Results of ab initio Hartree–Fock calculations for the electronic structure of aluminum nitride in the (high-pressure) rocksalt phase are reported. In the rocksalt phase, the calculated lattice constant is 3.982 Å with the bulk modulus of 329 GPa. The band structure is predicted to be indirect at the X point with a gap of 8.9 eV. In this phase, the bonding is shown to be essentially ionic between Al and N. The direct gap shows a stronger linear dependence on pressure with a pressure derivative of 68 meV/GPa compared to that of the indirect gap with a pressure derivative of 31.7 meV/GPa.

High-quality single crystals of 6H–SiC have been indented at 1170 °C in vacuum. A TEM study of the indented regions shows that a 6H → 3C polytypic transformation has occurred, further confirming that this phase transformation can be induced by an applied stress.

Rutherford backscattering spectrometry (RBS) was used to measure the titanium concentration profile for hydrogen-reduced, vacuum-reduced, and as-received, stoichiometric rutile. These profiles give the degree of reduction, specifically, the extent of oxygen deficiency, as a function of depth below the sample surface. Using forward-recoil spectrometry (FRES), the hydrogen-reduced rutile was found to contain more bulk and near-surface hydrogen than the as-received, stoichiometric rutile. This observation provides additional evidence for a hydrogen-diffusion model for the reduction of rutile in a hydrogen environment.

Tungsten/silicon multilayers with tungsten layers of a thickness of 1–2 nm were prepared by means of electron beam deposition. Their structure and thermal stability under rapid thermal annealing were investigated by a combination of x-ray diffraction techniques and cross-sectional transmission electron microscopy. The crystallization behavior was found to depend on the interdiffusion and mixing at the tungsten/silicon interfaces during deposition as well as during annealing. The as-deposited tungsten/silicon multilayers were amorphous and remained stable after annealing at 250 °C/40 s. Interdiffusion and crystallization occurred after annealing all samples from 500 °C/40 s up to 1000 °C/20 s. By performing the same heat treatment in the tungsten/silicon multilayers, the formation of body-centered cubic W was observed with a layer thickness ratio δW/δsi = 1, whereas tetragonal WSi2 was detected in tungsten/silicon multilayers with a layer thickness ratio of δw/δsi ∼0.25. This dependence of the crystallization products on the layer thickness ratio δw/δsi originates from the different phenomena of interdiffusion and mixing at the tungsten/silicon interfaces. The possible formation of bcc tungsten as a first stage of crystallization of tungsten-silicon amorphous phase, rich in tungsten, is discussed.

Unilamellar vesicles, formed spontaneously by mixing single-tailed cationic (cetyl trimethyl ammonium tosylate, CTAT) and anionic aqueous solutions of (sodium dodecyl benzene sulfonate, SDBS) surfactants have been used as reactors for the aqueous phase precipitation of nanometer sized particles within their inner cores. AlCl3 solution was encapsulated within these vesicles, aluminum ions were replaced with sodium ions in the extravesicular phase, and sodium hydroxide was then added to the extravesicular region. Hydroxyl ions penetrate through the vesicle walls and react with the available aluminum in the intravesicular region to form the product. The morphology and sizes of these particles were examined by transmission electron microscopy, while their phase and crystalline nature were probed by electron and x-ray diffraction. The product particles were nanometer-sized with near spherical morphology. Good control of particle size was achieved by varying the initial concentration of electrolyte. Single particle electron diffraction revealed a symmetric pair of spots, indicating that the particles were either single crystals or polycrystalline with á low number of grain boundaries or defects. Although wide area electron diffraction showed that the product was δ–Al2O3, powder x-ray diffraction revealed that these particles were, in fact, Al(OH)3. It is likely that heating of these nanoparticles by the high energy electron beam in a high vacuum environment causes a phase transformation, resulting in the difference between the electron and x-ray diffraction results. These results represent the first demonstration of precipitation within vesicles produced spontaneously by mixing appropriate ratios of inexpensive single-tailed surfactants, and may potentially make intravesicular precipitation a commercially viable route for making nanometer-sized particles.

Cylindrical moldings of 20 and 40 mm diameter were injection molded with the application of modulated hold pressure using a well-characterized alumina-polypropylene suspension. The effect of frequency on sprue solidification was explored. For the smaller moldings, very little extension to sprue solidification time was obtained with pressures up to 140 MPa, and this is attributed to the low reciprocating volume flow. For the larger moldings, pressures of 98 MPa were sufficient to produce moldings with neither voids nor cracks, and the sprue solidification time corresponded to the time needed for solidification of the molding. The use of higher pressures resulted in internal residual stresses which were qualitatively detected by the defomation on annealing of polished diametral sections.

