COMPETING PROCESSES AND CONTROLLING ENERGIES AT THE AG/SI(111) INTERFACE

The atomic processes occurring during deposition of Ag onto the Si(111) surface at elevated temperatures have been studied experimentally using UHV-SEM based techniques, including biassed secondary electron imaging and (micro-) Auger electron spectroscopy. Published data are reviewed, and new data are presented on the coverage of the surface layer (with the square-root 3 structure), and on annealing processes on and within this layer. These atomic processes are modelled using rate and diffusion equations. A detailed comparison is made between the experiments and these models, in order to extract the controlling activation energies. Diffusion over the layer is shown to be in competition with evaporation at high, and nucleation of islands at low deposition temperatures. These processes are controlled by energies for adsorption (E(R)), diffusion (E(d)) and pair binding (E(b)); comparison with experiment yields E(n) - 2.45 + 0.03. E(d) = 0.40 +/- 0.05 and E(h) = 0.05 +/- 0.03 eV. The coverage, theta, of the square-root 3 layer is found to be temperature and history dependent (2/3 < 0 < 1 ML), in a way that can be modelled by two extra energies, an "embedding" energy E(c) -0.60 +/- 0.05 eV, and an activation barrier E(t) -1.9 +/- 0.05 eV which must be surmounted by adatoms to complete the theta - 1 layer. These different energies for competing processes mean that the late of Ag adatoms can be very different for different experimental situations. Numerical illustrations are provided and discussed. It is shown that quantitative consideration of these competing processes can resolve some previous controversies about Ag/Si(111), and may be applicable more generally.