The pressure shifts of the 418 and 379 cm−1 Raman lines of polycrystalline α-Al2O3 ceramic were measured at room temperature to 3190 MPa. A diamond anvil high pressure cell was used in conjunction with a microRaman spectrometer system. Pressures were measured by the ruby fluorescence method. Distilled water was used as the pressure transmitting medium. The pressure dependence of the wave number for the hydrostatic range (to 1585 MPa) was found to be 0.00220 ± 0.00007 cm−1 MPa−1 for the 418 cm−1 Raman line and 0.0011 ± 0.0001 cm−1 MPa−1 for the 379 cm−1 line. Both shifts are based on a linear least squares fit to the data within a 95% confidence interval. Measurements that included the nonhydrostatic regime (to 3190 MPa) gave similar shifts, but with almost twice the uncertainty. Absolute residual stresses in alumina ceramics are in the 200 to 600 MPa range with higher values, 1790 MPa, reported for single-crystal alumina. For the 418 cm−1 Raman line, these values correspond to shifts of 0.4, 1.4, and 3.9 cm−1, respectively. The sensitivity of the microRaman technique is sufficient to detect and measure residual stresses of this magnitude.

The surface morphology (001)-oriented single-crystal magnesium oxide (MgO) implanted with xenon ions has been examined using atomic force microscopy. It was found that at the lowest fluence used in this study (1.0 × 1014/cm2), a slight roughening of the (001) surface occurred. The magnitude of this roughening remained fairly constant with increases in fluence in the range 1.0 × 1014/cm2 to 3.0 × 1016/cm2. Implantation at fluences of ≥ 1.0 × 1017/cm2 caused significant surface roughening with the concomitant formation of micron-sized blisters. The appearance of some of these blisters resembles the rosette pattern that is also observed when the cleaved surfaces of MgO crystals are etched following indentation using a spherical indenter. This observation suggests that these blisters are formed by the growth of xenon inclusions, during implantation, by a dislocation loop punching mechanism.

The mechanism and kinetics of the chemical reaction between Nb(s) and C(s) under self-propagating high-temperature synthesis (SHS)-like (or combustion synthesis-like) conditions have been studied. Experiments were designed and conducted in order to produce a transport-resistance-free reaction between Nb and C under time-temperature conditions that are characteristic of the combustion synthesis process. To do so, a reaction couple, consisting of carbon and either a thin niobium foil or a fine niobium wire, was used. The effects of the temperature history and the formation of a liquid phase on the reaction were studied. In addition, theoretical experiments of the reaction were also conducted. The results showed that at high temperatures, layered niobium carbide phases formed in a direction that was parallel to the original carbon-niobium interface. As might be expected, local melting played a very significant role in the reactions. The mechanism and kinetics of these reactions provide a fundamental understanding of the manner and rate by which a powder-based Nb/C SHS process takes place, and, by extension, to a large, general class of solid-solid material synthesis processes that are based on the SHS (or combustion synthesis) process.

In the context of studying the feasibility of photocatalytically self-cleaning windows and windshields, clear, abrasion resistant, photocatalytic films of TiO2 were formed on soda lime glass and on fused quartz by a sol-gel process. The rate of photooxidation of contaminant deposits was estimated by measuring the rate of decrease in the integrated IR absorbance associated with the C-H stretching vibrations of a thin solution-cast film of stearic acid under 365 nm (2.4 mW/cm2) or 254 nm (0.8 mW/cm2) irradiation. Approximately 3 × 10−4 stearic acid molecules were stripped per 365 nm photon in either front- or back-illuminated soda lime glass, and 6 × 10−4 molecules when the films were coated on fused quartz. For thin TiO2 films on fused quartz, the rate of photooxidation, normalized by the number of photons absorbed per unit area, was independent of the wavelength. In contrast, for films on soda lime glass, the rate of photooxidation, when similarly normalized, was higher for the less penetrating wavelength. The reduced photoactivity on glass at the deeply penetrating wavelength (365 nm), as well as the greater photoefficiency on quartz than on glass, are attributed to diffusion of sodium oxide from the glass into the inner glass-contacting zone of the TiO2 layer.

