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Electronics Applications for Graphene Still Hold Center Stage

Posted By Terrance Barkan, Wednesday, September 21, 2016

While membranes for separation technologies may be an attractive application for graphene, it will continue to be offered up as an alternative in electronic applications


The applications that have really spurred the huge amount of graphene and other two-dimensional (2D) material research over the years have come from the field of electronics. The fear that complementary metal–oxide–semiconductor (CMOS) technology is quickly nearing the end of its ability to ward off Moore’s Law, in which the number of transistors in a dense integrated circuit doubles approximately every two years, has been the spur for much graphene research.


However, there has always been the big problem for graphene that it does not have an intrinsic band gap. It’s a pure conductor and not a semiconductor, like silicon, capable turning on and off the flow of electrons through it. While graphene can be functionalized in a way that it does have a band gap, research for it in the field of electronics have looked outside of digital logic where an intrinsic band gap is such an advantage. 


In the stories below, we see how graphene’s unrivaled conductivity is being exploited to take advantage of its strengths rather than trying to cover up for its weaknesses


Graphene Comes to the Rescue of Li-ion Batteries



The role of graphene in increasing the charge capacity of the electrodes in lithium-ion (Li-ion) batteries has varied. There’s been “decorated graphene” in which nanoparticles are scattered across the surface of the graphene, and graphene nanoribbons, just to name a few of the avenues that have been pursued.


Another way in which graphene has been looked at is to better enable silicon to serve as the electrode material for Li-ion batteries. Silicon is a great material for increasing the storage capacity of electrodes in Li-ion batteries, but there’s one big problem: it cracks after just few charge/discharge cycles. The aim has been to find a way to make silicon so that it’s not so brittle and can withstand the swelling and shrinking during the charge charging and discharing of lithium atoms into the electrode material In these efforts, like those out of Northwestern University, the role of graphene has been to sandwich silicon between layers graphene sheets in the anode of the battery.


Now, Yi Cui from both Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory, who has been at the forefront of research to get silicon to be more flexible and durable for Li-ion batteries, has turned to graphene to solve the issue. 


Cui and his colleagues were able to demonstrate in research described in the journal Nature Energy, a method for to encasing each particle of silicon in a cage of graphene that enables the silicon to expand and contract without cracking. In a full-cell electrochemical test, the graphene-infused silicon anodes retained 90 percent of their charge capacity after 100 charge-discharge cycles. 


Previous attempts by Cui and many others to create nanostructured silicon has been very difficult, making mass production fairly impractical. However, based on these latest results, Cui believes that this approach is not only technologically possible, but may in fact be commercially viable.


The process involves coating the silicon particles with a layer of nickel. The nickel coating is used as the surface and the catalyst for the second step: growing the graphene. The final step of the process involves using an acid on the graphene-coated silicon particles so that the nickel is etched away.


“This new method allows us to use much larger silicon particles that are one to three microns, or millionths of a meter, in diameter, which are cheap and widely available,” Cui said in a press release. “Particles this big have never performed well in battery anodes before, so this is a very exciting new achievement, and we think it offers a practical solution.”


While a practical manufacturing approach was much needed, the technique also leads to an electrode material with very high charge capacity.


“Researchers have tried a number of other coatings for silicon anodes, but they all reduced the anode’s efficiency,” said Stanford postdoctoral researcher Kai Yan, in a press release. “The form-fitting graphene cages are the first coating that maintains high efficiency, and the reactions can be carried out at relatively low temperatures.”


Graphene Provides the Perfect Touch to Flexible Sensors


Flexible sensors are the technological backbone of artificial skin technologies. The idea is that you can impart the sense of touch to a flexible sensor, making it possible to cover a prosthetic device for either a robot or replacement limb so it can feel. Creating materials that tick the boxes of flexibility, durability and sensitivity has been a challenge. Over the years, researchers have increasingly turned to nanomaterials, and graphene in particular, as a possible solution. 


Researchers at the University of Tokyo have found that nanofibers produced from a combination of carbon nanotubes and graphene overcomes some of the big problems facing flexible pressure sensors: they’re not that accurate after being bent or deformed. The researchers have suggested that the flexible sensor they have developed could provide a more accurate detection breast cancer.


In research described in the journal Nature Nanotechnology, the scientists produced their flexible sensor by employing organic transistors and a pressure sensitive nanofiber structure.


The researchers constructed the nanofiber structure using nanofibers with diameters ranging between 300 to 700 nanometers. The researchers produced the nanofibers by combining carbon nanotubes and graphene and mixing that into a flexible polymer. The nanofibers entangled with each other to form a thin, transparent structure.


