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It’s closeness that counts: how proximity affects the resistance of graphene

Posted By Graphene Council, Tuesday, January 28, 2020
Graphene is often seen as the wonder material of the future. Scientists can now grow perfect graphene layers on square centimetre-sized crystals. A research team from the University of Göttingen, together with the Chemnitz University of Technology and the Physikalisch-Technische Bundesanstalt Braunschweig, has investigated the influence of the underlying crystal on the electrical resistance of graphene.

Contrary to previous assumptions, the new results show that the process known as the ‘proximity effect’ varies considerably at a nanometre scale. The results have been published in Nature Communications.

The composition of graphene is very simple. It is a single atomic layer of carbon atoms arranged in a honeycomb structure. The three-dimensional form is already an integral part of our everyday lives: we see it in the lead of an ordinary pencil for instance. However, the two-dimensional material graphene was not synthesized in the laboratory until 2004. To determine the electrical resistance of graphene at the smallest scale possible, the physicists used a “scanning tunnelling microscope”. This can make atomic structures visible by scanning the surface with a fine metal tip. The team also used the tip of the scanning tunnelling microscope to measure the voltage drop and thus the electrical resistance of the tiny graphene sample.

Depending on the distance that they measured, the researchers determined very different values for the electrical resistance. They cite the proximity effect as the reason for this. “The spatially varying interaction between graphene and the underlying crystal means that we measure different electrical resistances depending on the exact position,” explains Anna Sinterhauf, first author and doctoral student at the Faculty of Physics at the University of Göttingen.

At low temperatures of 8 Kelvin, which is around minus 265 degrees Centigrade, the team found variations in local resistance of up to 270 percent. “This result suggests that the electrical resistance of graphene layers epitaxially grown on a crystal surface cannot simply be worked out from an average taken from values measured at a larger scale,” explains Dr Martin Wenderoth, head of the working group. The team assumes that the proximity effect might also play an important role for other two-dimensional materials.

Tags:  2D materials  Anna Sinterhauf  Graphene  Martin Wenderoth  University of Göttingen 

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Skeleton Technologies Signs a Large-Scale Deal with Medcom to Supply Ultracapacitor Energy Storage to Warsaw Tram

Posted By Graphene Council, Tuesday, January 28, 2020
Skeleton Technologies has signed a large-scale contract with Medcom, a leading innovator in electric traction market, to provide ultracapacitors in the Warsaw tram networks.

Energy efficiency is becoming the key design criteria for any public transportation system, and ultracapacitors, due to 1 million lifecycles and immediate charging, are now enabling applications that have not been viable with batteries, which meet their end of life at 2000-3000 cycles and cannot charge quickly enough to take advantage of kinetic energy recovered while trams brake.

Skeleton Technologies’ ultracapacitor systems are situated onboard trams and provide energy savings by recuperating braking energy and reusing it for acceleration, decreasing the total energy consumption significantly. The ultracapacitor system also shaves power peaks, protecting the grid infrastructure in Warsaw.

Pawel Chodun, Chief Financial Officer at Medcom, explains:
“The high efficiency of ultracapacitor energy storage is well suited to electric trams, enabling both energy savings as well as protection for the infrastructure from high peaks of power”.

For us, it’s a major move as it shows the value of fast energy storage in electric transportation and provides a model to follow for other cities, seeking energy-saving solutions as they electrify public transportation. Although people don’t often think about Poland when they think about energy-efficiency, Warsaw tram will become one of the most energy-efficient ones.

“Skeleton Technologies is known as a trusted supplier of energy storage solutions in transportation applications. Together with Medcom, known globally for the high quality of their solutions for electrified public transportation systems, Skeleton Technologies’ ultracapacitor systems will make the Warsaw tram one of the most modern and energy-efficient in the world.”, said Taavi Madiberk, CEO of Skeleton Technologies.

Transport represents almost a quarter of Europe's greenhouse gas emissions and is one of the main causes of air pollution in cities. According to the European Commission, a 90 percent reduction in transport emissions will be needed by 2050 to achieve climate-neutrality. As we often explain, the EU Green Deal is the biggest business opportunity for Europe since the Internet revolution. Every sector will be impacted and will have to adapt.

