NCAFM2023 Programme Booklet

Tuesday 1100 - 1120

COMBINING NC AFM WITH TIP ENHANCED RAMAN SPECTROSCOPY

Shijing Tan

1 Hefei National Research Center for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026, China Email: tansj@ustc.edu.cn

The fast development of non-contact atomic force microscope (NC-AFM) has enabled chemical-bond resolution of the skeleton structures of single molecules, nano-graphene, and on-surface synthesized nanostructures1-2. But NC-AFM is still lack of chemical sensitivity in recognizing chemical species. One strategy to achieve chemical resolution is to measure the localized vibrational normal modes, which is known as the “chemical fingerprints” in determining chemical bonds and functional groups3. Recent advancements in tip-enhanced Raman spectroscopy based on scanning tunneling microscope (STM-TERS) with a “picocavity”, has reached ~1.5 ångström resolution in detecting the localized vibrational modes in real-space3-4. At this stage, it can be anticipated that a combination of NC-AFM and STM-TERS can provide a comprehensive means to interrogate the geometrical and chemical structures of nano structures with chemical-bond resolution. Along this line, I will present two progresses: (1) determining single-bond chemical reaction. We find even a single C-H bond breaking of pentacene molecule can substantially change not only the molecular stereo configuration, but also the electronic structures and localized vibrational normal modes. Such structure-property relationship is correlated directly by combining NC-AFM and STM-TERS5. (2) determining intramolecular isotope effect. The NC-AFM cannot distinguish the isotope substitutions, such as in pentacene and its fully-deuterated form. We report a combination of NC-AFM and STM-TERS can detect the isotope D atoms induced changes not only in vibrational frequencies, but also in vibrational distributions in real-space.

Fig. 1 Left panel is a schematic drawing that shows a pentacene molecule should contain the skeleton, organ and muscle similar as the human body. Right panel is an example of STM, AFM and TERS images that show the electronic, geometric and chemical structures of a pentacene molecule, respectively. References [1] L. Gross, F. Mohn, N. Moll, P. Liljeroth, G. Meyer, The Chemical Structure of a Molecule Resolved by Atomic Force Microscopy. Science 2009 , 325, 1110-1114. [2] Q. Fan, et al., Biphenylene network: A nonbenzenoid carbon allotrope. Science 2021 , 372, 852-856. [3] R. Zhang, et al., Chemical mapping of a single molecule by plasmon-enhanced Raman scattering. Nature 2013 , 498, 82. [4] J. Lee, K. T. Crampton, N. Tallarida, V. A. Apkarian, Visualizing vibrational normal modes of a single molecule with atomically confined light. Nature 2019 , 568, 78-82. [5] J. Xu, et al., Determining structural and chemical heterogeneities of surface species at the single-bond limit. Science 2021 , 371, 818-822.

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