Posted By Graphene Council,
Thursday, September 17, 2020
By varying the energy and dose of tightly-focused electron beams, researchers have demonstrated the ability to both etch away and deposit high-resolution nanoscale patterns on two-dimensional layers of graphene oxide. The 3D additive/subtractive “sculpting” can be done without changing the chemistry of the electron beam deposition chamber, providing the foundation for building a new generation of nanoscale structures.
Based on focused electron beam-induced processing (FEBID) techniques, the work could allow production of 2D/3D complex nanostructures and functional nanodevices useful in quantum communications, sensing, and other applications. For oxygen-containing materials such as graphene oxide, etching can be done without introducing outside materials, using oxygen from the substrate.
“By timing and tuning the energy of the electron beam, we can activate interaction of the beam with oxygen in the graphene oxide to do etching, or interaction with hydrocarbons on the surface to create carbon deposition,” said Andrei Fedorov, professor and Rae S. and Frank H. Neely Chair in the George W. Woodruff School of Mechanical Engineering at the Georgia Institute of Technology. “With atomic-scale control, we can produce complicated patterns using direct write-remove processes. Quantum systems require precise control on an atomic scale, and this could enable a host of potential applications.”
The technique was described in the journal ACS Applied Materials & Interfaces ("High-Resolution Three-Dimensional Sculpting of Two-Dimensional Graphene Oxide by E-Beam Direct Write"). The work was supported by the U.S. Department of Energy Office of Science, Basic Energy Sciences. Co-authors included researchers from Pusan National University in South Korea.
Creation of nanoscale structures is traditionally done using a multistep process of photoresist coating and patterning by photo- or electron beam lithography, followed by bulk dry/wet etching or deposition. Use of this process limits the range of functionalities and structural topologies that can be achieved, increases the complexity and cost, and risks contamination from the multiple chemical steps, creating barriers to fabrication of new types of devices from sensitive 2D materials.
FEBIP enables a material chemistry/site-specific, high-resolution multimode atomic scale processing and provides unprecedented opportunities for “direct-write,” single-step surface patterning of 2D nanomaterials with an in-situ imaging capability. It allows for realizing a rapid multiscale/multimode “top-down and bottom-up” approach, ranging from an atomic scale manipulation to a large-area surface modification on nano- and microscales.
“By tuning the time and the energy of the electrons, you can either remove material or add material,” Fedorov said. “We did not expect that upon electron exposure of graphene oxide that we would start etching patterns.”
With graphene oxide, the electron beam introduces atomic scale perturbations into the 2D-arranged carbon atoms and uses embedded oxygen as an etchant to remove carbon atoms in precise patterns without introduction of a material into the reaction chamber. Fedorov said any oxygen-containing material might produce the same effect. “It’s like the graphene oxide carries its own etchant,” he said. “All we need to activate it is to ‘seed’ the reaction with electrons of appropriate energy.”
For adding carbon, keeping the electron beam focused on the same spot for a longer time generates an excess of lower-energy electrons by interactions of the beam with the substrate to decompose the hydrocarbon molecules onto the surface of the graphene oxide. In that case, the electrons interact with the hydrocarbons rather than the graphene and oxygen atoms, leaving behind liberated carbon atoms as a 3D deposit.
“Depending on how many electrons you bring to it, you can grow structures of different heights away from the etched grooves or from the two-dimensional plane,” he said. “You can think of it almost like holographic writing with excited electrons, substrate and adsorbed molecules combined at the right time and the right place.”
The process should be suitable for depositing materials such as metals and semiconductors, though precursors would need to be added to the chamber for their creation. The 3D structures, just nanometers high, could serve as spacers between layers of graphene or as active sensing elements or other devices on the layers.
“If you want to use graphene or graphene oxide for quantum mechanical devices, you should be able to position layers of material with a separation on the scale of individual carbon atoms,” Fedorov said. “The process could also be used with other materials.”
Using the technique, high-energy electron beams can produce feature sizes just a few nanometers wide. Trenches etched in surfaces could be filled with metals by introducing metal atoms contained in precursors.
Beyond simple patterns, the process could also be used to grow complex structures. “In principle, you could grow a structure like a nanoscale Eiffel Tower with all the intricate details,” Fedorov said. “It would take a long time, but this is the level of control that is possible with electron beam writing.”
