NANOPHASE MATERIALS ASSEMBLED FROM ATOM CLUSTERS

Nanometer-scale atom clusters (with average diameters below 20 nm) of a variety of materials, including both metals and ceramics, have been synthesized by precursor evaporation and condensation in high-purity g ases. The gas-entrained clusters can be collected and subsequently con solidated in situ under ultrahigh vacuum or other controlled atmospher e conditions to create bulk nanophase materials. These ultrafine-grain ed materials have properties that are often significantly different an d considerably improved relative to those of their coarser-grained cou nterparts. The observed property changes relate to both their small gr ain sizes and the large percentage of their atoms in grain boundary en vironments. Since it is becoming apparent that their properties can be engineered during gas-phase synthesis and subsequent processing, nano phase materials assembled from atom clusters should have significant p otential for technological development in a variety of applications. S ome of the recent research on nanophase materials is reviewed.