Prof. Nan Jiang
(University of Illinois Chicago)

Probing the Ångström-Scale Chemistry and Physics of Surfaces via Tip-Enhanced Raman Spectroscopy

My research group is interested in investigating how local environments affect single-molecule and nanostructure properties on surfaces with Ångström scale resolution. This talk will start with 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;1 (2) adsorbate-substrate interactions in the ordering of molecular building blocks in supramolecular nanostructures;2 (3) atomic-scale insights into the oxygen reactivity of 2D materials;3, 4 (4) local strain effects in an organic/2D materials heterostructure.5 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.6 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.

 
Reference:
1. S. Mahapatra, Y. Ning, J. F. Schultz, L. Li, J. -L. Zhang, N. Jiang, “Angstrom Scale Chemical Analysis of Metal Supported Trans- and Cis-Regioisomers by Ultrahigh Vacuum Tip-Enhanced Raman Mapping”, Nano Letters,19, 3267-3272 (2019).
2. J. F. Schultz, L. Li, S. Mahapatra, C. Shaw, X. Zhang, N. Jiang, “Defining Multiple Configurations of Rubrene on a Ag(100) Surface with 5 Angstrom Spatial Resolution via Ultrahigh Vacuum Tip-Enhanced Raman Spectroscopy”, The Journal of Physical Chemistry C, 124, 2420-2426 (2020).
3. L. Li, J. F. Schultz, S. Mahapatra, Z. Lu, X.  Zhang, and N. Jiang, “Chemically identifying single adatoms with single-bond sensitivity during oxidation reactions of borophene”, Nature Communications, 13, 1796 (1-9) (2022).
4. L. Li, J.F. Schultz, S. Mahapatra, X. Liu, X. Zhang, M. Hersam, N. Jiang, "Atomic-Scale Insights into the Interlayer Characteristics and Oxygen Reactivity of Bilayer Borophene", Angewandte Chemie International Edition, 62, e202306590 (2023).
5. L. Li, J. F. Schultz, S. Mahapatra, X. Zhang. X. Liu, C. Shaw, M. Hersam, N. Jiang, “Probing interfacial interactions in an organic/borophene heterostructure with angstrom resolution”, Journal of the American Chemical Society, 143, 38, 15624-15634 (2021).
6. S. Mahapatra, J. F. Schultz, L. Li,  X. Zhang, and N. Jiang, “Controlling Localized Plasmons via an Atomistic Approach: Attainment of Site-Selective Activation inside a Single Molecule”, Journal of the American Chemical Society, 144, 5, 2051-2055 (2022).