My research group is interested in investigating how local chemical environments affect single-molecule behaviors with angstrom scale resolution. This talk will start from Tip-Enhanced Raman Spectroscopy (TERS), which affords the spatial resolution of traditional Scanning Tunneling Microscopy (STM) while collecting the chemical information provided by Raman spectroscopy. By using a plasmonically-active material for our scanning probe, the Raman signal at the tip-sample junction is incredibly enhanced, allowing for 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; (2) the configurations and orientations of individual molecules on the surface; (3) adsorbate-substrate interactions in the ordering of molecular building blocks in supramolecular nanostructures; (4) local strain effects in an organic/2D materials heterostructure. By investigating substrate structures, superstructures, 2D materials lattices, and the adsorption orientations obtained from vibrational modes, we extract novel surface-chemistry 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. Our method can interrogate the mechanisms of forming and breaking chemical bonds at the angstrom scale in various chemical environments, which is critical in designing new atom- and energy-efficient materials and molecular assemblies with tailored chemical properties.



Nan Jiang (University of Illinois Chicago)