Bistability of Nanoscale Ag Islands on Anisotropic Si(111)-(4x1)-In Surface Stress Template

We present a combined experimental and theoretical study of stability of Ag nanoislands grown on Si(111)-(4x1)-In surface. Experiments show the existence of two stability regimes: a conventional regime at low temperature where only one island shape is stable, and an unconventional regime at room temperature (RT) where isotropic compact islands coexist with anisotropic elongated ones. First-principles calculations show the unusual bistability at RT arises from the fact that the Ag nanoislands are under anisotropic stress, further supported by a continuum model of island shape evolution as a function of island size.