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Prototype of future phone completed at University of Tartu

Posted By Graphene Council, The Graphene Council, Wednesday, March 6, 2019
Updated: Wednesday, March 6, 2019

Physicists at the University of Tartu have been working on a graphene-based sensor for the last five years. This sensor, to be integrated into mobile phones, will actively monitor toxic substances in the ambient air and recommend to the person carrying it to choose a safer route. The prototype has now been completed and was introduced to mobile phone manufacturers at a major event in Barcelona.

“Whereas earlier we were only able to test it in the laboratory, now we have the chance to test the technology in the real environment – outdoors,” said Raivo Jaaniso, Senior Research Fellow at the University of Tartu. “There’s still a long way to go, and since we’re getting closer to our goal, the need for investment is increasing quite a lot.”

The World Mobile Congress, which was held in Barcelona from 25-28 February, is the largest fair in the world showcasing future technology. The aims of the researchers on the graphene project are to establish closer relations with mobile phone manufacturers on site and to continue development work. “Our next goal is to make a new prototype in which everything’s considerably smaller and from which it’ll be just one more step to the finished product,” explained Jaaniso. Among other things, long-term stability still needs to be thoroughly tested. According to Jaaniso, 30-40 people should test the device in daily use during the pilot project.

The sensor developed by the researchers at the University of Tartu differs from others available on the market in terms of its sensitivity. It also works successfully outside when the concentration of toxic substances is low, warning the person carrying it against, for example, vehicle exhaust emissions. “It works in more or less the same way as the human nose,” said Jaaniso.

The researchers at the University of Tartu are developing a graphene-based sensor within the framework of the pan-European research partnership project ‘Graphene Flagship’. With a budget of €1 billion, the project aims to develop graphene-based future technology solutions and brings together researchers from 23 countries. Besides the sensor the Estonians are working on, touch screens, superbatteries, smart clothes and 5G Internet hardware are also being developed.

Tags:  Graphene  Raivo Jaaniso  Sensors  University of Tartu 

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Graphene-alumina heterostructures show their strength

Posted By Graphene Council, The Graphene Council, Monday, March 4, 2019
Updated: Monday, March 4, 2019

Heterostructures of graphene and other 2D or ultrathin materials have potential applications in sensing, electronics, and battery technology. For example, graphene transistors encapsulated with alumina (Al2O3) are of interest for flexible electronics, and graphene/metal oxide heterostructures are widely used in lithium ion batteries.

The mechanical strength, properties and stability of these structures is important for applications that make use of flexibility, or for applications that put to test the mechanical robustness of the materials, such as in high-performance electrochemical cells. Nevertheless, the mechanical properties of graphene heterostructures have not been widely and carefully investigated.



Now, an international team from the US, Germany and Spain have performed careful tests of graphene/alumina heterostructures for varying thickness of the alumina layer. The research revealed that graphene enhances the stiffness (Young’s modulus) compared to bare alumina, and that the alumina film strengthens the resistance of graphene to fracture under load. These findings indicate that such heterostructures have good mechanical strength and can thus be utilized in many devices. The measured values of stiffness and breaking strength add to the expanding body of knowledge of mechanical properties of graphene-related materials.

The method presented in the paper, published in the journal Nanotechnology, blends state-of-the-art fabrication, characterization, and calculation. The basis of the heterostructures is graphene on TEM grids, a single atomic layer of graphene deposited on a grid of circular holes. The monolayer graphene is thus suspended over the holes, making membranes with a diameter of two micrometers.

Alumina is deposited on top of the graphene with atomic layer deposition (ALD), with thickness ranging from 1.5nm to 4.5nm. The mechanical properties are tested with atomic force microscopy, by landing an extremely sharp tip on top of the membrane, pushing on the membrane and studying the deflection. In strength tests, the membrane is pushed until it ruptures under load. The resulting force-distance curves are compared to results of finite element numerical calculations, yielding a quantitative measure of the mechanical properties.

The calculations further revealed a nonintuitive shear stress distribution which indicates a maximum shear away from the line of symmetry and closer to the point of contact of diamond tip and the film, which is a key finding for reliable mechanical performance of the composite devices.

Additionally, these findings illustrate the versatility of ALD techniques for use in heterostructure fabrication, and ease of implementation of graphene into thin-film hybrid structures in order to take advantage of its superior mechanical properties.

