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Khalifa University Researchers Develop Hybrid Graphene-Sand Material to Remove Pollutants from Industrial Wastewater

Posted By Graphene Council, Thursday, June 18, 2020
Khalifa University of Science and Technology today announced a team of researchers has developed a graphene-sand hybrid material capable of absorbing pollutants from industrial wastewater, using two natural resources of great abundance in the UAE – sand and dates.

Safely and affordably removing pollutants from industrial wastewater is a primary focus area for governments worldwide. Conventional methods that are used for removing different harmful pollutants from wastewater suffer from drawbacks such as cost-effectiveness, efficiency, range of applicability, and reusability. Comparatively, adsorption method is a relatively mature, globally-acclaimed, economically feasible, and efficient technology for arresting environmental pollutants.

The Khalifa University research team has developed the graphene-sand hybrid material capable of adsorbing pollutants, which involves attaching pollutants onto small particles that are then easily removed.

While synthesizing graphene-sand adsorbents can be prohibitively expensive, the Khalifa University researchers have turned to a previously unused resource – date syrup – to provide the carbon needed to produce the graphene. The adsorbent can be used as an environmentally benign and scalable option for decontaminating wastewater, with the adsorption capacity far surpassing that of similar reported graphene-based adsorbents.

Led by Dr. Fawzi Banat, Professor, Chemical Engineering, the team includes Anjali Edathil, former Research Engineer, and Shaihroz Khan, visiting Research Assistant. The in-situ strategy used to produce the graphene-sand hybrid with date syrup is described in a paper published in Scientific Reports.

Dr. Banat’s team used pyrolysis – the process of chemically decomposing organic materials at high temperatures in the absence of oxygen – to decompose the date syrup. This triggers a change of chemical composition and the synthesis of a large volume of graphene material, that subsequently attaches to desert sand without the use of any external chemical agents. Moreover, graphene’s high surface area, combined with its versatile chemistry and highly water-repellent surface physical property, makes it an ideal adsorbent for removing pollutants.

Dr. Banat’s graphene-sand hybrid adsorbent was tested in the laboratory and showed remarkable efficiency in simultaneously removing both dye and heavy metals from multicomponent systems. The researchers concluded that their adsorbent had great potential as an exceptional material resource of water purification.

“This will undoubtedly open new avenues for the practicability of graphene to curb the existing water shortage,” said Dr. Banat. “We hope our material will help in increasing water resources in the UAE, reducing energy consumption in wastewater treatment processes and be used to convert oily wastewaters from waste-to-commodity that can be used in applications such as industrial recycling and agriculture.”

Tags:  Fawzi Banat  Graphene  Khalifa University  Water Purification 

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Vittangi Project Supported by National Interest Demarcation

Posted By Graphene Council, Thursday, June 18, 2020
Battery anode and graphene additives company Talga Resources Ltd is pleased to advise of positive developments at its 100% owned Vittangi graphite project in northern Sweden (“Vittangi”).

A recent decision by the Swedish Geological Survey (“SGU”) completed the demarcation of Vittangi as a mineral deposit of national interest1. This designation adds support to consider the exploitation of Vittangi as a mineral deposit when government authorities review development plans and any potential competing land uses.

Under the Swedish Environmental Code, deposits of valuable substances or materials can be defined as being of national interest, meaning municipalities and central government agencies may not authorise activities that might prevent or significantly hinder exploitation of the mineral deposit. The national interest area covers the entirety of Talga’s currently defined Vittangi graphite resources (see Table 1 below), and undrilled extensional deposits, as detailed in Figure 1.

The SGU noted the Vittangi graphite deposit's significance to the country's supply capacity and its special material properties and concluded the deposit constitutes a unique natural asset of valuable substances or materials.

Further, they consider locally produced graphite could help strengthen the competitiveness of the Swedish battery manufacturing industry and that, as the known highest grade graphite deposit in the world, Vittangi could “meet a great need not only within Sweden but internationally”.
The decision2 takes note of the European Commission’s listing of graphite as a critical raw material and their warning that a lack of access to such critical commodities could slow the development of fossil-free energy sources.

