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New production method for carbon nanotubes gets green light

Posted By Graphene Council, Thursday, January 9, 2020
A new method of producing carbon nanotubes - tiny molecules with incredible physical properties used in touchscreen displays, 5G networks and flexible electronics - has been given the green light by researchers, meaning work in this crucial field can continue.

Single-walled carbon nanotubes are among the most attractive nanomaterials for a wide range of applications ranging from nanoelectronics to medical sensors. They can be imagined as the result of rolling a single graphene sheet into a tube.

Their properties vary widely with their diameter, what chemists call chirality - how symmetrical they are - and by how the graphene sheet is rolled.

The problem faced by researchers is that it is no longer possible to make high quality research samples of single-walled carbon nanotubes using the standard method. This was associated with the Carbon Center at Rice University, which used the high-pressure carbon monoxide (HiPco) gas-phase process developed by Nobel Laureate, the late Rick Smalley.

The demise of the Carbon Center in the mid-2010s, the divesting of the remaining HiPco samples to a third-party entity with no definite plans of further production, and the expiration of the core patents for the HiPco process, meant that this existing source of nanotubes was no longer an option.

Now however, a collaboration between scientists at Swansea University (Wales, UK), Rice University (USA), Lamar University (USA), and NoPo Nanotechnologies (India) has demonstrated that the latter's process and material design is a suitable replacement for the the Rice method.

Analysis of the Rice "standard" and new commercial-scale samples show that back-to-back comparisons are possible between prior research and future applications, with the newer HiPco nanotubes from NoPo Nanotechnologies comparing very favourably to the older ones from Rice.

These findings will go some way to reassure researchers who might have been concerned that their work could not continue as high-quality nanotubes would no longer be readily available.

Professor Andrew Barron of Swansea University's Energy Safety Research Institute, the project lead, said:
"Variability in carbon nanotube sources is known to be a significant issue when trying to compare research results from various groups. What is worse is that being able to correlate high quality literature results with scaled processes is still difficult".

Erstwhile members of the Smalley group at Rice University, which developed the original HiPco process, helped start NoPo Nanotechnologies with the aim of updating the HiPco process, and produce what they call NoPo HiPCO® SWCNTs.

Lead author Dr. Varun Shenoy Gangoli stated:
"It is in the interest of all researchers to understand how the presently available product compares to historically available Rice materials that have been the subject of a great range of academic studies, and also to those searching for a commercial replacement to continue research and development in this field."

Tags:  Andrew Barron  carbon nanotubes  Graphene  Medical  nanoelectronics  Rice University  Sensors  Swansea University  Varun Shenoy Gangoli 

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Graphene nanoarchitectures for diverse applications

Posted By Graphene Council, Wednesday, January 1, 2020

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

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

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

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

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

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

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

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Saving Moore’s Law

Posted By Graphene Council, Tuesday, December 31, 2019
It’s a well-known observation: The number of transistors on a microchip will double roughly every two years. And, thanks to advances in miniaturization and performance, this axiom, known as Moore’s Law, has held true since 1965, when Intel co-founder Gordon Moore first made that statement based on emerging trends in chip manufacturing at Intel. 

However, integrated circuits are hitting hard physical limits that are rendering Moore’s Law obsolete — elements on a dense integrated circuit (IC) can get only so small and so tightly packed together before they begin to interfere with each other and otherwise lose their functionality.

“Apart from fundamental physical limits to the scaling of transistor feature sizes below a few nanometers, there are significant challenges in terms of reducing power dissipation, as well as justifying the incurred cost of IC fabrication,” said Kaustav Banerjee, a professor of electrical and computer engineering at UC Santa Barbara. As a result, the very devices that we rely on for their steadily improving performance and versatility — computers, smartphones, internet-enabled gadgets — would also hit a limit, he said.

