Cs and Q2adsorption, Cs+O2co-adsorption on Mo(110): anomalous behaviour of electronic surface states studied by ARUPS using synchrotron radiation

Abstract

Adsorption of caesium and oxygen and co-adsorption of oxygen and caesium on the Mo(110) surface are studied at room temperature by Angle Resolved Ultraviolet Photoemission Spectroscopy (ARUPS) using synchrotron radiation. Similar to the high-lying surface state of the Mo(100) surface, the sharp peak observed for Mo(110) at normal emission angle 1.15 eV below the Fermi energy, is markedly attenuated by caesium adsorption and shifted by 0./55 eV to higher binding energies. In contrast, adsorption of oxygen on the Mo(110) surface does not affect the energy and linewidth of this peak even at oxygen exposures up to 8 L (corresponding to about 0.7 monolayer of oxygen). This behaviour provides evidence that on Mo(110), oxygen is bonded differently than on Mo(100). As in the case of Cs/Mo(100) a covalent bonding between Cs(6s) and Mo(d) states is assumed. Co-adsorption of oxygen on to a Cs-covered Mo(110) surface is observed to restore the initial energy of the peak at 1.15 eV.