The relationships among weight loss, gas evolution, and other changes during sintering were investigated for silicon nitride powders synthesized by silica reduction and imide decomposition. Small weight losses were detected for all powders at low temperatures (below 1400 °C), and large weight losses were found to occur for the silica-reduction powders at high temperatures (1400–1800 °C). Only CO was detected in the sampled gases during sintering, and CO evolution peaks were seen at around 900–1200 (broad), 1400, and 1600 °C. The main deposited material around the samples was SiO. The weight losses at low temperatures were thought to be caused by evaporation of residual binder or adsorbed substances. The main causes of the large weight losses at high temperatures were thought to be CO and SiO evolutions, and CO evolution at around 1600 °C probably originated from the liquid phase accompanied by α–Si3N4 to β–Si3N4 transformation.

The thermal conductivity of silicon nitride prepared with varying sintering additive compositions was studied. Samples of Si3N4 + 0.5 mol% Y2O3 + 0.5 mol% Nd2O3 and a further additional agent were gas pressure sintered at 2173 K. MgO or Al2O3 was employed as the additional agent. While both agents improved sinterability, the former promoted grain growth and the latter suppressed it. Thermal conductivity increased with increasing MgO content, and a maximum value of 128 Wm-1 K-1 was attained when 2 mol% MgO was added. In contrast, addition of Al2O3 degrades thermal conductivity. This is probably due to the suppression of grain growth and the dissolution of Al2O3 into Si3N4 grains.

We present results of a large-scale atomistic study of the annihilation of oppositely signed screw dislocations in an fcc metal using molecular dynamics (MD) and an Embedded-Atom-Method (EAM) potential for Cu. The mechanisms of the annihilation process are studied in detail. From the simulation results, we determined the interaction energy between the dislocations as a function of separation. These results are compared with predictions from linear elasticity to examine the onset of non-linear-elastic interactions. The applicability of heuristic models for annihilation of dislocations in large-scale dislocation dynamics simulations is discussed in the light of these results.

An in situ high temperature heat treatment was used to investigate the crystallization and growth behavior of AlB2 flakes in aluminum. Aluminum samples containing 1.8% boron were heated above the liquidus and then rapidly cooled through the Al(L) + AlB12 region to avoid the formation of AlB12 crystals. Subsequently, a homogeneous distribution of high aspect ratio AlB2 flakes crystallized upon holding below the peritectic transition temperature. Growth rate in the (a) and (c) dimensions increased during elevated hold temperatures below the peritectic transition temperature. Surprisingly, faster cooling rates from above the liquidus to room temperature resulted in thinner, wider flakes. Similar to graphite this phenomenon is believed to result from a need to accommodate a changing misfit strain energy between the solidifying aluminum and the growing AlB2 flakes.

Mechanochemical reactions in the system FeTiO3 –Si have been investigated as functions of the powder composition and milling conditions, using x-ray diffraction and thermal analyses. Reduction reactions of FeTiO3 by Si were observed during room-temperature milling with the formation of α–Fe, amorphous SiOx, nanocrystalline TiO2, or intermetallic compounds, depending on the Si content. The mechanochemical reaction process consists of a mechanical activation stage and a reaction stage. Higher milling intensity leads to a shorter activation step and a higher reaction rate.

The rate of movement of liquid drops toward their equilibrium position on smooth, horizontal solid surfaces (spreading kinetics) is considered in this study. A model for nonreactive liquid spreading which was developed for low-temperature liquids is applied to results for a set of high-temperature liquids and room-temperature liquids. These data were generated in a single laboratory following a consistent experimental methodology. The liquid-solid pairs were chosen to result in weak or no interfacial chemical reaction. Furnace atmospheres were chosen to provide data for liquid metals with submonolayer, thin or thick oxide films. Analysis of the high-temperature spreading kinetics for liquids covering a broad range of viscosity, surface tension, and density shows that they can be predicted with a constant shift factor applied to the deGennes expression for nonreactive spreading. The consequences of gravitational and inertial forces, substrate roughness, weak interfacial reactions, and liquid-metal oxide films are discussed.

Epitaxially grown (Ba, Sr)TiO3 thin films were prepared on (100)MgO and (100)Pt ║ (100)MgO substrates by molecular chemical vapor deposition (MOCVD). The lattice parameter increased with increasing Ba/(Ba + Sr) ratio in the film and was higher than the reported value for bulk (Ba, Sr)TiO3. The dielectric constant at room temperature reached the maximum value at a lower Ba/(Ba + Sr) ratio compared to the reported one for bulk (Ba, Sr)TiO3. The temperature showing the maximum dielectric constant was higher than the reported value for bulk (Ba, Sr)TiO3. These results can be explained by the compressive stress applied to the film under the cooling process after the deposition.

During the nanoindentation process, the load and depth data are continuously recorded. A single load-displacement curve is thus expected to contain material property information from the whole depth range indented. In the present paper, a new method to obtain the hardness-depth curve has been derived for small depths from the load-displacement curve measured at a large depth, based on the assumption that the elastic properties of the indented material can be obtained from the indentation depth. Using this method, hardness values can be computed for various small depths from a single load-displacement curve. From a series of nanoindentation experiments, it has been proven that the method can be used on both homogeneous and surface-modified materials, such as fused silica, single crystal tungsten, and plasma nitrided steel with and without an iron nitride Fe4N compound layer. Testings on a series of Ni–P films coated on 15 MnB steel also gave fairly good results.