But according to Banerjee, one of world’s leading scientific minds in the field of nanoelectronics, there is a way to maintain Moore’s Law indefinitely, by taking advantage of relatively new and promising two-dimensional (2D) materials and combining them with monolithic 3D (M3D) integration practices to create ultra-compact, yet high-performing electronic chips that could overcome the challenges that face conventional integrated circuits. While Banerjee first disclosed this idea in a visionary article back in 2014, more detailed research evaluating this technology from his Nanoelectronics Research Lab was recently published in the IEEE Journal of the Electron Devices Society.

“Two-dimensional materials can be stable in their monolayer form with atomic scale thickness – 0.5 nanometer or 5 Angstroms for graphene (a conductor) and hexagonal-boron-nitride (an insulator), and ~6.5 Angstroms for 2D transition metal dichalcogenides (semiconductors) such as molybdenum-disulphide (MoS2) or tungsten-disulphide/diselenide (WS2/WSe2).” Banerjee said. “In addition, due to their layered nature, they offer pristine surfaces relatively free of defects and are excellent conductors of heat in the in-plane direction. All these properties, along with the possibility to directly synthesize these materials on top of prefabricated devices, offer unprecedented advantages over conventional 3D ICs that are already in the market or M3D integration with conventional electronic materials.”

The Benefits of Thinness 

According to the Banerjee Group’s study, there’s a limit to how thin conventional semiconductor materials can get before their desirable electronic properties begin to fade. 

“Thickness scaling of common semiconductor materials, such as Si, becomes challenging below a few nanometers due to rapid degradation of their mobility caused by the increase in electron scatterings from surface roughness,” Banerjee said. “In fact, below ~1 nm, conventional materials like Si or Ge may not be thermodynamically stable.”

On the other hand, atomically thin and stable 2D materials, such as graphene, hexagonal boron nitride (h-BN), and transitional metal dichalcogenides (MoS2, WS2, WSe2, etc) are highly space-efficient, thickness-wise. Moreover, due to their layered nature and pristine interfaces, the 2D semiconductors exhibit reasonably high mobilities and immunity against surface defects, according to the paper. In addition, 2D materials tend to be a lot more flexible than their conventional counterparts, which make them ideal for state-of-the-art electronics applications, such as flexible displays.  Stacked 2D materials, in contrast to their stacked 3D counterparts, meanwhile, can also minimize the inter-tier signal delays, thermal resistance, and reduce potential overheating.

By selecting certain 2D materials and stacking them, according to the researchers, not only does the monolithic 3D conserve precious space on the chip, but also allows for configuration based on the combined electronic properties of the materials.

For example, owing to the atomically-thin vertical dimensions of 2D materials, and carefully-designed inter-tier electrostatics with graphene shielding layer that also benefits from enhanced heat dissipation, aggressive scaling of tier thickness down to sub-μm can be achieved,” Banerjee said. “Such scaling allows over 10-folds higher integration density with respect to conventional 3D integration, and over 150% greater integration density with respect to conventional M3D integration, with plenty of room for further improvements.” 

“Thus, 2D materials can help realize the ultimate density scaling of integrated electronics — both laterally and vertically — which can usher an unprecedented era of innovation and economic growth for the worldwide semiconductor industry,” he added.

Manufacturing Outlook

As with many innovations with potential to become mainstream technologies, there are challenges to consider to pave the way toward their mass manufacturing. For monolithic 3D devices, the challenges are to be able to fabricate these components at relatively low temperatures (lower than 500 degrees Celsius) to avoid degradations and damages to prefabricated devices located in the lower tiers; electromagnetic interference; and heat dissipation.

Last year, Banerjee’s group demonstrated a CMOS compatible graphene synthesis method that essentially addressed the low-temperature and transfer-free synthesis challenge for graphene. Similar efforts are underway in his laboratory to synthesize other 2D materials directly on wafers at low temperatures.

“Additionally, careful design is needed to electrically shield the generated electromagnetic waves from affecting the operations of devices on adjacent or nearby tiers,” said Junkai Jiang, the lead author of the article and recent recipient of a doctoral degree in electrical and computer engineering from Banerjee’s laboratory. The researchers noted that by using a thin graphene shielding layer between tiers (preferably doped to enhance electromagnetic screening effect), interference can be prevented even as the vertical layers are scaled down. 

