Electronic structure investigation of the Ag(1 1 0)(n×1)O surfaces––new photoemission results for an old problem

We have used angle-resolved photoelectron spectroscopy to investigate the occupied antibonding electron states of the Ag(1 1 0)(n×1)O surface along different directions in the surface Brillouin zone. We present experimental evidence that several earlier results obtained along Γ–Y (along the Ag–O chains) contain admixtures from contamination, most probably from carbonate-like contributions. New results are obtained along Γ–X and Γ–S (perpendicular to the chains). These data indicate that the n=2 structure is stabilized by repulsive electronic interaction between neighbouring chains, which diminishes drastically for n=3 and disappears almost completely at n⩾4. This observation points to a strain field within the substrate which stabilizes the geometry between n=3 (interchain distance 8.7 Å) and n=8 (23.1 Å). Its existence is indirectly seen in the n-dependence of the surface phonon energies at Γ, which can be explained quantitatively by umklapp-processes induced by the lateral periodicity of the strain field. We compare our photoemission results for (2 × 1)O with available surface band structure calculations.