Design, Characterization, and Manufacturing of Ultra-sharp Metallic Probes for Near-field Optics

Abstract

The ability to manipulate and nanofocus light has many potential applications such as surface-enhanced spectroscopy, optical trapping, heat-assisted magnetic recording, and near-field imaging. In this thesis a new method to fabricate devices for nanofocusing is introduced and then demonstrated for use in near-field imaging. This method uses a sharp, metallic tip to confine and focus the light. Current methods to produce these sharp tips suffer from low reliability and low-throughput processing methods. Here a fabrication method called template stripping is introduced. With this method, precise control over the fabrication of metal films with integrated bumps, grooves, and holes is shown. Next, the method is used to fabricate sharp, metallic tips. The tips are used for near-field imaging and show a resolution of < 20 nm and observed fluorescence enhancements of ~200x from single fluorescent molecules. The tips are also demonstrated for near-field Raman imaging of carbon nanotube bundles and show good results. These tips provide high-quality results, but one of the more important features is that the yield of the tips is around 95%, much higher than current methods for fabricating sharp, metallic tips. Also, different schemes to create nanofocusing are presented. One method makes use of an asymmetric metal deposition and another a C-shaped aperture around the tip to focus light illuminating the tip from inside itself. Both of these methods show significant nanofocusing and provide new structures for nanofocusing studies. The processes to fabricate these structures are developed with the hope that they will be widely disseminated to allow more researchers access to reliable tips and hopefully bringing more people into the field of near-field imaging.