Intramolecular insight into adsorbate-substrate interactions via low-temperature, ultrahigh-vacuum tip-enhanced Raman
Jordan M Klingsporn1, Nan Jiang, Eric A Pozzi
1Northwestern University , Department of Chemistry, 2145 Sheridan Road, Evanston, IL 60208, United States.
Abstract:
Tip-enhanced Raman spectroscopy (TERS) provides chemical information for adsorbates with nanoscale spatial resolution, single-molecule sensitivity, and, when combined with scanning tunneling microscopy (STM), Ångstrom-scale topographic resolution. Performing TERS under ultrahigh-vacuum conditions allows pristine and atomically smooth surfaces to be maintained, while liquid He cooling minimizes surface diffusion of adsorbates across the solid surface, allowing direct STM imaging. Low-temperature TER (LT-TER) spectra differ from room-temperature TER (RT-TER), RT surface-enhanced Raman (SER), and LT-SER spectra because the vibrational lines are narrowed and shifted, revealing additional chemical information about adsorbate-substrate interactions. As an example, we present LT-TER spectra for the rhodamine 6G (R6G)/Ag(111) system that exhibit such unique spectral shifts. The high spectral resolution of LT-TERS provides intramolecular insight in that the shifted modes are associated with the ethylamine moiety of R6G. LT-TERS is a promising approach for unraveling the intricacies of adsorbate-substrate interactions that are inaccessible by other means.
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