Sum Frequency Generation Vibrational Spectroscopy Using Evanescent Waves-Toward Probing Irregular and Complex Surfaces of Mesoscopic-Scale Materials.

With the rapid development of materials science, on-demand techniques are highly needed with the capability to characterize materials in the micrometer and nanometer scales. In this work, we show that, by employing a prism geometry, total internal reflection sum frequency generation (SFG) vibrational spectroscopy allows for characterizing mesoscopic materials with irregular or complex surfaces. Four representative examples were presented. First, we reveal that mechanical grinding can subtly alter the surface molecular structures of original materials. Second, spin coating can substantially change the surface molecular structures of particle samples. Third, surface restructuring of carboxylated multiwalled carbon nanotubes can happen in response to the surrounding environment. Fourth, surface adsorption and desorption dynamics of toluene on activated charcoal can be traced. Such experiments demonstrate that there are still a broad range of research fields ahead SFG can be directed to, where materials in mesoscopic scales with irregular or complex surfaces can be studied.