Electronic structure calculations are used to study the bonding at diamond/BeO interfaces. The {110} interface between zinc blende BeO and diamond is used as a representative model for general reconstructed interfaces characterized by an equal amount of Be–C and O–C bonds. The interface energy is calculated to be 2 J/m2 and combined with the estimated free surface energies to obtain an estimate of the adhesion energy. It is found to be close to the adhesion of BeO to itself, but somewhat lower than that of diamond to itself. The effects of the 7% lattice mismatch on the total energy and the band structure for a biaxially strained pseudomorphic diamond film are investigated. The effect of misfit dislocations, expected to occur for thicker films, on the adhesion energy is estimated to be lower than 10%. The bulk properties, such as equilibrium lattice constant, bulk modulus, cohesive energy, and band gap of BeO are shown to be in good agreement with experimental values and previous calculations. The valence-band offset is calculated to be 3.9 eV and found to take up most of the large band gap discontinuity. The nature of the bonding is discussed in terms of the local densities of states near the interface. The interface localized features are identified in terms of Be–C and O–C bonding and antibonding states.

Si3N4 deposited by CVD on the surface of single crystal SiC was studied by SEM, x-ray diffraction, and TEM techniques. Characterization of the thick Si3N4 deposit was made by SEM and x-ray diffraction. The main emphasis, however, was on the analysis of the Si3N4/SiC interface and this analysis was carried out by electron diffraction studies in TEM. Both x-ray diffraction and TEM studies revealed that the CVD Si3N4 deposit has almost entirely the α-form except for occasional large β crystals. The structure of the SiC substrate in the interior was 6H but the surface structure close to the interface was always microtwinned β. Diffraction studies of the bulk Si3N4 deposit showed not only the presence of preferred growth directions but also different growth orientations near the substrate interface. TEM investigations at the interface also revealed that preferred growth orientations at the Si3N4/SiC interface are different from those in the bulk. The prominent orientation relationship at the interface is [0001]Si3N4//[101]SiC; Si3N4//SiC; a second one, namely Si3N4//[101]SiC; Si3N4//SiC relationship was also occasionally observed. Microindentation tests at the interface indicated that the Si3N4/SiC interface bonding is strong at ambient temperatures but weakens at high temperatures.

Spectrally resolved cathodoluminescence (CL) images and spatially resolved CL spectra were obtained from two specimens grown by hot-filament chemical vapor deposition. Each specimen consisted of a large number of unconnected diamond particles with cubo-octahedral and pseudo-fivefold twinned growth habits. The growth temperature was nominally 600 °C for one specimen and 750 °C for the other. In the 1.5–3.5 eV range, the spectra are composed of four defect and impurity related bands: there are three bands with zero-phonon lines at 1.68 eV, 2.156 eV, and 2.325 eV, and one broad band centered at 2.85 eV. A weak peak at 5.27 eV, due to exciton recombination, was also observed. Spectrally resolved images of the two most intense CL bands, at 2.156 eV and 2.85 eV, were obtained for several particles. In the low-temperature specimen, bright regions in images of the 2.156 eV band are correlated with {111} facets; bright regions in images of the 2.85 eV band are correlated in some cases with the central regions of {100} facets and in other cases with {111} facets. In the intermediate-temperature specimen, bright regions in the images of both bands are correlated with {100} facets. A model of competing recombination at different types of CL centers and nonradiative centers is proposed to facilitate the interpretation of the experimental results. For the low-temperature specimen, the model suggests that the 2.156 eV CL centers are located primarily in {111} growth sectors and the 2.85 eV CL centers are distributed relatively uniformly; images of the two dominant CL bands are predicted to have a complementary relationship in particles where there are few competing nonradiative centers. For the intermediate-temperature specimens, the model suggests that nonradiative recombination is dominant, and that the CL image contrast arises primarily from a nonuniform distribution of nonradiative centers.

A model has been previously proposed to describe the energy associated with emission of dissociated superlattice dislocations from crack tips in ordered intermetallic alloys. In the present paper, the model is applied to several B2 intermetallic alloys. The results of the analysis reveal a correlation between the range of slip system orientations for which emission of a dislocation from a crack tip is energetically favorable and the macroscopic fracture mode of the alloy. Additionally, the effects of changing the active slip system, increasing the thermal energy available for thermally activated dislocation emission, and changing the {111} APB energy on the fracture mode of NiAl and FeAl are discussed.

