Studies of separate adsorption and coadsorption of Cs andO2on Cu(100)

Abstract

The adsorption of Cs, ${\mathrm{O}}_{2}$, and their coadsorption on Cu(100) surfaces has been studied with LEED, AES, and work-function measurements in UHV. The work function during Cs deposition on clean Cu(100) shows a minimum, ${\ensuremath{\varphi}}_{min}=1.65$ eV at ${\ensuremath{\theta}}_{\mathrm{Cs}}=0.135$ and a subsequent ${\ensuremath{\varphi}}_{max}=2.07$ eV at ${\ensuremath{\theta}}_{\mathrm{Cs}}=0.27$, which corresponds to a hexagonal close-packed structure of Cs. Preadsorption of oxygen on Cu(100) causes both ${\ensuremath{\varphi}}_{min}$ and ${\ensuremath{\varphi}}_{max}$ to decrease and shift to longer time of Cs deposition. The presence of oxygen on Cu(100) causes disordering of the Cs layer and increases substantially the amount of Cs that can be deposited on the surface. Adsorption of oxygen on Cu(100) is indicated to be an activated process which prevents the growth of oxide at low temperature and pressure. The presence of Cs increases drastically the sticking coefficient and the maximum amount of subsequently adsorbed oxygen. The adsorption of ${\mathrm{O}}_{2}$ on cesiated Cu(100) is controlled by the Cs overlayer and is almost independent of the substrate. Independent of the sequence of Cs and ${\mathrm{O}}_{2}$ deposition, ${\mathrm{O}}_{2}$ is bound directly to the Cu substrate.