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.
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.
An international team of researchers have recently published a review article on nanoelectromechanical (NEMS) sensors based on suspended two-dimensional (2D) materials in the journal Research ("Nanoelectromechanical Sensors Based on Suspended 2D Materials"), an open-access multidisciplinary journal launched in 2018 as the first journal in the Science Partner Journal (SPJ) program.
The paper is an invited contribution to a special issue on “Progress and challenges in emerging 2D nanomaterials – preparation, processing, and device integration”, and has the purpose of contributing to the development of the field of 2D materials for sensor applications and to their integration with conventional semiconductor technology.
“I believe NEMS sensors based on 2D materials will be essential for satisfying the demand for integrated, high-performance sensors set by applications such as the Internet of Things (IoT) and autonomous mobility”, says Lemme, first author of the paper.
The review summarizes the many studies that have successfully shown the feasibility of using membranes of 2D materials in pressure sensors, microphones, mass and gas sensors – explaining the different sensor concepts and giving an overview of the relevant material properties, fabrication routes, and operation principles.
“Two-dimensional materials are ideally suited for sensors”, says Lemme, “as they allow realizing free-standing structures that are just one of a few atoms thick. This ultimate thinness can be a decisive advantage when it comes to nanoelectromechanical sensors, since the performance often depends critically on the thickness of the suspended part. Furthermore, many 2D materials have unique electrical, mechanical and optical properties that can be exploited for completely new concepts of sensor devices.”
The review – which includes contributions from RWTH Aachen University, AMO GmbH, Universität der Bundeswehr Munich, KTH Royal Institute of Technology, TU Delft, Infineon and the Kavli Institute of Nanoscience – discusses the different readout and integration methods of different sensors based on 2D materials, and provides comparisons against the state of the art devices to show both the challenges and the promises of 2D-materials based nanoelectromechanical sensing.
“Proof-of-concept sensor devices based on suspended 2D materials are almost always smaller than their conventional counterparts, show improved performances, and sometimes even completely novel functionalities”, says Peter G. Steeneken, leader of work-package 6 (Sensors) in the Graphene Flagship and co-author of the paper. “However, there are still enormous challenges to demonstrate that 2D material-based NEMS sensors can outperform conventional devices on all important aspects – for example, the establishment of high-yield manufacturing capabilities. The Graphene Flagship represents the ideal platform to address these challenges, as it fosters collaborations between world-leading groups to achieve a set of well-defined goals. This paper is an example of how, by bringing together complementary expertise, we can achieve more.”
Researchers at Graphene Flagship partners CNR-IMM, Italy, CNRS-CRHEA, France, and STMicroelectronics, Poland, in collaboration with Graphene Flagship Associate Member TopGaN, Poland, collaborated on the Partnering Project GraNitE to produce graphene-enabled hot electron transistor (HET) devices. Thanks to nitride semiconductors, they achieved devices with current densities a million times higher than previous prototypes.
Nitride semiconductors are in the spotlight for their potential to be incorporated into HETs to improve their properties and performance. HETs are a type of vertical transistor that can operate at frequencies in the terahertz (THz) range, making them very valuable for applications in communications, medical diagnostics and security. Graphene is promising for applications in HETs, owing to its thinness and high conductivity. They are typically made from nitrides of gallium, aluminium or indium, or alloys of these metals. Aluminium and gallium nitrides are key ingredients in high-electron mobility transistors (HEMTs) – one of the technological foundations of 5G communications.
Gallium-based technologies do have their limitations, however, and GraNitE seeks to take advantage of graphene and layered materials to overcome them. The GraNitE team incorporated graphene as an active ingredient into high-powered aluminium-gallium nitride (AlGaN) and gallium nitride (GaN) based nitride transistors to better dissipate heat, by taking advantage of graphene's high thermal conductivity. The devices also operate at higher frequency thanks to the incorporation of high-quality graphene.
