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Talga Boosts European Natural Graphite Resources

Posted By Graphene Council, Saturday, September 19, 2020
Talga Resources is pleased to announce significant increases in the Company’s natural graphite mineral resources within its wholly-owned Vittangi Graphite Project in northern Sweden.

Talga has completed a review of its four JORC (2012) compliant graphite mineral resources within Vittangi to standardise parameters for increased accuracy in upcoming feasibility studies and enable better mine planning, permitting and reporting.

The review also identified significant new Exploration Targets to be tested along strike and at depth from current resources, providing potential for future additional resource growth. Highlights  of results of the review include:

• Updated Nunasvaara South Mineral Resource Estimate defines 15% increase in total natural graphite resources at Vittangi

• Vittangi graphite mineral resource now stands at 19.5 million tonnes at 24.0% graphite (based on a revised 10% cut-off grade across the project)

• Vittangi remains the world’s highest grade natural graphite resource1, set to play a significant role in battery anode production for the booming electric vehicle market

• Talga’s total graphite resource inventory in Sweden increases to 55.3 million tonnes at 17.5% graphite, representing the largest source of natural graphite defined in Europe2

• Additional growth Exploration Targets totalling 26–46 million tonnes at 20–30% graphite defined within Vittangi and set to be drill-tested for potential further increases in scale

Note that the potential quantity and grade of the Exploration Target is conceptual in nature, there has been insufficient exploration to estimate a Mineral Resource and it is uncertain if further exploration will result in the estimation of a Mineral Resource.

Commenting on the resource upgrade, Talga Managing Director Mark Thompson said: “We are pleased to continue defining and growing these globally significant and strategically important European graphite deposits.“

“The European Commission recently published an updated list of Critical Raw Materials necessary for the energy transition to a more sustainable society. Natural graphite features on this list of materials vital to European development as it forms nearly half the volume of active materials in electric vehicle batteries, where it is used as the anode.”

“With projected anode demand set to reach 3.2 million tonnes by 20303 the potential of Talga’s Swedish integrated natural graphite anode production facility is significant for the European electric vehicle supply chain and the ‘green’ economy.

Tags:  Batteries  Graphene  Graphite  Mark Thompson  Talga Resources 

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Projects Led by Pitt Chemical Engineers Receive more than $1 million in NSF Funding

Posted By Graphene Council, Saturday, September 19, 2020
Two projects led by professors in the Department of Chemical and Petroleum Engineering at the University of Pittsburgh’s Swanson School of Engineering have recently received funding from the National Science Foundation.

Lei Li, associate professor of chemical and petroleum engineering at Pitt, is leading a project that will investigate the water wettability of floating graphene. Research over the past decade by Li and others has shown that water has the ability to “see through” atomic-thick layers of graphene, contributing to the “wetting transparency” effect. 

“This finding provides a unique opportunity for designing multi-functional devices, since it means that the wettability of an atomic-thick film can be tuned by selecting an appropriate supporting substrate,” said Li. “Because the substrate is liquid, one can control the wettability in real-time, a capability that would be very useful for water harvesting of moisture from the air and in droplet microfluidics devices.”

The current project will use both experimental and computational methods to understand the mechanisms of wetting transparency of graphene on liquid substrates and demonstrate the real-time control of surface wettability. Li and his co-PIs Kenneth Jordan, Richard King Mellon Professor and Distinguished Professor of Computational Chemistry at Pitt and co-director of the Center for Simulation and Modeling; and Haitao Liu, professor of chemistry at Pitt, received $480,000 for the project titled, “Water wettability of floating graphene: Mechanism and Application.” 

The second project will develop technology to help enable the widespread adoption of renewable energy, like solar and wind power. James McKone, assistant professor of chemical and petroleum engineering at Pitt, is collaborating with researchers at the University of Rochester and the University at Buffalo to develop a new generation of high-performance materials for liquid-phase energy storage systems like redox flow batteries, one of McKone’s areas of expertise. The project, “Collaborative Research: Designing Soluble Inorganic Nanomaterials for Flowable Energy Storage,” received $598,000 from the National Science Foundation, with $275,398 designated for Pitt.

