CONDUCTION-ELECTRON SCREENING AND SURFACE-PROPERTIES OF CS METAL

In Cs 5p core-electron photoemission spectra obtained with He resonance radiation, the response from the first atomic layer is well resolved and shifted 228 meV from the bulk line at 11.79 eV. The singularity index of the conduction-electron screening response is 0.18, i.e., comparable to the values close to 0.20 obtained for the other alkali metals. In contrast, the edge exponent of the Cs 5p absorption edge is only 1/6 that of the Na 2p edge and is incompatible with the phase shifts deduced from the Cs singularity index. This result sharpens a long-standing problem regarding the interpretation of the emission and absorption edges.