Tags:  Battery  Graphene  Li-ion batteries  Sensors 

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Grolltex Drives Dramatic Increase of Single Layer CVD Graphene Production

Posted By Graphene Council, The Graphene Council, Monday, February 25, 2019
Updated: Monday, February 25, 2019

Graphene and 2D materials producer,Grolltex has completed its recent capacity expansion and released production for 30,000 eight-inch wafer equivalents per year at its CVD monolayer fabrication facility in San Diego, California. This ‘single atomic layer’ type of graphene is used in advanced electronics and other nano-devices and supports many use cases in wearables, IoT, photonics, semiconductors, biosensing and other next generation devices.

“This is the only commercial CVD monolayergraphene production facility in California and in fact it is the largest capacity plant of its kind in the U.S.”, said CEO, Jeff Draa. “Demand for our electronics grade graphene has never been better.  Our production lines are capable of producing single layer graphene or single layer hexagonal Boron Nitride”.
Otherwise known as ‘white graphene’, hexagonal Boron Nitride (or ‘hBN’) is the single atom thick insulator complement to graphene, which is a conductor.  The material hBN also has many other interesting characteristics, including being highly transparent, very strong, possesses anti-microbial and flame-retardantproperties and is additionally a performance accelerator for graphene.  The Grolltex factory expansion supports the growth, production and transfer of both of thesesingle layer materials.

“Maybe even more exciting, we currently have four active evaluations where our customers’advanced nano-factories are testing our graphene for use as the basis for their final devices and each factory eval is going very well”, said Draa.  “The biosensing area is an early adopter for our graphene, as evidenced by customers using our material to detect DNA, find diseases in blood, monitor glucose in sweat in the form of a wearable patch and validating the safety and efficacy of new drugs in previously unthinkably short times and low costs.”

Grolltex, short for ‘graphene-rolling-technologies’, makes large area, single atom thick graphene sheets using chemical vapor deposition or ‘CVD’; essentially the process is depositing gas in a chamber, then allowing it to cool, which leaves a continuous one atom thick layer of carbon on a target substrate.  This type of graphene is highly valued for its electrical characteristics, strength and flexibility and some see it as‘next generation silicon’.

The company uses patented research and techniques initially developed at the University of California, San Diego, to produce high quality, single layer graphene, hexagonal Boron Nitride and other 2D materials and products.  The company is a practitioner of, and specializes in, exclusively sustainable graphene production methods and is committed to advancing the field of graphene to improve the future of leading-edge materials science and product design through the optimization of single atom thick materials.

Tags:  Biosensor  CVD  Graphene  Grolltex  Jeff Draa  Sensors 

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Graphene Sensors will be part of the International Space Station

Posted By Graphene Council, The Graphene Council, Friday, February 22, 2019
Updated: Friday, February 22, 2019

A new version of equipment developed in Brazil – the Solar-T –  will be sent to the International Space Station (ISS) to measure solar flares. It is estimated that the Sun-THz, the name given to the new photometric telescope, will be launched in 2022 on one of the missions to the ISS and will remain there to take consistent measurements.



The photometric telescope works at a frequency of 0.2 to 15 THz, which can only be measured from space. In parallel, another telescope, the HATS, will be installed in Argentina. That instrument, which will be ready in 2020, will work at a frequency of 15 THz on the ground. The HATS is being constructed as part of a Thematic Project led by Guillermo Giménez de Castro, a professor at the Mackenzie Radio Astronomy and Astrophysics Center (CRAAM) at Mackenzie Presbyterian University (UPM).

The equipment was part of the subject matter presented during the session given by Giménez de Castro at FAPESP Week London, February 11-12, 2019.

The researcher explained that solar explosions, or flares, are phenomena that occur on the Sun’s surface, causing high levels of radiation in outer space. 

The Sun THz is an enhanced version of the Solar-T, a double photometric telescope that was launched in 2016 by NASA in Antarctica in a stratospheric balloon that flew 12 days at an altitude of 40,000 m.     

The Solar-T captured the energy emitted by solar flares at two unprecedented frequencies: from 3 to 7 terahertz (THz) that correspond to a segment of far infrared radiation.

The Solar-T was designed and built in Brazil by researchers at CRAAM together with colleagues at the Center for Semiconductor Components at the University of Campinas (UNICAMP).

