Tip-Enhanced Raman Spectroscopy: Chemical Analysis with Nanoscale to Angstrom Scale Resolution

Fundamental understandings of chemistry and physical properties at the nanoscale enables the rational design of interface-based systems. Surface interactions underlie numerous technologies ranging from catalysis to organic thin films to biological systems. Since surface environments are especially prone to heterogeneity, it becomes crucial to characterize these systems with spatial resolution sufficient to localize individual active sites or defects. Spectroscopy presents as a powerful means to understand these interactions, but typical light-based techniques lack sufficient spatial resolution. This talk describes a new sub-nanoscale spectroscopic technique, tip-enhanced Raman spectroscopy (TERS), with a focus on developments that reveal the intricacies of adsorbate-adsorbate/ adsorbate−substrate interactions. We have designed a series of TERS experiments to obtain chemical information for individual molecules with high precision. We were the first to differentiate adjacent regio-isomers that are nearly identical in their structures by using their unique vibrational fingerprints obtained with TERS at a spatial resolution of 8 Å, providing significant insights into the chemical properties and intermolecular interactions of a molecular heterojunction. Using our methods, we can also characterize the binding configurations of non-planar organic molecules that result in multiple self-assemblies on the same or different substrates, providing insight into highly localized chemical effects.