Observation and Origin of Extraordinary Atomic Mobility at Metal-Semiconductor Interfaces at Low Temperatures.

Extraordinarily high mobility of Si and Ge atoms at semiconductor (Si, Ge)-metal (Al) interfaces is observed at temperatures as low as 80 K during thin metal film deposition. In situ x-ray photoemission spectroscopic valence-band measurements reveal a changed chemical bonding nature of the semiconductor atoms, from localized covalentlike to delocalized metalliclike, at the interface with the Al metal. The resulting delocalized bonding nature of the interfacial semiconductor atoms brings about the observed extreme enhancement of their mobility. The finding opens avenues for tailoring reaction kinetics and phase transformations in nanostructured materials, as functional thin-film systems, at ultralow temperatures by dedicated interfacial design.