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 gases. The gas-entrained clusters can be collected and subsequently consolidated in situ under ultrahigh vacuum or other controlled atmosphere conditions to create bulk nanophase materials. These ultrafine-grained materials have properties that are often significantly different and considerably improved relative to those of their coarser-grained counterparts. The observed property changes relate to both their small grain sizes and the large percentage of their atoms in grain boundary environments. Since it is becoming apparent that their properties can be engineered during gas-phase synthesis and subsequent processing, nanophase materials assembled from atom clusters should have significant potential for technological development in a variety of applications. Some of the recent research on nanophase materials is reviewed.