BONGIOVANNI guillermina Azucena
congresos y reuniones científicas
Grazing-incident and Grazing-exit Experiments at the D09B XRF Fluorescence Beamline of the LNLS.
Conferencia; 13th conference on Total Reflection X-Ray Fluorescence Analysis and Related Methods (TXRF 2009); 2009
AUTORES Y FILIACION: Pérez C. A. y Gobbi A. L.: Laboratório Nacional de Luz Síncrotron Carvalho H. W. P. Universidade Estadual de São Paulo, Araraquara-SP, Brazil Ramalho T. C: Universidade Federal de Lavras, Lavras-MG, Brazil Martins S. B. Universidade Federal do Pampa, Bagé-RS, Brazil Bongiovanni G. A.: Universidad Nacional del Comahue, Neuquén, Argentina Avedaño E.: CromGenics AB, Uppsala, Sweden Rodriguez Torres C.E.: Univ. Nacional de la Plata, La Plata Bs.As, Argentina Sánchez, H. J.: Universidad Nacional de Córdoba, Córdoba, Argentina; Abstract It is well known that synchrotron radiation X-ray fluorescence (SR-XRF) analysis is a powerful tool for the analytical determination of trace element concentration in different matrices. Substantial improvements in detection limits can be achieved using external total reflection on a flat and smooth surface for the detection of XRF. Using broad band energy excitation delivered from bending magnets sources, it could possible to reach absolute detection limits in the range of fentograms using the total reflection x-ray fluorescence (TXRF) method. Although the use of perfect crystals as x-rays monochromator imposes a significant reduction on the photons flux at the sample position, this configuration still have enough sensitivity to perform experiments related to chemical depth profiling analysis of trace impurities in flat surfaces as well as to combine grazing incidence an energy scan near the absorption edge of a given element to study its chemical form and also oxidation state at trace levels (TXRF-XANES). Surface characterization techniques also needs spatial resolution in order to be able to analyze their properties in different points. In this way, according to the optical reciprocity theorem , a grazing-exit experiment (GE) also provides the same information as grazing-incident (GI) condition. Since in this case, the excitation is normal to the sample surface, the combination of GE-XRF and synchrotron x-ray microprobe allows surface-sensitive with spatial resolution. In this work, we will make an overview of the main results we have obtained in the last two years from several experiments using the grazing-incident as well as grazing-exit setups available at the XRF fluorescence beamline of the Brazilian Synchrotron Light Source (LNLS) located in Campinas, SP (Brazil). Firstly, I will show some of the results obtained in relation to the investigation of the possibility of studying interfacial diffusion in layered thin films by depth profiling combining x-ray microbeam and grazing–exit detection conditions . As a second part of my talk, I will focused in some experiments related to the determination of the chemical depth distribution of metal impurities in semiconductor, with particular interest in understanding aspect such as photocatalytic activity as well as magnetic behavior of nonmagnetic semiconductors , . Finally, I will show some preliminary results on the study of chemical form and oxidation states of arsenic, present at trace levels in animal tissues, by combining TXRF and XANES spectroscopy.