Adsorbate-induced surface resonances on tungsten at energies above the vacuum level

Abstract In angle-resolved secondary electron emission normal to a W(110) surface, spectral structure, due to adsorbate-induced (i.e. “extrinsic”) surface resonances lying above the vacuum level, is resolved when the energy of the emitted electron corresponds to a gap in the energy bands of the substrate. Results are presented for ordered monolayers of O 2 and CO. The adsorbate resonances are interpreted in terms of excited two-dimensional Bloch states produced by the lattice periodicity of the adsorbate.