30 June 2013

Molecular electronics meets the #graphene rescue squad

The IEEE’s excellent nanotechnology blog, Nanoclast has an interesting take on research at the University of Copenhagen and the Chinese Academy of Sciences in Beijing. The story, Graphene Comes to the Rescue of Molecular Electronics, describes a chip design “whose initial application could be testing the molecular chips researchers envision”.

The news item leads us to a paper in Advanced Materials, Ultrathin Reduced Graphene Oxide Films as Transparent Top-Contacts for Light Switchable Solid-State Molecular Junctions. The paper's abstract, you'll have to pay to read the whole thing, describes "A new type of solid-state molecular junction ... which employs reduced graphene oxide as a transparent top contact that permits a self-assembled molecular monolayer to be photoswitched in situ, while simultaneously enabling charge-transport measurements across the molecules".

The IEEE based its write up on a press release from the University of Copenhagen, Danish chemists in molecular chip breakthrough. (Scientists always complain when journalists write in terms of 'breakthroughs' but don’t seem to mind using them when it suits their own needs.) The Danish take on the research is that "for the first time, a transistor made from just one molecular monolayer has been made to work where it really counts". It seems that Kasper Nørgaard, an associate professor in chemistry at the University of Copenhagen, sees the work as a first step towards proper integrated molecular circuits.

New platform for memory and chips

MIT was bound to be an active player with graphene, even though, excellent as it is, the place isn't quite as all conquering as the reputation might suggest. It does, though, have a world class media machine and its has just come up with the press release Ferroelectric-graphene-based system could lead to improved information processing. This tells us that "a new system that combines ferroelectric materials — the kind often used for data storage — with graphene, a two-dimensional form of carbon known for its exceptional electronic and mechanical properties".

The release reports on a paper in Applied Physics Letters by associate professor of mechanical engineering Nicholas Fang, postdoc Dafei Jin and three others. Like the Danish paper, this one makes some pretty bold claims. as the MIT release put its "The system would provide a new way to construct interconnected devices that use light waves, such as fiber-optic cables and photonic chips, with electronic wires and devices. Currently, such interconnection points often form a bottleneck that slows the transfer of data and adds to the number of components needed."

Unlike some papers on graphene, this one is based on a real device rather than a theoretical notion. “The team’s initial proof-of-concept device uses a small piece of graphene sandwiched between two layers of the ferroelectric material to make simple, switchable plasmonic waveguides.”

An interesting twist to the story is where the release quotes Dimitri Basov, a professor of physics at the University of California at San Diego “who was not connected with this research”. He told them that the MIT team has “proposed a very interesting plasmonic structure, suitable for operation in the technologically significant [terahertz] range”. But then he goes on to warn that “The key issue, as in all of plasmonics, is losses. Losses need to be thoroughly explored and understood.”

It isn't often that you read a press release that raises the sort of question that a writer should pose when following up a press release. But MIT's PR machine is seriously good, which partly explains the wider perceptions of the place.

Plasmonic switches on the infrared

There’s another contribution to graphene’s possibilities with  plasmonic devices over at Optics Express (open access). The paper, Graphene-based plasmonic switches at near infrared frequencies, describes research done at the École Polytechnique Fédérale de Lausanne where they designed various switches that can “dynamically control the propagation of plasmons on graphene surfaces at near infrared frequencies”. The Swiss researchers say that their results “have demonstrated that controlling the properties of very reduced graphene areas provides extremely large isolation levels between the input and output ports”.

22 June 2013

Papers with embedded #graphene

Not every paper about the wonder material advertises its presence from the hilltops, or even in the title. Take Measuring the lateral size of liquid-exfoliated nanosheets with dynamic light scattering. This is another of those ‘catch it while you can’ papers in the IoPP journal Nanotechnology (doi:10.1088/0957-4484/24/26/265703). They do flag graphene in the abstract, saying that “we prepared a range of dispersions of graphene, MoS2 and WS2 nanosheets with different mean lateral sizes”. In essence, though, they are interested in working with “two-dimensional materials”, including graphene. The idea behind this research seems to have been to develop “a simple method to estimate the lateral dimensions of nanosheets dispersed in a liquid”.

