PHOTOEMISSION LINEWIDTH STUDIES OF D-LIKE TAMM STATES AT THE CU(100) AND CU(100) AU ALLOY SURFACES/

We report a high-resolution study of the well-known Tamm surface state existing on Cu(100) around the (M) over bar point of the surface Bril louin zone. From temperature-dependent spectra its intrinsic width (fu ll width at half maximum) is extrapolated to be <13 meV at T-->0. Spec ial attention is given to the linewidth during formation of the Cu(100 )/Au surface alloy at room temperature, when going from clean Cu(100) to the fully developed Cu(100)-c(2x2)Au alloy surface. The observed in itial increase in linewidth (coverages less than or equal to 0.3 ML) i s explained by scattering due to the statistically distributed Au-''de fects'' incorporated in the surface layer. Al coverages between 0.3 an d 0.5 ML additional umklapp processes are induced by surface reciproca l lattice vectors supplied by the c(2x2) geometry. These umklapps may scatter the photohole to regions where no projected bulk band gaps exi st, which results in additional decay channels into bulk states and a correspondingly shortened hole-lifetime. (C) 1997 Elsevier Science B.V .