Though systems have been built to use multiple electron beams in parallel, Fedorov doesn’t see them being used in high-volume applications. More likely, he said, is laboratory use to fabricate unique structures useful for research purposes.
“We are demonstrating structures that would otherwise be impossible to produce,” he said. “We want to enable the exploitation of new capabilities in areas such as quantum devices. This technique could be an imagination enabler for interesting new physics coming our way with graphene and other interesting materials.”
Posted By Graphene Council,
Thursday, September 17, 2020
Graphene, the one-atom-thick sheet of carbon atoms, which is a boon for energy storage, coatings, sensors as well as superconductivity, is difficult to produce while retaining its single layered properties.
A new low-cost method of upscaling production of graphene while preserving its single layered properties, developed by Indian scientists, may reduce the cost of producing this thinnest, strongest and most conductive material in the world.
Researchers from Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR) an autonomous institute under the Department of Science & Technology, Government of India through their recent research work have upscaled graphene production while retaining its thin layered properties. This was made possible by a simple, affordable method wherein naphthalene coated nickel foil was heated for a few minutes in an ordinary vacuum by joule heating and was cooled to get twisted layers of graphene. Careful study using electronic diffraction and Raman scattering showed that the 2D single-crystal nature of the atomic lattice of the graphene is retained even in the multilayer stack. The twisted multilayer graphene that results is also highly conducting.
In the research by Nikita Gupta (Ph.D. student, JNCASR) and Prof. G.U. Kulkarni (corresponding author ) published in the ‘Journal of Physical Chemistry Letters’, the scientists have also defined a formula to quantify how much single layer like behaviour exists in such a system. The twisted system has multiple layers, each behaving like a single layer, allows variation in the experimental data within one sample, thus making quantification possible to achieve. The derived formula provides an insight into any twisted hexagonal multilayer system and may be used to tune superconductivity.
The researchers used a combination of two techniques to understand and quantify how much single layer like behaviour exists in the graphene system. Raman spectroscopy---a technique to understand whether a graphene species has single layer like behaviour arising because of no interlayer interaction and electron diffraction--a technique to study the morphology of the given twisted system.
Observing fascinating properties of twisted multilayer graphene such as visible absorption band, efficient corrosion resistance, temperature-dependent transport, influencing the crystalline orientation of source material, helped the JNCASR team to understand the landscape of the given twisted multilayer graphene system.
Recent publication in the journal ‘Nature’ by James M. Tour, an eminent peer on this research discovery (https://doi.org/10.1038/s41586-020-1938-0), confirms the upper limit of relative Raman intensity predicted by this work, experimentally. The present understanding of twisted multilayer graphene will help in understanding any twisted hexagonal system. It gives an upper limit of relative Raman intensity which can exist in a particular multilayer graphene system.
Haydale has announced the signing of contracts for the provision of services for the collaborative development of graphene and nano material enhanced products for use in Dowty Propellers’ products. Haydale will assist Dowty in examining the feasibility and development of various material technologies, pertinent to Dowty’s future product development, involving the incorporation of graphene and other nano materials.
Haydale will work with Dowty to develop erosion-resistant coatings with the addition of Haydale’s proprietary Silicone Carbide (SiC) Microfibers. Further development work is ongoing to establish the feasibility of potential industry-changing technology for the turboprop sector. In addition to these topics, Haydale will develop graphene-enhanced functional inks for strain sensing using its surface engineered HDPlas graphene nanomaterials.
Jonathan Chestney, Dowty Propellers Engineering Director, said: “We are excited by the partnership with Haydale as we believe the exploration of the benefits of nanomaterial technology for our future products will significantly enhance our offering to our customers. We continue to strive for improvement in both our current and future products and developing partnerships like this are key to making that a success.”
Keith Broadbent, Haydale CEO, said: “We are really pleased that Dowty Propellers has engaged Haydale as a collaborative development partner. The team is ideally placed to assist with research, development and enhanced materials for evaluation and commercialization by Dowty in their products and/or processes. I anticipate some great developments from the projects carried out.”