McKone’s team will investigate the molecular properties of soluble, earth-abundant nanomaterials for use in liquid-phase battery systems. These batteries are designed to store massive amounts of electricity from renewable energy sources and provide steady power to the grid.

“Unlike the batteries we normally think of in phones and laptop computers, this technology uses liquid components that are low-cost, safe and long-lasting,” said McKone. “With continued development, this will make it possible to store all of the new wind and solar power that is coming available on the electric grid without adding a significant additional cost.” 

McKone is collaborating with Dr. Ellen Matson, Wilmot Assistant Professor of Chemistry at the University of Rochester, and Dr. Timothy Cook, Associate Professor of Chemistry at the University at Buffalo.

Tags:  Batteries  energy storage  floating graphene  Graphene  James McKone  Lei Li  nanomaterials  National Science Foundation  University of Pittsburgh 

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WHAT HAPPENS BETWEEN THE SHEETS? ‘FLOATING’ GRAPHENE ON A BED OF CALCIUM ATOMS

Posted By Graphene Council, Saturday, September 19, 2020
Adding calcium to graphene creates an extremely-promising superconductor, but where does the calcium go?

Adding calcium to a composite graphene-substrate structure creates a high transition-temperature (Tc) superconductor.

In a new study, an Australian-led team has for the first time confirmed what actually happens to those calcium atoms: surprising everyone, the calcium goes underneath both the upper graphene sheet and a lower ‘buffer’ sheet, ‘floating’ the graphene on a bed of calcium atoms.

Superconducting calcium-injected graphene holds great promise for energy-efficient electronics and transparent electronics.

STUDYING CALCIUM-DOPED GRAPHENE: THROWING OFF THE DUVET

Graphene’s properties can be fine-tuned by injection of another material (a process known as ‘intercalation’) either underneath the graphene, or between two graphene sheets.

This injection of foreign atoms or molecules alters the electronic properties of the graphene by either increasing its conductance, decreasing interactions with the substrate, or both.

Injecting calcium into graphite creates a composite material (calcium-intercalated graphite, CaC6) with a relatively ‘high’ superconducting transition temperature (Tc). In this case, the calcium atoms ultimately reside between graphene sheets.

Injecting calcium into graphene on a silicon-carbide substrate also creates a high-Tc superconductor, and we always thought we knew where the calcium went in this case too…

Graphene on silicon-carbide has two layers of carbon atoms: one graphene layer on top of another ‘buffer layer’: a carbon layer (graphene-like in structure) that forms between the graphene and the silicon-carbide substrate during synthesis, and is non-conducting due to being partially bonded to the substrate surface.

“Imagine the silicon carbide is like a mattress with a fitted sheet (the buffer layer bonded to it) and a flat sheet (the graphene),” explains lead author Jimmy Kotsakidis.

Conventional wisdom held that calcium should inject between the two carbon layers (between two sheets), similar to injection between the graphene layers in graphite. Surprisingly, the Monash University-led team found that when injected, the calcium atoms’ final destination location instead lies between buffer layer and the underlying silicon-carbide substrate (between the fitted sheet and the mattress!).

“It was quite a surprise to us when we realised that the calcium was bonding to the silicon surface of the substrate, it really went against what we thought would happen”, explains Kotsakidis.

Upon injection, the calcium breaks the bonds between the buffer layer and substrate surface, thus, causing the buffer layer to ‘float’ above the substrate, creating a new, quasi-freestanding bilayer graphene structure (Ca-QFSBLG).

This result was unanticipated, with extensive previous studies not considering calcium intercalation underneath the buffer layer. The study thus resolves long-standing confusion and controversy regarding the position of the intercalated calcium.

X-ray photoelectron spectroscopy (XPS) measurements at the Australian Synchrotron were able to pinpoint the location of the calcium near to the silicon carbide surface

Results were also supported by low-energy electron diffraction (LEED), and scanning tunnelling microscopy (STM) measurements, and by modelling using density functional theory (DFT).

