Abstract
Sphere-segment void (SSV) cavities have emerged as promising substrates for reproducible Surface Enhanced Raman Scattering (SERS), offering strong and uniform electromagnetic enhancement associated with the excitation of cavity-like localized surface plasmon resonances tunable across the UV–vis-near IR range, with a facile large-scale fabrication process. High-resolution electron micrographs of these structures reveal a considerable departure from the idealized smooth spherical cavity shape; notably, the electrochemical deposition of gold yields an important surface roughness. We investigate this contribution to the SERS activity of SSV substrates with a series of experiments, varying the degree of surface roughness using thermal annealing and gradual electrochemical roughening. Notably, we observe that both roughness features and cavity-like modes operate in conjunction as a multiscale antenna to provide larger SERS efficiency than the two mechanisms considered separately. We conclude that the main role ...
Highlights
The optical properties of gold nanostructures have been the object of intense research activity in the past decades, owing to their promising potential in a variety of technological applications ranging from solar cells, electronics, wave guiding, sensing, display technology, and so on.[1,2] As light interacts with noble metals, the high density of free conduction electrons may sustain collective oscillations known as surface plasmon resonances, which entail these nanostructures with unique optical properties, such as strongly enhanced scattering and absorption, as well as focusing of incident radiation into localized regions of space with enhanced near-fields
In order to correlate the effect of surface roughness in sphere-segment void (SSV) arrays, we started with experiments on a flat, unpatterned gold surface
We have demonstrated that SSV arrays obtained by electrodeposition present stronger Surface Enhanced Raman Scattering (SERS) enhancement factors when both nanoscale surface roughness and plasmon modes resulting from the patterned structure are acting in concert
Summary
The optical properties of gold nanostructures have been the object of intense research activity in the past decades, owing to their promising potential in a variety of technological applications ranging from solar cells, electronics, wave guiding, sensing, display technology, and so on.[1,2] As light interacts with noble metals, the high density of free conduction electrons may sustain collective oscillations known as surface plasmon resonances, which entail these nanostructures with unique optical properties, such as strongly enhanced scattering and absorption, as well as focusing of incident radiation into localized regions of space with enhanced near-fields. In attempting to correlate spectral reflectivity maps for a variety of samples with observed SERS enhancement factors for a probe molecule uniformly deposited over the cavities, plasmon resonances were seen to have a role in the response, but were not the only factor at play.[17,18] SSV arrays are complex nanostructures presenting numerous unavoidable fabrication defects and intrinsic roughness. Their complex geometry yields many plasmonic excitations that can be hard to capture even with state-of-the-art electromagnetic modeling tools. In this context, detailed and systematic experimental studies are often needed to fully explore the rich optical response of such samples
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