The ability to detect the vibrational fingerprint originating from the individual atoms within the single-molecule is the utmost dream of chemists. As such, conventional spectroscopic techniques are limited by the optical diffraction limit to about half wavelength that offers about 200 nm × 200 nm microscopic zone for working in the visible light range. In that context, tip-enhanced Raman spectroscopy (TERS) emerges as an advanced analytical technique, where the plasmonically active probe is not only used to detect the tunneling current but also to interrogate the local chemical environment of surface adsorbed molecules with angstrom scale precision. In TERS, the incident laser irradiation is focused on the tip apex which excites localized surface plasmon (LSP) polaritons and causes the electromagnetic enhancement at the tip-sample junction. In this work, we report a topological and chemical analysis of two porphodilactone regioisomers (positional isomers) by scanning tunneling microscopy (STM), ultrahigh vacuum (UHV) TERS on Ag(100) with the spatial resolution down to 8 Å, which has a wide range of applications in various field of surface science & nanotechnology such as regioselective catalysis reaction, chemical reactions, molecular electronics, etc. We have shown, it is possible to distinguish these two structurally very similar forms with high accuracy & precision. Furthermore, these new classes of porphyrinoids have been studied on different single crystals such as Cu(100) and Au(100) in order to probe the surface-sensitive interactions. In contrary to the “saddle” configuration observed on the Ag(100) and Au(100), an “inverted” configuration is characterized on the Cu(100) as a direct effect of strong molecule-substrate interaction. This work demonstrates STM combined TERS is a complementary technique to characterize a system completely at the angstrom scale.

Exploring chemistry of surface-supported nanostructures at the Angstrom scale using ultrahigh vacuum tip-enhanced Raman spectroscopy

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.