Commenting on SGU’s decision, Talga Managing Director Mark Thompson said: "We welcome SGU’s decision as a positive and timely development following Talga’s recent lodgement of the Vittangi Graphite Project mining permit applications, towards becoming Europe’s first vertically integrated producer of Li-ion battery active anode material."

SGU Decision Background
In preparing the demarcation SGU obtained extensive information on the Vittangi Graphite Project including details relating to its geology and material properties. The demarcation defines the boundaries of the original declaration of Nunasvaara as a deposit of national interest which contained only a centre co-ordinate. Results from Talga’s extensive exploration work were made available during the investigation and SGU carried out their own detailed electromagnetic survey to assist in the demarcation, which covers approximately 20km strike of graphite mineralisation.

Competent Persons Statement
The Nunasvaara Mineral Resource estimate was first reported in the Company’s announcement dated 27 April 2017 titled ‘Talga Substantially Increases Flagship Graphite Resource Size, Grade and Status’. The Company confirms that it is not aware of any new information or data that materially affects the information included in the previous market announcement and that all material assumptions and technical parameters underpinning the Resource estimate in the previous market announcement continue to apply and have not materially changed.

The Niska Mineral Resource estimate was first reported in the Company’s announcement dated 15 October 2019 titled ‘Talga boosts Swedish graphite project with maiden Niska resource’. The Company confirms that it is not aware of any new information or data that materially affects the information included in the previous market announcement and that all material assumptions and technical parameters underpinning the Resource estimate in the previous market announcement continue to apply and have not materially changed.

Tags:  Graphene  Graphite  Mark Thompson  Talga Resources 

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ZEN Graphene Solutions Ltd. Reports on Expressions of Interest for Non-Brokered Private Placements of Units

Posted By Graphene Council, Thursday, June 18, 2020
ZEN Graphene Solutions Ltd. is pleased to announce it has received expression of interest from investors in an amount of $1,777,000 for the non-brokered private placement announced on June 15, 2020. These expressions of interest have far exceeded management’s expectation and, subject to TSX Venture Exchange approval, the Company is working diligently to complete the Offering. Management believes that this highlights the progress ZEN has made in becoming an advanced materials graphene company. Following completion of the Offering, ZEN’s cash balance will exceed any balance in recent years thereby ensuring the Company can continue executing its business plan during the COVID-19 pandemic. A subsequent news release will be issued concurrently with the closing of the Offering.

The proceeds of the Offering will be used to fund ongoing work on the Albany Graphite Project including: Graphene research and scale up, COVID-19 initiatives and other graphene application development, and general corporate purposes. All securities issued to purchasers under the Offering will be subject to a four-month hold period from the closing date of the Offering, pursuant to applicable securities legislation and policies of the Exchange. Finders’ fees may be paid, as permitted by Exchange policies and applicable securities law.

Tags:  Graphene  Graphite  ZEN Graphene Solutions 

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Engineers advance insights on black phosphorus as a material for future ultra-low power flexible electronics

Posted By Graphene Council, Thursday, June 18, 2020
Black phosphorus is a crystalline material that is attracting growing research interest from semiconductor device engineers, chemists and material scientists to create high-quality atomically thin films.

From the perspective of a 2D layered material, black phosphorus shows promise for applications in next-generation flexible electronics that could enable advances in semiconductors, medical imaging, night vision and optical communication networks.

As a prospective graphene and silicon substitute, it has outstanding properties like tunable bandgap, which graphene lacks. A bandgap, an energy band in which no electron states can exist, is essential for creating the on/off flow of electrons that are needed in digital logic and for the generation of photons for LEDs and lasers.

Unfortunately, black phosphorus is hard to make and hard to keep. It degrades quickly when exposed to air. Why this happens and the exact mechanisms by which it happens—whether oxygen or moisture in the air degrade or both—remain a topic of active debate in the research community.

