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Graphene hits the right note at high frequencies

Posted By Graphene Council, The Graphene Council, Tuesday, January 15, 2019

Graphene holds the potential to deliver a new generation of ultrafast electronic devices. Current silicon technology can achieve clock rates – a measure of how fast devices can switch – of several hundred gigahertz (GHz). Graphene could achieve clock rates up to a thousand times faster, propelling electronics into the terahertz (THz) range. But, until now, graphene’s ability to convert oscillating electromagnetic signals into higher frequency modes has been just a theoretical prediction.


Now researchers from the Helmholtz Zentrum DresdenRossendorf (HZDR) and University of Duisburg-Essen (UDE), in collaboration with the director of the Max Planck Institute for Polymer Research (MPI-P) Mischa Bonn and other researchers, have shown that graphene can covert high frequency gigahertz signals into the terahertz range [Hafez et al., Nature (2018)].

“We have been able to provide the first direct proof of frequency multiplication from gigahertz to terahertz in a graphene monolayer and to generate electronic signals in the terahertz range with remarkable efficiency,” explain Michael Gensch of HZDR and Dmitry Turchinovich of UDE.

Using the novel superconducting accelerator TELBE terahertz radiation source at HZDR’s ELBE Center for High-Power Radiation Sources, the researchers bombarded chemical vapor deposition (CVD)-produced graphene with electromagnetic pulses in the frequency range 300–680 GHz. As previous theoretical calculations have predicted, the results show that graphene is able to convert these pulses into signals with three, five, or seven times the initial frequency, reaching the terahertz range.

“We were not only able to demonstrate a long-predicted effect in graphene experimentally for the first time, but also to understand it quantitatively at the same time,” points out Turchinovich.

By doping the graphene, the researchers created a high proportion of free electrons or a so-called Fermi liquid. When an external oscillating field excites these free electrons, rather like a normal liquid, they heat up and share their energy with surrounding electrons. The hot electrons form a vapor-like state, just like an evaporating liquid. When the hot Fermi vapor phase cools, it returns to its liquid form extremely quickly. The transition back and forth between these vapor and liquid phases in graphene induces a corresponding change in its conductivity. This very rapid oscillation in conductivity drives the frequency multiplication effect.

“In theory, [this] should allow clock rates up to a thousand times faster than today’s silicon-based electronics,” say Gensch and Turchinovich.

The conversion efficiency of graphene is at least 7–18 orders of magnitude more efficient than other electronic materials, the researchers point out. Since the effect has been demonstrated with mass-produced CVD graphene, they believe there are no real obstacles to overcome other than the engineering challenge of integrating graphene into circuits.

“Our discovery is groundbreaking,” says Bonn. “We have demonstrated that carbon-based electronics can operate extremely efficiently at ultrafast rates. Ultrafast hybrid components made of graphene and traditional semiconductors are also now conceivable.”

Nathalie Vermeulen, professor in the Brussels Photonics group (B-PHOT) at Vrije Universiteit Brussel (VUB) in Belgium, agrees that the work is a major breakthrough.

“The nonlinear-optical physics of graphene is an insufficiently understood field, with experimental results often differing from theoretical predictions,” she says. “These new insights, however, shine new light on the nonlinear-optical behavior of graphene in the terahertz regime.”

The researchers’ experimental findings are clearly supported by corresponding theory, Vermeulen adds, which is very convincing.

“It is not often that major advances in fundamental scientific understanding and practical applications go hand in hand, but I believe it is the case here,” she says. “The demonstration of such efficient high-harmonic terahertz generation at room temperature is very powerful and paves the way for concrete application possibilities.”

The advance could extend the functionality of graphene transistors into high-frequency optoelectronic applications and opens up the possibility of similar behavior in other two-dimensional Dirac materials. Marc Dignam of Queen’s University in Canada is also positive about the technological innovations that the demonstration of monolayer graphene’s nonlinear response to terahertz fields could open up.

“The experiments are performed at room temperature in air and, given the relatively short scattering time, it is evident that harmonic generation will occur for relatively moderate field amplitudes, even in samples that are not particularly pristine,” he points out. “This indicates that such harmonic generation could find its way into future devices, once higher-efficiency guiding structures, such as waveguides, are employed.”

