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Graphene-Based Transistor Opens Up Terahertz Spectrum

Posted By Dexter Johnson, IEEE Spectrum, Friday, March 10, 2017

Terahertz radiation represents a range of the electromagnetic spectrum extending from the highest frequency radio waves to the lowest frequency infrared light. While many attempts have been made to create compact, solid-state devices that can harness it, terahertz radiation has proven difficult to exploit.

However, if such devices can be developed that can tap into the terahertz spectrum, we could see it make a big impact in non-invasive imaging in industry, medicine and security where they are less harmful than X-rays and because of the shorter wavelength and provide sharper images than those produced by microwaves.

Graphene has begun to show some real promise in terahertz devices for everything from wireless communications to improved quantum cascade lasers that can reverse their emission, offering a complete change to fiber optic telecommunications. 

Now researchers at the University of Geneva (UNIGE), working with the Federal Polytechnic School in Zurich (ETHZ) and two Spanish research teams, have developed a technique, based on the use of graphene, that can potentially control both the intensity and the polarization of terahertz light very quickly

The researchers believe that their research, which is described in the journal Nature Communications, could lead to the development of practical uses of terahertz waves to imaging and telecommunications. They key to their development was the fabrication of a graphene-based transistor adapted to terahertz waves.

Because the interaction between terahertz radiation and the electrons in graphene is very strong, the researchers believed that it should be possible to use graphene to manage terahertz waves. With this graphene-based transistor, the researchers believe this kind of control over a complete range of terahertz frequencies is now possible.

"By combining the electrical field, which enables us to control the number of electrons in graphene and thus allows more or less light to pass through, with the magnetic field, which bends the electronic orbits, we have been able to control not just the intensity of the terahertz waves, but also their polarization," said Jean-Marie Poumirol, a member of the UNIGE research team and the first author of the study, in a press release. "It is rare that purely electrical effects are used to control magnetic phenomena."

The researchers envision the graphene-based devices being used in communications and imaging.

"Using a film of graphene associated with terahertz waves, we should be potentially able to send fully-secured information at speeds of about 10 to 100 times faster than with Wi-Fi or radio waves, and do it securely over short distances," explained Poumirol.

 The initial imaging applications are thought to be in security. Alexey Kuzmenko, team leader of the research at UNIGE added: “Terahertz waves are stopped by metals and are sensitive to plastics and organic matter. This could lead to more effective means of detecting firearms, drugs and explosives carried by individuals, and could perhaps serve as a tool to strengthen airport safety."

Tags:  communications  fiber optics  imaging  security  terahertz  transitor  wireless 

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Graphene Interlayer Fixes the Schottky Diode

Posted By Dexter Johnson, IEEE Spectrum, Friday, February 10, 2017

Schottky diodes are the grand daddy of semiconductor devices. They are formed when a semiconductor material is combined with a metal and the junction between the two materials creates the Schottky diode. Despite being around since forever, it’s never been quite possible to make them into an ideal diode in which when a voltage is applied it acts as conductor and when the voltage is reversed it serves as a insulator.

Now researchers at the Ulsan National Institute of Science and Technology (UNIST) in Korea have been able to produce the ideal version of the Schottky diode by inserting a graphene layer between the semiconductor and the metal, and in the process have eliminated 50 years of head scratching over this issue. 

In research described in the journal Nano Letters, the UNIST researchers discovered that graphene serves to prevent the intermixing of atoms that occurs when the semiconductor and metal are touching each other directly.

“The space between the carbon atoms that make up the graphene layer has a high quantum mechanical electron density and therefore no atoms can pass through it,” said Kibog Park, a professor at UNIST and co-author of the paper, in a press release. “Therefore, by inserting the graphene layer between metal and semiconductor, it is possible to overcome the inevitable atomic diffusion problem.”

While the research solved this problem, it also confirmed a prediction that it didn’t matter what kind of metal was used to form the Schottky junction; the performance does not change significantly.

The applications for Schottky diodes are pretty broad, but the main use is that of a rectifier, which converts alternating current (AC) to direct current (DC). But so many electronic devices use these diodes that this research is expected to resolve what has been a long-standing issue within the electronic industry.

Tags:  electronics  graphene interlayer  metal  rectifier  Schottky diodes  semiconductor 

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NanoXplore Brings Unique Perspective to Graphene Production

Posted By Dexter Johnson, IEEE Spectrum, Thursday, January 26, 2017

 

After Montreal-based NanoXplore launched in 2011, its initial business was contract research in the field of carbon-based technologies. But its identity as a contract R&D company changed in 2014 when it filed a series of patents focused on graphene production.

