Abstract
A study is presented of anisotropy effects in x-ray absorption in the layered compounds of and . In the measurements it was essential to separate the thickness effect from the true anisotropy effect which is dependent on the angle between the x-ray polarization and the crystal axes. The Se edge and the W and Ta edges were measured. Anisotropy in the white line of Se was found but no anisotropy was discerned in the W and Ta white lines. It is pointed out that x-ray absorption in general, and the extended x-ray absorption fine structure (EXAFS) in particular, have the anisotropy dependence of a second-order tensor and the theoretical expression for the EXAFS anisotropy at the edges is explicitly displayed. The anisotropy of the EXAFS in the Se and W absorption was measured and a good agreement with theory is found. The anisotropy of EXAFS at the edges has the new feature of a cross term between the final and states, which permits a determination from the measurements that the average contributions of the final state is 0.02 of that of the final states to the total absorption of the W edge. Finally, only qualitative agreement is obtained between band calculations and the near edge x-ray absorption structure, as expected theoretically.
- Received 18 July 1977
DOI:https://doi.org/10.1103/PhysRevB.16.5549
©1977 American Physical Society