Abstract
X-ray absorption spectroscopy (XAS) is a powerful element-specific technique that allows the study of structural and chemical properties of matter. Often an indirect method is used to access the X-ray absorption (XA). This work demonstrates a new XAS implementation that is based on off-axis transmission Fresnel zone plates to obtain the XA spectrum of La0.6Sr0.4MnO3 by analysis of three emission lines simultaneously at the detector, namely the O 2p-1s, Mn 3s-2p and Mn 3d-2p transitions. This scheme allows the simultaneous measurement of an integrated total fluorescence yield and the partial fluorescence yields (PFY) of the Mn 3s-2p and Mn 3d-2p transitions when scanning the Mn L-edge. In addition to this, the reduction in O fluorescence provides another measure for absorption often referred to as the inverse partial fluorescence yield (IPFY). Among these different methods to measure XA, the Mn 3s PFY and IPFY deviate the least from the true XA spectra due to the negligible influence of selection rules on the decay channel. Other advantages of this new scheme are the potential to strongly increase the efficiency and throughput compared with similar measurements using conventional gratings and to increase the signal-to-noise of the XA spectra as compared with a photodiode. The ability to record undistorted bulk XA spectra at high flux is crucial for future in situ spectroscopy experiments on complex materials.
Highlights
X-ray absorption spectroscopy (XAS) is a widely used spectroscopic technique that has gained increasing interest in the last decades because of its capability to obtain electronic as well as spatial information of many different sample classes
Depending on the proximity of the incident photon energy to the absorption edge of the investigated material, XAS is subdivided into near-edge X-ray absorption fine structure (NEXAFS) and extended X-ray absorption fine structure (EXAFS)
We introduce a new analyzer scheme for XAS that uses transmission off-axis Fresnel zone plates (TZPs)
Summary
X-ray absorption spectroscopy (XAS) is a widely used spectroscopic technique that has gained increasing interest in the last decades because of its capability to obtain electronic as well as spatial information of many different sample classes. Besides TFY and PFY, the measurement of inverse partial fluorescence yield (IPFY) has gained some attention (Achkar et al, 2011) In this method, one emission energy is chosen for a detailed spectral analysis, where the fluorescence is non-resonant with respect to the X-ray absorption and stems ideally from another element in the compound. The complete setup consists of two off-axis transmission Fresnel zone plates that collect the emitted fluorescence from the sample and disperse it across a region of the CCD detector (Fig. 1) This two-color scheme allows for focusing on two emission energies at the same time so that, under excitation at the Mn L-edge, two PFYs (Mn 3d to 2p transition and Mn 3s to 2p transition) and the IPFY (O 2p to 1s transition, resulting from non-resonant O K-edge emission) can be detected using both zone plates at the same time. The ability to focus on two different emitted energies can be very interesting for measurements of complex materials or diluted samples, especially for in situ measurements where ambient conditions are varied
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