Ultrafine particles (UFPs) of aluminum oxide, formed by arc discharge, were sintered in an ultrahigh vacuum (UHV) furnace system and characterized by high resolution electron microscopy (HREM) under UHV conditions. The UFPs produced range in size from 20 to 50 nm and have highly faceted surfaces. The atomic structure of the UFPs corresponds to the cubic (γ) and orthorhombic (δ) variants of the spinel structure. In UFPs, surface faceting plays a major role in determining the final sintering geometry with sintering occurring predominantly on the closed-packed (111) facets. Surface diffusion is the predominant mechanism for sintering, as evidenced by the fact that many sintered particles have their initial adhesion structure ‘;lockedin’ during sintering with no reorientation occurring. Furthermore, the necks formed during sintering have well-defined, atomically-sharp contact angles suggesting that the neck growth process is controlled by the faceted structures and may be modeled by a mechanism similar to crystal growth due to ledges, grain boundaries, and twins. The driving force for sintering can be considered as a chemical potential difference between facet surfaces and the neck region.

Sinter-forging experiments were performed on cylindrical samples of n-TiO2 at various stresses and temperatures and with varying initial densities. The results are described on the basis of a constitutive law similar to creep deformation of dense bodies. The activation enthalpy measured is consisted with a grain boundary diffusion limited process, whereas the stress exponent found excludes simple diffusional creep. Furthermore, a threshold stress was found to exist. The results are discussed in terms of existing models and it is shown that the threshold stress can be explained in terms of the creation of additional surface area due to grain boundary sliding.

The excess enthalpy and excess heat capacity of nanophase TiO2 prepared by a chemically-derived process and by inert gas condensation have been measured using differential scanning calorimetry. In comparison to the chemically-derived samples, the excess enthalpy of the inert gas condensed samples is significantly larger, perhaps due to the presence of intragranular planar defects that accomm oate oxygen deficiency. Significant extraneous contributions from planar defects, lattice strain, phase transformation, oxidation, or sintering have been ruled out for the chemically-derived samples. A grain boundary enthalpy of 13-1.6 J/m2 in the temperature range 600-1000°C is obtained from scanning measurements. However, the data also indicate a grain size and/or temperature dependence of the grain boundary enthalpy.

The controlled hydrolysis of Al(O-sec-Bu)3 and Y(O-iso-Pr)3 or the reaction of Y(OOCCH)3 with partially hydrolyzed Al(O-sec-Bu)3 [AlO0.75(O-sec-Bu)1.5] resulted in the formation of soluble polymeric materials. Pyrolysis of these materials under a flow of oxygen led to the formation of yttrium aluminum garnet (YAG) at 650-1500°C. YAG was the only crystalline phase observed during pyrolysis, and the Al/Y ratio of the pyrolysis products and the starting material was identical. However, infrared spectroscopy indicated that carbonate groups and entrained CO2 existed in the products at temperatures up to 1250°C. The pyrolysis chemistry of the precursors and the microstructure of the products were studied by FT-IR, TGA, XRD, SEM and elemental analyses.

The nanophase ionic conductors Ca1-xLaxF2+x with x=0 and 0.25 were synthesized by an inert gas condensation and in situ compacting technique. The samples with average grain size of 16 na for nanophase CaF2 and 11 nm for nanophase Ca0.75 La0.25F2.25 were prepared under the compacting pressure of 0.5 GPa. The alternating ionic conductivity was deduced from the temperature dependence of the complex impedance.

The results indicated that the logarithm of ionic conductivity obeys Arrhenius relation in the temperature range from 300 °C to 530 °C both for nanophase CaF2 and for nanophase Ca0.75La0.25F2.25. Their activation energies are 1.14 eV and 1.00 eV, respectively. The ionic conductivity of nanophase CaF2 is about one and two orders of magnitude higher than that of polycrystalline and single crystal CaF2, respectively. While the ionic conductivity of nanophase Ca0.75La0.25F2.25 is about one order of magnitude higher than that of nanophase CaF2. Further analysis indicated that the enhanced ionic conductivity of nanophase Ca1-xLaxF2+x is related to the large volume fraction of interfaces.

The morphological properties of cubic, faceted MgO microcrystals have been exploited in the formation of textured coatings. Coatings exhibiting a <100> “fiber” texture were formed by centrifugal sedimentation of colloidal suspensions onto a flat substrate. A decrease in the degree of preferred orientation in the coatings with increasing areal coverage of the particles was quantified for several particle-size distributions by using x-ray diffraction. Novel methods for the deposition of particles exhibiting an in-plane preferred orientation in addition to fiber texture have been investigated.