The team devised two approaches. Their first was to deposit graphene onto the surface of the nitride semiconductor using chemical vapour deposition (CVD). This resulted in highly homogeneous, nanocrystalline graphene films,1 which could lead to uptake by industry. The second was to grow monolayer graphene using CVD on a copper surface, then to transfer and integrate it into thin layers of AlGaN and GaN. This method resulted in a graphene/AlGaN junction with excellent rectifying properties, ideal for applications in switches, with an injection mechanism tuneable by modifying the AlGaN composition and thickness.2
Graphene Flagship partnering project GraNitE used their graphene nitride junction as a key building block to fabricate prototype HET devices. Their devices had a low voltage threshold and an electric current density six orders of magnitude higher than those in previous silicon tests,2 representing an important advance in the development of hybrid graphene/nitride semiconductors, and paving the way for future exploitation of this technology.
"The integration of graphene and nitride semiconductors is one of the most viable approaches to harness the unique properties of these materials for industrial applications," says Filippo Giannazzo, GraNitE Project Leader and Senior Scientist at Graphene Flagship partner CNR-IMM, Italy.
Scientists at Graphene Flagship partners the University of Padova, the University of Trieste and CNR-IMM, Italy, in collaboration with researchers from other European institutions, have developed a new strategy to boost the performance of magnesium-based rechargeable batteries. Combining vanadium and graphene oxide, they obtained a high-power cathode that shows excellent promise for sustainable energy storage.
Rechargeable batteries are widespread in modern electronics, as they can repeatedly accumulate, store and discharge energy through a reversible electrochemical reaction. This makes them vital for the lasting function of mobile phones, laptops and electric vehicles, all of which endure hundreds of charge cycles over their lifetime. Typical rechargeable batteries are made using lithium anodes, but magnesium anodes have a number of properties that make them promising alternatives.
"Several factors make magnesium-based rechargeable batteries attractive," begins first author Vito Di Noto, from Graphene Flagship partner the University of Padova, Italy. "They have a higher volumetric capacity than those made with lithium, and they can be safely handled in air." Moreover, magnesium is a cheaper and more abundant raw material. "In fact, it is one of the most abundant elements in the Earth's crust," explains Di Noto. Magnesium anodes also represent a safer alternative: they are less prone to dendrite formation, a phenomenon that can lead to short circuits and, in rare circumstances, battery explosion.
However, the development of magnesium batteries has been hindered by their poorly performing cathodes, which often result in significantly worse-performing devices than their lithium-based counterparts.
To tackle this challenge, the researchers developed an all-new cathode material for magnesium batteries based on graphene and vanadium oxides. The material exhibits a peculiar chrysalis-like microstructure that enhances the performance of the battery. Graphene oxide flakes encircle a nanoparticle core based on vanadium oxide: "the structures are fixed together thanks to a layer of ammonium ions," explains Di Noto. The chrysalis-like material combines vanadium's high redox activity and graphene oxide's electrical properties. "This yields a cathode with very strong chemical and electrochemical stability," he continues.
The new graphene-enhanced cathode has allowed researchers to operate a coin cell at very high current rates and power, with a promisingly high specific capacity. "The synergistic effects provided by graphene oxide, vanadium and the chrysalis morphology enable the coin cell to operate with 500% more sustained current than state-of-the-art magnesium batteries, at a 40% higher working potential." These properties could be exploited to make batteries for mobile devices that last longer between charges or deliver more power.
Furthermore, magnesium's high natural abundance means that magnesium-based rechargeable batteries could be an environmentally friendly solution. This work brings graphene batteries one step closer to the market. "Magnesium is one of the most sustainable metals in the world, and can be easily recycled – up to 100%," Di Noto continues. "We hope that our work will contribute to the turning point towards the establishment of a greener and more sustainable energy economy."
Daniel Carriazo, Graphene Flagship Work Package Deputy for Energy Storage, comments: "As the production of lithium-ion batteries increases exponentially to fulfil the demand of new applications, it is necessary to develop alternative energy storage technologies made out of accessible and environmentally friendly materials." Carriazo says that this work shows very promising results when a vanadium-based graphene composite is used as the positive electrode in a potassium-ion battery. "The incorporation of graphene enables fast charging, overcoming one of the limitations associated with this technology," he continues.
