INVESTIGADORES
SANCHEZ Hector Jorge
congresos y reuniones científicas
Título:
Grazing-incident and Grazing-exit Experiments at the D09B XRF Beamline of the LNLS
Autor/es:
C. A. PÉREZ; H. CARVALHO; T. RAMALLO; S.B. MARTIN; G.A. BONGIOVANNI; A. L. GOBBI; E. AVENDANO; HECTOR JORGE SANCHEZ
Lugar:
Goteborg
Reunión:
Conferencia; TXRF 2009; 2009
Resumen:
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[1],
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 grazingexit detection conditions[2].
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[3],[4].
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.
[1] L. D. Landau and E. M. Lifshitz, Electromagnetic
of Continous Media, Pergamon, Oxford, England (1981)
[2] C. A. Pérez et.al., LNLS
2007 Activity Report, Brazilian Synchrotron Light Source
[3] T. C. Ramalho et. al., J. Mater. Sci., 44 1029-1034 (2008) ; Spectrochimica
Acta Part. A (submitted).
[4] F. Golmar et. al., Appl. Phys. Lett., 92, 262503 (2008).