Polarization dependent X-ray absorption study of Cu xNbS 2 ( x=0.00, 0.16) and Cu x NbSe 2 ( x=0.00, 0.38)

Abstract

The X-ray absorption fine structure (XAFS) of single crystals of NbS 2, Cu 0.16NbS 2, NbSe 2 and Cu 0.38NbSe 2 is investigated at the Nb, Se and Cu edges. Measurements are made for different angles between the crystallographic c-axis and the X-ray beam. Nearest-neighbor and next-nearest-neighbor distances, as well as their variances, are extracted from the extended XAFS (EXAFS), indicating that intercalation of copper does not affect the average distances within the Nb-chalcogen layers while, at the same time, a structural disorder is introduced. The X-ray absorption near edge structure (XANES) of Cu x NbSe 2 is sensitive to the direction of empty electronic states and indicates that empty states with z-symmetry are separated from empty states with x- and y-symmetry by about 2.5 eV. It also shows that intercalation is accompanied by charge transfer from the Cu to the NbSe 2 host lattice.