl. Phys. 63, 910 (1987) it was found that the addition of g-BN inhibited dynamic consolidation. Good consolidation was achieved with a 4–8 μm particle size C–BN powder admixed with 15 wt.% SNW or 20 wt.% SCW whereas a 37–44 μm particle size C–BN mixture was only poorly consolidated. Scanning electron microscopy (SEM) analysis demonstrates that SCW and SNW in the mixtures were highly deformed and indicated melt textures. A skin heating model was used to describe the physics of consolidation. Model calculations are consistent with SEM analysis images that indicate plastic deformation of SCW and SNW. Micro-Vickers hardness values as high as 50 GPa were obtained for consolidated C–BN and SNW mixtures. This compares to 21 GPa for single-crystal Al2O3 and 120 GPa for diamond.

Intermetallic alloys with the nominal compositions Al–24.5Nb, Al–25Nb, and Al–25.5Nb (at.%) were fabricated by hot-pressing of pre-alloyed powders in graphite dies in vacuum. The hot-pressed disks contained substantial porosity even at processing temperatures of 0.95 Tm, where Tm is the absolute melting point. In addition to some copper and silicon contamination, significant concentrations of oxygen and carbon were measured in Al–25.5Nb. Alpha alumina precipitates as well as niobium-enriched precipitates were identified. The fracture toughness of pre-cracked bend specimens with the nominal composition Al–25.5Nb was found to be 2.5 ± 0.5 MPa m1/2. Possibilities for improving this value are discussed.

The nucleation of the amorphous phase by solid-state reactions has been investigated on single-crystal Zr films grown by molecular beam epitaxy and covered in situ with either polycrystalline Ni, amorphous (a-) NiZr, or single-crystalline Zr99N01 films. Interfacial reactions were investigated by backscattering analysis or secondary ion mass spectroscopy. The amorphizing reaction occurred only in the specimen with the a-NiZr over layer, although fast Ni diffusion through the single-crystalline Zr layer was observed in all three specimens. The nucleation behavior of a-NiZr is attributed to the combination of high-Ni and low-Zr mobility in crystalline Zr.

The mechanisms of steady-slate creep in compression in a sintered SiC produced via sintering of β-SiC powders derived from gaseous reactants in a plasma are have been determined from (1) kinetic data within the ranges of temperature and constant stress of 1770–2020 K and 17–208 MPa, respectively, and (2) the results of transmission electron microscopy (TEM) and other microbeam characterization techniques. The stress exponent was 2.06 ± 0.04; the values of activation energy were 913 ± 13 and 630 ± 14 kJ/mol above and below, respectively, a knee of ∼∼ 1920 K. Gliding dislocations and B4C precipitates, which developed within the grains during creep, and their interaction were the dominant microstructural features of the crept material. Apparent nonmechanical pinning of the dislocations at the precipitates indicated that the latter attracted the dislocations rather than acting as classical obstacles to dislocation movement. A synthesis of this information leads to the conclusion that the controlling creep mechanisms in this SiC were grain boundary sliding accommodated by grain boundary diffusion at T < 1920 K and lattice diffusion at T > 1920 K. The parallel mechanism of dislocation glide also contributed to the total strain.

The liquidus relations in the system YO1.5–BaO–CuOx in air in the compositional region near the superconducting oxide YBa2Cu3Ox were studied by differential thermal analysis, x-ray diffraction, electron microprobe analysis, and visual observation. The temperatures of 11 invariant points and the corresponding reactions were determined. YBa2Cu3Ox was found to melt incogruently at 1015 °C to Y2BaCuO5, which in turn melts incongruently to Y2O3 at 1270 °C. These reactions mean that preparing the superconducting phase by melting and rapid cooling will result in the presence of these two phases as well. The peritectic reaction YBa2Cu3Ox + CuO⇉Y2BaCuO5 + liquid at 940 °C accounts for the observation of partial melting, improved synthesis purity, and grain growth at temperatures of 950 °C. The determination of these invariant temperatures and reactions provide insight into optimal processing conditions.