In terms of heat dissipation, the thinness of the material itself is conducive to allowing the heat from densely packed stacked components to dissipate efficiently. Kamyar Parto, a co-author of the study and a member of Banerjee’s lab, remarked that “the 2D materials have much higher in-plane thermal conductivity compared to thinned-down conventional materials like silicon, which helps fast lateral heat transport, thereby reducing the risks of any hot-spot formation.”  

“Ultimately, we envision heterogeneously integrated devices and technologies enabled by 2D materials to realize the world’s tallest and densest ‘chip-cities’ with unprecedented performance, storage capacity, and energy-efficiency,” he added.

Tags:  2D materials  Electronics  Graphene  Hexagonal boron nitride  Intel  Junkai Jiang  Kamyar Parto  Kaustav Banerjee  nanoelectronics  Semiconductor 

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Converting graphene into diamond film without high pressure

Posted By Graphene Council, Wednesday, December 11, 2019
Can two layers of graphene be linked and converted to the thinnest diamond-like material? Researchers of the Center for Multidimensional Carbon Materials (CMCM) within the Institute for Basic Science (IBS, South Korea) have reported in Nature Nanotechnology ("Chemically Induced Transformation of CVD-Grown Bilayer Graphene into Fluorinated Single Layer Diamond") the first experimental observation of a chemically induced conversion of large-area bilayer graphene to the thinnest possible diamond-like material, under moderate pressure and temperature conditions.

This flexible, strong material is a wide-band gap semiconductor, and thus has potential for industrial applications in nano-optics, nanoelectronics, and can serve as a promising platform for micro- and nano-electromechanical systems.

Diamond, pencil lead, and graphene are made by the same building blocks: carbon atoms (C). Yet, it is the bonds’ configuration between these atoms that makes all the difference. In a diamond, the carbon atoms are strongly bonded in all directions and create an extremely hard material with extraordinary electrical, thermal, optical and chemical properties. In pencil lead, carbon atoms are arranged as a pile of sheets and each sheet is graphene. Strong carbon-carbon (C-C) bonds make up graphene, but weak bonds between the sheets are easily broken and in part explain why the pencil lead is soft. Creating interlayer bonding between graphene layers forms a 2D material, similar to thin diamond films, known as diamane, with many superior characteristics.

Previous attempts to transform bilayer or multilayer graphene into diamane relied on the addition of hydrogen atoms, or high pressure. In the former, the chemical structure and bonds’ configuration are difficult to control and characterize. In the latter, the release of the pressure makes the sample revert back to graphene. Natural diamonds are also forged at high temperature and pressure, deep inside the Earth. However, IBS-CMCM scientists tried a different winning approach.

The team devised a new strategy to promote the formation of diamane, by exposing bilayer graphene to fluorine (F), instead of hydrogen. They used vapors of xenon difluoride (XeF2) as the source of F, and no high pressure was needed. The result is an ultra-thin diamond-like material, namely fluorinated diamond monolayer: F-diamane, with interlayer bonds and F outside.

For a more detailed description; the F-diamane synthesis was achieved by fluorinating large area bilayer graphene on single crystal metal (CuNi(111) alloy) foil, on which the needed type of bilayer graphene was grown via chemical vapor deposition (CVD).

Conveniently, C-F bonds can be easily characterized and distinguished from C-C bonds. The team analyzed the sample after 12, 6, and 2-3 hours of fluorination. Based on the extensive spectroscopic studies and also transmission electron microscopy, the researchers were able to unequivocally show that the addition of fluorine on bilayer graphene under certain well-defined and reproducible conditions results in the formation of F-diamane. For example, the interlayer space between two graphene sheets is 3.34 angstroms, but is reduced to 1.93-2.18 angstroms when the interlayer bonds are formed, as also predicted by the theoretical studies.

