Oxidation of lanthanum overlay ers on Cu(111)

The oxidation of ultrathin lanthanum overlayers on Cu(111) has been studied by XPS, ISS, TPD and LEED. At 300 K the deposited La films are readily oxidised by exposure to O2 to give a disordered La2O3 film. This oxide may then be ordered by annealing at over 700 K in vacuum, producing a surface analogous to La2O3(001). Further heating in a low pressure of oxygen induces an irreversible structural transformation to a more complex oxide structure which still exhibits a coincidence relationship with the substrate. All the oxide films are stable to 873 K, after which a gradual reduction in the apparent surface La and O concentrations is observed.