Alteration of X-Ray Emission Band Spectrum Under Bragg Diffraction

We use a Zr/Si multilayer presenting a gradient of period to probe the shape of the Si L2,3 emission band (maximum around 92 eV) in and out of Bragg conditions. The sample was prepared by magnetron sputtering and its reflectance measured in the photon energy range of interest with synchrotron radiation. The study is performed on an electron microprobe equipped with a reflection zone plate spectrometer operating in the 40–120 eV photon energy range. Outside Bragg conditions, the observed spectrum is that of amorphous silicon as expected from the small thickness of the Si layers. In Bragg conditions, that is to say when the period of the multilayer, the emitted photon energy and detection angle fulfill the Bragg law, the shape and intensity of the emission band change. The main change is the intensity decrease of the shoulder present around 97 eV. Purcell-Kleppner and Kossel effects, or a combination of both, are suggested to explain the evolution of the Si L2,3 emission band when going through the Bragg conditions.