“This simple fluorination method works at near-room temperature and under low pressure without the use of plasma or any gas activation mechanisms, hence reduces the possibility of creating defects,” points out Pavel V. Bakharev, the first author and co-corresponding author.

Moreover, the F-diamane film could be freely suspended. “We found that we could obtain a free-standing monolayer diamond by transferring F-diamane from the CuNi(111) substrate to a transmission electron microscope grid, followed by another round of mild fluorination,” says Ming Huang, one of the first authors.

Rodney S. Ruoff, CMCM director and professor at the Ulsan National Institute of Science and Technology (UNIST) notes that this work might spawn worldwide interest in diamanes, the thinnest diamond-like films, whose electronic and mechanical properties can be tuned by altering the surface termination using nanopatterning and/or substitution reaction techniques. He further notes that such diamane films might also eventually provide a route to very large area single crystal diamond films.

Tags:  2D material  bilayer graphene  Center for Multidimensional Carbon Materials  chemical vapor deposition  Graphene  Institute for Basic Science  Ming Huang  nanoelectronics  Nature Nanotechnology  Pavel V. Bakharev  Rodney S. Ruoff  semiconductor  Ulsan National Institute of Science and Technology 

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NANOMAGNETS MADE OF GRAPHENE FOR FASTER AND MORE SUSTAINABLE INFORMATION TECHNOLOGIES

Posted By Graphene Council, Tuesday, November 26, 2019
Updated: Tuesday, November 26, 2019
The meeting marks the starting point of a 4-year research project that is coordinated by CIC nanoGUNE and integrates IBM Research, Donostia International Physics Center, and University of Santiago de Compostela, Technical University of Delft and the University of Oxford. The consortium of these 6 leading European research institutions has been granted a total of €3.5 million from the European Commission under the highly competitive Horizon 2020 FET-Open call, which funds cutting-edge high-risk / high-impact interdisciplinary research projects that must lay the foundations for radically new future technologies.

The SPRING project combines recent scientific breakthroughs from the consortium members to fabricate custom-crafted magnetic graphene nanostructures and test their potential as basic elements in quantum spintronic devices. The targeted long-term vision is the development of an all-graphene – environmentally friendly – platform where spins can be used for transporting, storing and processing information.

As the name suggests, spin can be loosely understood as the rotation of a fundamental particle of matter around itself. For instance, every electron in any material carries both a charge and a spin, the latter playing a key role in magnetism.

Within the scientific community there is consensus that spin is the ideal property of matter to expand the performance of current charge-based nanoelectronics into a class of faster and more power-efficient components, being the basis for the emerging technology called quantum spintronics. The SPRING project will investigate the fundamental laws for creating and detecting spins in graphene, this is to read and write spins, and using them to transmit information.

Jose Ignacio Pascual, Ikerbasque Research Professor at CIC nanoGUNE and scientific coordinator of the project, explains that “graphene is ideal to host spins and to transport them. This atomically thin material can now be fabricated with atomic precision, opening the door to fabrication of designer structures with precise shape, composition, spin arrangement, and interconnected by graphene electrodes for electrostatic or quantum gates. The potential is a platform for the second quantum revolution as qubit elements for quantum computation.”

Tags:  CIC nanoGUNE  Donostia International Physics Center  Graphene  IBM Research  Jose Ignacio Pascual  nanoelectronics  Technical University of Delft  University of Oxford  University of Santiago de Compostela 

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Creating 2D heterostructures for future electronics

Posted By Graphene Council, Thursday, November 7, 2019
Updated: Thursday, November 7, 2019
While many nanomaterials exhibit promising electronic properties, scientists and engineers are still working to best integrate these materials together to eventually create semiconductors and circuits with them.

Northwestern Engineering researchers have created two-dimensional (2D) heterostructures from two of these materials, graphene and borophene, taking an important step toward creating intergrated circuits from these nanomaterials.

"If you were to crack open an integrated circuit inside a smartphone, you'd see many different materials integrated together," said Mark Hersam, Walter P. Murphy Professor of Materials Science and Engineering, who led the research. "However, we've reached the limits of many of those traditional materials. By integrating nanomaterials like borophene and graphene together, we are opening up new possibilities in nanoelectronics."

