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.
Graphene is a paradox: it is the thinnest material known to science, yet also one of the strongest. Now, research from U of T Engineering shows that graphene is also highly resistant to fatigue — able to withstand more than a billion cycles of high stress before it breaks.
Graphene resembles a sheet of interlocking hexagonal rings, similar to the pattern you might see in bathroom flooring tiles. At each corner is a single carbon atom bonded to its three nearest neighbours. While the sheet could extend laterally over any area, it is only one atom thick.
The intrinsic strength of graphene has been measured at more than 100 gigapascals, among the highest values recorded for any material. But materials don’t always fail because the load exceeds their maximum strength. Small repetitive stresses can weaken materials by causing microscopic dislocations and fractures that slowly accumulate over time, a process known as fatigue.
“To understand fatigue, imagine bending a metal spoon,” says Professor Tobin Filleter (MIE), one of the senior authors of the study, which was recently published in Nature Materials. “The first time you bend it, it just deforms. But if you keep working it back and forth, eventually it’s going to break in two.”
The research team — consisting of Filleter, fellow U of T Engineering professors Chandra Veer Singh (MSE) and Yu Sun (MIE), their students, and collaborators at Rice University — wanted to know how graphene would stand up to repeated stresses. Their approach included both physical experiments and computer simulations.
“In our atomistic simulations, we found that cyclic loading can lead to irreversible bond reconfigurations in the graphene lattice, causing catastrophic failure on subsequent loading,” says Singh, who along with postdoctoral fellow Sankha Mukherjee (MSE) led the modelling portion of the study. “This is unusual behaviour in that while the bonds change, there are no obvious cracks or dislocations, which would usually form in metals, until the moment of failure.”
PhD candidate Teng Cui, who is co-supervised by Filleter and Sun, used the Toronto Nanofabrication Centre to build a physical device for the experiments. The design consisted of a silicon chip etched with half a million tiny holes only a few micrometres in diameter. The graphene sheet was stretched over these holes, like the head of a tiny drum.
Using an atomic force microscope, Cui then lowered a diamond-tipped probe into the hole to push on the graphene sheet, applying anywhere from 20 to 85 per cent of the force that he knew would break the material.
“We ran the cycles at a rate of 100,000 times per second,” says Cui. “Even at 70 per cent of the maximum stress, the graphene didn’t break for more than three hours, which works out to over a billion cycles. At lower stress levels, some of our trials ran for more than 17 hours.”
As with the simulations, the graphene didn’t accumulate cracks or other tell-tale signs of stress — it either broke or it didn’t.
“Unlike metals, there is no progressive damage during fatigue loading of graphene,” says Sun. “Its failure is global and catastrophic, confirming simulation results.”
The team also tested a related material, graphene oxide, which has small groups of atoms such as oxygen and hydrogen bonded to both the top and bottom of the sheet. Its fatigue behaviour was more like traditional materials, in that the failure was more progressive and localized. This suggests that the simple, regular structure of graphene is a major contributor to its unique properties.
“There are no other materials that have been studied under fatigue conditions that behave the way graphene does,” says Filleter. “We’re still working on some new theories to try and understand this.”
In terms of commercial applications, Filleter says that graphene-containing composites — mixtures of conventional plastic and graphene — are already being produced and used in sports equipment such as tennis rackets and skis.
In the future, such materials may begin to be used in cars or in aircraft, where the emphasis on light and strong materials is driven by the need to reduce weight, improve fuel efficiency and enhance environmental performance.
“There have been some studies to suggest that graphene-containing composites offer improved resistance to fatigue, but until now, nobody had measured the fatigue behaviour of the underlying material,” he says. “Our goal in doing this was to get at that fundamental understanding so that in the future, we’ll be able to design composites that work even better.”
Two-dimensional materials are atomically thin, the most well-known being graphene, a single-atom-thick layer of carbon atoms. "People have struggled to make these 2D materials without defects," said Mauricio Terrones, Verne M. Willaman Professor of Physics, Penn State. "That's the ultimate goal. We want to have a 2D material on a four-inch wafer with at least an acceptable number of defects, but you want to evaluate it in a quick way."
