Growth, stability and morphology evolution of Pb films on Si(1Â 1Â 1) prepared at low temperature

Room temperature morphology evolution of Pb thin films, prepared on the Si(1 1 1)-7 × 7 substrate at a low temperature (145 K), is investigated by reflection high energy electron diffraction, scanning tunnelling microscopy and angle-resolved photoemission spectroscopy. A critical thickness of 10 monolayers (ML) is identified, below which all the flat films formed at low temperature are unstable against evolution into interconnected islands at room temperature. From 10 ML to 21 ML, Pb films become stable at room temperature and grow via a bi-layer mode. Above 21 ML, the film growth turns into a layer-by-layer mode. A “beating effect” is observed to modulate this special growth mode, which changes the film stability from even (odd) layers to odd (even) layers with a 9 ML period. Morphology and electronic structure analysis show that the quantum size effect is responsible for the different morphology evolution behaviour and the magic stability of Pb films.