The chemical diffusion in thin trilayer films of TM–TM100−xZrx–TM with an amorphous middle layer where TM = Co, Ni, or Fe and in amorphous Fe–Zr and Ni–Zr films with composition gradients has been investigated using Rutherford backscattering spectrometry. The growth of the amorphous layer in the trilayers, due to in-diffusion of cobalt and nickel, is initially found to be proportional to the square root of the time, t1/2, and subsequently found to level off before the compositions corresponding to metastable equilibria are reached. Irradiation, with 500 keV Xe+ ions, is found to promote the in-diffusion. This behavior is discussed in terms of structural relaxation effects and their influence on the metastable equilibrium. In amorphous Fe–Zr the chemical diffusivity is observed to be very sluggish. Contrary to the behavior in Co–Zr and Ni–Zr trilayers, the direction of the iron diffusion in Fe–Zr trilayers suggests a broad positive peak in the Gibbs free energy at a composition around 50 at. % Zr. It is argued that the sluggish chemical diffusivity of iron is directly related to the unusual composition-dependence of the Gibbs free energy for amorphous Fe–Zr.

The compatibility of phases in the Ti–Si–C system was studied for pressures from 10 to 20 kbars (1 to 2 GPa) and temperatures from 1200 °C to 1500 °C via an interfacial reaction between titanium and silicon carbide. The interface was characterized by backscattered electron imaging and electron probe microanalysis. Ti3Si was stabilized at high pressures exhibiting an appreciable solubility for carbon (up to 9 at. %). At higher temperatures and lower pressures, it decomposed to Ti5Si3, Ti(Si, C), and TiCx according to the relation Ti3Si (Cz) = (0.70588)TiCx + (0.32437)Ti5Si3 + (0.67227)Ti (Si, C), where the mathematical coefficients were calculated using z = 0.4 and x = 0.5. No detectable quantities of carbon dissolved in Ti5Si3 under these conditions. A clapeyron slope of 0.08 (±0.01) kbar/K was measured for this reaction. The microstructure of the reaction zone and other general thermodynamic and kinetic characteristics are discussed for different experimental conditions.

The epitaxial growth of Cu2O films is of significant interest for the unique potential they offer in the development of multilayer devices and superlattices. While fundamental studies may be carried out on epitaxial films prepared by any technique, the growth of artificially layered superlattices requires that films grow epitaxially during deposition. The present study examined the growth of Cu2O on MgO substrates directly during deposition by sputtering. Although epitaxial thin films of Cu2O could be produced, a mosaic structure was observed. The structure of the film may be related to the growth mechanism in which islands coalesce to form a continuous film.

Yttrium aluminum garnet (YAG) powders were synthesized by normal and reverse strike precipitation from a mixed solution containing aluminum and yttrium nitrates. The precipitates were characterized by FTIR, DTA, and TGA techniques. The amorphous precipitates were crystallized under various atmospheres (air, argon, hydrogen) at different temperatures and the product analyzed by x-ray diffraction. Only reverse strike precipitation followed by crystallization in hydrogen consistently yielded phase pure YAG.

Oxide films are grown on a silicon wafer at low temperatures through the catalytic action of a thin gold film. Our results indicate that the oxide film thickness and morphology vary with the initial gold film thickness but do not significantly depend on the temperature. A Fourier analysis of the film structure suggests that the growth mechanism may include a spinodal decomposition where a binary alloy undergoes a phase separation. It is argued that gold silicide is the most likely candidate for spinodal decomposition.

The change in the surface morphology of metallic glasses Fe78B13Si9 during the early stage of the crystallization process has been studied mainly by atomic force microscopy (AFM). Specimens of 50-μm thickness have been heated up to 323 K, 373 K, 423 K, and 523 K with a heating rate of 30 K/min in vacuum, and then the surface morphology of each specimen has been observed by AFM in air. In the surface image of the specimen heated to 323 K, many holes are observed and inside the holes single or plural protrusions can be observed. Clusters composed of aggregated protrusions are also found like islands in the amorphous sea. The specimen heated to 323 K has also been observed by a high-resolution transmission electron microscope and crystalline structures among the amorphous matrix have been detected. From the selected area diffraction study, the crystalline structure is found to be α–Fe crystallites. In contrast, in the AFM image of the surface of the specimen heated to 423 K, no holes are seen and many protrusions are found to extend above the surface and form several parallel lines. The spatial density of protrusions above the surface becomes much higher in the specimen heated to 523 K. We propose that this change in the surface morphology during heat treatments indicates the process of nucleation and growth of α–Fe crystallites in the surface of metallic glasses. It is also found that the stage of many protrusions extending above the surface corresponds with the beginning of exoelectron emission from the surface. This result suggests that exoelectron emission and surface crystallization connect with each other.

