Substrates with a periodic surface structure in grazing-exit X-ray microanalysis

The angular distribution of X-ray radiation from a point source and a small particle situated near a substrate with a periodic (diffraction grating-like) surface structure is analyzed theoretically. Due to diffraction on the surface grating, the radiation, reflected from the substrate, can be concentrated near certain directions depending on the wavelength and the grating parameters. As a result, distinct peaks appear in the X-ray signal angular dependence, whose magnitude, depending on the detector angle resolution, can exceed several times the usual value of X-ray intensity available under the same conditions of excitation with the use of a flat substrate. Different substrate structures containing amplitude as well as phase gratings with rectangular, triangular or smooth (sinusoidal) grooves are numerically investigated, predominantly for the case of low-energy characteristic X-ray radiation (O, N and C Kα lines), and the most favorable groove shapes and grating periods are revealed. The proposed method of X-ray signal enhancement is expected to be especially useful if the primary emission is relatively weak, i.e. for trace analysis, small specimens and/or analysis of low-Z elements. The angular separation of peaks for different elements forms an additional analytical advantage. The prospects for experimental realization of the method and possible further developments are discussed.