Sintered compacts of nanophase ZnO (∼60 nm average grain size, presintered at 600 °C) were made from powders (∼13 nm) prepared by the gas-condensation technique. Impedance spectra were taken as a function of temperature over the range 450–600 °C and as a function of oxygen partial pressure over the range 10−3−1 atm (550 and 600 °C only). The activation energy was determined to be 55 kJ/mole (0.57 eV) and was independent of oxygen partial pressure. The oxygen partial pressure exponent was −1/6. Impedance spectra exhibited nonlinear I-V behavior, with a threshold of approximately 6 V. These results indicate that grain boundaries are governing the electrical properties of the compact. Ramifications for oxygen sensing and for grain boundary defect characterization are discussed.

TiN films were ehemical-vapor-deposited on the inner wall of a tubular reactor. Films deposited in the upstream region of the reactor consisted of small and sharp crystals with (111)-preferred orientation or random orientation. On the other hand, films deposited in the downstream region or at lower partial pressure of TiCl4 consisted of columnar crystals with (110)-preferred orientation, having polyhedral shapes on the surface. For the films deposited under different conditions at different axial positions, relationships were investigated among the temperature, the calculated concentrations on the substrate, and the degree of preferred orientation of the films. As a result, it was shown that formation of films with (110)-preferred orientation is related to the conditions of high temperature and low partial pressure of TiCl4. Films deposited at the higher gas flow rate had lower degrees of (110)-preferred orientation. Decrease in partial pressure of TiCl4 along the axial direction in the reactor was calculated to be smaller at higher gas flow rate, and provided suitable conditions for deposition of films having small and sharp crystals.

Tungsten silicide (WSix) thin tilms have been investigated for use as integrated circuit interconnect and self-aligned MESFET (metal-semiconductor field-effect transistor) gates because of their low resistivity and thermal and chemical stability. These same characteristics make them interesting materials for prospective use in micromechanical structures. However, little information on residual stresses, elastic moduli, or other micromechanical properties has been available for refractory metal silicide thin films. This paper presents the morphology and stress characteristics of cosputtered WSix thin films, including crystal structure variations and orientation-dependent stresses, as a function of the deposition pressure. The compositions of WSix thin films were analyzed by Rutherford backscattering spectrometry (RBS). The biaxial elastic modulus and thermal coefficient of expansion were found for the sputtered films. Stress-measurement methods and annealing are discussed. Released diaphragms of different sizes and shapes, having controlled residual stress, have been fabricated.

Diamond deposition on group VIII transition metals of Cr, Mn, Fe, Co, and Ni has been achieved by a multi-step chemical vapor deposition process consisting of (i) seeding the substrate with diamond powders, (ii) annealing the seeded substrate in hydrogen at high temperatures, and (iii) diamond nucleation and growth. It was found that high quality diamond can be grown on these substrates, and the often accompanied graphite formation, which has been the main obstacle in the deposition of diamond on these metal surfaces, can be largely suppressed by the above step-deposition procedure. This technique was further extended to the processes of depositing diamond on steels and Co-bonded WC materials.

A this paper the influence of surface roughness on contact angles in the system of liquid Al wetting solid surfaces of Al2O3 has been studied. It was observed that contact angles of liquid Al vary significantly on different rough surfaces of Al2O3. A model is proposed to correlate contact angles with conventional roughness measurements and wavelengths by assuming a cosine profile of rough grooves with a Gaussian distribution of amplitudes. In comparison with the experimental results, the model provides a good estimate for describing the influence of surface roughness on contact angles of liquid Al on Al2O3.

AJ-Mg alloy (5052) composite reinforced with Si3N4 particulates was investigated by transmission electron microscopy and electron energy loss spectroscopy. Partial melting was observed at matrix/reinforcement interfaces and matrix grain boundaries at a temperature near an optimum superplastic temperature. Segregation of solute elements (Mg and Si) was observed at the interfaces and grain boundaries. Both partial melting and solute segregation were found to depend on grain boundaries. The obtained results were explained by a decrease of the solidus temperature due to segregation whose extent depends on the type of the grain boundary structure.