The people behind the work, at Trinity College Dublin and Imperial College London, warn that their technique “is not highly accurate” but it has the advantage that it is “fast, simple and used equipment available in most analytical labs”. They conclude that “it it is perfectly suited to preliminary measurements or comparison of samples where a large size differential is expected”.

Lost in spacetime

There’s another embedded reference to graphene in Analogue Transformations in Physics and their Application to Acoustics Nature Scientific Reports (doi:10.1038/srep02009). This time the paper is all about “invisibility cloaks”, materials that can play tricks with electromagnetic radiation (EMR), that’s light to most of us, and hide things from prying eyes. The science soon gets hairy with references to “a complete transformation method using the idea of analogue spacetimes”. In this case, they are more interested in sound waves than in EMR.

Graphene comes into the picture because, according to the researchers from all over Europe, well from Finland to Spain taking in The Netherlands, “The method is general and could be considered as a new paradigm for controlling waves in different branches of physics, from acoustics in quantum fluids to graphene electronics.” They even went so far as to “give explicit designs of a dynamic compressor, a spacetime cloak for acoustic waves and a carpet cloak for a moving aircraft”.

17 June 2013

A sheaf of papers on #graphene

It is impossible to keep up with the torrent of papers on our wonder material. So let's just look at a few from the past few days.

How to make vertically oriented graphene nanosheets

The journal Nanoscale has just published a paper, a review article no less, with the title “Plasma-enhanced chemical vapor deposition synthesis of vertically oriented graphene nanosheets”.  All behind a paywall, of course.

The abstract gives a good idea of what you will get if you cough up your £36. “This paper attempts to summarize the state-of-the-art research on [plasma-enhanced chemical vapour deposition] growth of [vertically oriented graphene] nanosheets to provide guidelines on the design of plasma sources and operation parameters, and to offer a perspective on outstanding challenges that need to be overcome to enable commercial applications of VG.”

It comes with an interesting picture:

Pity there isn’t a caption. Guess you have to buy the paper for that.

More in Nanoscale

Nanoscale also bills several other graphene papers in the same issue:

  • Graphene plasmon enhanced photoluminescence in ZnO microwires
  • Atomistic modelling of CVD synthesis of carbon nanotubes and graphene
  • Self-assembled graphene quantum dots induced by cytochrome c: A novel biosensor for trypsin with remarkable fluorescence enhancement

  • Another paper turns up in the journal's roster of This week’s HOT articles

  • Mechanical reinforcement fibers produced by gel-spinning of poly-acrylic acid (PAA) and graphene oxide (GO) composites 

  • In theory

    Nice to see the theoreticians are on the case. This in Phys. Rev. Lett. from folks at the Institute for Theoretical Physics at the University of Regensburg.

    Spin-Orbit Coupling in Hydrogenated Graphene offers “First-principles calculations of the spin-orbit coupling in graphene with hydrogen adatoms in dense and dilute limits”. So now you know.

    Laser peels off graphene layers

    Thanks to the excellent regime over at IoP Publishing, everyone has 30 days in which to grab the paper Thinning of large-area graphene film from multilayer to bilayer with a low-power CO2 laser from the journal Nanotechnology, a constant source of new papers on graphene. The abstract tells us that “Bilayer graphene has attracted a great deal of attention for many electronic and optical applications”.

    This paper describes a way of turning the multilayer graphene you get when you make graphene with chemical vapour deposition into a ‘bilayer’ material. This isn’t the first time that people have used layers to thin down graphene, but this time, the researchers claim, the approach “enables high-efficiency thinning of large-area graphene film whilst using a significantly reduced power density and an increased laser beam diameter”.

    There’s an interesting connection to Manchester University. This time it isn’t the world famous graphene group that chipped in, but the Laser Processing Research Centre. The graphene expertise seems to have come from Tsinghua University in Beijing.

    Graphene on silicon

    Another interesting paper over at IoPP is in the open access publication New Journal of Physics, so no need to rush for this one. Strongly confined gap plasmon modes in graphene sandwiches and graphene-on-silicon comes from Imperial College. The researchers have been slapping payers of graphene on top of one another, or, as they put it, “two infinitely long graphene ribbons vertically offset by a gap”.

