Adsorption of oxygen on clean and barium covered copper surfaces: an XPS, UPS and AES study

Abstract

XPS studies of oxygen on barium covered copper surface show two types of dissociatively chemisorbed species, viz. O^x- (529.5 eV) and O^y- (531.6 eV) (x) < y < 2). This is supported by He II spectra which show two peaks at 6 and 9.2 eV below E_F. While dissociatively chemisorbed oxygen on clean copper seen at 530 eV is strongly held even up to 700 K, the oxygen on barium covered surface starts desorbing at 450 K. The surface stoichiometry of oxygen to barium has been estimated both as functions of barium coverage and of temperature for a given barium concentration. The Cu(L₃VV)/Cu(L₃M₂₃M₂₃) Auger ratio technique has been employed to show charge transfer from barium to copper on the barium covered surface and from copper to oxygen on subsequent oxygen adsorption.