Development was possible thanks to a Thematic Project and a Regular Research Grant from FAPESP. The principal investigator for both was Pierre Kaufmann, a researcher at CRAAM and one of the pioneers of radioastronomy in Brazil, who died in 2017.

The new equipment, with Kaufmann as one of its creators, will be the product of a partnership with the Lebedev Physics Institute in Russia.  

“The idea now is to use a set of detectors to measure a full spectrum, from 0.2 THz to 15 THz,” Giménez de Castro told Agência FAPESP.

Most of the new photometric telescope will be built in Russia, but it will have parts made in Brazil, such as the equipment that will be used to calibrate the entire instrument.

“The technology and concept behind the telescope were developed here [in Brazil]. The Russians liked the idea and are reproducing it and adding more elements. We are working on the cutting edge of technology. Forty years ago, the cutting edge for what could be done was 100 gigahertz. With the results obtained over the years, we are seeking higher frequencies, and prospects for the future are good,” said the researcher. 

The future of the equipment lies in its graphene sensors. Highly sensitive to terahertz frequencies, graphene sensors are able to detect polarization and be adjusted electronically.  

Experiments in creating these detectors are currently underway at the Center for Advanced Graphene, Nanomaterials and Nanotechnology Research (MackGraphe) at Mackenzie Presbyterian University, a FAPESP-funded center.

The project also enjoys collaboration from the University of Glasgow, as part of the PhD work of Jordi Tuneu Serra, who is currently on a FAPESP-funded doctoral research internship abroad and who also attended FAPESP Week London.

Tags:  CRAAM  Graphene  Guillermo Giménez de Castro  Jordi Tuneu Serra  MackGraphe  Sensors 

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Graphene Enables Sensitive HIV Sensor

Posted By Terrance Barkan, Tuesday, June 19, 2018

If you manage to get one of the big corporate research institutes to tell you what they’ve looking at  when it comes to graphene, the response is usually: sensors.

 

Now researchers at the University of Pennsylvania have leveraged both graphene and DNA to produce a new sensor that increase the sensitivity of diagnostic devices used to monitor HIV

 

Just as in other uses of graphene for sensors, in this application graphene’s property of being only one-thick and highly conductive makes it extremely sensitive to detecting biological signals. The way the actual device exploits that property is that when DNA or RNA molecules bind to the graphene surface, they dramatically change the materials conductivity. 

 

This is not the first time that this basic design has been used as a biological sensor. However, in this case instead of using a single-stranded DNA that can only bind to the target DNA molecule, they developed what they have dubbed a “DNA hairpin” in which its curled structure opens up when the target molecule binds to it.

 

When it opens, another DNA molecule that has been added to the system kicks the target molecule out, making it possible to bind with many different sites on the graphene.


Tags:  DNA  HIV  Penn State  Sensors 

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Graphene Changes the Game in Optoelectronics

Posted By Dexter Johnson, IEEE Spectrum, Tuesday, April 24, 2018

Photons are faster than electrons. This has lead scientists to see if they can harness light (photons) to operate an integrated circuit. While this should result in faster circuits, there’s a hitch: wavelengths of light are much larger than the dimensions of today’s computer chips. The problem is that you simply can’t compress the wavelengths to the point where they work in these smaller chip-scale dimensions.

Scientists have been leveraging a new tool lately to shrink the wavelengths of light to fit into smaller dimensions: plasmonics. Plasmonics exploits the waves of electrons—known as plasmons—that are formed when photons strike a metallic structure. Graphene has played a large role in this emerging field because it has the properties of a metal—it’s a pure conductor of electrons.

The Institute of Photonic Sciences (ICFO) in Barcelona,  which has been a leader in this field for years, is now reporting they have taken the use of graphene for shrinking the wavelengths of light to a new level. In research described in the journal Science, ICFO researchers have managed to confine light down to a space one atom thick in dimension. This is certainly the smallest confinement ever achieved and may represent the ultimate level for confining light.

The way the researchers achieved this ultimate confinement was to use graphene along with one of its two-dimensional (2D) cousins: hexagonal boron nitride, which is an  insulator.

