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Carbon Nanotubes Provide Reinforcement to Composites Instead of Merely Filler

I have at times made out the use of carbon nanotubes in fillers for composite resins as much a marketing ploy as it was a structural improvement.

It seems researchers of a joint research project between Applied NanoStructured Solutions LLC (ANS, Baltimore, Md.), a Lockheed Martin subsidiary, and Owens Corning (Toledo, Ohio) were not altogether satisfied either with just using carbon nanotubes in these fillers.

The researchers were frustrated that resin loading of the carbon nanotubes was limited to little more than 3% or else the filler would become to viscous. So instead they started to look for ways of using carbon nanotubes in reinforcements rather than resins.

Back in 2007 when they embarked on this project they were looking to develop a way to incorporate nanoparticles directly into the fibers themselves. Now they have done that and also managed to do it in a way that it can be dropped into composites processors.

“We have developed a way to grow carbon nanostructures on fabrics,” Dr. Tushar Shah, ANS’ chief technology officer, is quoted as saying in the article from Composites World. “We’re not making CNTs and then transferring them,” he clarifies. “This is a continuous, direct growth process, directly onto the reinforcing fibers.”

The first application area being targeted is in electronics for electromagnetic interference (EMI) shielding. But that is really just a starting off point.

Because the composites developed with this process exhibit an inherent conductivity they are likely strong candidates for structural health monitoring (SHM) applications in which the material itself could serve as an in situ nanosensor in “smart” body armor.

If this industrial partnership is successful in getting these composites into more products, I think my reflex to scoff at the use of carbon nanotubes in them will have been cured.

Viruses Enable Carbon Nanotubes to Better Conduct Electrons in Solar Cells

One of the fundamental problems in using carbon nanotubes (CNTs) for solar cell applications is that you often get a mix of  semi-conducting nanotubes and conducting (metallic) CNTs.

While a couple of years back researchers discovered that adding imperfections to CNTs used in dye-sensitized solar cells helped in their catalytic function, it did not seem to do much for their conductivity, or really make much of a marked effect on their overall efficiency.

But now Angela Belcher and her research associates at MIT, who have been using viruses to improve lithium-ion batteries, have found that they can use viruses to sort out the various nanotubes and create a better material for transporting electrons through it

The research, which was initially published in the journal Nature Nanotechnologydescribes how by the manipulation of the protein sequence of the M13 virus it created a pH switch that attracts the carbon nanotubes to it.

While the research used dye-sensitized solar cells, the researchers believe that the technique could be used with quantum-dot and organic solar cells.

It is the level of improved efficiency that is obtained through this technique that has impressed. It is reported that this method can improve the efficiency of the dye-sensitized solar cells by 30%, bringing their conversion rate to 8 to 10%. Not earth shattering numbers, but an improvement with these types of solar cells. 

In the article cited above, Prashant Kamat, a professor of chemistry and biochemistry at Notre Dame University who has done extensive work on dye-sensitized solar cell, comments, “Dye-sensitized solar cells have already been commercialized in Japan, Korea and Taiwan,” he says. “If the addition of carbon nanotubes via the virus process can improve their efficiency, “the industry is likely to adopt such processes.”

"Ground Breaking" Research in Nanotechnology Doesn't Appear to be Related to Nanotechnology At All

About 12 years ago, the world of physics was abuzz with the news that researchers led by Lene Hau had slowed down the speed of light from 186,282 miles a second to about the speed of grandma on the highway (38 miles an hour). 

Now we have news that researchers in Australia are using silicon photonic crystals to slow down light to generate individual pairs of photons.

The device the researchers from the Centre of Excellence for Ultrahigh Bandwidth Devices for Optical Systems (CUDOS) nodes at the University of Sydney and Macquarie University developed is 100 microns long, making it 100 times smaller than the one-centimeter devices used by other groups.

