Facilitating Tip-Enhanced Raman Scattering on Dielectric Substrates via Electrical Cutting of Silver Nanowire Probes

TERS is a powerful tool for nanoscale optical characterization of surfaces. However, even after 20 years of development, the parameters for optimal TERS tips are still up for debate. As a result, routine measurements on bulk or dielectric substrates remain exceptionally challenging. Herein we help to alleviate this by using electrical cutting to strategically modify silver nanowire TERS probes. Following cutting, the tips present a large, spherical apex and are often nanostructured with numerous nanoparticles, which we argue improve light collection and optical coupling. This doubles TERS signals on a highly enhancing, gap-mode substrate compared to our standard nanowire tips while maintaining a high reproducibility and resolution. More interestingly, on a dielectric substrate (graphene on SiO2) the tips give similar to 7x higher signals than our standard tips. Further investigations point to the nonlocal nature of the enhancement using standard, smooth TERS probes without gap-mode, making such nanostructuring highly beneficial in these cases.