Vanderbilt engineering researchers have shown for the first time that the reaction of black phosphorus to oxygen can be observed at the atomic scale using in situ-transmission electron microscopy (TEM).  See YouTube videos.

The results are reported in their paper—Visualizing Oxidation Mechanisms in Few-Layered Black Phosphorus via In Situ Transmission Electron Microscopy—in the American Chemical Society’s Applied Materials & Interfaces journal.

“In research, a lot of times different and often contradictory hypothesis exist in the scientific community. However, the ability to observe a reaction at atomic resolution in real-time offers much needed clarity to propel advances. We are using the insights from our in-situ TEM experiments at atomic resolution in our lab to develop novel synthesis and preservation methods for black phosphorus,” said Piran Kidambi, assistant professor of chemical and biomolecular engineering.

“Current approaches have looked at encapsulating it with an oxide or polymer layer without really understanding why or how the oxidation proceeds,” said Andrew E. Naclerio, second year graduate student in the Department of Chemical and Biomolecular Engineering and the paper’s first author.

“Most understanding of black phosphorus oxidation has been based on results from spectroscopic probes,” said Kidambi, Naclerio’s adviser. In collaboration with Dmitri Zakharov, staff scientist at Brookhaven National Laboratory in Upton, New York, the team used environmental transmission electron microscopy (ETEM), which provides real time in-situ observation of structural  information on a sample and reaction at atomic resolution.

“This is one of the few microscopes in the United States and the world with the capability to perform atomic resolution imaging while introducing gases and heating,” Kidambi said. The collaboration grew from a peer-reviewed user proposal and is funded by Department of Energy (DOE).

“Some insights we obtained were that the reaction proceeds via the formation of an amorphous layer that subsequently evaporates. Different crystallographic edges lead to varying degrees of etching and this agrees well will with theoretical calculations,” Kidambi said.

The collaboration for theoretical calculations with two of the paper’s authors, researchers  Jeevesh Kumar and Mayank Shrivastava at the Indian Institute of Science in Bangalore, was formed at a conference where Kidambi was invited to give a talk.

The team aim to synthesize atomically thin films of black phosphorus using chemical vapor deposition, and insights on oxidation can be used to develop effective passivation techniques.

The Kidambi Research Group in the School of Engineering’s Department of Chemical and Biomolecular Engineering is affiliated with the Vanderbilt Institute of Nanoscale Science and Engineering (VINSE), the Interdisciplinary Materials Science Program and the Vanderbilt University Data Science Institute.

Tags:  Andrew E. Naclerio  Electronics  Graphene  photonics  Piran Kidambi  Vanderbilt Institute of Nanoscale Science and Engi 

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Sulfur Provides Promising 'Next-Gen' Battery Alternative

Posted By Graphene Council, Thursday, June 18, 2020
With the increasing demand for sustainable and affordable energy, the ongoing development of batteries with a high energy density is vital. Lithium-sulfur batteries have attracted the attention of academic researchers and industry professionals alike due to their high energy density, low cost, abundance, nontoxicity and sustainability. However, Li-sulfur batteries tend to have poor cycle life and low energy density due to the low conductivity of sulfur and dissolution of lithium polysulfide intermediates in the electrolytes, which are generated when pure sulfur reacts with Li-ions and electrons.  

To circumvent these challenges, a multi-institutional research team led by Chunsheng Wang at the University of Maryland has developed a new chemistry for a sulfur cathode, which offers increased stability and higher energy of Li-sulfur batteries. Chao Luo - an assistant professor of chemistry and biochemistry at George Mason University - served as first author on the study, published in the Proceedings of the National Academy of Sciences (PNAS) on June 15.

Numerous conductive materials such as graphene, carbon nanotube, porous carbon and expanded graphite were used to prevent the dissolution of polysulfides and increase the electrical conductivity of sulfur cathodes - the challenge here is encapsulating the nano-scale sulfur in a conductive carbon matrix with a high sulfur content to avoid the formation of polysulfides.

