Light-Directed Tuning of Plasmon Resonances via Plasmon-Induced Polymerization Using Hot Electrons

Abstract

The precise morphology of nanoscale gaps between noble-metal nanostructures controls their resonant wavelengths. Here we show photocatalytic plasmon-induced polymerization can locally enlarge the gap size and tune the plasmon resonances. We demonstrate light-directed programmable tuning of plasmons can be self-limiting. Selective control of polymer growth around individual plasmonic nanoparticles is achieved, with simultaneous real-time monitoring of the polymerization process in situ using dark-field spectroscopy. Even without initiators present, we show light-triggered chain growth of various monomers, implying plasmon initiation of free radicals via hot-electron transfer to monomers at the Au surface. This concept not only provides a programmable way to fine-tune plasmons for many applications but also provides a window on polymer chemistry at the sub-nanoscale.

“Hot” in Plasmonics: Temperature‐Related Concepts and Applications of Metal Nanostructures

“…The authors were able to track the NP oscillations in real time by observing the spectral shift of the plasmonic resonance due to the change in the nanocavity width between the Au NP and the bulk Au substrate . In addition, in a similar experimental setup Ding et al demonstrated that the plasmon resonance of Au NPs could be controllably tuned by triggering a polymerization reaction within the gap between the NP and the Au substrate . In this experiment, the Au substrate was coated with a self‐assembled monolayer of thiophenol and Au NPs were then drop‐cast on top.…”

“…Thermoplasmonics is an emerging hot topic that offers a route to controllable actuation at the nanoscale and reversible plasmon tuning of sensing devices . The ability to manipulate nanoparticles in order to create and steer nanostructures is essential in many applications such as drug delivery, noninvasive microsurgery, nanoassembly, and fabrication …”

“…A similar effect was also observed for NIPAM polymerization. The proposed mechanism to explain the in situ polymerization reaction within the nanocavity between the Au NP and the substrate is based on plasmon generated hot electrons and was demonstrated to be self‐limiting . Such tunable plasmonic hot spots are exciting candidates for studying localized hot electron photochemical reactions and for plasmon‐tuned sensing devices.…”

“…Recent key results have demonstrated that the actuation from the ANTs can be coordinated along a common direction, and that ANTs can power DNA origami constructs . Moreover, the polymer can be grown within the plasmonic hotspots, in a light‐guided and well‐controlled fashion . Additionally, some polymers are best attached to the plasmonic nanoparticles using for instance NH 2 groups (compared to SH, COOH, and H terminations); this is because the terminal group determines how close the nanoparticles are brought together in the contracted state .…”

From active plasmonic devices to plasmonic molecular electronics

“…Note that saturated polymers have also been generated locally on AuNPs. Polymerization took place even without initiators, implying plasmon initiation of free radicals via hot‐electron transfer to monomer at the Au surface …”