Spontaneous soft x-ray fluorescence from a superlattice under Kossel diffraction conditions

Abstract

The present study gives the proof of principle of a technique that is an extension of Kossel diffraction both from crystals to superlattices and toward the soft x-ray region, allowing the characterization of the interfaces within a periodic structure. We measure the intensity of the Co Lα and Mg Kα characteristic fluorescence emissions from a Mg/Co superlattice upon soft x-ray excitation. The observation is made so that the angle between the sample surface and the detection direction is scanned around the first and second Bragg peaks of the fluorescence emissions. Clear modulations of the emitted intensities are observed and well reproduced by simulations based on the reciprocity theorem and assuming a perfect stack. The present work gives evidence that such a superlattice plays the role of an optical cavity for the spontaneous emission generated within the stack. This should also be the case for stimulated emission, which when combined with pumping free electron laser, will open the road to innovative x-ray distributed feedback lasers.

X-ray emission from layered media irradiated by an x-ray free-electron laser

“…We first consider a sample consisting in a stack of 30 bilayers (Mg/Co) of thichnesses e 1 = 5.45 nm and e 2 = 2.55 nm respectively. This sample has already been considered in a context of excitation by synchrotron radiation [36]. It will be considered below in the context of intense irradiation.…”

Kossel interferences of proton-induced X-ray emission lines to study thin film waveguides

“…The ionization source can be energetic electrons [5][6][7], X-ray photons [8,9], charged particles including protons or ions [10,11]. Kossel diffraction associated to X-rays is related to the grazing exit X-ray fluorescence (GEXRF) technique [2,12].…”

Kossel interferences of proton-induced X-ray emission lines in periodic multilayers

“… Electrons from an electron gun [3][4][5][6] or a scanning electron microscope [7];  X-ray photons from an x-ray tube [8][9][10] or synchrotron radiation [11][12][13][14]; this case is analogous to the x-ray standing wave technique [14,15] used to study the interfaces of multilayers [16] or x-ray waveguides [17] as well as superficial thin films [18];  Rapid charged particles (proton or ion beam) from an accelerator [19][20][21][22][23][24][25].…”

“…The combination of the Kossel measurements and their simulation, will be a useful tool to obtain a good description of the multilayer stack and thus to study nanometer-thick layers and their interfaces.  X-ray photons from an x-ray tube [8][9][10] or synchrotron radiation [11][12][13][14]; this case is analogous to the x-ray standing wave technique [14,15] The technique requires a periodic structure to diffract the emitted radiation, thus it has been applied to study crystals and interferential multilayers. However, to the best of our knowledge, Kossel lines have never been observed in multilayers upon particle excitation.…”