Acta Phys. -Chim. Sin. ›› 1987, Vol. 3 ›› Issue (05): 514-519.doi: 10.3866/PKU.WHXB19870513

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Deng Jingfa; Bao Xinhe   

  1. Department of Chemistry; Fudan University; Shanghai
  • Received:1986-05-02 Revised:1987-03-31 Published:1987-10-15

Abstract: The adsorption and desoption of oxygen on Ag and Ag-Pd alloy surfaces have been investigated by AES, TDS and by the continuous measurement of work func- tion change. Two kinds of different adsorbed bonding configurations have been revealed: The adsorbed atomic oxygen increases the surface work function, which is due to the transfer of electron from metal to adsorbate, forming the O_(ads)~(-δ) species. For the saturated surface of Ag and Ag-Pd alloy the dipole moment per adsorbed oxygen is 0.24 and 0.34 Debye respectively. The adsorption of molecular oxygen leads to a decrease of work function, which can be explained with the electron feedback from the metal surfaces to molecular oxygen species. Work function change as a function of the exposure of oxygen was also obtained. From these data an approximate experimental sticking coefficient has been derived by using the expression: S=K·P~(-1)·dΔφ/dt. It is shown that the sticking coefficient of oxygen on Ag-Pd alloy surface is slightly less than that on Ag surface, which implies that the alloying of Ag and Pd decreases the surface activity. A continuous change of surface composition for Ag-Pd alloy has been realized by using argon ion bombardment and subsequently annealing. A conclusion has been reached that both the transformation of the surface structure from disorder to order and the surface enrichment of silver during the annealing of alloy result in the decrease of surface work function.