Quantum size effects in quasi-free-standing Pb layers

Quantum well states in thin metal films are strongly influenced by the electronic and geometric structure of the underlying substrate. This impedes a comparison to ab initio calculations generally based on free-standing films. Here we show that Pb films deposited on single-crystalline, epitaxial graphite are an excellent approximation to free-standing metal films. We find Pb islands of four monolayer height to be most stable, followed by other even-numbered islands, in excellent agreement with theoretical predictions for the formation of preferred island heights.