He believes that the key to the success of the work is the low-noise, multi-cycle terahertz source (TELBE) used by the researchers. However, Dignam is less convinced by the team’s theoretical explanation of graphene’s nonlinear response. No doubt these exciting results will spur further microscopic theoretical investigations examining carrier dynamics in graphene in more detail.

Tags:  CVD  Electronics  Graphene  graphene production  Terahertz 

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Novel Production Technique Offers Start-up New Approach to Markets

Posted By Dexter Johnson, IEEE Spectrum, Thursday, December 20, 2018

California-based NTherma is leveraging a proprietary graphene production method based on the unzipping of multiwalled carbon nanotubes into graphene nanoplatelets or nanoribbons.

The backgrounds of NTherma’s co-founders Cattien V. Nguyen, President & CEO, and Thuy Ngo, VP Business Developments & Investor Relations, cover both the science of graphene as well as its business development. Nguyen’s background contains some of the heavy hitters in nanomaterials research over the last 20 years: IBM Almaden Research Center and Stanford University.

With their manufacturing process offering a high degree of customization, NTherma is targeting applications that exploit this inherent flexibility that other manufacturing techniques can’t so easily deliver on.

As a new Corporate Member of The Graphene Council, we got the opportunity to ask them about how they are approaching the market with their novel manufacturing technique, some of the challenges they are facing and how they plan to overcome them.

 Q: Could you provide us more details about your method for producing graphene? It appears from your website that it may be a bottom-up approach. Is it a CVD-enabled process or direct chemical synthesis? And what kind of graphene does it produce?

Our graphene production method is different from the two current production processes.  We don't produce graphene by CVD of single layer directly on a metal substrate and we don't produce graphene by exfoliating graphite.  Both of these production methods have a number of tradeoffs including cost, purity, and control of structural parameters.

NTherma's unique approach to the production of graphene starts with our patent-pending method of producing carbon nanotubes (CNTs) that have high purity and high degree control of lengths and diameters, and most importantly a much lower production cost.  NTherma's graphene is then derived by the chemical conversion of high quality CNTs. 

Depending on the degree of chemical oxidation process, the produced graphene can be nanoplatelets or nanoribbons, or a combination of the two types.  Our ability to control the CNT length and their high purity together translates to high quality graphene at a much lower cost.  Of particularly importance is the availability of graphene nanoribbons at a large scale with controlled length, high purity, and much lower cost. This will open up a number of applications not currently feasible with commercially available graphene.

Could you let us know what applications you are targeting for your graphene? And can you tell us a bit about how you came to target these applications?

We are currently focusing on the following applications:

1.  Graphene for Oil Additives:  These reduce engine friction, improved fuel efficiency and lower emissions.  We differentiate our graphene as an oil additive in that our graphene forms a stable dispersion in oil with a demonstrated shelf life of greater than 12 months.

2.  Coatings:  There are many coating applications employing graphene and currently we are working with a few partners to integrate our graphene products.  We are also focusing on applications such as touchscreen and display as well as smart windows that other graphene materials have not been able to effectively address. 

3.  Lithium-ion (Li-ion) Batteries:  Preliminary test results are positive.  We're looking for partners to continue developing and testing the process. 

Because of our unique customization ability, we can alter length, layers and uniformity of our graphene per customers' requests.  Realizing that our high quality and consistent materials can unlock previous bottlenecks that other graphene products couldn't resolve, we chose these applications in the order provided as we see these applications and markets having the highest potential and where our technology will have the highest impact.

You are also producing multi-walled carbon nanotubes (MWCNTs). How do you see this fitting with your graphene production?

We produce MWCNTs for several other applications such as thermal management and also carbon nanotube yarns in development with a commercial partner. 

We also produce our graphene by the chemical conversion of MWNTs.

Is your strategy to remain a graphene and MWCNT producer, or do you see yourself moving further up the value chain to make devices from these materials?

We will focus on scaling up the production of high quality MWCNTs and graphene for the near future.  At the same time, we are developing, or have plans to develop, other applications and markets by ourselves or with partners in order to add more value to our business by strategically positioning our unique technology in a variety of verticals.

What do you see as the greatest challenge for your business in making an impact the commercialization of graphene, i.e. customer education, lack of standards, etc.? And what do you believe can be done to overcome these challenges?

