Berlin 2005 – wissenschaftliches Programm

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CPP: Chemische Physik und Polymerphysik

CPP 36: Single molecules II

CPP 36.3: Vortrag

Mittwoch, 9. März 2005, 11:45–12:00, TU C243

Near-field tip-enhanced Raman spectroscopy – towards single molecule sensitivity — •Catalin C. Neacsu and Markus B. Raschke — Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, D-12489 Berlin

The local-field enhancement at a sharp metallic tip in combination with resonance Raman spectroscopy provide an optical scanning probe method with ultrahigh spatial resolution and in principle sensitivity down to the single molecule level. Illuminating the apex of a Au wire tip in close proximity to the sample the resonance Raman response of malachite green and rhodamine 6G adsorbed on flat gold surfaces has been studied. The strong near-field coupling between Au tip and sample results in a high degree of field-confinement within several nm of tip-sample distance and is responsible for the Raman intensity enhancement. Spectral Raman line narrowing compared to the ensemble average and spectral diffusion is observed for submonolayer coverages: temporal fluctuations of spectral position and relative peak intensities as well as transient line splitting in time series of sequentially recorded spectra are indicative of probing only a small ensemble or cluster of molecules. These results indicate that with further improvements in tip preparation and illumination/detection efficiency single molecule Raman microscopy and spectroscopy is achievable in scattering-type near-field microscopy.