EXCITED-STATE BANDS OF CU DETERMINED BY VLEED BAND FITTING AND THEIR IMPLICATIONS FOR PHOTOEMISSION

We derive the excited-state bands of Cu above the vacuum level along t he Gamma X and Gamma L lines, utilizing very-low-energy electron diffr action (VLEED) experimental data from the (100) and (111) surfaces, re spectively. This is done by a band-fitting technique, based oil empiri cal pseudopotential calculations of the excited-state bands and the co rresponding reflectivity R(E). The calculations are iterated until a g ood fit is obtained between calculated and experimental energies of dR /dE extrema, each of which corresponds to a band irregularity point. W e analyze how the excited-state bands are connected with VLEED and pho toemission, and introduce a partial transmission (PT) to characterize the coupling properties of each band: If the absorption V-i is small, the current adsorbed in the, crystal from an incident-beam-excited Blo ch wave in VLEED, or the photocurrent from a photoexcited final-state Bloch wale, are both proportional to the PT of the Bloch wave. The exc ited-state bands, obtained from VLEED band fitting, ire found to devia te from free-electron bands notably enough to influence photoemission spectra. In particular, along Gamma X we identify two different bands, which constitute final states in the photoemission from the (100) sur face. As similar effects are far more prominent for nonmetals, we cond uce that determination of the upper bands by VLEED is essential for ac curate photoemission band mapping.