Great! Chapeau…and all the rest. But could someone explain to me how this story constitutes research into nanotechnology as the headline states. I became even more bewildered when the article claimed that the device is on the nanoscale. I don’t get it 100 microns is small for sure, but 100 microns is equal to 100,000 nanometers, just sayin’.

I do not know where the research was originally published so I don’t have any place to check this information. Maybe there is some kind of explanation for it being considered a “nanotechnology-related” story. I’d be glad if anyone could comment with an explanation. 

But then again perhaps the market analysis and investment folks are not the only ones engaged in pointlessly hyping nanotechnology. It’s being given credit for a development that apparently is more within the field of photonics than nanotechnology, and is being plastered all over Twitter like the biggest breakthrough in nanotechnology since…well, ever.

Will Science or Politics Ultimately Define Nanotechnology?

Recently I reported on the strained efforts of an EU commission to define nanomaterials that could possilby shape nanotech regulations into the foreseeable future.

At the time I wrote the article, my thought was that for all of their struggle on deciding whether a nanomaterial was best defined as “how many” nanoparticles or “how much” it didn’t really seem to address whether there was in fact any risk from either.

Andrew Maynard commented on the entry and promised an analysis of the situation, which we now have.

Maynard’s insights get far deeper into the fundamental problems that occur when bureaucrats attempt to define nanotechnology. According to Maynard, what you risk ending up with is politics dictating health and safety regulations rather than science.

And the politics in this instance are a powder keg of misinformation. As Maynard relates in his analysis, “This situation has been exacerbated by the underlying assumption that nanomaterials present a unique risk.  And all too often the science has been co-opted to support this position rather than to evaluate it.”

We are given the example of how European Commission Directorate General for Health and Consumers Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR) last year published a paper, which Maynard describes as one containing “a palpable sense of the authors contorting themselves to serve an assumption that doesn’t align well with the facts.” He adds, “It’s no surprise therefore that the conclusions they reach are peppered with caveats that seem to call into question the assumption on which their task was based.”

Maynard points out that just five years ago he was among the chorus of those calling for a definition of nanomaterials. But it seems the more science reveals about the properties and possible risk of nanomaterials and nanoparticles the less beneficial it will be to arrive at this definition.

“Five years ago, the state of the science was such that it still seemed feasible that a regulatory definition of nanomaterials could be crafted.  Today, that hope is looking increasingly tenuous.  We know that size matters when it comes to understanding the risks presented by materials generally – and particles more specifically – and that characteristics such as physical form and chemistry are also important.  But these are relevant from diameters of tens of micrometers – where particles begin to be able to penetrate organisms – down to the nanometer size range.  At different length scales, different material-biology interactions lead to different mechanisms of action that have the potential to cause harm in different ways.  But there are no rules that are generalizeable to the nanoscale specifically – that much the science is clear on.  And this alone calls into question the scientific-basis of enforcing nanoscale-specific regulations.”

This is a crucial point and is linked to the idea that inspired one of my recent blogs in which I point out that there now exists a commonplace knee-jerk reaction to the term nanotechnology that is uninformed about the most recent science looking into the risks of nanomaterials.

I myself have bemoaned how politics are taking on a dangerously influential role in guiding the question of nanotechnology’s risk some years ago. I fear that science is not in a fair fight when it comes up against those who are expert at manipulating a political debate.

Is the Future of Nanotechnology Limited to Three Nanometers?

I was a bit stunned when I saw that Professor Mike Kelly at Cambridge University for Advanced Photonics and Electronics had claimed that structures with dimensions three nanometers or less could not be mass-produced

I became somewhat relieved when I clicked on the source story for the above link to discover that Kelly had added that this 3-nm limit only applied to “using a top-down approach.” 

My sense of relief was short lived when it seems in the source article that Kelly wasn’t really sure that a bottom-up approach could do it either since the processes used were too prone to unpredictable defects.

So, I thought I might find some respite in the original paper published by the UK’s Institute of Physics IOP (The paper is currently free if you register on the site).