AND MAGNESIUM TOO…
With this information at hand, the Australian team also decided to investigate if magnesium–which is notoriously difficult to inject into the graphite structure –could be inserted (intercalated) into graphene on a silicon-carbide substrate.

To the researchers’ surprise, magnesium behaved remarkably similarly to calcium, and also injected between the graphene and substrate, again ‘floating’ the graphene.

Both magnesium- and calcium-intercalated graphene n-type doped the graphene, and resulted in a low workfunction graphene, an attractive aspect when using graphene as a conducting electrical contact for other materials.

But unlike calcium, magnesium-intercalated graphene remained stable in ambient atmosphere for at least 6 hours, overcoming a major technical hurdle for alkali and alkaline earth intercalated graphene.

“The fact that Mg-QFSBLG is a low workfunction material and n-type dopes the graphene while remaining quite stable in ambient atmosphere is a huge step in the right direction for implementing these novel intercalated materials in technological applications,” explains co-author Prof Michael Fuhrer.

“Magnesium-intercalated graphene could be a stepping stone towards discovery of other similarly stable intercalants.”

Tags:  Electronics  Graphene  Graphite  Jimmy Kotsakidis  Monash University  superconductor 

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Graphene enables the smallest, most sensitive sensors

Posted By Graphene Council, Saturday, September 19, 2020
We interview Peter Steeneken, from Graphene Flagship partner TU Delft, and Leader of the Graphene Flagship Sensors Work Package, on the advantages of graphene and related materials in the development of sensing devices – particularly NEMS. NEMS stands for nanoelectromechanical systems: a class of miniaturised devices that detect stimuli like air pressure, sound, light, acceleration or the presence of gases and chemical compounds.

NEMS production methods resemble those of the manufacture of classic transistors, so they can achieve similar production costs and widespread commercialisation. The Graphene Flagship is integrating graphene and related materials in NEMS. Keep reading to discover the future of miniaturised sensing!

"Graphene allows for ultimate force sensitivities in high-performance pressure sensors, microphones and accelerometers."- Peter Steeneken, Graphene Flagship 'Sensors' Leader

What exactly are NEMS sensors?

The NEMS acronym, meaning nanoelectromechanical systems, comprises a family of electric and electronic devices with nanometric dimensions that are mechanically movable. In the Graphene Flagship Sensors Work Package, we are mostly interested in NEMS sensors, which can measure air pressure, sound, light intensity, acceleration, or the presence of gases. To measure such forces you need motion, so movable parts are essential for NEMS.

Currently, MEMS (NEMS' micrometric 'big' cousins) have similar functionalities and are already produced in high volumes – up to billions of MEMS sensors per year – for devices like smartphones. Since they are produced using similar methods as CMOS electronics, they can be made small and with low production costs, which has accelerated their widespread commercialization.

NEMS are nanoscale devices – much smaller devices than classic MEMS. Their smaller size has several advantages: NEMS have higher sensitivity, and many of them can be placed on the same area that would be taken up by a single MEMS sensor. Moreover, NEMS are potentially cheaper, because they need less material to make, so more sensors can be produced from a single silicon wafer. The nanometric size of NEMS also enables new sensing functionalities. For instance, NEMS can even detect individual molecules and count them.

What innovative features does graphene bring to the NEMS field?

Since graphene is only one atom thick, it is the thinnest NEMS device-layer one can imagine. In terms of mechanical properties, graphene is stiff yet very flexible – suspended graphene can be deflected out-of-plane, allowing for ultimate force sensitivities in high-performance pressure sensors, microphones and accelerometers.

At the same time, graphene membranes are very robust. By tensioning graphene like a guitar string, its spring constant can be tuned and engineered to the desired value. The high electrical conductivity of graphene is also advantageous in electrical actuation, needed to provide the readout of sensors.

