Experimental evidence of EXAFS patterns in x-ray resonant Raman spectra

LEANI J.; H. J. SÁNCHEZ; PEREZ, R.D.; C.A. PÉREZ

Santa Marta

Seminario; XIII Seminario Latinoamericano de análisis por técnicas de rayos x-SARX2012; 2012

When atoms are irradiated by X-ray photons different kinds of interactions take place: the photon can be absorbed by the photoelectric effect or can suffer a Rayleigh or Compton scattering. However, under resonant conditions, other low probability interactions can occur. One of these interactions is the x-ray resonant Raman scattering (RRS). The X-ray resonant Raman scattering is an inelastic process that presents significant differences compared to other scattering interactions between X-rays and atoms; when the energy of the incident photon approaches from below to the absorption edge of a target element, a strong resonant behaviour takes place making the Raman process dominant over other effects. Contrasting fluorescent process where the emitted photon has a fixed energy, in a X-ray Raman process for an incident photon energy a variety of emitted photon energies are possible. In this work we isolated and study the oscillations present in the RRS spectra from different metal compounds (Mn, Fe and Cu). With this aim, we also isolated the oscillation patterns from different EXAFS spectra. After a data processing, taking into account the instrumental resolution, a direct comparison between the oscillation patterns of both experiments was carried out. A remarkable similitude between both patterns was observed in all the compounds. For the first time EXAFS-like modulations, i.e. interference information, has been observed in a scattered spectrum using a low resolution EDS system. These results open up the possibility of a new emission-spectroscopy technique allowing chemical characterizations. In this regard, due to the versatility of emission techniques, a lot of possibilities appear from the combination of RRS spectroscopy with other X-ray techniques, as total reflection for surface studies and even three-dimensional analysis by RRS combined with confocal setups. In these cases, this new spectroscopic tool can obtain detailed 3D spatially resolved information, which would be not viable to achieve by conventional absorption techniques. This novel RRS chemical-environment technique will offer an unique opportunity to study the oxidation state of different kind of samples (such as mineral, environmental and/or biological ones) in the nano and micro regime, reaching a complete characterization, impossible to achieve by other methods.