Posted By Graphene Council,
Tuesday, September 15, 2020
Graphene is a modern wonder material possessing unique properties of strength, flexibility and conductivity whilst being abundant and remarkably cheap to produce, lending it to a multitude of useful applications -- especially true when these 2D atom-thick sheets of carbon are split into narrow strips known as Graphene Nanoribbons (GNRs).
New research published in EPJ Plus, authored by Kristians Cernevics, Michele Pizzochero, and Oleg V. Yazyev, Ecole Polytechnique Federale de Lausanne (EPFL), Lausanne, Switzerland, aims to better understand the electron transport properties of GNRs and how they are affected by bonding with aromatics. This is a key step in designing technology such chemosensors.
"Graphene nanoribbons -- strips of graphene just few nanometres wide -- are a new and exciting class of nanostructures that have emerged as potential building blocks for a wide variety of technological applications," Cernevics says.
The team performed their investigation with the two forms of GNR, armchair and zigzag, which are categorised by the shape of the edges of the material. These properties are predominantly created by the process used to synthesise them. In addition to this, the EPFL team experimented p-polyphenyl and polyacene groups of increasing length.
"We have employed advanced computer simulations to find out how electrical conductivity of graphene nanoribbons is affected by chemical functionalisation with guest organic molecules that consist of chains composed of an increasing number of aromatic rings," says Cernevics.
The team discovered that the conductance at energies matching the energy levels of the corresponding isolated molecule was reduced by one quantum, or left unaffected based on whether the number of aromatic rings possessed by the bound molecule was odd or even. The study shows this 'even-odd effect' originates from a subtle interplay between the electronic states of the guest molecule spatially localised on the binding sites and those of the host nanoribbon.
"Our findings demonstrate that the interaction of the guest organic molecules with the host graphene nanoribbon can be exploited to detect the 'fingerprint' of the guest aromatic molecule, and additionally offer a firm theoretical ground to understand this effect," Cernevics concludes: "Overall, our work promotes the validity of graphene nanoribbons as promising candidates for next-generation chemosensing devices."
These potentially wearable or implantable sensors will rely heavily on GRBs due to their electrical properties and could spearhead a personalised health revolution by tracking specific biomarkers in patients.
Posted By Graphene Council,
Friday, September 11, 2020
The National Institute for Materials Science (NIMS) has developed a memory device capable of storing multiple values using both optical and voltage input values. This device composed of layered two-dimensional materials is able to optically control the amount of charge stored in these layers. This technology may be used to significantly increase the capacity of memory devices and applied to the development of various optoelectronic devices. The research was published in Advanced Functional Materials ("Laser-assisted multilevel non-volatile memory device based on 2D van-der-Waals fewlayer-ReS2/h-BN/Graphene Heterostructures").
Memory devices used to store information (e.g., flash memory) play an indispensable role in today’s information society. The recording density of these devices has substantially increased in the past 20 years. In anticipation of widespread adoption of IoT technologies in the near future, it is desirable to accelerate the development of higher speed, larger capacity memory devices.
However, the current approach to increasing memory capacity and energy efficiency through silicon microfabrication is about to reach its limits. Development of memory devices with different working principles therefore has been awaited.
To meet expected technology needs, this research group has developed a transistor memory device composed of layered two-dimensional materials, including rhenium disulfide (ReS2) – a semiconductor – serving as a channel transistor, hexagonal boron nitride (h-BN) used as an insulating tunnel layer and graphene functioning as a floating gate.
This device records data by storing charge carriers in the floating gate in a manner similar to conventional flash memory. Hole-electron pairs in the ReS2 layer are prone to excitation when irradiated with light. The number of these pairs can be regulated by changing the intensity of the light.
The group succeeded in creating a mechanism that allows the amount of charge in the graphene layer to gradually decrease as the exited electrons once again couple with the holes in this layer. This success enabled the device to operate as a multivalued memory capable of efficiently controlling the amount of stored charge in stages through the combined use of light and voltage.
Moreover, this device can operate energy efficiently by minimizing electric current leakage—an achievement made possible by layering two-dimensional materials, thereby smoothening the interfaces between them at an atomic level.
This technology may be used to significantly increase the capacity and energy efficiency of memory devices. It also may be applied to the development of various optoelectronic devices, including optical logic circuits and highly sensitive photosensors capable of controlling the amount of charge stored in them through combined use of light and voltage.
