Multiwavelength Raman Spectroscopic Analysis of Superficial Iron-Chromium Oxides Generated Using Laser Irradiation

In order to characterize iron-chromium oxides generated by laser irradiation on the surface of stainless steel plates, an ultraviolet-visible (UV-Vis) near-infrared (NIR) multiwavelength excitation Raman analysis has been performed using both austenitic SS304 and ferritic SS430 stainless steel samples. Raman spectra were obtained using five different excitation wavelengths from blue (455 nm) to NIR (830 nm). These measurements have allowed us to observe and identify four Raman bands, among which two have not been previously observed for iron-chromium oxides, and characterize the existence of different resonant excitation conditions for the different excitation wavelengths. For example, when using 455 nm as excitation wavelength the band at 485 cm^-1 did not show up, although that when using 830 nm as excitation wavelength is a clear characteristic band for iron-chromium oxide. In addition, the dependence of the spectra profile with the excitation wavelength for films and microspheres features was observed. This experimental Raman analysis shows the importance of the excitation wavelength for the characterization of metallic oxides with different features.