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

 

 

Hot Electron Applications & Technology Showcase

Reactive Plasmonics (RPLAS) researchers were joined by representatives from industry this week to showcase potential applications of the hot-electron plasmonics.

The day started with talks on catalysis with Professor Stefan Maier giving an overview of nanophotonic approaches for energy-efficient chemical reactions. Dr Wayne Dickson then discussed scalable and reactive nanophotonics nanostructures.

Following on there were talks on nanoscale heat. Ryan Bower started by giving a presentation about refractory matierals, photo-acoustics and thermometery, and Dr Luke Nicholls talked about electron temperature.

Finally there were talks on sensing, Professor Rupert Oulton presented hot-electron photodetectors and RPLAS principal investigator Professor Anatoly Zayats then disscussed plasmonic nanostructures for gas sensing.

 

The showcase also had digital posters for each theme that  were circulated in advance. You can view short presentations for each poster at the bottom of the page.

[envira-gallery slug=”hot-electron-applications-technologies”]

 

 

 

 

Socially distanced laboratories

Experimental researchers are returning to the socially distanced laboratories as lockdown measures have been eased.

As the country starts emerging from lockdown, the laboratories have now reopened with strict social distancing rules in place.

As the country starts emerging from lockdown, the laboratories have now reopened with strict social distancing rules in place.  We asked some of our researchers to send photos of their first days back in the lab and how it feels to return to campus.

The majority of laboratory work at King’s was suspended in mid-March as the UK was put in lockdown due to the COVID-19 pandemic. This meant that the experimental elements of projects were temporarily paused as data could not be collected.

 

It’s amazing to resume work in the labs and be able to do one of the things we like the most: keep doing cutting edge research in the generation of plasmonic metamaterials with potential applications ranging from bio sensing to energy harvesting, areas of increasing interest and need in our current and post-pandemic world.– PhD Student Mayela Romero Gómez

It feels great to be back in the labs and working (>2m apart) alongside my colleagues again. It’s quite a relief that I can remember how to do experimental physics at all! Now it’s time to conduct various CO2 reduction experiments with my latest plasmonic metamaterials as nanocatalysts!– PhD Student Anastasia Zaleska

 

London Plasmonics Forum goes digital

The London Plasmonics Forum has been held annually at King’s College London since 2015, but in 2020 this was not possible due to COV-ID 19.

Instead of cancelling the event, the committee decided to move it online, and it went ahead on the scheduled date of 11 June.

Reactive Plasmonics PI’s Professor Anatoly Zayats from King’s College London and Professor Stefan Maier from Imperial College London chaired the online Forum.

Professor Thomas Ebbesen from the University of Strasbourg opened the event with the keynote talk on The Alchemy of Vacuum, overviewing how vacuum modes can influence chemistry and superconductivity,  with a busy Q&A session after.

LPF2020


 

Other speakers included Dr Diane Roth from King’s College London with the presentation on holography with metamaterials. This was followed by Daniel Glass from Imperial College London presenting details of photo-enhanced Raman spectroscopy. Finally, Dr Emilie Ringer from the University of Cambridge gave a talk focused on plasmonics with magnesium nanoparticles.

 

As the event was online, it allowed the wider plasmonics community to get involved, with delegates tuning in from time zones ranging from Japan in the east, to the Pacific coast of the US in the west. – See the infographic below for details.

 

The digital poster session drew entries from researchers from all over the world, including Russia, India, the UK and Europe. It was judged by science journalist Dr Anna Demming, Dr Nina Menzier from Nature Physics, and Dr Rachel Won from Nature Photonics.

 

The standard of the posters was excellent; we would like to congratulate everyone who entered the competition. We want to thank those who visited our website to view the posters and watch the flash poster presentations. We hope to meet everyone again in person in 2021 for the 7th London Plasmonics Forum.

 

Eric Goerlitzer form University of Erlangen-Nuremberg won a prize for his poster and flash presentation entitled ‘Chiral Surface Lattice Resonances.’

Eric Goerlitzer

 

Dr Ana Sousa-Castillo from Nanoinstitute Munich won a prize for her poster ‘Efficiency of Hot Electron Injection in Plasmon-Assisted PhotoCatalysis

Sousa-Castillo, Anna London Plasmonic Forum-ASC

You can view the rest of the posters here and watch the flash poster presentations below.

 

Synthetic synapses get more like a real brain

The human brain easily outperforms today’s state-of-the-art supercomputers fed on just the calorie input of a modest diet, as opposed to the full-scale power station energy input that a supercomputer guzzles through. The difference stems from the multiple states the brain processes with versus the two binary states of digital processors, as well as the ability to store information without power consumption – ‘non-volatile memory’. These inefficiencies in today’s conventional computers have prompted great interest in developing ‘synthetic synapses’ for use in computers that can mimic the way the brain works. Now RPLAS reseachers at King’s College London, UK, report in ACS Nano Letters an array of nanorod devices that mimic the brain more closely than ever before. The devices may find applications in artificial neural networks.