The researchers' -- who represent Penn State, Northeastern University, Rice University and Universidade Federal de Minas Gerais in Brazil -- solution is to use laser light combined with second harmonic generation, a phenomenon in which the frequency of the light shone on the material reflects at double the original frequency. They add dark field imaging, a technique in which extraneous light is filtered out so that defects shine through. According to the researchers, this is the first instance in which dark field imaging was used, and it provides three times the brightness of the standard bright field imaging method, making it possible to see types of defects previously invisible.
"The localization and identification of defects with the commonly used bright field second harmonic generation is limited because of interference effects between different grains of 2D materials," said Leandro Mallard, a senior author on a recent paper in Nano Letters and a professor at Universidade Federal de Minas Gerais. "In this work we have shown that by the use of dark field SHG we remove the interference effects and reveal the grain boundaries and edges of semiconducting 2D materials. Such a novel technique has good spatial resolution and can image large area samples that could be used to monitor the quality of the material produced in industrial scales."
Vincent H. Crespi, Distinguished Professor of Physics, Materials Science and Engineering, and Chemistry, Penn State, added, "Crystals are made of atoms, and so the defects within crystals -- where atoms are misplaced -- are also of atomic size.
"Usually, powerful, expensive and slow experimental probes that do microscopy using beams of electrons are needed to discern such fine details in a material," said Crespi. "Here, we use a fast and accessible optical method that pulls out just the signal that originates from the defect itself to rapidly and reliably find out how 2D materials are stitched together out of grains oriented in different ways."
Another coauthor compared the technique to finding a particular zero on a page full of zeroes. "In the dark field, all the zeroes are made invisible so that only the defective zero stands out," said Yuanxi Wang, assistant research professor at Penn State's Materials Research Institute.
The semiconductor industry wants to have the ability to check for defects on the production line, but 2D materials will likely be used in sensors before they are used in electronics, according to Terrones. Because 2D materials are flexible and can be incorporated into very small spaces, they are good candidates for multiple sensors in a smartwatch or smartphone and the myriad of other places where small, flexible sensors are required.
"The next step would be an improvement of the experimental setup to map zero dimension defects -- atomic vacancies for instance -- and also extend it to other 2D materials that host different electronic and structural properties," said lead author Bruno Carvalho, a former visiting scholar in Terrones' group.
A new process introduced by the Rice University lab of chemist James Tour can turn bulk quantities of just about any carbon source into valuable graphene flakes. The process is quick and cheap; Tour said the “flash graphene” technique can convert a ton of coal, waste food or plastic into graphene for a fraction of the cost used by other bulk graphene-producing methods.
“This is a big deal,” Tour said. “The world throws out 30% to 40% of all food, because it goes bad, and plastic waste is of worldwide concern. We’ve already proven that any solid carbon-based matter, including mixed plastic waste and rubber tires, can be turned into graphene.”
As reported in Nature, flash graphene is made in 10 milliseconds by heating carbon-containing materials to 3,000 Kelvin (about 5,000 degrees Fahrenheit). The source material can be nearly anything with carbon content. Waste food, plastic waste, petroleum coke, coal, wood clippings and biochar are prime candidates, Tour said. “With the present commercial price of graphene being $67,000 to $200,000 per ton, the prospects for this process look superb,” he said.
Tour said a concentration of as little as 0.1% of flash graphene in the cement used to bind concrete could lessen its massive environmental impact by a third. Production of cement reportedly emits as much as 8% of human-made carbon dioxide every year.
“By strengthening concrete with graphene, we could use less concrete for building, and it would cost less to manufacture and less to transport,” he said. “Essentially, we’re trapping greenhouse gases like carbon dioxide and methane that waste food would have emitted in landfills. We are converting those carbons into graphene and adding that graphene to concrete, thereby lowering the amount of carbon dioxide generated in concrete manufacture. It’s a win-win environmental scenario using graphene.”
“Turning trash to treasure is key to the circular economy,” said co-corresponding author Rouzbeh Shahsavari, an adjunct assistant professor of civil and environmental engineering and of materials science and nanoengineering at Rice and president of C-Crete Technologies. “Here, graphene acts both as a 2D template and a reinforcing agent that controls cement hydration and subsequent strength development.”