In contrast to other flexible sensors in which the striving for accuracy makes the sensors too sensitive to being deformed in any way, the fibers in this new flexible sensor does not lose their accuracy in measuring pressures. These fibers achieve this because of their ability to change their relative alignment to accommodate the bending. This allows them to continue measuring pressure because it reduces the strain in individual fibers.


Tunable Graphene Plasmons Lead to Tunable Lasers



A few years ago, researchers found that the phenomenon that occurs when photons strike a metallic surface and stir up the movement of electrons on the surface to the point where the electrons form into waves—known as surface plasmons—also occurs in graphene


This discovery along with the ability to tune the graphene plasmons has been a big boon for the use of graphene in optoelectronic applications. Now research out of the University of Manchester, led by Konstantin Novoselov, who along with Andre Geim were the two University of Manchester scientists who won the Nobel Prize for discovering graphene, has leveraged the ability of tuning graphene plasmons and combined it with terahertz quantum cascade lasers, making it possible to reversibly alter their emission. 


This ability to reversibly the alter the emission of quantum cascade lasers is a big deal in optoelectronic applicatiopns, such as fiber optics telecommunication technologies by offering potentially higher bandwidth capabilities.


“Current terahertz devices do not allow for tunable properties, a new device would have to be made each time requirements changed, making them unattractive on an industrial scale,” said Novoselov in a press release. “Graphene however, can allow for terahertz devices to be switched on and off, as well as altering their state.”


In research described in the journal Science, were able to manipulate the doping levels of a graphene sheet so that it generated plasmons on its surface. When this doped graphene sheet was combined with a terahertz quantum cascade laser, it became possible to tune the transmission of the laser by tuning the graphene plasmons, essentially changing the concentration of charge carriers.


Graphene Flakes Speed Up Artificial Brains



Researchers out of Princeton University have found that graphene flakes could be a key feature in computer chips that aim at mimicking the function of the human brain. 

In the human brain, neurons are used to transmit information by passing electrical charges through them. In artificial brains, transistors would take the place of neurons. One approach has been to construct the transistors out of lasers that would turn and off and the time intervals between the on and off states of the lasers would represent the 1s and 0s of digital logic.


One of the challenges that researchers have faced in this design is getting the time intervals between the laser pulses down to picosecond time scales, one trillionth of a second.


In research described in the journal Nature Scientific Reports, the Princeton researchers placed graphene flakes inside a semiconductor laser to act as a kind of “saturable absorber,” that absorbed photons and then was able to emit them in a quick burst. 


It turns out graphene possesses a number of properties that makes it attractive for this application. Not only can it absorb and release photons extremely quickly, but it can also work at any wavelength. What this means is that even if semiconductor lasers are emitting different colors, the graphene makes it possible for them to work together simultaneously without interfering with each other, leading to higher processing speeds.

Tags:  Batteries  Electronics  Flexible electronics  Lasers  Li-ion  Sensors 

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The Graphene Supply Chain is Maturing, But It Still Needs Some Guidance

Posted By Dexter Johnson, Friday, August 26, 2016

An interview with the Tom Eldridge, Director of UK-based Fullerex Limited


One of the big stories for graphene going forward is the continued maturation of its supply chain. 


Producers of graphene are getting better at understanding not only how to make graphene more cost effectively and with a higher quality, but also are figuring out what kind of graphene to make. The intermediaries—the companies that functionalize graphene and have the knowhow to disperse it in a material matrix—are gaining a more defined role in the supply chain. And finally, the companies who are trying to make something out of graphene, like a tennis racquet, or a supercapacitor, are developing a greater sense of trust in the supply chain.


One company that has been at the forefront of securing that supply chain is UK-based Fullerex Limited. Fullerex helps both ends of the supply chain work out how unmet needs can be satisfied. 


In this interview we discuss with the director of Fullerex, Tom Eldridge, the nature of the company’s business and how sees the market developing over the short term.


Q: For people that come to The Graphene Council website, they may be familiar with Fullerex’s pricing index and your Bulk Graphene Pricing Report, but that is only a small part of your business, correct? Could you describe what service Fullerex provides and to whom?


Our main activity as a business includes providing a brokering service for advanced materials and technology, specializing in nanomaterials and nano-intermediates. The company has twenty partners worldwide, which it represents on an agency basis. These firms include producers of various nanomaterials such as novel carbon allotropes for example fullerenes, carbon nanotubes and graphene and also technology solutions providers related to the downstream processing of these materials.


Fullerex supports these strategically placed partners in developing the market for their products and technologies by identifying suitable collaborators and potential early adopters in industry. Typically we help end-users looking to address an unmet need through material innovations. We are able to generate interest in trialing and testing certain nanomaterial types and key enabling technologies by making introductions between the right people.