    To demonstrate the relevance of their work, the authors report “an unprecedented level of confinement of a terahertz wave of nearly five orders of magnitude when a graphene ribbon is placed on top of a highly doped silicon substrate”. They add that these phenomena and semiconducting substrates “could be the building blocks for both graphene-based integrated optics and ultrasensitive sensing modalities”. Now it just needs someone to do the experiments to show that this is not a mad idea.

    14 June 2013

    Graphene wired – atom by atom, and other stories

    It can take just one chemical bond to make an electrical connection to a graphene ribbon. Researchers at Aalto University in Finland and Utrecht University in the Netherlands did this with “single atom contacts between gold and graphene nanoribbons”.

    The researchers describe their work in a paper in Nature Communications, sadly, hidden behind a paywall. Fortunately, the people behind the research are so enthused about their work that they have produced a press release. This points out the small at which graphene electronics can work, less than 10 nanometres. “This means that the graphene nanostructures have to be only a few tens of atoms in width.” 

    The experiments described in the paper, “Suppression of electron-vibron coupling in graphene nanoribbons contacted via a single atom” showed how to do this. The research involved using atomic force microscopy and scanning tunnelling microscopy “to map the structure of the graphene nanoribbons with atomic resolution”.

    The most significant discovery, they say, is that “a single chemical bond forms an electronically transparent contact with the graphene nanoribbon”. They conclude that this finding “may be the key to using graphene nanostructures in future electronic devices, as the contact does not change the intrinsic ribbon properties”.

    Tie a graphene ribbon round your battery
    Problems with lithium ion (LI) batteries may have given Boeing a headache, but this popular energy store has plenty of fans and down to earth applications. Now researchers at Rice University in Houston, Texas, have come up with a new way of enhancing the efficiency of the LI battery. Their idea, according to the university’s press release, is to employ ribbons of graphene that start as carbon nanotubes.

    The researchers made anodes out of graphene nanoribbons (GNRs) and tin oxide. (The anode is the bolt hole for the lithium ions, which move to the cathode as the battery discharges.) This novel anode material, “showed an initial capacity better than the theoretical capacity of tin oxide alone”.

    It will cost you US$35 to read the paper in ACS Nano, “Graphene Nanoribbon and Nanostructured SnO2 Composite Anodes for Lithium Ion Batteries”. (If it is worth writing a press release, isn’t it also worth providing free access to potential readers?)  So we have to rely on what the release says for signs of the true significance of the research. This claims that “After 50 charge-discharge cycles, the test units retained a capacity that was still more than double that of the graphite currently used for LI battery anodes.”

    As much as anything, the team sees the work as a testbed for applications of GNRs, a fertile area of research for our wonder material. A member of the group, Jian Lin, a postdoctoral researcher at Rice, describes the research as “starting point for exploring the composites made from GNRs and other transition metal oxides for lithium storage applications.”
    The Manchester PR machine rolls on
    There was an odd story in the Financial Times this week. The print edition carried the tag “Graphene research” but there wasn’t much of that in sight. The on-line version makes it appear even more graphene oriented, with its title “Graphene breakthrough shows Manchester’s science credentials”. In reality it was mostly a gushing piece about Manchester University and its commercialisation of research that goes on there.

    The peg for the articles seems to have been the recent press release that we flagged up earlier in the week (see Manchester untied). That was all about magnetism in graphene. Only time will tell us whether or not the paper described there was, as the FT dubs it, another “breakthrough”, but it is certainly a breakthrough in PR.  What on earth do we make of the statement that “The university is also home to Professor Brian Cox, the physicist and broadcaster, Sir John Sulston, the Nobel Prize winner who was involved in decoding the human genome, and Jeanette Winterson, the novelist.”

    The FT’s article also has some numbers that do not seem to have any relationship with the graphene bit of the story. What do we make of the information that “the university had won £200m in research funding in the first 10 months of the academic year”? How much for graphene?

    Then there is the bit that says that the university’s “£32m spin-out fund is funding several attempts to find commercial uses for graphene”. How much of that money has gone into graphene? Can’t they tell us something about those investments?

