Light depolarization induced by sharp metallic tips and effects on Tip-Enhanced Raman Spectroscopy

Tip-Enhanced Raman Spectroscopy is based on the field enhancement and confinement provided by sharp metallic tips, used to locally excite the Raman emission from molecules, crystals and nanostructures. This technique has recently demonstrated capabilities for nanometer scale optical resolution in Raman analysis and has enormous potential applications in nano- and bio-technologies. In this paper we describe the state-of-the-art experimental techniques, focusing the attention on the strategies to reduce the far-field background, on new processes to fabricate sharp metallic tips and on the effect of the depolarization produced by metallic tips on Tip-Enhanced Raman spectra of bulk crystals.