Momentum microscopy of the layered semiconductor TiS2 and Ni intercalated Ni1/3TiS2

The detailed electronic structure of a layered semiconductor 1T-TiS2 and its modification in Ni-intercalated Ni1/3TiS2 were studied beyond the full surface Brillouin zone by use of a momentum microscope and He-I light source on their in-situ cleaved surfaces. Clear dispersions associated with the electron Fermi surface (FS) pockets induced by the self-intercalated Ti in non-doped 1T-TiS2 around theMpoints, as well as the hole FS pocket induced by the surface Ni in Ni1/3TiS2 around the G point, were confirmed in the observed high-resolution E-B(k(x), k(y)) band cross sections. A bird's eye view of the two-dimensional band dispersions E-B(k(x), k(y)) clarified many complex band dispersions. The experimental results are compared with first-principles band calculations performed for the bulk as well as the one monolayer (ML)-TiS2 and surface-1ML-Ni1/3TiS2. The characteristic changes of the band dispersions near the Fermi level (E-F) are ascribed to the contribution of the 3d states of the surface Ni atoms with the C-3v symmetry in contrast to the 'D-3d' symmetry of the intercalated Ni. The importance of experimental studies of band dispersions in the full Brillouin zone is demonstrated, showing the high potential of momentum microscopy.