    After all, the writer just needed to read some back issues of the FT. It was on in January that Clive Cookson wrote the article Graphene: Faster, stronger, bendier. This mentioned one of the Manchester businesses, Graphene Industries. Over on the university;s own site, the paper’s journalist could have read the PDF file that describes the launch, last February, of another company, 2-­DTech Ltd.

    Manchester is a fine university, one of the best, and has an excellent record in knowledge transfer, the sometimes fraught business of getting research into the hands of people who can make money out of it. And you can hardly blame it for the FT’s decision to write something as baffling as this, with its strange mixture of graphene researcher, general university background and throwaway comments from the likes of Eric Schmidt, the chairman of Google.
    Heavy metal and the graphene connection
    The eyebrows rise when a paper begins “Heavy metal ions and humic acid (HA) in underground water pose a severe threat to public health and ecological systems”. Lots of buzz words in there to appeal to a science watcher. Throw in the title of the paper, “Synergistic Removal of Pb(II), Cd(II) and Humic Acid by Fe3O4@Mesoporous Silica-Graphene Oxide Composites”, and you ask yourself what is graphene doing in there?

    The paper appears in PLOS One, a peer reviewed open access journal, so anyone can read it and work out for themselves what is going on. It is about hierarchically structured composites containing polyethylenimine-modified magnetic mesoporous silica and graphene oxide (MMSP-GO), whatever they are. The good bit appears to be that “MMSP-GO composites have shown promise for use as adsorbents in the simultaneous removal of heavy metals and humic acid in wastewater treatment processes.”

    So you can add cleaning up the environment to graphene’s repertoire.

    This blog is a random sample of the many stories on graphene that gush by. Think of it as a poor person's alternative to the expensive newsletters that you can subscribe to from commercial organisations that really do know what they are talking about. 

    12 June 2013

    Spintronics doctors and other graphene stories

    The week started well for graphene. No less an accolade than a paper in the Proceedings of the National Academy of Sciences. The trouble comes when you try to make head or tail of the title, Valley Chern numbers and boundary modes in gapped bilayer graphene. It seems to be something to do with topological states and defects.

    The researchers at the University of Pennsylvania and the University of Texas at Austin conclude that “gapless interface modes at a LSW are topologically stable when the potential difference between layers is the dominant energy scale and the valley index can be regarded as a good quantum number”. Doubtless this is a truly significant finding for some folks, or it wouldn’t have got into the PNAS. Sadly, the journal does not deem it important enough to have written one of its reader friendly briefs.

    Graphene meets silicon
    There doesn’t seem to have been much recent graphene activity in Norway, so it is interesting to see a press release on “potential products from the union of semiconductors and graphene”. As the release from The Research Council of Norway puts it “Semiconductors grown on graphene at the Norwegian University of Science and Technology (NTNU) may be the most important research breakthrough of 2012 in Norway.”

    The release also has an interesting historical anecdote. It seems that the NNTU was put on to the case of graphene six months before the material collected a Nobel prize for its ‘inventors’ and “before graphene had become an item of interest”.  A South Korean post-doctoral fellow Dong Chul Kim at NTNU suggested to Helge Weman and Bjørn-Ove Fimland “that they should take a closer look at precisely this material”. The researchers had already grown gallium arsenide nanowires on silicon substrates, so they looked into the possibility of growing semiconductor nanowires on graphene instead. You can follow how they did it in a video on YouTube.

    Grow your own nanowires on graphene
    The Norwegian researchers aren’t blind to the potential of their work. As they said when they first touted their breakthrough, patented of course, they have set up a business, CrayoNano to turn the science into money.
    Manchester untied
    They are at it again in the labs that brought us graphene. According to the latest press release “a University of Manchester team led by Dr Irina Grigorieva shows how to create elementary magnetic moments in graphene and then switch them on and off”. The report is another part of the armoury of graphene electronics.

    The news, trailing a paper in Nature Communications, comes with some entertaining notions “Graphene is a chicken wire made of carbon atoms.” On a more scientific note, it quotes Dr Rahul Nair, who led the experimental effort: “Graphene already attracts interest in terms of spintronics applications, and I hope that the latest discovery will make it a frontrunner.”

