An apparatus for acquisition of highly resolved macroscopic photoluminescence topograms has been developed, using a laser scanner for PL excitation, and a linear diode array as imaging device. As a typical application, room temperature PL-topograms of various 2″ In P wafers are presented and discussed. Substrate inhomogeneities revealed in these topograms are growth striations, dendrites, and subsurface damage from wafer handling and processing.

The internal tensile stress in heteroepitaxial films of cubic (β) SiC grown on Si substrates by chemical vapor deposition at 1520–1650 K has been determined from the resonant frequencies of membrane samples formed by removal of a central circular region of the substrate. At 293 K, the stress falls in the range 250–500 MPa, and tends to be larger for samples grown at higher temperatures. The temperature dependence of the stress has been studied over the range 90–670 K and found to exhibit a reversible, mild, but convoluted variation that includes a minimum near 160 K and a maximum near 400 K. Analysis of this behavior reveals that the thermal expansion of β–SiC is remarkably close to that of Si, with an expansion curve that intersects that of Si near 80 K and 500 K. This behavior is different from that obtained from available handbook data for α–SiC, and suggests that data for α–SiC should not be relied on to estimate the overall magnitude of the thermal stress component in β–SiC films. Annealing studies carried out in the range 673–1473 K on as-prepared membranes indicate a high degree of membrane stability, with no evidence of stress relaxation. It has also been observed that annealed membranes may exhibit very low levels of mechanical damping, corresponding to Q-values in the range 106−107.

Smooth, continuous TiB2 films were deposited on TiB2−AlN composites and Si substrates by sputtering in high vacuum. Excellent adhesion between films and substrates was indicated; no film delamination was induced by Vickers indentation at high loads. Analyses by secondary ion mass and x-ray photoelectron spectroscopies showed that the films were of high purity and contained H, C, O, N, and Na elements as trace impurities. Quantitative depth profile by the elastic recoil detection (ERD) nuclear scattering technique using 30 MeV 35Cl beam revealed that the Ti/B atomic ratio was very close to 0.5 while the 10B/11B isotopic ratio was 0.250.

Porosity control in ceramic membranes has been achieved by controlling particle packing densities in sol-gel processing. TiO2 xerogels with two mean pore radii of 0.7 and 1.7 nm and a porosity varying from 30% to 52% have been obtained. ZrO2 xerogels with a mean pore radius of 0.7 nm and a porosity varying from 7% to 34% have also been prepared. The principle of controlling porosity is to make spongy aggregates and to control the degree of aggregation. Experiments have been conducted to show that spongy aggregates can be produced by gradually removing protons from the strongly charged particles. Viscosity techniques have been used to measure the relative volume fraction of the dispersed phase which, in turn, provides information on aggregate structures. Two aggregation models have been proposed to explain different structural aggregates formed through thermal destabilization in the highly charged system and through charge neutralization by gradually removing charge from the particles in the system.

Highly concentrated solid-in-liquid suspensions find applications in a number of areas such as electronics, ceramics, paints, coatings, etc. Highly loaded, stable suspensions which exhibit desirable rheological characteristics (moderate viscosity, shear thinning behavior, thixotropy, and a small yield stress, for example), and which have high thermal or electrical conductivities are frequently sought after. We describe here some techniques which can be used to obtain such highly concentrated suspensions. These involve employing mixed size grades of particles and effective dispersants. For thermal paste applications, for example, compliant pastes of up to 78 vol. % solids with thermal conductivity values as high as 6 W/mK (hence, a few times greater than the values reported previously by others), low electrical conductivity, and moderate viscosity have been prepared by mixing different particle size grades of materials such as Al2O3, SiC, AlN, Al, and diamond. Effective dispersants, both commercial as well as those synthesized in our laboratory as novel variations of previously known molecular architectures, have been used to facilitate the achievement of these very high loading and stable suspensions.

Sodium silicates are investigated to enhance the strengths of Bayer process muds and develop structural ceramics without sintering. With an impregnation of sodium silicate from 2% to 10% concentration in red mud, the fracture toughness is enhanced from 0.2 to 0.9 MPa. Compression strengths of 25.1 MPa (3628 psi) have been attained with red mud at 10% silicate concentration. Similar enhancements by a factor of 4 to 5 have been obtained for modulus of rupture and Brinell hardness number. It is shown that these properties do not deteriorate in acidic and neutral environment in water, implying stability to weathering conditions. SEM investigations reveal elongated crystal formation, possibly of aluminum and iron silicates in the aggregate. These crystals act like whiskers enhancing the strength. The process is applicable for development of low-cost construction components.

Novel composite films with a monolayer of organic molecules included between single molecular layers of MoS2 can be prepared with a recently described technique. Styrene-included MoS2, before and after polymerization, is discussed as an example that exhibits interesting properties. The sensitivity to humidity of the styrene-included MoS2 system is monitored in situ with x-ray diffraction where reversible incorporation and removal of water molecules are observed. Films with an anisotropy of electrical conductivity of about 108 are obtained by polymerizing the monomer between the layers.

Two-step carbonization was found on a polyimide film, Upilex, similar to that observed on another polyimide, Kapton: large weight loss up to about 22 wt. % and linear shrinkage along the film surface to 30% in a narrow temperature range from 500 to 650 °C, and an additional small weight loss and shrinkage in a wide range between 700 and 1000 °C. The yield of carbonization agreed roughly with that calculated by assuming the release of non-carbon atoms as simple species of CO, O2, and N2. A 25 μm Upilex film yielded a relatively high degree of graphitization after heat treatment at 3000 °C: a layered structure under SEM, high magnetoresistance, and a sharp 002 x-ray diffraction peak at a d-spacing of 0.336 nm. The degree of graphitization was lower than for a similar Kapton film, which is attributed to the lack of flatness in the Upilex molecule. A very much lower degree of graphitization was observed for 50 μm Upilex films. This difference is tentatively attributed to constraints that must have influenced the orientation of the Upilex molecules near the surface of the films as they were formed.

Group theoretical methods are used to obtain the form of the elastic moduli matrices and the number of independent parameters for various symmetries. Particular attention is given to symmetry groups for which 3D and 2D isotropy is found for the stress-strain tensor relation. The number of independent parameters is given by the number of times the fully symmetric representation is contained in the direct product of the irreducible representations for two symmetrical second rank tensors. The basis functions for the lower symmetry groups are found from the compatibility relations and are explicitly related to the elastic moduli. These types of symmetry arguments should be generally useful in treating the elastic properties of solids and composites.