Alloying of Co ultrathin films on Pt(111) with Ag buffer layers

The structure at the interfaces of Co/Ag/Pt(111) was studied by low-energy electron diffraction, ultraviolet photoelectron spectroscopy, Auger electron spectroscopy, and depth profiling. An atomic exchange occurs between Co and Ag before the formation of a Co-Pt alloy. Ag atoms start moving to the top at 425 K when the coverage of Co is one monolayer. The temperature of the complete exchange between Ag atoms and Co atoms is dependent on the thickness of the Ag buffer layer. The Co-Pt alloy develops after the atomic exchange is complete. The especially small surface free energy of Ag and large strain energy in this system are proposed as the driving force for the exchange.