Tip-based plasmonics: squeezing light with metallic nanoprobes

Nanofabricated metallic tips are at the core of important research in single-molecule imaging, near-field scanning optical microscopy, tip-enhanced Raman spectroscopy, as well as potential commercial applications such as heat-assisted magnetic recording. While challenging to fabricate, much progress has been made towards the reliable production of extremely sharp (10 nm) metallic probes. In this review, the various factors that go into the design of metallic tips, their fabrication, packaging and system integration, characterization, passivation, and eventual use are discussed. Fabrication challenges, implementation issues, optical excitation schemes, and various current and emerging applications are also discussed. For the rapidly emerging fields of plasmonics and nanophotonics, the use of sharp metallic tips has generated significant scientific progress and will play an integral role well into the future.