Reactive Plasmonics hosts the 7th London Plasmonics Forum

The 7th Annual London Plasmonics Forum was held online on 9 June 2021. Hosted by Professor Anatoly Zayats, PI of the EPSRC Programme Grant Reactive Plasmonics, the event was held online for the 2nd year in a row due to restrictions still being in place for large events.

As Reactive Plasmonics is coming to an end, this event also functioned as the final advisory board for the grant.  It showcased the plasmonics research carried out during the past six years, including the discovery of new materials for hot electron applications, plasmonics chemistry and photocatalysis and the use of hot electron in optoelectronics.

In the afternoon, the Plasmonics Forum welcomed two external speakers. Ruben Haman from Vrije Universiteit Amsterdam gave a talk entitled ‘Super-resolution mapping of a chemical reaction driven by plasmonic near-fields’ and Dr Wouter Koopman from Universität Potsdam spoke about ‘The importance of heat in plasmon driven coupling reactions.’

After the talks, Plasmonics researchers participated in a round table discussion about the future of the field, with new ideas for nanostructures and materials.

As the Plasmonics Forum poster session was online, entries to the poster session came from far and wide. Dr Nina Meinzer from Nature Physics, Dr Rachel Won from Nature Photonics and Dr Anna Demming from New Scientist formed the judging committee, with two winners being picked. When judging the posters, the committee considered the science presented, the poster’s design, and the flash poster presentation.

Congratulations to the winners Dr Ming Fu from Imperial College London ‘Directional Enhanced Raman Scattering Coupled into Plasmonic Waveguide with Near-Unity Couple Efficiency’ and Dr Joannna Symonowicz from the University of Cambridge for ‘Real-Time In-Situ Optical Tracking of Memrisitive Switching.’

You can watch recording so of the event below and see the posters from the AM session here and PM session here



Plasmonic nanoparticles as photocatalysts: How much energy can they supply?

Catalysts play a key role in many industrial processes, as more than 85% of the energy consumed daily by our essential-routine devices is generated by processes that involve them. Recently, it has been found that under visible light illumination, metallic nanoparticles can effectively catalyse a chemical reaction. In this work, we quantify the energy contribution of these illuminated metal nanoparticles to a chemical reaction.

When metallic nanoparticles are illuminated, their conduction electrons are excited in collective oscillations inside the nanoparticle originating what is called a surface plasmon. After excitation, the plasmon has to lose energy (decay process) to return the electrons to their original energetic state. If properly harvested, this released energy can be fruitfully used in many technological processes. Indeed, this is the idea behind plasmon-induced-photocatalysis, a new emerging area where the energy lost by plasmon-decay processes is used for triggering chemical reaction, i.e. to converter a chemical A into the chemical B.

Between all the possible surface-plasmon-decay processes, there are two that have been exploited in plasmon-induced-catalysis: the generation of highly energetic hole/electron pairs and the temperature increase at the interface. Even though both phenomena have been successfully employed as catalysts in numerous chemical reactions, in most of the cases is hard to disentangle the contribution of each of them separately. The other remarkable question behind plasmon-induced-catalysis is associated with the hot-electron/hole pair. These two entities have been theoretically proposed to be as energetic as the energy of the incident light employed for the plasmon excitation. However, this fact has been weakly explored experimentally.

In their work, RPLAS researchers at Imperial College London addressed the two aforementioned questions by implementing an opto-electrochemical setup. This microscope allowed them to:  illuminate a single gold nanoparticle (AuNP) with different CW lasers (different plasmon-excitation energies), determine the AuNP surface temperature (by the photoluminescence properties of illuminated AuNPs) and follow its catalytic behaviour (by the scattering properties of AuNPs using a dark-field microscope). Their results show that the illuminated AuNP can catalyse the chemical reaction under study by using less input energy from external sources. This could help in the future to convert sunlight energy into chemical energy or green fuels by finding catalysts that can perform this energy conversion step efficiently.

Link to research paper: Spectral Screening of the Energy of Hot Holes over a Particle Plasmon Resonance

Controlling optical response with designed electron temperature distributions in plasmonic nanostructures.

RPLAS researchers at King’s College London have discovered how to control light at ultrafast timescales by designing the distribution of energy of electrons in nanostructures. These metallic nanostructures are manmade materials that can have interesting optical properties, not found in naturally occurring materials. It has been found that these nanostructures can have regions of very high light-matter interaction, with the study of this interaction known as the field of plasmonics. By using intense pulses of laser light, electrons in these regions absorb larger amounts of energy, changing the electrons’ characteristic temperature. When the electron temperature increases, the optical properties of the material change. They can become more opaque or transparent at certain wavelengths in the spectrum of light. By altering the distribution of this electron temperature within the nanostructure, the researchers found a way to control the speed at which the optical properties of the nanostructure change. Using this they demonstrated control over the intensity of light passing through the nanostructure on a sub-300 fs time scale.

One of the researchers Luke Nicholls said, “The ability to change the dynamic optical response of nanostructures by proper design of electron temperature distributions could have wide ranging applications for technology in telecommunications and chemistry.” The switching of optical properties at faster speeds in data processing and communication, would help with the ever-growing demand on access to data, which is straining current infrastructure. Furthermore, the ability to generate hot electrons in specific locations within a nanostructure could provide added functionality in photo-assisted catalysis and nonlinear optics.

Link to research paper: Designer photonic dynamics by using non-uniform electron temperature distribution for on-demand all-optical switching times