Probing Chemistry at the Ångström-Scale via Scanning Tunneling Microscopy and Tip-Enhanced Raman Spectroscopy
Associate Professor Nan Jiang - College of Liberal Arts and Sciences, University of Illinois
Host: Charles Campbell

My research group is interested in investigating how local chemical environments affect single-molecule behaviors 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) local strain effects in an organic/2D materials heterostructure.4 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.5 Our method can interrogate the mechanisms of forming and breaking chemical bonds at the Ångström scale in various chemical environments, which is critical in designing new atom- and energy-efficient materials and molecular assemblies with tailored 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, 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).
4. 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).
5. 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)."

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