The greatest challenges as a business for us have been our efforts to work with the end users and to understand as well as to educate the potential customers of our unique graphene products for any particular applications and product development processes.  Not all graphene products are the same in their purity, structural parameters such as size and number of layers, and cost.  These facts have to be made known to the end users and have to match with the end user's specific application.

Additionally, we also have to overcome clients' negative experiences with using other producers' inconsistent quality products.  We have to resolve these issues by continuing to work closely with our potential customers and partners by helping them to understand the materials and also optimizing and testing products for specific applications ourselves to provide clients with testing procedures and data (both in a lab environment and in real life).

Tags:  carbon nanotubes  coatings  CVD  Li-ion batteries  lubricants 

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Grolltex Releases ‘Enhanced Performance Graphene’ for Electronic Devices

Posted By Terrance Barkan, Monday, October 15, 2018

San Diego based graphene and 2D materials producer Grolltex has completed characterization and is releasing for commercial sale a configuration of large area, single layer graphene that exhibits dramatically improved ‘electron mobility’, which translates to better graphene performance.  This ‘heterostructure’ contains a layer or layers of hexagonal Boron Nitride (or ‘hBN’) underneath graphene, enabling enhanced graphene capabilities.  

Grolltex has begun commercial pre-sales to customers of this ‘Enhanced Performance Graphene’ product, which can significantly improve device performance for sensing, transistors, connectivity and other key aspects of nano-devices.  This type of material performance improvement is often a stepping stone for new applications enabling large market growth toward faster, smaller, cheaper and more sensitive silicon-based devices.

“The data back from our large European device partner showed carrier mobility performance improvements starting at 30%, and our internal work shows us that with some configuration adjustments, we can even build on this toward electron mobility improvements in exponential regimes”, said Jeff Draa, Grolltex CEO and co-founder.  “We believe this is going to be incredibly important to many of our customers that build things on silicon”.

The first reason for the improvement of graphene electron mobility performance, when layered on top of hBN on a wafer, is that the underlying layer of hBN, between the wafer and the graphene, planarizes the surface of the silicon wafer and allows graphene to sit on a surface (hBN) far more conducive to graphene electron flow.  

Another reason has to do with the electron interference of the oxide coming out of the underlying Si/SiO2 wafer, if graphene sits directly on top of it.  With the hBN layer between the graphene and the wafer, the negative effect of the oxide from the wafer on graphene electron performance is greatly reduced, allowing a much freer flow of graphene electrons.  Additional advantages are lower processing temperatures and a much stronger adhesion of the graphene layer to the underlying substrate, with hBN present.

“So, when graphene sits on hBN, it performs much closer to the theoretical ‘electron superhighway’ that graphene users expect”, according to Draa. “We have characterized and are selling this heterostructure to our pre-qualified customers in up to 8” (200mm) diameter configurations and can layer hBN and graphene in any combination”. 

“Device designers, especially advanced sensor makers, are really keyed in to electron mobility. There are many variables that affect this and he who can square those away and show dramatic improvements in mobility can help add real, unique and substantial value to device performance”, said Draa. “Next on our characterization list is MoS2, which is an important ‘band-gap’ material that has been missing in 2D offerings.”

Grolltex, short for ‘graphene-rolling-technologies’, 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.

About Grolltex:

Grolltex, Inc., is a nanotechnology materials, products and equipment company focusing on the optimization and advancement of the key monolayer material ‘graphene’ and related 2D materials.  The company holds a number of strategic patents and technological advantages in areas relating to the manufacture of high quality, monolayer ‘CVD’ graphene and hexagonal Boron Nitride as well as on several advanced products made of graphene and 2D materials, such as hyper efficient solar cells, next generation sensors, advanced fuel cells and futuristic super-thin and flexible displays for use in wearables, smart phones and other electronics.  

For complete information, please visit: https://grolltex.com/

 

Media Contact:

Attn: Media Relations, Grolltex, Inc.