Diamond-like (amorphous) carbon (DLC) films were prepared by dc magnetron sputtering and plasma enhanced chemical vapor deposition (PECVD) and diamond films were prepared by microwave plasma enhanced chemical vapor deposition (MPECVD). For the first time, chemical and mechanical characterization of the films from each category are carried out systematically and a comparison of the chemical and physical properties is provided. We find that DLC coatings produced by PECVD are superior in microhardness and modulus of elasticity to those produced by sputtering. PECVD films contain a larger fraction of sp3-bonding than the sputtered hydrogenated carbon films. Chemical and physical properties of the diamond films appear to be close to those of bulk diamond.

AgGaSe2 crystals are useful for nonlinear optical applications after a post-growth heat-treatment in the presence of Ag2Se to eliminate an unavoidable precipitate phase that degrades their optical properties. To understand better the heat-treatment procedure, surface migration and volume diffusion were investigated in the Ag2Se–AgGaSe2 system using reactive diffusion couples which were analyzed by x-ray diffraction, optical microscopy, and electron probe microanalysis. Surface diffusivities of all mobile species were found to be much larger than volume diffusivities. Specific values determined were DsAg = 5.43 × 10−4 exp(-0.46 eV/kT) and DvAg = 2.40 × 10−7 exp(-0.84 eV/kT), where DsAg and DvAg are effective surface diffusivity and effective volume diffusivity of Ag, respectively. The corresponding diffusivities for Ga and Se were found to be almost the same, indicating that Ga and Se move together with Ag to maintain binary (Ag2Se and Ga2Se3) stoichiometry and electroneutrality. These findings are consistent with the pattern of annihilation of the second phase precipitates in the AgGaSe2 matrix during heat treatment.

Kinetics of cristobalite precipitation in a binary glass composite, containing a low-softening borosilicate (BSG) and a high-softening high silica (HSG) glass, have been investigated. XRD results show that the pure glasses do not crystallize under the sintering conditions used, but when mixed in appropriate proportions the cristobalite gradually precipitates out of the initial amorphous binary glass mixture as the sintering continues at temperatures ranging from 800 to 1000 °C. Average linear thermal expansion coefficient (TCE) results show that the TCE increases significantly with increasing precipitation of cristobalite as a function of sintering time. Comparing the experimental TCE results with those theoretically calculated, it is concluded that the precipitation originates most likely in the HSG rather than in the BSG. The precipitation kinetics follow the Avrami equation, and the results show an apparent activation energy of 82 kJ/mol which is close to those for the diffusion of alkali ions in silicate glasses, suggesting mass-transport controlled kinetics. The values of the Avrami exponent are 1.7–1.8, which could be interpreted as a 3-dimension diffusional growth at zero nucleation rate. The linear growth rates of cristobalite, calculated from the precipitation curve, are in the range of 4–8 × 10−5 μm/min, and show slight temperature dependence from 800 to 1000 °C. The linear growth rates of cristobalite are also calculated theoretically using the equation derived by Turnbull et al.,2 and the data are 0–3 orders of magnitude smaller than those observed experimentally. This disparity is attributed to the catalytic effect of the OH and O in air and in the glass network, as well as the diffusion of alkali ions from BSG to HSG.

A microtwinned monoclinic phase is observed to occur within the grains of the hard magnetic phase in Nd2Fe14B-based permanent magnet alloys. This phase seems to be the product of a displacive solid state phase transformation of tetragonal Nd2Fe14B, distinguished from Nd2Fe14B by the presence of an ordered substitution into alternating unit cells parallel to the crystallographic c-axis and by a small shear of the type 〈100〉 {011}. The four different orientational variants of this monoclinic phase with respect to the parent tetragonal phase are arranged into two distinct colonies of twin-related plates. The observation that Nd2Fe14B can undergo a displacive solid state transformation has broad implications for the entire field of Nd2Fe14B permanent magnets.