Activated carbon fibers (ACF's), already used widely as absorbent materials, are now expected to be useful as new electrical and electronic materials, for their very large specific surface areas (SSA). Chemical adsorption as well as x-ray diffraction have been mainly used for characterizing the ACF structure. While TEM observations reveal the texture of ACF's, such observations have not yet yielded quantitative information about the microstructure. To promote the quantitative interpretation of the TEM images, computer image analysis is used in this work to clarify the pore structure of ACF's. The microstructures of three samples, which are all isotropic pitch-based ACF's but with different SSA values, have been investigated. Operations such as noise reduction, low frequency cut-off filtering, and binary image formation are used to clarify the pore images of the ACF's. The distribution of the ACF porosity size is clearly shown by a frequency analysis of the two-dimensional fast Fourier transform (FFT). The results suggest that TEM images include contributions from many different pore sizes. Pores in different size ranges are extracted by the inverse FFT (IFFT) operation by selecting the specific frequency range, and by-this analysis the pore structure is shown to have fractal characteristics.

The surface of commercial pitch and PAN-based carbon fibers has been modified by coating the structures with catalytically formed carbon nanofibers. Reaction conditions have been established that enable one to achieve optimum coverage by the secondary nanostructures without inducing any degradation in the mechanical properties of the parent fibers. Using this approach it is possible to produce a dramatic increase in the surface area of the fibrous structure from a nominal value of about 1.0 m2/g (untreated condition) up to between 250 and 300 m2/g (complete nanofiber coverage). This process results in a significant enhancement in the adhesion properties at the interface between the fiber and matrix components in a composite material. Mechanical tests performed on single uncoated and coated T300 carbon fibers demonstrated that it was possible to obtain an improvement of over 4.75 times in the interfacial shear strength of the fibers following deposition of a critical amount of nanofibers.

The dielectric and electrostrictive properties of (1 - x) PMN−xPMW (x ⋚ 0.2) using chloride salts were investigated as a function of x. When the PMN-PMW powders were calcined at 700 °C for 1 h, the perovskite phase formed was 92%–97% at any given PMW composition (x ⋚ 0.2). With the increase of PMW content up to 0.2, the relative density of the specimens increased slightly, and the electrostrictive coefficient Q11 of the 0.8 PMN−0.2 PMW specimen increased about 6 × 10−2 m4/C2. However, the dielectric constant and electrostrictive strain of the specimens decreased despite the improved sinterability.

New structural features observed in heat-treated vapor-grown carbon fibers (VGCF's), produced by the thermal decomposition of hydrocarbon vapor, are reported using image analysis of the lattice plane structure observed by transmission electron microscopy (TEM) and atomic force microscopy (AFM). The TEM lattice image of well-ordered graphite fibers (heat-treated VGCF's at 2800 °C) was treated by a two-dimensional fast Fourier transform, showing sharp bright spots associated with the 002 and 100 lattice planes. The heat-treated VGCF's consist of a polygonally shaped shell, and the long and short fringe structures in the TEM lattice image reflect the 002 and 100 lattice planes, respectively. From this analysis, new facts about the lattice structure are obtained visually and quantitatively. The 002 lattice planes remain and are highly parallel to each other along the fiber axis, maintaining a uniform interlayer spacing of 3.36 Å. The 100 lattice planes are observed to make several inclined angles with the 002 lattice planes relative to the plane normals, caused by the gliding of adjacent graphene layers. This work visually demonstrates coexistence of the graphitic stacking, as well as the gliding of the adjacent graphene layers, with a gliding angle of about 3–20°. These glide planes are one of the dominant stacking defects in heat-treated VGCF's. On the other hand, turbostratic structural evidence was suggested by AFM observations. The structural model of coexisting graphitic, glide, and turbostratic structures is proposed as a transitional stage to perfect three-dimensional stacking in the graphitization process. These structural features could also occur in common carbons and in carbon nanotubes.

Two reaction routes have been tried for the synthesis of magncsium sulfide by applying microwave irradiation. In the first trial, finely ground Mg and S were mixed thoroughly and heated in a microwave oven for various lengths of time (5 + 5 + 8 + 10 and 12 + 12 + 35 + 45 min) in a sealed quartz tube. In the second trial, the pro-heating medium (PHM) of graphite was introduced into the mixture of Mg and S and microwaved for only 1 min. Results of x-ray diffraction analyses of the reaction products indicated that MgS polycrystallites (cubic, a0 = 5.201 ± 0.001) had formed in the second trial, and that the MgS yield was greater than 98%. Data of EDAX and EPMA gave a formula of MgS with atomic ratio of Mg:S = 1.0:1.0. In contrast, MgS could not be identified in the reaction mixtures in the first trial. Obviously, graphite, as a PHM, played a key role in the dramatic enhancement of the rate of the reaction between Mg and S powders. Furthermore, the effect of different molar ratios of graphite to Mg on the rate of microwave synthesis was investigated.