By using these 2D cousins together, the researchers created what’s known as van der Waals heterostructures in which monolayers of different 2D materials are by stacked on top of each other and held together by van der Waal forces to create materials with tailored electronic properties—like different band gaps for stopping and starting the flow of electrons. In this case, the layers included hexagonal boron nitride layered on top of the graphene and then involved adding an array of metallic rods on top of that. This structure had the graphene sandwiched between an insulator and a conductor. The graphene in this role served to guide the plasmons that formed when light struck the outer metallic rods.

In the experiment, the ICFO researchers sent infrared light through devices made from the van der Waal heterostructures to see how the plasmons propagated in between the outer metallic rods and the graphene.

To get down to the dimensions of one atom for confining the light, the researchers knew that they had to reduce the gap between the metal and the graphene. But the trick was to see if it was possible to reduce that gap without it leading to additional energy losses.

To their surprise, the ICFO researchers observed that even when a monolayer of hexagonal boron nitride was used as a spacer, the plasmons were still excited by the light, and could propagate freely while being confined to a channel of just on atom thick. They managed to switch this plasmon propagation on and off, simply by applying an electrical voltage, demonstrating the control of light guided in channels smaller than one nanometer of height.

The researchers believe that these results could to lead a new generation of optoelectronic devices that are just one nanometer thick. Down the road, this could lead to new devices such as ultra-small optical switches, detectors and sensors.

Tags:  graphene  Hexagonal boron nitride  optical switches  optoelectronics  plasmonics  sensors 

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GrollTex Tackles Sensor Markets With High Quality Graphene

Posted By Dexter Johnson, IEEE Spectrum, Thursday, March 1, 2018

  Jeffrey Draa, CEO, GROLLTEX

 

Last month, The Graphene Council's Executive Director, Terrance Barkan, and its Editor-in-Chief, Dexter Johnson, had the opportunity to have a talk with the CEO of California-based Grolltex Inc., Jeffrey Draa, about the company's business strategies in bringing graphene products to market and his views on graphene's future. Here is that conversation.

Could you tell us a little bit about the background of GrollTex. How did the company get started and how did you get involved with graphene? In particular, could you provide the history of Grolltex as a company?

Sure, so the name Grolltex is short for graphene rolling technologies and the brief history of the company is that my partner and co-founder and really the inventor, Dr. Alexander Zaretski, was a researcher at University of California San Diego.

He was involved with graphene growth and really got deep into graphene manufacturing techniques while he was at the University of California San Diego. One of the issues with this specific kind of graphene, as generated by chemical vapor deposition (CVD), of course, is the ‘transfer’ issue: How does one get single-layer graphene synthesized from copper off of the copper growth substrate and onto a substrate of interest without destroying the copper growth substrate? Of course, the current state-of-the art is to either acid etch the copper off of CVD graphene, or to use an electrolytic solution to sort of bubble the graphene off of the copper and have it rise to the top after a long period of time.

So both of these two processes, which had been state-of-the art, impact the copper in a very negative way so it's very expensive and not manufacturable. And my partner, Alexander, decided if graphene is going to go forward, there has to be a way to manufacture graphene and not destroy or impact that copper.  So he came up with a process to do that, a process that has a rolling schema where we reuse that growth copper over and over again. So that's kind of the background of the company. Alex had decided that he wanted, and felt so passionately about, this transfer technology and bringing it to graphene manufacturing that after completing his work as a researcher at UCSD, he broke out on his own and he asked me if I would be the business side of the company and he had the technical side. So that's kind of a brief background of Grolltex and how we came to be.

I understand you’re privately held company, correct?

We are, yes. We were funded roughly a year and a half ago with our seed funding and we've since about six months ago taken another round.

In terms of your graphene manufacturing that you just laid out, as you said you focused on producing single-layer graphene of the highest quality, so what are the markets that this product offering opens up to you? And what do you see as your strongest market now and do you see that market changing five years from now?

Well, as anybody that has knowledge of the graphene markets knows, single-layer high purity graphene like that synthesized via CVD has many theoretical use cases. We see on the short-term horizon three particular applications that are really kind of starting to command our attention. Those three are number one: sensing. So graphene given its electrical and mass properties makes an excellent sensor at a very, very small level. So sensing is number one.

We also are doing some work in the advanced solar cell arena and we have a grant from the California Energy Commission where we're working on a two-sided solar cell where graphene not only plays the part of barrier material but it's also the electrode material. So that's really exciting.

