Raman scattering is a tensorial quantity. In ensemble measurements the orientationally averaged polarizability tensor determines the spectrum. Since, for single molecules or for ensembles with net orientation, as is the case for plasmonic nano-junctions, orientational averaging is not justified and the spectra will be determined by the local vector fields. More importantly, relative intensities of lines contain information about the molecular position and orientation in 3-D space.Raman trajectories can be used to follow molecular motion in real space. In the case of nano junctions with short gaps, in addition to plasmonic enhancement, plasmonic current through the molecule can lead to enhanced scattering and significant spectral perturbation. This mechanism can be used to track bond formation and breaking of molecules that can bridge the gap. Experimentally, we combine SERS with various microscopy (AFM, STM, SEM & TEM) techniques to identify and correlate the correspondence of spectral and structural fluctuations.

Tracking motions of single molecules through tensorial SERS

246th National Meeting (2013)

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