10085 Scripps Ranch Court, Suite D

San Diego, CA 92131

support@grolltex.com

Tags:  CVD  Electronics  Graphene  Grolltex  HbN  Jeff Draa 

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A World Leader in Graphene Production Sees Itself as a "Platform Play" in Advanced Materials

Posted By Dexter Johnson, IEEE Spectrum, Friday, October 12, 2018

With well over a decade in the business, XG Sciences is considered one of the most established graphene producers in the world.  It is behind one of graphene’s most high-profile applications in Callaway’s introduction of its so-called Chrome Soft golf ball that employs graphene supplied by XG Sciences to make the golf balls both softer and harder where they need to be.

XG Sciences recently became a corporate partner of the Graphene Council and we took that occasion to discuss with the company’s CEO, Philip Rose, the graphene market in general and how XG Science’s product line fits into that market.

We also were able to learn how graphene supply chains are developed and secured and how the introduction of graphene into many different products can be supported and promoted. Here’s our interview.

 Q: XG Sciences produces graphene platelets. Could you explain where that places you in the graphene marketplace (as opposed to monosheets of graphene)? What sort of applications does that product open up for you?

A:  The term “graphene” is often used to cover a variety of specific forms of the material, but we generally think about two broad classes of graphene materials – monolayer and nanoplatelet. One-atom thick films are commonly referred to as monolayer graphene and are manufactured from gases by assembling molecules to form relatively large, transparent sheets of material. We do not manufacture these films and do not participate in the markets for these films. In general, we believe that the markets for these films do not compete with those for graphene nanoplatelets.

XG Sciences offers an advanced material platform in the form of varying grades of xGnP® graphene nanoplatelets produced from two processes, each of which can be customized in many ways. Our proprietary manufacturing processes control the attributes of graphene nanoparticles. These attributes contribute to a range of properties that can be mapped to various end-market applications from automotive to sporting goods to packaging.

Because we have multiple production processes, and because we have invested in application know-how and development of value-added product formulations, we are able to address a range of needs in multiple market segments in a cost effective manner, providing breadth to our base capabilities and product portfolio. We believe these are all key differentiators in the market.

Based on the past 10 years of customer development activity, we understand that performance of graphene nanoplatelets in a specific application is primarily a function of the platelet’s diameter, thickness, planarity (or more broadly – morphology), and to some extent, the nature and concentration of any chemical groups on the platelets. There are other factors that may impact performance, such as optimized dispersion, product form delivered to the customer (powder vs. slurry), and so on. However, for the most part, performance in an application is related to the physical characteristics of the nanoplatelets. XG Sciences is skilled in the design and manufacture of graphene nanoplatelets, and our two proprietary manufacturing processes allow for the production of a broad product portfolio that can meet many needs across diverse end-use markets.

We sell bulk graphene nanoplatelets under the brand name xGnP®. These materials are produced in various grades, which are analogous to average particle thickness and average particle diameters. There are three commercial grades (Grades H, M and R), each of which is offered in three standard particle sizes and a fourth, C Grade, which is offered in three standard surface areas.

These bulk materials, which can be shipped in the form of a dry powder, are especially applicable for use as additives in polymeric or metallic composites, or in coatings or other formulations where particular electrical, thermal and/or barrier applications are desired. We also offer our materials in the form of dispersions of nanoplatelets in liquids such as water, alcohol and other organic solvents, or mixed into resins or polymers such as PET, polypropylene and urethanes.

As stated previously, we use two different commercial processes to produce these bulk materials. Grade H/M/R materials are produced through chemical intercalation of natural graphite followed by thermal exfoliation using a proprietary process developed by XG Sciences. Some of our process components are patented but we have chosen to keep others as trade secrets.  The “grade” designates the thickness and surface characteristics of these materials, and each grade is available in various average particle diameters. Surface area, calculated by the Brunauer, Emmet, and Teller (BET) Method, is used as a convenient proxy for thickness. So, each grade of products produced through chemical intercalation is designated by its average surface area, which ranges from 50 to 150 m2/g of material.

We also use direct methods to measure layer thickness such as tunneling electron microscopy (TEM) and atomic force microscopy (AFM). We are able to extend the surface area higher than those listed here (and therefore, to fewer layer nanoplatelets) but are not yet producing these materials commercially. As the market need emerges for few-layer graphene, we will consider making these materials available commercially.