The effects of Si1−xGex alloy composition on the Ti-Si1−xGex solid phase reaction have been examined. Specifically, effects on the titanium gcrmanosilicide phase formation sequence. C54 Ti(Si1−yGey)2 nucleation temperature, and C54 Ti(Si1−yGey)2 morphology were examined. It was determined that the Ti-Si1−xGex reaction follows a “Ti-Si-like” reaction path for Si-rich Si1−xGex alloys and follows a “Ti-Ge-like” reaction path for Ge-rich Si1−xGex alloys. The coexistence of multiple titanium germanosilicide phases was observed during Ti-Si1−xGex reactions for Si1−xGex alloys in an intermediate composition range. The morphology and stability of the resulting C54 germanosilicides were directly correlated to the Ti-Si1−xGex reaction path. Smooth continuous C54 titanium germanosilicide was formed for samples with Si1−xGex compositions in the “Ti-Si-like” regime. Discontinuous islanded C54 germanosilicides were formed for samples with Si1−xGex compositions in the mixed phase and “Ti-Ge-like” regimes. Using rapid thermal annealing techniques, it was found that the C54 titanium germanosilicides were stable to higher temperatures. This indicated that the morphological degradation occurs after C54 phase formation. The C54 Ti(Si1−xGex)2 formation temperature was examined as a function of alloy composition and was found to decrease by ≍ 70 °C as the composition approached x ≍ 0.5. An optimum Si1−xGex alloy composition range of 0 ⋚ x ⋚ 0.36 was determined for the formation of stable-continuous-low-resistivity-C54 titanium germanosilicide films from the solid phase reaction of Ti and Si1−xGex alloy. The results were described in terms of the relevant nucleation processes.

High-quality Ta2O5 thin films for high-density memory devices were prepared at low temperatures by electron cyclotron resonance plasma-enhanced chemical vapor depostion (ECR-PECVD) without postannealing treatment. The effects of deposition temperature on the microstructure, composition, and electrical properties of the dielectric films were studied. The increase in deposition temperature from 145 °C to 205 °C improved the stoichiometry of the Ta2O5 thin films. As a consequence, EBD increased from 3.3 MV/cm to 4.4 MV/cm, and ∊Ta2O5, increased from 14 to 25. Interfacial SiO2 layer was observed by cross-sectional TEM, and its effects on the electrical properties of the overall dielectric film were also studied. The incubation period in which interfacial SiO2 grows was discussed with regard to reactivity between oxygen and Si substrate.

Extraordinary adhesion of a Nb-based/Au-Sn metallization structure on a SiO2/Si substrate has been observed by a tensile pull test. The metallization bond fails mostly via fracture through either the Si substrate or epoxy adhesive. The intrinsic adhesion pull strength of the metallization scheme is concluded to be greater than 10 kpsi, and the adhesion exceeds the Si-Si cohesive strength. The Nb-Si and Nb-O bonds at the interface are thermodynamically stable.

CO2 laser pyrolysis has been used to synthesize carbon black (particle diameter ∼30 nm) via a catalytically driven pyrolysis of benzene vapor. The H : C ratio is found to be ∼1 : 10, which is unusually high for carbon blacks. Subsequent heat treatment of the “laser black” to temperatures up to ∼2800 °C produces well-graphitized faceted particles with central polygonal cavities. High resolution TEM lattice imaging, Raman scattering, and x-ray diffraction have been used to characterize the morphological structure of these carbon particles in their as-synthesized and heat-treated forms. Furthermore, KOH treatment at ∼800 °C has been employed to activate the as-synthesized particles, producing a tenfold increase in the surface area from 50 to 700 m2/g. Possible pore structures generated during this activation process have been identified by high resolution TEM imaging.