Supported by the Office for Naval Research and the National Science Foundation, the results were published October 11 in the journal Science Advances. In addition to Hersam, applied physics PhD student Xiaolong Liu co-authored this work.

Creating a new kind of heterostructure

Any integrated circuit contains many materials that perform different functions, like conducting electricity or keeping components electrically isolated. But while transistors within circuits have become smaller and smaller -- thanks to advances in materials and manufacturing -- they are close to reaching the limit of how small they can get.

Ultrathin 2D materials like graphene have the potential to bypass that problem, but integrating 2D materials together is difficult. These materials are only one atom thick, so if the two materials' atoms do not line up perfectly, the integration is unlikely to be successful. Unfortunately, most 2D materials do not match up at the atomic scale, presenting challenges for 2D integrated circuits.

Borophene, the 2D version of boron that Hersam and coworkers first synthesized in 2015, is polymorphic, meaning it can take on many different structures and adapt itself to its environment. That makes it an ideal candidate to combine with other 2D materials, like graphene.

To test whether it was possible to integrate the two materials into a single heterostructure, Hersam's lab grew both graphene and borophene on the same substrate. They grew the graphene first, since it grows at a higher temperature, then deposited boron on the same substrate and let it grow in regions where there was no graphene. This process resulted in lateral interfaces where, because of borophene's accommodating nature, the two materials stitched together at the atomic scale.

Measuring electronic transitions

The lab characterized the 2D heterostructure using a scanning tunneling microscope and found that the electronic transition across the interface was exceptionally abrupt -- which means it could be ideal for creating tiny electronic devices.

"These results suggest that we can create ultrahigh density devices down the road," Hersam said. Ultimately, Hersam hopes to achieve increasingly complex 2D structures that lead to novel electronic devices and circuits. He and his team are working on creating additional heterostructures with borophene, combining it with an increasing number of the hundreds of known 2D materials.

"In the last 20 years, new materials have enabled miniaturization and correspondingly improved performance in transistor technology," he said. "Two-dimensional materials have the potential to make the next leap."

Tags:  2D materials  Graphene  Mark Hersam  nanoelectronics  nanomaterials  Northwestern University  Xiaolong Liu 

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Laser-induced graphene composites are eminently wearable

Posted By Graphene Council, Monday, June 24, 2019
Graphene has a unique combination of properties that is ideal for next-generation electronics, including mechanical flexibility, high electrical conductivity, and chemical stability. The burgeoning field of wearable electronics – 'smart' fabrics with invisibly integrated energy harvesting, energy storage, electronics and sensor systems – benefits from graphene in numerous ways. Graphene materials, be they pristine or composites, will lead to smaller high-capacity and fast-charging supercapacitors, completely flexible and even rollable electronics and energy-storage devices, and transparent batteries.

To realize the commercial potential of graphene, it is necessary to develop reliable, cost-effective and facile processes for the industry-scale fabrication of graphene-based devices.

One possible route is inkjet printing, already extensively demonstrated with conductive metal nanoparticle inks. Although liquid-phase graphene dispersions have been demonstrated, researchers are still struggling with sophisticated inkjet printing technologies that allow efficient and reliable mass production of high-quality graphene patterns for practical applications.

A novel solution comes from the team at Joseph Wang's Laboratory for Nanobioelectronics at UC San Diego. Reporting their findings in Advanced Materials Technologies ("Laser-Induced Graphene Composites for Printed, Stretchable, and Wearable Electronics"), they demonstrate the synthesis of high-performance stretchable graphene ink using a facile, scalable, and low-cost laser induction method for the synthesis of the graphene component.

As a proof-of-concept, the researchers fabricated a stretchable micro-supercapacitor (S-MSC) demonstrating the highest capacitance reported for a graphene-based highly stretchable MSC to date. This also is the first example of using laser-induced graphene in the form for a powder preparation of graphene-based inks and subsequently for use in screen-printing of S-MSC.

