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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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New studies on particle entanglement dynamics in graphene for alternative quantum computing protocols

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.

Tags:  Graphene  ICN2  ICREA  quantum materials  Stephan Roche 

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Fast electrical modulation of nanoscale erbium-graphene systems towards quantum technology applications

Posted By Graphene Council, Thursday, August 27, 2020
Quantum technologies promise to revolutionize information technology and communications by taking advantage of some peculiar aspects of quantum physics, such as quantum state superposition and entanglement. Research is moving forward in different directions with the goal of building optimal devices for quantum information processing, secure communication, and high-precision sensing.

Systems based on rare-earth ions, such as erbium, are very relevant to this quest, in particular because they typically have very long decoherence times, which means that quantum states persist longer than in other systems.  Furthermore, erbium emits light at a wavelength of 1.5 micrometers, one of the main bands for optical communications systems. Hybrid systems containing nanoscale rare-earth components may prove highly versatile and useful to meet the needs of various (quantum) optoelectronic applications.

A team of researchers including Dr Klaas-Jan Tielrooij, leader of the Ultrafast Dynamics in Nanoscale Systems group at the ICN2, and scientists from the Institute of Photonic Sciences (ICFO) and the Institut de Recherche de Chimie Paris (IRCP) have combined a 10 nm thin film of an erbium-doped oxide crystal with monolayer graphene. This hybrid system exhibits extremely strong emitter-environment interactions due to the physical closeness of the emitters to graphene, and the strong dipole-dipole coupling to Dirac electrons.

Their study, recently published in Nature Communications, showed that a large fraction of excited erbium ions decays more than a thousand times faster than normal due to the presence of graphene. This implies that more than 99.9% of the energy flows from these excited emitters to graphene through near-field interactions – where the near-field is the region of the electromagnetic field closest to the object that emits the radiation; in this specific case, it means at a distance from the emitter much smaller than the wavelength of the emitted light. The energy that is transferred from excited emitters to graphene leads to either electron-hole pair generation or plasmon launching (see illustration) in graphene, depending on the Fermi energy of graphene.

Moreover, as reported in the paper, the authors were able to efficiently control the near-field interactions of this hybrid system and to modulate them dynamically by applying a small electrical voltage of just a few volts. This is possible because the gate voltage allows for tuning graphene’s Fermi energy over a large range. The emitter-environment interactions were controlled with high modulation frequencies — up to 300 kHz, which is three orders of magnitude higher than the emitter’s normal radiative decay rate.

This fast dynamic modulation can lead to interesting phenomena and applications, such as the emission of single photons with controlled waveform and quantum entanglement generation by collective plasmon emission. The development of hybrid systems enabling fast control over the near-field interactions, as this erbium-graphene platform, also provides an interesting tool to manipulate quantum states in nanoscale solid state devices by means of conventional electronics. Further studies on these structures will certainly open the way to wider applications in optoelectronic, plasmonic and quantum technologies.

Tags:  Graphene  ICN2  Klaas-Jan Tielrooij  optoelectronics  quantum materials 

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New investors for INBRAIN to develop graphene-based implants against brain disorders

Posted By Graphene Council, Friday, June 12, 2020
INBRAIN Neuroelectronics, a spin-off of the Catalan Institute of Nanoscience and Nanotechnology and ICREA, receives funding from Sabadell Asabys and Alta Life Sciences, as well as ICF and Finaves, which will allow the company to speed up the development of novel graphene-based implants to optimise the treatment of brain disorders, such as Parkinson's and epilepsy.

According to a 2010 study commissioned by the European Brain Council, the cost of brain disorders in Europe alone reaches approximately 800 billion euros a year, with more than one-third of the population affected. The high incidence of brain-related diseases worldwide and their huge social cost call for greater investments in basic research in this field, with the aim of developing new and more efficient therapeutic and diagnostic tools.

INBRAIN Neuroelectronics, a spin-off of the Catalan Institute of Nanoscience and Nanotechnology (ICN2) and ICREA, was established in 2019 with the mission to develop brain-implants based on graphene technology for application in patients with epilepsy, Parkinson’s and other neuronal diseases. These smart devices, built around an innovative graphene electrode, will decode with high fidelity neural signals from the brain and produce a therapeutic response adapted to the clinical condition of the specific patient.

Additional resources have been recently injected into this endeavour by new investors — in particular Asabys and Alta Life Sciences, through the Sabadell-Asabys funds, followed by the Institut Català de Finances (ICF) and Finaves (fund promoted and managed by IESE Business School) — and other existing shareholders, such as the ICN2 and ICREA themselves. It will allow INBRAIN to accelerate the development of these novel intracranial implants for patients affected by brain disorders.

