Non-monotonic changes in conductance of Bi(111) films induced by Cs adsorption

Abstract

Effects of Cs adsorption on the conductance of Bi(111) films were studied using scanning tunneling microscopy (spectroscopy) observations and in situ transport measurements at low temperatures. Based on the obtained results and the known data on the Bi(111) electronic band structure, Cs-induced modifications of the band structure were shown to control the changes in the Bi(111) film conductance. Adsorbed Cs atoms donate electrons to Bi(111), causing the shifting of the system Fermi level upward along the energy scale. Due to the peculiarities of the Bi(111) band structure, the density of states at the Fermi level, which is directly related to the carrier density, varies non-monotonically with shifting of the Fermi level. Conductance changes in the same way with Cs coverage, namely, decreases almost twice at 0.011 ML of Cs, restores to the initial value at 0.025 ML of Cs, and grows gradually up to 0.167 ML; the maximal coverage when adsorbed Cs remains an assembly of the individual adatoms. Thus, Cs adsorption shows up as an effective tool to tune the electronic and transport properties of the Bi(111) films. The results also prove an effective surface characteristic of the electron transport in the Bi films.