As the company further developed its technology since then, the main focus of the company has become providing graphene-enhanced polymers for plastics that have enhanced electrical, thermal and mechanical properties.

The company website suggests that these graphene-based polymers have a variety of applications, ranging from photovoltaics to supercapacitors

We wanted to get to know how a relatively new company that started out as an R&D contractor evolved into a graphene-enhanced polymer manufacturer and how they now see the downstream market for their product. To do that, we took the opportunity of NanoXplore becoming a corporate member of The Graphene Council to talk to the company’s chief operating officer, Paul Higgins, and here is that interview.

Q: NanoXplore started out as an R&D contractor in carbon-based technologies. How is it that the company was able to file a patent in graphene production patent just two years after being formed? Were you always doing research in this area, or did you make a concerted effort to find a place in the graphene market?

Working with other carbon-based materials, especially CNTs, it became evident that many commercialization challenges were due to the production processes. The processes had been developed in research environments and were not designed from the ground up with an industrial mindset. We focused from the beginning on low cost, high-yield processes, using existing capital equipment, and with no pre- and post-processing. For example, our graphene production process functionalizes the graphene in-situ, avoiding costly functionalization post-processing for most applications. We were also very cognizant of the need for sustainable, “green” processes; our patented process is water-based, uses no strong acids, and no organic solvents.

A key insight underpinning our patents is that high energy and strong chemical processes create many downstream problems in graphene production. High-energy processes are inefficient and create defected planar structures, resulting in graphene with poor electrical and thermal benefits, in turn requiring high, non-economic loadings of graphene in nanocomposites.  Strong chemical processes require complicated post-processing and recycling processes to be cost effective and require very tightly controlled production environments, adding costs.

Once we had established the frame of potential solutions based upon the above, developing our new technology platform was relatively straightforward.

Q: Were you looking to enter a particular niche of the graphene supply chain or did the process you came up with dictate somewhat the point in the supply chain that you now occupy?

Our process is high yield, large volume, low cost, and produces graphene powder with very high quality. This allows us to target mass industrial material markets such as polymers, markets requiring large volumes of material. And due to the quality of our graphene, we can provide significant benefit to industrial materials at low loadings and viable price points.

Of course, the graphene must be effectively mixed into the polymer matrix. To do this we have developed production processes for the manufacture of graphene-enhanced plastic masterbatches. These masterbatches, which we have been manufacturing and selling since early 2016, are the perfect form factor for the plastic industry. Plastic formers, such as injection and blow molders, and compounders are very comfortable with masterbatches and easily incorporate them into their existing processes.

Q: Do you see the company evolving to develop products further up the supply chain? For instance, it appears you’re involved in energy storage technologies enabled by graphene. Is this where you see your business moving or do you see this is just diversification of your portfolio?

NanoXplore is focusing our current commercial efforts on graphene-enhanced polymers. We see this as a large market, hungry for innovative materials, where our graphene has a strong competitive advantage.

We also have a patent on a unique graphene-graphite composite material that is useful for energy storage applications. This material was the impetus for our original research in the energy field. This initial research showed great promise and leads us into development of a range of materials for Si-graphene anodes and S-graphene cathodes.

From our current polymer efforts and the emerging energy storage materials, we see a sustainable growth model for the company. Our core research efforts develop graphene-based technologies for a target market, and then transition to product development. During the transition, we will develop technologies for the next target industry. And repeat. Graphene is so broadly applicable that we foresee being able to continue in this vein for some time.

Q: How does your company envision the landscape for the graphene market evolving over the next five years, i.e. are there particular markets that will be winners and losers, what applications are not being sufficiently targeted, etc.?

The graphene market has changed significantly over the last three years. Three years ago the challenge for end users was to obtain decent material, in volume, at a reasonable price. Today there are several producers, including NanoXplore, producing large volumes of good quality graphene. Prices per kg for high quality graphene have fallen during this period from $30,000 kg to $100 Kg and are set to fall to $30 kg over the next five years.

[NB: Above and subsequent comments pertain to high quality - low defect, functionalized few layer graphene and graphene nanoplatelets. Graphene from CVD is excluded as is reduced Graphene Oxide (rGO)].

The current challenge for the graphene industry is to incorporate graphene into real-world products and industrial processes. One of the major hurdles is that graphene is sold into a supply chain, with many players between the graphene producer and the final product. And each of these players has their own calculus of risk versus benefit. To be successful the graphene producer must demonstrate benefits to each player at every step along the supply chain, while meeting standards, helping to modify processes, overcoming regulatory hurdles and minimising supply chain disruptions. The successful companies will expand to cover several steps in the supply chain – for example graphene material, polymer compounds, plastic forming – and develop partnerships with other key supply chain players.

