Polarized X-ray absorption spectroscopy and XPS of TiS₃: S K- and Ti L-edge XANES and S and Ti 2p XPS

Sulfur and Ti 2p XPS and polarized S K- and L_2,3- and Ti L _2,3-edge XANES spectra have been obtained from oriented ribbon-like crystals of TiS₃ grown by vapor transport. The S 2p XPS spectrum for (0 0 1) crystal faces has line widths of 0.53 eV and is completely accounted for by partially overlapped 2p_3/2/2p_1/2 doublets for sulfide (S^2-) and disulfide (S22-) species, which are separate and independent entities in TiS₃. Evidence of unsaturated surface states is lacking, consistent with a surface monolayer for the (0 0 1) growth face of disulfide atoms oriented with their charge-neutral sides outward. The S K-edge XANES spectra show pronounced anisotropy in the (0 0 1) plane of TiS₃ crystals, associated with the photoelectron transition channel S 1s→3pxσ*_u with the electric vector (E) parallel the a-axis (and the S-S bond of the disulfide group), and transitions to unoccupied antibonding orbitals of S-Ti bonds with E parallel to the b-axis (the direction of the well-known quasi-one-dimensional character of TiS₃). The XPS and ultrasoft and soft X-ray region XANES spectra confirm the surface and near-surface structural integrity of TiS₃.