Modifying the electronic structure of TiS2by alkali metal intercalation

Angle-resolved photoelectron spectroscopy has been used to study in situ intercalation of the layered compound TiS 2 with Na and Cs. The intercalation was verified by core-level spectroscopy. The valence bands of pure TiS 2 and the intercalated compounds Na x TiS 2 and Cs x TiS 2 were characterized and compared to self-consistent LAPW band-structure calculations. Remarkable agreement between experimental and calculated bands was found for the dispersion along the layers. The calculations predicted perpendicular dispersion also for the intercalation compounds, although significantly reduced. No significant perpendicular dispersion was seen in normal-emission spectra, which might be an effect of intercalation-induced stacking disorder. Charge transfer to the TiS 2 host layers was evident from the much increased conduction band emission, and from the asymmetric S 2p core-level lineshape after intercalation. The intercalation produced electronic structure changes which are not well described by the rigid-band model, but as these changes occur at an early stage, the model can still be used, with modified bands, to describe the continued intercalation.