Graphene suspended over grids for transmission electron microscopy (TEM) can have numerous interesting applications in studies of material properties for technological applications. Two recent publications from TU Wien demonstrate the use of graphene on TEM grids for studies of material quality and integration with indium oxide, another technologically relevant material.
The quality of growth of other materials on graphene is of fundamental importance for device applications. The crystallinity and orientation of indium oxide grown on graphene affects the quality of displays and sensors produced from such a heterostructure. In a study published in Advanced Functional Materials, researchers have shown that arrangement of indium oxide crystals on graphene depends on the pressure on which the crystals form. That can have a major impact on the application properties of the combined materials.
Crucial to the success of this study was the availability of free-standing graphene, on which indium oxide is grown. Having graphene which is suspended in vacuum provides a clean picture of the crystal structure, without any background from a substrate. This is achieved by using commercially available graphene suspended over a metallized mesh – a TEM grid. Transmission electron microscopy across such graphene has the best possible resolution, down to the atomic level.
In a second study, the team of scientists showed that graphene on TEM grids can be used to gauge the quality of the graphene itself. Although grown at a high quality on metal substrates with chemical vapour deposition, transfer of graphene to any useful substrate or a TEM grid requires first coating it with a transfer polymer. Numerous polymer removal processes are used at the industrial scale today, nevertheless it has been shown that some residue persists regardless of the cleaning process. The amount of residue directly impacts graphene film performance.
The study, published in the Journal of Chemical Physics, reveals that ion beam spectroscopy can be used as a tool to map with high resolution the local cleanliness of graphene. The results indicate that although some residue always remains, it clusters in small areas, leaving large clean areas that can be used for devices.
These novel studies highlight the usefulness of graphene on TEM grids as a tool in material science and technology research.
A team of scientists from the UK and Portugal has produced graphene-coated polypropylene (PP) fibres that can be used in wearable textiles as temperature sensors. Operating in the range of 30 to 45 oC at voltages as low as 1 V, textiles incorporating these fibres could be used to actively measure body temperature of the wearer.
Fibres with integrated sensing functionality overcome some key issues related to the use of monolithic sensors that are attached to either clothes or skin, such as ease of use and wearer comfort. Moreover, many attachable sensors are not robust against washing, and some require external high-power voltage supplies. The new graphene-PP based solution resolves all these issues, as described in the application-driven work published in ACS Applied Materials & Interfaces.
PP is a textile fibre material that is strong and transparent, lightweight, eco-friendly and recyclable. The researchers coat PP, an electrical insulator, with graphene to create fibres that are electrically conductive, their resistance changing with temperature. With an outlook for practical device development, the researchers tested two types of graphene that is suitable for mass production, CVD grown and shear exfoliated. The CVD grown graphene exhibited higher sensitivity to temperature, due to its better uniformity. The resistance changes by several percent across temperatures of interest, which is suitable for practical use.
Figure: Graphene on polypropylene fibre temperature sensor – real life use test. Reprinted with permission from ACS Appl. Mater. Interfaces 2020, 12, 26, 29861–29867. Copyright 2020 American Chemical Society.
In order to simulate real-life usage, the novel fibres were tested against bending for up to 1000 cycles and washing in laundry detergent at different temperatures. The devices exhibited excellent stability under all tested conditions. These sensors have potential applications in continuous measurement of human body temperature through integration in garments, or ambient temperature through integration in upholstery.
Fabrication of flexible and wearable electronics often requires integrating various types of advanced carbon nanomaterials - such as graphene, nanotubes, and nanoporous carbon - because of their remarkable electrical, thermal, and chemical properties. However, the extreme environments needed to chemically synthesize these nanomaterials means they can only be fabricated on rigid surfaces that can withstand high temperatures. Printing already-made nanocarbons onto flexible polymeric materials is generally the only option, but limits the potential customization.
To overcome this limitation, researchers at the University of Pittsburgh Swanson School of Engineering are investigating a new scalable manufacturing method for creating customizable types of nanocarbons on-demand - directly where they are needed - on flexible materials.