Over the next 3-5 years, one can imagine the commercial introduction of novel graphene enabled subsystems and systems. This category of products will include strong, light weight and highly functional nanocomposites for electric transportation vehicles, greatly improved energy systems (e.g., next generation batteries), high barrier packaging, smart textiles, and others. Solutions for highly regulated industries (e.g., medical, aerospace), some being demonstrated today, will start to exit their testing regimes and enter the marketplace.

Ultimately graphene will be part of building a sustainable future, playing a significant role in the replacement of costly, single function, or scarce materials with abundant, cheaper, and higher-performing ones. It will replace multiple and occasionally toxic additives with a single multi-functional material. It will reduce weight while increasing strength for a wide range of structural polymers and composites often leading to significant fuel savings in vehicles. It will extend the useful lifetime of paints, coatings and lubricants. And it will improve thermal management and energy storage in a wide range of applications, again improving efficiency while husbanding scarce resources.

NanoXplore is very well positioned to help customers participate in this emerging new world. With the combination of high quality graphene material, expertise in mixing graphene with a wide array of industrial materials, and a team of seasoned business leaders and material scientists with broad industrial experience, NanoXplore enables customers to achieve significant and affordable product improvements with very little added graphene.

Tags:  masterbatches  photovoltaics  polymers  supercapacitors 

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From the Lab to the Financial Markets: Applied Graphene Materials Leads the Way

Posted By Dexter Johnson, IEEE Spectrum, Wednesday, January 25, 2017

 

 

Back in 2010, Karl Coleman, a professor at Durham University in the UK, spun out a company at first known as Durham Graphene Science and then later floated on the stock market (AIM) as Applied Graphene Materials (AGM). 

The word quickly spread about AGM’s approach to producing graphene. The company’s manufacturing techniques did not require either a graphite source or a metal catalyst, with the latter leading to highly pure graphene platelets with little oxygen content.

From the outset, AGM has always been considered to have a flexible position in the graphene supply chain, with their product being adaptable to the needs of their clients. The company's graphene has been proposed for applications ranging from an indium-tin oxide (ITO) replacement in flexible displays to electrode material in batteries and supercapacitors. With its first production order and commercial application announced last October, we should begin to see the company’s flexibility demonstrate itself in the coming year. 

AGM is one of the few publicly traded graphene companies, which gives it a fairly unique position to observe the developing graphene markets. As one of The Graphene Council’s newest corporate members, we had the opportunity to ask some questions of AGM’s CEO, Jon Mabbitt, to get their view of graphene’s commercial development.

Q: The development of Applied Graphene Materials from university research to an AIM-traded business is a story that many lab research groups working with graphene and other 2D materials would like to duplicate.  What were a few of the most important factors that contributed to the success of your company bridging that gap between the lab and the fab?

A: Universities provide a fantastic environment in which to be creative, but often ideas do not progress beyond a single experiment or perhaps being the topic of a research paper. In our case the close connection between the Inorganic Chemistry department at Durham University and the Technology Transfer office facilitated the opportunity for the manufacturing processes to be financially supported. Without this early stage investment the ideas would probably have gone no further, but with seed capital and self-belief the people involved at this stage were able to deliver proof-of-concept. Another significant step was that the inventor recognised they were not necessarily best placed to lead the company going forward and was comfortable enough to pass on the responsibility to an experienced growth management team.

Q: Your corporate literature describes your production of graphene as a “bottom-up” process. Is this a chemical vapor deposition process or some kind of chemical exfoliation process? And do you see your process being adapted in some way that it could be used to produce monolayer graphene for electronic or optoelectronic applications in larger capacities than they are currently?

We describe our process as “bottom up” because we synthesize our graphene and do not exfoliate it from graphite. However, this is not a CVD process because we do not require a substrate on which to deposit the vapor. It is a chemical decomposition of alcohol, which is then reassembled to create the graphene nanoplatelets.

Q: It would seem that your current business model is that of a producer of graphene dispersions that supplies different product manufacturers to further enable their products? Do you see your business model evolving over time where you move further up the supply chain and eventually you would be manufacturing the products that are sold rather than the dispersions?

Our strategy is very simple: make graphene and format it. We only want to produce graphene and supply it in a format that can be easily handled by our customers and easily incorporated into their products. It is our customers who will create end products. Clearly by this approach working extremely closely with our customers is mutually beneficial to enable the optimum results.

Q: In your own business lines, what applications are showing the most potential for growth, i.e. coatings, composites, functional fluids, etc.? And why do you think this is the case: The underlying markets did not have any solution to the issues that the graphene-enabled products offered, or the graphene-enabled product outperformed what was currently in the market?