The close-spaced vapor transport (CSVT) is an efficient and cost-effective technique that allows the growth of polycrystalline as well as epitaxial thin layers of semiconductors. The close spacing between a source and a substrate, introduced in 1963 as a special feature in the vapor phase method, has been applied to about 18 semiconductors with a special focus on CdTe and GaAs. This paper reviews the close-spaced technique, the models presented to explain the film growth rates, the transport reactions, and film characteristics for all the semiconductors that have been obtained by CSVT. All-thin-film structures for solar cells or other applications are certainly feasible with the use of the CSVT technique when a good lattice matching exists between the successive layers.

The suspension spinning of a Ba2Y1Cu3Ox superconductor under various conditions was studied to prepare a long filament with high Jc. The oxide powder was suspended in a PVA solution containing a dispersant. The viscous suspension was extruded as a filament into a precipitating medium and coiled on a winding drum. The obtained filament was heated to remove volatile components and to generate the layered perovskite phase. The spinning was examined in an aqueous system and a nonaqueous system. The filament with higher Jc was obtained for the nonaqueous solution. The Jc was dependent on the fineness of the starting oxide powder, solvent, precipitating medium, degree of polymerization of PVA, the kind of dispersant used, and the oxide powder contents of the spinning dope, as well as the heating condition. The highest Jc value obtained by resistivity measurement at 77 K and zero field, 680 A/cm2, was attained for the filament spun under optimum spinning conditions. The magnetization curve of the filament showed that the material was a type II superconductor. The hysteresis of thin filaments was relatively small compared with that for the thick filaments. The Jc at 79 K, estimated from the magnetization curve, was one order of magnitude higher than the Jc measured by the resistivity method and decreased drastically with increasing field.

The cracking and decohesion of thin films can be characterized by critical values of a nondimensional parameter governed by the residual stress, the film thickness, and a fracture resistance. This article reviews the status of understanding concerning the magnitude of this number for various types of adherent film on either brittle or ductile substrates. Important effects of elastic properties, substrate thickness, and yield strength are described.

The superconducting properties of heat-treated mixtures of Y1Ba2Cu3O9−x (A) and Y1.8Ba0.2Cu1O5−y (B) have been studied. As the concentration of B increases, the Meissner effect decreases, while the resistance jump near the superconducting transition increases. When the fraction of B approaches about 0.5, the superconducting transition disappears. Four different phases are identified in the mixture from the x-ray spectra, i.e., Y1Ba2Cu3O9−x, Y2Ba1Cu1O5–z, Y2Cu2O5, and Y2O3. The results agree well with the published phase diagram of this system.

The influence of sintering temperature, sintering and annealing atmospheres, and quench rate on the properties of the high-temperature superconductor YBa2Cu3Oy has been investigated by electrical resistivity and magnetic susceptibility measurements, thermogravimetric analysis, powder x-ray diffraction, and scanning electron microscopy. Room-temperature resistivity and the transition width decreased, and the fraction of the superconducting material and the bulk density increased with increase in the sintering temperature, but had no effect on the transition temperature (Tc) for samples fired in flowing oxygen. A sample that was rapidly quenched from 930 °C to room temperature after sintering in air had a perovskite structure and Tc (onset) ∼90 K but its resistance did not become zero even at 77 K. A sample sintered in air at 930 °C and furnace cooled had Tc (midpoint) of ∼89.6 K and transition width (10%–90%) of ∼2.6 K. The loss and gain of oxygen occurs reversibly in YBa2Cu3Oy.

Grain growth as a function of annealing temperature in Y–Ba–Cu oxide superconducting thin films is presented. Effects of excess Cu on the temperature dependence of the resistance, grain growth, and sheet resistivity are discussed. This is the first systematic study of the microstructure of thin films formed by the nonvacuum technique of metallo organic deposition. The Cu-rich films show an anomalous behavior in the resistivity at 220–240 K. The presence of excess Cu was found to enhance grain growth for films annealed below the melting point of the 1–2–3 phase. Films deposited on 〈100〉 SrTiO3 and rapid thermal annealed showed partial epitaxial growth of the 1–2–3 phase. The analytical techniques of Rutherford backscattering spectrometry, ion channeling, x-ray diffraction, scanning electron microscopy, electron microprobe analysis, sheet resistivity, and temperature versus resistance measurements have been used in this study.