In the past, Tour said, “graphene has been too expensive to use in these applications. The flash process will greatly lessen the price while it helps us better manage waste.”
“With our method, that carbon becomes fixed,” he said. “It will not enter the air again.”
The process aligns nicely with Rice’s recently announced Carbon Hub initiative to create a zero-emissions future that repurposes hydrocarbons from oil and gas to generate hydrogen gas and solid carbon with zero emission of carbon dioxide. The flash graphene process can convert that solid carbon into graphene for concrete, asphalt, buildings, cars, clothing and more, Tour said.
Flash Joule heating for bulk graphene, developed in the Tour lab by Rice graduate student and lead author Duy Luong, improves upon techniques like exfoliation from graphite and chemical vapor deposition on a metal foil that require much more effort and cost to produce just a little graphene.
Even better, the process produces “turbostratic” graphene, with misaligned layers that are easy to separate. “A-B stacked graphene from other processes, like exfoliation of graphite, is very hard to pull apart,” Tour said. “The layers adhere strongly together. But turbostratic graphene is much easier to work with because the adhesion between layers is much lower. They just come apart in solution or upon blending in composites.
“That’s important, because now we can get each of these single-atomic layers to interact with a host composite,” he said.
The lab noted that used coffee grounds transformed into pristine single-layer sheets of graphene.
Bulk composites of graphene with plastic, metals, plywood, concrete and other building materials would be a major market for flash graphene, according to the researchers, who are already testing graphene-enhanced concrete and plastic.
The flash process happens in a custom-designed reactor that heats material quickly and emits all noncarbon elements as gas. “When this process is industrialized, elements like oxygen and nitrogen that exit the flash reactor can all be trapped as small molecules because they have value,” Tour said.
He said the flash process produces very little excess heat, channeling almost all of its energy into the target. “You can put your finger right on the container a few seconds afterwards,” Tour said. “And keep in mind this is almost three times hotter than the chemical vapor deposition furnaces we formerly used to make graphene, but in the flash process the heat is concentrated in the carbon material and none in a surrounding reactor.
“All the excess energy comes out as light, in a very bright flash, and because there aren’t any solvents, it’s a super clean process,” he said.
Luong did not expect to find graphene when he fired up the first small-scale device to find new phases of material, beginning with a sample of carbon black. “This started when I took a look at a Science paper talking about flash Joule heating to make phase-changing nanoparticles of metals,” he said. But Luong quickly realized the process produced nothing but high-quality graphene.
Atom-level simulations by Rice researcher and co-author Ksenia Bets confirmed that temperature is key to the material’s rapid formation. “We essentially speed up the slow geological process by which carbon evolves into its ground state, graphite,” she said. “Greatly accelerated by a heat spike, it is also stopped at the right instant, at the graphene stage.
“It is amazing how state-of-the-art computer simulations, notoriously slow for observing such kinetics, reveal the details of high temperature-modulated atomic movements and transformation,” Bets said.
Tour hopes to produce a kilogram (2.2 pounds) a day of flash graphene within two years, starting with a project recently funded by the Department of Energy to convert U.S.-sourced coal. “This could provide an outlet for coal in large scale by converting it inexpensively into a much-higher-value building material,” he said.
Tour has a grant from the Department of Energy to scale up the flash graphene process, which will be co-funded by the start-up company, Universal Matter Ltd.
Co-authors of the paper include Rice graduate students Wala Ali Algozeeb, Weiyin Chen, Paul Advincula, Emily McHugh, Muqing Ren and Zhe Wang; postdoctoral researcher Michael Stanford; academic visitors Rodrigo Salvatierra and Vladimir Mancevski; Mahesh Bhatt of C-Crete Technologies, Stafford, Texas; and Rice assistant research professor Hua Guo. Boris Yakobson, the Karl F. Hasselmann Chair of Engineering and a professor of materials science and nanoengineering and of chemistry, is co-corresponding author.
