Abstract: 
This talk explores a new path forward toward the goal of probing single-molecule processes via scanning tunneling microscopy (STM) and tip-enhanced Raman spectroscopy (TERS). The combination of STM imaging and optical spectroscopy will be discussed as a promising approach to raise both the spatial and spectral resolution of molecules to an unprecedented level. At the beginning of this talk, I will show you the molecular resolution imaging with multiple vibration modes detection by a plasmonic STM probe. The probe plays a key role both in achieving atomic resolution and enabling single molecule chemical sensitivity through plasmonic enhancement. Besides chemical identification of these molecular adsorbates, intramolecular vibrational distribution can be used for unraveling the intricacies of adsorbate-asorbate/adsorbate−substrate interactions. We have unraveled the orientation of PPDI molecules at the dynamic molecular domain boundary with ~4 nm spatial resolution by TERS mapping. TERS provides access to molecular adsorption geometries when STM provides no topographical information. Next, the strong adsorbate-substrate interaction between the meso-tetrakis-(3,5-ditertiarybutylphenyl)-porphyrin (H2TBPP) and the underlying Cu(111) substrate leads to the formation of the bowl up/down conformations at room temperature. Through simultaneous TERS and STM analysis on the neighboring conformational isomers, we have observed ~15 cm-1 spectral shift in one of the porphyrin-ring Raman modes and analyzed the origin of this shift using DFT calculations. The Angstrom-scale spatial resolution in TERS has been achieved in this study. The last topic illuminates that a new two-dimensional molecular superstructure of subphthalocyanine (SubPc). The organic molecular thin layer consists of two distinct molecular binding configurations, both of which interact relatively weakly with the underlying metallic substrate as revealed by high-signal-to-noise enhanced Raman.

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Reference:  
[1] N. Jiang, N. Chiang, L. Madison, E. Pozzi, M. Wasielewski, T. Seideman, M. Ratner, M. Hersam, G. Schatz, and R. P. Van Duyne, “Nanoscale Chemical Imaging of a Dynamic Molecular Phase Boundary with Ultrahigh Vacuum Tip-Enhanced Raman Spectroscopy”, Nano Lett., 16, 3898 (2016).

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[2] N. Chiang, X. Chen, G. Goubert, D. Chulhai, X. Chen, E. Pozzi, N. Jiang, M. Hersam, T. Seieman, L. Jensen, and R. P. Van Duyne, “Conformational Contrast of Surface-Mediated Molecular Switches Yields Angstrom-Scale Spatial Resolution in Ultrahigh Vacuum Tip-Enhanced Raman Spectroscopy”, Nano Lett., 16, 7774 (2016).

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[3] N. Chiang, N. Jiang, L. Madison, E. Pozzi, M. Wasielewski, M. Ratner, M. Hersam, T. Seideman, G. Schatz, and R. P. Van Duyne, “Probing Intermolecular Vibrational Symmetry Breaking in Self-Assembled Monolayers with Ultrahigh Vacuum Tip-Enhanced Raman Spectroscopy”, J. Am. Chem. Soc., 139,18664 (2017).

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[4] P. J. Whiteman, J. F. Schultz, Z. D. Porach, H. Chen., N. Jiang, “Dual Binding Configurations of Subphthalocyanine on Ag(100) Substrate Characterized by Scanning Tunneling Microscopy, Tip-Enhanced Raman Spectroscopy, and Density Functional Theory”, J. Phys. Chem. C, 122, 5489 (2018).

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Biography: 
Nan Jiang is currently an assistant professor of Chemistry at University Illinois at Chicago. He received his B.S. form the University of Science and Technology of China in 2004, and Ph.D. from the Institute of Physics, Chinese Academy of Sciences (Advisor: Professor Hongjun Gao) in 2010. He was also a Joint Ph.D. student in Max Planck Institute for Solid State Research with Professor Klaus Kern. Before he started his independent faculty career at UIC, he worked as a postdoctoral fellow with Professor Richard Van Duyne, who is known for the discovery of surface-enhanced Raman spectroscopy (SERS), at Northwestern University. Prof. Jiang's group focuses on applying scanning probe-based nanotechnology, including scanning probe microscopy (SPM) and tip enhanced Raman spectroscopy (TERS), to design, synthesize and characterize new nanomaterials and molecular assemblies. They are interested in fundamental science and applications at the nano-scale, including charge transfer, electron localization and generation, photoabsorption and photoemission, which are at the heart of the next generation single-molecule devices. Prof. Jiang published more than 30 articles, including Nano Letters, J. Am. Chem. Soc., Phys. Rev. Lett. etc, which received more than 1500 times citations.