PHOTOEMISSION BY SCREENED PHOTON FIELDS FROM LAYERED SOLIDS

As an example for the layered dichalcogenides the photon screening in photoemission is investigated for TiS2. The normal emission spectra ar e computed within the one-step model. The calculation of the initial a nd final states of the photoemission process as well as the integratio n of the matrix elements follow conventional three-dimensional methods . However, the vector potential entering the matrix elements usually i n the dipole approximation, is obtained here from a surface response t reatment within a one-dimensional model of crystallinity. The influenc es of the induced surface-near field and the induced local fields in t he bulk are considered separately. The evaluation shows that the bulk crystallinity can lead to a pronounced screening effect in the shape o f the spectra. In addition, the bulk local fields dominate the surface induced field. In contrast to a jellium metal, the latter yields only a faint resonance in the spectra of these materials below the plasmon frequency.