Micro-Determination of Oxidation-States by means of Confocal X-Ray Raman Spectroscopy

JUAN JOSÉ LEANI; H.J. SÁNCHEZ; C.A. PEREZ

Viena

Congreso; European Conference on X-Ray Spectrometry (EXRS 2012); 2012

IAEA

Micro X-Ray Fluorescence (μXRF) analysis is one of the latest branches of XRF. This spectroscopic technique has been quickly developed over the last years, mainly due to the use of synchrotron facilities. Since nowadays 3D-mapping becomes viable in micrometer regime, μXRF is a established analytical method in a variety of fields, since it is a non-destructive method, such as material science and environmental sciences, geology, biology, archaeometry, etc. A remarkable field of application is the investigation of stratified materials. This technique was opened up by the arrival of new X-ray optics, especially by the improvement of capillary optics [1]. These optics are currently widely used in synchrotron setups. In the last few years, quantification procedures reasonably accurate have been developed [1,2]. The most important problem in these quantification procedures is the existence of light elements in the sample from which no fluorescence is detected. This ?dark matrix? problem is not yet solved and is now one of the most serious limitations of this technique [2]. Lately, it has been successfully employed X-ray Raman scattering spectroscopy to determine oxidation states of metals [3,4]. This work presents results concerning the possibility of determining the oxidation state of an element, in a three-dimensional regime, by resonant Raman scattering using an energy dispersive system combined with a confocal setup. It was carried out a depth scanning in multilayer samples at the XRF Beamline of the LNLS [5] (Brazil) using a confocal setup. The samples consisted of an arrangement of layers with different diluted transition metal oxides each, over a substrate. These samples were irradiated with monochromatic photons having energy close but lower than the K absorption edge of the elements of interest. The X-ray Raman peaks were analyzed with specific programs for fitting the experimental data to theoretical expressions. After that, residuals were determined in the low energy side of the RRS peaks. Finally, a FFT smoothing procedure, in order to take into account the instrument functions of the detecting system, was applied. The results show an oscillation pattern that depends on the oxidation state of the analyzed element. The result allows the discrimination of the oxidation state of the elements present in a sample in a 3D-micrometer regime by means of X-ray Raman scattering combined with a confocal setup. In addition, this result could be used as a tool to determine the dark matrix present in a sample with the aim of establishing 3D-μXRF as a reliable and complete analytical tool.