Anisotropy of x-ray reflectivity: chemical and structural effects on K-shell excitations in hexagonal BN crystal

The experimental investigation of the B and N K-reflection spectra using both s-polarized synchrotron radiation and unpolarized radiation for different crystal orientations with respect to the electric field vector E was carried out. The absorption spectra calculated from the reflection spectra using Kramers-Kronig analysis are presented. A strong orientation dependence of both reflection and absorption spectra is exhibited. Analysis of the orientation dependences of the x-ray reflection and absorption spectra near both edges strongly supports a possibility of tracing the role of each excitation canal in the formation of fine structure. The high sensitivity of the reflection spectra fine structure to the vibronic interaction connected with Jahn-Teller distortions as well to the core-hole relaxation is discussed. A very strong dependence of the absolute values of the reflectivity on planar crystal anisotropy was discovered