The company is designing the least invasive and smartest neural interface on the market that, powered by artificial intelligence and the use of Big Data, will have the ability to read and modulate brain activity, detect specific biomarkers and trigger adaptive responses to deliver optimal results in personalised neurological therapies. So far, the technology has been validated in in-vitro and in-vivo biocompatibility and toxicity tests and it has been successfully used to complete studies on small animals. Recently, INBRAIN has begun tests on large animals with the aim of ensuring that these graphene devices are safe, as well as superior to current solutions based on metals such as platinum and iridium. The company also plans to start soon human studies.

INBRAIN was founded, among others, by ICREA Prof. Jose Garrido, leader of the ICN2 Advanced Electronic Materials and Devices Group, Prof. Kostas Kostarelos, leader of the ICN2 Nanomedicine Group, and Dr Anton Guimerà, a researcher at the Spanish National Centre of Microelectronics (IMB-CNM). "Within the framework of the Graphene Flagship, which is a European macroproject”, explains Prof. Garrido, "we were able to develop this novel graphene-based technology that will allow measuring and stimulating neuronal activity in the brain with a resolution much higher than that of current commercial technologies”. During 2019, the incorporation of INBRAIN was a priority project for the ICN2 Business and Innovation Department, which coordinated the technology transfer process and successfully orchestrated the licensing of this high-potential technology.

“Minimally invasive electronic therapies represent a revolutionary alternative with less potential cost for health systems,” comments Carolina Aguilar, CEO of INBRAIN and a former global executive at Medtronic in the field of neuro-stimulation. "In our case, the application of new 2D materials such as graphene represents a real opportunity to understand how the brain works in order to optimise and personalise the treatment.”

Tags:  Carolina Aguilar  Graphene  ICN2  ICREA  IMB-CNM  INBRAIN 

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Layered heterostructures put a spin on magnetic memory devices

Posted By Graphene Council, Thursday, January 9, 2020
Graphene is a unique material with great potential for the long-distance transportation of spin information. However, spin-to-charge interconversion (SCI) in graphene and graphene-based heterostructures to date could not be performed at room temperature. But now, researchers at Graphene Flagship partners ICN2 and Universitat Autònoma de Barcelona, Spain, and the University of Groningen, the Netherlands, have achieved efficient room temperature SCI in graphene-based structures, and devised a way to make this process tuneable using an external electric field. The findings, published in Nature Materials and Nano Letters, could allow scientists to use layered heterostructures for ultra-compact, low-power consumption magnetic memory devices.

Spintronics is a branch of electronics which uses electrons' spin to store, manipulate and transfer information. Spintronics could benefit many emerging markets, like motion sensing and next-generation memory devices. Developing efficient and versatile spin-based technologies requires both high-quality materials for long-distance spin transfer, and suitable engineering methods to generate and manipulate spin currents, to ensure electrons move in a controlled way with their spins oriented along a given direction.

Generally, spin currents are generated and detected using ferromagnetic contacts. But as an alternative, spin-orbit interactions could enable spin currents to be controlled entirely by an electric field, resulting in a far more versatile tool to be implemented in large-scale spin devices. Now, Graphene Flagship researchers ICREA Prof. Sergio O. Valenzuela, ICREA Prof. Stephan Roche, and colleagues have exploited the unique spin properties of graphene to transport spin information across long distances in large-scale SCI electronics. Additionally, by interfacing graphene with transition metal dichalcogenides (TMDs), another family of layered materials with strong spin-orbit coupling, they were able to precisely control spin transport in these devices. "Thanks to this research, the Graphene Flagship's Spintronics Work Package has made a major step towards the engineering of SCI in quantum devices, with genuine potential for spintronics applications," explains Roche.

By fabricating a high-quality device and using very sensitive detection techniques to evaluate the spin Hall and inverse spin Galvanic effects – focusing in particular on spin precession and non-local measurements – they demonstrated experimentally that the SCI in graphene–TMD heterostructures is in good agreement with theoretical models. Furthermore, using these techniques, Graphene Flagship researchers not only demonstrated the spin-related character of the signals, but also tailored the efficiency of their SCI and sign using electrostatic gating. This important feature directly showcases their ability to manipulate spin information in the heterostructures with an electric field, and this could soon lead to new applications in magnetic memory devices. Most notably, they found that the room temperature SCI efficiencies were just as high as the best results using other materials.

"We're very excited to report the first unambiguous evidence of large and tuneable SCI in van der Waals heterostructures at room temperature," comments Valenzuela, from Graphene Flagship partner ICN2. "This is a significant step forward towards the long sought-after goal of electrostatic control of spin information," he continues. Additionally, Prof. Bart van Wees, from Graphene Flagship partner the University of Groningen, elaborates: "It is difficult to imagine how complex it is to fabricate spin devices combining various types of magnetic and non-magnetic materials, graphene, boron nitride, and strong spin-orbit coupling materials such as TMDs. Thanks to this work, the Spintronics Work Package has developed a unique expertise in realizing operational spin devices which really show the full potential of layered materials."

