NEAR-THRESHOLD ENHANCEMENT IN PHOTOEMISSION FROM ALKALI-METAL OVERLAYERS

The total surface photoabsorption and the emitted part of it are calcu lated for thin Cs layers adsorbed on a semi-infinite metallic substrat e. The jellium model is used to evaluate the electronic properties of this system and the dynamical response is treated within the time-depe ndent density functional approach. It is shown that the self-consisten tly screened electronic excitations lead to an enhancement of the p-po larized emission current in the vicinity of the threshold. Photoemissi on measurements for Cs overlayers on Ag are carried out at various cov erages. These spectra indeed show a striking increase of the p-polariz ed intensity within about 1 eV above threshold.