This project was carried out by a research group consisting of Yutaka Wakayama (Leader of the Quantum Device Engineering Group (QDEG), International Center for Materials Nanoarchitectonics (MANA), NIMS), Bablu Mukherjee (Postdoctoral Researcher, QDEG, MANA, NIMS) and Shu Nakaharai (Principal Researcher, QDEG, MANA, NIMS).
This study was conducted in conjunction with another project entitled “Development of a ultra-sensitive photosensor using two-dimensional atomic film layers” funded by the Grant-in-Aid for JSPS Fellows.
Posted By Graphene Council,
Friday, September 11, 2020
Note: This content was developed by the Graphene Flagship.
Tamara Blanco Varela works as a Research and Technology Engineer at Graphene Flagship Partner company Airbus, based near Madrid in Spain. Her extensive experience encompasses over 15 years of work on aeronautical composite materials and processes. She leads all Airbus activities related to graphene, and her ultimate goal is to fully exploit the properties of graphene to enhance Airbus's composites and endow them with new functionalities.
Graphene has a wide range of potential applications in the aeronautics industry. Among them, Blanco Varela is currently working on anti-/de-icing systems, as well as enhancing the mechanical properties of materials and decreasing resin moisture absorption. She has been actively involved with the Graphene Flagship since its inception in 2013, and she is currently part of the Graphene Flagship's Work Package for Composites, the Work Package for Production and the Spearhead Project GICE.
We spoke about her background, her career choices and what drives her to succeed, and she was and discuss how graphene-enriched multifunctional materials can contribute to more sustainable aircraft.
What made you choose a career in science, and how did you end up working at Airbus?
When I was just a kid in the 1980s, and people were asking "what do you want to be when you grow up?", I never would've thought that I'd end up working as an engineer for a leading company like Airbus. This was unimaginable for a girl in a little town in north-western Spain, where I grew up.
Just to give you an idea, there are more than ten times as many Airbus employees than people living in my hometown! I decided to break the mold and study engineering, because I liked the sciences more than humanities.
I left my beloved hometown and family to go to Madrid, and then after an internship, my great opportunity arrived: I started to work as a subcontractor for Airbus in the Composite Materials and Processes Department. Soon, I knew I'd made the best choice, and I'm still extremely proud of and passionate about this company and my job.
Can you tell us about what you're working on now?
My project centres around using graphene and layered materials to enhance commercial aircraft – mainly their structural elements. Within this field, we aim to devise new materials with high damage tolerance, strength and stiffness.
Moreover, we want to design multifunctional materials with new features and functionalities, like electrical conductivity to cope with lightning strikes, thermal conductivity for anti-icing, heat exchange and other purposes, and self-sensing materials that can identify potential damage and cracks.
Why does graphene have so much potential for the aerospace industry?
The current composites used for structural elements are made of resins and carbon fibers. The problem is that resins absorb water and moisture in wet conditions. Graphene can contribute to improving the design, weight and barrier properties of these composites, slowing moisture absorption and also acting as fire-retardant.
Graphene has the potential to decrease the energy consumption of several manufacturing processes, including resin curing, adhesive joining, welding, additive manufacturing and 3D printing.
In aircraft, the properties of graphene can be also exploited for anti-/de-icing, electrical conductivity, anti-corrosion and anti-contamination, anti-bacterial, easy-cleaning, anti-static surfaces, electromagnetic interference shielding and so on.
How can these new graphene technologies help us work towards a sustainable future?
By reducing CO2 emissions and moving towards zero emissions aircraft, the aeronautical sector is already tackling many great challenges in the fight against climate change. We aim to halve our carbon footprint from 2005 levels by 2050, and the advanced, multifunctional and sustainable composites created by Airbus are key players in the move towards aircrafts, which consume less fuel. Graphene is one of the most promising materials to contribute to these future composites.
What are the biggest milestones in your career so far?
I participated in failure analysis, qualifying composites for the Airbus A380 and A350 aeroplanes. I was also involved in the development of new, enhanced thermoset resins and thermoplastic materials, with a recent focus on cost reduction.
I have always been very active in communication and dissemination by participating in plenty of conferences, publications, patents and technology-watch activities. I have built a wide network of people working at research centers, material suppliers, universities, and other divisions of Airbus. I can say that I'm known within my field!