The rheological properties of boehmite-coated silicon nitride aqueous suspensions and gels are reported. In unidirectional rheological tests, it was found that the boehmite coating reduces the viscosity of the suspensions over a wide range of shear rates and volume fractions of particles. The suspension shear stress as a function of shear rate can be described by the Bingham model, and the Bingham yield stresses of boehmite-coated silicon nitride suspensions are lower than those of the uncoated suspensions. The reduction in the viscosity and the Bingham yield stress is attributed to a shallower secondary minimum in the Derjaguin-Landau-Verwey-Overbeek (DLVO) potential between coated particles than that for uncoated silicon nitride particles. Moreover, at low values of pH, the coated silicon nitride suspensions gelled over time, and the viscoelastic behavior of the gels was studied by dynamic oscillatory tests. It was found that the shear modulus (G′) and loss modulus (G″) remain constant up to a certain strain amplitude, γ°, beyond which G′ and G″ begin to vary. The value of G′ in the linear region increases exponentially, whereas γ° decreases exponentially with the volume fraction of coated silicon nitride particles. The exponential behavior of the shear modulus G′ of the gels is similar to the exponential pressure-density relationship found in the previous pressure filtration study, indicating that particulate rearrangement occurs as volume fraction of particles is increased.

We have grown thin films of La0.84Sr0.16MnO3 on SrTiO3 (100), MgO (100), CeO2 (100)/Al2O3, and (100) oriented yttria-stabilized zirconia (YSZ) substrates by using a 90°off-axis RF magnetron sputtering deposition. X-ray diffraction analysis and ion beam channeling experiments reveal that the deposited films grow epitaxially on SrTiO3, biaxially textured on MgO, and highly textured on YSZ. Scanning tunneling microscopy reveals that the thin films possess extremely smooth surfaces.

Crystalline Nb5Si3/Nb microlaminates were fabricated to a thickness of 20 μm by depositing the materials onto elevated temperature (750 °C) substrates. Modulation wavelengths of the microlaminates were varied (λ = 40 and 200 nm) while holding their silicide volume fraction constant to assess the effect of layer thickness on the composite properties. X-ray and selected area diffraction confirmed that both the metal and silicide layers exhibited a polycrystalline structure in the as-deposited microlaminates. Nanoindentation measurements of both microlaminates indicated that calculated elastic modulus values were similar to the values obtained by the rule-of-mixtures (ROM). Nanohardness values of the microlaminates increased with decreasing wavelength in a manner described by the Hall-Petch relationship. Vickers hardness (Hv) measurements were also found to be a function of the modulation wavelength, decreasing from 7.32 GPa at λ = 40 nm to 3.04 GPa at λ = 200 nm. Even with a Nb volume fraction of 50%, the λ = 40 nm microlaminate and the monolithic Nb5Si3 film exhibited similar Vickers hardness values of 7.5 GPa. These results show the significant role of modulation wavelength on the hardness, compressive strength, and toughness characteristics of a microlaminate composite.

Pure and La-doped magnesium titanate (MgTiO3) microwave ceramics were sintered and structurally and dielectrically characterized. Doping provides small inclusions of a second phase found to correspond to the La2Ti2O7 compound. It increases the microwave dielectric loss appreciably and gives rise to three absorption peaks in the submillimeter range assigned to polar phonons of the La2Ti2O7 structure. This assignment was confirmed by a direct reflectivity measurement on La2Ti2O7 ceramics. From the temperature dependence of submillimeter losses in the pure sample, one can estimate that from 1000 down to at least 8 GHz about half of the room temperature losses are intrinsic, i.e., due to two-phonon absorption processes.

