Spectroscopic imaging of surfaces-Sum frequency generation microscopy (SFGM) combined with compressive sensing (CS) technique.

Surface chemistry is notoriously difficult to study, in part, due to the decreased number of molecules that contribute to the properties compared to the bulk phase but often has significant effects on the chemical activity of the material. This is especially true in topics such as corrosion, catalysis, wetting, and many others in nature and industry. Sum frequency generation (SFG) spectroscopy was developed for interface studies due to its high molecular selectivity and surface sensitivity, which is quite useful to study the effects of structural inhomogeneity in microscopy. Compressive sensing (CS) combined with SFG spectroscopy minimizes the imaging time while still producing quality images. Selected systems are presented here to demonstrate the capability of CS-SFG microscopy. CS-SFG microscopy successfully distinguished the static monolayer molecular mixtures, the orientations and adsorption of adsorbed molecules by the dip-coating technique, and the localized CO behaviors on polycrystalline Pt electrodes. Further discussion includes dynamic imaging as a future direction in CS-SFG microscopy. As materials and surfaces become more complex, imaging with chemical contrast becomes indispensable to understanding their performance and CS-SFG microscopy seems highly beneficial in this respect.