ANGLE-RESOLVED PHOTOEMISSION FROM CU(001) - LINE WIDTHS AT HIGHEST ANGULAR RESOLUTION

A detailed experimental study of the effect of angular resolution on the line widths of transitions from Cu(001) is presented. We find a dramatic narrowing of the direct transition lines from the volume sp band when reducing the angular acceptance cone much below 1-degrees to an ultimate value of a few tenths of a degree. This effect occurs for transitions located in the 2nd Brillouin zone (BZ) and for the d band surface state near the MBAR point of the surface BZ, whereas such a strong effect is not observed for transitions from sp bands in the first BZ. In the 2nd BZ we obtain widths of 0.25eV as close as 1.0eV from the Fermi edge, while previously published widths for transitions from the 1st BZ are of the order of 0.7eV or more for the Cu sp transitions. We find a more or less linear increase of line width as the Fermi level is approached.