Room-Temperature Atomic Structure and Lattice Instability of In Nanowires on Si(111)

Abstract

One-dimensional indium chains on Si(111) exhibit both temperature-and defect-induced perioddoubling (x2) structural transitions, and their natures have been focus of recent investigations. Using density functional perturbation theory calculations, we examined the vibrational properties of the room-temperature Si(111)In-4x1 structure. The phonon band structure revealed two unstable modes at the zone-boundary in the chain direction, which lead to a lattice instability towards a structure with parallel trimers. This lattice-instability-driven 4 x 2 structure is different from the low-temperature 4x2 (LT-4x2) structure (hexagon structure). The result suggests that the roomtemperature phase is neither a static 4x1 phase nor the dynamical fluctuation of the LT-4x2 phase. We demonstrate that the room-temperature phase is a dynamically fluctuating parallel-trimer 4x2 phase, and the fluctuations become suppressed near the defects to result in the defect-induced x2 structure.