Although graphene is impermeable to gases in its pristine form – something that can be essential for pressure sensors – we can also tailor it with small pores and make it permeable or semi-permeable for gases and liquids, enabling completely new sensing functions. Compared to other types of thicker membranes, fluids can permeate at higher rates through graphene, which enables faster and lower power operation of sensing and separation devices. During the last years, the feasibility and potential of graphene for realizing novel and improved graphene NEMS sensors has become more apparent, as we describe in a recent review.1

"Graphene sensors could also increase our safety, [...] warn us in case of poor ventilation or remind us to wear a mask." - Peter Steeneken, Graphene Flagship 'Sensors' Leader

Graphene is one material in a huge family – can other layered materials be applied to NEMS devices as well?

Certainly. MEMS devices already use combinations of materials in the suspended layers: electrical conductors, semiconductors, insulators, optical and magnetic active layers, as well as piezoresistive and electric layers for sensing and actuation. We envisage that similar suspended heterostructures might be realised in NEMS by combining different types of layered materials.

We have already shown NEMS that use layered materials with high piezoresistive constants and others that showcase resistances that make them very sensitive to changes in gas compositions. Another approach for NEMS sensors would be to cover graphene with thin functionalisation layers, enabling new types of gas and biosensors as outlined in a recent focus issue edited by Arben Merkoci, from Graphene Flagship partner ICN2, Spain, and member of the Sensors Work Package.2

What are the applications of graphene-based NEMS sensors?

There is a wide range of applications that can be targeted. We could replace sensors in our mobile phones by smaller, more sensitive devices. These will allow better indoor navigation, thanks to acceleration and pressure sensors and directional low-noise microphones.

Graphene sensors could also increase our safety: our phone could warn us in case of poor ventilation, detecting increased CO2 levels in the environment – or remind us to wear a mask, if it senses that air pollution reaches dangerous thresholds. Beyond, high-end laboratory instruments, such as scanning probe microscopes, might also benefit from the flexibility of graphene.2

"With graphene, we could replace sensors in our smartphones by smaller, more sensitive devices." -  Peter Steeneken, Graphene Flagship 'Sensors' Leader

For you, which is the most exciting application of graphene for sensing?

I am excited about creating sensor platforms by combining multiple graphene sensors together. By making new combinations, sensors can become more selective and undesired crosstalk can be eliminated. Moreover, by combining the output of multiple sensors, we can extract more information about our environment.

For gas sensors, the combination of outputs provides a "fingerprint" of gas composition. Similarly, by combining outputs of accelerometers, pressure sensors, magnetometers, and microphones, we can deduce if someone is walking, biking, climbing stairs or driving a car.

I believe that some of the most exciting and impactful new applications of these graphene sensors will be in the medical domain: by developing graphene sensor platforms that can help us better detect and diagnose diseases. In fact, one of the latest Graphene Flagship spin-offs, INBRAIN Neuroelectronics, will design graphene-based sensors and implants to optimise the treatment of brain disorders, such as Parkinson's and epilepsy. Moreover recently, the production of graphene biosensors has advanced, and Graphene Flagship partner VTT, in Finland, already sells CMOS integrated multiplexed biosensor matrices for testing and development purposes.

Are graphene-enabled NEMS ready to jump onto the market?

During the last few years, we showed that graphene NEMS sensors can outperform current commercial MEMS sensors in several aspects. To get to the market, we need to show that graphene sensors can outperform current products in all aspects – including high-volume reliable production at a competitive cost.

To achieve this, more development is needed. The push of the Graphene Flagship towards industrialisation and large-scale manufacturing, will accelerate the NEMS sensors entry into the market. 

Just like MEMS, graphene NEMS have benefited from established CMOS fabrication methods, which facilitate high-volume low-cost production. Introducing a new material into a CMOS factory often takes between five and ten years of development.

These advances are achieved through international and multidisciplinary collaboration. In fact, the Graphene Flagship Sensors Work Package comprises a collaborative endeavour between industry and academia: Chalmers University of Technology (Sweden), ICN2, ICFO, Graphenea (Spain), RWTH Aachen, Bundeswehr University of Munich, Infineon Technologies (Germany), University of Tartu (Estonia), VTT (Finland) and TU Delft (Netherlands) - all Graphene Flagship partners.

