Photoemission from Cu valence bands using 50-175-eV synchrotron radiation

Photoemission spectra of the $3d$ valence band of polycrystalline Cu were studied using synchrotron radiation of energy 50≤hν≤175 eV. The detailed shape of the spectrum was found to change distinctly with photon energy. The observed energy dependence was compared to calculated photoemission energy distributions (PED's) assuming a direct transition model. PED's obtained with this model predicted the experimental intensity distribution quite well for hν<70 eV and hν>120 eV but failed in the region hν≈90 eV. Fair agreement between experiment and theory was obtained when momentum broadening in the final state was included. The largest broadening was required around hν=90 eV. A minimum in the photoelectron mean free path at this energy is discussed as a possible source of broadening. The observed changes in spectral shape for 50≤hν≤70 eV are attributed to direct transitions; the changes are found to arise mainly from the angular part of the transition matrix element.