Back in 2014, researchers at Rice University created flexible, patterned sheets of multilayer graphene from a cheap polymer by burning it with a computer-controlled laser, a technique they called laser-induced graphene (LIG). This high-yield and low-cost graphene synthesis process works in air at room temperature and eliminates the need for hot furnaces and controlled environments, and it makes graphene that is suitable for electronics or energy storage.

"LIG can be prepared from a few polymeric substances, such as Kapton polyimide and polyetherimide, as well as various sustainable biomasses, including wood, lignin, cloth, paper, or hydrothermal carbons," Farshad Tehrani, the paper's first author. "On the other hand, LIG has considerably enhanced dispersion in typical solvent and binders due to its inherently abundant defects and surface functional groups."

He points out that the team's novel method, while maintaining the distinct advantages of the direct-written LIG, unlocks untapped potentials of the LIG material in several areas:

Mechanical stretchability: In this study, the inherently brittle and mechanically fragile LIG electrodes are turned into a mechanically robust, highly stretchable electrodes, with the new ink attractive for diverse wearable electronic devices.

Enhanced electrochemical performance: The areal capacitance of the team's S-MSC has far surpassed that of direct-written laser LIG and has produced the highest areal capacitance reported for highly stretchable supercapacitors.

Customized composite formulations: The basic ink formulation is compatible with a wide range of compositions using the LIG as an attractive conductive filler.

Substrate versatility: Unlike direct-laser writing, which is limited to polymeric substrates and several biomasses, the LIG ink can be printed on almost any stretchable and non stretchable substrate, such as polymeric substrates, fabrics, or textiles.

"During the development of our new supercapacitor, we discovered a specific synergic effect between polymeric binders poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) mixed with Polyurethane (PU), PEDOT:PSS-PU and graphene sheets in producing exceptional electromechanical performances," adds Fernando Soto, a co-author of the paper. "We realized that when both sides of the graphene sheets are thoroughly covered with the conductive/elastic PEDOT:PSS/PU polymer, it results in a robust composite that withstands severe shear stresses during stretching."

"Not only that, but it also maintains above 85% of its electrochemical performance such as its charge storing capacitance properties, composite conductivity and electrochemical stability at high charge-discharge cycles," he adds.

In developing wearable electronic devices, researchers need to deal with a range of issues where stretchability and mechanical performance of the device is as important as its electronic properties such as conductivity, charge storage properties and, generally, its high electrochemical performance.

Rather than focusing on one of these specific problems, the team's work addresses a series of challenges that include high mechanical and electrochemical performance while keeping the costs at their lowest possible point for realistic commercialization scenarios.

"From the design to the implementation stages of our study, the primary focus has been devoted to scalability, versatility and cost efficiency of a high performance platform that can potentially spark further innovations using nanocomposite materials in the field of wearable electronics," notes Tehrani.

The next stages of the team's work in this area of wearable applications will see the integration of these high-performance S-MSCs with batteries and energy harvesting systems such as biofuel cells, triboelectrics, and piezoelectrics.

Tags:  Farshad Tehrani  Graphene  Joseph Wang  nanocomposites  nanoelectronics  Sensors  UC San Diego 

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From 2D to 1D: Atomically quasi '1D' wires using a carbon nanotube template

Posted By Graphene Council, Wednesday, April 24, 2019
Updated: Tuesday, April 23, 2019
Researchers from Tokyo Metropolitan University have used carbon nanotube templates to produce nanowires of transition metal monochalcogenide (TMM), which are only 3 atoms wide in diameter. These are 50 times longer than previous attempts and can be studied in isolation, preserving the properties of atomically quasi "1D" objects. The team saw that single wires twist when perturbed, suggesting that isolated nanowires have unique mechanical properties which might be applied to switching in nanoelectronics.