How the brain works

Conventional computers have processors and memory components connected by wires in a circuit. However, in the brain the connections themselves also have memory functions. Signals pass from one biological neuron to another thanks to connecting synapses, and the connectivity of these synapses changes depending on what signals they have transferred in the past – practise makes perfect because repetition improves these synaptic connections.

Efforts to emulate biological synapses have revolved around types of ‘memristors’ – circuit elements that have a resistance that changes depending on what signals have passed through previously. “A memristor is very similar to how a synapse works,” explains Anatoly Zayats, a professor at King’s College London who led the team behind the recent results. Previous synthetic synapses based on memristors have responded to an input voltage through material changes such as the formation of filaments in insulator layers or a chemical change. This might be detected as a change in the electrical resistivity or the light emission characteristics. However, unlike the brain the devices reported so far have all needed a reverse polarity electrical voltage to reset them to the initial state.

“In the brain a change in the chemical environment changes the output,” explains Zayats. These chemical changes may be fluctuations in the ion concentrations around the synapse. Exposure to different chemicals then reverts the changes, even though the polarity of the electric field remains unchanged. The King’s College London researchers have now been able to demonstrate this brain-like behaviour in their synaptic synapses as well.

Synapse-like polymer junctions

Zayats and team build an array of gold nanorods topped with a polymer (poly-L-histidine, PLH) junction to a metal contact. Either light or an electrical voltage can excite plasmons – collective oscillations of electrons that release hot electrons into the PLH, changing the chemistry of the polymer. Depending on the chemical environment around the synthetic synapse, the chemical changes will increase or decrease the electrical conductivity or light emission intensity of the junction. In air oxidative dehydrogenation reactions gradually take place, changing the junction’s characteristics in a series of multiple levels until the polymer is fully dehydrogenated. In a 2% molecular hydrogen environment this reaction reverses, gradually resetting the junction to its initial state with no change in the polarity of the electric field across the junction. A chemically inert nitrogen chemical environment will preserve the state without any energy input required so that it acts as non-volatile memory.

The junction can also be set and read either optically or electrically or set one way and read the other allowing great versatility in the device. “The advantages of optical control is you can wirelessly switch and read the device,” says Zayats. The preference for electrical or optical operations depends on the application, but as he points out, there have been a number of attempts to create neuromorphic circuits that compute the way the brain does, and if you introduce optical switching or read out you can compute faster.

The researchers stumbled on the polymer junction’s neatly synaptic behaviour during experiments to develop a nanoscale light source. They had constructed different tunnel PLH junctions, and noticed the light source was not stable in air or hydrogen. “By chance I read a paper about synapses and thought – that is our light source,” says Zayats. “It was completely by chance.”

Catching up with the brain

Another impressive feature of the human brain is the sheer density of synaptic connections, which can reach 7.2 x 108 synapses/mm3. The first realisations of synthetic synapses were based on CMOS electronics and limited by the density of elements that could be fabricated on a chip, several orders of magnitude lower than that found in the brain.

Progress in memristor technology has made some inroads in closing this gap. The synaptic nanorod arrays Zayats and colleagues report gets impressively close, falling short by just a factor of a thousand or so. The next challenge will be finding a way to switch individual nanorods instead of the whole array. Exposing single nanorods to different chemicals may prove problematic but Zayats suggests there may be a way to expose just some from the array to a bias voltage or excitation light to change the state, which would bring them yet another step closer to mimicking the brain.

Arrays of gold nanorods topped with polymer junctions contacted to a metal mimic synapses in the brain closer than ever before. Credit: Nano Letters

Optoelectronic synapses based on hot-electron-induced chemical processes Pan Wang, Mazhar E. Nasir, Alexey V. Krasavin, Wayne Dickson and Anatoly V. Zayats Nano Lett. 2020, articles ASAP https://doi.org/10.1021/acs.nanolett.9b03871

Plasmonics Meets Catalysis – Meeting @ Catalysis Hub

On the 26th November, the RPLAS team travelled to the Catalysis Hub at the Harwell Research Campus to co-host Plasmonics Meets Catalysis.
This meeting brought together physicists and chemists in overlapping but distinct areas of research to learn more about the current research landscape and also encourage and foster new collaborations.

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Professor Richard Catlow

Richard Catlow (Catalysis Hub) opened the event, followed by Anatoly Zayats (King’s) who gave an overview of Plasmonics.

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Professor Anatoly Zayats

The morning was split into two sessions, the first on Hot-Electron Chemistry the second on the Applications of Hot-Electron Chemistry.

