Investigating the effect of Ag nanocube polydispersity on gap-mode SERS enhancement factors

Abstract

High Raman enhancement factors (EFs) have been observed for surface-enhanced Raman spectroscopy (SERS) substrates fabricated from colloidal metal nanoparticles. Electrodynamic models of single nanoparticles often do not accurately predict the Raman EFs measured experimentally for such colloidal substrates, which often consist of nanoparticles that exhibit heterogeneity in both size and shape. Here, we investigate the size and shape dispersity of colloidal Ag nanocube samples and their effect on Raman EF. We generate an analytical model that incorporates nanocube size dispersion and calculates the Raman EF associated with an ensemble of differently sized nanocubes. For nanocubes that are ∼70-80 nm in size, this model is sufficient to correct the inaccuracies for electrodynamic simulations of a single nanocube model. For nanocubes >90 nm, size dispersity alone fails to account for the high EFs observed when these substrates are excited off-resonance. We hypothesize that shape defects may play a significant role in optical response at these larger sizes and discuss how these factors can play a role in our analytical model.

Colloidal Plasmonic Nanocomposites: From Fabrication to Optical Function

“…Moreover, the polymer matrix serves as a convenient medium for capturing desired plasmonic structures as they evolve, enabling long-term stability of the structures. A major challenge, however, is achieving precise nanojunction orientation, rather than a distribution of orientations and cluster sizes. , The morphologies of these pNCs typically result from diffusion-limited NP assembly, since NPs must move through a high viscosity polymer medium. As a result, structures of pNCs are limited to optical functions that are highly defect-tolerant or do not place a stringent requirement on periodicity.…”

“…Of all the pINCs, the NP-on-metal absorbers are perhaps the most mature and well-studied nanocomposite structure. The layer-by-layer techniques used to fabricate these pINCs have proven to be successful over large scales within a variety of platforms, such as chemical sensing. , In contrast to other pINCs, NP-on-metal absorbers have also been demonstrated with nonprecious metals. In addition, the ability to control the geometric parameters of the optical gap characteristic of these pINCs has the potential to allow fundamental studies of optical device physics, such as quantum plasmonic effects and hot-electron generation.…”

Directed assembly and concentrating of micro/nanoparticles, cells, and vesicles via low-power near-infrared laser generated plasmonic microbubbles

“…The localization of highly enhanced electric fields, also known as "hotspots", has profound impact to light-matter interactions on plasmonic nanostructures. Nano-gaps of less than 10 nm in nanostructures or between nanoparticles support gap-mode LSPR and induce remarkable electric field localization [16,17]. Various methods have been proposed and implemented for nano-gap generation via lithography patterning of nano-gaps in gold film [18], nano-gap formation between nanoparticle or nanowire assembly [19,20], gold nanoparticle (AuNP) aggregation [21], and bi-continuous gold ligaments and porous network in nanoporous gold [22].…”

Nanoporous Gold Nanocomposites as a Versatile Platform for Plasmonic Engineering and Sensing

“…In addition to placing the LSPR resonance at the desired wavelength, plasmonic coupling-induced “hot-spots” provide additional E-field enhancement to further intensify light-matter interactions [ 17 , 18 , 19 , 20 ]. The coupling between closely located nanoparticles was shown to be efficient for both purposes: the near-field coupling can effectively shift the LSPR peak position [ 21 ] and the nano-gaps between particles can generate strong E-field due to gap-mode resonance [ 22 , 23 ].…”