We report the formation of a novel solid form of carbon + oxygen. Exposure of C60 to high oxygen pressure [P(O2) ≍ 100 MPa] for several days at slightly above ambient temperature results in absorption of significant amounts of oxygen (up to ∼48% by weight after 3 days). X-ray diffraction measurements showed that the C60 pellets had become amorphous. Although part of the added weight is slowly lost in flowing oxygen at ambient pressure and temperature, most remains up to at least 100 °C. Heating in flowing He at 200 °C brought the weight back to near the original value. The reaction appears to be specific to C60 since the amorphous outgassed material had lost the capacity to absorb oxygen at high P(O2), and the oxygen absorption effect was absent in powdered graphite and in commercial amorphous carbon. The Raman spectrum differs from those of C60, soot, amorphous carbon, graphite, and diamond.

Highly oriented diamond films were grown on single-crystal silicon substrates. Textured films were first nucleated by a two-step process that involved the conversion of the silicon surface to an epitaxial SiC layer, followed by bias-enhanced nucleation. The nucleation stage, which produced a partially oriented diamond film, was immediately followed by a (100) textured growth process, thus resulting in a film surface where approximately 100% of the grains are epitaxially oriented relative to the silicon substrate. The diamond films were characterized by both SEM and Raman spectroscopy. Structural defects in the film are discussed in the context of their potential effect on the electrical characteristics of the resulting film.

Comparing experimental CVD Si(1–x)Gex, thin film data of different authors with independently published results of thermodynamic equilibrium calculations leads to the conclusion that thermodynamically calculated compositions of thin films do not fit the experimentally obtained data. Further it will be shown in the paper that the discussed experimental data of Si(1–x)Gex layer composition can be uniquely interpreted by applying a transport-reaction controlled mechanism, which includes the hypothetical formation of silicon atoms containing intermediates of the germanium source compound as well as the germanium atoms forming chemical reaction to be of first order.

The recently developed energy principle of indentation mechanics was applied to the continuous indentation test performed on pure sapphire. Three crystallographic planes, M = (10$\overline 1$0), A = (1$\overline 1$10), and C = (0001), have been indented by a symmetrical triangular pyramid (Berkovich). The distinct anisotropic behavior of the indented crystal has been observed for the maximum indentation loads of 1.961 N, 0.686 N, and 0.392 N. The indentation hysteresis loop energy and the related “true hardness parameter” have been determined for various crystallographic orientations, as well as for two different orientations of the indenter. The observed effects have been discussed in terms of the energy principle of indentation with crystallographic considerations. The effective resolved shear stresses for the slip and twinning systems were calculated and applied to the anisotropic indentation behavior. It was concluded that the energy principle is highly recommended for analyzing the data of continuous indentation tests.

The recently reported hysteretic behavior of silicon under indentation (Clarke et al.1 and Pharret al.2-5) is investigated using an ultra-micro-indentation system with an 8.5 μm spherical-tipped indenter. The onset of “plastic” behavior during loading and hysteresis during unloading was readily observed at loads in excess of 70 mN. Cracking about the residual impression was observed only at loads of 350 mN and higher. An analysis of the data is presented that estimates the following: (1) the initial onset of deformation occurs at a mean pressure of 11.8 ± 0.6 GPa, (2) the mean pressure at higher loads is 11.3 ± 1.3 GPa, and (3) the hysteretic transition on unloading occurs at mean pressures between 7.5 and 9.1 GPa. These values are in good agreement with the accepted literature values for the known silicon transformation pressures. A simulation of the force-displacement data based on the analysis and model is presented and is found to fit the observations very well.

The thermal expansion coefficient of LaCo1−xFexO3 averaging between 25 and 1000 °C decreased linearly with the Fe content, x. The thermal expansion of LaCo1−xNixO3 decreased with increasing the Ni content, but those for x = 0.67 and 1.0 were almost identical at 1000 °C due to the transition of the crystal system of LaNiO3. The behavior of thermal expansion was interpreted in terms of the formation enthalpy of the perovskites and the bond length between a B-site cation and an oxide anion. LaCo0.67Ni0.33O3, which has the electrical conductivity of 4 × 102 S/cm, could be a good candidate for the air electrode material.

Diphasic yttrium-aluminum garnet (Y3Al5O12, YAG) sols were made by hydrolysis of aluminum and yttrium isopropoxides. The sols were gelled across TEM grids to make films. The films were heat-treated up to 1550 °C for as long as 300 h. Heat-treatments of bulk gel were also done. Microstructure and phase evolution were observed by TEM. Some observations were done in situ in a TEM hot-stage. YAG fraction and grain size, matrix grain size, nuclei/area, and film thickness were measured. Bulk samples were characterized by x-ray, DTA, and TGA. Yttrium-aluminum monoclinic (YAM) and transition alumina appeared at 800 °C. YAG nucleated between 800 °C and 950 °C. Nucleation was weakly correlated with the transient presence of YAlO3 garnet, and was eventually site-saturated at 0.3/μm3. The change in grain growth rate of the YAM and transition alumina matrix correlated with the change in the growth rate of YAG. Between 850 °C and 1000 °C YAG growth had t1/2 dependence and 280 kJ/mole activation energy. Below 850 °C nucleation was continuous, and growth had t0.85 dependence. Above 1000 °C YAG growth had t1/4 dependence, and the matrix grains coarsened with t1/4 dependence. Thicker films reacted faster because the nuclei/area and the growth rate after nucleation scaled with thickness. YAG growth was accompanied by formation of 20–100 nm subgrains. In the late stages of matrix grain coarsening there was also some reaction to YAG by a different process. Nucleation and growth kinetics are compared with other systems. Possible mechanisms are discussed.

