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Royal Canadian Navy Partners with ZEN Graphene and Evercloak to Test Graphene Oxide Dehumidification Membrane Technology

Posted By Terrance Barkan, Thursday, October 1, 2020
ZEN Graphene Solutions is pleased to announce that the Naval Material Technology Management (NMTM) section of the Royal Canadian Navy (RCN) has partnered with ZEN and Evercloak Inc. as a testing organization, and has agreed to provide in-kind donations of test services from the Naval Engineering Test Establishment (NETE). The tests will compare the efficiency of an HVAC unit produced with the Evercloak dehumidification membrane technology to the incumbent HVAC system that is currently in use on the RCN’s Halifax-class frigates.

Evercloak is evaluating the advantages of its dehumidification membrane technology against the current dehumidification system used by the RCN. Based on lab testing and modelling, Evercloak estimates up to 75% energy savings and anticipates that the equipment will have a smaller footprint and also require minimal maintenance as there will be fewer parts to replace.

As reported in ZEN’s July 9, 2020 news release, Evercloak and ZEN were recently awarded $125,000 each as part of a Next Generation Manufacturing Canada (NGen) Project. The project entitled “Advancing Large-Scale Graphene and Thin-Film Membrane Manufacturing” will support the scale up of graphene oxide (GO) production by ZEN to supply GO to Evercloak for their scale up and optimization activities.

Francis Dubé, ZEN CEO commented, “Having the opportunity to test ZEN’s GO in Evercloak’s dehumidification technology with the Royal Canadian Navy is an excellent platform to showcase how nanotechnology can improve performance compared to current technologies. This could provide significant commercial opportunities beyond RCN should the testing prove successful.”

Evelyn Allen, Evercloak CEO stated, “We are thrilled to be working closely with the Royal Canadian Navy, ZEN, and our proto-type manufacturing partner Environmental System Corporation to showcase Evercloak’s graphene-based membrane performance in these critical environments.”

Evercloak’s patent-pending HydroAM printer is capable of depositing both 1D and 2D nanomaterials and transferring these ultra-thin films onto flexible substrates with a controlled density for various applications ranging from transparent conductors for flexible electronics to more efficient membranes for industrial separations. Through the NGen grant, and in collaboration with Evercloak, ZEN will optimize and scale-up the electrochemical exfoliation (ECE) process that was developed by Prof. Aicheng Chen and his team at the University of Guelph to produce graphene oxide from its unique precursor Albany PureTM Graphite. The ECE process was designed to be scalable, low cost, low energy, and environmentally friendly to produce high quality, few-layer graphene oxide at ZEN’s Guelph facility.

Tags:  Aicheng Chen  Evelyn Allen  Evercloak  Francis Dubé  Graphene  graphene oxide  nanomaterials  nanotechnology  Royal Canadian Navy  University of Guelph  ZEN Graphene Solutions 

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Better wastewater treatment? It’s a wrap

Posted By Graphene Council, Wednesday, July 22, 2020
A shield of graphene helps particles destroy antibiotic-resistant bacteria and free-floating antibiotic resistance genes in wastewater treatment plants.

Think of the new strategy developed at Rice University as “wrap, trap and zap.”

The labs of Rice environmental scientist Pedro Alvarez and Yalei Zhang, a professor of environmental engineering at Tongji University, Shanghai, introduced microspheres wrapped in graphene oxide in the Elsevier journal Water Research.

Alvarez and his partners in the Rice-based Nanosystems Engineering Research Center for Nanotechnology-Enabled Water Treatment (NEWT) have worked toward quenching antibiotic-resistant “superbugs” since first finding them in wastewater treatment plants in 2013.

“Superbugs are known to breed in wastewater treatment plants and release extracellular antibiotic resistance genes (ARGs) when they are killed as the effluent is disinfected,” Alvarez said. “These ARGs are then discharged and may transform indigenous bacteria in the receiving environment, which become resistome reservoirs.

“Our innovation would minimize the discharge of extracellular ARGs, and thus mitigate dissemination of antibiotic resistance from wastewater treatment plants,” he said.

The Rice lab showed its spheres — cores of bismuth, oxygen and carbon wrapped with nitrogen-doped graphene oxide — inactivated multidrug-resistant Escherichia coli bacteria and degraded plasmid-encoded antibiotic-resistant genes in secondary wastewater effluent.

