Microscopic Aspects of Thin Metal Film Epitaxial Growth on Metallic Substrates

Abstract

AbstractMicroscopic processes in epitaxial growth of thin metal films on metal substrates are discussed in the light of recent scanning tunneling microscopy data. Details on the nature and role of different atomic processes, though too fast for direct observation, can be inferred from the characteristic development of the film morphology with increasing coverages and its modification upon varying the deposition rate and temperature. It is shown that for deposition at room temperature or moderately increased temperatures film growth and the resulting film morphology are dominated by kinetic effects, and that film growth proceeds via nucleation and growth of 2D islands. — At room temperature, where adatoms are sufficiently mobile to allow efficient intralayer mass transport, film growth begins by nucleation of supercritical clusters in a supersaturated 2D gas of mobile metal adatoms. These clusters can grow into 2D islands. The correlation between adatom mobility, substrate temperature and deposition rate on the one hand and island density on the other are demonstrated. The shape of the growing islands can vary widely, from dendritic to compact island forms. The different shapes are shown to result from kinetic limitations, specifically from a limited adatom mobility along island edges. — For kinetically controlled film growth in the multilayer regime the film morphology is determined by the amount of interlayer mass transport from higher to lower layer levels. 2D layer growth prevails for practically unhindered interlayer mass transport, while multilayer or 3D growth dominates where mass transport is strongly hindered or even absent. Different processes and kinetic effects determining this interlayer transport are discussed, in particular the effect of modifications in the adatom potential at island or step edges. Only for deposition at or annealing to higher temperatures the film morphologies resemble those expected from the thermodynamically controlled growth modes. In agreement with expectations layer‐by‐layer growth is found for homoepitaxial growth, layer‐plus island growth with one or two layers critical thickness, respectively, for the hetero‐epitaxial growth systems investigated.