Aggregate Structure in Thin Nickel Films

Abstract

IT is recognized that in the initial stages of metal film growth by vacuum deposition the incident atoms may possess sufficient mobility on the substrate to form aggregates (clusters of crystallites)1,2. The degree of aggregation is chiefly a function of the substrate temperature and rate of deposition, and is conveniently thought of as a film thickness above which the films have a continuous structure. Various investigators have obtained electron microscopic evidence of the aggregated structure in thin films of a number of metals prepared under various conditions3–6. In addition, precise density measurements have indicated that aggregation in the initial portion of the film formation may result in a decrease in the observed density7. Severe aggregation may also be detected by electrical resistivity measurements. In contrast to the foregoing procedures, a simple chemical etching technique has been successfully used to observe metallographically the aggregate structure in thin nickel films. Despite the difference in magnification, such photomicrographs bear a striking resemblance to the published electron micrographs indicating aggregated structures in thin metal films.