The only real hopeful bit that escapes Kelly’s rather pessimistic theorem is that he doesn’t specifically discuss bottom-up approaches to manufacturing structures below 3nm, except to say, “There is a vanishing probability of generating a wide-area defect-free (especially line-defect-free) arrays.”

The main thrust of Kelly’s argument is one that is not altogether that radical, which is that you may be able to fabricate one-off structures that have dimensions below 3nm but you won’t be able to duplicate that in a full-scale manufacturing process.

While most have noted the difficulty of ramping up to a manufacturing process, or implied that new techniques would be developed to enable these manufacturing processes, Kelly is not quite as hopeful. From the IOP paper: 

“If this (top-down) manufacturing process is to be based on the most modern forms of deposition (including epitaxy), e-beam or ultra-deep UV lithography and precision etching, the mainstay of microelectronics and optoelectronics fabrication, then there are strict limits described below for which one-off fabrication is possible, but manufacture is not.”

So, metaphorically speaking Kelly has laid down the gauntlet, challenging the nanoscience community to either disprove his theorem, or, if they cannot, to start developing techniques for manufacturability rather than continuing to develop structures that will never be able to be manufactured.

"If I am wrong, and a counterexample to my theorem is provided, many scientists would be more secure in their continued working, and that is good for science,” says Kelly. "If more work is devoted to the hard problem of understanding just what can be manufactured and how, at the expense of more studies of things that cannot be manufactured under the conditions of the present theorem, then that too is good for science and for technology."

The Etch-a-SketchTM of Microscopy Creates Single Electron Transistors

Many of us grew up playing with an Etch-a-SketchTM toy in which a stylus cuts into an aluminum powder that coats in the inside of the toy’s screen revealing the dark inside the toy.

About three years ago, researchers at the University of Pittsburgh, led by Jeremy Levy, a professor of Physics and Astronomy in Pitt's School of Arts and Sciences, developed a technique that employed the tip of an atomic force microscope to etch patterns into the interface between two materials: a crystal of strontium titanate and a 1.2 nanometer-thick layer of lanthanum aluminate. At the time, the researchers likened the technique to a kind of microscopic Etch-a-SketchTM since like the toy it can erase the devices it makes and start anew.

Jump ahead three years to today and researchers from Pitt, University of Wisconsin at Madison and HP Labs, again led by Levy, have used the Etch-a-SketchTM technique to build a single-electron transistor, which they have dubbed SketchSET (sketch-based single electron transistor).

The research, which was initially published in the journal Nature Nanotechnologymarks the first time that a single-electron transistor has been made from oxide materials.

The foundation of the transistor is a conducting oxide “island” only 1.5nm in diameter that serves to have electrons tunnel resonantly between the source and drain electrodes. The island can only contain 0, 1 or 2 electrons, which provides it with unique conducting capabilities.

In addition to being extremely sensitive to electric charge, the oxide materials that make up the transistor possess ferroelectricity properties, which make it possible for the transistor to serve as a solid-state memory. These ferroelectric properties could also make it attractive as nanoscale charge and force sensor.

In the grander scheme of things, this transistor is being considered another tool for creating quantum computers. In fact, since last year Levy has been part of a U.S. Air Force Office of Scientific Research’s Multi-University Research Initiative (MURI) program to build a semiconductor for use in quantum super computers

 

Silver Nanoparticles Enable Palladium to Become More Effective Catalyst for Fuel Cells

In the continuing saga of nanotechnology’s application for fuel cells in this blog (see here and here) I have come to realize that there is a fervent belief among some that the reason we don’t have fuel cells powering our automobiles today is the result of a conspiracy among certain interests (presumably the oil industry) to block their use.

I really try to avoid taking sides in this rather fruitless debate. Instead I merely point out how nanotechnology has sometimes failed or succeeded in its intended applications for fuel cells. In either case, I try to put it into context. The current context by the way is that fuel cells power all sorts of things today, but when it comes to automobiles it is only for prototypes.