Tour is the T.T. and W.F. Chao Chair in Chemistry as well as a professor of computer science and of materials science and nanoengineering at Rice.
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."
Microbiomes play essential roles in the natural processes that keep the planet and our bodies healthy, so it's not surprising that scientists' investigations into these diverse microbial communities are leading to advances in medicine, sustainable agriculture, cheap water purification methods, and environmental cleanup technology, just to name a few. However, trying to determine which microbes contribute to an important geochemical or physiological reaction is both incredibly challenging and slow-going, because the task involves analyzing enormous datasets of genetic and metabolic information to match the compounds mediating a process to the microbes that produced them.
But now, researchers have devised a new way to sort through the information overload.
Writing in Nature Methods, a team led by UC San Diego describes a neural network-based approach called microbe-metabolite vectors (mmvec), which uses probabilities to identify the most likely relationship of co-occurring microbes and metabolites. The team demonstrates how mmvec can outperform traditional correlation-based approaches by applying mmvec to datasets from two well-studied microbiomes types - those found in desert soils and cystic fibrosis patients' lungs - and gives a taste of how the approach could be used in the future by revealing relationships between microbially-produced metabolites and inflammatory bowel disease.
"Previous statistical tools used to estimate microbe-metabolite correlations performed comparably to random chance," said Marc Van Goethem, a postdoctoral researcher who is one of three study authors from Berkeley Lab. "Their poor performance led to the detection of spurious relationships and missed many true relationships. Mmvec is a powerful new tool that accurately links metabolite and microbial abundances to solve this problem. There could be wide-ranging applications from clinical trials to environmental engineering. Ultimately, mmvec will allow us to begin moving away from simple pattern recognition towards unravelling mechanisms."
When Solids and Liquids Meet: In Nanoscale Detail
How a liquid interacts with the surface of a solid is important in batteries and fuel cells, chemical production, corrosion phenomena, and many biological processes.
To better understand this solid-liquid interface, researchers at Berkeley Lab developed a platform to explore these interactions under real conditions ("in situ") at the nanoscale using a technique that combines infrared light with an atomic force microscopy (AFM) probe. The results were published in the journal Nano Letters.
The team explored the interaction of graphene with several liquids, including water and a common battery electrolyte fluid. Graphene is an atomically thin form of carbon. Its single-layer atomic structure gives the material some unique properties, including incredible mechanical strength and high electrical conductivity.
Researchers used a beam of infrared light produced at Berkeley Lab's Advanced Light Source and they focused it at the tip of an AFM probe that scanned across a section of graphene in contact with the liquids. The infrared technique provides a nondestructive way to explore the active nanoscale chemistry of the solid-liquid interface.
By measuring the infrared light scattered from the probe's tip, researchers collected details about the chemical compounds and the concentration of charged particles along the solid-liquid interface. The same technique, which revealed hidden features at this interface that were not seen using conventional methods, can be used to explore a range of materials and liquids.
Researchers from the Lab's Materials Sciences Division, Molecular Foundry, and Energy Storage and Distributed Resources Division participated in the study. The Molecular Foundry and Advanced Light Source are DOE Office of Science user facilities.
Underwater telecom cables make superb seismic network
Fiber-optic cables that constitute a global undersea telecommunications network could one day help scientists study offshore earthquakes and the geologic structures hidden deep beneath the ocean surface.
In a recent paper in the journal Science, researchers UC Berkeley, Lawrence Berkeley National Laboratory (Berkeley Lab), Monterey Bay Aquarium Research Institute (MBARI), and Rice University describe an experiment that turned 20 kilometers of undersea fiber-optic cable into the equivalent of 10,000 seismic stations along the ocean floor. During their four-day experiment in Monterey Bay, they recorded a 3.5 magnitude quake and seismic scattering from underwater fault zones.
Their technique, which they had previously tested with fiber-optic cables on land, could provide much-needed data on quakes that occur under the sea, where few seismic stations exist, leaving 70% of Earth's surface without earthquake detectors.