"We used the chemical bonding between sulfur and oxygen/carbon to stabilize the sulfur," Luo said. "This included a high temperature treatment to vaporize the 'pristine' sulfur and carbonize the oxygen-rich organic compound in a vacuum glass tube to form a dense oxygen-stabilized sulfur/carbon composite with a high sulfur content."

In addition, scanning electron microscope (SEM) and transmission electron microscopy (TEM) instruments, X-ray photoelectron spectroscopy (XPS) and pair distribution function (PDF) were used to illustrate the reaction mechanism of the electrodes.

"In the dense S/C composite materials, the stabilized sulfur is uniformly distributed in carbon at the molecular level with a 60% sulfur content," Wang said. "The formation of solid electrolyte interphase during the activation cycles completely seal the sulfur in a carbon matrix, offering superior electrochemical performance under lean electrolyte conditions."

Li-sulfur batteries have applications in household and handheld electronics, electric vehicles, large scale energy storage devices and beyond.

Tags:  Battery  carbon nanotube  Chao Luo  Chunsheng Wang  George Mason University  Graphene  Li-sulfur batteries  University of Maryland 

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Skeleton teams up with TalTech and Tartu University to develop flexible ultracapacitors

Posted By Graphene Council, Thursday, June 18, 2020
Researchers at TalTech's Polymers and Textile Technology Laboratory are working with Skeleton Technologies and the Institute of Chemistry at the University of Tartu to develop ultracapacitors with special durability properties. The project is supported by the European Space Agency (ESA).

Skeleton is at the forefront of ultracapacitor technology. Working with universities and the European Space Agency is instrumental in keeping our technological edge by pushing us to explore new development pathways, says Egert Valmra, Programme Director at Skeleton.

These new types of ultracapacitors are specifically being developed for space technology because they are flexible, light and at the same time very strong. Researchers are using Curved Graphene to make bendable electrodes, which can be made into any shape. It can be useful in applications with extreme space constraints where you need to shape energy storage according to what kind of volume shapes you have.

"The importance of supercapacitors in today's technology is growing. By their nature, ultracapacitors are used primarily in situations where a large amount of electricity needs to be released quickly, " explains Andres Krumme, head of the working group and professor at TalTech's Polymers and Textile Technology Laboratory.

These ultracapacitors are made by electrospinning and consist of nanofibrous nonwovens. The fibers in these materials are 10 to 100 times thinner than a hair. Inside the fibers one can find Skeleton’s proprietary Curved Graphene material that stores electricity and are held together by a polymeric binder. The fibrous structure developed by the researchers is flexible and up to 20 times stronger than the materials used in conventional supercapacitors. Curved Graphene has two important properties for storing electricity: an exceptionally large specific surface area (area per unit mass) and a particularly good energy storage capacity.

The ultracapacitors under development could be used to provide a strong short-term current pulse in rocket engine launchers and controls, cyclic power to satellites when exposed to sunlight, and to open and mechanically move satellite panels.

The working group has managed to turn the idea to laboratory prototype, and hopes to have the first products in the next 3-5 years with the support of ESA.

Tags:  Andres Krumme  Egert Valmra  European Space Agency  Graphene  polymers  Skeleton  supercapacitors  TalTech  University of Tartu 

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First Graphene Re-opens UK Laboratories

Posted By Graphene Council, Wednesday, June 17, 2020
Advanced materials company, First Graphene Limited is pleased to advise the re-opening of its laboratories at the Graphene Engineering and Innovation Centre (GEIC), Manchester.

The GEIC laboratories were closed by the University of Manchester on 18th March 2020 as a response to the Covid-19 pandemic. The First Graphene UK team has been working remotely since the closure.

Following extensive risk assessment and planning in collaboration with the University facilities management team the UK laboratories are now ready to restart operations. A range of risk controls are now in place including social distancing markings, access restrictions and carefully planned activities. The formal clearance to proceed was given by the University on Monday 15th June.

