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On the one hand different penetration depths are reached by tuning the excitation energy. On the other hand the angle of incidence or observation can be varied. Thus the effective path length of X-ray photons in the specimen is different

In typical XRF measurements the sample is irradiated by a collimated X-ray beam and the X-ray fluorescence signal detected by an energy- or wavelength dispersive detector in a 90°-geometry. The obtained information is integral, i.e. originates from different depth of the analyzed sample. To resolve gradient information of stratified specimen the excitation of depths has to be varied. The figure below depicts how the sensitivity for gradient measurements is obtained by varying parameters of excitation and detection. By performing angle scans of the incidence radiation close to the critical angle of total external reflection grazing incidence (GI-) XRF becomes feasible. A typical GIXRF plot shows the evolution of the intensity of one specific fluorescence line for the various angles. For grazing exit (GE-) XRF the incidence radiation is focussed onto a small spot and the angle of detection is varied accordingly. While for GIXRF an energy-dispersive detector can be placed close to the sample, in GEXRF the angle-resolution must be achieved in the detection channel, necessitating slits or large distances from the sample to the detector. Information depths range from a few nanometers to several micrometers, depending on the matrix of the specimen, the used excitation energy and the experimental set up.   Point of contact: Jonas Baumann, Veronika Szwedowski Relevant publications:   Streeck, C; Brunken, S; Gerlach, M; Herzog, C; Honicke, P; Kaufmann, CA; Lubeck, J; Pollakowski, B; Unterumsberger, R; Weber, A; Beckhoff, B; Kanngiesser, B; Schock, HW; Mainz, R, Appl. Phys. Lett., 2013, 103(11), 113904    

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