A study of group 1b metal adsorption on iridium

Abstract Field emission probe hole microscopy has been used to study the changes in work function φ of annealed (100)-oriented iridium tips which are produced by vapour deposition of submonolayer copper, silver and gold in ultrahigh vacuum. The commonly observed bright ring around (100) lowers φ for clean Ir(100) from 6.00 eV to 5.8 eV but has little effect on metal adsorption, φ(100) changing progressively with addition of metal to that expected for (100) of the bulk metal. Measurement of binding energies of copper and silver by thermal desorption confirms the general similarity of the ringed and ring-free surfaces. The three metals differ sharply in their capacity to populate Ir(100). Gold is present on Ir(100) at all coverages, silver at > 10 20 atoms m −2 , and copper at > 4 × 10 19 atoms m −2 . The temperature dependence of copper invasion taken together with changes in the field emission image around (100) suggests a surface reaction with iridum atoms which commences at the plane edge. On the basis of this and other work it is tentatively suggested that the ringed plane has the (5 × 1) superstructure and the ring-free surface the (1 × 1) structure.