Imogolite is a structurally microporous tubular clay comprising one-dimensional pore channels that are ∼1 nm in diameter. In addition to its novel tubular morphology, a notable structural characteristic of imogolite is its occurrence in paracrystalline tube bundles in which the individual tubes are close-packed with their axes in parallel alignment. We have developed a technique that aligns and tightly packs the tube bundles over macroscopic dimensions, in a manner analogous to the alignment and packing of the individual imogolite tubes within the bundles. This extends the range of imogolite paracrystallinity, effectively eliminating mesoporosity and nontubular phases.

The discrete molecular clusters of clusters, M1140[(CO)9Co3CCO2]6, M = Co, Zn undergo thermolysis with the production of highly porous solid materials. Evaluation of the catalytic properties of these materials has been investigated using the hydrogenation of 1,3- butadiene as a test reaction. These experiments suggest it is the unique structure of the porous materials that is responsible for the high activities and the selectivities observed.

Nanostructured Ge granular thin films were prepared by magnetron sputtering of composite targets pressed from mixtures of Ge and ceramic powders. The ceramics used were Al2O3, MgO and SiO2. Films in the Gex(Al2O3)l-x system were composed of Ge particles 10-60 nm in size uniformly embedded in the ceramic matrix, particularly for low Ge concentration films. X-ray photoelectron spectroscopy (XPS) was used to characterize these films. Samples were identified according to the coordination of Ge with the oxygen as (i) Ge-Ge4, (ii) Ge-Ge3O, (iii)Ge-Ge2O2, (iv) Ge-GeO3 and (v) Ge-O4. Using the modified Sanderson model1 and its modifications2, we found Ge oxidation to be largely composition dependent. Similar results were obtained for Ge granular films in MgO and SiO2 matrices.

The mechano-chemical effects of high-energy attrition milling on the microstructure evolution and superconducting properties of Bi2Sr2CaCu2Ox oxide powder were investigated by a combination of x-ray diffraction, scanning electron microscopy, and magnetization techniques. The powder was attrition-milled under an argon atmosphere, using a standard laboratory attritor with yittria-stabilized ZrO2 balls having a ball-to-powder weight ratio of ∼10:1. After selected time increments the mechanical attrition was interrupted and a small quantity of the milled powder was removed for analysis. The results indicate that (1) the crystal size decreases, (2) this decrease in crystal size is accompanied by degradation of crystallinity of the powder and accumulation of atomic-level strain, (3) the Bi-2212 phase decomposes under conditions of excessive deformation, and (4) the superconducting transition is depressed from 70 K to 60 K in the early stages of milling and completely vanishes upon prolonged deformation. The influence of defects (created during cold work) on the current carrying capacity is also presented and discussed.

Nanophase (n-) ZrO2 was produced in its pure and partially stabilized form by the gas-phase condensation method. The material was examined by x-ray diffraction and Raman scattering to obtain information on the structural evolution of the material during sintering. Two types of Y2O3 doped ZrO2 nanophase materials were made one by co-deposition of n-Y2O3 and n-ZrO2 in a consecutive manner and the second by mechanically mixing n-Y2O3 and n-ZrO2. We have determined that the co-deposition process is the most effect means of doping the n-ZrO2.

Nanostructured ZnO materials were synthesized by a novel reactive sublimation process, followed by cluster consolidation. The zinc oxide nanometer-sized grains were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and photoacoustic Fourier-transform infrared spectroscopy (PA-FTIR). These techniques illustrate the crystallization and grain growth of the ZnO nanostructured materials in a sequence of heat treatments. Peak sharpening and red-shifting of the phonon band in PA-FTIR spectra of ZnO nanoclusters demonstrate the reduction of finite crystal size effects during annealing. The high surface area and adsorbed species in ZnO nanoclusters were eliminated after sintering at a low temperature of 800 °C. The nanometer-sized ZnO particles have promising electronic and optical properties associated with the quantum size effects.

The surface chemistry of 35 Å diameter CdSe quantum crystallites is varied by bonding different molecules to the surface of the crystallites. There are two main variables. The steric hindrance of the molecule is altered to control the density of dangling bonds at the surface. In addition, different bond types between the ligand and surface atoms were used to control the surface electron density. Nanosecond hole burning experiments were used to compare ground state recovery times. Luminescence revealed information on excited state recombination pathways. Analysis suggests that increased surface passivation reduces the fast nonradiative recombination.

The optical properties of semiconductor nanocrystallites, or small quantum dots, are well understood, but little is known about nanocrystallite networks. Here we report preliminary results on a glassy network of CdSe nanocrystallites connected by molecular bridges. This network has been analyzed by transmission electron microscopy (TEM) and small angle X-ray scattering to determine its structure, and to see if long range order is present. The effect of nanocrystallite interactions on electron-hole recombination is inferred from characterization by UV-VIS absorption and photoluminescence.

