One-side metal-coated pyramidal cantilever tips for highly reproducible tip-enhanced Raman spectroscopy.

Tip-enhanced Raman spectroscopy (TERS) has been recognized as a useful tool for nanoscale chemical analysis, and it can further reach down to the sub-nanometer scale in the gap-mode configuration. Using an atomic force microscopy (AFM) in gap-mode TERS for position control of a metallic tip, a unique and correlative analysis can be even realized at the single molecule level. However, one of crucial issues in AFM-based gap-mode TERS is the fabrication of reliable and reproducible cantilver metallic tips. Here, we propose a simple, cost-effective fabrication method of metal-coated tips for AFM-based gap-mode TERS by means of the physical vapor deposition technique in a reproducible way. Our plamonic tips have extremely smooth silver layers on one side of the pyramidal tip, which is totally different from the regular metallic tips that hold granular metallic structures randomly arranged on their bodies. Importantly, all fabricated tips exhibited a reasonably high enhancement factor of more than 104, which indicates that the reproducibility of our plasmonic tip is virtually 100% in the gap-mode configuration. The excellent reproducibility of gap-mode TERS measurement holds great promise for rendering AFM-based TERS as a powerful analytical technique in a broad range of fields.