Characterization of superconducting Bi–Sr–Ca–Cu oxides has been carried out by electrical measurements, x-ray diffraction, conventional and high-resolution electron microscopy, and electron microprobe analysis. Nominal starting compositions with cation ratios of 1:1:1:2 and 2:2:1:2 show considerably different superconducting behavior. In both cases multiphase materials are formed. The predominant superconducting phase occurs as thin platelets with an orthorhombic, modulated structure. These particles often have edges aligned along [110], [100], and [010] directions and contain subgrain boundaries. Electron diffraction patterns and high-resolution micrographs taken along several zone axes are consistent with an incommensurate centered modulation along the b axis with a magnitude of 4.7 ± 0.1 times b. Unexpectedly, two distinct chemical compositions were found in platelets with the same apparent structure: Bi4Sr3Ca3Cu4O16±δ for the lower Tc phase in the 1:1:1:2 material, and Bi2Sr2CaCu2O8±δ for the isomorphic higher Tc phase present in the 2:2:1:2 samples.

High-resolution synchrotron x-ray powder diffraction studies on samples of La2−xMxCuO4 (M = Sr,Ba) prepared by standard ceramic techniques show that macroscopic compositional inhomogeneities may exist that are unlikely to be revealed by conventional x-ray diffraction methods. Rietveld refinement of neutron data collected at 200, 50, and 11 K from one such sample, nominally La1.8Sr0.2CuO4, gave satisfactory fits to a tetragonal structure of K2NiF4 type at all three temperatures. However, careful individual peak fits revealed that part of the sample transforms to orthorhombic between 200 and 50 K. It is suggested that this multiphase character has an important influence on the superconducting properties.

A new, apparently metastable, Mo–Ni boride phase has been observed in transmission electron microscope samples of rapidly consolidated MoNiFeB metallic glass powders. The phase is cubic with lattice parameter 1.083 nm. Its space group as determined by electron diffraction is Fd $\overline 3$m and its approximate composition is Mo3Ni3B. Because its structure, its composition, and its role as a transition phase are analogous to those of η carbide (M6C) in steels and cemented carbides, this phase has tentatively been named “η boride.”

The annealing behavior of amorphous and icosahedral Al–17Mn and Al–20Mn–4Si films, prepared by sputter deposition, have been studied. Both hot stage transmission electron microscopy of thin (20–200 nm) films and furnace annealing plus x-ray diffration of thicker (1–10μm) films were utilized to study the various transformations resulting from elevated temperature exposures. The results are presented and correlated with the reactions anticipated from the phase diagrams and the results reported in previous studies.

The hydrogen occupation characteristics of the ternary amorphous alloy system Ni–Zr–B are investigated using gas-phase and electrochemical hydrogen-absorption techniques. Boron concentrations of as little as 1% are observed to cause large changes in the hydrogen storage properties relative to the binary Ni–Zr. Generalizations of a site statistical model, which accurately accounted for H storage in thebinary Ni–Zr and is based on tetrahedral interstitial hydrogen sites, cannot account for the hydrogen absorption properties of the boron-containing alloys, suggesting a structural transition between two amorphous phases induced by only 1% boron. A simple model in which the new amorphous phase stores H in higher-coordinated interstitial sites is shown to be consistent with the electrochemical and gas-phase data.

The mullite matrix of a reaction-sintered mullite/zirconia composite has been characterized by various electron microscopy techniques. The mullite was determined to be stoichiometrically Al4.76Si1.23O9.61 (1.7:1 mullite) with a disordered vacancy structure and Pbam symmetry. The atomic structure of the mullite has been described in terms of an average unit cell.