With the support of the European Commission, the Graphene Flagship will soon start setting up set up an experimental pilot line to integrate graphene and related layered materials in a semiconductor platform. This will not only accelerate graphene device fabrication, but also accelerate the development of new graphene-enabled devices, providing an identical repeatable device fabrication flow.

Tags:  Arben Merkoci  Graphene  Graphene Flagship  ICN2  INBRAIN Neuroelectronics  Peter Steeneken  Sensors  TU Delft 

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AMD joins the WSRF framework programme

Posted By Graphene Council, Thursday, September 17, 2020
Advanced Material Development has been selected to join the WSRF framework programme led by QinetiQ and involving over 100 leading industrial and academic suppliers, all focused on developing exploitable technologies for the UK Armed Forces.

John Lee, CEO of AMD, said “This is a highly significant development for AMD in acknowledging both the important role materials science has to play and more specifically, the core need for nanomaterials development, in new defence-sector technologies. AMD is delighted to be welcomed into such esteemed company and we look forward to making a fundamental contribution to this vital programme, combining our R&D expertise with highly experienced companies in this sector.”

Tags:  Advanced Material Development  defence  Graphene  John Lee  nanomaterials  QinetiQ 

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Process approach to making graphene dispersion decisions

Posted By Graphene Council, Thursday, September 17, 2020

Applied Graphene Materials was invited by The Graphene Council to participate in a webinar to look at how to use and apply graphene materials, in particular how to disperse into host materials. Some of the discussion points touched upon in this webinar include:

Making graphene work
If you can add graphene to it correctly you can make great use of the materials advantages

The Keys
• Application Technology - clear understanding of end-use
• 'How-to' data enables easy use of graphene
• Unlocking use of graphene

Dispersion decision flow chart
• What could graphene do for product enhancement?
• Understand where it will be used and when to be added
• Compatibility - will graphene addition upset the balance of the rest of the formulation?

Stability
• Is the dispersion stable or does it sediment out?
• Can it be recovered? How?
• What are the implications for end-customer use?

Tags:  Applied Graphene Materials  Graphene  The Graphene Council  webinar 

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LIGC announces $3M USD Series A funding from Hubei Forbon Technology Co. Ltd

Posted By Graphene Council, Thursday, September 17, 2020
Israeli startup LIGC announced a $3M USD Series A round from public listed Wuhan-based Hubei Forbon Technology Co. Ltd (300387.SZ). The funding will be used to scale and manufacture LIGC's Laser-Induced Graphene filters (LIG).

The technology was developed by Houston's Rice University in partnership with Ben-Gurion University (BGU) of the Negev in Israel and was licensed from BGN technologies, the technology transfer company of BGU. It utilizes graphene's conductivity to run an electric current through the filter.

"For a simplified analogy, one can see the graphene as an electric fence to the micron and submicron level with similar functionality as a mosquito zapper," said LIGC Co-founder & CEO Yehuda Borenstein. "When an airborne bacteria or virus touches the graphene surface, it's electrified and damaged, and only low voltages and currents that are safe for use are needed."

Since the LIGC filter uses active means to eliminate bacteria and viruses, lower density filtration media can be used, resulting in significantly less energy consumption. In addition, LIGC active filters require lower maintenance than other filters and are safe to the operator during maintenance and replacement.

Air filters are all around us in airplanes, ships, schools, offices, and homes. In some cases, like airplanes, they already have HEPA filters that remove viruses and bacteria from the air circulated but at high energy and maintenance costs.

While 2020 has underlined the importance of protecting against airborne viruses, the post-pandemic world will likely show us how important it is to do so without increasing energy costs past the point of affordability.

"There's still much to learn about COVID-19, but it's now established that airborne transmission is possible," said Borenstein. "In the absence of better filtration technology, the indoor spaces where we used to spend most of our 'normal' life--schools, stores, offices-- present a real risk."