The graphene-wrapped spheres kill nasties in effluent by producing three times the amount of reactive oxygen species (ROS) as compared to the spheres alone.

The spheres themselves are photocatalysts that produce ROS when exposed to light. Lab tests showed that wrapping the spheres minimized the ability of ROS scavengers to curtail their ability to disinfect the solution.

The researchers said nitrogen-doping the shells increases their ability to capture bacteria, giving the catalytic spheres more time to kill them. The enhanced particles then immediately capture and degrade the resistant genes released by the dead bacteria before they contaminate the effluent.

“Wrapping improved bacterial affinity for the microspheres through enhanced hydrophobic interaction between the bacterial surface and the shell,” said co-lead author Pingfeng Yu, a postdoctoral research associate at Rice’s Brown School of Engineering. “This mitigated ROS dilution and scavenging by background constituents and facilitated immediate capture and degradation of the released ARGs.”

Because the wrapped spheres are large enough to be filtered out of the disinfected effluent, they can be reused, Yu said. Tests showed the photocatalytic activity of the spheres was relatively stable, with no significant decrease in activity after 10 cycles. That was significantly better than the cycle lifetime of the same spheres minus the wrap.

Deyi Li of Tongji University, Shanghai, is co-lead author of the paper. Co-authors are Xuefei Zhou and Zhang of Tongji and Jae-Hong Kim, the Henry P. Becton Sr. Professor and Chair of Chemical and Environmental Engineering at Yale University. Alvarez is the George R. Brown Professor of Civil and Environmental Engineering, a professor of chemistry, of materials science and nanoengineering, and of chemical and biomolecular engineering and director of NEWT.

The National Science Foundation, the National Natural Science Foundation of China and the National Key R&D Program of China supported the research.

Tags:  Graphene  nanotechnology  Pedro Alvarez  Rice University 

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PLASTIX, Denmark and Titan Bioplastics, USA Team Up to Provide Innovative Sustainable Recycled 'Super Plastics' with Food Safe Nano Technology

Posted By Graphene Council, Thursday, July 16, 2020
PLASTIX in Lemvig Denmark, a plastics recycling company dedicated to mechanically recycling post-use maritime fibers such as fishing nets and ropes, has formed an Alliance Partnership with nano technology and bio composite experts Titan Bioplastics, USA. Their collaborative agenda, to support sustainable circular economy initiatives for a new generation of 'Super Plastics,' in compliance of forthcoming plastic mandates throughout the EU.

"The goal here" says Hans Axel Kristensen, CEO of PLASTIX, "is to increase the content of recycled plastics in basically all products to meet the requirements of the New Circular Plastics Economy, not just by recycling plastic waste, but ensuring these materials are on par with virgin materials, making them applicable for a multitude of uses including food contact packaging."

A Unique Recycling Solution: PLASTIX is a unique recycling solution provider for one of the most challenging plastic waste streams, fishing nets and ropes, that would otherwise end up in landfill or the ocean. PLASTIX' recycled product, OceanIX, is available today for a wide range of applications and additionally represents a strong branding narrative for companies looking to implement green strategies by reducing the environmental footprint of their products.

Food Safe Nano Technology: Titan Bioplastics' proprietary Titan Nanofill™ is a USA FDA food contact approved mineral additive supporting physical barrier properties which can be uploaded into a variety of polymers. Small loading rates of Titan Nanofill™ can provide 100% increase in barrier properties in polymers, blocking moisture, oxygen and some UV. Additionally, Titan Nanofill™ prevents leaching, which during recycling prevents other plastics from leaching as well.

"We see this as an advancement to many packaging solutions, as well as serious technology supporting companies adapting production in order to meet directives by the European Commission and the Extended Producer Responsibility Act," says Tanya Hart, CEO of Titan Bioplastics. 

Established mandates with timelines have been issued by The European Commission; with an emphasis on recycled plastics and their uses to protect the environment. It sets a 90% collection target for plastic bottles by 2029, and it mandates that plastic bottles be made of at least 25% recycled plastic by 2025 and 30% by 2030.

In the European Union, recycled plastics and additives can only be used in food and beverage packaging if they are first reviewed by EFSA (European Food Safety Authority) for safety.

"Technologies and solutions advancing the plastics industry towards a circular economy, are imperative" says Kristensen "and companies like PLASTIX and Titan Bioplastics, will lead by working collaboratively with companies on targeted solutions in support of upcoming changes for the EU mandates".