And for number three we’re also starting to get some inquiries for an application that actually Dr. Andre Geim at the University of Manchester, who, of course, was the discoverer of graphene was very passionate about. This is one of the very first applications that he thought futuristically would really make the world a better place, and that third application that we're starting to see on the horizon is graphene as a proton exchange membrane in a hydrogen fuel cell.

So those are kind of the three leading candidates we see right now. We’re judging that by some initial business that we’re getting in those areas.

You were discussing a number of applications you are pursing, including sensors. On your website you talk about enabling sensors that could be used for the Internet of Things. Can you explain why you see graphene playing such an important role in the development Internet of Things?

I’ll speak a little about graphene as a sensor material. When you combine the electrical conductivity properties along with the fact that graphene is one atom thick, you've got the potential for a sensor that could take us into the future for the next hundred years. We have patents around some designs of graphene-based sensing materials that are so sensitive that, for example, in the biotech world we had some bioengineering folks at Stanford use our sensor to sense the ability of individual heart cells to contract. Currently there only exists a different kind of test that can only count the number of contractions, but our sensor is so sensitive that it picks up the strength of contraction of the individual heart cell when it beats and it's a very robust signal; there's no mistaking it. So that's just one example of the potential of graphene as a sensor and we're seeing good activity there.

What is consistently your biggest challenge when you're talking to potential customers and convincing them how to use your product? Are they worried about pricing of graphene, the quality of product, a consistent supply chain? What stands out as one of the key issues that keeps coming up when you're speaking to these people?

So, I think the first consistent theme would surprise no one, and it's price. Almost any inquiry goes down along the lines of price, especially for a field like solar. If solar is implemented it’s going to need miles and miles of cheap graphene. Now the case of a sensor is not quite as price sensitive, but with regards to the big kind of large applications people think about like flexible displays and some of the other big idea changes for graphene those are really price sensitive. So price is the first one.

We don't get too many concerns with regards to the supply chain. Quality of product is sometimes discussed and that's partly because graphene is such a new field. But a lot of folks have what they are calling graphene and maybe debatably it is not. We don't necessarily have that problem because no one argues that single-layer graphene made by CVD is not graphene, so we don't have any discussion of the quality, but that sometimes can be an issue. So to kind of summarize, and get back to your main question, really price is the first thing that people want and that's the first hurdle you have to get over with almost everyone.

In addition to your graphene product, you're also producing hexagonal boron nitride (sometimes called white graphene). How do you see this material filling out your portfolio and what are the applications for this material that you're currently targeting and do you expect to develop other two-dimensional materials?

Hexagonal boron nitride is something we’re very excited about for several reasons. For the folks that aren't familiar with hexagonal boron nitride, you need to understand how it works with graphene. Graphene is, of course, the most conductive substance known at room temperature; it's on the order of seven times more conductive than copper depending on who you talk to. So as a conductor, graphene is really unparalleled. Now if you're going to design an electronic device of any type, of course, you worry about a conducting material because you can make the wire, the battery, and the switch with the conductive material. But the other thing you have to worry about is the insulating material. What are you going to use for the insulation for graphene? You have to separate the layers of the devices and hexagonal boron nitride is as good an electrical insulator as graphene is a conductor. And hexagonal boron nitride has a hexagonal pattern when it is synthesized in the proper way and that pattern lines up perfectly with the hexagonal lattice pattern of graphene so it also provides the strength benefit too. So it is really the ideal cousin of graphene. If you're an electronic designer, you're going to want both a conductor and an insulator and now we're going to be delivering both.

So that answers your first question and your second question, which was “are we going to develop other two dimensional materials?” As far as basic building blocks, we are going to rest on graphene and hexagonal boron nitride for a time because again those are your two basic building blocks: you need the insulation and the conducting but we also are developing other materials that go into specific devices. So, an example of this is the sensors I talked about that require some precious metal in small quantity—atomic quantity.  There are other materials involved when you go to make a specific device, but as far as the basic building blocks we're going to stand pat on graphene and hBN probably for a while.

What is your perspective on hybrid graphene materials? I am referring to this combination of a conductor and an insulator, or even a conductor with a semiconductor, and based on that will you look to develop those hybrids yourself or have your client make the next step in the value chain?