Andrea C. Ferrari, Science and Technology Officer of the Graphene Flagship and Chair of its Management Panel, adds: "Graphene and layered materials have recognised potential in energy storage, and graphene is already present in commercial devices. This approach tackles the need to produce more environmentally sustainable batteries, and thanks to the introduction of graphene oxide into the cathode, shows how magnesium could be used, which is easier to recycle. Sustainable development always guides the technology and innovation roadmap of the Graphene Flagship, and this research is yet another promising example."
World-class research and innovation at the ‘Home of Graphene’ is back on site, as The University of Manchester reopens its facilities following the campus-wide closure of buildings in March.
Staff at the National Graphene Institute (NGI) and the Graphene Engineering Innovation Centre (GEIC) have spent a number of weeks carefully managing the process of reopening their laboratories and multi-user facilities.
NGI Director Professor Vladimir Falko (pictured right) said the graphene research community remained active throughout lockdown and, with researchers returning to their labs, they will rapidly reboot their fundamental and applied research programmes.
“During the COVID-19 closure, NGI researchers continued to work remotely, analysing data, developing theoretical models for 2D materials, planning new experiments and attending the popular Friday afternoon graphene seminars online – but everyone is more than eager to get back to action in their labs,” said Vladimir.
“Thanks to the effort of the NGI’s professional support staff, the building has been efficiently prepared for reopening - and special thanks must go to [technical managers] John Whittaker, Polly Greensmith and colleagues in Estates and Cleaning Services.”
Phased reopening By the end of July, as part of a phased programme, all of the NGI labs will reopen and be operating at about 25% personnel capacity, with researchers keeping social distancing in the labs and throughout the building. This includes the world-first ultra-high vacuum 2D materials transfer system - the bespoke ‘UHV 2DM press’ - which has been designed for the research group led by Dr Roman Gorbachev.
Several characterisation laboratories have now reopened, including the metrology-class magneto-transport suite hosting a 10 milli-Kelvin cryostat and a 14 Tesla magnet, optical characterisation facilities, and the nanocomposites laboratories.
“I am sure that the NGI groups will be able to deliver on the international collaboration projects such as European Graphene Flagship and European Quantum Technology Flagship, collaborations with partners in the US, Singapore and Japan, and multiple projects with industry,” added Vladimir.
“We will also do our best to support PhD students and several students from our Centre of Doctorial Training, Graphene NOWNANO, are already making samples for their projects on 2D materials.”
Safe systems of working Meanwhile, all labs at the GEIC are now open, with similarly limited personnel capacity and distancing protocols, allowing staff and industry partners to resume operations.
GEIC Technical Services Manager Philip Hirst said: “The re-opening of the GEIC has been a learning process for all of us. Our aim has been to get to full operation for our industrial and academic partners in a safe manner, following the government guidance closely.
"The process has been measured and iterative to ensure that we are doing what we can to protect our staff and partners. All of the labs are now operational with tight controls over numbers and safe systems of working. It is great to see the GEIC working again.”
Laboratories now open include facilities for rapid development of graphene and 2D materials towards commercialisation in fields such as coatings and composites, batteries, printed electronics and more.
Brazilian steel giant Gerdau - a Tier 1 GEIC partner - has been working in the Masdar Building on anti-corrosion coatings, composites for the automotive industry, membranes and energy storage materials.
Danilo Mariano, Head of Graphene R&D for Gerdau, said: “We were in the first wave of people to get back in the GEIC [in early July]. It’s a different experience, with all the COVID protocols in place, but it feels so good to be back in – talking to the technicians, getting things done. It feels like coming out of a coma.”
Advanced materials company, First Graphene Limited is pleased to provide this update on its financial and operational performance for the quarter ended 30 June 2020. Appendix 4C quarterly cash flow report follows this update.
• Major sales agreements executed – large scale manufacturing of protective face masks and new resin composites for swimming pools • Cash receipts from customers quadruple, quarter-onquarter • Successful entitlement issue raises A$6.2 million • Strengthened leadership with new appointments • FGR becomes first Australian company to join EU Graphene Flagship group • GEIC facility re-opens after COVID-19 restrictions lift
Arguably, a better understanding of the working principles of the human brain remains one of the major scientific challenges of our time. Despite significant advances made in the field of neurotechnology in recent years, neural sensing interfaces still fall short of equally meeting requirements on biocompatibility, sensitivity, and high spatio-temporal resolution. The European Union Horizon 2020 research project BrainCom, coordinated by the ICN2 Advanced Electronic Materials and Devices Group led by ICREA Prof. José A. Garrido, is tackling these problems. BrainCom brings together experts from the fields of neurotechnology, neuroscience, and ethics to develop novel technologies capable of overcoming these limitations and shed light onto the mechanisms of information encoding and processing in the brain.
