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    Experimental estimate of electron escape depth in Fe
    (PERGAMON-ELSEVIER SCIENCE LTD, 2009) Akgul, G.; Aksoy, F.; Ufuktepe, Y.; Luning, J.
    Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy is a powerful experimental tool to investigate the electronic and atomic structure of materials. The great power of NEXAFS derives from its elemental specificity and symmetry selection rules. Because the various elements have different core level energies, NEXAFS permits extraction of the signal from a surface monolayer or even a single buried layer in the presence of a huge background signal. We have calculated electron escape depth (lambda(e)) in Fe at the L-2,L-3 edge using pure Fe thin films of different thickness by soft x-ray absorption spectroscopy measurements. We have recorded high-resolution x-ray absorption spectra in transmission of Fe thin films resolving the near edge x-ray absorption fine structure. As a conclusion we found the mean escape depth of emitted electrons to be lambda(e) = 22 +/- 2 angstrom We believe our results provide important information for the improved understanding of theory of the photo absorption mechanism. (C) 2008 Elsevier Ltd. All rights reserved.
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    Study of the L-2,L-3 edges of 3d transition metals by X-ray absorption spectroscopy
    (ELSEVIER SCIENCE SA, 2008) Akguel, G.; Aksoy, F.; Bozduman, A.; Ozkendir, O. M.; Ufuktepe, Y.; Luening, J.
    In the soft X-rays energy region, near edge X-ray absorption fine structure (NEXAFS) spectra are generally recorded by monitoring yield signals of secondary particles. These secondary particles, electrons or fluorescence photons, follow from the decay of the core hole excited in the primary absorption process. In general the yield signals are, to a good approximation, proportional to the absorption coefficient. However, in several applications it would be desirable to measure the absorption coefficient quantitatively. To derive the absorption coefficient quantitatively from a yield spectrum, one needs to know the escape depth of the emitted electrons (Ne) of the applied yield technique in the material of interest. Since this quantity is difficult to calculate, it is unknown for most materials. In this paper we present the first results of our systematic investigation of the total electron-yield (TEY) escape depth of the 3d transition metals (Fe, Co and Cu). In addition our results gave important information on the variation of the TEY escape depth with the filling of the 3d band. (C) 2008 Elsevier B.V. All rights reserved.
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    Thickness and angular dependence of the L-edge X-ray absorption of nickel thin films
    (WILEY-BLACKWELL, 2011) Ufuktepe, Y.; Akgul, G.; Aksoy, F.; Nordlund, D.
    We report on the near-edge X-ray absorption fine structure spectroscopy of the L(3) (2p(3/2)) and L(2) (2p(1/2)) edges for ferromagnetic pure nickel transition metal and show that the L(2,3) edge peak intensity and satellite feature at similar to 6 eV above the L(3) edge in nickel increase with increasing nickel film thickness both in the total electron yield and transmission modes. The absorption spectra of nickel metal, however, exhibit strong angular-dependent effects when measured in total electron yield mode. In addition, we calculated the mean electron escape depth of the emitted electrons (lambda(e)), which was found for pure nickel metal to be lambda(e) = 25 +/- 2 angstrom. We point out the advantages of the total electron yield technique for the study of the L-edge of 3d transition metals. Copyright (C) 2011 John Wiley & Sons, Ltd.
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    Thickness dependence of the L-2,L-3 branching ratio of Cr thin films
    (ELSEVIER SCIENCE SA, 2010) Aksoy, F.; Akgul, G.; Ufuktepe, Y.; Nordlund, D.
    We report the electronic structure of chromium (Cr) thin films depending on its thickness using two measures, total electron yield (TEY) and transmission yield mode. The Cr L edge X-ray absorption spectroscopy (XAS) spectrum shows strong thickness dependence with broader line widths observed for L-2,L-3 edge peaks for thinner films. The white line ratio (L-3/L-2) was found to be 1.25 from the integrated area under each L-3 and L-2 peak and 1.36 from the ratio of the amplitudes of each L-3 and L-2 peak after the deconvolution. Additionally, we show that full-width at half-maximum (FWHM) at the L-2 and L-3 edges and the branching ratio of Cr change as a function of film thickness and these are discussed in detail. Using L-2,L-3 resonance intensity variation as a function of film thickness we calculated the electron escape depth and X-ray attenuation length in Cr. Comparing our results with the literature, there was good agreement for the L-3-L-2 ratio although the detailed shape can show additional solid state and atomic effects. (c) 2010 Elsevier B.V. All rights reserved.