Ohmic losses in valence-band photoemission experiments

Photoemission experiments involve the motion of an electron near a conducting surface. This necessarily generates heat by ohmic losses from eddy currents. This inelastic scattering of the electrons will result in a downward shift in observed spectra. This effect is most pronounced in poorly conducting metals: in good metals the electron's field is screened out of the material, while insulators are by definition unable to absorb electromagnetic energy at low frequencies. We give a classification of photoemission processes which shows that the affect is an extrinsic process distinct from final state effects. The shift is illustrated by a model system with a Drude-like conductivity function and a temperature-dependent relaxation time. We give a brief experimental survey of systems in which the ohmic losses may be significant, without making definitive claims about any one of them. (C) 2001 Elsevier Science B.V. All rights reserved.