A new study by the European Investment Bank (EIB) shows Europeans rank irreversible climate change as one of the biggest threats to the continent, over terrorism and unemployment, and two-thirds of people in Europe, the US and China think their individual behaviour can help tackle climate change. Public transportation can play a major role towards a climate-neutral Europe.

Tags:  Graphene  Medcom  Pawel Chodun  Skeleton Technologies  Taavi Madiberk  ultracapacitor 

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Rice lab turns trash into valuable graphene in a flash

Posted By Graphene Council, Tuesday, January 28, 2020
A new process introduced by the Rice University lab of chemist James Tour can turn bulk quantities of just about any carbon source into valuable graphene flakes. The process is quick and cheap; Tour said the “flash graphene” technique can convert a ton of coal, waste food or plastic into graphene for a fraction of the cost used by other bulk graphene-producing methods.

“This is a big deal,” Tour said. “The world throws out 30% to 40% of all food, because it goes bad, and plastic waste is of worldwide concern. We’ve already proven that any solid carbon-based matter, including mixed plastic waste and rubber tires, can be turned into graphene.”

As reported in Nature, flash graphene is made in 10 milliseconds by heating carbon-containing materials to 3,000 Kelvin (about 5,000 degrees Fahrenheit). The source material can be nearly anything with carbon content. Waste food, plastic waste, petroleum coke, coal, wood clippings and biochar are prime candidates, Tour said. “With the present commercial price of graphene being $67,000 to $200,000 per ton, the prospects for this process look superb,” he said.

Tour said a concentration of as little as 0.1% of flash graphene in the cement used to bind concrete could lessen its massive environmental impact by a third. Production of cement reportedly emits as much as 8% of human-made carbon dioxide every year.

“By strengthening concrete with graphene, we could use less concrete for building, and it would cost less to manufacture and less to transport,” he said. “Essentially, we’re trapping greenhouse gases like carbon dioxide and methane that waste food would have emitted in landfills. We are converting those carbons into graphene and adding that graphene to concrete, thereby lowering the amount of carbon dioxide generated in concrete manufacture. It’s a win-win environmental scenario using graphene.”

“Turning trash to treasure is key to the circular economy,” said co-corresponding author Rouzbeh Shahsavari, an adjunct assistant professor of civil and environmental engineering and of materials science and nanoengineering at Rice and president of C-Crete Technologies. “Here, graphene acts both as a 2D template and a reinforcing agent that controls cement hydration and subsequent strength development.”

In the past, Tour said, “graphene has been too expensive to use in these applications. The flash process will greatly lessen the price while it helps us better manage waste.”

“With our method, that carbon becomes fixed,” he said. “It will not enter the air again.”

The process aligns nicely with Rice’s recently announced Carbon Hub initiative to create a zero-emissions future that repurposes hydrocarbons from oil and gas to generate hydrogen gas and solid carbon with zero emission of carbon dioxide. The flash graphene process can convert that solid carbon into graphene for concrete, asphalt, buildings, cars, clothing and more, Tour said.

Flash Joule heating for bulk graphene, developed in the Tour lab by Rice graduate student and lead author Duy Luong, improves upon techniques like exfoliation from graphite and chemical vapor deposition on a metal foil that require much more effort and cost to produce just a little graphene.

Even better, the process produces “turbostratic” graphene, with misaligned layers that are easy to separate. “A-B stacked graphene from other processes, like exfoliation of graphite, is very hard to pull apart,” Tour said. “The layers adhere strongly together. But turbostratic graphene is much easier to work with because the adhesion between layers is much lower. They just come apart in solution or upon blending in composites.

“That’s important, because now we can get each of these single-atomic layers to interact with a host composite,” he said.

The lab noted that used coffee grounds transformed into pristine single-layer sheets of graphene.

Bulk composites of graphene with plastic, metals, plywood, concrete and other building materials would be a major market for flash graphene, according to the researchers, who are already testing graphene-enhanced concrete and plastic.

The flash process happens in a custom-designed reactor that heats material quickly and emits all noncarbon elements as gas. “When this process is industrialized, elements like oxygen and nitrogen that exit the flash reactor can all be trapped as small molecules because they have value,” Tour said.

