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Tip-enhanced Raman Spectroscopy (TERS) is a nanoscale chemical analysis and imaging method with a spatial resolution of <10 nm, even at ambient conditions [1]. TERS relies on the enhancement of the local electromagnetic field by a plasmonic metal nanostructure that is scanned over the sample by means of a scanning probe microscope, using either AFM or STM feedback. Analogous to SERS, the local electromagnetic field of Raman scattered light is enhanced by many orders of magnitude in TERS, large enough to render monomolecular films and 2D materials spectroscopically visible that would otherwise be optically too thin to be analyzed with conventional vibrational spectroscopy.

In the first part of the presentation, the working principle, experimental realization, and capabilities of TERS will be presented [1]. Several practical aspects will be discussed, including interpretation (and misinterpretation) of TERS spectra due to issues such as tip contamination and sample decomposition triggered by the very high local field under the TERS tip. Recent data from our lab shows that this is due not primarily a thermal effect, but rather due to plasmon-driven, photocatalytic reactions [2]. Strategies to mitigate sample decomposition, for imaging studies of fragile samples over extended periods of time, and strategies to improve the reproducibility of TERS, especially for investigation of biological samples, will be presented.
In the second part of the presentation, applications of TERS to the spatially resolved chemical analysis and imaging of molecular nanomaterials and surfaces at the nanoscale will be discussed. Examples from recent TERS studies in our laboratory will be chosen, such as two-dimensional polymers [3], biological nanostructures such as amyloid forming proteins, self-assembled monolayers, model membranes, and cell membranes [4, 5], and catalysts [6, 7].

 

[1] J. Stadler, T. Schmid, and R. Zenobi, Developments in and Practical Guidelines for Tip-Enhanced Raman Spectroscopy, Nanoscale 4 (2012) 1856-1870.
[2] J. Szczerbiński, L. Gyr, J. Kaeslin, and R. Zenobi, Plasmon-driven Photocatalysis Leads to Products Known from E-Beam and X-Ray-induced Surface Chemistry, Nano Lett. 18 (2018) 6740-6749.
[3] F. Shao, W. Wang, W. Yang, Z. Yang, Y. Zhang, J. Lan, A.D. Schlüter, and R. Zenobi, In-Situ Nanospectroscopic Imaging of Plasmon-Induced Two-Dimensional [4+4] Photopolymerization on Au(111), Nature Commun. 12 (2021) 4557.
[4] Y. Pandey, N. Kumar, G. Goubert, and R. Zenobi, Nanoscale Chemical Imaging of Supported Lipid Monolayers using Tip-Enhanced Raman Spectroscopy, Angew. Chem. Int. Ed. Engl. 50 (2021) 19041-19046.
[5] D. Mrđenović, W. Ge, N. Kumar, and R. Zenobi, Nanoscale Chemical Imaging of Human Cell Membrane using Tip-Enhanced Raman Spectroscopy, Angew. Chem. Int. Ed. Engl. 61 (2022) e202210288.
[6] H. Yin, L.-Q. Zheng, W. Fang, Y.-H. Lai, N. Porenta. G. Goubert, H. Zhang, H.-S- Su, B. Ren, J.O. Richardson, J.-F. Li, and R. Zenobi, Nature Catal. 3 (2020) 834-842.
[7] Z.-F. Cai, J.P. Merino, W. Fang, N. Kumar, J.O. Richardson, S. De Feyter, and R. Zenobi, Molecular-Level Insights on Reactive Arrangement in On-Surface Photocatalytic Coupling Reactions Using Tip-Enhanced Raman Spectroscopy, J. Am. Chem. Soc. 144 (2022) 538-546.
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