Cross-sectional and plan-view transmission electron microscopy were used to characterize a BaTiO3 thin film deposited on a (100) MgO single-crystal substrate at 1000 °C. The major observations were as follows: interdiffusion between the film and substrate; a large number of antiphase boundaries in the BaTiO3; a two-phase microstructure in the film composed of perovskite BaTiO3 and a second nonperovskite phase, Ba2MgTi5O13 (2:1:5); and a well-defined orientation relationship between the 2 : 1 : 5 and BaTiO3 phases. We propose a mechanism for the formation of the 2 : 1 : 5 phase based on the similarities between the crystal structure of this phase and the structure of (210) antiphase boundaries in BaTiO3.

Young's moduli of nanocrystalline Fe, Cu, Ni, and Cu-Ni alloys prepared by mechanical milling/alloying have been measured by the nanoindentation technique. The results indicate that Young's moduli of nanocrystalline Cu, Ni, and Cu–Ni alloys with a grain size ranging from 17 to 26 nm are similar to those of the corresponding polycrystals. The dependence of Young's modulus of nanocrystalline Fe on grain size corresponds well to a theoretical prediction, which suggests that the change in the Young and shear moduli of nanocrystalline materials, free of porosity, with a grain size larger than about 4 nm, should be very limited (<10%). It is likely that reported large decreases in the Young and shear moduli of nanocrystalline materials prepared by gas-condensation/vacuum consolidation result from a relatively large volume fraction of pores.

Atomistic techniques are used to study brittle fracture under opening mode and mixed mode loading conditions. The influence of the discreteness of the lattice and of the lattice-trapping effect on crack propagation is studied using an embedded atom potential for nickel to describe the crack tip. The recently developed FEAt (Finite Element-Atomistic) coupling scheme provides the atomistic core region with realistic boundary conditions. Several crystallographically distinct crack-tip configurations are studied and commonly reveal that brittle cracks under general mixed mode loading situations follow an energy criterion (G-criterion) rather than an opening-stress criterion (Kl-criterion). However, if there are two competing failure modes, they seem to unload each other, which leads to an increase in lattice trapping. Blunted crack tips are studied in the last part of the paper and are compared to the atomically sharp cracks. Depending on the shape of the blunted crack tip, the observed failure modes differ significantly and can drastically disagree with what one would anticipate from a continuum mechanical analysis.

The variation of apparent hardness observed in previously reported Vickers indentation tests of metals is reexamined. Common deseriptions of the effect are shown to be inaccurate: the variation of apparent hardness is monotonic but not simple. The effect is consistent with varying size of a previously postulated “plastic hinge” at the perimeter of the indent. This complexity confers uncertainty on the estimation of characteristic macrohardness from small scale tests. Association of the indentation size effect with friction and with strain hardening is confirmed.

Interstitial diffusion along twist grain boundaries was studied using the Embedded Atom Method (EAM). Six (100) twist grain boundaries (8.79°–43.6°) in copper were investigated. Interstitial formation energies were found to be much lower (0.26-0.78 eV) than in the bulk, and migration energies were found to be comparable (0.01 eV-0.24 eV) to the bulk values (0.09 eV). The vacancy mechanism is favored for low angle boundaries, and the interstitial mechanism is favored for high angle boundaries. The trends in formation energy versus twist angle were partly explained in terms of the volume expansion of the grain boundary. The total diffusion rate due to both mechanisms was calculated, and agreed reasonably well with experimental data for Cu in polycrystalline Cu. The calculated diffusion rate for specific twist boundaries also agreed well with experimental measurements for Zn/Al.

Four-point bending creep tests were conducted in air on two alumina matrix composites reinforced with 18 and 30 vol% of silicon carbide whiskers, respectively. In both materials, the SiC whiskers tended to form agglomerates. In the temperature range from 1673 to 1823 K, the stress exponents, n, were ∼3.9 and ∼6.3 and the activation energies for creep, Q, were ∼690-740 and ∼930-1010 kJ mol−1 for the composites containing 18 and 30 vol % of SiC, respectively. It is shown that the higher value of n in the composite with 30 vol % of SiC whiskers may be lowered to ∼3 by incorporating a threshold stress. The creep strength of both composites was enhanced by comparison with a similar composite containing 9.3 vol % of SiC whiskers, but there was only a very minor improvement in creep strength when the volume fraction of whiskers was increased from 18 to 30 vol %.

