Near-field optical spectroscopy with 20 nm spatial resolution

A near-field optical method is introduced that makes use of the strongly enhanced electric field close to a sharply pointed metal tip under laser illumination. The tip is held a few nanometers above the sample surface so that a highly localized interaction between the enhanced field and the sample is achieved. The method has been successfully combined with vibrational spectroscopy by making use of the well-known effect of surface enhanced Raman scattering (SERS). We mapped out the vibrational modes of individual single-walled carbon nanotubes (SWNT) with a resolution better than 20 nm. The technique has great potential for becoming a routine tool for the chemical analysis of surfaces at high spatial resolution.