Tip-enhanced Raman spectroscopy and imaging: an apical illumination geometry.

Results are presented illustrating the use of tip-enhanced Raman spectroscopy (TERS) and imaging in a top-illumination geometry. A radially polarized beam is used to generate an electric field component in the direction of beam propagation, normal to the surface, resulting in a 5x increased enhancement compared to a linearly polarized beam. This multiplicative enhancement facilitates a discrimination of the near-field signal from the far-field Raman background. The top illumination configuration facilitates the application of TERS for investigating molecules on a variety of surfaces, such as Au, glass, and Si. The near-field Raman spectra of Si(100), rhodamine B, brilliant cresyl blue, and single wall carbon nanotubes are presented. Sufficient enhancement is obtained to permit a sub-diffraction-limited resolution Raman imaging of the surface distribution of large bundles of carbon nanotubes of various diameters.