Single-molecule vibrational Raman spectroscopy of malachite green adsorbed on planar metal surfaces is achieved by means of optical local-field enhancement provided by a scanning nanoscopic metallic tip. The single-molecule signature is evident from spectral diffusion and a discretization of Raman peak intensities. The optical tip-sample coupling gives rise to a localization of the response down to a sub-100.3em0exnm length scale and a Raman enhancement up to ~5×10⁹. This combines vibrational spectroscopy with high resolution scanning-probe microscopy for ultrasensitive in situ analysis of individual molecules.
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Neacsu et al. (2006) studied this question.