At the moment our clients are doing that work. Now I'm not going to say that we won't get into it, but we're going to be opportunistic with regard to that. With regard to opportunistic roads that we can go down today, our plate is pretty full, but there are several routes we can take. We are seeing folks in the semiconductor world, which is my background, starting to use other materials and creating devices out of some of those second and third level hybrids as you described and that's really exciting work. So we may get into some of that, but again we have a lot on our plate right now just based on what I described already.

I’d like to get your view of the overall industry over the short, middle and long term—five, ten, fifteen years expectations of graphene and the industry. And what is your strategy for best placing your company in the environment that you see developing?

With regard to our company, just saying the word “graphene” to a lot of people opens up so many thought patterns, channels and ideas that one of the things that's going to have to happen is the standards are going to need to be put in place fairly soon so that people can know what they're saying when they say “graphene”.

There's a lot of graphitic solutions out there and hybrids and powders and all kinds of things that debatably aren't graphene (of course, I would say that because of my company is involved in the area that there is no argument that it is pure graphene). But the point of that is we will need some standards and some nomenclature put in place to help take this whole field to the next level.

There's all kinds of great use cases for graphitic solutions that aren't graphene—great use cases, don't get me wrong—but let's make sure that we can assign proper nomenclature so people know what they are talking about and looking at. With regard to my company specifically, one of our challenges is picking our targets because again there are so many kinds of different opportunities. And when we first started out we decided we were going to have a two-phased approach to our business and we're doing the phase one part of that now.

Phase one for us is to make and sell graphene material as research material. So our core customer for our phase one is the university lab and commercial lab. So we sell graphene on copper substrates, on wafers, we sell graphene on customer specific substrates. You send us your substrate of interest and we’ll put our graphene on it and send it back to you. That phase one of our business that I just described to you is allowing us to pursue all kinds of exciting applications and some of them are helping us go in new directions. So, our challenge in the first five years I think is; number one stay on that phase-one path, get to profitability just as a business and number two really pick our paths carefully with regard to what are going to be the first real big market businesses out there in graphene—the ones that have paying customers.

So from a commercialization perspective, I think what you mention is that the majority, or is it basically all, of your customers are they in the testing or R&D category right now?

Yes, that’s fair to say. There's a population of big players in the industry that have their own graphene “skunkworks” that they're just not talking about. For example, I'm just going to throw some names around freely about big companies that we happen to know that do have graphene labs internally that it's just really very hush-hush. The reason we know this is because we know some of the people that have been hired out of other graphene places into these big companies. For example, Apple is one of them. They don't talk about it but they have a big graphene effort. Hewlett Packard is of one of those. Samsung is not bashful about their graphene efforts. So there are a lot of big companies where there is a lot of activity going on but nobody is talking about it so I think there's a lot more happening in graphene than people are even aware of because it’s not being leaked.

One of the things we’re very interested in doing as the Graphene Council is helping to act as a catalyst and accelerate commercialization.

One of the biggest obstacles to commercialization we’ve seen is simply the education of potential end users and consumers.  Can you talk a little bit about that? I mean as a company trying to educate potential clients one by one is a time consuming and expensive proposition.

What are the some of the other vertical markets or specific application areas—you mentioned sensors, of course? Are there some other specific areas where you think there's good commercial opportunity where we can help educate those populations?

The first one that comes to mind is the display market. So the display folks, of course, have been using indium tin oxide (ITO) as their core material for decades. ITO is really not a great material for them; it's expensive, it involves dirty mining and it is very prone to pollution when getting it out of the earth. It's also brittle which is why everyone’s display on their phone, their laptop, their television, all displays are brittle; they're like glass.

Graphene is actually a plug and play replacement for ITO and graphene enables flexible displays. So, the first big use case I can think of and that would be the most exciting and the most impactful for the most people is ITO replacement for making flexible displays.

But also I think it’s a use case that's pretty far down the road. It’s very price sensitive for one reason and number two there is a huge infrastructure with multiple large multinational corporations already in place and has been in place for decades with a big manufacturing schema, billions of dollars all lined up to process ITO, etc.. That's not going to shut off overnight and just accept a graphene replacement, right? So, from a price perspective and from an implementation perspective there are some challenges with ITO replacement, but I think that it strikes me as the kind of area where we can start hammering away at some of the existing thinking.

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The Graphene Council thanks Jeffrey Draa, CEO of GROLLTEX for his time and unique insights into the developing market for graphene. 

