Morphology of ultrathin Ag films grown on Mo(1 1 1)

Ultrathin films of Ag grown on Mo(1 1 1) and vicinal surfaces have been studied using temperature programmed Auger, LEED and thermal desorption spectroscopy. We confirmed that Ag does not induce faceting of Mo(1 1 1) and growth of Ag follows the Stranski–Krastanov mode as reported previously. In addition, we found that (1) on top of the wetting layer; there is a two-dimensional (2-d) gas-like phase in coexistence with the Ag 3-d clusters. The density of this gas increases with temperature and can reach a very high value of about 0.8 monolayer at 900 K. (2) 2-d films deposited at 120 K show an anomalous coverage dependent stability against 3-d cluster formation. (3) If the total coverage is not more than 0.3 monolayer above the wetting layer, the film deposited at low temperature is unstable and 3-d clusters readily form when annealed around 450 K. However, once annealed to 750 K, the 3-d clusters fully re-spread and the 2-d film formed is trapped in a supersaturated state, i.e. although its coverage is larger than the wetting layer, cluster formation no longer occurs whatever way we anneal it. Auger and LEED evidences suggest that films annealed above 600 K undergo interface confined mixing of Ag and Mo. (4) On the vicinal surface we studied, although nucleation of 3-d clusters can occur at a temperature 50 K lower than that on the singular surface, the density of the 2-d gas-like phase on the vicinal surface is basically the same as on the singular surface.