Reversible intercalation of TiS2 with potassium imaged by backscattered electrons

The initial stages of in situ intercalation of TiS2(0001) with K are invest igated by incoherent medium-energy electron diffraction. It is shown that d eposition of a few monolayers of K onto the crystal surface leads to sponta neous intercalation of K atoms into the van der Waals gaps, and an associat ed reconstruction of the near-surface region due to sliding of adjacent S l ayers relative to each other, which transforms the initial 1T structure of the host material to the 3R(I) structure with trigonal prismatic coordinati on of the K ions. Another consequence of the process is a considerable expa nsion 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. (C) 2001 Elsevier Science B.V. All rights reserved.