Grade C materials, and some related composite materials, are produced through a high-shear mechanical exfoliation using a proprietary and patented process with equipment that we invented, designed, and constructed. The Grade C materials are smaller particles than those grades produced through chemical exfoliation. Grade C materials are designated by their BET surface area, which ranges from 300 to 800 m2/g. We are able to produce surface areas as low as 150 m2/g and as high as 900 m2/g but are not yet making those commercially available.  Should the market need them, we are ready to supply them.

We consider ourselves a “platform play” in advanced materials because our proprietary manufacturing processes allow us to produce varying grades of graphene nanoplatelets that can be mapped to a variety of applications in many market segments. However, we prioritize our efforts in specific areas that have the greatest technical, processing, environmental or economic challenges; places where customers are highly motivated to find solutions. At this time, we are focused on a few high-priority areas.

One such area is composites. Incorporation of our xGnP® graphene nanoplatelets into various thermoplastic, thermoset and elastomeric polymers have been shown to impart improvements in strength, electrical conductivity, thermal conductivity and/or barrier performance. We pursue several end-use applications that may benefit from one or more properties and believe that composites represent a potentially large opportunity for commercial sales.

For example, Callaway adopted xGnP® in their new Chrome Soft and Chrome Soft X golf balls. This new Callaway Golf® ball line incorporates XG Sciences’ high-performance graphene nanoplatelets into the outer core of the Chrome Soft balls, resulting in a new class of product that enables increased control, higher driving speeds and greater distance. We have other customers using our materials commercially in sporting goods equipment ranging from field hockey sticks to water sports equipment.

Automotive is another market segment adopting our materials. Ford Motor Company recently announced adoption of our materials in polyurethane based foam for use in fuel rail covers, pump covers and front engine covers.  Incorporation of our high-performance materials results in a 17 percent reduction in noise, a 20 percent improvement in mechanical and a 30 percent improvement in heat endurance properties, compared with that of the foam used without graphene.

We are also getting commercial traction in packing applications with a large U.S.-based water bottling company who is shipping product that incorporates our graphene nanoplatelets into PET.  Where use of xGnP® enables light weighting, improved modulus and shelf life as well providing energy savings during processing. 

XG was founded back in 2006. Since that time, we have sold products to over 1,000 customers in over 47 countries and many are in various stages of testing our products for numerous applications. For most customers, the process of “designing-in” new materials is relatively complex and involves the use of relatively small amounts of the new material in laboratory and engineering development for an extended period of time. We believe following successful development, customers that incorporate our materials into their products will then order much larger quantities of material to support commercial production.

Although, our customers are under no obligation to report to us on the usage of our materials, some have indicated that they have introduced, or will soon introduce, commercial products that use our materials. Thus, while many of our customers are currently purchasing our materials in kilogram (one or two pound) quantities, some are now ordering at multiple ton quantities and we believe many will require tens of tons or even hundreds of tons of material as they commercialize products that incorporate our materials. We also believe that those customers already in production will increase their order volume as demand increases and others will begin to move into commercial volume production as they gain more experience in working with our materials.

In 2017, our customer shipments increased by over 600% to almost 18 metric tons (MT) of products from the 2.5 MT shipped in 2016. In the three months ending June 30, 2018, we shipped 15.4 MT of product (11.2 MT of graphene nanoplatelets in the form of dry powders and 4.2 MT of slurry, cakes or other integrated products containing graphene nanoplatelets), an increase of 716% over the three months ending June 30, 2017 (1.9 MT mostly in the form of dry powder) and an increase of 5% as compared to the three months ending March 31, 2018 (10.4 MT of dry powder and 4.4 MT of slurry, cakes or other integrated products containing graphene nanoplatelets). This demand profile is further evidence that we are transitioning into higher-volume production. It’s a really exciting time for XG Sciences as we see our customers move into commercial production in multiple applications and end-use markets.

 Q: That leads to my next question, which is: are you moving up the value chain? For instance, you said you’ve invested and done a lot of work on energy storage and batteries, which is a very complicated business and physics and science to invest in. Are you looking to move up the value chain there? Creating perhaps a lithium-ion battery based on graphene, or are you still looking at yourselves as suppliers of the material for graphene and for battery producers?

A:  It's a great question. We don’t see ourselves making water bottles or golf balls. However, we do make a range of advanced materials we have coined as “integrated products”. These are all products that contain graphene nanoplatelets.