    The media friendly quotes may owe something to the fact that the Manchester team now seems to have a full time communications person. The contact for the story is Daniel Cochlin who is billed as Graphene Communications and Marketing Manager.

    07 June 2013

    A busy week for four carbon bonds

    Where graphene hits the headlines, and other nooks and crannies
    Another week, and more news of weird stuff that four carbon bonds can get up to when they get properly organised. Over on the Knowledge Transfer Network (KTN) Materials group they write about Hybrid graphene flame retardants in epoxy improve fire and high temperature performance. Apart from the fact that it is yet another use of our wonder material, the interesting bit is the source of the work. As the KTN write up puts it “Lei Song from University of Science and Technology of China used an in-situ sol-gel process to make organic-inorganic hybrid flame retardants.” The item has a link to the paper in the Journal of Materials Chemistry A, which you’ll have to pay for.
    The China connection is just another sign of the attention that the local research community is lavishing on us. Of 614 papers that mention graphene in a random selection of publications retrieved over the past decade from the IoPP’s fine library 88 mention the “People’s Republic of China”.
    Boiling under
    Always nice to see someone finding a new use for graphene, as in another paper from Nature Scientific Reports. Here’s another one with a safety angle. A Novel Role of Three Dimensional Graphene Foam to Prevent Heater Failure during Boiling, describes “a novel boiling heat transfer in reduced graphene oxide suspended in water near critical heat flux, which is traditionally the dangerous limitation of nucleate boiling heat transfer because of heater failure”. The writers claim that this phenomenon “would provide the safer margin of the heat transfer and the amazing impact on the thermal system as the first report of graphene application”. The bottom line, they say, is that “This novel boiling phenomenon can effectively prevent heater failure because of the role played by the self-assembled three-dimensional foam-like graphene network.”
    Strong stuff
    Even engineers of a decidedly mucky nature are muscling in on graphene. Those fine observers of everything manufacturing over at The Manufacturer have found a story from Columbia University. Following the trail we get to the original item “Even with Defects, Graphene Is Strongest Material in the World”. This then leads us to a paper in Science where the more prosaic title “High-Strength Chemical-Vapor–Deposited Graphene and Grain Boundaries” explains why The Manufacturer liked the item. The paper tells us that even graphene of a less than pristine nature – “polycrystalline and thus contain grain boundaries” – is still strong stuff, as strong as the scientifically pure graphene so long as “post-processing steps avoid damage or rippling”.
    Elephant memory
    We’ve been here before it seems. The latest Columbia paper is a follow up to a five-year old publication from the same group that gave us the press release “Columbia Engineers Prove Graphene is Strongest Material”. It was this release that arrived with the quote from James Hone “It would take an elephant, balanced on a pencil, to break through a sheet of graphene the thickness of Saran Wrap.” (This is believed to be a local reference to what Brits might call ‘clingfilm’.)
    Apple files patent
    The newshounds over at New Scientist spotted a patent application from Apple that could see graphene in heat sinks for portable electronic devices. The patent’s claims include:
    “A method for facilitating the use of a portable electronic device, comprising-  arranging a set of components and a battery within an enclosure of the portable electronic device; disposing a heat dissipator comprising graphene over a surface of the battery; and providing thermal contact between one or more of the components and the heat dissipator.”
    Few patents make it into production. If this one does, will Apple pay taxes on anything that comes from this invention?
    Electrodes on the brain
    Nanotechnology, the journal, has a more substantial offering on graphene in electronics in The application of graphene as electrodes in electrical and optical devices. With all of the authors working in Korea, where they make electronic stuff by the container load, there’s a better chance that this work, a review of activity in the area, will see light of day. Clearly people are reading this paper: published last year, when we last looked it was number two in the list on the journal’s home page of papers “most read” in the past 30 days.