At the end of 2019, I was proud to be selected by Airbus as an expert in multifunctional materials.
What are your views for the future?
I think we are starting a new era where multifunctional materials are key actors to cope with great technical challenges. I would like to be part of this endeavour, by leading and aligning all stakeholders to include these materials in the aircraft as soon as possible.
Do you have a role model or someone who inspires you to achieve?
My role model is the CTO of Airbus, Grazia Vittadini. She is the first female on the Airbus Executive Committee and Chief Technology Officer in the aeronautical industry, whose engineering workforce is made up of just 17 percent women worldwide. Furthermore, she served as the Director of the Airbus Foundation Board and is a member of the Inclusion and Diversity Steering Committee.
I really respect her professional philosophy and open mindset. She is very inspirational for me.
To quote Vittadini: "The only limits are the ones we impose ourselves."
Why do you feel that diversity in science and technology is important for the Graphene Flagship's progress?
Diversity is key in science and technology since it inspires innovation. I fully support diverse and inclusive work scientific or industrial environments, which attract the best talents, no matter their nationality, colour, gender, sexual orientation. Promoting diversity is essential for innovation, technology and success. It should be in the DNA of any company and research project.
Posted By Graphene Council,
Thursday, September 10, 2020
Quantum properties of matter as entanglement, which can allow controlling quantum states of physical systems, are key to the development of quantum computing and higher-performance information processing. Entanglement usually defines a nonlocal correlation between two or more particles, such that the quantum state of each of them cannot be described independently of the state of the others, even when particles become separated by an extremely large distance. Entanglement can be also observed between internal degrees of freedom of a single particle, which are independent parameters describing the state of a system, as physical coordinates define the position of a point in space. The comprehension of these phenomena, called inter- and intra-particle entanglement, can lead to manipulating the quantum states of physical systems, including materials as graphene and topological matter as a whole.
In a paper recently published in Physical Review B as a Rapid Communication, researchers from the ICN2 Theoretical and Computational Nanoscience group, led by ICREA Prof. Stephan Roche, present a study on the origin, dynamics and magnitude of intra-particle entanglement between various degrees of freedom of electrons propagating in graphene. In particular, they explore the quantum correlations between the spin, defined as the intrinsic angular momentum of particles, and the pseudo-spin, which is a property analogous to spin that emerges in lattice structures and depends on their specific geometrical symmetries.
The authors of this study show that large intra-particle entanglement is a general feature of graphene supported onto a substrate and that its generation and evolution is independent of the initial state of the system. In addition, it may be robust to disorder and dephasing, which means that, if an interaction compromised the intra-particle entanglement, it would regenerate. This research also suggests that the properties of intra-particle entanglement in graphene should be relevant to the dynamic of inter-particle entanglement between pairs of electrons: in fact, the evolution of the first phenomenon is reflected in the second. Because of this, intra-particle entanglement might be detected indirectly in experiments via inter-particle correlations.
These results unveil unexplored paths to understanding and manipulating entanglement phenomena in a family of materials, called Dirac materials, which includes graphene: this name is due to the fact that they are systems that can be described by the Dirac equation of relativistic quantum mechanics. The ability to detect and manipulate entanglement in such materials could become an unprecedented resource for future research on the application of this phenomenon to quantum information processing.
Posted By Graphene Council,
Thursday, September 10, 2020
The Henry Royce Institute for advanced materials research and innovation celebrated a key milestone earlier this year ahead of the new national hub becoming fully operational in 2021.
The Royce Hub Building based at The University of Manchester forms part of a growing network of facilities across the Institute’s Partner organisations: the National Nuclear Laboratory, UK Atomic Energy Authority, Imperial College London and the Universities of Cambridge, Leeds, Liverpool, Oxford and Sheffield, providing access to state-of-the-art equipment to academia and industry.
Extending across 9 floors and located at the heart of The University of Manchester's campus, it will foster world-class collaborative research in tandem with industry to act as an international convener for materials research excellence.
Following the construction phase, the Royce Hub Building was handed over by the contractors Laing O’Rourke in March 2020 and the first operational staff were just hours away from moving in before non-essential facilities closure was initiated in line with government guidance.
