Direct transition and matrix element effects in the ultraviolet- photoemission-spectroscopy spectra of Cu-Ni (110)

We report angle-integrated ultraviolet-photoemission-spectroscopy (UPS) studies of Cu-Ni (110) in the photon energy range 9 to 23 eV. Two surfaces of a single sample, with bulk atomic composition of 90-at.% and 10-at.% Cu, were studied. One surface was Cu rich 65-at.% Cu), the other Ni rich (60-at.% Ni). We observed both matrix-element and direct-transition effects in the spectra. Thus, even though the photoemission spectra reflect the general features of the density of states, a detailed theoretical calculation of spectra of even random alloys must include such effects. In addition, the theory must also take into account the compositional gradient of the alloy in the surface region and the sampling depth of the UPS measurements. For comparison, we show some data obtained from pure Cu. © 1980 The American Physical Society.