He said the flash process produces very little excess heat, channeling almost all of its energy into the target. “You can put your finger right on the container a few seconds afterwards,” Tour said. “And keep in mind this is almost three times hotter than the chemical vapor deposition furnaces we formerly used to make graphene, but in the flash process the heat is concentrated in the carbon material and none in a surrounding reactor.

“All the excess energy comes out as light, in a very bright flash, and because there aren’t any solvents, it’s a super clean process,” he said.

Luong did not expect to find graphene when he fired up the first small-scale device to find new phases of material, beginning with a sample of carbon black. “This started when I took a look at a Science paper talking about flash Joule heating to make phase-changing nanoparticles of metals,” he said. But Luong quickly realized the process produced nothing but high-quality graphene.

Atom-level simulations by Rice researcher and co-author Ksenia Bets confirmed that temperature is key to the material’s rapid formation. “We essentially speed up the slow geological process by which carbon evolves into its ground state, graphite,” she said. “Greatly accelerated by a heat spike, it is also stopped at the right instant, at the graphene stage.

“It is amazing how state-of-the-art computer simulations, notoriously slow for observing such kinetics, reveal the details of high temperature-modulated atomic movements and transformation,” Bets said.

Tour hopes to produce a kilogram (2.2 pounds) a day of flash graphene within two years, starting with a project recently funded by the Department of Energy to convert U.S.-sourced coal. “This could provide an outlet for coal in large scale by converting it inexpensively into a much-higher-value building material,” he said.

Tour has a grant from the Department of Energy to scale up the flash graphene process, which will be co-funded by the start-up company, Universal Matter Ltd.

Co-authors of the paper include Rice graduate students Wala Ali Algozeeb, Weiyin Chen, Paul Advincula, Emily McHugh, Muqing Ren and Zhe Wang; postdoctoral researcher Michael Stanford; academic visitors Rodrigo Salvatierra and Vladimir Mancevski; Mahesh Bhatt of C-Crete Technologies, Stafford, Texas; and Rice assistant research professor Hua Guo. Boris Yakobson, the Karl F. Hasselmann Chair of Engineering and a professor of materials science and nanoengineering and of chemistry, is co-corresponding author.

Tour is the T.T. and W.F. Chao Chair in Chemistry as well as a professor of computer science and of materials science and nanoengineering at Rice.

Tags:  CVD  Graphene  James Tour  Rice University  Rouzbeh Shahsavari 

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First Graphene's Strong Advances in VFD Development

Posted By Graphene Council, Tuesday, January 28, 2020

First Graphene Limited  is pleased to provide an update of the work conducted in conjunction with 2D Fluidics Pty Ltd on the Vortex Fluidic Device (VFD) at the Company’s facilities at the Graphene Engineering and Innovation Centre (GEIC) in Manchester, UK and Flinders University

Background Summary on Graphene Oxide
Graphene oxide (GO) is the chemically modified derivative of graphene, whereby the basal planes and edges have been functionalised with oxygen containing functional groups such as hydroxyl, epoxy and carboxyl groups. These oxygen functionalities make GO hydrophilic and therefore dispersible, forming homogenous colloidal suspensions in water and most organic solvents. This makes it ideal for use in a range of applications.

To date, the most widely used process for the synthesis of graphene oxide is Hummer’s method. This typically  requires strong acids and oxidants, such as potassium chlorate (KClO3), nitric acid (HNO3), concentrated sulfuric acid (H2SO4) and potassium permanganate (KMnO4). Much work has been done to improve the synthesis methods while maintaining high surface oxidation, however these all required strong acids and oxidants.

Through its subsidiary 2D Fluidics Pty Ltd, FGR is developing a more benign processing route for oxidised graphene. The objective is to provide controlled levels of surface oxygen functionality to give better easier compatibility in aqueous and organic systems. This will not incur the higher oxygen (and other defect) levels which result from Hummer’s method and its subsequent reduction steps. It will also provide the ability to “tune or optimise” the surface oxidation level to suit respective applications.

