Abstract:
Our research investigates how local environments influence single-molecule and nanostructure properties on surfaces with Ångström-scale resolution. Tip-Enhanced Raman Spectroscopy (TERS) combines the spatial resolution of Scanning Tunneling Microscopy (STM) with the chemical sensitivity of Raman spectroscopy. By utilizing a plasmonically active scanning probe, the Raman signal at the tip-sample junction is greatly enhanced, enabling single-molecule probing. This method, further aided by the benefits of ultrahigh vacuum, is uniquely capable of controlling localized plasmons via an atomistic approach. We are able to obtain (1) single-molecule chemical identification;1 (2) quantum characterization of adsorbate-substrate interactions at the single chemical bond level;2-4, (3) atomic-scale insights into the oxygen reactivity on surfaces;5, 6 (4) local strain effects in an organic/2D materials heterostructure.7 By investigating single molecules, superstructures, 2D materials lattices, and the adsorption orientations obtained from the vibrational modes, we extract novel surface information at an unprecedented spatial (< 1 nm) and energy (< 10 wavenumber) resolution. Another application of localized surface plasmons is to achieve site-selective chemical reactions at sub-molecular scale. We recently selectively and precisely activated multiple chemically equivalent reactive sites one by one within the structure of a single molecule by scanning probe microscopy tip-controlled plasmonic resonance.8 Our method can interrogate the mechanisms of forming and breaking chemical bonds at the Ångström scale in various local environments, which is critical in designing new atom- and energy-efficient materials and molecular assemblies with tailored physical and chemical properties.