Kevin Garello, Graphene Flagship Work Package Leader for Spintronics, comments: "Devices involving the spin–orbit torque phenomenon, such as the spin Hall effect and the spin Galvanic effect, are great candidates for future spintronics applications as they require low power input and are capable of ultra-fast performance. It is great to see that spin-orbit torques can be electrically manipulated and improved by the smart engineering of layered materials, which has now been unequivocally confirmed independently by two experimental teams in Work Package Spintronics. This opens the door for new and exciting perspectives and strategies to manipulate spin information and further advance applications in spintronics based on layered materials."

The success of these studies is the result of the joint effort between experimental and theoretical researchers working closely together in the EU-funded Graphene Flagship framework. The results provide valuable insights for the spintronics and layered materials communities, and the researchers hope that their findings will enable scientists to explore new theoretical models and further experiments in the future.

Andrea C. Ferrari, Science and Technology Officer of the Graphene Flagship and Chair of its Management Panel, adds: "The Graphene Flagship has invested in spintronics research since the very beginning. The great potential of graphene and related materials in this area has been showcased by world-leading work done in the Flagship. These results indicate that we are getting close to the point where the fundamental work can be translated into useful applications, as foreseen in our science and technology and innovation roadmaps."

Tags:  Andrea C. Ferrari  Electronics  Graphene  Graphene Flagship  ICN2  ICREA  Kevin Garello  Sergio O. Valenzuela  Stephan Roche  Universitat Autònoma de Barcelona  University of Groningen 

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Graphene nanoarchitectures for diverse applications

Posted By Graphene Council, Wednesday, January 1, 2020

Graphene is an exceptional material with many potential applications. The on-surface synthesis of covalent architectures with atomic precision has emerged as one of the most promising methods for providing new functionalities to graphene.

Researchers from the ICN2 Atomic Manipulation and Spectroscopy Group and the DIPC discuss it in an article published in the Revista Española de Física.

This method allows creating a wide range of graphenic architectures from precursor molecules that are designed practically à la carte.

ICN2 researcher César Moreno and ICREA Prof. Aitor Mugarza (Leader of the Atomic Manipulation and Spectroscopy Group), together with 

Ikerbasque researcher Aran Garcia-Lekue (DIPC) have written an article for the Revista Española de Física discussing these topics.

They present the milestones achieved and the challenges and opportunities ahead regarding the top-down and the bottom-up approaches to build graphene nanoarchitectures. They focus on the potential applications of graphene nanostrips for nanoelectronics and photonics and of nanoporous graphene for advanced filtering.

Tags:  Aitor Mugarza  Aran Garcia-Lekue  César Moreno  Graphene  ICN2  nanoelectronics  photonics 

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Graphene is wonderful – The Graphene Flagship project presents innovations in Brussels

Posted By Graphene Council, Thursday, September 26, 2019
European Commission funded research project, the Graphene Flagship, will demonstrate a selection of the project’s most exciting innovations at the Science is Wonderful exhibition in Brussels, Belgium, on 25 and 26 September 2019. The free exhibition, held at Tour & Taxis, a redeveloped industrial space in Brussels, is part of the European Research and Innovation Days and aims to bring a world of science and technology to the general public.

Demonstrations from the Graphene Flagship include technology that has been developed for human health and wellbeing. For example, a graphene-based brain implant that could be used to provide information on the onset of seizures. The new technology, which has been developed by Graphene Flagship partners the Microelectronic Institute of Barcelona (IMB-CNM, CSIC), the Catalan Institute of Nanoscience and Nanotechnology (ICN2) and ICFO, demonstrates a major step in understanding the functions of the human brain.

The exhibition will also showcase examples of graphene dispersions and graphite electrodes manufactured by Graphene Flagship partner Talga. As a high-tech materials company and a leader in bulk graphene and graphite supply, Talga will demonstrate how graphene can easily be exfoliated from graphite, illustrating the journey from material exfoliation, right through to commercialisation.

Other demonstrations at Science is Wonderful include a newly developed virtual reality (VR) system which can be used to construct, manipulate and build graphene and other layered material structures. Developed by Graphene Flagship partner the Technical University of Denmark (DTU), the VR system demonstrates clearly how graphene can be modified and manipulated, with the ability to edit molecules and perform calculations on their electronic properties in real-time.

The VR system gives students and other citizens an unforgettable, low-barrier to entry for the complex machinery of atomic-scale materials and technology. However, it can also provide even experienced researchers with a unique sandbox for scientific problem solving, quantitative analysis, idea generation and discovery.

“The Graphene Flagship’s presence at Science is Wonderful will bolster its efforts to promote the use of graphene in commercial products,” explained Jari Kinaret, director of the Graphene Flagship. “During the first five years of our ambitious Graphene Flagship project, we managed to bring together academic researchers and industrial business leaders to create and commercialise technologies that are already improving European society — the demonstrations at Science is Wonderful will showcase some beautiful examples.”

Tags:  CSIC  Graphene  Graphene Flagship  Healthcare  ICFO  ICN2  Jari Kinaret  Technical University of Denmark 

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