Scanning tunneling microscopy of oxygen-induced two-state oscillators on Si(111)-7×7

We investigate a novel molecular oscillator that exhibits switching motion at room temperature and above. Scanning tunneling microscopy images show that the structure, produced by dosing oxygen onto a clean Si(111)-7×7, switches between two states expressed by a triad of center adatoms that operate as a stationery site and two alternating hopping sites within a single half-unit cell. Bias-dependent analysis indicates stationery and alternating sites are chemically distinct from each other. The occasional decomposition of the structure shows that it consists of metastable species, whose decay produces typical oxygen-induced chemisorbed states in the aftermath. The origin of such metastable, switching structures is attributed to the strong intermolecular interaction within the triad and with its neighboring sites. Copyright © 2011 John Wiley & Sons, Ltd.