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

Abstract

Proton-induced X-ray emission (PIXE) combined in Kossel geometry was developed as a non-destructive structural characterization method of nanometer thin films deposited on Si. The method is applied to study Pt/Fe/Pt and Ta/Cr/Pt thin films designed as X-ray planar waveguides. With the help of an energy dispersive X-ray camera, the intensities of characteristic X-ray emissions versus the detection angle (grazing exit), called Kossel curves, were measured. It is found that an interfacial compound is formed in Pt/Fe/Pt waveguide, whereas oxidation and mixing occur in the Ta/Cr/Pt system. It was not possible to obtain the description of the successive layers when considering only grazing incidence x-ray reflectivity. When PIXE-Kossel experiments are also considered, supplementary constraints have to be fulfilled when fitting the values of the stack parameters (number, composition, thickness, roughness and density of the layers) which restrict the possible descriptions of waveguides. Thus PIXE-Kossel is suitable to characterize stacks of nanometer thin films designed to be applied as an x-ray waveguide.

Grazing Emission X‐Ray Fluorescence: Novel Concepts and Applications for Nano‐Analytics

“…[ 46,69,70 ] The GEXRF scheme has also been applied to PIXE setups to enable depth‐discrimination properties for the analysis of thin films and multilayers. [ 48,69,71 ] A possible advantage of using protons for fluorescence excitation with respect to quantification is the fluorescence generation function, which can typically be assumed constant within the information depth. [ 48,71 ]…”

“…[ 48,69,71 ] A possible advantage of using protons for fluorescence excitation with respect to quantification is the fluorescence generation function, which can typically be assumed constant within the information depth. [ 48,71 ]…”

“…In laboratory setups, where photon densities on the detector are usually lower, charge‐coupled devices (CCDs) have been successfully applied for scanning‐free GEXRF measurements. [ 38,57,71 ] Although those detectors are usually applied in an integrating mode, such that the information about X‐ray energy is lost, they can also be applied in a single photon detection mode. In this case, on each recorded CCD frame, single photons must be distinguishable.…”

Combined x‐ray reflectivity and grazing incidence x‐ray fluorescence study of Ta/Cr/Pt thin film stacks

“…This work demonstrated the ability of the PIXE‐Kossel methodology to characterize the stacks of nano‐scale thin films, through the analysis of two waveguide systems: namely Pt/Fe/Pt and Ta/Cr/Pt. However, the analysis of the Ta/Cr/Pt system was not definitive, as the obtained description of the stack, that is, intermixing taking place between the Ta and Cr layers to form a compound that was subsequently partly oxidized, could still be improved 14 …”

“…[9][10][11][12] In this framework, we showed the feasibility of applying Kossel diffraction 13 combined with particle induced x-ray emission (PIXE) for the study of planar x-ray waveguides. 14 These devices are made of thin films, a guiding layer generally made of a light material surrounded by two cladding layers made of heavy materials. This work demonstrated the ability of the PIXE-Kossel methodology to characterize the stacks of nano-scale thin films, through the analysis of two waveguide systems: namely Pt/Fe/Pt and Ta/Cr/Pt.…”