While working remotely the UK team has continued to provide technical support to global customers, completed background research in preparation for technical projects and supported the activities for the Henderson site.  In addition, the website hosting service has been upgraded and a number of technical enhancements have been made to the website backend to improve performance and security.  Also, multiple announcements and articles for publication were authored during this period.  The team is well prepared for the immediate restart of technical programmes in rubber and TPU additives, supercapacitor materials, fire retardancy and customer application development.

Craig McGuckin, Managing Director of First Graphene Ltd. said “The UK team has played a critical role supporting our business throughout the lockdown. We are all very pleased to be re-starting operations and getting back to technical projects and customer application development in our laboratories”

Tags:  Covid-19  Craig McGuckin  First Graphene  Graphene  Graphene Engineering and Innovation Centre  Healthcare 

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Researchers Advance Graphene Electronics

Posted By Graphene Council, Wednesday, June 17, 2020
In recent years, atomically flat layered materials have gained significant attention due to their prospects for building high-speed and low-power electronics. Best known among those materials is graphene, a single sheet of carbon atoms. Among the unique qualities of this family of materials is that they can be stacked on top of each other like Lego pieces to create artificial electronic materials.

However, while these van der Waals (vdW) heterostructures are critical to many scientific studies and technological applications of layered materials, efficient methods for building diverse vdW heterostructures are still lacking.

A team of researchers has found a versatile method for the construction of high-quality vdW heterostructures. The work is a collaboration between the laboratory of Davood Shahrjerdi, a professor of Electrical and Computer Engineering at the NYU Tandon School of Engineering and a faculty member of NYU WIRELESS; a group led by Javad Shabani at  the Center for Quantum Phenomena, New York University; and Kenji Watanabe and Takashi Taniguchi of National Institute for Materials Science, Japan. Their study was published this week in Nature Communications. 

A crucial step for building vdW graphene heterostructures is the production of large monolayer graphene flakes on a substrate, a process called mechanical “exfoliation.” The operation then involves transferring the graphene flakes onto a target location for the assembly of the vdW heterostructure. An optimal substrate would therefore make it possible to efficiently and consistently exfoliate large flakes of monolayer graphene and subsequently release them on-demand for constructing a vdW heterostructure.

The research team applied a simple yet elegant solution to this challenge involving the use of a dual-function polymeric film with a thickness of below five nanometers (less than 1/10,000th the width of a human hair). This modification allows them to “tune” the film properties such that it promotes the exfoliation of monolayer graphene. Then, for the Lego-like assembly, they dissolve the polymeric film underneath the monolayer graphene using a drop of water, freeing graphene from the substrate.

“Our construction method is simple, high-yield, and generalizable to different layered materials,” explained Shahrjerdi. “It enabled us to optimize the exfoliation step independently of the layer transfer step and vice versa, resulting in two major outcomes: a consistent exfoliation method for producing large monolayer flakes and a high-yield layer transfer of exfoliated flakes. Also, by using graphene as a model material, we further established the remarkable material and electronic properties of the resulting heterostructures.”

Tags:  Davood Shahrjerdi  Electronics  Graphene  graphene heterostructures  New York University 

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Dirac Electrons Come Back to Life in Magic-Angle Graphene

Posted By Graphene Council, Wednesday, June 17, 2020
In 2018 it was discovered that two layers of graphene twisted one with respect to the other by a “magic” angle show a variety of interesting quantum phases, including superconductivity, magnetism and insulating behaviours. Now a team of researchers from the Weizmann Institute of Science led by Prof. Shahal Ilani of the Condensed Matter Physics Department, in collaboration with Prof. Pablo Jarillo-Herrero’s group at MIT, have discovered that these quantum phases descend from a previously unknown high-energy “parent state,” with an unusual breaking of symmetry.

Graphene is a flat crystal of carbon, just one atom thick. When two sheets of this material are placed on top of each other, misaligned at small angle, a periodic “moiré” pattern appears. This pattern provides an artificial lattice for the electrons in the material. In this twisted bilayer system the electrons come in four “flavours”: spins “up” or “down,” combined with two “valleys” that originate in the graphene’s hexagonal lattice. As a result, each moiré site can hold up to four electrons, one of each flavour.