Titan Bioplastics was recently recommended by European 'Startus Magazine', as one of 4 top companies out of 97 globally reviewed, able to provide barrier properties and UV degradation protection in polymers.  

"Although Nano technology as an additive was tried and commercialized unsuccessfully around a decade ago" says David Abecassis, Director of Technology for Titan Bioplastics, who is actually the first scientist to invent a nano organoclay in a continuous batch process, "our technology is a differentiator and one we are able to master and prove".

Tags:  composites  Graphene  Hans Axel Kristensen  nanotechnology  plastics  PLASTIX  Tanya Hart  Titan Bioplastics 

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Tour scores prestigious Centenary Prize

Posted By Graphene Council, Friday, June 26, 2020
Rice University chemist James Tour has won a Royal Society of Chemistry Centenary Prize. The award, given annually to up to three scientists from outside Great Britain, recognizes researchers for their contributions to the chemical sciences industry or education and for successful collaborations. Tour was named for innovations in materials chemistry with applications in medicine and nanotechnology.

The prestigious award, established in 1947, comes with a 5,000-pound (about $6,260) cash prize and a medal. Winners are invited to undertake a lecture tour of the United Kingdom, but the COVID-19 pandemic has delayed that until 2021.

Additional winners this year are Teri Odom, the chair and Charles E. and Emma H. Morrison Professor of Chemistry at Northwestern University, and Eric Anslyn, the Welch Regents Chair and University Distinguished Teaching Professor at the University of Texas at Austin. 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.

“Receiving the Royal Society of Chemistry 2020 Centenary Prize is an enormous honor,” Tour said. “The award recognizes the accomplishments of my research group over a period of 32 years. I am greatly indebted to a host of students, postdocs and collaborators that have carried the weight of this research endeavor.

“We have sought to use chemistry to extend the boundaries of new materials development for use in medicine, electronic devices, nano-enhanced structures and renewable energy platforms,” he said. “It is a joy to realize the work done by this array of people in and with my laboratory has afforded such advances that are being recognized by this Centenary Prize.”

Work by Tour and his group in recent years includes the development of versatile laser-induced graphene, flash graphene from waste material, light-activated nanodrills that destroy cancer cells and “superbug” bacteria, silicon-oxide memory circuits that have flown on the International Space Station, the development of graphene quantum dots from coal, asphalt-based materials to capture carbon dioxide from gas wells, and the use of nanoparticles to quench damaging superoxides after an injury or stroke.

“We live in an era of tremendous global challenges, with the need for science recognized now more so than ever — so it is important to recognize those behind the scenes who are making significant contributions towards improving the world we live in,” said acting Royal Society of Chemistry chief executive Helen Pain. “In recognizing the work of Professor Tour, we are also recognizing the important contribution this incredible network of scientists makes to improve our lives every day.”

Tags:  Graphene  Healthcare  Helen Pain  James Tour  Medicine  nanotechnology  Rice University  Royal Society of Chemistry 

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Production-scale nanocharacterization of graphene within reach

Posted By Graphene Council, Friday, May 15, 2020
European project “Real time nano CHAracterization reLatEd techNoloGiES” (CHALLENGES) aims to adapt nanoscale metrology for the manufacturing industry, scaling up high resolution imaging for CMOS electronics, silicon photovoltaics, and 2D materials.

The project, having kicked off with an online meeting on April 23rd, started April 1st and will last for three years under the “Research and innovation actions” (RIA) programme. With a total budget of nearly 4.7 million EUR, the project is run by a consortium of 14 partners from 7 countries.

CHALLENGES is coordinated by a large silicon foundry company and it is strongly driven by industrial and applicative needs. The Consortium includes renowned EU research labs with top-class facilities and capacities, industry leading enterprises and innovative SMEs with a worldwide collaboration network that will boost the international dimension and impact of the project.

The overarching goal is to apply unconventional plasmonic materials in unconventional spectrum ranges, coupled with tip-enhanced local probing spectroscopy, to develop a revolutionary spectroscopic system for real time nanotechnology characterization compatible with semiconductor production. The end goal is a fully automated AFM-based tool not requiring human intervention in routine operations. The solution will lean on current advances in machine learning for automatic detection of relevant sites on large samples to be probed with high resolution.