SiC whiskers were synthesized by the carbothermal reduction of silica with an addition of halide (3NaF · AlF3 or NaF) as an auxiliary bath. The whiskers were β phase (3C) and grew in the [111] direction. Three distinctive morphologies were observed: (1) Type A: thin and straight; (2) Type B: thick and bamboo-like; and (3) Type C: thick, straight, and smooth. Type A whiskers contained a high density of basal plane (111) stacking faults along their entire length, whereas Type B whiskers showed periodic changes between stacking faults and well-defined single crystals. Type C whiskers showed stacking faults on the other {111} planes instead of on the basal (111) plane. Silica formed molten fluorosilicate with halide and SiC grew via a vapor-solid reaction mechanism through gaseous SiO. These reactions can be expressed as (SiO2) + C (s) = SiO (g) + CO (g) and SiO (g) + 3CO (g) = SiC (s) + 2CO2 (g). The effects of processing parameters on the morphology and size of the whiskers were examined and the relationship between the morphological development of the whiskers and the stacking fault energy was determined.

Particles of gadolinium iron garnet, Gd3Fe5O12, were produced primarily by an aerosol spray pyrolysis technique starting with solutions of gadolinium and iron nitrates. The as-prepared particles were polydisperse solid spheres. Average diameters in the range 0.05 to 0.8 μ could be obtained by variation of the initial solution concentration. Larger particles to 2 μ were created by direct, non-aerosol, pyrolysis of the solutions. Heat treatment caused sintering and particle coalescence and yielded ∼95% garnet phase. The reaction time to create the garnet phase scaled with the square of the particle diameter, the smallest particles transforming the quickest. Magnetic measurements showed bulk behavior for the saturation magnetization, but the coercivity could be varied with particle size with a maximum near the single domain size.

Diffusion bonds of Ni/ZrO2 and Ni/NiO/ZrO2 fabricated in vacuum have been investigated using flexural 4-point bending tests and optical and electron microscopy. It is found that subsequent annealing in air after bonding improves bond strength, and annealing in vacuum reduces strength. This is attributed to the formation of a thin oxide layer during annealing in air which enhances adhesion to the ceramic, whereas annealing in vacuum creates debonding voids at the specimen edges. The transformation of NiO in vacuum to Ni explains why the strength of bonds using preoxidized Ni foil does not show any increase, as it is essentially still the diffusion bonding of Ni to ZrO2 in the configuration of Ni/NiO/Ni/ZrO2. The presence of extensive void necklaces on grain boundaries in the metal where they intersect the bonding interface shows the importance of the metal grain boundaries acting as vacancy sinks during diffusion bonding.

Effects of surface roughness and crystallinity of polycrystalline diamond films on their tribological characteristics, as well as the effects of test environment, have been investigated. Friction and wear characteristics of the diamond films deposited on sintered SiC disks have been examined with a ball-on-disk tester in the absence of any lubricant. The friction coefficients of polished diamond films against SiC and Si3N4 balls were below 0.10 at room temperature while those of as-deposited films were around 0.20. The specific wear of counterparts on the polished film was five orders of magnitude smaller than on the as-deposited film. The friction coefficient between the polished diamond film and a AISI 52100 steel ball was about 0.20. Transfer of a small amount of AISI 52100 material to the diamond film was observed along the wear track of the polished diamond surface. Diamond films of high quality were more resistant to wear than the ones of low quality. On the other hand, the friction coefficients were not affected by the crystallinity of the diamond films in the present study. Tribological characteristics of the diamond films deteriorated with increasing sliding speed and ambient temperature. At 600 °C in dry N2, the friction coefficient of diamond films against a SiC ball was about 0.8, which was about ten times higher than that at room temperature in air.

This paper deals with the electrical characterization of thin layers of cubic SiC, grown on (100) Si substrates. The resistivity and Hall coefficient for undoped SiC layers were measured between 10 K and 500 K. The influence of inhomogeneities on the electrical properties of the as-grown films has been established. The Hall data show a clear sign of a transition to impurity band conduction. The donor concentrations studied are in the “intermediate” range. The donor activation energy has been shown to decrease with increasing nitrogen concentration. The nitrogen concentration was measured by SIMS. The variation in nitrogen concentration is also seen in changes in the shape of the ESR spectrum. The presence of nitrogen in the intermediate concentration range is the most likely reason for the conflicting values reported for the donor ionization energy as measured by Hall and PL measurements.

An apparatus was constructed that measured hardness under load. The instrument measured hardness using a strain-gauge load cell and a linear voltage displacement transducer. Loading rates were less than 1 μm/s. Results were similar to the results of other electronic hardness measurement devices, in that the hardness fell with increasing load. Glasses measured have Meyers indexes from 1.6 to 1.75, while polycrystalline materials showed much more complex behaviors. A model was formulated to explain the data for glasses based on expansion of shear planes.