Near-field optical microscopy and spectroscopy with pointed probes.

In recent years, developments in near-field techniques exploiting far-field illumination of a pointed, apertureless probe have demonstrated a newfound excitement. This is due in part to the advantages afforded by apertureless techniques that allow for the practical implementation of spectroscopic contrast mechanisms at length scales below 100 nm. These mechanisms include Raman and infrared absorption for chemical contrast, as well as materials contrast based on dielectric dispersion. In this review, we briefly describe the evolution of the field from the "classical" aperture-based approach toward the development of near-field optical microscopy with pointed probes. We highlight advances in state-of-the-art theory that describe the field distribution under an illuminated probe, as well as advances in the experimental implementation of scattering and excitation probe techniques.