Angle-resolved photoemission studies of the band structure of TiSe2and TiS2

The electronic structure of high-quality Ti${\mathrm{Se}}_2$ and Ti${\mathrm{S}}_2$ crystals has been investigated using angle-resolved photoemission with HeI, HeII, and NeI resonance radiation. Results compare well with recent self-consistent energy-band calculations although differences occur which may be due to the three- rather than two-dimensional nature of specific bands. Occupied $d$ states at the zone edge are observed in both materials. A small overlap with the $\frac{s}{p}$ valence band at $\Gamma$ is observed in the case of Ti${\mathrm{Se}}_2$ in approximate agreement with other workers. Ti${\mathrm{S}}_2$ appears to be a defect semiconductor with a band gap of 0.3 ± 0.2 eV.