In four research articles published between March and April 2020 -- featured in Elsevier’s Carbon, IOP’s 2D Materials, Wiley’s Small, and American Chemical Society’s Nano Letters -- researchers from the BrainCom consortium present the technological advances achieved in the project, discuss in-depth methodology, and demonstrate novel capabilities for high resolution sensing of the brain’s electrical activity. The recent developments exploit the unique properties of graphene, an atom-thick layer of carbon, which conforms with the soft and convoluted surface of the brain providing an excellent neural sensing interface. Graphene sensors have an additional advantage that represents a turning point in neural engineering: the sensing mechanism of these graphene active sensors (so-called transistors) is compatible with electronic multiplexing, a technology that enables transmitting the signals detected by multiple sensors through a single micrometric wire. This implies that the number of sensors on the neural implants can be increased while minimizing the footprint of the connectors required to link the implants to external electronic equipment.
This technology, developed in close collaboration with Dr Anton Guimerà at the CSIC Institute of Microelectronics of Barcelona (IMB-CNM, CSIC), has been evaluated in pre-clinical studies at the laboratory of neuroscientist Prof. Anton Sirota at Ludwig-Maximilians Universität (LMU, Munich). A collaborative and multidisciplinary approach is crucial for the success of the project, which aims at addressing a very hard scientific and technological challenge. The human brain has an astonishing complexity, consisting out of as many as 100 billion neurons. To fully understand the underlying principles of such a convoluted system requires the simultaneous detection of the electrical activity of large neural populations with a high spatial and temporal resolution. Unfortunately, current neural sensing technologies present a trade-off between spatial resolution and large-area coverage of the brain surface. The work carried out by the BrainCom project’s researchers shows how graphene-based sensors represent an outstanding building block for such large scale and highly sensitive neural interfaces. As explained in the recently published papers, graphene sensors can be reduced in size to the dimension of about one single neuron, while maintaining a high signal quality. In addition, their sensitivity expands over a wide range of frequencies; from infra-slow oscillations to very fast signals elicited by individual cells.
These findings clear the path for a scale-up of graphene sensor technology towards arrays with an ultra-high-count of sensors. Such biocompatible and high bandwidth neural interfaces can have a great impact on the development of neuroprosthesis, which enable a direct communication between the brain and a computer. These results represent the fruition of long-term EU research initiatives, which pursue the ambitious goal of restoring speech to impaired patients by reading the signals in their brains, which are related to their intentional speech. The research consortium will now focus on upscaling the production of these neural interfaces and testing their performance in safe human clinical trials. This and other applications of graphene sensors are also supported by the EU Graphene Flagship within the Biomedical Technologies work package.
Friction between moving parts can significantly degrade mechanical components and devices. The introduction of graphene-enabled superlubricity, a state of ultra-low friction between two surfaces, could reduce wear and tear and enable longer-lasting, more durable dry-lubricated machinery. This could be particularly important for the next generation of wind turbines, electrical switches, and micro- and nano-electromechanical systems.
We interviewed Costas Galiotis, Graphene Flagship Work Package Leader for Composites, based at Graphene Flagship partner FORTH, Greece, who speaks about his research and emphasises the potential of superlubric graphene as a new and effective dry lubricant for moving components.
What is superlubricity and how does it arise?
Superlubricity is a state of motion in which friction is very low, or even vanishes – although there is not a strict definition from a quantitative perspective. Roughly speaking, for superlubric behavior, the friction coefficient needs to be less than 0.01.
Superlubricity arises when two crystalline surfaces are in an incommensurate stacking state: in other words, the two surfaces slip and slide against each other under dry conditions, with very low friction.
Why superlubricity a useful property?
When two solid surfaces in contact are subjected to relative motion, friction between them converts kinetic energy to thermal energy. Friction can cause serious wear problems by damaging moving components.
