Reversible intercalation of TiS2 with potassium imaged by backscattered electrons

The initial stages of in situ intercalation of TiS2(0 0 0 1) with K are investigated by incoherent medium-energy electron diffraction. It is shown that deposition of a few monolayers of K onto the crystal surface leads to spontaneous intercalation of K atoms into the van der Waals gaps, and an associated reconstruction of the near-surface region due to sliding of adjacent S layers relative to each other, which transforms the initial 1T structure of the host material to the 3R(I) structure with trigonal prismatic coordination of the K ions. Another consequence of the process is a considerable expansion of the crystal lattice along the c-axis. Strong evidence is found for a reverse effect of de-intercalation, obtained by adsorption of oxygen on the surface of the intercalated crystal.