Shockley surface state on [alpha]-brass(111) and its response to oxygen adsorption

Angle-resolved photoelectron spectroscopy has been applied to investigate the Shockley-type surface state on the (111) surface of [alpha]-brass, a Cu-Zn alloy with a face-centered cubic structure. An energy position and an effective mass of the Shockley-state band are determined, respectively, to be 0.51 eV and 0.52m sub(e) with m sub(e) being the rest mass of an electron. A decay length of the Shockley-state wave function into the bulk is also estimated to be 0.43 nm. These parameters are compared with those of the Shockley state on Cu(111), and it is concluded that the Cu sp orbitals in [alpha]-brass have a more isolated nature than those in Cu. Also examined in this study is the response of the Shockley state to oxygen adsorption. The behavior of the Shockley state upon oxygen adsorption strongly depends on the substrate temperature. At room temperature, the Shockley state is quenched along with the binding-energy shift towards the Fermi level. Contrastingly, oxygen adsorption at low temperatures ([< or =] 180 K) hardly affects the energy position of the Shockley state. The conversion of the surface oxidation process at a certain temperature between 180 K and room temperature is proposed.