THE INTERACTION OF OXYGEN WITH A RHODIUM (110) SURFACE

We have studied the interaction of oxygen with a Rh(110) surface between 270 and 1300 K by means of Video-LEED, thermal desorption spectroscopy (TDS) and work function change measurements. We find the successive formation of at least six ordered oxygen phases, among others (non-primitive) 2 × 3 and c(2 × n) phases (n = 6, 8, 10) corresponding to coverages between 0.16 and 0.9 monolayers. The TD spectra reveal six different oxygen binding states (β0-β5) having temperature maxima at 1150 (β5), 1095 (β4), 909 (β3), 835 (β2), 797 (β1) and 780 K (β0). They are reversibly populated and closely correlated with the oxygen LEED phases. The work function exhibits a strong initial increase until β3 is filled; thereafter, β2-β0 contribute only little to the overall observed Δ of + 790 meV. The initial sticking probability is quite high (s0 ≈ 0.95); adsorption into and desorption from the highest oxygen state follows second-order kinetics indicative of dissociative adsorption and recombinative desorption, respectively. The desorption kinetics provides some evidence of minor diffusion of O into the bulk which may lead to a gradual accumulation of subsurface oxygen which in turn influences particularly the β5 state. We have developed structure models for the oxygen phases on the basis of LEED and TDS results. © 1990 Pergamon Press plc.