Session 1: Hot Electron Chemistry
Chair: Richard Catlow
Emiliano Cortes: “Photochemistry with Hot Electrons”
Anastasia Zaleska: “CO2 reduction using Hot Electrons”
Alexey Krasavin: “Electrically driven Chemical Reactions”
Simon Freakly: “Plasmonic enhancement on glycerol oxidation using nanostructured AuPd nanoparticle catalysts”

Morning session A
Dr Emiliano Cortés, Anastasia Zaleska, Dr Alexey Krasavin, Dr Simon Freakely

 

Session 2: Applications of Hot Electron Chemistry
Chair: Anatoly Zayats
Daniel Glass: “Photo-induced enhanced Raman Spectroscopy” Jorge Salmon Gamboa: “Degradation of Organic Pollutants”
Helen Daly: “Heterogeneous Photocatalytic reactions”

Morning session B
Jorge Salmon Gamboa, Daniel Glass, Dr Helen Daly

In the afternoon, there was a lab tour followed by self-assembled breakout sessions to discuss new and novel ideas in catalysis and plasmonics.

Speaking at the end of the event, both Catlow and Zayats commented on the success of the event. They both also expressed their desire to foster the new relationships and ideas that came out of the day in the coming months and years ahead.

RPLAS researcher receives career advice from Nobel Laureate Serge Haroche.

Once every year, around 30-40 Nobel Laureates convene in Lindau to meet the next generation of leading scientists: 600 undergraduates, PhD students, and post-doc researchers from all over the world. The Lindau Nobel Laureate Meetings foster the exchange among scientists of different generations, cultures, and disciplines.

This year, RPLAS researcher Margoth Cordova Castro attended the meeting shortly after successfully defending her PhD thesis. Whilst at the meeting, Margoth had the excellent opportunity to talk with Nobel Laureate Serge Haroche who shared the Nobel Prize in Physics in 2012 with David J. Wineland. In the video below, Serge offers advice to young researchers who like himself and Margoth, come from a developing country.

Since their beginnings in 1951, the Lindau Meetings have evolved into a unique international forum for scientific exchange. It was the two Lindau physicians Franz Karl Hein and Gustav Wilhelm Parade who approached Count Lennart Bernadotte af Wisborg of nearby Mainau Island to jointly develop and implement the idea that marked the start of a long and continuing history.

Count Bernadotte – a grandson of King Gustaf V of Sweden – had excellent connections to Stockholm. Especially due to his efforts, seven Nobel Laureates agreed to participate in the first “European Meeting of Nobel Laureates in Medicine” held at Lindau in 1951. This extraordinary meeting was conceived as a European initiative of post-war reconciliation among scientists.

The initial success led to the establishment of periodic meetings of Nobel Laureates in Lindau, dedicated alternately to the Nobel Prize disciplines physiology or medicine, physics, and chemistry. Already back in 1953, the decision was made to have undergraduates, PhD students, and post-doc researchers join the dialogue. In 2004, the first of the additional regular Lindau Meetings on Economic Sciences was held.

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

 

King’s hosts the 5th annual London Plasmonics Forum

The Fifth London Plasmonics Forum was held at Kings College London on 14 June in the Anatomy Museum at the Strand Campus, this time as part of the London Tech Week.

The event has been running since 2015, and it typically attracts approximately 100 participants from London, UK, Europe and beyond. It aims to engage and connect researchers and industry who work in the ever-expanding field of Plasmonics.

Dr Charles Footer from QinetiQ gave the keynote talk; explaining the way that materials and metamaterials are used in industry.  Following on from the keynote, we had several talks from early career researchers (you can see the agenda herefor more details), Dr Andres Neira from Seagate Technology gave a talk on progress in heat-assisted magnetic recording, and Dr Dominic Gallaher from Photon Design talked about the development of new simulation tools for nanophotonics.

Over lunchtime there was a lab tour of the nanophotonics lab running alongside the annual poster competition. As usual, the standard of the competition was very high; Rachel Won and David Pile from Nature Photonics announced the winner as Ediz Herkert from the University of Stuttgart for his poster entitled ‘Computing the influence of disorder in plasmonic metasurfaces’.

From L-R - Rachel Won (Nature Photonics), Ediz Herkert (University of Stuttgart), Anatoly Zayats (RPLAS PI) & David Pile (Nature Photonics)
From L-R – Rachel Won (Nature Photonics), Ediz Herkert (University of Stuttgart), Anatoly Zayats (RPLAS PI) & David Pile (Nature Photonics)

Professor Anatoly Zayats, PI of the EPSRC programme grant Reactive Plasmonics said “This is the 5th year we’ve run the London Plasmonics Forum, and it is amazing to see how plasmonic research changed over this relatively short period. It has diversified in so many different areas which we could not even think about 5 years ago. It continues to be a very active and imaginative area of photonics, chemistry and biological research and we always have very lively discussions at the Forum with our colleagues from all around the world.”

The event continues to build on its excellent reputation for researchers and industry to come together to discuss, exchange ideas and disseminate cutting edge research and plans for the 6th London Plasmonics Forum are already in place for 2020.