ANISOTROPIC X-RAY ABSORPTION IN LAYERED COMPOUNDS
ANISOTROPIC X-RAY ABSORPTION IN LAYERED COMPOUNDS
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DOI：
10.1103/physrevb.16.5549
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发表时间：
1977-01-01
影响因子：
3.7
通讯作者：
STERN, EA
中科院分区：
文献类型：
--
作者：
HEALD, SM;STERN, EA
研究了2h - wse - 2和1t - tas2层状化合物对x射线吸收的各向异性效应。在测量中，必须将厚度效应与真正的各向异性效应分离开来，这取决于x射线偏振与晶体轴之间的角度。测量了Se K边、W边和Ta L边。Se白线存在各向异性，而W和Ta白线未发现各向异性。指出一般的x射线吸收，特别是扩展x射线吸收精细结构（EXAFS）具有二阶张量的各向异性依赖，并明确地给出了EXAFS各向异性在l2,3边的理论表达式。实验结果表明，EXAFS在Se和W吸收中的各向异性与理论基本一致。EXAFS在l3边缘的各向异性具有最终s态和最终d态之间的交叉项的新特征，这使得从测量中可以确定最终s态对l3边缘总吸收的平均贡献为最终d态的0.02。最后，在波段计算和近边x射线吸收结构之间只得到了定性的一致，正如理论上所期望的那样。
A study is presented of anisotropy effects in x-ray absorption in the layered compounds of 2 H− W Se 2 and 1 T− T a S 2. 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 K edge and the W and Ta L 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 L 2, 3 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 L 2, 3 edges has the new feature of a cross term between the final s and d states, which permits a determination from the measurements that the average contributions of the final s state is 0.02 of that of the final d states to the total absorption of the W L 3 edge. Finally, only qualitative agreement is obtained between band calculations and the near edge x-ray absorption structure, as expected theoretically.