The research is led by Mostafa Bedewy, assistant professor of industrial engineering at Pitt, who received a $244,748 EAGER award from the National Science Foundation in support of this effort. The project, “Transforming Flexible Device Manufacturing by Bottom-up Growth of Nanocarbons Directly on Polymers,” will enable patterning functional nanocarbons needed for a number of emerging flexible-device applications in healthcare, energy, and consumer electronics.
Bedewy’s group is already working on another NSF-funded project that utilizes a custom-designed reactor to grow “nanotube forests” through a process called chemical vapor deposition (CVD). This enables the synthesis of carbon nanotubes from catalyst nanoparticles by the decomposition of carbon-containing gases. The process, however, is not suitable for growing nanocarbons directly onto commercial polymers.
“When we grow nanocarbons by CVD on silicon, it requires temperatures exceeding 700 degrees Celsius, in the presence of hydrocarbon gases and hydrogen,” explained Bedewy, who leads the NanoProduct Lab in the Swanson School's Department of Industrial Engineering. “While silicon can tolerate those conditions, polymers can’t, so CVD is out of the question.”
Instead, Bedewy’s group will utilize a laser in a similar way that common laser engraving machines function. When manufacturing flexible devices, current methods of printing carbon on polymers are limited in scalability and patterning resolution. This new laser-based method addresses these limitations.
Rather than printing graphene from graphene ink, nanotubes from nanotube ink, and so on, the polymer material itself will act as the carbon source in the new process, and different types of nanocarbons can then grow from the polymer, like grass in a lawn - but instead of using sunlight, through a controlled laser.
“This approach allows us to control the carbon atomic structure, nanoscale morphology, and properties precisely in a scalable way,” said Bedewy. “Our research provides a tremendous opportunity to rapidly customize the type of nanocarbon needed for different devices on the same substrate without the need for multiple inks and successive printing steps.”
Producing functional nanocarbons in this manner will also enable high-rate roll-to-roll processing, which can potentially make manufacturing flexible electronics as fast and as inexpensive as printing newspapers.
“The multi-billion dollar global market for flexible electronics is still in its infancy, and is expected to grow exponentially because of accelerating demand in many applications,” Bedewy said “Exploring potentially transformative carbon nanomanufacturing processes is critical for realizing cutting-edge technologies.”
Versarien plc is pleased to announce that, following an open innovation call, multinational engineering company Rolls-Royce has selected to work with The University of Manchester's Graphene Engineering Innovation Centre and its Tier 1 partner, Versarien subsidiary, 2-DTech Limited.
The initial programme of work will use the state-of-the-art chemical vapour deposition (CVD) equipment located within the GEIC. The collaboration will look to explore, understand and create technological advances surrounding the use of graphene and other 2D materials used in wiring for next-generation aerospace engine systems.
The work conducted will seek to use the unique properties of these 2D materials to reduce the weight of electrical components, improve electrical performance and also increase resistance to corrosion of components in future engine systems.
The programme aims to present potential economic benefits, through the possibility of significant cost reductions, and global environmental benefits, through the reduction of energy use and lower emissions from electrification.
Neill Ricketts , Chief Executive of Versarien commented:
"The pursuit of sustainability has become an important goal for many companies in recent years. Rolls-Royce is one of the world's leading industrial technology companies and today, the size and impact of the markets its serves makes this task more urgent than ever. Taking advantage of advanced materials such as graphene, has the potential to revolutionise these markets and add real benefit.
" The partnership with Rolls-Royce is a significant endorsement to 2-DTech's work over the years and we are delighted it has been chosen by such a renowned business and look forward to working together."
Dr Al Lambourne , Materials Specialist at Rolls - Royce, commented:
" Partnering with the GEIC and its members makes perfect sense to Rolls-Royce as we explore the opportunities and properties of a new class of 2D materials. Using the unique capabilities of 2-DTech and the GEIC we hope to address some of the challenges facing materials in the global aerospace industry , as we pioneer the electrification of future aircraft . "
James Baker, Graphene@Manchester CEO, commented:
"The GEIC is intended to act as an accelerator for graphene commercialisation, market penetration and in the creation of the material supply chain of graphene and 2D materials. It's great to see a company like Rolls-Royce partner with us and our other Tier 1 member, 2-DTech, to capitalise on our world-leading expertise and experience, along with specialist equipment, which will accelerate the product and process development and market entry."