 

Tags:  chemical vapor deposition  Hexagonal boron nitride  ITO  photovoltaics  sensors 

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Fraunhofer IPA Maps Out Its Graphene Strategy

Posted By Dexter Johnson, IEEE Spectrum, Thursday, November 30, 2017

The Fraunhofer Institute for Manufacturing Engineering and Automation IPA uses the tagline: “We manufacture the future”.

Certainly as one of the leading research institutes in the world for the development of automotive technology, Fraunhofer has a global reputation for delivering the latest cutting edge breakthroughs in any technology associated with the automotive industry from energy storage to lightweight engineering.

Based on Fraunhofer’s titanic reputation in R&D, it was a stroke of luck that The Graphene Council was able to meet up with Fraunhofer’s Head of Functional Materials, Ivica Kolaric, at the Economist’s “The Future of Materials Summit” held in Luxembourg in mid-November.

In his role as leader of the functional material group at Fraunhofer, Kolaric has been conducting research on nanoscale carbon materials, like graphene, for almost 20 years. The aim of all this work has consistently been to produce functionalized nanoscale carbon materials to bring them to industrial applications.

Kolaric and his team have been working specifically on graphene since 2008 and have been synthesizing graphene using both chemical vapor deposition (CVD) as well as exfoliation techniques. With these various grades of graphene, the Fraunhofer researchers have experimented with a variety of applications.

“We first started with applications in the field of energy storage and transparent conductive films,” said Kolaric in an interview at the Luxembourg conference.  “As you may remember there was a big discussion a few years back going on if graphene could serve as a replacement for idium tin oxide (ITO).  But we determined that this is maybe not the right application for graphene because when you use it large areas for conductive films it’s competing with commodity products.”

Kolaric also explained that Fraunhofer had collaborated with battery manufacturer Maxell in the development of different types of energy storage devices, specifically supercapacitors. They had some success in increasing the energy density of these devices, which is an energy storage device’s ability to store a charge. With the graphene, the increased surface area of graphene did give a boost to storage capabilities but it just couldn’t deliver enough of an increase in performance over its costs, according to Kolaric.

Now Kolaric says that Fraunhofer is looking at graphene in sensor applications, in particular biosensors. “Graphene is really a perfect substrate for doping, so you can make it sensitive for any kind of biological effects,” said Kolaric. “This could make it a very good biosensor.”

But Kolaric cautions that avenues for purification have to be developed. If this and other issues can be addressed with graphene, there is the promise of a sensor technology that could be very effective at detecting gases, which currently is tricky for automotive sensors that are restricted to detecting pressure and temperature. “I think graphene can play an important role in this,” added Kolaric.

In addition to next generation sensors, Kolaric believes that graphene’s efficiency as a conductor could lead to it being what he terms an “interlink” on the submicron level. Kolaric believes that this will lead to its use in power electronics.

Kolaric added: “I would say sensors and serving as an interlink, so these are the two occasions where we think graphene can be effective.”

Tags:  biosensors  energy storage  Fraunhofer Institute  indium tin oxide  ITO  sensors  supercapacitors 

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Plasmonics Without Light Just Flipped Nanophotonics on its Head

Posted By Dexter Johnson, IEEE Spectrum, Monday, October 23, 2017

The use of graphene in the growing field known as plasmonics—in which the waves of electrons known as surface plasmons that are generated when photons strike a metallic structure—has been transforming the world of photonics and optoelectronics, enabling the possibility of much smaller devices operated by photons rather than electrons.

The Graphene Council has covered the work being performed at one of the leading research institutes in the world in this field of plasmonics, the Institute of Photonic Sciences (ICFO) in Barcelona. 

We had the opportunity to visit ICFO last week and speak to a number of their researchers, which we will be sharing in the coming weeks. In particular, we spoke to F. Javier García de Abajo from the Nanophotonics Theory research group at ICFO,  who has proposed a revolutionary approach of exploiting graphene for plasmonics.

It’s worth providing a bit of background on the field of plasmonics before jumping to this latest research. The use of photons instead of electrons for something like an integrated circuit has the clear benefit that photons travel much faster than electrons, promising much faster devices. However, the use of light in these applications is limited by the relatively large size of wavelengths of light. Light is fast, but their wavelengths are much larger than nanometer-scale dimensions of most integrated circuits.

