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Deviation from the x-ray absorption cross section in fluorescence yield detection?
  Molecular Physics seminar

Monday 22 October 2012
from 10:15 to 11:00
at FA31
Speaker : Reshmi Kurian (Chemistry and Catalysis Group, Debye Institute of Nanomaterials Science, Utrecht University, The Netherlands)
Abstract : The electron yield (EY) and fluorescence yield (FY) measurements are generally used in the study of metal L-edge x-ray absorption spectra of 3d transition metal systems [1]. The FY measurements of core-level absorption edge spectra have a variety of advantages over the EY measurements, such as low background and insensitivity to applied electric and magnetic fields. In contrast to EY, FY also is a bulk probe, and hence it is generally used as a good measure of the x-ray absorption (XAS) cross section. In FY, care has to be taken for self-absorption and saturation effects, limiting FY to the study of the dilute elements in absorbing matrices or thin films. However, it has been shown that FY spectra differ from true XAS spectra not only due to saturation effects and self-absorption, but also due to the intrinsic processes of the FY decay. In 1994 it was shown that the FY detected spectrum of a nickel-cyanide complex does not relate to the 2p X-ray absorption spectrum due to the state dependent intensity fluctuations of the fluorescence decay channels [2]. Therefore we carried out a systematic investigation on the divalent transition metals from 3d1 to 3d9, based on a theoretical approach according to which the FY signal is approximated as the coherent convolution of 2p XAS and 2p3d X-ray emission. It is evident from the results that the FY spectra systematically differ from true absorption due to relaxation processes of the intermediate state and the state dependence of the fluorescence channels [3]. References: [1] F. de Groot, A. Kotani, Core level spectroscopy of solids, (CRC Press, 2008). [2] F. de Groot, M. Arrio, P. Sainctavit, C. Cartier, C.T. Chen, Solid State Com. 92 (1994). [3] R. Kurian, K. Kunnus, P. Wernet, S. Butorin, P. Glatzel and F. de Groot accepted in J. Phys. Cond. Matt. (2012).

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