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.

RPLAS exhibit demos at Knowledge Transfer Network event

Representatives from King’s College London travelled to Birmingham this week to exhibit demos at SET 2019 Metamaterials.

Showcasing Emerging Technology is a series of events organised by the Knowledge Transfer Network (KTN) where groundbreaking research can be shared with industry.  The KTN, which is part of Innovate UK, helps businesses get the best out of creativity, ideas and the latest discoveries, to strengthen the UK economy and improve people’s lives.

The RPLAS team were exhibiting their Ultrasensitive Metamaterial Sensor for the Optical Detection of Gases. This technology is based on optical metamaterials
comprised of subwavelength metallic nanorods. The sensor is made up of an LED light source and a photodetector. When hydrogen is present there is a change in the reactive index of the palladium nanorods in the metamaterial which can be plotted and detected.

The team believes that this set up could be miniaturised and reproduced relatively cheaply and could be useful to the chemical industry. Look out for the RPLAS team at other events over the coming months.

KTN

 

 

 

 

 

 

 

 

 

 

 

 

New open access journal Advanced Photonics

Professor Anatoly Zayats (RPLAS PI) is the co-editor-in-chief of a new journal that is published by SPIE and Chinese Laser Press. Advanced Photonics is a collaborative, open-access journal, featuring the most impactful fundamental and applied research across optics and photonics technologies.

Advanced Photonics, designed to address a growing demand within the photonics community to publish and share significant, innovative research results as rapidly, accurately, and accessibly as possible, will highlight scientific and technological discoveries as well as news and commentaries by leading experts and visionaries in the field.

Advanced Photonics will also incorporate a personal approach to science, with interviews and the personal views of authors and how their new ideas emerged. Speaking about this approach, the editors said ‘We hope this will make an exciting mixture of scientific and general material for our readers’

Advanced Photonics Cover Issue 1

New hyperbolic metamaterial fabricated by RPLAS researchers.

A new type of hyperbolic metamaterial has been developed by Reactive Plasmonics at King’s College London (KCL) allowing scientists to have greater flexibility of manipulating light-matter interactions at the nanoscale.

Hyperbolic Metamaterials are artificial subwavelength-structured media that exhibit unusual optical properties and display indefinite dispersionThey are usually fabricated as metal nanorod assemblies or multilayers on substrates. Researchers in the Department of Physics at KCL have now developed a version of a hyperbolical metamaterial in colloidal form. Published in Laser & Photonics Reviews these hyperbolic metaparticles are dispersed in a solution and may find applications in plasmonenhanced spectroscopy, nanolasers, design of nonlinear phenomena, photothermal conversions, and hotelectron generation.

 

Dr Pan Wang was able to make hyperbolic metaparticles using a wet chemistry method coating nano-objects with alternating silica and gold multishells. The highly anisotropic silica/gold multishells display a hyperbolic dispersion and allow the engineering of refractive index on demand, providing great flexibility in the design of the optical properties of the metaparticles. 

 

The concept of creating hyperbolic metaparticles by coating nano-objects with curved metal-dielectric multilayers.

 

 

 

 

 

Compared with traditional bulk hyperbolic metamaterials, metaparticles in the colloidal form show many interesting advantages such as high flexibility in use (e.g., can be dispersed in a solvent, self-assembled on a surface, or embedded in a bulk matrix) and easy excitation of hyperbolic modes by direct illumination, making them promising for many applications. For example, they can be used as optical antennas for the enhancement of spontaneous emission rate of emitters by directly dispersing them into an active solution or spreading them on an active surface. It is also possible to make metaparticles active by incorporating optical gain, such as dye molecules or quantum dots, directly into the silica shells, which is attractive for developing ultra-small nanolasers. In addition, single metaparticles can work as building blocks for the creation of complex hyperbolic structures via self-assembly, which are difficult to realize using existing fabrication methods.

RPLAS researchers participate in the Photonics Innovation Village 2018

The Reactive Plasmonics team from King’s College London took a trip under the channel to France this week to attend SPIE Photonics Europe 2018.

As well as participating in the main conference, the team took part in the 2018 Photonics Innovation Village which aimed to showcase the research and innovative products from universities, nonprofits, and research centres.  It enabled the researchers to share their latest findings to industry innovators and other photonics visionaries.

One of the items on show was an ultrasensitive metamaterial sensor for the optical detection of gases. The sensor is made up of an LED light source and a photodetector. When hydrogen is present there is a change in the reactive index of the palladium nanorods in the metamaterial which can be plotted and detected.

The team believes that this set up could be miniaturised and reproduced relatively cheaply and could be useful to the chemical industry.

RPLAS scientist takes her research to Parliament


 RPLAS researcher Margoth Cordova Castro is a PhD student at King’s College London.


Margoth attended Parliment on the 12th March to present her physics research to a range of politicians as part of STEM for BRITAIN 2018. Her poster was shortlisted from hundreds of applicants to appear in Parliament. (You can view the poster at the bottom of the page)

On presenting her research in Parliament, she said, “It’s an honor be part of this multidisciplinary event and meet brilliant young researchers and know about the very interesting research all around UK. Sharing with politicians some of the results we achieved with our everyday hard work with the same motivation: push the boundaries of knowledge and try to bring new ideas and solutions to the real problems we are currently facing.’

Stephen Metcalfe MP, Chairman of the Parliamentary and Scientific Committee, said: “This annual competition is an important date in the parliamentary calendar because it gives MPs an opportunity to speak to a wide range of the country’s best young researchers.

“These early career engineers, mathematicians and scientists are the architects of our future and STEM for BRITAIN is politicians’ best opportunity to meet them and understand their work.”

The Parliamentary and Scientific Committee runs the event in collaboration with the Royal Academy of Engineering, the Royal Society of Chemistry, the Institute of Physics, the Royal Society of Biology, The Physiological Society and the Council for the Mathematical Sciences, with financial support from the Clay Mathematics Institute, Research Councils UK, Warwick Manufacturing Group, Society of Chemical Industry, the Nutrition Society, Institute of Biomedical Science and the Heilbronn Institute for Mathematical Research.

11111printsTEMargoth

 

New journal in Advanced Photonics to be published in 2019

RPLAS Principal Investigator, Anatoly Zayats is to become Co-Editor-in-Chief of a new journal that will be published next year.

Advanced Photonics will be published by SPIE, the international society for optics and photonics and Chinese Laser Press. It is being sponsored by Shanghai Institute of Optics and Fine Mechanics and the Chinese Optical Society.

This will be a highly selective, open access, international journal, publishing innovative fundamental and applied research in optics, photonics, and related fields.  Advanced Photonics will feature top-quality original papers, letters, and review articles, reflecting significant advances and breakthroughs in theoretical and experimental research, and promising novel applications. The journal will include news and commentaries covering scientific and technological discoveries, breakthroughs, and achievements.

Anatoly Zayats said : “We aim to make Advanced Photonics a trusted source of groundbreaking research in optics and optical technologies. With the benefits provided by open access, we hope the journal will be on a reading list of all researchers interested in new trends in photonic sciences.”

More details can be found here