Chemical reactions such as bond dissociation and formation assisted by localized surface plasmons (LSPs) of noble metal nanostructures hold promise in solar-to-chemical energy conversion. However, the precise control of localized plasmons to activate a specific moiety of a molecule, in the presence of multiple chemically equivalent parts within a single molecule, is scarce due to the relatively large lateral distribution of the plasmonic field. Herein, we have shown the plasmon-assisted dissociation of a specific molecular site (C–Si bond) within a polyfunctional molecule adsorbed on a Cu(100) surface in the scanning tunneling microscope (STM) junction. The molecular site to be activated can be selected by carefully positioning the tip and bringing the tip extremely close to the molecule (atomistic approach), thereby achieving plasmonic nanoconfinement at the tip apex. Furthermore, multiple reactive sites are activated in a sequential manner at the sub-molecular scale, and different sets of products are created and visualized by STM topography and density functional theory (DFT) modeling. The illustration of site-selective activation achieved by localized surface plasmons implies the realization of molecular-scale resolution for bond-selected plasmon-induced chemistry.

This work has been highlighted in C&EN News and NSF Research by Chemistry Division (CHE). JACS has selected the communication as their Front Cover Art.

Journal of the American Chemical Society (Communication) 2022, 144, 5, 2051–2055; DOI: 10.1021/jacs.1c11547

Real-space chemical analysis of two structurally very similar components, that is, regioisomers lies at the heart of heterogeneous catalysis reactions, modern-age electronic devices, and various other surface-related problems in surface science and nanotechnology. Herein, we report the first topological and chemical analysis of two regioisomers, trans- and cis-H₂F₂₀TPPDL molecules by high-resolution scanning tunneling microscopy, and ultrahigh vacuum tip-enhanced Raman spectroscopy (UHV-TERS). Both isomeric structures are investigated individually on Ag(100) at liquid nitrogen temperature. Following that, the major break-through in successfully distinguishing these two regioisomeric molecules simultaneously through TERS with an angstrom scale (8 Å) spatial resolution is achieved.

Nano Letters 2019, 19, 5, 3267-3272; DOI: 10.1021/acs.nanolett.9b00826.

Nanoscale 2019, 11, 19877-19883; DOI: 10.1039/c9nr06830a.

After joining the lab in 2017, I was involved in fabrcating plasmonically active silver probes for STML and STM-TERS experiments. The basic instrumentation was developed and significantly upgraded in order to produce active silver probes. All the critical parameters such as etching current, etching potential were optimized. With this, I can produce the sharp silver tips that are incorporated inside UHV for the first time. Also, the preservation of the probes for more than two months was verified via experiments.

The Journal of Raman Spectroscopy 2021, 52, 573-580.; DOI: 10.1002/jrs.5951