Wearable technology refers to any class of electronic items that can be comfortably worn on the body. This covers an ever-growing range of application and product segments, from health and fitness trackers to immersive infotainment systems. They are governed by many of the same principles and trends as other electronics markets, namely extremely high consumer demand for greater functionality in smaller formats. Developers are consistently tasked with miniaturizing devices without compromising on battery life or performance, which mandates next-generation material solutions like graphene sensors.
Graphene Wearable Electronics
The wearable electronics market continues to experience enormous commercial growth due to the release of coveted commercial goods like smartwatches and virtual reality (VR) headsets, contributing to an estimated compound annual growth rate (CAGR) of 15.5%. Provided the market continues to grow as expected, the global wearable electronics market will be worth over $67 billion by 2024.
Although commercialized wearable electronics are now well-cemented in the consciousness of global consumers, they occupy a novel segment of the market. Medical and military-grade wearables have been used routinely for years, while professional sports have exploited health and wellness trackers integrated into clothing for almost as long. Graphene wearable electronics are expected to bridge the gap between these more sophisticated market segments and consumers, allowing the general public to benefit from advanced functionality wearables in increasingly ergonomic formats.
Graphene Wearables: UV-Detection Patch
One interesting graphene wearable prototype is a flexible, transparent substrate that can be directly applied to the wearer’s skin. The patch detects and monitors exposure to ultraviolet (UV) rays and, with advanced internet of things (IoT) connectivity, and can alert the user once they have reached a pre-defined threshold of exposure to sunlight. This could help prevent a range of harmful conditions, from sunburn to melanoma.
Graphene-Based Health & Wellness Sensors
Using the same key technology as the previous application, researchers are increasingly hopeful of integrating graphene-based sensors and substrates into fitness trackers with unprecedented levels of functionality. Currently, commercial devices such as smartwatches often feature rudimentary heart-rate monitors based on infrared (IR) sensors, and movement trackers based on integrated accelerometers.
With superior biocompatibility, graphene sensors could offer more detailed insights into a wide range of health and wellness signals, including hydration, oxygen saturation, continuous blood pressure monitoring and temperature. Additionally, graphene sensors are being developed for pregnant mothers in the form of a wearable patch, that can monitor and track fetal movements in real time, sending potential indicaitons of a problem to medical professionals.
Graphene Sensor Materials from Grolltex
Grolltex is one of the industry-leading producers of single-layer graphene for sensor applications. We utilise a proprietary chemical vapour deposition (CVD) methodology to produce monolayer materials on substrates of your choosing. We are increasingly servicing researchers and product developers with graphene solutions for sensor and wearable applications and are eager to see how the market progresses in the coming years.
These are scary times, aren't they? First and foremost, my thoughts and prayers go out to anyone who is directly affected by the current global crisis caused by the SARS-CoV-2 coronavirus. It's an extremely serious issue that will require worldwide cooperation to overcome.
I have very clear and distinct memories of the previous SARS epidemic. In March 2003, while working at Rice University, I was helping to lead a group of ~50 science and engineering students on an overseas study trip to Hong Kong and Singapore with my former Rice colleague, Dr. Cheryl Matherly (who is now at Lehigh University). We were caught in the middle of the rapidly developing crisis and our travel itinerary had us departing Singapore for Hong Kong on the day the Singapore government warned its own citizens not to travel to Hong Kong!
Fortunately, everyone in our student group made it through that experience safely, and as unsettling as it was, the current situation is much much worse, with as yet unknown - but sure to be significant - social, economic and political ramifications that will most definitely impact future generations around the world.
I am currently based in Bangkok, Thailand, which is a global tourist destination. While we were fortunately to escape the first wave of of the SARS-CoV-2 virus that emanated from China, we're now faced with a second wave imported from Europe. We're not quite under total lockdown here, but things appear to be headed in that direction. It is clear to me form observation that the several governments in the region (Singapore, Hong Kong, and Taiwan, to be specific) are applying the lessons they learned from the previous SARS epidemic to help control the current pandemic. This give me hope, and the circumstances in general have given me plenty of time to think and reflect about what - if anything - I and my company, planarTECH, can do to improve this situation.