Two-dimensional materials have gone from theoretical curiosity to real-life application in the span of less than two decades; the most well-known example of these, graphene, consists of well-ordered sheets of carbon atoms. Though we are far from leveraging the full potential of graphene, its remarkable electrical and thermal conductivity, optical properties and mechanical resilience have already led to a wide range of industrial applications. Examples include energy storage solutions, biosensing, and even substrates for artificial tissue.

Yet, despite the successful transition from 3D to 2D, the barrier separating 2D and 1D has been significantly more challenging to overcome. A class of materials known as transition metal monochalcogenides (TMMs, transition metal + group 16 element) have received particular interest as a potential nanowire in precision nanoelectronics. Theoretical studies have existed for over 30 years, and preliminary experimental studies have also succeeded in making small quantities of nanowire, but these were usually bundled, too short, mixed with bulk material or simply low yield, particularly when precision techniques were involved e.g. lithography. The bundling was particularly problematic; forces known as van der Waals forces would force the wires to aggregate, effectively masking all the unique properties of 1D wires that one might want to access and apply.

Now, a team led by Assistant Professor Yusuke Nakanishi from Tokyo Metropolitan University has succeeded in producing bulk quantities of well-isolated single nanowires of TMM. They used tiny, open-ended rolls of single-layered carbon, or carbon nanotubes (CNTs), to template the assembly and reaction of molybdenum and tellurium into wires from a vapor. They succeeded in producing single isolated wires of TMM, which were only 3-atoms thick and fifty times longer than those made using existing methods. These nanometer-sized CNT "test tubes" were also shown to be not chemically bound to the wires, effectively preserving the properties expected from isolated TMM wires. Importantly, they effectively "protected" the wires from each other, allowing for unprecedented access to how these 1D objects behave in isolation.

While imaging these objects using transmission electron microscopy (TEM), the team found that these wires exhibited a unique twisting effect when exposed to an electron beam. Such behavior has never been seen before and is expected to be unique to isolated wires. The transition from a straight to twisted structure may offer a novel switching mechanism when the material is incorporated into microscopic circuits. The team hope the ability to make well-isolated 1D nanowires might significantly expand our understanding of the properties and mechanisms behind the function of 1D materials.

Tags:  2D materials  Carbon Nanotubes  Graphene  nanoelectronics  Tokyo Metropolitan University  Yusuke Nakanishi 

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New method of synthesising nanographene on metal oxide surfaces

Posted By Graphene Council, Tuesday, March 5, 2019
Updated: Tuesday, March 5, 2019

Nanostructures based on carbon are promising materials for nanoelectronics.

However, to be suitable, they would often need to be formed on non-metallic surfaces, which has been a challenge – up to now. Researchers at FAU have found a method of forming nanographenes on metal oxide surfaces. Their research, conducted within the framework of collaborative research centre 953 – Synthetic Carbon Allotropes funded by the German Research Foundation (DFG), has now been published in the journal Science.



Two-dimensional, flexible, tear-resistant, lightweight, and versatile are all properties that apply to graphene, which is often described as a miracle material. In addition, this carbon-based nanostructure has unique electrical properties that make it attractive for nanoelectronic applications. Depending on its size and shape, nanographene can be conductive or semi-conductive – properties that are essential for use in nanotransistors. Thanks to its good electrical and thermal conductivity, it could also replace copper (which is conductive) and silicon (which is semi-conductive) in future nanoprocessors.

Nanographene on metal oxides

The problem: In order to create an electronic circuit, the molecules of nanographene must be synthesised and assembled directly on an insulating or semi-conductive surface. Although metal oxides are the best materials for this purpose, in contrast to metal surfaces, direct synthesis of nanographenes on metal oxide surfaces is not possible as they are considerably less chemically reactive. The researchers would have to carry out the process at high temperatures, which would lead to several uncontrollable secondary reactions.

A team of scientists led by Dr. Konstantin Amsharov from the Chair of Organic Chemistry II have now developed a method of synthesising nanographenes on non-metallic surfaces, that is insulating surfaces or semi-conductors.

