Ultrafine—grained polycrystalline metallic components (Cu, Au, Fe) have been prepared by means of the inert gas evaporation technique combined with an integrated uniaxial cold compaction device. The average grain sizes ranaed typically from 20 nm to about 100 nm. The microstructure and Imourity content of the as-pressed samples have been investigated by means of TEM and AES, respectively. The yield strength of ultrafine (30 nm) grained Cu specimens obtained in tensile tests compares well with respective values for heavily cold—worked coarse grained copper. Al slight heat treatment (150ºC/30min) improves the strain—to—fracture at slightly reduced yield strength values. The results are discussed within the picture of two concurrent processes determining the strength of ultrafine grained metals: Coble creep vs. grain boundary strengthening effect.

A new method of preparing amorphous solids is presented. X-ray diffraction, thermal stability and Mgssbauer spectroscopy give evidence for an atomic structure with reduced short–range order in Si75Auz5 and Pd72FeloSil8 alloys prepared by this method.

A brief study of the fabrication of granular materials by high-pressure sputtering is presented. This method utilizes sputtering at high pressures (p > 100 mTorr) in a thermal gradient to produce nanoscale particles, which are then embedded in a matrix by normal sputtering (p ∼ a few mTorr). The shape, size and the degree of aggregationof these nanoscale crystals can be changed by varying such processing parameters as the sputtering gas pressure and the target voltage. Examples are presented of nanocomposite films containing Mo nanocrystals (grain size ranging from 3 to 20 nm ) in an Al matrix.

Within all electrophotographic (or xerographic) copiers and laser printers are development systems where the image is reproduced. Usually these development systems contain 200 μm diameter metallic, magnetic balls called carrier particles. Attached electrostatically to these balls are 10μm diameter polymer particles called toner which eventually end up on the paper forming the black images given to customers. The process bywhich the toner leaves the carrier and ends up on the paper is driven by electric fieldsin the development system. These fields are determined by the applied voltage and the dielectric properties of the granular mixture of metal carrier balls, polymeric toner, andair. The average electric field is determined by the dielectric constant of this granular mixture. But on a microscopic scale that a toner would experience, i.e. 10 μm, the electric field has significant structure. This structure has been determined both experimentally and theoretically. For example, the electric field peaks underneath a chainof carrier particles (which are chained up by a magnetic field). Models of the development process clearly indicate that toner particles transfer from the carrier particles only when the toner particles are directly under a carrier chain, where one would expect the field to be a maximum. However, recently we have succeeded in showing experimentally that the value of the electric field that the toner particles experience is the average field, described by the dielectric constant. Theoretical questions concerning the calculation of the electric field in a granular system raised by this unexpected result will bediscussed.

Oxide nonlinear conductors are granular electronic ceramic materials whose electrical behavior is dominated by grain boundary interfaces states. The material is typically comprised of relatively conducting oxide grains with electrical barriers at the grain boundaries induced by segregated impurity ions. Oxide nonlinear conductors can exhibit a highlynonlinear current-voltage relationship with a 5% change in voltage serving to increase the current flow an order of magnitude or more.

This review outlines our understanding of the microstructure, grain boundary properties and electrical behavior of these variable resistor or “varistor” granular materials. ZnO varistors currently have widespread application in protecting power and signal level electrical circuits against dangerous voltage surges and a brief overview will be given of the applications of this material.

Pt-SiO2 granular metal films were produced by RF diode sputtering and characterized as thermistors for cryogenic temperature measurements at high magnetic fields. The devices were found to have high sensitivity and small magnetoresistance. This, together with ease of fabrication and stability, makes such thermistor useful candidates for cryogenic thermometry.

Polycrystalline CuInSe2 solar cells, fabricated by evaporation or by selenization of metal films, are granular and relatively porous. Grains are a few hundred nanometers in dimension, and hence about 1% of the atoms are at a surface. Despite the granularity, quantum efficiency is quite high and implies a diffusion length exceeding the grain dimension. The primary photovoltaic loss is excessive forward recombination current. The proposed model consists of single crystal CuInSe2 granules with an indium rich surface layer. When properly passivated, the otherwise uncoordinated indium bonds are terminated by oxygen. However, residual non-passivated crystalline surface states distributed throughout the depletion region provide the paths for enhanced recombination.