Adsorbate enhanced Ti-3d photoemission from layered TiSe2 surfaces

Angle resolved photoelectron spectra of 1T-TiSe₂ single crystals $\text{(}\text{h}\text{?}\text{ω = 21.2}\text{eV}\text{)}$ have been investigated as a function of exposure to H₂O, CO, N₂ and O₂ at room temperature. A significant enhancement of the Ti-3d emission near the Fermi energy E_F is observed for H₂O and CO exposures of several kL. As compared to the clean surface this emission extends over the entire Brillouin zone. The results indicate that by H₂O and CO adsorption the lowest d-subband is pulled below E_F possibly by local band bending. Additional relaxation effects at the surface associated with changes in d-band matrix elements may occur. The intensity of the Se-4p derived valence band emission down to 7 eV below E_F remains essentially unchanged.