Sub-nm resolved single-molecule Raman spectromicroscopy
Hefei National Laboratory for Physical Sciences at the Microscale and Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science and Technology of China (USTC), Hefei 230026, China
To access individual chemical identity of closely packed molecular species at the nanoscale in a reliable and unambiguous way is a scientific challenge but of important practical applications in materials science, biology, and molecular nanotechnology. Molecular vibrations provide a valuable "fingerprint" for this identification. The vibrational spectroscopy based on tip-enhanced Raman scattering (TERS) has opened a path to obtain enhanced vibrational signals thanks to the strong localized plasmonic field at the tip apex. In this talk, I shall demonstrate single-molecule Raman spectroscopic imaging with unprecedented sub-nm spatial resolution, resolving even the inner structure of a single molecule and its configuration on the surface . This is achieved by using a plasmon-enhanced nonlinear TERS technique that invokes a double-resonance process and resultant nonlinear optical effect, thanks to the exquisite control and tuning capability provided by low-temperature ultrahigh-vacuum scanning tunneling microscopy (STM) . I shall also demonstrate the power of this STM-controlled nonlinear TERS technique in distinguishing adjacent but different molecules on surfaces in real space and address the issue of how close and how similar these different molecules can be. These findings should open up new avenues for probing and controlling nanoscale structures, catalysis, photochemistry, and even DNA sequencing, all at the sub-nm and single-molecule scale.
 R. Zhang, Y. Zhang, Z. C. Dong*, S. Jiang, C. Zhang, L. G. Chen, L. Zhang, Y. Liao, J. Aizpurua, Y. Luo, J. L. Yang , and J. G. Hou*, Nature 498, 82-86 (2013)
 Z. C. Dong*, X. L. Zhang, H. Y. Gao, Y. Luo, C. Zhang, L. G. Chen, R. Zhang, X. Tao, Y. Zhang, J. L. Yang, J. G. Hou*, Nature Photon. 4, 50-54 (2010)