FGR’s method synthesises GO directly from bulk graphite using aqueous H2O2 as the green oxidant. Different energy sources have been used for the conversion of H2O2 molecules into more active peroxidic species, such as a combination of a pulsed Nd:YAG laser and/or other light sources. The irradiation promotes the dissociation of H2O2 into hydroxyl radicals which then leads to surface oxidation.

The technology has been successfully transferred to the FGR laboratories at the Graphene Engineering and Innovation Centre (GEIC) in Manchester where it has undergone further development and optimisation to identify, understand and resolve future upscaling issues.

XPS analysis showed that the use of pre-treatment step in combination with the near infrared laser gave oxidised graphene sheets with an average surface oxidation of ~30- 35%: this will enhance compatibility with aqueous systems.

Further trials have already demonstrated that the two-step process is reproducible and versatile, with the ability to process different starting materials of graphite. The multi- disciplinary team has identified that control of the feed rate and energy input will allow us to control the surface oxidation, providing a consistent material that can be tailored as required for a range of applications.

Figure 5 shows that increase in surface oxygen content for two starting materials: graphite ore (top) and PureGRAPH® graphene (bottom). As we go through the two-  stage process, in both cases the surface oxygen functionality increases. The end- product has a range of functional groups, including C-O, C=O and COOH.

Next Steps
Operating parameters will now be established to provide yield data for future use in scaling the system for commercial production. It will also commence examining the end applications including, but not limited to the use in electronic devices, testing levels of toxicity for biological applications, for water filtration membranes and incorporation in membranes for studying anti-fouling properties.

Craig McGuckin, Managing Director of FGR, said, “The complementary characterisation techniques used to confirm the synthesis of oxidised graphene gives us confidence we are on the right route towards fabricating a material which is comparable to  the historical GO fabricated using the conventional Hummers method. We are  now  reviewing end applications and thus exploring a number of avenues which include but are not limited to the use in devices, testing levels of toxicity for biological applications, for water filtration membranes and incorporation in membranes for studying anti-fouling properties.”

Tags:  2D Fluidics Pty Ltd  2D materials  Craig McGuckin  First Graphene  Flinders University  Graphene  Graphene Engineering and Innovation Centre  graphene oxide 

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Tuning of optical absorbance of graphene quantum dots by high magnetic fields

Posted By Graphene Council, Monday, January 27, 2020

Recently, a Chinese research team reported (Biomaterials, "Magnetic-induced graphene quantum dots for imaging-guided photothermal therapy in the second near-infrared window") the synthesis of graphene quantum dots (GQDs) under an external high magnetic field (HMF) and their applications in photothermal therapy (PTT).

GQDs plays an increasingly important role in medical areas due to tunable optical behavior, good chemical stability, excellent biocompatibility and easy removal by the kidney.

However, the optical absorption of reported GQDs is mainly concentrated in the NIR-I region, which limits their PTT application in the longer wavelength region ( >1000 nm) because of the absorption and scattering of skin and tissue.

At present, methods to adjust the absorbance of GQDs mainly include surface passivation, heteroatom doping and size correction, which cannot achieve NIR-II absorbance of GQDs.

By introducing HMF during the preparation of GQDs, the joint team used phenol molecules as single precursors and hydrogen peroxide as oxidant, and the resulting 9T-GQDs were expected to possess strong absorbance in NIR-II region for improvement of their applications in PTT.

Compared with the GQDs obtained without HMF (named as 0T-GQDs), 9T-GQDs showed obvious absorbance in NIR-II region (∼1070 nm).

At the same time, 9T-GQDs had a fluorescence quantum yield of 16.67% and a photothermal conversion efficiency of 33.45%. In vivo experiments showed that 9T-GQDs had a significant inhibitory effect on tumor growth in mice in the treatment of photothermal cancer guided by NIR-II region imaging.