    Makes you wonder
    Hard to know what to make of this “case study” from EPSRC. no doubt about the subject The wonder stuff but the PDF says no more than the minimal text on the page. there isn’t even a live link to the people the page describes. So we had to get Google to take us to Durham Graphene Science. It turns out to be a spinout from Durham University that has “developed a novel process for the manufacture of high specification graphene”. Smart move: in the early days any money to be made from graphene will go to people making the stuff and selling kit to the research community. Not much in the way of news since 2011 though.
    A sort of battery
    Spinouts are de rigeur for enterprising academics these days. Indeed, it looks like our four carbon bonds have sparked off a new business sector, the graphene battery. There is even a new company out there exploiting their tricks. Graphene Batteries, based in Oslo, “is engaged in development of safe and durable graphene based high energy battery materials”. The idea is to assemble “a key technology IP-portfolio for future licensing and production”.
    Another company with a finger in the battery business is Lomiko Metals Inc. Lomiko, which has its own graphite mines, recently put out a press release on a collaboration with the Research Foundation of Stony Brook University and Graphene Laboratories, Inc. “to investigate novel, energy-focused applications for graphene” with a specific mention of batteries. The release tells us that “the goal of this collaboration is to map commercially viable routes for the fabrication of graphene-based energy storage devices”.
    Graphene Laboratories, based on Long Island, New York, describes itself as “a world leading manufacturer and supplier of graphene products to R&D markets”. So the business reflects the level of maturity, or lack of it, of the graphene market. Perhaps it won’t be long before R&D becomes R, D & D (that’s research, development and demonstration) with the usual order-of-magnitude rise in the costs of projects.
    In the picture
    There’s another patent application in the works (see Apple above) for a neat use of our slithery carbon bonds, this time from a university group. Laser Focus World tells us that over at Nanyang Technological University (NTU) in Singapore Assistant Professor Wang Qijie has come up with a graphene based image sensor that will allow cameras “to take clear and sharp photos in dim conditions”. The NYU press release optimistically proclaims that we’ll see this development “soon”. The trick was to “create nanostructures on graphene which will “trap” light-generated electron particles for a much longer time, resulting in a much stronger electric signal”.

    Professor Wang Qijie slides on graphene that can see in the dark
    How facile can you get?
    It is always entertaining trying to work out just what the titles of papers mean when they give us a plug. Here’s one that provokes several lines of thought “Facile, scalable synthesis of edge-halogenated graphene nanoplatelets as efficient metal-free eletrocatalysts for oxygen reduction reaction”. It comes from Nature Scientific Reports which, as an open access journal, is free for all to read and ponder.
    The journal is a regular source of papers about graphene. Here’s one with an intriguing title Highly Sensitive and Selective Gas Sensor Using Hydrophilic and Hydrophobic Graphenes. This time you can see that we are into sensor territory. Oh, yes, the paper’s authors are in Korea.
    EuroGRAPHENE’s final fling
    They have been thinking about graphene in Strasbourg, where the European Science Foundation (ESF) put together EuroGRAPHENE, “the first coordinated European-wide cooperation on graphene science and technology”. The programme ends this year so the ESF has put together a report on Scientific Highlights (a 2.7 MB PDF file that you can shrink to half that size with the right software!). It lists seven Collaborative Research Projects carried out all over Europe. Well most of Europe, not much in there from the UK.
    Far from weak ending
    The IoPP rounds up a working week of papers with another interesting title Direct writing on graphene 'paper' by manipulating electrons as 'invisible ink. Again, the source is the journal
    , with authors from the Department of Energy Conversion and Storage at the Technical University of Denmark, and Beijing Key Laboratory of Green Chemical Reaction Engineering and Technology at Tsinghua University.
    As the abstract puts it “The combination of self-assembly (bottom up) and nano-imprint lithography (top down) is an efficient and effective way to record information at the nanoscale by writing.” The researchers say that they achieved “Direct high precision microscopic writing on graphene … through an EDX line scan with 1 nm probe in STEM mode”. They sum up their achievements with the observation “These results not only shed new light on an application of graphene concerning the interaction of different forms of carbon but also illuminate the interaction of forms of carbon through an electron beam.”
    This is just one of a batch of four papers in the journal. Also check out Control of density and LSPR of Au nanoparticles on graphene, Intrinsic loss due to unstable modes in graphene and Control of density and LSPR of Au nanoparticles on graphene.
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