Influence of quantum well states on the formation of Au-Pb alloy in ultra-thin Pb films

The thickness dependence of Au-Pb alloy formation on Pb quantum films is studied via in-situ low-temperature scanning tunneling microscopy/spectroscopy (STM/S). 2D islands with moiré pattern are observed on top of Pb films when sub-monolayer Au is deposited onto Pb films at a substrate temperature of 90 K. After annealing at up to 250 K, various types of 2D islands, including Au-Pb alloys, are formed and show very different electronic structures. A detailed STS study suggests that the formation of these islands is directly related to the quantum well states (QWS) of Pb films, indicating quantum size effects (QSE) on the formation of Au-Pb alloys.