Graphene: The "Wonder Material"
I was lucky to fall into the world of graphene and 2D materials by accident through acquaintance with another former Rice University colleague, Dr. James Tour, and conversations I had with him 8 years ago. I will not spend a lot of time here talking about the specific properties of graphene as such information is widely available. The European Union's Graphene Flagship project, for example, has an excellent overview. The University of Manchester - where graphene was first isolated and where planarTECH's Chairman, Ray Gibbs, currently serves as the Director of Commercialization for the Graphene Engineering and Innovation Centre - also has a fantastic YouTube channel with many instructive videos about graphene and its properties.
With all of the amazing properties of graphene, the question is, can it offer any kind of solution to the current pandemic and global crisis?
Academic Work: Graphene's Antiviral Properties
The short answer to the question above is "possibly," but with some caveats. In particular, it would appear that graphene oxide (GO) may play a role in providing a solution.
I should say that I am not a doctor, an epidemiologist or someone with formal training in the biological sciences. I am an engineer by trade, and for the last 8 years, an entrepreneur in the field of graphene. However, since entering the graphene industry, I have grown accustomed to reading academic papers in order to understand the potential applications for graphene.
A paper published in 2015 by researchers at the Huazhong Agricultural University (ironically located in Wuhan, China, where the current pandemic originated) explored the antiviral properties of graphene oxide, and the authors of the paper concluded "that GO and rGO exhibit broad-spectrum antiviral activity toward both DNA virus (PRV) and RNA virus (PEDV) at a noncytotoxic concentration," and that "the broad-spectrum antiviral activity of GO and rGO may shed some light on novel virucide development." While encouraging, it should be noted that the researchers looked specifically at pseudorabies virus (PRV) and porcine epidemic diarrhea virus (PEDV), not the SARS-CoV-2 virus responsible for the current global pandemic.
Another paper published in 2017 by researchers at Southwest University in China looked at cyclodextrin functionalized graphene oxide and it's possible role in combatting respiratory syncytial virus (RSV), concluding that "the curcumin loaded functional GO was confirmed with highly efficient inhibition for RSV infection and great biocompatibility to the host cells." Likewise, a third paper published in 2019 by researchers at Sichuan Agricultural University in China demonstrated that "GO/HY [graphene oxide/hypericin] has antiviral activity against NDRV [novel duck reovirus] both in vitro and in vivo."
The conclusion we can draw from these works is that graphene oxide may offer a platform to fight a variety of viral infections (such as the SARS-CoV-2 coronavirus), possibly as some form of coating, though certainly more work needs to be done.
(Note that my good friends over at The Graphene Council had a recent and excellent blog post covering the same 3 articles in a little more detail. And kudos to them for shining light on the topic before me!)
Productization: From Lab to Market
If there's one thing I've learned from the past 8 years being involved with graphene commercialization (and the past 14 years working directly in the Asian supply chain) is that it is one matter to write an excellent academic paper as a proof-of-concept, but it is an entirely different matter to take work from an academic lab and turn it into a real product.
With respect to graphene in general, what we are seeing today is definite movement on the Gartner hype cycle from the Trough of Disillusionment to the Slope of Enlightenment. Real products using graphene are now on the market. One such example is the recent announcement of of a collaboration between UK-based Haydale Graphene Industries plc and Korea-based ICRAFT Co., Ltd. that results in the release of a graphene cosmetic face mask. And I am pleased to be able to say that - in connection with my previous responsibilities for Haydale's Asia-Pacific operations - I had some role (together with my colleague Yong-jae "James" Ji) in getting this product off the ground and into the marketplace.
While this may seem like a trivial accomplishment given the context and seriousness of the current global pandemic, I offer this example as proof that graphene can be utilized in an everyday, cost-sensitive product, and it is not such a great conceptual leap to go from a cosmetic face mask to a protective face mask, which as we all know are in great demand these days (especially here in Asia). I would invite iCRAFT (or anyone else) to consider collaboration with planarTECH to develop such a product. (Above photo courtesy of Macau Photo Agency on Unsplash.)
