LOW-TEMPERATURE ADSORPTION OF CS ON LAYERED TIS2 STUDIED BY PHOTOELECTRON-SPECTROSCOPY

The adsorption of Cs on a TiS2 cleavage plane at 110 K was studied by core level and valence band photoelectron spectroscopy, using synchrot ron radiation. The Cs 4d core level spectra, together with LEED observ ations, reveal that the Cs at low coverage forms a disordered phase on the surface, but condenses to form ordered islands as the coverage is increased. A small amount of Cs was seen to intercalate even at 110 K . As the sample was allowed to warm up, the ordered Cs phase melted to form a disordered phase again, although with the binding energy being different from the disordered low-temperature phase. At this stage th e intercalation process accelerated, and before reaching room temperat ure most of the Cs had intercalated. The S 2p and Ti 3p core level spe ctra exhibits shifts and broadenings, and the valence band spectra pro vide clear evidence for charge transfer from both adsorbed and interca lated Cs to the host layers. (C) 1997 Elsevier Science B.V.