It’s all about the bond

The researchers’ method involves using a carbon fluorine bond, which is the strongest carbon bond. It is used to trigger a multilevel process. The desired nanographenes form like dominoes via cyclodehydrofluorination on the titanium oxide surface. All ‘missing’ carbon-carbon bonds are thus formed after each other in a formation that resembles a zip being closed.

This enables the researchers to create nanographenes on titanium oxide, a semi-conductor. This method also allows them to define the shape of the nanographene by modifying the arrangement of the preliminary molecules. New carbon-carbon bonds and, ultimately, nanographenes form where the researchers place the fluourine atoms.

For the first time, these research results demonstrate how carbon-based nanostructures can be manufactured by direct synthesis on the surfaces of technically-relevant semi-conducting or insulating surfaces. ‘This groundbreaking innovation offers effective and simple access to electronic nanocircuits that really work, which could scale down existing microelectronics to the nanometre scale,’ explains Dr. Amsharov.

Tags:  Friedrich-Alexander-Universität Erlangen-Nürnberg  Graphene  Konstantin Amsharov  nanoelectronics  nanographene  Semiconductor 

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Large, stable pieces of graphene produced with unique edge pattern

Posted By Graphene Council, Wednesday, February 6, 2019
Updated: Wednesday, February 6, 2019

Graphene is a promising material for use in nanoelectronics. Its electronic properties depend greatly, however, on how the edges of the carbon layer are formed. Zigzag patterns are particularly interesting in this respect, but until now it has been virtually impossible to create edges with a pattern like this. Chemists and physicists at FAU have now succeeded in producing stable nanographene with a zigzag edge.

Not only that, the method they used was even comparatively simple. Their research, conducted within the framework of collaborative research centre 953  – Synthetic Carbon Allotropes funded by the German Research Foundation (DFG), has now been published in the journal Nature Communications*.

Bay, fjord, cove, armchair and zigzag – when chemists use terms such as these, it is clear that they are referring to nanographene. More specifically, the shape taken by the edges of nanographene, i.e. small fragments of graphene. Graphene consists of a single-layered carbon structure, where each carbon atom is surrounded by three others. This creates a pattern reminiscent of a honeycomb, with atoms in each of the corners. Nanographene is a promising candidate for use in the field of microelectronics, taking over from silicon which is used today and bringing microelectronics down to the nano scale.

The electronic properties of the material depend greatly on its shape, size and above all, periphery, in other words how the edges are structured. A zigzag periphery is particularly suitable, as in this case the electrons, which act as charge carriers, are more mobile than in other edge structures. This means that using pieces of zigzag-shaped graphene in nanoelectronic components may allow higher frequencies for switches.

The problem currently faced by materials scientists who want to research only zigzag nanographene is that this form makes the compounds rather unstable, and unable to be produced in a controlled manner. This is a prerequisite, however, if the electronic properties are to be investigated in detail.

The team of researchers led by PD Dr. Konstantin Amsharov from the Chair of Organic Chemistry II have now succeeded in doing just that. Not only have they discovered a straightforward method for synthesising zigzag nanographene, their procedure delivers a yield of close to one hundred percent and is suitable for large scale production. They have already produced a technically relevant quantity in the laboratory.

First of all, the FAU researchers produce preliminary molecules, which they then fitt together in a honeycomb formation over several cycles, in a process known as cyclisation. In the end, graphene fragments are produced from staggered rows of honeycombs or four-limbed stars surrounding a central point of four graphene honeycombs, with the sought-after zigzag pattern to their edges. Why is this method able to produce stable zigzag nanographene? The explanation lies in the fact that the product crystallises directly even during synthesis. In their solid state, the molecules are not in contact with oxygen. In solution, however, oxidation causes the structures to disintegrate quickly.

This approach allows scientists to produce large pieces of graphene, whilst maintaining control over their shape and periphery. This breakthrough in graphene research means that scientists should soon be able to produce and research a variety of interesting nanographene structures, a crucial step towards finally being able to use the material in nanoelectronic components.

Tags:  Friedrich–Alexander University  Graphene  Konstantin Amsharov  nanoelectronics  nanographene 

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