Tags:  Ben-Gurion University  Graphene  graphene filters  Hubei Forbon Technology  LIGC Application  Rice University  Yehuda Borenstein 

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Energy harvesting goes organic, gets more flexible

Posted By Graphene Council, Thursday, September 17, 2020
Nanogenerators capable of converting mechanical energy into electricity are typically made from metal oxides and lead-based perovskites. But these inorganic materials aren't biocompatible, so the race is on to create natural biocompatible piezoelectric materials for energy harvesting, electronic sensing, and stimulating nerves and muscles.

University College Dublin and University of Texas at Dallas researchers decided to explore peptide-based nanotubes, because they would be an appealing option for use within electronic devices and for energy harvesting applications.

In the Journal of Applied Physics, from AIP Publishing, the group reports using a combination of ultraviolet and ozone exposure to generate a wettability difference and an applied field to create horizontally aligned polarization of nanotubes on flexible substrates with interlocking electrodes.

"The piezoelectric properties of peptide-based materials make them particularly attractive for energy harvesting, because pressing or bending them generates an electric charge," said Sawsan Almohammed, lead author and a postdoctoral researcher at University College Dublin.

There's also an increased demand for organic materials to replace inorganic materials, which tend to be toxic and difficult to make.

"Peptide-based materials are organic, easy to make, and have strong chemical and physical stability," she said.

In the group's approach, the physical alignment of nanotubes is achieved by patterning a wettability difference onto the surface of a flexible substrate. This creates a chemical force that pushes the peptide nanotube solution from the hydrophobic region, which repels water, with a high contact angle to the hydrophilic region, which attracts water, with a low contact angle.

Not only did the researchers improve the alignment of the tubes, which is essential for energy harvesting applications, but they also improved the conductivity of the tubes by making composite structures with graphene oxide.

"It's well known that when two materials with different work functions come into contact with each other, an electric charge flows from low to high work function," Almohammed said. "The main novelty of our work is that controlling the horizontal alignment of the nanotubes by electrical field and wettability-assisted self-assembly improved both the current and voltage output, and further enhancement was achieved by incorporating graphene oxide."

The group's work will enable the use of organic materials, especially peptide-based ones, more widely within electronic devices, sensors, and energy harvesting applications, because two key limitations of peptide nanotubes -- alignment and conductivity -- have been improved.

"We're also exploring how charge transfer processes from bending and electric field applications can enhance Raman spectroscopy-based detection of molecules," Almohammed said. "We hope these two efforts can be combined to create a self-energized biosensor with a wide range of applications, including biological and environmental monitoring, high-contrast imaging, and high-efficiency light-emitting diodes."

Tags:  Energy  Graphene  graphene oxide  LED  Sawsan Almohammed  University College Dublin  University of Texas 

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Northwestern Engineering Names Winners of 2020 Cole-Higgins Awards

Posted By Graphene Council, Thursday, September 17, 2020
Three members of the Northwestern Engineering community have received the school’s annual awards for outstanding teaching and advising. 

Jonathan Emery, assistant professor of instruction in materials science and engineering, and Muzhou Wang, assistant professor of chemical and biological engineering, received the 2020 Cole-Higgins Awards for Excellence in Teaching. Russell Joseph, associate professor of electrical and computer engineering and computer science, earned the Cole-Higgins Award for Excellence in Advising. 

Emery’s research interests include atomic layer deposition, oxides, and graphene. Honored for “creative deployment of diverse resources to engage students and promote their learning,” Emery was cited for his efforts to make classes engaging and his use of electronic materials to enhance education during the spring term. 

“He cares very much about his students and is always trying to make resources available for everyone,” one student nominator said. “In both the structure of the class and how he delivered the content, it was clear how much he cares that all of his students are learning and doing well in the class.” 

Wang was lauded for “clear and meticulous presentation of rigorous content, prioritizing student understanding.” 

“He teaches heat transfer, a difficult course with complicated math, so clearly that I always trust the topics will make perfect sense by the end of class,” one nominator said. “He clearly has a lot of knowledge on the subject, and has an engaging, thoughtful style of teaching. He explains concepts so thoroughly, making students feel they have an understanding of the material at a depth that most other classes cannot attain.” 

