Inelastic inverse lifetimes of medium-energy electrons: photoemission analysis of s,p-band direct transitions at Cu(1 0 0) and Cu(1 1 0)

We investigate the inelastic lifetime of electrons in copper at excitation energies Ef between 7 and 20 eV above the Fermi level. High-resolution photoemission experiments allow to determine the inelastic inverse lifetime of final state electrons precisely by measuring the line widths of s,p-band direct transitions. Energy coincidence measurements on Cu(1 0 0) and Cu(1 1 0) show dramatically different line widths which can be quantitatively explained by calculations within the one-step model of photoemission as well as by numerical line shape calculations. Our analysis shows that the distinct line widths on the differently oriented surfaces do not result from lifetime effects but from the influence of the band structure. All observations are in good agreement with a linearly increasing lifetime width Γe=a(Ef−EF), with a=(0.13±0.01) in the energy range mentioned above.