Superlubricity is a state of motion that generates ultra-low friction and, therefore it significantly suppresses friction-related wear and tear problems. Superlubricity has important implications for practical applications, such as in the dry lubrication of mechanical drive components like micro/nano-electromechanical systems (MEMS/NEMS), in electrical switches and in wind energy components.
How can graphene enable new superlubric components?
If we can better understand the interlayer shear stress reduction mechanism in a graphene–graphene system, such as bilayer graphene, then we can better exploit it as a superlubricant for state-of-the-art applications to minimize both energy loss and damage from wear and tear – which would improve the lifetime of the products and components as well.
Is it a challenge to introduce superlubricity to a graphene-based material such as bilayer graphene?
Yes. In graphite, which is considered a lubricant, there are many commensurate stacking domains, which lead to mechanical interlocking between the graphene layers – meaning there is high friction between them. Equally, in bilayer graphene, the two layers are strongly bonded to each other, and the friction is much higher – confirmed by the presence of a single characteristic 2D peak in the Raman spectrum.
Do you have any recent advances in this area?
We recently investigated how graphene could enable superlubric components for mechanical devices. We tested bilayer graphene in an incommensurate state, where graphene layers are stacked randomly by sequential transferring.
In bilayer graphene, the two layers are normally strongly bonded to each other, meaning the friction is higher. When the two layers are randomly stacked, they slide against each other with minimal friction. We confirmed this by measuring the interlayer shear stresses, which were very low, and found that the friction between the graphene layers drops to almost zero – as long as they are randomly stacked.
These graphene layers exhibited superlubricity.
What causes this behavior?
Using Raman spectroscopy, we found that in graphene with disordered stacking, less than half of the total strain applied to the bottom layer is transferred to the top layer, meaning the layers can freely slip and slide against each other. After verifying the mechanism using computational molecular dynamics simulations, we demonstrated the phenomenon in practice by coating two surfaces with disordered single-layer graphene. In line with our predictions, friction between them substantially decreased when we applied a strain. This persists even for large graphene monolayers produced by chemical vapour deposition (CVD) – as long as they are randomly stacked, paving the way for us commercial applications that use CVD graphene sheets.
What applications could graphene-based superlubricity have?
This technology could lead to a new generation of dry lubricants based on graphene and layered materials. The lubricants will also play a key role in the Graphene Flagship's Circuit Breakers project. One of a series of eleven new industry-focused Spearhead Projects, the initiative aims to develop maintenance-free circuit breakers for new, flexible and smart power distribution systems. The circuit breakers' moving components will be coated with graphene and layered material lubricants, enhancing their durability, lifetime and more.
First Graphene Ltd has been accepted as an Associate Member of the EU Graphene Flagship. The company joins the €1 billion EU funded programme at a crucial time as the Flagship transitions from R&D to commercialisation and requires graphene manufacturers with industrial supply capability.
The Graphene Flagship has a budget of €1 billion and coordinates nearly 170 academic and industrial research groups in 21 countries and has more than 90 associate members. FGR through its UK subsidiary is the first Australian entity to be admitted to the consortium.
The Graphene Flagship is tasked with bringing together academic and industrial researchers to take graphene from the realm of academic laboratories into European society in the space of 10 years, thus generating economic growth, new jobs and new opportunities.
This follows the Company also joining the BSI and ISO/TC229 working groups for the development of graphene characterisation standards, thereby ensuring alignment of the Company’s quality processes with the emerging international standards.
First Graphene intends to stay at the leading edge in terms of controlling the quality of graphene related products. The Company continues to invest in its processing capability through measurement and automation and is a Tier 1 Member of the Graphene Engineering Innovation Centre at the University of Manchester with direct access to world-class analytical equipment and techniques and supporting expertise. The Company will continue to invest in analytical methods and process tools to ensure world leading PureGRAPH® product quality for our customers.
Craig McGuckin, Managing Director for First Graphene Ltd, said, “FGR joining the EU Graphene Flagship at this time is auspicious, as FGR continues to commercialise it PureGRAPH® range of graphene powders. As the world leader in the production of large volume, high quality graphene powders membership of this organisation is at an appropriate time as various projects transition from R&D to commercialisation.”