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

Nucleation, growth and surface diffusion at the Ag/Ge(111) interface have been modelled using kinetic rate and diffusion equations. Characteristic energies on surface layers (with the root 3 and 4 x 4 structure) are estimated by comparison of the model with UHV-SEM based experiments; the results are compared with previous studies of Ag/Si(111). The energies for adsorption (E(a)), binding (E(b)) and diffusion (E(d)) processes on top of the root 3 layers of both systems are very similar, with (E(d) + 3E(b)) in the range 0.55-0.60 +/- 0.05 eV; on Ag/Ge(111) root 3, the difference between the bulk Ag sublimation (L) and (E(a) - E(d)) is 0.65 +/- 0.05 eV, which leads to rapid annealing above room temperature, whereas the value for Ag/Si(111) the value is some 0.25 eV higher. Rapid diffusion over the 4 x 4 layer is due to the corresponding energy (L(3) - E(a4) + E(d4)) = 0.85 +/- 0.05 eV, where L(3) is the sublimation energy of the root 3 layer, and the other parameters refer to the 4 x 4. The results show strong preference for the coverage of the 4 x 4 layer being larger than 0.25 ML. and for the root 3 layer being only marginally more stable than the Ag islands.