So, with this latest research coming out of Oxford University in the UK I am going to avoid pronouncements that it will usher in fuel-cell powered cars, or not.

The research, which was originally published in the journal Nature Nanotechnology, has shown how by applying an atomic layer of palladium on top of silver particles a catalyst is created for turning formic acid into hydrogen.

Despite all sorts of interminable calculations to the contrary, hydrogen is flammable and is not as easy or as safe to store as formic acid. As the Nature Nanotechnology abstract explains, “Formic acid (HCOOH) has great potential as an in situ source of hydrogen for fuel cells, because it offers high energy density, is non-toxic and can be safely handled in aqueous solution.”

Edman Tsang of Oxford University’s Department of Chemistry adds in the article reporting on the research “that the storage and handling of organic liquids, such as formic acid, is much easier and safer than storing hydrogen.” (Do I really need to add a video of hydrogen gas exploding?)

The main achievement of the research was the determination that the underlying silver nanoparticles enhance the catalytic properties of palladium. Tsang believes that these improved catalysts could “enable the production of hydrogen from liquid fuel stored in a disposable or recycled cartridge, creating miniature fuel cells to power everything from mobile phones to laptops.” However, I still argue carrying around a container for formic acid in your laptop or cell phone is a bit of a hard sell.

Even Tsang concedes, “There are lots of hurdles before you can get a real device, but we are looking at the possibility of using this new technology to replace lithium battery technology with an alternative which has a longer lifespan and has less impact on the environment.”

I’d argue that even if you got all the engineering perfectly sorted, you would still face just some commercial market realities that in the current environment would be hard to overcome.

The EU's Inability to Define Nanotechnology Stalls Regulatory Policy

I am tempted to start this entry with one of the numerous bureaucrat/light bulb jokes but add a European twist that whatever the number they first need to define what a light bulb is.

Unfortunately, this is no joke. After some years of trying to arrive at an “applicable” definition for nanotechnology as opposed to a “working” definition, the European Commission is still not ready to settle on one.

After sending out their draft definition for public input last year, the coordinator of the commission charged with developing the definition, Henrik Laursen feels the matter is still unsettled.

"It is clear that at a certain level many stakeholders are saying different things, and there is no absolute scientific definition," Laursen commented.

The hesitance to settle on a definition is due to the fact that whatever is finally arrived at will immediately dictate policy. The idea being that it’s better to get it right from the beginning rather than potentially screw up the development of nanotechnology products or risk human health and the environment with a regulatory framework built around a faulty definition.

"We still have some decisions to take but what we will come up with eventually will not be a working definition, it will be a definition that will be applicable,” Laursen is quoted as saying. “There is no room for us to introduce a definition by trial and error, we are expected to make sure we act and we need to come up with something."

The crux of the problem seems to hinge on whether they should base the definition around the number of nanoparticles in a given material or the weight of the nanoparticles in the material.

On the one hand, the European Chemical Industry Council (Cefic) is in favor of a weight-based definition since “"Weight is generally used in all chemical legislation and test procedures…” and on the other EU's scientific committee on emerging and newly identified health risks (SCENIHR) argues that “the potential hazards of using these particles relates to the number of them within a particular product."

If I were to flip a coin, it appears it’s going to go in the direction of number of nanoparticles. But if we take the old toxicity formula Hazard x Exposure = Risk, it’s hard to see where “exposure” is represented in this definition.

It makes the approach of the US Food & Drug Administration as outlined by Carlos Peña, director of emerging technology programmes of the FDA, seem not only more workable but more effective. Peña explains that instead of focusing on a definition of nanotechnology, the FDA is instead investigating how nanoparticles and materials are being used in different sectors and making sure that the regulations for those sectors (i.e. food, drugs and cosmetics) are adequate to address their introduction.

