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Tip enhanced Raman scattering with adiabatic plasmon focusing tips.

Bek, Alpan
De, Angelis
Di, Fabrizio
Tip-Enhanced Raman spectroscopy (TERS) is a promising microscopy technique which combines, in principle, outstanding spatial resolution with a detailed chemical analysis of the sample. However, as yet, it is not routinely used although an increasing number of research groups are becoming more actively involved in the field. Among the several reasons which can explain the relatively low usage of TERS, the lack of reproducibility of tips as field enhancers is probably the most critical. Here we propose and demonstrate a TERS microscope which uses photonic engineered tips. These tips are based on standard silicon nitride atomic force microscope (AFM) cantilevers. A photonic crystal together with a plasmonic waveguide focuses the Raman excitation laser to the apex of the waveguide, enabling a photon confinement equivalent to the radius of curvature of the nanofabricated tip. These tips were successfully applied here in both AFM imaging and high resolution Raman spectroscopy. The new tips produced AFM imaging performances comparable with the best AFM commercial tips. Moreover, we demonstrate that the photonic crystal combined with the plasmonic waveguide acts effectively as a localized near field emitter.