THE STUDY OF ISLAND GROWTH OF ION-BEAM SPUTTERED METAL-FILMS BY DIGITAL IMAGE-PROCESSING

The island growth of ultra-thin metal films of Au, Cu and Pt prepared by ion beam sputtering on an amorphous carbon substrate has been analy sed using digital image processing methods. The transmission electron microscopy pictures revealing topological evolution of the metallic fi lms with an increase in the film equivalent thickness, have been fed i nto the computer and processed to determine the area coverage of the d iscrete metallic particles for various thicknesses. The average partic le size has also been measured at a small area coverage. The behaviour has been analysed using a nucleation and growth model of metallic fil ms. It is found that the power exponent alpha of the function f = At(a lpha), where f is the fractional substrate area coverage and t the equ ivalent film thickness, for Pt is close to unity whilst those for Au a nd Cu are close to 0.64 and 0.71 respectively. The results are conside rably more accurate than those published earlier without using such im age processing methods, hence more reliable details of the island grow th of metallic films are revealed. It is also found that at a small ar ea coverage the average particle size of Au and Cu is proportional to the equivalent thickness. These findings, based on the theoretical mod el, give strong confirmation of a two-dimensional growth mechanism for Pt and three-dimensional ones with cluster (island) dissociation up t o a critical cluster size of m atoms for Au and Cu. It is indicated th at the dissociation value m for Cu is greater than that of Au.