Near-field Raman imaging of organic molecules by an apertureless metallic probe scanning optical microscope

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Abstract
Near-field Raman imaging of organic molecules is demonstrated by an apertureless near-field scanning optical microscope, the tip of which is a silver-layer-coated cantilever of an atomic force microscope (AFM). The virtue of the enhanced electric field at the tip apex due to the surface plasmon polariton excitations enhances the Raman scattering cross sections. This phenomenon allows us to reveal from near-field Raman images the molecular vibrational distributions of Rhodamine6G and Crystal Violet molecules beyond the diffraction limit of a light. These molecular vibrations cannot be distinguished by AFM topographic images.