For example, we have a platform of inks and coatings that incorporate proprietary grades of our xGnP® graphene nanoplatelets. These grades are specifically designed for a given application and may not be offered for sale as dry powder – we reserve their use only in an integrated product. We may add binders and surfactants and solvents depending on the final application.  We have a concrete additive product available on Amazon that may fall into that category as well. We also make masterbatches of various thermoplastics (PP, HDPE, PET, etc.) where we vary the nature of the graphene nanoplatelet and the concentration to target various end-use applications.

In the next 3-5 years, we target 50% of our revenue coming from bulk materials (powders, slurries, cakes, etc.) and the other 50% from various forms of integrated products. 

Q: I would just like to circle back to the iterative process and working with the end users you mentioned earlier, and turn to a question I sent to you previously and that is, what is the greatest challenge for you in working with someone who's new to graphene that you have to explain what it's capabilities are? You outlined that already, but if you could just pinpoint a particular issue that you find that raises itself over and over and over again I think that would be illustrative.

A: There really isn’t any one greatest challenge – there are many small challenges that vary from customer to customer. I think at a fundamental level, in order to be a viable supplier of any advanced material – and certainly graphene nanoplatelets are no different – suppliers must be able to demonstrate three key things: performance, cost and scale.

Until a supplier is able to demonstrate these characteristics, customers may only consider them as an academic curiosity – and that is not meant to cast any aspersions on our academic colleagues. That is to say that a customer will not risk putting a new material into their product unless they are certain that such material will perform, that its price allows for its adoption and that it can be supplied in sufficient volume to meet demand requirements over time.

Of course, there are other relevant requirements such as batch-to-batch consistency, IP, access to capital to enable growth, etc. So, the primary “challenge,” if we couch it in that context, is set by the broader customer base that requires demonstration of viability, capability and credibility as a supplier.  We are able to meet, and in many instances exceed, these criteria so our primary task is now one of execution.

We have commercial traction and expect customers to continue to ramp their own production. We have many customers who are approaching commercialization and will add to our revenue growth over the next several quarters. In the meantime, we will continue to grow our organizational capability as well as our capacity to meet rising demand.

We recently announced completion of the first phase of the capacity expansion in our newest 64,000 square foot facility. The expansion has added 90 metric tons of graphene nanoplatelet production capacity, bringing the total capacity of the facility up to approximately 180 metric tons per year. Phase two of the expansion is expected to be complete by year-end and will result in up to 400 metric tons of total graphene nanoplatelet output capacity at the facility. Our total graphene nanoplatelet output capacity across both of our manufacturing facilities currently exceeds 200 metric tons per year and will more than double over the next three months, reaching up to an approximate 450 metric tons by year-end. The expansions support our mission to continue commercializing the use of graphene in customer products across diverse industries.

Q: I noticed in your background you worked at Sigma Aldrich, which is one of the big chemical companies. Did that give you a better understanding of what was ahead for you in order to get your product qualified by these companies? In other words, it appears as though smaller graphene producers are on a different time scale than a big chemical company. A big chemical company doesn't have any rush to do anything until they have the supply chain firmed up the way they want it, whereas, a smaller graphene producer, would like to start moving product as soon as possible. Does that give you any insight? What value did that provide you?

A: I think it absolutely does. I worked for Rohm and Haas prior to Sigma Aldrich and between the two, and now with XG Sciences, I have been in advanced materials for my entire career – which I am reticent to admit is now almost 30 years!

I have been involved in successfully introducing new materials to semiconductor manufacturers like Intel, IBM and TSMC, and to display manufacturers such as LGD, Samsung and AU Optronics as well as in a number of other electronic and industrial applications and markets. The process for new-material adoption is fairly end-market agnostic and the fundamental requirements of a supplier that I previously articulated are still relevant. The timing for adoption may vary from customer to customer and from market to market, but the process is the same.

Having successfully installed new materials with multiple customers and in multiple end-markets is very advantageous in helping to direct XG Sciences’ growth. Of course, it takes a team, and XG Sciences has very capable people in each of the functional areas required for success.

Q: You are a publicly traded company, right?