One of the Achilles heels of start-up companies is that they try to do too much. We have identified specific areas where we know our graphene material delivers particular benefits and so for now we remain focused on those areas: coatings (barrier performance), composites (mechanical performance) and functional fluids (friction modification). All sectors are looking for improvements, normally performance enhancement or cost reductions. The particular attributes graphene brings is that you get a lot of performance for very little quantity added. The ultra-high surface area to weight ratio combined with the chemical composition and bonding regime of graphene makes it super interesting. However, not all graphene is produced equally and the method of manufacture dictates the resultant properties of the material. Also whilst graphene has several attributes they cannot all be delivered concurrently in certain applications.

Q: In your dealings with customers, what is typically their biggest reservation in adopting your graphene dispersions and how do you typically overcome these doubts?

To gain customer interest you must provide credible data to support your assertions. Industrial companies will not spend time on technology concepts that are unproven. Once we have grabbed their attention then we need to support the customer really closely – things will go wrong before they go right and so a dogged mentality is essential. You also need to demonstrate that your business will continue to exist and be able to supply the products repeatedly and consistently in the long term.

Q: What do you think the overall market for graphene needs in order to see wider development of graphene-enabled products, i.e. more defined industry standards, just more time in the market, manufacturing costs to go lower? If all of these and more, which is the most acute?

I don’t believe there is or will be a distinct market for graphene, moreover graphene can be adopted largely as an additive to enhance a range of materials across several existing market sectors. I don’t subscribe to the idea that standardization will enable acceptance. Graphene is, and will remain for many years to come, a specialty chemical and exist in many different forms. There are some issues where a common approach would be beneficial for all, such as regulatory controls and H&S. Everyone involved in graphene needs more application successes and to achieve this there needs to be a bolder commitment from producers and advisors to go and make it happen.

Tags:  graphene platelets  ITO  publicly traded  stock market  supercapacitors 

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Additive Manufacturing & 3D Printing with Graphene

Posted By Terrance Barkan, Friday, January 20, 2017

 

3d printing, also known as additive manufacturing (AM), represents significant potential for the use of graphene material as an additive to the fast growing range of printable materials. This is increasingly true as there is a clear shift towards producing functional parts for industrial end use, including aerospace and automotive applications. 

Despite being a relatively low volume market at the moment, AM has several useful properties than make it an attractive market to a graphene producer as well as to end users. The AM market has a strong appetite to test new materials and to identify innovative applications not just in the AM processes, but in the characteristics of the materials that are used. Rapid process and testing times for new products mean that there is also a low barrier to entry compared to supplying nano-enhanced materials in other manufacturing industries. 

Because traditional AM materials are often quite expensive on their own, adding a relatively expensive material like graphene has less of an impact on the final costs than it might in some other large scale commercial applications. 

One of the advantages of AM is the ability to make one-off or specialty parts with no loss in production speed. Parts are also essentially the same price regardless of whether you print a few or a few thousand pieces. 

Although there are a large number of different AM technologies, there are really just three formats of material, (powders, liquids and filaments) and there are three main classes of material (metals, plastics and ceramics). Graphene has the potential to add desirable characteristics across many of these technologies, formats and material classes. 

One of the most important materials in use with AM today is polymers. There is significant scope for graphene to gain traction and market share here as an additive, primarily due to the ease of processing graphene into polymers. Common thermoplastics used in sintering and extrusion AM techniques include  ABS, PLA, nylons (6 and 12), TPU, PET and HIPS. Thermosets such as epoxy and acrylics are also popular in UV cured AM applications. Despite the relatively difficult processing challenges for metals and ceramics, there is potential for graphene to also add value across those technologies.

Graphene has the ability to provide improvements to conventional AM materials and in some case, these material improvements are unique to graphene. In particular, graphene can have an impact on;


• Much lower solids content 
• Shift material into a printability window 
• Improve HDT and shrinkage 
• Mechanical reinforcement where certain macro additives can’t be used
• Significant multi-functionality (5+ uplifts with one additive) 

 

Essentially graphene is adding benefits to or improving on the performance of a given consumable as well as mitigating or reducing the negatives. Multifunctionality is also important; gaining multiple beneficial properties without resorting to using several additives that might be incompatible with each other and doing so with a low addition rate lowers the risk of adding negative performance into a polymer, such as lower processability or brittleness. 

3D Printing and AM is just another of the many areas where graphene is proving worthy of a much closer look by materials scientists, product designers, engineers and production specialist across a broad range of industries. 

 

Want to learn more? 