Silver has played a critical role for the fabrication of metal/high temperature superconductor composites. Phase equilibrium and microstructure in the ternary PbO-CuO-Ag system have been investigated using differential thermal analysis (DTA), thermogravimetry (TG), scanning electron microscope (SEM), and x-ray diffraction (XRD) techniques. Composition versus temperature diagrams have been established for these systems in air. In the ternary CuO-PbO-Ag system, there is a eutectic reaction CuO + PbO + Ag = L at 750 °C and a composition of 12.04 mol % Ag, 16.35 mol % CuO, and 72.62 mol % PbO. Two immiscible regions near the two binary tie lines PbO-Ag and CuO-Ag were detected. No binary or ternary compound was detected in these systems. SEM and EDS results confirm the presence of two liquid phases and the eutectic point

Silica gcls containing NiCl2 and dextrose have been reduced by heat-treating the gels under N2 atmosphere at 800 °C, 850 °C, 900 °C, and 950 °C, respectively. The influence of the volume ratio of ethyl alcohol to tetraethylorthosilicate and the amount of dextrose on the in situ reduction kinetics of NiCl2 in gel matrix have been investigated. The kinetic data on in situ reduction have been analyzed by a reduced time method which indicates that mixed mechanisms are operative. The predominant mechanism of reduction of NiCl2 in SiO2 gel matrix is of nucleation and growth type. The activation energies over different temperatures and fraction converted have been computed by the integration method.

The elastic properties of sodium borovanadate glasses have been studied over a wide range of composition using ultrasonic measurements. It is found that variation of different elastic moduli is very similar in any given series of composition. The bulk and shear moduli show a monotonic variation with the covalent bond energy densities calculated from the proposed structural model for these glasses. The bulk moduli also vary as a negative power function of the mean atomic volume. The Debye temperature varies linearly with the glass transition temperature. The implications of the observed behavior have been discussed.

A method for controlling the particle size of amorphous iron, which was prepared by the sonication of iron pentacarbonyl [Fe(CO)5], is reported in this paper. The sonolysis was performed on neat Fe(CO)5 and its solutions in decane whose concentrations were 4 M, 1 M, and 0.25 M. The iron nanoparticles were subjected to TEM (Transmission Electron Micrograph), ESR (Electron Spin Resonance), TGA (Thermogravimetric Analysis), DSC (Differential Scanning Calorimctry), and Quantum Design SQUID magnetization measurement. The measured properties demonstrated a strong dependence on the concentration of the solution, e.g., particle size.

We have studied the morphology of thin films of α-hexathienyl (α-6T), a hexamer of thiophene that is a very promising material for thin-film-transistor applications. Using electron- and atomic-force microscopies, we found that on both rigid (Si/SiO2 and glass) and flexible (polyimide) substrates, evaporated films show an apparently random, polycrystalline morphology. The crystals are lamellar, ca. 100-200 nm in lateral dimensions and 15-30 nm in thickness, and exhibit irregular boundaries. Nevertheless, electron-diffraction evidence from such films indicates that the constituent molecules are deposited preferentially end-on and assume a normal or nearly normal orientation with respect to their substrates. Rapid high-temperature annealing causes growth of much larger (μm-sized) crystalline grains and a partial transformation to a high-temperature polymorph; however, this process leads to formation of gaps in the film, which may cause deterioration of electronic performance.

The decomposition of topaz to mullite and other siliceous phases on heating above about 1100 °C was found to depend on sample size and the presence of water vapor in the heating atmosphere. The principal experimental technique employed was scanning electron microscopy, but the data were supported by x-ray diffraction, thermal analysis, mass spectroscopy of volatile emissions, and solid-state nuclear magnetic resonance. In relatively large samples, the transformation to mullite evidently takes place by a vapor phase mechanism within the bulk. The surface reaction that took place for samples heated in a wet atmosphere allowed the formation of high-silica glass, as well as mullite. The use of a hydrogenous heating atmosphere resulted in the sublimation and reformation of mullite whiskers, well outside the boundary of the original topaz.