The large number of SME’s involved in the project will benefit from the development milestones such as novel plasmonic tips, machine learning algorithms optimized for imaging, cleanroom-ready AFM system, industrial in-line quality control methods for production lines of graphene, CIS, nanowires, epitaxial silicon, TMD wafers, and thin silicon solar cells and modules.

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 861857.

Tags:  2D materials  CHALLENGES  CMOS  Graphene  Nanoscale  Nanotechnology  Semiconductor 

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COVID-19 is a chronic disease – and cancer care model is way forward, says Manchester expert

Posted By Graphene Council, Tuesday, April 28, 2020
As the UK government looks for an exit strategy to the COVID-19 lockdown a nanomedicine expert from The University of Manchester believes a care model usually applied to cancer patients could provide a constructive way forward.

Kostas Kostarelos, is Professor of Nanomedicine at The University of Manchester and is leading the Nanomedicine Lab, which is part of the National Graphene Institute and the Manchester Cancer Research Centre.

The Manchester-based expert believes more scientific research should be employed as we transform how we view the COVID-19 pandemic, or any future virus outbreak, and deal with it more like a chronic disease - an ever present issue for humanity that needs systematic management if we are ever to return to our ‘normal’ lives.

Professor Kostarelos makes this claim in an academic thesis entitled 'Nanoscale nights of COVID-19' that offers a nanoscience response to the COVID-19 crisis and will be published on Monday, April 27, by the journal Nature Nanotechnology.

“As for any other chronic medical condition, COVID-19 stricken societies have families, jobs, businesses and other commitments. Therefore, our aim is to cure COVID-19 if possible,” says Professor Kostarelos.

“However, if no immediate cure is available, such as effective vaccination,” Professor Kostarelos suggests: “We need to manage the symptoms to improve the quality of patients’ lives by making sure our society can function as near as normal and simultaneously guarantee targeted protection of the ill and most vulnerable.”

As for any other chronic medical condition, COVID-19 stricken societies have families, jobs, businesses and other commitments. Therefore, our aim is to cure COVID-19 if possible. However, if no immediate cure is available, such as effective vaccination we need to manage the symptoms to improve the quality of patients’ lives by making sure our society can function as near as normal and simultaneously guarantee targeted protection of the ill and most vulnerable Professor Kostas Kostarelos.

Professor Kostarelos says his experience in cancer research and nanotechnology suggests a model that could also be applied to a viral pandemic like COVID-19.

“There are three key principles in managing an individual cancer patient: early detection, monitoring and targeting,” explains Professor Kostarelos. “These principles, if exercised simultaneously, could provide us with a way forward in the management of COVID-19 and the future pandemics.

“Early detection has improved the prognosis of many cancer patients. Similarly, early detection of individuals and groups, who are infected with COVID-19, could substantially accelerate the ability to manage and treat patients.

“All chronic conditions, such as cancer, are further managed by regular monitoring. Therefore, monitoring should be undertaken not only for patients already infected with COVID-19, to track progression and responses, but also for healthy essential workers to ensure that they remain healthy and to reduce the risk of further spreading.

Finally, says Professor Kostarelos, nanomaterials - as well as other biologicals, such as monoclonal antibodies - are often used for targeting therapeutic agents that will be most effective only against cancer cells.

The same principle of ‘targeting’ should be applied for the management of COVID-19 patients to be able to safely isolate them and ensure they receive prompt treatment.

Also, a safeguarding strategy should be provided to the most vulnerable segments of the population by, for example, extending social distancing protocols in elderly care homes - but with the provision of emotional and practical support to ensure the wellbeing of this group is fully supported.

“Protection of the most vulnerable and essential workers, must be guaranteed, with protective gear and monitoring continuously provided,” he added. “Only if all three principles are applied can the rest of society begin to return to normal function and better support the activities in managing this and all future pandemics.”

Tags:  Graphene  Healthcare  Kostas Kostarelos  nanomaterials  nanotechnology  University of Manchester 

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Graphene from sugar, a sweet protocol

Posted By Graphene Council, Saturday, February 29, 2020

Scientists from the Centre for Nano and Soft Matter Sciences, Bengaluru, an autonomous institution under the Department of Science & Technology, Government of India have synthesised reduce graphene oxide (rGO) by the combustion of table-sugar.