Productization: Existing Products?
Very much related to this topic and very curious is a recent public announcement by LIGC Applications of its Guardian G-Volt face mask with a graphene-based filtration system. However, my understanding is that LIGC is not employing graphene specifically for it's potential antiviral properties but rather for its potential to enhance a filtration system, including (due to graphene's electrical conductivity) the ability to pass an electrical charge through the mask that "would repel any particles trapped in the graphene mask."
What I find very curious about this case is that subsequent to this announcement, LIGC's Indiegogo crowdfunding campaign, which was live, has now been placed under review, and the company's pitch video on YouTube has likewise been made private. I do not know what has happened here - perhaps is was perceived as poor timing? - but as a fellow entrepreneur who is conducting my own crowdfunding campaign, I wish LIGC the best of luck with its product development and ultimate launch. I definitely want to see more viable graphene products in the marketplace.
The Graphene Supply Chain: planarTECH's Role
One of the challenges the graphene industry faces overall is scalability. Very few graphene companies today (if any at all) can produce graphene at the scale, at the right cost, and with the consistent quality such that it can be used for truly high-volume applications. Over the past 8 years, I have met numerous customers, mostly in Asia, who want to use graphene in their products but cannot find a secure and stable supply that meets their expectations on specification, volume, and price.
At planarTECH we're interested in not only the end applications, but also in solving this problem of production scalability. While we have in the past mainly been focused on production systems for graphene and other 2D materials by Chemical Vapor Deposition (CVD), we also recently started offering continuous flow production systems for graphene oxide, which we believe can take graphene oxide production from lab-scale, high-cost (grams per week) to production-scale, low-cost (kilograms per hour). We're actively seeking partners to work with us on setting up production and exploration of the application space for graphene oxide, and we're currently conducting a crowdfunding campaign on Seedrs to help us expand our business and make graphene a commercial reality. As seen above, we think graphene oxide's antiviral properties can be exploited to make new and useful products.
I should clarify and caution that planarTECH is not in the position today to offer a graphene-based product that can immediately help alleviate current crisis and prevent widespread infection. Unfortunately, such a product is realistically 1-2 years away. But what we can offer is market expertise specific to graphene, production technologies, and experience in taking products from the idea phase to a reality in the marketplace.
Conclusion: Graphene is a Possible Solution
To conclude, I would like to reiterate a few broad points.
• Graphene (graphene oxide in particular) and coatings made from graphene would appear to have antiviral properties as reported in several published academic papers.
• Real commercial products exist that use graphene, but the industry as a whole still faces challenges around scalability, cost and quality.
• An immediate graphene-based solution to alleviate the effects of the global SARS-CoV-2 coronavirus pandemic is likely unrealistic, but could be possible in the future.
• planarTECH has a role in the supply chain and is seeking partners, as well as investors via its crowdfunding campaign, to expand its business and help end customers develop useful products.
The realistic mechanical properties of monolayer graphene have been successfully studied by a new method developed by a research team led by Dr Lu Yang, Associate Professor of Department of Mechanical Engineering at City University of Hong Kong (CityU). The groundbreaking discovery will promote the application of graphene in different areas, such as the touch monitor on flexible mobile phones.
Dr Lu’s research achievement has been published in the prestigious international journal Nature Communications, titled “Elastic straining of free-standing monolayer graphene.” This paper was also highlighted in “Editors' Choice” in the 21 February 2020 issue of Science.
A two-dimensional carbon substance, graphene is the strongest material known with excellent electrical and thermal conductivity. Hence, it is deemed a "super material", ideal for many fields, for example, transistors, biosensors and batteries.
Graphene’s structure as a single layer of atoms has made it extremely difficult for scientists to test its actual mechanical properties such as elasticity and tensile strength. The studies in this area so far have covered only its ideal limits by local indentation experiments and theoretical calculations.
“No one has really stretched a large-area, free-standing monolayer graphene and tested its elastic tensile properties,” Dr Lu said.
