Growth of atomically flat ultra-thin Ag films on Si surfaces

A two-step growth with deposition at low temperature and subsequent slow annealing to room temperature (RT) has been widely used to obtain atomically flat metal thin films on semiconductor substrates. In the case of Ag films, almost atomically flat films were obtained at a thickness of six monolayers (ML) on Si and GaAs. The flatness then gradually degraded with an increase in thickness. The existence of the critical thickness has been well explained by the “electronic growth theory”, which considers thickness-dependent change of vertically quantized electrons and their spilling out at the interfaces. However, several questions remain unanswered. How does the electronically grown Ag flat film accommodate the large misfit energy between the film and substrate? Up to what deposition temperature is the two-step growth effective to obtain atomically flat films? In this article, we review previous studies on the electronic growth of Ag films on Si(1 1 1) substrates, paying special attention to these two points. In addition, we also discuss the possibility of engineering electronic growth for artificial control of the critical thickness.