Angular resolved photoelectron spectroscopy of copper

The authors use plane polarised light at normal incidence in the spectral range up to 21 eV to measure the angular resolved energy distribution functions of photoelectrons emitted from Cu (001) and (111) surfaces. With the plane of detection parallel to a mirror plane of the crystal, the authors observe drastically different spectra for the planes of polarisation parallel and perpendicular to this mirror plane. Using this polarisation dependence, which is caused by optical selection rules, they are able to discriminate the various initial states of the 3d and the sp bands according to their parity with respect to the mirror reflection. The strong intensity variation of the observed peaks is caused by a correspondingly strong k dependence of the dipole matrix element. In addition to the intense zero-order structure, weaker features caused by surface umklapp are also identified.