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

Abstract

We systematically studied coverage ( θ Ag)- 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 θ Ag < ∼6 ML. At θ Ag ∼ 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 θ Ag > ∼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 θ Ag. The unusual preference for the formation of an atomically flat and perfectly wetting Ag film of θ Ag = 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 θ Ag = 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.