The structural transformation of polycrystalline Si induced by high energy ball milling has been studied. The structure and property characteristics of the milled powder have been investigated by x-ray diffraction, scanning electron microscopy, high-resolution electron microscopy, differential scanning calorimetry, Raman scattering, and infrared absorption spectroscopy. Two phase amorphous and nanocrystalline Si has been produced by ball milling of polycrystalline elemental Si. The nanocrystalline components contain some defects such as dislocations, twins, and stacking faults which are typical of defects existing in conventional coarse-grained polycrystalline materials. The volume fraction of amorphous Si is about 15% while the average size of nanocrystalline grains is about 8 nm. Amorphous elemental Si without combined oxygen can be obtained by ball milling. The distribution of amorphous Si and the size of nanocrystalline Si crystallites is not homogeneous in the milled powder. The amorphous Si formed is concentrated near the surface of milled particles while the grain size of nanocrystalline Si ranges from 3 to 20 nm. Structurally, the amorphous silicon component prepared by ball milling is similar to that obtained by ion implantation or chemical vapor deposition. The amorphous Si formed exhibits a crystallization temperature of about 660 °C at a heating rate of 40 K/min and crystallization activation energy of about 268 kJ/mol. Two possible amorphization mechanisms, i.e., pressure-induced amorphization and crystallite-refinement-induced amorphization, are proposed for the amorphization of Si induced by ball milling.

A simplified model of a direct current arcjet-assisted diamond chemical vapor deposition reactor is presented. The model is based upon detailed theoretical analysis of the transport and chemical processes occurring during diamond deposition, and is formulated to yield closed-form solutions for diamond growth rate, defect density, and heat flux to the substrate. In a direct current arcjet reactor there is a natural division of the physical system into four characteristic domains: plasma torch, free stream, boundary layer, and surface, leading to the development of simplified thermodynamic, transport, and chemical kinetic models for each of the four regions. The models for these four regions are linked to form a single unified model. For a relatively wide range of reactor operating conditions, this simplified model yields results that are in good quantitative agreement with stagnation flow models containing detailed multicomponent transport and chemical kinetics. However, in contrast to the detailed reactor models, the model presented here executes in near real-time on a computer of modest size, and can therefore be readily incorporated into process control models or global dynamic loop simulations.

The microstructure of Al/α-Al2O3 composites made by infiltrating molten Al into dense mullite preforms has been characterized using transmission electron microscopy. The growth of the Al/Al2O3 composites was found to proceed through three stages. Initially, Al infiltrates into a dense mullite preform through grain boundary diffusion, and reacts with mullite at grain boundaries to form a partial reaction zone. Then, a complete reaction takes place in the reaction region between the partial reaction zone and the full reaction zone to convert the dense mullite preform to a composite of α-Al2O3 (matrix) and an Al-Si phase (thin channels). Finally, the reduced Si from the reaction diffuses out of the Al/Al2O3 composite through the metal channels, whereas Al from the molten Al pool is continuously drawn to the reaction region until the mullite preform is consumed or the sample is removed from the molten Al pool. Based on the observed microstructure, infiltration mechanisms have been discussed, and a growth model of the composites is proposed in which the process involves repeated nucleation of Al2O3 grains and grain growth.

The simultaneous determination of light element contamination levels and accurate nitrogen-to-metal ratios in nitride thin films deposited on silicon substrates is demonstrated by using α-particle beam energies in the range 3–4 MeV. In this energy range, significant light element sensitivity enhancements are observed, while the heavy elements show classical Rutherford behavior. The use of resonance scattering at different resonance energies is shown to be the method of choice for analyzing BN films on silicon. Also, a technique is suggested for analyzing very thin films in which an aluminum foil substrate and buffer layer are used to enhance sensitivities.

Recently it was observed through cross-sectional TEM that the preferred orientation of the TiN thin film was changed from (200) to (111) with thickness. In this study, the process of the change in the preferred orientation was studied near the critical thickness by x-ray diffraction, and the value of the critical thickness could be estimated. The change of the critical thickness was also investigated with the strain energy per unit volume. The strain energy could be changed by controlling the energy of the bombarding particle, i.e., by adjusting the rf power, the working pressure, and the substrate bias in sputtering. The critical thickness was decreased monotonically in all cases as the energy of the bombarding particle or the strain energy per unit volume was increased. These results surely show the dependence of the change of the preferred orientation on the strain energy in the TiN thin films.