Seminar
Tuesday, September 19, 2017 - 12:00am
Graduate student Xiang Ao will present
"Accessing Single Molecule Dynamics with Tip-Enhanced Neville Raman Spectroscopy"
on September 19, 2017 at 4:10 PM in Neville Hall, Room 3.
Abstract: Vibrational spectroscopy is a powerful tool for directly providing structural information via characteristic spectral “fingerprints”. Raman spectroscopy works based on the inelastic scattering of light, and change in frequency is convenient to separate the photons of interests from the large background signal due to the excitation. However, the signal from the inelastic scattering process is too low for probing ultra small sample sizes, not to mention single molecules. Several orders of magnitudes amplification of Raman signal was observed in surface-enhanced Raman spectroscopy. By combining scanning probe microscopy and surface enhanced Raman spectroscopy, tip-enhanced Raman spectroscopy (TERS) recently advanced to chemical identification on the scale of individual molecules. In TERS, Raman scattering is enhanced by electronic resonances and plasmons for achieving high sensitivity characterization and nanoscale or sub nanoscale spatial resolution. Recent work on single molecule study using TERS has shown promising results. TERS was applied for studying the metal−adsorbate interactions in ultra high vacuum, where the conformational dynamics of a porphyrin molecule absorbed on Cu(111) surface was distinguished with Ångstrom-scale spatial resolution. A temperature-dependent TERS was performed to observe thermally activated broadening in the Raman spectra of malachite green, opening the possibility of TERS as a tool for obtaining information about single molecule dynamics beyond chemical identification. Ångstrom level of resolution can be explained by simulating the field confinement induced by the sharp tip in single molecule TERS experiments. Due to atomistic dimensions of the molecule and the plasmonic field with which it interacts in TERS, a consistent model should treat both components at the same scale as was demonstrated with a hybrid atomistic electrodynamics-quantum mechanical approach. This research has established TERS as a modern method to study single molecule dynamics. Reference: Chiang, N.; Chen, X.; Goubert, G.; Chulhai, D. V.; Chen, X.; Pozzi, E. A.; Jiang, N.; Hersam, M. C.; Seideman, T.; Jensen, L.; Van Duyne, R. P. Conformational Contrast of Surface-Mediated Molecular Switches Yields Ångstrom-Scale Spatial Resolution in Ultrahigh Vacuum Tip-Enhanced Raman Spectroscopy. Nano Lett. 2016, 16, 7774−7778. Park, K.; Muller, E. A; Kravtsov, V; Sass, P. M; Dreyer, J; Atkin, J. M; Raschke, M.B. VariableTemperature Tip-Enhanced Raman Spectroscopy of Single- Molecule Fluctuations and Dynamics, Nano Lett. 2016, 16, 479−487 Liu,P; Chulhai, D.V; Jensen, L. Single-Molecule Imaging Using Atomistic Near-Field Tip-Enhanced Raman Spectroscopy, ACS Nano. 2017, 11, 5094−5102