The joint research team was led by Prof. WANG Hui with High Magnetic Field Laboratory of the Chinese Academy of Sciences, Prof. CHEN Qianwang with University of Science and Technology of China and Prof. NIE Rongrong from Medical School of Nanjing University

Tags:  CHEN Qianwang  Chinese Academy of Sciences  Graphene  Healthcare  NIE Rongrong  WANG Hui 

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INST Mohali moving towards a globally competitive institution in Nano Science & Technology

Posted By Graphene Council, Monday, January 27, 2020
A cost-efficient and scalable method for graphene-based integrated on-chip micro supercapacitor, which is a miniaturized electrochemical storage device. A 'Nano-Spray Gel' that could be administered on-site for treatment of frostbite injuries and heal the wound; a novel low cost topical hemostatic device to address uncontrolled bleeding, purification devices for water and air respectively.

These are only some of the technologies rolled out by the Institute of Nanoscience and Technology (INST), one of the youngest autonomous institutions of the Department of Science and Technology. INST encourages all aspects of nanoscience and nanotechnology with major thrust in the areas of healthcare, agriculture, medical environment and energy with the ultimate goal to make a difference to society through nanoscience and technology.

INST brings together biologists, chemists, physicists, materials scientists, and engineers having an interest in nanoscience and technology. The scientists, having strengths in basic science together with more application-oriented minds from different backgrounds, work together by joining hands as a cohesive unit, under a congenial work environment, on a common platform apart from carrying out their individual research.

INST offers Ph.D. and Postdoctoral fellowships to students as part of its human resource development objective. Through its various activities, INST is committed to contribute significantly to the National Societal Programs like Swachh Bharat Abhiyan, Swasth Bharat, Smart Cities, Smart Villages, supporting the Strategic Sector, Make in India and Clean & Renewable Energy through scientific means and by generating processes, technologies and devices.

The institute encourages its scientists to publish their research in peer-reviewed international high impact journals which is reflected in their recent publication record in reputed journals like Energy and Environment, Nature Communication, JACS etc.INST supports industry’s through joint collaborations to address some of their needs like effluent management.

In addition, the institute imparts advanced training courses and laboratory techniques in the area of nanoscience, organizes important national and international level seminars and conferences, and supports the industry through joint industrial projects.INST is also promoting science amongst the young generation of the nation through its outreach program, especially for rural, remote and under-served schools by delivering talks to motivate the students to explore the world of science.

INST Mohali aims to emerge as India’s foremost research institution in Nano Science and Technology, which is globally competitive and contributes to the society through the application of nanoscience and nanotechnology in the field of healthcare, agriculture, energy and environment.

Tags:  Graphene  Institute of Nanoscience and Technology  nanotechnology  supercapacitor  water purification 

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First Graphene Announces Steel Blue Signs Supply Agreement

Posted By Graphene Council, Monday, January 27, 2020

First Graphene is pleased to announce the execution of a supply agreement with Footwear Industries Pty Ltd (trading as “Steel Blue”) for the exclusive supply of PureGRAPH®10 for a twenty-four month term (“Supply Agreement”).

In August 2019, FGR announced that it was able to successfully incorporate PureGRAPH® into a thermoplastic polyurethane (“TPU”). Previously, the ability to successfully disperse graphene into a TPU masterbatch had been a major limitation for the graphene industry. Extensive research by FGR has resulted in a manufacturing method which has overcome this.

While existing TPU’s already possess high abrasion resistance and tensile strength, the incorporation of PureGRAPH® has improved mechanical properties while providing additional benefits in thermal heat transfer and chemical resistance whilst also reducing permeability.

Steel Blue will look to release future work boots with graphene components, including a TPU sole. This will potentially provide new design solutions and improvements in manufacturing processes and the comfort of the boot.

As announced on 15 November 2019, tests on prototype boots were conducted at Viclab Pty Ltd, one of Australia’s leading NATA accredited and independent mechanical testing services. The prototype boots complied with the following test procedures:

Impact resistance
Upper to outsole bond
Interlayer bond strength
Slip resistance on ceramic tile floor with NaLS and on steel floor with glycerine
Sole crack resistance
Tear strength
Abrasion (TPU)
Tensile
Hydrolysis
Fuel oil resistance
Chemical exposure (NaOH)

By including PureGRAPH® additives into the sole, improvements in key properties such as tear strength and abrasion resistance have been measured. Steel Blue have continued to test different applications and processes, with ongoing measuring of outcomes by Viclab Pty Ltd.