Progress on the interiors still continues and the Institute can now share a first look inside the £105m building which will act as a national hub for driving advanced materials research, development, and commercialisation in the UK.
Contractors continue the fit-out to minimise disruption when equipment and staff move in following The University of Manchester’s phased reopening of the campus. The first labs are expected to be completed towards the end of 2020.
The building will host £45 million worth of new equipment, as well as existing facilities in Manchester for biomedical materials, metals processing, digital fabrication, and sustainable materials research including the new Sustainable Materials Innovation Hub part-funded by the European Regional Development Fund. Alongside this will be collaborative space for industry engagement, helping to accelerate the development and commercialisation of advanced materials for a sustainable society.
The building and new equipment, totalling £150 million, forms part of the wider £235m investment by the Engineering & Physical Sciences Research Council across Royce’s national partnership. Investment has also be made by The Wolfson Foundation to support the biomedical materials facility within the building.
“The new Royce Hub Building will act as a centre of scientific excellence for advanced materials and a meeting place for the national community. By bringing together the UK’s academic and industrial materials leaders, Royce will identify new opportunities, workshop ideas, and develop new strategies and approaches to tomorrow’s materials demands.” Prof Philip Withers, Regius Professor of Materials and Royce Chief Scientist
Regius Professor of Materials and Royce Chief Scientist Philip Withers said: “The new Royce Hub Building will act as a centre of scientific excellence for advanced materials and a meeting place for the national community. By bringing together the UK’s academic and industrial materials leaders, Royce will identify new opportunities, workshop ideas, and develop new strategies and approaches to tomorrow’s materials demands.”
Professor David Knowles, CEO of the Henry Royce Institute said: “Royce has come a long way since its inception in 2016 and the handover of the new Royce Hub Building in Manchester represents the next chapter in our story. Although COVID-19 has delivered some unprecedented challenges and delays, we are confident that the physical space will demonstrate that the national institute is truly open for business. We can now look to address challenge-led research that will have positive impact on UK and global citizens, underpinning the Royce vision of ‘Advanced Materials for a Sustainable Society’.”
Manchester is a world-leader in developing new and existing materials and is already known globally as the home of graphene – a game-changing two-dimensional material first isolated at The University of Manchester in 2004.
Dr Diana Hampson, Director of Estates for The University of Manchester commented “We are delighted to have successfully delivered the construction phase of the Henry Royce Institute Hub Building which sits alongside the University’s growing advanced materials campus including the National Graphene Institute and the Graphene Engineering Innovation Centre. The research that will take place in these buildings will consolidate Manchester’s role at the centre of materials characterisation – measuring and exploring materials that will help us fully understand their properties and potential.”
Professor Dame Lynn Gladden, EPSRC Executive Chair said: “Advanced materials research and innovation is essential to tackle global challenges from applications in the energy sector to advances in healthcare. The opening of the new Royce Hub Building is an important milestone to drive exciting advanced materials research that will extend our capabilities across a wide range of disciplines.”
The Royce Hub Building, under the Project and Cost Management of Arcadis was designed by NBBJ, an international architectural practice, alongside civil and structural engineers Ramboll and building services engineers Arup. The building was delivered by Laing O’Rourke, the appointed University of Manchester contractor.
Posted By Graphene Council,
Wednesday, September 9, 2020
Tohoku University Professor Taiichi Otsuji has led a team of international researchers in successfully demonstrating a room-temperature coherent amplification of terahertz (THz) radiation in graphene, electrically driven by a dry cell battery.
Roughly 40 years ago, the arrival of plasma wave electronics opened up a wealth of new opportunities. Scientists were fascinated with the possibility that plasma waves could propagate faster than electrons, suggesting that so-called "plasmonic" devices could work at THz frequencies. However, experimental attempts to realize such amplifiers or emitters remained elusive.
"Our study explored THz light-plasmon coupling, light absorption, and amplification using a graphene-based system because of its excellent room-temperature electrical and optical properties," said Professor Otsuji who is based at the Ultra-Broadband Signal Processing Laboratory at Tohoku University's Research Institute of Electrical Communication (RIEC).
The research team, which consisted of members from Japanese, French, Polish and Russian institutions, designed a series of monolayer-graphene channel transistor structures. These featured an original dual-gathering gate that worked as a highly efficient antenna to couple the THz radiations and graphene plasmons.
