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

Abstract

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 SiO 2 ) the tips give ∼7× 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.

Controlled Fabrication of Optical Signal Input/Output Sites on Plasmonic Nanowires

“…To date, various metal nanostructures have been investigated for plasmonic waveguiding, including metallic stripes, − nanoparticle arrays, − grooves/slots/teeth, − and tapered plasmonic waveguides. , Chemically synthesized silver nanowires (AgNWs) are especially promising with their well-defined crystallinity (thus smooth surfaces) and low absorption at both visible and near-infrared spectral ranges, affording them excellent plasmonic properties. − Their potential has been demonstrated in applications including plasmonic logic gates, ,, sensors, and lasers. , AgNWs are also excellent tools for nanoscopy, especially as they can allow for the separation in space of the points of optical excitation and probing. Remote excitation of single molecule fluorescence, surface-enhanced Raman scattering (RE-SERS), , and tip-enhanced Raman scattering (TERS) − have all been developed in this context. RE-SERS has even been applied inside single live cells, such that AgNWs become plasmonic endoscopes …”

Visualizing Ribbon‐to‐Ribbon Heterogeneity of Chemically Unzipped Wide Graphene Nanoribbons by Silver Nanowire‐Based Tip‐Enhanced Raman Scattering Microscopy

“…[31][32][33][34][35] Our group has recently developed a novel atomic-force microscopy-based TERS (AFM-TERS) probe by functionalizing chemically synthesized silver nanowires to a standard silicon AFM cantilever. [36][37][38][39] High TERS mapping stability as well as extremely high sensitivity aided by the silver nanowires allows us to map out a sample's nanoscale properties, such as defect characterizations on single CNTs below 10 nm resolution. [36][37][38][39] In this paper, we attempt to characterize ribbon-to-ribbon heterogeneity of DWNT unzipped GNRs (ribbon width: 10-40 nm) in terms of defect density and edge structure, focusing on the early unzipping reaction stage (1 h sonication).…”

Gold-coated silver nanowires for long lifetime AFM-TERS probes

“…Polarized laser light is focused on an apex of a metalized scanning probe, at which the freely propagating far-field light is converted to a nanoconfined near-field EM field through the excitation of the localized surface plasmon resonances (LSPRs). 22 The LSPRs could significantly enhance the Raman scattering from the target sample underneath the apex. Since the spatial resolution of TERS is determined by the confinement size of LSPRs, it depends on the size of the apex that is typically a range of 10–20 nm or higher.…”