Upon successful testing, Steel Blue will look to incorporate PureGRAPH into existing and future models of boots, including the mid-sole and Metguard.

Other Key Terms of Supply Agreement
Pursuant to the Supply Agreement, Steel Blue will exclusively source graphene and any other graphite or graphene products from FGR.

FGR’s supply of its graphene products to Steel Blue will initially be exclusive for application in the production of safety footwear for sale in Australia and New Zealand. Following the initial term, exclusivity will only be available to Steel Blue if Steel Blue has achieved (and continues to maintain) a minimum order quantity. The initial minimum order quantity to be achieved in the second year of the Supply Agreement is two (2) tonnes of PureGRAPH®. Based on the currently agreed ordering schedule, product supply to Steel Blue in year one is anticipated to progress to an annualised basis of one (1) tonne as adoption commences across the Steel Blue footwear range and product lines.

Each party has the right to early termination if there is a material breach of the obligations of the other party. Additionally, Steel Blue has the option to extend the initial 24-month term for an additional 48 months.
 
Craig McGuckin, Managing Director for First Graphene Ltd., said, “The execution of this Supply Agreement represents the first of several anticipated for 2020. We are pleased to have worked with Steel Blue to develop a unique range of safety boots for local and export markets. Graphene is helping our customers to develop new products not previously seen with non-graphene technologies. PureGRAPH® additives are a key enabler in taking elastomers, composites, coatings and concrete materials to a new level and we will continue to seek out further new applications and markets where graphene can add value.”

Garry Johnson, Chief Executive Officer of Steel Blue said “Steel Blue is committed to developing innovative solutions for our customers. We’re excited by the product we have developed with First Graphene. These are two innovative, Western Australian founded companies who are taking new technologies to a world market.’’

Tags:  Craig McGuckin  First Graphene  Garry Johnson  Graphene  Steel Blue 

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Well-designed substrates make large single crystal bi-/tri-layer graphene possible

Posted By Graphene Council, Sunday, January 26, 2020
Researchers of the Center for Multidimensional Carbon Materials (CMCM) within the Institute for Basic Science (IBS, South Korea) have reported in Nature Nanotechnology the fabrication and use of single crystal copper-nickel alloy foil substrates for the growth of large-area, single crystal bilayer and trilayer graphene films.

The growth of large area graphene films with a precisely controlled numbers of layers and stacking orders can open new possibilities in electronics and photonics but remains a challenge. This study showed the first example of the synthesis of bi- and trilayer graphene sheets larger than a centimeter, with layers piled up in a specific manner, namely AB- and ABA-stacking.

“This work provides materials for the fabrication of graphene devices with novel functions that have not yet been realized and might afford new photonic and optoelectronic and other properties,” explains Rodney S. Ruoff, CMCM Director, Distinguished Professor at the Ulsan National Institute of Science and Technology (UNIST) and leading author of this study. Coauthor and Professor Won Jong Yoo of Sungkyunkwan University notes that “this paves the way for the study of novel electrical transport properties of bilayer and trilayer graphene.”

For example, the same IBS research group and collaborators recently published another paper in Nature Nanotechnology showing the conversion of AB-stacked bilayer graphene film, grown on copper/nickel (111) alloy foils (Cu/Ni(111) foils), to a diamond-like sheet, known as diamane. Coauthor Pavel V. Bakharev notes that: “Less than one year ago, we produced fluorinated diamond monolayer, F-diamane, by fluorination of exactly the AB-stacked bilayer graphene films described in this new paper. Now the possibility of producing bilayer graphene of a larger size brings renewed excitement and shows how fast this field is developing.”

The right choice of substrate is essential for the correct growth of graphene. Foils made only of copper limit the growth of bilayer graphene and favor uniform monolayer growth. It is possible to obtain multilayer graphene sheets on nickel film, but these are not uniform, and tend to have small “patches” with different thicknesses. Finally, the commercially available foils that contain both nickel and copper are not ideal. Therefore, IBS researchers prepared ‘home-made’ single crystal Cu/Ni(111) foils with desired features, building further on a technique reported by the group in Science in 2018. Nickel films are electroplated onto copper(111)-foils so that the nickel and copper interdiffuse when heated and yield a new single crystal foil that contains both elements at adjustable ratios. Ruoff suggested this method and supervised Ming Huang’s evaluations of the best concentrations of nickel to obtain uniform graphene sheets with the desired number of layers.

