Surface Diffusion and Nucleation Processes in Thin Film Formation: The Case of Ag/Si(111)

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Abstract
Surface diffusion and crystal growth processes have been studied in the Stranski-Krastanov growth system Ag/Si(111), using several UHV-SEM techniques. By depositing Ag at various rates 0.2 ≤ R ≤ 1.4 ML-min−1 through a mask of holes, surface diffusion of Ag over the intermediate layer has been observed, in competition with re-evaporation at high, and nucleation at low substrate temperatures, in the range 620 < T < 850K. The Si(111) √3Ag intermediate layer has been visualized using biassed secondary electron imaging. The surface diffusion and nucleation processes observed have been analyzed in terms of kinetic models. Comparison with experiment yields values for the adsorption, diffusion and binding (Ea′ Ed and Eb) energies of Ag on the intermediate layer. These values are approximately Ea = 2.45 ± 0.1 eV, Ed 0.35 ± 0.05 eV and Eb = 0.10 ± 0.03 eV, where the uncertainties result at least as much from lack of knowledge of pre-exponential factors in the models as in the accuracy of the experiments.