ADSORBATE-INDUCED ENHANCEMENT OF SECONDARY-ELECTRON EMISSION FROM THELAYERED COMPOUND VSE2

It is demonstrated how adsorbates may drastically enhance the photoemi ssion yield at low kinetic energies from VSe2 surfaces. The reason for this enhancement seems to be that the adsorbate by reducing the work function phi creates a condition closely resembling negative electron affinity (NEA), i.e. the vacuum level is pulled down into an absolute band-gap. In contrast to true NEA systems, there are empty states (pre dominantly of V3d character) available below the vacuum level, but due to low probability for scattering into these states, the NEA-like beh aviour prevails. Since the involved band n-minimum is located close to the K symmetry point of the Brillouin zone, adsorbate induced diffuse scattering is vital to the observed enhancement.