Chapter 8 Near-field nano-Raman spectroscopy for molecular analysis and imaging

Abstract

This chapter presents the molecular distribution of nano-imaging colored by Raman-scattering spectral shifting, which is probed with a metallic tip. The metallic probe tip has been used to enhance the optical field only near the probe tip. Raman scattering and infrared absorption spectroscopy allow for the direct observation of molecular vibrations without necessarily photobleaching sample as well as quenching of the sample. The Raman scattering cross-sections of the molecules just below the enhanced electric field at the metallic tip are selectively enhanced and detected to provide a sufficiently high spatial resolution depending on the size of the enhanced electric field that corresponds to the diameter of the metallic tip. The tip-enhanced near-field Raman spectroscopy also allows to obtain localized molecular vibrational information without averaging the signal inside the diffraction limited focused spot and have not only high spatial resolution but also high signal sensitivity compared to far-field Raman spectroscopy that requires much more molecules to compensate for the small Raman scattering cross-section.