 

Join an in-depth Webinar on Graphene and 3D Printing

Tags:  3D Printing  Additive Manufacturing 

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Thermionic Energy Converters on the Rise Thanks to Graphene

Posted By Dexter Johnson, IEEE Spectrum, Tuesday, January 10, 2017

 

Schematic sketch of the TEC prototype.

At the height of the Cold War, thermionic energy converters (TECs) were often used as the energy source for both NASA and the Soviet space program satellites. However, the combination of decreased space funding since the end of the Cold War and some of the engineering challenges associated with TECs has left the development of the technology largely stagnant until quite recently.

Over the past ten years there has been a bit of renaissance in TECs due to developments in modern wafer-scale fabrication techniques, device physics and material science, as well as an increasing attention to clean and renewable energy globally. This has led to TECs again receiving a considerable amount of interest both in the academia and industry, including two startups: Spark Thermionics and Modern ElectronWhile these companies and general trends are signs of TECs resurfacing as an alternative energy source, there remain some pretty significant engineering hurdles that still need to be overcome.

Now a team of researchers at Stanford University has taken a huge step in solving a couple of the key problems with TEC technology: improving the efficiency and stability of the anodes.The result could be the TECs taken on a far larger role in alternative energy solutions.

In research published in the journal Nano Energy, the Stanford researchers have employed graphene as the anode material and in so doing have boosted the efficiency of the device by a factor of 6.7 compared with a traditional tungsten anode.

The researchers successfully demonstrated an electronic conversion efficiency in the graphene-based anode of 9.8%. Electronic conversion efficiency is the efficiency at which  an electron converts thermal energy to electrical energy. In other words, it is the efficiency of moving one electron from the cathode to the anode by heat.

“One of the major challenges for wider adoption of TECs is high anode work function, which directly reduces the output voltage as well as the net efficiency,” explained Hongyuan Yuan, a PhD candidate at Stanford and lead author of the research, in an e-mail interview with The Graphene Council. “The theoretical maximum efficiency for a TEC with a 2 electron volt (eV) work function anode is 3% at a cathode temperature of 1500 K, compared to an astonishing 10-fold increment of 32% with a 1 eV work function anode.”

The work function of a material is the energy difference between its vacuum level and Fermi level. Before the discovery of graphene, the world-record low work function for a conductor was around 1.1 eV to 1.2 eV, which is achieved by lowering the vacuum level through the deposition of a monolayer of cesium oxide on the surface.

In 2015, Stanford researchers discovered that the work function of graphene can be reduced by not only lowering its vacuum level, but also raising its Fermi level by electrostatic gating through a back gate at the same time. “In this ‘combo’ approach, we discovered that the work function of graphene reached a new world-low record of 1.0 eV in 2015,” added Yuan.

The second major challenge to the success of TEC has been the high space charge barrier between TEC’s cathode and anode, which directly reduces the output current and thus the net efficiency. In order to reduce the space charge barrier, TEC requires a very small vacuum gap to separate the cathode and anode, usually around 10 mm. If the gap is much larger than 10 mm, all the benefit that an ultra-low work function anode could bring would be diminished.

“In our most recent work, we successfully addressed the above mentioned two challenges, and demonstrated that the previously discovered ultra-low work function graphene can indeed be applied to TEC with a significant amount of efficiency enhancement. Compared to a traditionally used tungsten anode, the net efficiency is increased by a factor of 6.7,” said Yuan.

While applications for TECs remain limited at the moment, with improvement in efficiency and device stability, Yuan believes that TECs are expected to see an enormous market both in the centralized power plants, i.e. in a tandem cycle, as well as in the distributed systems, e.g. automobiles with internal combusting engines and domestic houses with water heaters.

The current demonstration of the TEC device has been performed in an ultra-high vacuum chamber, with many pumps constantly pumping down the pressure. “In reality, we need to fabricate such a TEC device and seal it in a vacuum ‘chip’ using the state-of-the-art nano/micro fabrication techniques,” added Yuan. “Only by making the device small and reliably stable would it be economically feasible in the sustainable energy industry.

Yuan added: “We envision such a TEC device in the future, which is sealed in a small and thin cell (TEC cell). To generate electricity, all you need to do is to attach one side of the cell to a heat source. You may attach a couple of the TEC cells to the water heater at your home to charge your phone. Or attach many TEC cells to a fossil-fuel power station to improve its overall efficiency.”

Tags:  alternative energy  anodes  cathodes  thermionic energy converters  water heaters 

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CealTech AS - Endless Possibilities

Posted By Dexter Johnson, IEEE Spectrum, Thursday, January 5, 2017