A: No. We have public reporting requirements by virtue of our self-underwritten public offering and S-1 registration statement, but we are not listed on any exchanges at this time. It is our intent to consider an up-listing event in the next 12 to 18 months.

 Q: With your background in advanced materials and while you're looking more at electronics like semi-conductors and flat panel displays, but when you mentioned the barrier for bottles and those containers, I remember some years back maybe 15 years back, people were talking about nano clays so that you could have plastic beer bottles at ball parks. What are the benefits over some of those other nanomaterials for graphene platelets?

A: That's a good question. It really depends on what performance they wish to achieve and then to assess whether that is achievable using a given material.  One of the clear advantages of graphene nanoplatelets over other nanomaterials is their ability to impart multi-functional performance. In the example I gave for PET-based water bottles, incorporation of our nanoplatelets improve physical strength, shelf life (barrier) and energy savings (thermal conductivity). A nanoclay, for example, would likely only impact barrier performance – and perhaps not to the extent one could achieve with graphene nanoplatelets.

We don’t typically see our materials competing with other nanomaterials for the same application. Graphene and graphene nanoplatelets are a relatively new material – they open up new performance and design options to engineers.  That’s what makes these materials so exciting and why we are focused on building a company around their manufacture and supply. We are beginning to see their adoption at large volumes and in multiple applications, which bring about more curiosity and provide evidence of the power of graphene to a wider audience. I have touched on just a few applications in our discussion so far, but the full breadth of the impact graphene nanoplatelets can have is nearly limitless. 

Tags:  Callaway  CVD  GNP  golf ball  graphene platelets  Li-ion batterie  sporting goods 

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There is no quality graphene without quality control

Posted By Terrance Barkan, Thursday, December 14, 2017

A group of researchers from Denmark, UK and Spain within the Graphene Flagship project, explains in a recent review paper why the graphene industry needs better and faster electrical characterisation methods. The Graphene Flagship is a large European project, with more than hundred research groups collaborating on development of novel graphene technologies and applications. 

Just 5 years after the first announcement that graphene could be isolated at all, Rod Ruoff (2009) and Samsung (2010) showed that graphene can be synthesized in a deceptively simple way; by decomposing hydrocarbons at high temperature, leaving single layer graphene sheets to crystallise on a copper surface. 

Today, just 7 years later, graphene sheets are produced and used in large quantities – or areas – for instance for cell phone touch screens, according to Chinese researchers. 

While large-area fabrication is taking off fast, the methods for quality control are lagging behind – and this is particularly true with respect to the electronic properties that are central to many applications. 

Electrical measurements are most often done by turning the graphene film into a number of electrical devices, where field effect measurements give the “key performance indicators” of conductivity, carrier density and mobility. Depending on the number of devices, and the time spent on measuring, such tests can also give an idea about the variability. The two main drawbacks are ; (1) the process is fundamentally destructive – the graphene is irreversible damaged in the process, and (2) the throughput is many orders of magnitude smaller than the CVD-based fabrication of the graphene in the first place creating a bottleneck. 

Researchers at the Technical University of Denmark and at the National Physics Laboratory in UK have over the past several years developed a number of fast, large-scale, non-destructive characterisation techniques of electronic properties that they believe have the potential to become game changing technologies. 

A recent review focuses on one of these: terahertz time-domain spectroscopy (THz-TDS).

THz-TDS shoots terahertz pulses through the graphene and measures how much the film absorbs. The absorption spectrum up to 2 THz depends distinctly on the conductivity as well as on the scattering time – a measure of the average time the carrier spend between collision with obstacles.

Knowing these two, the carrier density and mobility can be computed. The technique has been meticulously verified against electrical measurements and is now being proposed as a metrology standard, in collaboration with the Spanish company DasNano, who are the first to manufacture terahertz-based conductivity mapping equipment for graphene. 

Peter Bøggild, professor at DTU puts it like this: “Trivially, there can be no industry without quality, and there can be no quality without quality control. Non-contact mapping is fast and non-destructive, so anyone interested in consistency, reproducibility and reliability of graphene films, should pay attention.”

The review paper is available as open access at IOP 2D Materials.

 

Tags:  carrier density and mobility  conductivity  CVD  Graphene  Quality  terahertz time-domain spectroscopy  Touch Screens 

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