IBS researchers grew bi- and tri-layer graphene sheets on Cu/Ni(111) foils by chemical vapor deposition (CVD). Huang achieved AB-stacked bilayer graphene films of several square centimeters, covering 95% of the substrate area, and ABA-stacked trilayer graphene with more than 60% areal coverage. This represents the first growth of high coverage ABA-stacked trilayer graphene over a large area and the best quality obtained for AB-stacked bilayer graphene so far.

In addition to extensive spectroscopic and microscopic characterizations, the researchers also measured the electrical transport (carrier mobility and band gap tunability) and thermal conductivity of the newly synthesized graphene. The centimeter-scale bilayer graphene films showed a good thermal conductivity, as high as ~2300 W/mK (comparable with exfoliated bilayer graphene flakes), and mechanical performance (stiffness of 478 gigapascals for the Young’s modulus, and 3.31 gigapascals for the fracture strength).

The team then investigated the growth stacking mechanism and discovered it follows the so-called “inverted wedding cake” sequence as the bottom layers are positioned after the top one. “We showed with three independent methods that the 2nd layer for bilayer graphene, and the 2nd and 3rd layers of the trilayer sheet grow beneath a continuous top layer. These methods can be further used to study the structure and stacking sequence of other 2D thin film materials,” notes Huang.

Ruoff notes that these techniques for synthesizing and testing large-scale ultrathin films could stimulate worldwide interest in further experimenting with single crystal Cu/Ni alloy foils, and even in exploring fabrication and use of other single crystal alloy foils. This research was performed in collaboration with UNIST and Sungkyunkwan University.

Tags:  2D materials  Center for Multidimensional Carbon Materials  Graphene  Institute for Basic Science  nanomaterials  nanotechnology  Rodney S. Ruoff 

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Physicist obtain atomically thin molybdenum disulfide films on large-area substrates

Posted By Graphene Council, Thursday, January 23, 2020
Researchers from the Moscow Institute of Physics and Technology have managed to grow atomically thin films of molybdenum disulfide spanning up to several tens of square centimeters. It was demonstrated that the material's structure can be modified by varying the synthesis temperature. The films, which are of interest to electronics and optoelectronics, were obtained at 900-1,000 degrees Celsius. The findings were published in the journal ACS Applied Nano Materials.

Two-dimensional materials are attracting considerable interest due to their unique properties stemming from their structure and quantum mechanical restrictions. The family of 2D materials includes metals, semimetals, semiconductors, and insulators. Graphene, which is perhaps the most famous 2D material, is a monolayer of carbon atoms. It has the highest charge-carrier mobility recorded to date. However, graphene has no band gap under standard conditions, and that limits its applications.

Unlike graphene, the optimal width of the bandgap in molybdenum disulfide (MoS2) makes it suitable for use in electronic devices. Each MoS2 layer has a sandwich structure, with a layer of molybdenum squeezed between two layers of sulfur atoms. Two-dimensional van der Waals heterostructures, which combine different 2D materials, show great promise as well. In fact, they are already widely used in energy-related applications and catalysis. Wafer-scale (large-area) synthesis of 2D molybdenum disulfide shows the potential for breakthrough advances in the creation of transparent and flexible electronic devices, optical communication for next-generation computers, as well as in other fields of electronics and optoelectronics.

"The method we came up with to synthesize MoS2 involves two steps. First, a film of MoO3 is grown using the atomic layer deposition technique, which offers precise atomic layer thickness and allows conformal coating of all surfaces. And MoO3 can easily be obtained on wafers of up to 300 millimeters in diameter. Next, the film is heat-treated in sulfur vapor. As a result, the oxygen atoms in MoO3 are replaced by sulfur atoms, and MoS2 is formed. We have already learned to grow atomically thin MoS2 films on an area of up to several tens of square centimeters," explains Andrey Markeev, the head of MIPT's Atomic Layer Deposition Lab.