Based on several experimental observations, Hwang et al. recently proposed “the charged cluster model” [J. Cryst. Growth, 162, 55–68 (1996)] to disentangle the “puzzling thermodynamic paradox” encountered in the gas-activated chemical vapor deposition (CVD) of diamond. Many unusual phenomena observed in the CVD diamond process can be successfully approached by the charged cluster model. However, there are a couple of important subjects still unsolved quantitatively. The first question is connected with the main driving force for this unusual nucleation in the gas phase. The second issue is related to the difference in the thermodynamic stability between graphite and diamond for a nanometer-sized cluster during the growth. In this study, we have theoretically examined the thermodynamic driving forces for the charge-induced nucleation, in general, and have applied this idea to the nucleation of the charged carbon-atom cluster. It was shown that the short-range ion-induced dipole interaction and the ion-solvation electrostatic effect (Born term) were mainly responsible for this unusual nucleation in the gas phase. The theoretical analysis presented in this article is quite generic and, thus, can be applied to any process that involves the charge-induced nucleation.

To account for the dominant formation of diamond over graphite in the gas-activated chemical vapor deposition (CVD) process we have theoretically examined the free energy function of a small carbon-atom cluster as a function of the cluster size. The scalar potential around a charged spherical cluster was derived using the linearized Poisson–Boltzmann equation. It was shown that the repulsive electrostatic energy associated with the growth of the charged diamond cluster was proportional to the fifth power of the cluster size. This suggests the existence of a deep potential-energy-well for the cluster size larger than the critical size corresponding to the free energy barrier for the nucleation. Thus, the growing diamond cluster will be trapped in this potential well before it transforms to the thermodynamically stable graphite. Considering all the relevant thermodynamic driving forces, we have constructed the free energy function in terms of the cluster size. The numerical computation also supports the existence of the potential-energy-well. Therefore, the present theoretical model clearly explains why the charged diamond cluster does not transform to the neutral graphite cluster when the thermodynamic stability is reversed above a certain critical size during the growth.

Through the complexation of cobalt phthalocyanine (CoPc) and a film of poly[4-vinyl- pyridine] (PVP) polarized by an electric field, a new type of preferentially oriented self-assembled film (PVP-CoPc) was obtained. The characterization of the film by differential scanning calorimetry (DSC), angle-dependent x-ray photoelectron spectroscopy (XPS), and Fourier transform infrared reflection absorption spectroscopy (FTIR-RAS) revealed that the planes of pyridine rings oriented perpendicular to the film surface, while the planes of phthalocyanine rings were oriented parallel with, and coordinated on, the film surface. Photoconductivity study showed that the photoconductivities of the photoreceptors (PR's) made from the PVP-CoPc self-assembled film were much better than those from CoPc alone. These changes were ascribed to the charge transfer and the unique and ordered structure of PVP-CoPc self-assembled film.

A superlayer test has been adapted for the measurement of the fracture energy between epoxy thin films and self-assembled monolayers (SAM's) on Au/Ti/Si substrates. The “arrest” mode of analysis has been shown to provide consistent results, particularly when relatively wide lines are used to encourage lateral decohesions. The fracture energy, Γi, of the interface between the monolayer and the epoxy is varied by adjusting the ratio of COOH/CH3 terminal groups. Connections among Γi, the surface energies, and the inelastic deformations occurring in the epoxy are explored upon comparison with interface crack growth simulations.

Crystallization of poly(ethylene terephthalate) (PET) is accompanied by significant changes in surface topography, easily detected by atomic force microscopy (AFM). Phase imaging by AFM qualitatively indicates contrast in mechanical properties of nanometer scale areas of an annealed PET surface, but cannot provide quantitative data. Using interfacial force microscopy (IFM), we have, for the first time, made quantitative measurements of the elastic moduli of such nm-scale areas on a homopolymer surface. Values of 2.2 GPa, 4.3 GPa, and 11.8 GPa, were found, respectively, for amorphous PET and for phase segregated regions on the surface of an annealed homopolymer PET sample. The method is applicable to any phase segregated surface with nm-sized domains of differing elastic moduli.

The effects of different growth parameters on the microstructure of the SiC films formed during simultaneous two-source molecular-beam-epitaxial (MBE) deposition have been investigated. Substrate temperatures as low as 750–900 °C have been used. The relationship between a number of different growth morphologies and deposition conditions has been established. The formation of single-crystal 3C films has been found to occur at low growth rates but within a limited Si: C adatom ratio. A combination of transmission electron microscopy (TEM) and atomic force microscopy (AFM) has been used to examine the different films, and the results of these investigations are described.

A detailed study has been made of the control and optimization of partial melting of dipcoated Bi2Sr2Ca1Cu2O8+δAg0.1 (Bi-2212) tapes using reduced oxygen partial pressures. A coulometric titration technique has been employed to vary the oxygen partial pressure in a region of the phase diagram corresponding to binary melting, and the amount of partial melting has been quantified. Using this information, tapes have been processed using both isothermal and isobaric techniques. An optimum processing route was determined which combined isothermal and isobaric processes. Highly aligned material at the point of optimum melting was obtained.