The annual graphene pricing report forms part of our ancillary services. Fullerex first released the Bulk Graphene Pricing Report in 2014, which has now seen three editions with continual updates each year to the data and analysis contained within the pricing study.


Q: It would seem then that you enable both graphene producers and the end users to better understand what kind of graphene might best work for each potential application, correct?


Our value proposition is to accelerate growth in the market for materials such as graphene. This not only entails understanding the potential applications for graphene and finding end-users that are committed to materials R&D but yes, also having knowledge of the relevant types of graphene for those uses. Producers themselves have differing degrees of expertise between them when it comes to certain application areas.


A core role of Fullerex is to select the technical expertise and materials from our range of partners to best meet the requirements of a given end-user. In addition, a critically important component of pre-screening these opportunities involves understanding the cost implications and whether the use of graphene makes sense for the target market. These technical and commercial considerations combined are at the forefront of the decision making and strategy for our business.


Q: What range of applications for graphene do you offer for this kind of service? Could you provide some examples of the kind of information that it is important for both graphene producers and end users to understand before the material can be effectively applied?


Graphene can be very broadly thought of as supplied in two main material forms: as a powder or as a continuous thin film. Fullerex focuses very much on the former type of product. By adding the graphene powder to various base materials you can improve properties of the base material or add properties that perhaps were not there before, creating multifunctional materials.


The markets for this type of graphene include polymers and composites, coatings, inks, lubricating oils, construction materials etc. For an effective application it is important to establish what performance goals the end-user is looking to achieve and for what purpose, what is the price sensitivity of the target market and what are the potential quantity demands if the new product is successfully developed. Essentially, is there a good business case?


Q: Where is the biggest gap in information? Do the producers not understand how their product should be targeted or are the end users lacking an understanding of the kind of graphene that will work for them?


There are information gaps on both sides. Many potential end-users are simply not aware of all the potential applications for graphene and remain unconvinced until a producer can demonstrate clear advantages with a product that can be easily trialed, that is compatible with existing manufacturing processes and does not require significant investment to implement (by acquiring new technical capabilities in terms of equipment or expertise). To get to this stage takes development work which some end-users may be prepared to fund to generate unique IP but for the most part, it is expected of the producer to build that capability internally or through its close network and partnerships.


Q: Further to the previous information gap question, how do you see the investment community at this point when it comes to graphene? Are you explaining what it is and what it can do for them, or are you discussing investment opportunity points with them?


Our client base is exclusively comprised of commercial enterprises and not members of the investment community. However, as a general comment, one aspect of business strategy for graphene companies which may have an impact in terms of attracting investors is the potential to position the business either in terms of offering a product geared towards a particular market or offering a platform technology with wider scope than just one application.


This comes back to expertise, since to focus on one application area in particular may make it quicker and easier to develop those applications and demonstrate a clear advantage to potential customers but it also narrows the addressable market for the business and therefore may remain interesting only to certain investors looking in that area.


Q: At this point, do you have a breakdown of the graphene market, i.e. how much graphene is being sold worldwide and how that amount breaks down into material types and appropriate applications?


The analysis that we have carried out for our pricing report extends to including some top line figures about the market in terms of the overall market size and segmentation between bulk graphene and graphene thin films.


Q: As this market stands now, what application area do you see as being the most successful today? And where do you see the most promise in the near term of the next five years?


The first commercial applications have arrived in the form of sporting goods ranging from tennis rackets, skis, bicycle tires and sports clothing. The criticism often laid against these examples is that consumer products can be marketed successfully on perceived advantages rather than necessarily offering any demonstrable improvement.


Industrial applications on the other hand are more uncompromising and certainly demand an obvious cost-benefit. As such there are fewer examples of this kind to point towards. Industry uses are starting to emerge however and I see polymer applications being the area, which will bring the majority of uses for graphene over the next few years, in plastics, composites, coatings and 3D printing in particular.


Q: Based on your work, what would be some of the key points of advice you would pass on to producers and end users to start exploiting graphene to its full potential?


Collaboration is key, whether that is between graphene producers and early adopters, enabling technology companies, manufacturing partners, or academia. Applications cannot be developed unless there are all the right elements of the value chain in sync. Moving towards large-scale adoption of the technology requires consistency in supply and this is one of the reasons there is such a strong focus on characterization and standards across the emerging industry. This is an international effort.


Finally, graphene has such unique properties with potential to make a positive impact in economic terms and societal terms across so many areas that it is important to engage as many relevant organizations as possible to build the community of stakeholders.


Tags:  Commercialization  Fullerex  Graphene  Products 

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