Plasmonics provides a way to convert that light—photons—into waves of electrons that can be tuned to have much smaller dimensions than those of light. The dimensions of these plasmon waves can be a hundred times smaller than the smallest wavelengths of light. This means that light can serve as the basis of photonic integrated circuits, but many more devices than that.

The field of plasmonics has really taken in off in the last half-decade, and ICFO has been at the forefront of a lot of that work, especially in using graphene to enable the effect. However, what Garcia de Abajo has proposed is a new theoretical approach to generate visible plasmons in graphene not from light but from tunneling electrons.

In research published in the journal ACS Photonics, Garcia de Abajo and his colleague Sandra de Vega have suggested that there are more efficient ways of generating surface plasmons on graphene than using an external light source and have instead shown through models that graphene plasmons can be efficiently excited via electron tunneling in a sandwich structure formed by two graphene monolayers separated by a few atomic layers of hexagonal boron nitride.

As mentioned, it’s possible to tune the size of the plasmon waves, especially graphene plasmons, which can be changed in size according to the amount of doping level (an addition of other materials). While high doping levels can push the wavelength of the graphene plasmons towards the visible range, these grpahene plasmons primarily reside in the mid-infrared region, which translates into a weak coupling between far-field light and graphene.

What de Vega and García de Abajo have proposed is a methodology for visible-plasmon generation in graphene that requires no light at all. Instead, plasmons are generated from tunneling electrons, which are electrons that are able to pass through a material on the quantum level that they could not otherwise pass through.

To achieve this photon-less plasmonics, the researchers propose a graphene–hexagonal boron nitride (hBN)–graphene sandwich structure. In their model, the hBN layer is 1-nm thick that is sandwiched between two graphene monolayers.

When the right amount of voltage (bias) is applied between the two graphene sheets, it produces tunneling electrons through the gap. The researchers discovered a particular voltage window in which the tunneling electrons lose energy through the excitation of a propagating optical plasmon rather than dissipate through coupling with the vibrations of the crystal lattice of hBN that carry heat, which are known as phonons, (low bias) or electron–electron interactions (high bias).

One of the side benefits of plasmonic devices that operate in this way—without the need for photons—can also be used in reverse as sensors. In this way when a change occurs in the graphene plasmon properties, that change could lead to a voltage readout.

Tags:  electrons  graphene  hexagonal boron nitride  ICFO  photonics  photons  plasmonics  sensors 

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MIT's Michael Strano turns plants into chemical detectors

Posted By Terrance Barkan, Monday, October 31, 2016

Scientists have transformed the humble spinach plant into a bomb detector.

Source: MIT

By embedding tiny tubes in the plants' leaves, they can be made to pick up chemicals called nitro-aromatics, which are found in landmines and buried munitions. Real-time information can then be wirelessly relayed to a handheld device.

The MIT (Massachusetts Institute of Technology) work is published in the journal Nature Materials. The scientists implanted nanoparticles and carbon nanotubes (tiny cylinders of carbon) into the leaves of the spinach plant. It takes about 10 minutes for the spinach to take up the water into the leaves.

To read the signal, the researchers shine a laser onto the leaf, prompting the embedded nanotubes to emit near-infrared fluorescent light. This can be detected with a small infrared camera connected to a small, cheap Raspberry Pi computer. The signal can also be detected with a smartphone by removing the infrared filter most have.

Co-author Prof Michael Strano, from MIT in Cambridge, US, said the work was an important proof of principle. "Our paper outlines how one could engineer plants like this to detect virtually anything," he told the BBC News website.

Prof Strano's lab has previously developed carbon nanotubes that can be used as sensors to detect hydrogen peroxide, TNT, and the nerve gas sarin. When the target molecule binds to a polymer material wrapped around the nanotube, it changes the way it glows. "The plants could be use for defence applications, but also to monitor public spaces for terrorism related activities, since we show both water and airborne detection," said Prof Strano.

"Such plants could be used to monitor groundwater seepage from buried munitions or waste that contains nitro-aromatics." Using the set-up described in the paper, the researchers can pick up a signal from about 1m away from the plant, and they are now working on increasing that distance.

Source: BBC News

Tags:  Carbon Nanotubes  Michael Strano  MIT  Sensors 

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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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