C60 films simultaneously exposed at T = 300 K to oxygen and visible-ultraviolet light are found to exhibit rapid diffusion of oxygen into the deep bulk of the film. The diffusion rate is found to be ∼10 times faster in the presence of light. Vibrational and optical absorption spectroscopy indicate that the photoassisted reaction of O2 with solid C60 involves two coupled reactions: (i) the photoassisted diffusion of molecular oxygen into solid C60 and (ii) oxidation of C60.

The microstructure of pressureless sintered silicon carbide (SiC) materials with alumina (Al2O3) addition was investigated using analytical electron microscopy and nuclear magnetic resonance. A sintered body with a density of higher than 99% theoretical was obtained with an addition of 5 wt.% Al2O3. The sintered body (SiC–Al2O3) has high strength, high fracture toughness, and high fatigue resistance. Its fracture toughness is approximately 5 MPa-m1/2, which is twice as high as that of pressureless sintered SiC materials with boron and carbon additions (SiC–B–C). The correlation between the microstructure and the mechanical properties is presented here. The starting β–SiC powder is mostly transformed to α–SiC with various polytype distributions during the sintering process. The microstructure has homogeneously distributed, fine, plate-like interlocking gains with a high aspect ratio. Well-developed basal planes form parallel and elongated boundaries, and the crystal structure is mostly the 6H polytype (56%) mixed with thin lamellar 4H.

The early stages of the thermally induced epitaxial realignment of undoped and As-doped polycrystalline Si films deposited onto crystalline Si substrates were monitored by transmission electron microscopy. Under the effect of the heat treatment, the native oxide film at the poly-Si/c-Si interface begins to agglomerate into spherical beads. The grain boundary terminations at the interface are the preferred sites for the triggering of the realignment transformation which starts by the formation of epitaxial protuberances at these sites. This feature, in conjunction with the microstructure of the films during the first instants of the heat treatment, explains the occurrence of two different realignment modes. In undoped films the epitaxial protuberances, due to the fine grain structure, are closely distributed and grow together forming a rough interface moving toward the film's surface. For As-doped films, the larger grain size leaves a reduced density of realignment sites. Due to As doping some of these sites grow fast and form epitaxial columns that further grow laterally at the expense of the surrounding polycrystalline grains.

70Ge and 74Ge isotopes were successfully separated from natural Ge and zone purified. Several highly enriched, high purity 70Ge and 74Ge single crystals were grown by the vertical Bridgman method. The growth system was designed for reliable growth of low dislocation density, high purity Ge single crystals of very small weight (∼4 g). A 70Ge and a 74Ge crystal were selected for complete characterization. In spite of the large surface to volume ratio of these ingots, both 70Ge and 74Ge crystals contain low electrically active chemical net-impurity concentrations of ∼2 × 1012 cm−3, which is two orders of magnitude better than that of 74Ge crystals previously grown by two different groups.1,2 Isotopic enrichment of the 70Ge and the 74Ge crystals is 96.3% and 96.8%, respectively. The residual donors and acceptors present in both crystals were identified as phosphorus and copper, respectively. In addition, less than 1011 cm−3 gallium, aluminum, and indium were found in the 70Ge crystal.

Monolithic nanocomposite aerogels of two aluminosilicate compositions have been prepared and characterized by different techniques. The results show that high surface area and mesoporosity can be preserved in the above nanocomposite aerogels by heating at 1000 °C, unlike the single component aerogels. The presence of alumina as a second phase prevented their densification which resulted in surface areas on the order of 500–600 m2/g and mesopores of about 5–6 nm in diameter after heat treatment at 1000 °C. These novel nanocomposite aerogels are expected to find applications at high-temperatures in separations, insulation, catalysis, etc.

Bombardment of a growing thin film by negative ions can lead to changes in the film through the process of resputtering. Macro-effects of resputtering (effects on the film thickness) include a slowing of the film growth rate and, in some cases, a complete suppression of the film growth as well as an etching of the substrate materials. To study this result of resputtering, rf-diode sputtering was used to deposit BaTiO3 films under a variety of conditions, varying deposition time, rf-power level, substrate-to-target distance, total gas pressure, and argon, oxygen, and hydrogen partial pressures. The effect resputtering had on the thickness was seen to be a result of the competition between deposition and etching of the thin film material. The relative influence of the various sputtering parameters and the effect each of these has on the thickness distribution were examined. It was found that the greatest influence was system geometry, followed by rf-power level. Various methods of controlling resputtering are discussed.

Mo5Si3 precipitates in MoSi2 single crystals have been studied. The orientation relationship between the long rectangular lath-like precipitates and the matrix is [110] MoSi2[110] Mo5Si3 and (002) MoSi2(2$\overline 1$0)Mo5Si3. Two sets of misfit dislocations extend along the long dimensions of the precipitates.