While researchers already knew that the system behaves as a simple insulator when all the moiré sites are completely full (four electrons per site), Jarillo-Herrero and his colleagues discovered to their surprise, in 2018, that at a specific “magic" angle, the twisted system also becomes insulating at other integer fillings (two or three electrons per moiré site). This behaviour, exhibited by magic-angle twisted bilayer graphene (MATBG), cannot be explained by single particle physics, and is often described as a “correlated Mott insulator.” Even more surprising was the discovery of exotic superconductivity close to these fillings. These findings led to a flurry of research activity aiming to answer the big question: what is the nature of the new exotic states discovered in MATBG and similar twisted systems?

Imaging magic-angle graphene electrons with a carbon nanotube detector
The Weizmann team set out to understand how interacting electrons behave in MATBG using a unique type of microscope that utilizes a carbon nanotube single-electron transistor, positioned at the edge of a scanning probe cantilever. This instrument can image, in real space, the electric potential produced by electrons in a material with extreme sensitivity.

“Using this tool, we could image for the first time the ‘compressibility' of the electrons in this system – that is, how hard it is to squeeze additional electrons into a given point in space,” explains Ilani. “Roughly speaking, the compressibility of electrons reflects the phase they are in: In an insulator, electrons are incompressible, whereas in a metal they are highly compressible.”

Compressibility also reveals the “effective mass” of electrons. For example, in regular graphene the electrons are extremely “light,” and thus behave like independent particles that practically ignore the presence of their fellow electrons. In magic-angle graphene, on the other hand, electrons are believed to be extremely “heavy” and their behaviour is thus dominated by interactions with other electrons ‒ a fact that many researchers attribute to the exotic phases found in this material. The Weizmann team therefore expected the compressibility to show a very simple pattern as a function of electron filling: interchanging between a highly-compressible metal with heavy electrons and incompressible Mott insulators that appear at each integer moiré lattice filling. 

To their surprise, they observed a vastly different pattern. Instead of a symmetric transition from metal to insulator and back to metal, they observed a sharp, asymmetric jump in the electronic compressibility near the integer fillings.

"This means that the nature of the carriers before and after this transition is markedly different," says study lead author Uri Zondiner. "Before the transition the carriers are extremely heavy, and after it they seem to be extremely light, reminiscent of the ‘Dirac electrons’ that are present in graphene."

The same behaviour was seen to repeat near every integer filling, where heavy carriers abruptly gave way and light Dirac-like electrons re-emerged.

But how can such an abrupt change in the nature of the carriers be understood? To address this question, the team worked together with Weizmann theorists Profs. Erez Berg, Yuval Oreg and Ady Stern, and Dr. Raquel Quiroez; as well as Prof. Felix von-Oppen of Freie Universität Berlin. They constructed a simple model, revealing that electrons fill the energy bands in MATBG in a highly unusual “Sisyphean” manner: when electrons start filling from the “Dirac point” (the point at which the valence and conduction bands just touch each other), they behave normally, being distributed equally among the four possible flavours. “However, when the filling nears that of an integer number of electrons per moiré superlattice site, a dramatic phase transition occurs,” explains study lead author Asaf Rozen. “In this transition, one flavour ‘grabs’ all the carriers from its peers, ‘resetting’ them back to the charge-neutral Dirac point.”  

“Left with no electrons, the three remaining flavours need to start refilling again from scratch. They do so until another phase transition occurs, where this time one of the remaining three flavours grabs all the carriers from its peers, pushing them back to square one. Electrons thus need to climb a mountain like Sisyphus, being constantly pushed back to the starting point in which they revert to the behavior of light Dirac electrons,” says Rozen. While this system is in a highly symmetric state at low carrier fillings, in which all the electronic flavours are equally populated, with further filling it experiences a cascade of symmetry-breaking phase transitions that repeatedly reduce its symmetry.