Using these devices allowed the researchers to demonstrate tunable resonant plasmon absorption that, with an increase in current, results in THz radiation amplification. The amplification gain of up to 9% was observed in the monolayer graphene -- far beyond the well-known landmark level of 2.3% that is the maximum available when photons directly interact with electrons without excitation of graphene plasmons.
To interpret the results, the research team used a dissipative plasmonic crystal model, capturing the main trends and basic physics of the amplification phenomena. Specifically, the model predicts the increase in the channel dc current that drives the system into an amplification regime. This indicates that the plasma waves may transfer the dc energy into the incoming THz electromagnetic waves in a coherent fashion.
"Because all results were obtained at room temperature, our experimental results pave the way toward further THz plasmonic technology with a new generation of all-electronic, resonant, and voltage-controlled THz amplifiers," added Professor Otsuji.
Posted By Graphene Council,
Wednesday, September 9, 2020
Physicists at the University of Basel have developed a minuscule instrument able to detect extremely faint magnetic fields. At the heart of the superconducting quantum interference device are two atomically thin layers of graphene, which the researchers combined with boron nitride. Instruments like this one have applications in areas such as medicine, besides being used to research new materials.
To measure very small magnetic fields, researchers often use superconducting quantum interference devices, or SQUIDs. In medicine, their uses include monitoring brain or heart activity, for example, while in the earth sciences researchers use SQUIDs to characterize the composition of rocks or detect groundwater flows. The devices also have a broad range of uses in other applied fields and basic research.
The team led by Professor Christian Schönenberger of the University of Basel's Department of Physics and the Swiss Nanoscience Institute has now succeeded in creating one of the smallest SQUIDs ever built. The researchers described their achievement in the scientific journal Nano Letters.
A superconducting ring with weak links
A typical SQUID consists of a superconducting ring interrupted at two points by an extremely thin film with normal conducting or insulating properties. These points, known as weak links, must be so thin that the electron pairs responsible for superconductivity are able to tunnel through them. Researchers recently also began using nanomaterials such as nanotubes, nanowires or graphene to fashion the weak links connecting the two superconductors.
As a result of their configuration, SQUIDs have a critical current threshold above which the resistance-free superconductor becomes a conductor with ordinary resistance. This critical threshold is determined by the magnetic flux passing through the ring. By measuring this critical current precisely, the researchers can draw conclusions about the strength of the magnetic field.
SQUIDs with six layers
"Our novel SQUID consists of a complex, six-layer stack of individual two-dimensional materials," explains lead author David Indolese. Inside it are two graphene monolayers separated by a very thin layer of insulating boron nitride. "If two superconducting contacts are connected to this sandwich, it behaves like a SQUID - meaning it can be used to detect extremely weak magnetic fields."
In this setup, the graphene layers are the weak links, although in contrast to a regular SQUID they are not positioned next to each other, but one on top of the other, aligned horizontally. "As a result, our SQUID has a very small surface area, limited only by the constraints of nanofabrication technology," explains Dr. Paritosh Karnatak from Schönenberger's team.
The tiny device for measuring magnetic fields is only around 10 nanometers high - roughly a thousandth of the thickness of a human hair. The instrument can trigger supercurrents that flow in minuscule spaces. Moreover, its sensitivity can be adjusted by changing the distance between the graphene layers. With the help of electrical fields, the researchers are also able to increase the signal strength, further enhancing the measurement accuracy.
Analyzing topological insulators
The Basel research team's primary goal in developing the novel SQUIDs was to analyze the edge currents of topological insulators. Topological insulators are currently a focus of countless research groups all over the world. On the inside, they behave like insulators, while on the outside - or along the edges - they conduct current almost losslessly, making them possible candidates for a broad range of applications in the field of electronics.
"With the new SQUID, we can determine whether these lossless supercurrents are due to a material's topological properties, and thereby tell them apart from non-topological materials. This is very important for the study of topological insulators," remarked Schönenberger of the project. In future, SQUIDs could also be used as low-noise amplifiers for high-frequency electrical signals, or for instance to detect local brainwaves (magnetoencephalography), as their compact design means a large number of the devices can be connected in series.