"This is really a study on the frontier of seismology, the first time anyone has used offshore fiber-optic cables for looking at these types of oceanographic signals or for imaging fault structures," said Jonathan Ajo-Franklin, a geophysics professor at Rice University in Houston and a faculty scientist at Berkeley Lab. "One of the blank spots in the seismographic network worldwide is in the oceans."
Rice University researchers determined complementarity between growing hexagonal boron nitride crystals and a stepped substrate mimics the complementarity found in strands of DNA. The Rice theory supports experiments that have produced large, oriented wafers.
Very small steps make a big difference to researchers who want to create large wafers of two-dimensional material. Atom-sized steps in a substrate provide the means for 2D crystals growing in a chemical vapor furnace to come together in perfect rank. Scientists have recently observed this phenomenon, and now a Rice University group has an idea why it works.
Rice materials theorist Boris Yakobson and researcher Ksenia Bets led the construction of simulations that show atom-sized steps on a growth surface, or substrate, have the remarkable ability to keep monolayer crystal islands in alignment as they grow. If the conditions are right, the islands join into a larger crystal without the grain boundaries so characteristic of 2D materials like graphene grown via chemical vapor deposition (CVD). That preserves their electronic perfection and characteristics, which differ depending on the material.
Atom-sized steps in a substrate provide the means for 2D crystals growing in a chemical vapor furnace to come together in perfect rank. Scientists have recently observed this phenomenon, and now a Rice University group has an idea why it works.
Rice materials theorist Boris Yakobson and researcher Ksenia Bets led the construction of simulations that show atom-sized steps on a growth surface, or substrate, have the remarkable ability to keep monolayer crystal islands in alignment as they grow.
If the conditions are right, the islands join into a larger crystal without the grain boundaries so characteristic of 2D materials like graphene grown via chemical vapor deposition (CVD). That preserves their electronic perfection and characteristics, which differ depending on the material.
The Rice theory appears in the American Chemical Society journal Nano Letters.The investigation focused on hexagonal boron nitride (h-BN), aka white graphene, a crystal often grown via CVD. Crystals nucleate at various places on a perfectly flat substrate material and not necessarily in alignment with each other.
However, recent experiments have demonstrated that growth on vicinal substrates -- surfaces that appear flat but actually have sparse, atomically small steps -- can align the crystals and help them merge into a single, uniform structure, as reported on arXiv. A co-author of that report and leader of the Korean team, Feng Ding, is an alumnus of the Yakobson lab and a current adjunct professor at Rice.
But the experimentalists do not show how it works as, Yakobson said, the steps are known to meander and be somewhat misaligned.
"I like to compare the mechanism to a 'digital filter,' here offered by the discrete nature of atomic lattices," he said. "The analog curve that, with its slopes, describes a meandering step is 'sampled and digitized' by the very grid of constituent atomic rows, breaking the curve into straight 1D-terrace segments. The slope doesn't help, but it doesn't hurt. Surprisingly, the match can be good; like a well-designed house on a hill, it stands straight.
"The theory is simple, though it took a lot of hard work to calculate and confirm the complementarity matching between the metal template and the h-BN, almost like for A-G-T-C pairs in strands of DNA," Yakobson said.
It was unclear why the crystals merged into one so well until simulations by Bets, with the help of co-author and Rice graduate student Nitant Gupta, showed how h-BN "islands" remain aligned while nucleating along visibly curved steps.
"A vicinal surface has steps that are slightly misaligned within the flat area," Bets said. "It has large terraces, but on occasion there will be one-atom-high steps. The trick by the experimentalists was to align these vicinal steps in one direction."
In chemical vapor deposition, a hot gas of the atoms that will form the material are flowed into the chamber, where they settle on the substrate and nucleate crystals. h-BN atoms on a vicinal surface prefer to settle in the crook of the steps.
"They have this nice corner where the atoms will have more neighbors, which makes them happier," Bets said. "They try to align to the steps and grow from there.
"But from a physics point of view, it's impossible to have a perfect, atomically flat step," she said. "Sooner or later, there will be small indentations, or kinks. We found that at the atomic scale, these kinks in the steps don't prevent h-BN from aligning if their dimensions are complementary to the h-BN structure. In fact, they help to ensure co-orientation of the islands."