A “parent state”
“What is most surprising is that the phase transitions and Dirac revivals that we discovered appear at temperatures well above the onset of the superconducting and correlated insulating states observed so far,” says Ilani. “This indicates that the broken symmetry state we have seen is, in fact, the ‘parent state’ out of which the more fragile superconducting and correlated insulating ground states emerge.”

The peculiar way in which the symmetry is broken has important implications for the nature of the insulating and superconducting states in this twisted system.

“For example, it is well known that stronger superconductivity arises when electrons are heavier. Our experiment, however, demonstrates the exact opposite: superconductivity appears in this magic-angle graphene system after a phase transition has revived the light Dirac electrons. How this happens, and what it tells us about the nature of superconductivity in this system compared to other more conventional forms of superconductivity remain interesting open questions,” says Zondiner.

A similar cascade of phase transitions was reported in another paper published in the same Nature issue by Prof. Ali Yazdani and colleagues at Princeton University. "The Princeton team studied MATBG using a completely different experimental technique, based on a highly-sensitive scanning tunneling microscope, so it is very reassuring to see that complementary techniques lead to analogous observations,” says Ilani.

The Weizmann and MIT researchers say they will now use their scanning nanotube single-electron-transistor platform to answer these and other basic questions about electrons in various twisted-layer systems: What is the relationship between the compressibility of electrons and their apparent transport properties? What is the nature of the correlated states that form in these systems at low temperatures? And what are the fundamental quasiparticles that make up these states?

Tags:  bilayer graphene  Graphene  Massachusetts Institute of Technology  Pablo Jarillo-Herrero  Shahal Ilani 

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Discovery of graphene switch

Posted By Graphene Council, Wednesday, June 17, 2020
Researchers at Japan Advanced Institute of Science and Technology (JAIST) have successfully measured the current-voltage curve of graphene nanoribbons (GNRs) that were suspended between two electrodes. Measurements were performed using transmission electron microscopy (TEM) observation. Results revealed that, in contrast to the findings of previous reports, the electrical conductance of GNRs with a zigzag edge structure (zigzag GNRs) abruptly increased above the critical bias voltage. This finding is worth noting because the abrupt change in these GNRs can be applied to switching devices, which are the smallest devices in the world.

The electrical structure of GNRs have been systematically investigated through theoretical calculations. Studies have reported that both zigzag and armchair GNRs exhibit semiconducting behavior below several nm in width, although the origin of the energy gap is different. On the other hand, the electrical transport properties have rarely been calculated owing to the non-equiribrium calculations required. In 2009, Nikolic et al. predicted that sharp increments in electrical conductance would occur for extremely thin and short zigzag GNRs as the magnetic-insulator-nonmagnetic-metal phase transition occurs above a certain bias voltage [Phys. Rev.B 79, 205430 (2009)]. The obtained experimental results correspond closely to the results of this non-equilibrium calculation.

A research team led by Ms. Chumeng LIU, Professor Yoshifumi OSHIMA and Associate Professor Xiaobin ZHANG (now of Shibaura Institute of Technology) has developed a special in situ TEM holder and a GNR device for TEM observation. This combination is aimed at clarifying the relationship between the edge structure of GNRs and electrical transport properties. Ms. Liu, the doctoral student of JAIST, said, "The fabrication process of our GNR device is much more difficult than the conventional one because we need to make very narrow GNR which should be stably suspended between both electrodes." She reviewed the literature focused on the fabrication process of GNR devices and verified their process en route to establishing her original fabrication method. Assoc. Prof. ZHANG said, "We were really happy to see that the I-V curve obviously changed when changing the edge structure to zigzag. I suppose we have encountered new possibilities for graphene nanoribbons." The team has successfully performed the in situ TEM observation of extremely narrow GNRs, and they plan to continue identifying electrical transport properties that are sensitive to the edge structure of these GNRs.

Tags:  Graphene  graphene nanoribbons  Japan Advanced Institute of Science and Technology  Xiaobin ZHANG 

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