Probing the Angstrom-Scale Chemistry and Physics on Surfaces via Tip-Enhanced Raman Spectroscopy

Abstract:  

Our research focuses on materials at the single-molecule and atomic scale, investigating how local environments govern the physical and chemical properties of functional materials, nanostructures, and surface-supported molecular systems with Ångström-scale resolution. Tip-Enhanced Raman Spectroscopy (TERS) uniquely integrates the atomic 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. When combined with ultrahigh vacuum conditions, this approach allows atomistic control of localized surface plasmons with exceptional stability and precision. Using TERS, we have achieved: (1) single-molecule chemical identification;1 (2) quantum-level characterization of adsorbate-substrate interactions down to individual chemical bonds;2-4, (3) atomic-scale insights into the oxygen reactivity on surfaces;5, 6 (4) direct measurements of local strain effects in organic/2D materials heterostructures.7 By probing single molecules, molecular superstructures, and 2D material lattices, we extract previously inaccessible materials information with unprecedented spatial (<1 nm) and energy (<10 cm⁻¹) resolution. Beyond spectroscopy, localized surface plasmons enable materials transformation through site-selective chemistry at the submolecular 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.