The researchers determined that the structure of the film depends on the sulfurization temperature. The films sulfurized at 500 ? contain crystalline grains, a few nanometers each, embedded in an amorphous matrix. At 700 ?, these crystallites are about 10-20 nm across and the S-Mo-S layers are oriented perpendicular to the surface. As a result, the surface has numerous dangling bonds. Such structure demonstrates high catalytic activity in many reactions, including the hydrogen evolution reaction. For MoS2 to be used in electronics, the S-Mo-S layers have to be parallel to the surface, which is achieved at sulfurization temperatures of 900-1,000 ?. The resulting films are as thin as 1.3 nm, or two molecular layers, and have a commercially significant (i.e., large enough) area.

The MoS2 films synthesized under optimal conditions were introduced into metal-dielectric-semiconductor prototype structures, which are based on ferroelectric hafnium oxide and model a field-effect transistor. The MoS2 film in these structures served as a semiconductor channel. Its conductivity was controlled by switching the polarization direction of the ferroelectric layer. When in contact with MoS2, the La:(HfO2-ZrO2) material, which was earlier developed in the MIPT lab, was found to have a residual polarization of approximately 18 microcoulombs per square centimeter. With a switching endurance of 5 million cycles, it topped the previous world record of 100,000 cycles for silicon channels.

Tags:  2D materials  ACS Applied Nano Materials  Andrey Markeev  Graphene  Moscow Institute of Physics and Technology  Optoelectronics  Semiconductors 

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Universities Minister celebrates Manchester’s materials reputation

Posted By Graphene Council, Wednesday, January 22, 2020
Advanced Materials were at the centre of the agenda for the Minister for Universities, Science, Research and Innovation, Chris Skidmore, last week during a thorough tour of The University of Manchester campus.

The Minister visited the University to discover more about the soon-to-open Henry Royce Institute, hear about the most recent graphene developments, discover more about how the AI and robotics are helping to solve challenges faced by the nuclear industry and finally tour the north campus and future home of IDManchester.

During the tour, the Minister, who was accompanied by President and Vice-Chancellor, Professor Dame Nancy Rothwell, met with leading academics and discussed breakthrough developments at the University since he last visited the campus just over a year ago.

Professor Phil Withers greeted the Minister to discuss and take-in the the new soon-to-open £150m Royce building, a new national hub for advanced materials research and commercialisation.

During the visit Chris Skidmore said: “The University of Manchester is doing amazing research in areas like x-ray imaging systems and the super material graphene. Outstanding university research like this will help build our reputation as a global science superpower while growing our economy, and it was a privilege to witness it first-hand.”

The University of Manchester is doing amazing research in areas like x-ray imaging systems and the super material graphene. Outstanding university research like this will help build our reputation as a global science superpower while growing our economy, and it was a privilege to witness it first-hand, Chris Skidmore, Minister of State for Universities, Science, Research and Innovation.

The delegation then visited state-of-the-art research facilities of the National Graphene Institute (NGI) with Professor Sir Andre Geim, who received a Nobel Prize for his work on initially isolating the two-dimensional (2D) material in 2004 and continues to explore and develop the untapped potential of related 2D materials in Manchester.

The NGI, along the with Graphene Engineering Innovation Centre (GEIC) forms the heart of Graphene City, an entire city-centre based end-to-end ecosystem to research, develop and commercialise unique graphene applications in tandem with industry.

A tour of the Manchester Institute of Biotechnology (MIB) was also on the agenda to visit the labs at the heart of the pioneering research led by Professor Nigel Scrutton and team which was recently honoured with the Queen's Anniversary Prize. The MIB was singled out as a beacon of excellence for being at the forefront of designing a sustainable future for the UK and communities across the world by developing disruptive bio-based technologies.

The visit concluded with the Minister heading to the RAIN project which uses robotic and AI technologies to solve challenges faced by the nuclear industry. It is led by Barry Lennox, Professor of Applied Control in the School of Electrical and Electronic Engineering,

Tags:  2D materials  Chris Skidmore  Dame Nancy Rothwell  Graphene  Graphene Engineering Innovation Centre  Phil Withers  University of Manchester 

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