Honored for “forging caring relationships with students focused on their needs and success,” Joseph’s work focuses on computer architecture, microprocessor design for reliability and variability tolerance, and power-aware computing. 

“Everybody loves Russ,” one student said. “He is a kind person who always tries to connect with his students.” 

“Russ Joseph is absolutely great!” another student nominator wrote. “He’s super accommodating, looks out for his students, and is entirely focused on their success.”

Tags:  Graphene  Jonathan Emery  Muzhou Wang  Northwestern Engineering  Russell Joseph 

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Physicists 'trick' photons into behaving like electrons using a 'synthetic' magnetic field

Posted By Graphene Council, Thursday, September 17, 2020
Scientists have discovered an elegant way of manipulating light using a "synthetic" Lorentz force -- which in nature is responsible for many fascinating phenomena including the Aurora Borealis.

A team of theoretical physicists from the University of Exeter has pioneered a new technique to create tuneable artificial magnetic fields, which enable photons to mimic the dynamics of charged particles in real magnetic fields.

The team believe the new research, published in leading journal Nature Photonics, could have important implications for future photonic devices as it provides a novel way of manipulating light below the diffraction limit.

When charged particles, like electrons, pass through a magnetic field they feel a Lorentz force due to their electric charge, which curves their trajectory around the magnetic field lines.

This Lorentz force is responsible for many fascinating phenomena, ranging from the beautiful Northern Lights, to the famous quantum-Hall effect whose discovery was awarded the Nobel Prize.

However, because photons do not carry an electric charge, they cannot be straightforwardly controlled using real magnetic fields since they do not experience a Lorentz force; a severe limitation that is dictated by the fundamental laws of physics.

The research team have shown that it is possible to create artificial magnetic fields for light by distorting honeycomb metasurfaces -- ultra-thin 2D surfaces that are engineered to have structure on a scale much smaller than the wavelength of light.

The Exeter team were inspired by a remarkable discovery ten years ago, where it was shown that electrons propagating through a strained graphene membrane behave as if they were subjected to a large magnetic field.

The major drawback with this strain engineering approach is that to tune the artificial magnetic field one is required to modify the strain pattern with precision, which is extremely challenging, if not impossible, to do with photonic structures.

The Exeter physicists have proposed an elegant solution to overcome this fundamental lack of tunability.

Charlie-Ray Mann, the lead scientist and author of the study, explains: "These metasurfaces, support hybrid light-matter excitations, called polaritons, which are trapped on the metasurface.

"They are then deflected by the distortions in the metasurface in a similar way to how magnetic fields deflect charged particles.

"By exploiting the hybrid nature of the polaritons, we show that you can tune the artificial magnetic field by modifying the real electromagnetic environment surrounding the metasurface."

For the study, the researchers embedded the metasurface between two mirrors -- known as a photonic cavity -- and show that one can tune the artificial magnetic field by changing only the width of the photonic cavity, thereby removing the need to modify the distortion in the metasurface.

Charlie added: "We have even demonstrated that you can switch off the artificial magnetic field entirely at a critical cavity width, without having to remove the distortion in the metasurface, something that is impossible to do in graphene or any system that emulates graphene.

"Using this mechanism you can bend the trajectory of the polaritons using a tunable Lorentz-like force and also observe Landau quantization of the polariton cyclotron orbits, in direct analogy with what happens to charged particles in real magnetic fields.

"Moreover, we have shown that you can drastically reconfigure the polariton Landau level spectrum by simply changing the cavity width."

Dr Eros Mariani, the lead supervisor of the study, said: "Being able to emulate phenomena with photons that are usually thought to be exclusive to charged particles is fascinating from a fundamental point of view, but it could also have important implications for photonics applications.

"We're excited to see where this discovery leads, as it poses many intriguing questions which can be explored in many different experimental platforms across the electromagnetic spectrum."

Tags:  2D materials  Charlie-Ray Mann  Eros Mariani  Graphene  photonics  University of Exeter 

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