Photoemission from Surface State of W(100): Evidence forp→·A→Mode of Photoionization

The surface resonance peak is a prominent feature in the photoelectron spectrum of the clean W(100) surface when $hv=16.8\mathrm{}$ eV, but is not observed when $hv=26.9\mathrm{}$ eV. This indicates that the intensity of this peak is critically dependent upon the $\overrightarrow{\mathrm{p}}·\overrightarrow{\mathrm{A}}$ matrix element, which should be large for photon energies below the tungsten plasmon energy of 23 eV, but small for photon energies above it. The consequences of this on the nature of the surface resonance are discussed.