Over the years, Dr Lu has researched the mechanical properties of various nanomaterials. His research team has successfully developed a new method for transferring large-area graphene onto his unique nanomechanical testing platform, performing in situ tensile tests in a scanning electron microscope to study changes in stretching and shaping.
“One major challenge in our study is how to transfer and lay an extremely light and thin monolayer graphene sample onto a testing platform without damage, and apply the strain evenly when stretching it,” Dr Lu said.
The experiment showed that the tensile strength of chemical vapour deposition (CVD)-grown monolayer graphene can reach 50 to 60 GPa (gigapascal), with elastic strain up to 6%, and the measured Young’s modulus (or the “elastic modulus”) is 920 GPa, which is very close to the theoretical value of ~1,000 GPa. Pascals are units of measurement for stress.
“It took us nearly four years to overcome a lot of difficulties for the experiment, but our work has revealed the realistic mechanical properties of graphene for engineering relevance,” Dr Lu said.
Its strength and stretchability make graphene a suitable material for manufacturing flexible electronic devices, such as transistors with better robustness, organic light-emitting diodes, and other mechanical components.
It can also be used for the production of composite materials and in the areas of biomedical research, aviation and national defence.
Dr Lu said he was grateful to CityU for providing top-notch facilities for his team to conduct their research, such as the Nano-Manufacturing Laboratory at the CityU Shenzhen Research Institute, the Centre for Super-Diamond and Advanced Films, and the Centre for Advanced Structural Materials.
In addition, CityU’s emphasis on interdisciplinary collaboration helped his research. “Our experiment required experts from the disciplines of mechanics, materials science, chemistry and physics to work together, and the outstanding talents in these fields can be readily found at CityU,” Dr Lu said.
Members of the research team include PhD students Cao Ke and Han Ying in the Department of Mechanical Engineering and Dr Ly Thuc-hue, Assistant Professor in the Department of Chemistry, at CityU, as well as experts from Tsinghua University and Xidian University.
Graphene is a material that has been gaining fame in recent years due to its magnificent properties. In particular, for spintronics, graphene is a valuable material because the spins of the electrons used remain unaltered for a relatively long time. However, graphene needs to be produced on a large scale in order to be used in future devices. With that respect, chemical vapour deposition (CVD) is the most promising fabrication method.
CVD involves growing graphene on a metallic substrate at high temperatures. In this process, the generation of graphene starts at different points of the substrate simultaneously. This produces different single-crystal domains of graphene separated from one another through grain boundaries, consisting of arrays of five-, seven- or even eight-member carbon rings. The final product is, thus, polycrystalline graphene.
Is polycrystalline graphene as good as single-crystal graphene for spintronics? Grain boundaries are a significant source of charge scattering, increasing the electric resistance of the material. How do they affect spin transport?
Some experiments suggest that grain boundaries do not play a major role on spin transport. In this context, Dr Aron W. Cummings, from the ICN2 Theoretical and Computational Nanoscience Group, led by ICREA Prof. Stephan Roche, together with researchers from the Université catholique de Louvain (Belgium), have used first-principles simulations to study the impact of grain boundaries on spin transport in polycrystalline graphene. The study is published in Nano Letters.
The researchers have considered two different mechanisms by which spins could lose their original orientation (spin relaxation). One accounts for the randomisation of spins within the grains due to spin-orbit coupling, the other considers the possibility of the spins to flip due to scattering in a grain boundary. However, the researchers found that the latter case did not happen. Grain boundaries do not have any adverse effect on spin transport.
Therefore, spin diffusion length in polycrystalline graphene is independent of grain size and depends only on the strength of the substrate-induced spin-orbit coupling. Moreover, this is valid not only for the diffusive regime of transport, but also for the weakly localized one, in which quantum phenomena begin to prevail. This is the first quantum mechanical simulation confirming that the same expression for spin diffusion length holds in both regimes.
The research highlights the fact that single-domain graphene may not be a requirement for spintronics applications, and that polycrystalline CVD-grown graphene may work just as well. This puts the focus on other aspects to enhance in graphene production, such as the elimination of magnetic impurities.