Endosemiconductors, materials produced when atom constituents of bulk semiconductors are reorganized into ordered arrays of single size and shape clusters encapsulated within a nanoporous host, are introduced with the report of a novel tin(IV) sulfide endosemiconductor synthesized by a two-step MOCVD-like self-assembly process. Template-mediated hydrothermal syntheses of phase-pure and large single crystal tin(IV) sulfide exosemiconductors, materials resulting from reorganization of those same atomic constituents into an open-framework crystalline nanoporous structure is also discussed. The properties of these nanomaterials are considered in terms of the degree of coupling between molecule-like constituent clusters, a concept which mediates the nanoworld of matter intermediate between molecular and bulk.

Monodispersed, spherical, submicron size zinc sulfide powders were previously prepared in our laboratory utilizing homogeneous precipitation by thermal decomposition of thioacetamide in acidic aqueous solutions. Electron microscopic investigations of these powders indicated that the individual particles were agglomerates of 8∼14 nm size crystallites. It has been known that zinc sulfide does not sinter under ambient pressure due to the covalent nature of its bonding, high melting point, and relatively high vapor pressures at elevated temperatures. The heat treatment of these nano-crystalline zinc sulfide powders, however, showed some degree of sintering at temperatures as low as 600°C under vacuum.

Nanostructured silicon nitride solids (NANO–SSNS) were investigated by x–ray photoelectron spectroscopy (XPS), electron spin resonance (ESR) and dielectric measurements. It is found that the dielectric constant of NANO–SSNS depends strongly on the measuring frequency, f. When f<100Hz, at room temperature it is forty times as much as that of conventional Si3N4. ESR measurements show that a large number of unbinding electrons exist in interfaces. This suggests that the NANO–SSNS possess strong polarity. The study on the bond properties indicates that a large number of unsaturated and dangling bonds exist in interfaces of NANO–SSNS.

SiC fine particles were synthesized by the gas-phase thermal decomposition of tetramethylsilane (Si(CH3)4) in hydrogen under microgravity of 10−4G for 10 sec. Rapid heating to the temperature over 800°C which is required for thermal decomposition of Si(CH3)4) under short-time microgravity was attained using a chemical oven where the heat of exothermic reaction of combustion synthesis of Ti-A1-4B composites was used as the heat source. Monodisperse and spherical SiC fine particles were synthesized under microgravity, whereas aggregates of SiC fine particles were synthesized under 1 G gravity. The SiC particles synthesized under microgravity (150-200 nm) were bigger in size and narrower in size distribution than those under 1 G gravity (100-150 nm).

Ultra fine particles(UFP) of organic and inorganic materials can be formed by the gas evaporation method(gas condensation method). In the gas deposition method, particles formed by the gas evaporation method in an evaporation chamber are carried to another chamber (a deposition chamber) through a pipe. Particles are accelerated in the pipe with a gas flow and come out of a nozzle located in the deposition chamber which is being evacuated down to less than 10 torr and deposited on a substrate to form UFP films. The final speed of the particles depends on the pressure difference between the evaporation chamber and the deposition chamber. The particles speed exceeds 500m/s and adhesion strengths of the films reach 50OKgf/cm2 as well as vacuum deposition films in the condition that the pressure of the evaporation chamber is at 4 atms. Patterns of spots and lines with 50μm size and also wider films can be formed on a substrate without a masking system. The process is effective for repairing electric connecting lines or producing electrodes and condensers on an industrial scale.

Metal Clusters may be synthesized in the interior of surfactant aggregates called inverse micelles. These nanosize chemical reactors permit the controlled growth of several types of metal clusters. We describe this process for the formation of Au, Ag, Pd, Pt and Ir clusters and cluster alloys. Two size-control strategies are described: 1)variation of micelle size by alteration of the surfacant and/or solvent combination used, and 2) judicious use of micelle interactions or phase behavior. Using these two methods size control in the range of 1-100 nm is possible. The optical properties of metal clusters of gold, silver, and gold/silver alloys are described and the surface plasmon resonances are shown to have dramatic blue shifts and extensive line broadening with decreasing size in the range of 10-1 nm. In the case of gold clusters, the distinct resonancein the visible disappears for sizes less than 2.0 nm and new features appear in the UV. The optical spectra of alloys of gold and silver are shown to differ dramatically from their homoatomic counterparts of the same average size. We use electron and X-ray diffraction to determine the phase structure of the metal clusters and small angle X-ray scattering, neutron scattering, light scattering and TEM to characterize the average size and size distributions of these clusters. Finally, we describe measurements of the catalytic activity of Pd clusters and demonstrate a dramatic increase in hydrogenation activity on the size range of 2-10 nm.