Displacive Phase Transition and Surface-Phonon Anomalies in fcc fe Films on Cu(100)

A reversible structural transition from (1 ×{} 1) to (2 ×{} 1) is observed for 2-monolayer (ML) Fe films deposited on Cu(100) when the substrate is cooled to temperatures below 300 K. The disperson of the Rayleigh wave displays a pronounced anomaly indicative of a repulsive stress in the Fe film. The phase transition for the 2-ML system, irreversible order-disorder transitions for the 4- and 5-ML systems, and the termination of the epitaxial layer-by-layer growth beyond 5 ML may be understood in terms of the repulsive stress between the Fe atoms.