Because the steps the Rice lab modeled are 1.27 angstroms deep (an angstrom is one-billionth of a meter), the growing crystals have little trouble surmounting the boundary. "Those steps are smaller than the bond distance between the atoms," Bets said. "If they were larger, like two angstroms or higher, it would be more of a natural barrier, so the parameters have to be adjusted carefully."
Two growing islands that approach each other zip together seamlessly, according to the simulations. Similarly, cracks that appear along steps easily heal because the bonds between the atoms are strong enough to overcome the small distance.
Any path toward large-scale growth of 2D materials is worth pursuing for an army of applications, according to the researchers. 2D materials like conductive graphene, insulating h-BN and semiconducting transition metal dichalcogenides are all the focus of intense scrutiny by researchers around the world. The Rice researchers hope their theoretical models will point the way toward large crystals of many kinds.
The U.S. Department of Energy (DOE) supported the research. Computer resources were provided by the National Energy Research Scientific Computing Center, supported by the DOE Office of Science, and the National Science Foundation-supported DAVinCI cluster at Rice, administered by the Center for Research Computing and procured in partnership with Rice's Ken Kennedy Institute for Information Technology.
Posted By Graphene Council,
Monday, February 18, 2019
Updated: Monday, February 18, 2019
Laser-induced graphene (LIG), a flaky foam of the atom-thick carbon, has many interesting properties on its own but gains new powers as part of a composite.
The labs of Rice University chemist James Tour and Christopher Arnusch, a professor at Ben-Gurion University of the Negev in Israel, introduced a batch of LIG composites in the American Chemical Society journal ACS Nano that put the material’s capabilities into more robust packages.
By infusing LIG with plastic, rubber, cement, wax or other materials, the lab made composites with a wide range of possible applications. These new composites could be used in wearable electronics, in heat therapy, in water treatment, in anti-icing and deicing work, in creating antimicrobial surfaces and even in making resistive random-access memory devices.
The Tour lab first made LIG in 2014 when it used a commercial laser to burn the surface of a thin sheet of common plastic, polyimide. The laser’s heat turned a sliver of the material into flakes of interconnected graphene. The one-step process made much more of the material, and at far less expense, than through traditional chemical vapor deposition.
Since then, the Rice lab and others have expanded their investigation of LIG. Last year, the Rice researchers created graphene foam for sculpting 3D objects.
“LIG is a great material, but it’s not mechanically robust,” said Tour, who co-authored an overview of laser-induced graphene developments in the Accounts of Chemical Research journal last year. “You can bend it and flex it, but you can’t rub your hand across it. It’ll shear off. If you do what’s called a Scotch tape test on it, lots of it gets removed. But when you put it into a composite structure, it really toughens up.”
To make the composites, the researchers poured or hot-pressed a thin layer of the second material over LIG attached to polyimide. When the liquid hardened, they pulled the polyimide away from the back for reuse, leaving the embedded, connected graphene flakes behind.
Soft composites can be used for active electronics in flexible clothing, Tour said, while harder composites make excellent superhydrophobic (water-avoiding) materials. When a voltage is applied, the 20-micron-thick layer of LIG kills bacteria on the surface, making toughened versions of the material suitable for antibacterial applications.
Composites made with liquid additives are best at preserving LIG flakes’ connectivity. In the lab, they heated quickly and reliably when voltage was applied. That should give the material potential use as a deicing or anti-icing coating, as a flexible heating pad for treating injuries or in garments that heat up on demand.
“You just pour it in, and now you transfer all the beautiful aspects of LIG into a material that’s highly robust,” Tour said.
Rice graduate students Duy Xuan Luong and Kaichun Yang and former postdoctoral researcher Jongwon Yoon, now a senior researcher at the Korea Basic Science Institute, are co-lead authors of the paper. Co-authors are former Rice postdoctoral researcher Swatantra Singh, now at the Indian Institute of Technology Bombay, and Rice graduate student Tuo Wang. 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.
The Air Force Office of Scientific Research and the United States-Israel Binational Science Foundation supported the research.
