X-ray fluorescence induced by standing waves in the grazing-incidence and grazing-exit modes: study of the Mg–Co–Zr system

Abstract

The characterization of Mg-Co-Zr tri-layer stacks using X-ray fluorescence induced by X-ray standing waves, in both the grazing-incidence (GI) and the grazing-exit (GE) modes, is presented. The introduction of a slit in the direction of the detector improves the angular resolution by a factor of two and significantly improves the sensitivity of the technique for the chemical characterization of the buried interfaces. By observing the intensity variations of the Mg Kα and Co Lα characteristic emissions as a function of the incident (GI mode) or detection (GE mode) angle, it is shown that the interfaces of the Si/[Mg/Co/Zr] × 30 multilayer are abrupt, whereas in the Si/[Mg/Zr/Co] × 30 multilayer a strong intermixing occurs at the Co-on-Zr interfaces. An explanation of this opposite behavior of the Co-on-Zr and Zr-on-Co interfaces is given by the calculation of the mixing enthalpies of the Co-Mg, Co-Zr and Mg-Zr systems, which shows that the Co-Zr system presents a negative value and the other two systems present positive values. Together with the difference of the surface free energies of Zr and Co, this leads to the Mg/Zr/Co system being considered as a Mg/CoxZry bi-layer stack, with x/y estimated around 3.5.

Kossel Effect in Periodic Multilayers

“…We present an example of Kossel curves obtained upon photon excitation. 17 Experiments took place at the BEAR beamline of the Elettra synchrotron working in the soft X-ray range. The multilayers, prepared by magnetron sputtering, were periodic tri-layers: Mg/Co/Zr and Mg/Zr/Co and correspond respectively to the following stacks, going from the Si substrate to the superficial capping layer: They only change by their deposition order.…”

“…This very first interpretation of X-ray diffraction given in 1912 by M. von Laue, was established about twenty years later by Kossel using electron excitation of a crystal, leading to the observation of the so-called Kossel lines. 2 Different ionizing radiations can be used to generate Kossel lines: 3 -electrons from an electron gun, 4-7 a scanning electron microscope 8 or a transmission electron microscope; 9 -X-ray photons from an X-ray tube, 10-12 a plasma source 13 or synchrotron radiation; [14][15][16][17][18] this case is analogous to the X-ray standing wave (XSW) technique 17 19 20 used to study the interfaces of multilayers 21 or X-ray waveguides 22 as well as thin surface films; 23 -rapid charged particles (proton or ion beam) from an accelerator. [24][25][26][27][28][29][30] In order to diffract X-rays the periodic medium can be a crystal 2 31 or a multilayer made of a periodic alternation of two or more nanometer-thick thin films.…”

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.…”

Characterization of Pd/Y multilayers with B4C barrier layers using GIXR and X-ray standing wave enhanced HAXPES

“…Such distribution can be modulated by varying the grazing incident angle of the photon beam. The effect can be observed by measuring the related phenomena such as characteristic x-ray emission [8,9] and photoemission [10] as a function of the incident angle. The combination of HAXPES and XSW brings unique advantages of a non-destructive characterization method with which detailed information on the multilayer structure can be obtained such as chemical compound formed at the interfaces.…”