Enhancement of Raman Signals with Silver-Coated Tips

Abstract

Silver coated SiN and SiO₂ tips have been fabricated for use with a bottom-illumination tip-enhanced Raman spectroscopy (TERS) setup with a 488 nm laser excitation. SiN tips with 50–60 nm of deposited Ag give the best TERS enhancements for brilliant cresyl blue test analyte spin-coated on a glass slide. Ag nanoparticles on SiN or SiO₂ rather than Si tips are better for TERS because of the proximity of the wavelengths of their surface plasmon resonance to 488 nm. Adjustments of tilt angle of the metallized tip with respect to the surface plane is shown to considerably raise the intensities of the TERS signals, even from tips that initially appear to be rather non-enhancing. This work helps to enable the more frequent use of the 488 nm laser for nanoscale chemical analysis with both TERS and fluorescence imaging in the same setup.