The two-dimensional growth of Au on Ru(0001) in the submonolayer range has been investigated with scanning tunneling microscopy. Upon deposition at room temperature, highly dendritic islands of one layer thickness grow on large Ru terraces. These irregular island shapes are removed upon annealing to 650 K. The dendritic islands exhibit a fractal character, and a dimensional analysis yields a fractal dimension of 1.72 ±0.07. The results are in quantitative agreement with a two-dimensional diffusion-limited-aggregation growth mechanism.

The nucleation and growth of several metal/metal thin film systems have been studied and compared using scanning tunneling microscopy (STM). Homogeneous and heterogeneous nucleation have been observed and the effect of surface inhomogeneities on the nucleation behavior has been studied. Systematic measurements of the film morphology as a function of coverage and annealing temperature have allowed different two- and three-dimensional growth mechanisms to be studied. Both kinetic and thermodynamic factors are found to determine these growth processes and in some cases could be separately identified. In addition, the effect of chemically modifying the substrate by oxygen preadsorption has been studied and compared to the clean substrate systems. A variety of changes in the growth behavior were found to occur, which can be understood in terms of changes in both the kinetics and thermodynamics due to the oxygen adlayer.

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Crystal Growth I Metals I Nonequilibrium Phenomena I Nucleation I SurfacesMicroscopic 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 heteroepitaxial growth systems investigated.