The group led by Prof. C. N. R. Rao consisting of Dr. P. Chithaiah from CeNS and Prof. G. U. Kulkarni from JNCASR, Bengaluru has developed a rapid and simple route for the synthesis of rGO by the combustion of table-sugar. This method being single-step and reproducible is advantageous compared to the reported protocols used presently. Further, the synthesis doesn’t involve any metal catalysts, expensive reagents, solvents, hazardous chemicals, and, most importantly, it has the ability to produce graphene oxide in large quantities at rapid rates.

Graphene, a one-atom-thick, two-dimensional sheet of sp2 hybridized carbon atoms is known as a wonder material, as it is stronger than diamond, conducts better than copper along with many other interesting properties. However, the production of graphene in large scale has many challenges to address. 

Till date, methods like chemical vapor deposition, arc discharge, aerosol pyrolysis, mechanical exfoliation, solvothermal, hydrothermal synthesis, laser reduction of graphite oxide have been developed to prepare graphene (reduce graphene oxide, rGO).

All these methods either involve hazardous chemicals, high temperatures, and inert atmosphere making them expensive and thus becoming irrelevant for bulk scale applications.

The team believes that the process developed may have a significant impact on various products, including batteries. Their work has been published in the ‘Beilstein Journal of Nanotechnology.’

Tags:  2D materials  C. N. R. Rao  Centre for Nano and Soft Matter Sciences  chemical vapor deposition  G. U. Kulkarni  Graphene  graphene oxide  nanotechnology  P. Chithaiah 

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

Posted By Graphene Council, The 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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Well-designed substrates make large single crystal bi-/tri-layer graphene possible

Posted By Graphene Council, The 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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Graphene Surprises Researchers Again: Strange ‘Melting’ Behavior

Posted By Graphene Council, The Graphene Council, Monday, January 6, 2020
Physicists from the Moscow Institute of Physics and Technology and the Institute for High Pressure Physics of the Russian Academy of Sciences have used computer modeling to refine the melting curve of graphite that has been studied for over 100 years, with inconsistent findings. They also found that graphene “melting” is in fact sublimation. The results of the study came out in the journal Carbon.

Graphite is a material widely used in various industries — for example in heat shields for spacecraft — so accurate data on its behavior at ultrahigh temperatures is of paramount importance. Graphite melting has been studied since the early 20th century. About 100 experiments have placed the graphite melting point at various temperatures between 3,000 and 7,000 kelvins. With a spread so large, it is unclear which number is true and can be considered the actual melting point of graphite. The values returned by different computer models are also at variance with each other.

A team of physicists from MIPT and HPPI RAS compared several computer models to try and find the matching predictions. Yuri Fomin and Vadim Brazhkin used two methods: classical molecular dynamics and ab initio molecular dynamics. The latter accounts for quantum mechanical effects, making it more accurate. The downside is that it only deals with interactions between a small number of atoms on short time scales. The researchers compared the obtained results with prior experimental and theoretical data.

Fomin and Brazhkin found the existing models to be highly inaccurate. But it turned out that comparing the results produced by different theoretical models and finding overlaps can provide an explanation for the experimental data.

As far back as 1960s, the graphite melting curve was predicted to have a maximum. Its existence points to complex liquid behavior, meaning that the structure of the liquid rapidly changes on heating or densification. The discovery of the maximum was heavily disputed, with a number of studies confirming and challenging it over and over. Fomin and Brazhkin’s results show that the liquid carbon structure undergoes changes above the melting curve of graphene. The maximum therefore has to exist.

The second part of the study is dedicated to studying the melting of graphene. No graphene melting experiments have been conducted. Previously, computer models predicted the melting point of graphene at 4,500 or 4,900 K. Two-dimensional carbon was therefore considered to have the highest melting point in the world.

“In our study, we observed a strange ‘melting’ behavior of graphene, which formed linear chains. We showed that what happens is it transitions from a solid directly into a gaseous state. This process is called sublimation,” commented Associate Professor Yuri Fomin of the Department of General Physics, MIPT. The findings enable a better understanding of phase transitions in low-dimensional materials, which are considered an important component of many technologies currently in development, in fields from electronics to medicine.

The researchers produced a more precise and unified description of how the graphite melting curve behaves, confirming a gradual structural transition in liquid carbon. Their calculations show that the melting temperature of graphene in an argon atmosphere is close to the melting temperature of graphite.

Tags:  2D materials  Graphene  Graphite  Moscow Institute of Physics and Technology  Nanotechnology  Vadim Brazhkin  Yuri Fomin 

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