Carbon Nanotube Solution Could Eliminate Need for Indium Tin Oxide in Electronic Displays

It is altogether possible that the best solution to the current rare earth mineral squeeze is for countries other than China to restart their mining of the minerals that they more or less abandoned over twenty years ago.

But based on some recent nanotechnology research it seems this is not the way people want to go. While Japan is pursuing new mineral deposits after their run-in with China last year, there seems to be some sense afoot that nanotechnology could offer a solution without resorting to new mining.

In a Cientifica white paper published last year the solutions take the form of electronics that negate the need for the rare earth minerals. “Through the use of nanotechnologies we can now start to develop processes that do not use rare resources, for example using carbon nanotubes and metallic nanoparticles in polymers to make them conducting rather than applying thin layers of indium tin oxide.”

It appears that this is what researchers at Eindhoven University of Technology in the Netherlands have just done in their development of a material that can replace indium tin oxide (ITO) in electronic displays.

The research, which was originally published in the journal Nature Nanotechnology, proposes as a replacement a material made of carbon nanotubes and plastic nanoparticles and produced in water.

Apparently, the key to the production of the new material is the proportions of carbon nanotubes (CNTs) and the conducting latex. Too high a concentration of CNTs and the film becomes dark and opaque. But by keeping the concentration low they are able to achieve a high conductivity.

While the conductivity is high, it is still a factor of a 100 lower than that provided by ITO. However, the two lead researchers on the project theoretical physicist Paul van der Schoot and polymer chemist Cor Koning believe that this gap can be quickly closed.

"We used standard carbon nanotubes, a mixture of metallic conducting and semiconducting tubes", says Cor Koning in the Nanowerk cited above. "But as soon as you start to use 100 percent metallic tubes, the conductivity increases greatly. The production technology for 100 percent metallic tubes has just been developed, and we expect the price to fall rapidly."

While the price for 100-percent-metallic carbon nanotubes continues to go down, the material is good enough now to be used as an anti-static layer for displays, according to the researchers.

If the new material were to replace ITO in electronic displays, it would not only ease the rare earth squeeze but might also appease the environmentalists since it would be entirely water based without using any heavy metals. But then again, as I’ve stated previously, it would seem environmentalists would only really be satisfied if we eliminated TVs and cell phones altogether. 

Graphene's Use in RF transistors Gets a Boost from Faster and Easier Manufacturing Technique

IBM, and in particular Phaedon Avouris and his colleagues at IBM’s T.J. Watson Research Center, has been focused on developing graphene for use in electronics applications.

Last year we reported on their work in creating a band gap for graphene and now Avouris and his team are reporting on a new route to fabricating graphene-based transistors that is compatible with current manufacturing techniques.

The research was initially published in the journal Nature and focused its efforts with graphene in one of its favored potential electronic applications: radio frequency (RF) transistors.

Where previous attempts to create RF transistors out of graphene suffered from a fabrication process that was a manual and time consuming process, the IBM researchers employed a clever vapor deposition method that avoided both the adverse effects other vapor deposition techniques had on the electronic properties of graphene and kept away from the labor intensive techniques.

The researchers grew the graphen on copper film and then deposited it on a diamond-like carbon with a resulting transistor that has “…cut-off frequencies as high as 155GHz…for 40-nm transistors.”

In the Chemical & Engineering News article cited above Frank Schwierz, a device physicist at the Technical University of Ilmenau, in Germany, offered some context for the work.

“The approach of the IBM team is very interesting because it is compatible with common semiconductor processing,” Schwierz is quoted as saying in the C&E News article. “At this early stage, before the fabrication method has been optimized, Schwierz is cautious about calling the technique a breakthrough. “But it may turn out to be very useful in the future.”

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Nanoclast

IEEE Spectrum’s nanotechnology blog, featuring news and analysis about the development, applications, and future of science and technology at the nanoscale.

 
Editor
Dexter Johnson
Madrid, Spain
 
Contributor
Rachel Courtland
Associate Editor, IEEE Spectrum
New York, NY
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