Damping Effects in Angular-Resolved Ultraviolet Photoemission Spectroscopy on Cu(111)

Abstract

Previously published photoemission spectra taken at several discrete photon energies from the (111)-surface of copper are analyzed with the purpose of extracting information on the broadening effects involved. In the low energy case (6.40 eV) the effect of surface disorder on the spectral shape of a surface state is explained as the result of a reduced coherence length parallel to the surface, while sensitivity to disorder normal to the surface is the prevailing effect for the bulk transition of the same spectrum. The use of angular instead of frequency tuning is proposed as a feasible alternative to extract electronic lifetimes in favourable cases. Numerical values of inverse lifetimes are derived and found to agree well with the trend in recent measurements of energy dependent inverse lifetimes. Finally, accounting for our instrumental broadening, the residual K ||-dependent width of a dispersive peak is compared with values predicted from the band structure of copper and published lifetimes measured in normal emission. Inhomogeneous damping is proposed as a possible explanation of a deviation seen from the calculated widths as the final state crosses a Brillouin zone boundary.