Depth Profiling Analysis of Nano-Layers using Resonant Raman Spectroscopy

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

Campinas

Congreso; 21st edition of the International Congress on X-Ray Optics and Microanalysis (ICXOM); 2011

Brazilian Synchrotron Light Laboratory

Total Reflection of X-rays is a largely proved spectroscopic technique that allows the study of material surfaces. As the refractive index is less than unity, X-rays incident on a material are, theoretically, totally reflected if the glancing angle is less than a critical angle derived from the Snell´s law. Making use of this relation, different depths of a sample could be studied by means of the correct election of the incident radiation angle. Resonant Raman scattering is an inelastic scattering process which presents fundamental differences compared to other scattering interactions. This phenomenon becomes dominant when atoms are irradiated with incident energy lower and close to an absorption edge. Recently, a spectroscopic technique in formation based in this process showed to be useful to distinguish surrounded chemical environments. For the first time, both total reflection and resonant Raman scattering techniques are used combined in order to discriminate oxidation states in nano-layers of materials. Samples of pure Cu and Fe oxidized in water and salty water respectively, were studied in the LNLS of Brazil scanning the incident radiation angle around the critical angle with incident energy lower and close to the K absorption edge of both elements. The RRS spectra were analyzed with specific programs for fitting the experimental data to theoretical expressions. Then, residuals were determined in the low energy side of the RRS peaks. These residuals were treated with FFT smoothing methods taking into account the instrument functions of the detecting system. The residuals show an oscillation pattern that change smoothly with the incident angle, i.e. with the depth, allowing a depth study of the oxidation state with nano-metric resolution. A RRS chemical environment technique in total reflection geometry will offer an opportunity to study how the oxidation state change with the depth in different kind of samples in which a complete characterization is impossible to achieve by other methods, such as conventional absorption techniques.