Competing processes and controlling energies at the Ag/Si(111) interface

• Published in: Surface science 1992-01, Vol.261 (1), p.251-266
• Main Authors: Raynerd, G., Doust, T.N., Venables, J.A.
• Format: Article
• Language: English
• Subjects: Applied sciences; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Metals. Metallurgy; Physics; Solid surfaces and solid-solid interfaces; Surface and interface dynamics and vibrations; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Thin film structure and morphology
• ISSN: 0039-6028; 1879-2758
• DOI: 10.1016/0039-6028(92)90237-Z

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 √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 a), diffusion ( E d) and pair-binding ( E b); comparison with experiment yields E a = 2.45 ± 0.05, Ed = 0.40 ± 0.05 and E b = 0.05 ∓ 0.03 eV. The coverage,θ, of the √3 layer is found to be temperature and history dependent ( 2 3 < θ < 1 ML) , in a way that can be modelled by two extra energies, an “embedding” energy E e = 0.60 ± 0.05 eV, and an activation barrier E r = 1.9 ± 0.05 eV which must be surmounted by adatoms to complete the θ = 1 layer. These different energies for competing processes mean that the fate 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.