Near-Field Raman and Luminescence Spectroscopies to Evidence Chemical Heterogeneity of Surfaces with Sub-wavelength Spatial Resolution

Near-field scanning optical microscopy (NSOM or SNOM) opens the fascinating opportunity to access the richness of spectroscopic information at a sub-micronic resolution. Shear-force topography coupled to localized spectral information evidence chemical heterogeneity at this challenging spatial scale, which can be crucial to understand the relationship between microscopic features and macroscopic behavior of the samples. Three examples are reported to evidence the potentiality of SNOM using aluminum-coated silica probes. Two are devoted to nearfield Raman spectroscopy applied to i) a small crystal of lead sulfate covered by nano-phases of copper sulfate and ii) well-oriented single crystals of rutile TiO2. The last example uses near-field time-resolved luminescence spectroscopy to evidence heterogeneity of the local environment of Europium(III) cations at the surface of a glass sample doped with a small amount of Eu2O3 oxide.