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High-Resolution Tip-Enhanced Raman Scattering Probes Sub-Molecular Density Changes

preprint
submitted on 10.04.2019 and posted on 11.04.2019 by Xing Chen, Pengchong Liu, Zhongwei Hu, Lasse Jensen

Tip-enhanced Raman spectroscopy (TERS) exhibits new selection rule and sub- nanometer spatial resolution, which is attributed to the plasmonic near-field confinement. Despite recent advances in simulations of TERS spectra under highly confined fields, a simply physical mechanism has remained elusive. In this work we show that single-molecule TERS images can be explained by local sub-molecular density changes induced by the confined near-field during the Raman process. The local sub-molecular density changes determine the spatial resolution in TERS and the gradient-based selection rule. Using this approach we find that the four-fold symmetry of meso-tetrakis(3,5- di-tert-butylphenyl)porphyrin (H2TBPP) TERS images observed in experiments arises from the combination of degenerate normal modes localized in the functional side groups rather than the porphyrin ring as previously considered. As an illustration of the potential of the method, we demonstrate how this new theory can be applied to microscopic structure characterization.

Funding

NSF Grant CHE-1414466

History

Email Address of Submitting Author

jensen@chem.psu.edu

Institution

Department of Chemistry, Pennsylvania State University, University Park, Pennsylvania 16802

Country

United States

ORCID For Submitting Author

0000-0003-1237-5021

Declaration of Conflict of Interest

none

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