Thickness- and deposition temperature-dependent morphological change in electronic growth of ultra-thin Ag films on Si(1 1 1) substrates

We systematically studied coverage (θAg)- and deposition temperature (T)-dependent change in the surface morphology of ultra-thin Ag films on Si(1 1 1)7 × 7 substrates grown by the two-step process (i.e. by electronic growth). In the deposition at 80 K followed by subsequent annealing to 300 K, scanning tunneling microscope (STM) images indicate that flat-top, dislocation-free Ag islands formed networks at θAg < ∼6 ML. At θAg ∼ 6 ML, the substrate was covered completely by an atomically flat Ag film. However, as the substrate became completely covered, many partial dislocations were introduced in the film. At θAg > ∼6 ML, islands of several layer heights nucleated on the atomically flat top of the islands, increasing its roughness, though the dislocation density decreased with θAg. The unusual preference for the formation of an atomically flat and perfectly wetting Ag film of θAg = 6.4 ML in two-step growth at T = 80 K was degraded with increasing deposition temperature T. Small pin-holes appeared on the Ag film surface at T = 160 K. The pin-holes joined with each other, extending to form continuous large gaps at T > 230 K. The film of θAg = 12.8 ML also showed a similar T-dependence of its morphology. The observed changes in the film morphology were attributed to the competition between the electronic and mechanical energy of the grown films.