This image from a high-resolution transmission electron microscope shows one of Rice University’s graphene-based MRI contrast agents, nanoparticles measuring about 10-nanometers in diameter that are so thin that they are difficult to distinguish. Credit: C.S. Tiwari/Rice University
Graphene, the atomically thin sheets of carbon that materials scientists are hoping to use for everything from nanoelectronics and aircraft de-icers to batteries and bone implants, may also find use as contrast agents for magnetic resonance imaging (MRI), according to new research from Rice University.
"They have a lot of advantages compared with conventionally available contrast agents," Rice researcher Sruthi Radhakrishnan said of the graphene-based quantum dots she has studied for the past two years. "Virtually all of the widely used contrast agents contain toxic metals, but our material has no metal. It's just carbon, hydrogen, oxygen and fluorine, and in all of our tests so far it has shown no signs of toxicity."
The initial findings for Rice's nanoparticles—disks of graphene that are decorated with fluorine atoms and simply organic molecules that make them magnetic—are described in a new paper in the journal Particle and Particle Systems Characterization.
Pulickel Ajayan, the Rice materials scientist who is directing the work, said the fluorinated graphene oxide quantum dots could be particularly useful as MRI contrast agents because they could be targeted to specific kinds of tissues.
"There are tried-and-true methods for attaching biomarkers to carbon nanoparticles, so one could easily envision using these quantum dots to develop tissue-specific contrast agents," Ajayan said. "For example, this method could be used to selectively target specific types of cancer or brain lesions caused by Alzheimer's disease. That kind of specificity isn't available with today's contrast agents."
Rice University graduate student Sruthi Radhakrishnan spent two years developing a process to make graphene-based quantum dots that could be used as MRI contrast agents. Credit: Jeff Fitlow/Rice University
MRI scanners make images of the body's internal structures using strong magnetic fields and radio waves. As diagnostic tests, MRIs often provide greater detail than X-rays without the harmful radiation, and as a result, MRI usage has risen sharply over the past decade. More than 30 million MRIs are performed annually in the U.S.
Radhakrishnan said her work began in 2014 after Ajayan's research team found that adding fluorine to either graphite or graphene caused the materials to show up well on MRI scans.
All materials are influenced by magnetic fields, including animal tissues. In MRI scanners, a powerful magnetic field causes individual atoms throughout the body to become magnetically aligned. A pulse of radio energy is used to disrupt this alignment, and the machine measures how long it takes for the atoms in different parts of the body to become realigned. Based on these measures, the scanner can build up a detailed image of the body's internal structures.
MRI contrast agents shorten the amount of time it takes for tissues to realign and significantly improve the resolution of MRI scans. Almost all commercially available contrast agents are made from toxic metals like gadolinium, iron or manganese.
"We worked with a team from MD Anderson Cancer Center to assess the cytocompatibility of fluorinated graphene oxide quantum dots," Radhakrishnan said. "We used a test that measures the metabolic activity of cell cultures and detects toxicity as a drop in metabolic activity. We incubated quantum dots in kidney cell cultures for up to three days and found no significant cell death in the cultures, even at the highest concentrations."
Unlike most currently used MRI contrast agents, Rice University’s fluorinated graphene oxide quantum dots contain no toxic metals and could potentially be targeted to specific kinds of tissues. Credit: Jeff Fitlow/Rice University
The fluorinated graphene oxide quantum dots Radhakrishnan studies can be made in less than a day, but she spent two years perfecting the recipe for them. She begins with micron-sized sheets of graphene that have been fluorinated and oxidized. When these are added to a solvent and stirred for several hours, they break into smaller pieces. Making the material smaller is not difficult, but the process for making small particles with the appropriate magnetic properties is exacting.
Radhakrishnan said there was no "eureka moment" in which she suddenly achieved the right results by stumbling on the best formula. Rather, the project was marked by incremental improvements through dozens of minor alterations.
"It required a lot of optimization," she said. "The recipe matters a lot."
Radhakrishnan said she plans to continue studying the material and hopes to eventually have a hand in proving that it is safe and effective for clinical MRI tests.
"I would like to see it applied commercially in clinical ways because it has a lot of advantages compared with conventionally available agents," she said.