AN STM STUDY OF THE INITIAL-STAGES OF OXIDATION OF NI3AL(110)

The initial stages of oxygen adsorption on Ni3Al(110) at 9700 K have b een studied by scanning tunneling microscopy (STM) and low energy elec tron diffraction (LEED). We report the observation of two different re constructed surface phases. First, on the well-ordered surface, after exposure to O-2 at 970 K for doses < 5L, a saturation coverage (1/4 ML ) of Ni3Al{110} c(2 x 2)-O is observed. Secondly, we report an oxygen- induced reconstruction which is incommensurate with the substrate, res ulting after an incomplete annealing of the suface following Ar+ bomba rdment. A structure model for this phase is proposed.