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One of the editors at Nature has written a good (free) article that provides some of important perspective about the movement of nano-carbon products (fullerenes, carbon nanotubes and, more recently, graphene) from lab to sustainable markets.

Richard Van Noorden, with quotes from a number or researchers and business reps, describes what a tricky path it can be to go from super-promising materials to specific applications to efficiency-scaled production capacity.

He notes that the first of these to emerge, fullerene, has been pretty much a commercial flop. CNTs emerged in the early 1990s and their semiconducting and metallic-type properties, not to mention their ruggedness, has teased R&D groups and investors ever since. But, CNTs electrical properties can be difficult to control and manufacturing pure bulk CNTs in predictable dimensions and orientations has been illusive. The same same problems are being faced with the newer graphene.

The problem with electronics is that a decent and cheaper alternative is readily available: silicon chips. Van Noorden quotes one organic chemist who points out that, “There have been millions and person-years and trillions of dollars put into the development of silicon electronics. Asking graphene to compte with silicon now is like asking a 10-year-old to be a concert pianist because we’ve been giving him piano lessons for the last six years.”

Van Noorden provides an overview of some of the pros and cons of CNTs and graphene in various applications and how the cost-benefit model can shift over time (e.g., graphene looks more promising in touch-screen applications as the cost of indium – and thus ITO  – trends upwards .)

But even in less esoteric applications, such as using CWTs and graphene flakes in composites, these materials that can retail in the hundreds of dollars/kg are competing with substitutes that sell for less than a dollar/kg. Even with an expected stream of science and manufacturing innovations, experts like Lux Research estimate the $/kg for CNTs will only drop by half in the next ten years.

That’s not a blazing speed for price reduction, but one of the experts Van Noorden interviews points out, the arc of now-ubiquitous carbon fiber began very slowly, eventually found usage in less cost-conscious military applications and much later made its way into large-scale commercial usage.

Nevertheless, manufacturers are bringing more and more capacity on line, and as they do so, they will be scrambling for outlets. Some early niches for graphene will emerge like they have for CWTs (Van Noorden speculates that supercapacitors, such as the one I recently wrote about, electrodes and flexible electronics may pay off), but despite the excitement everyone will have to be patient — perhaps very patient — until they see the first truly transformational uses.

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Depiction of chromophores attaching to a transistor made from a single carbon nanotube. Credit SNL.

Research being conducted at Sandia National Lab might eventually be applied to an optical detector with nanometer-scale resolution, ultra-tiny digital cameras, solar cells with more light absorption capability and a better device for genome sequencing. However, the near-term purpose of the research is basic science.

The Sandia researchers report they have created the first carbon nanotube device that can detect the entire visible spectrum of light. This might allow them to study single-molecule transformations, how the molecules respond to light and change shape as well as other fundamental interactions between molecules and nanotubes.

As with many other recent studies, the researchers went back to nature, in this case the human eye, and they improved on the model. A cascade of chemical and electrical events that ultimately trigger nerve impulses occur when light strikes a chromophore on the molecules in the eye’s retina. Likewise, when light strikes a chromophore in the nanoscale color detector, it causes a conformational change in the molecule. This, in turn, causes a threshold shift on a transistor made from a single-walled carbon nanotube.

“In our eyes the neuron is in front of the retinal molecule, so the light has to transmit through the neuron to hit the molecule,” says Sandia researcher Xinjian Zhou. “We placed the nanotube transistor behind the molecule - a more efficient design.”

That carbon nanotubes are light sensitive has been known for a long time, but earlier efforts using an individual nanotube were only able to detect light in narrow wavelength ranges, and then only at laser intensities. The Sandia team nanodetector is orders of magnitude more sensitive, down to about 40 W/m2, which is about 3 percent of the density of sunshine reaching the ground. “Because the dye is so close to the nanotube, a little change turns into a big signal on the device,” says Zhou.

Zhou and his colleagues François Léonard, Andy Vance, Karen Krafcik, Tom Zifer and Bryan Wong created the device, which they described in a paper published in Nano Letters. Zhou and Krafcik created a tiny transistor made from a single carbon nanotube. They deposited carbon nanotubes on a silicon wafer and used photolithography to define electrical patterns to make contacts. Meanwhile, Vance and Zifer synthesized molecules to create three types of chromophores that respond to either red, green or orange bands of the visible spectrum. Zhou immersed the wafer in the dye solution until the chromosphores attached themselves to the nanotubes.

“Detection is now limited to about 3 percent of sunlight, which isn’t bad compared with a commercially available digital camera,” says Zhou. “I hope to add some antennas to increase light absorption.”

The team is now working on detecting infrared light. “We think this principle can be applied to infrared light, and there is a lot of interest in infrared detection,” says Vance. “So we’re in the process of looking for dyes that work in infrared.”

“A large part of why we are doing this is not to invent a photo detector, but to understand the processes involved in controlling carbon nanotube devices,” says Léonard, author of The Physics of Carbon Nanotubes, published September 2008.

The next step is to create a nanometer-scale photovoltaic device. Such a device on a larger scale could be used as an unpowered photo detector or for solar energy. “Instead of monitoring current changes, we’d actually generate current,” says Vance. “We have an idea of how to do it, but it will be a more challenging fabrication process.”

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Beware!

Maybe a newly rediscovered property of Scotch tape is the reason the 3M company has been doing better in the last few months than the rest of the stock market. The discovery/rediscovery, as reported in Nature, is that when you peel adhesive tape off its roll in a vacuum chamber, it emits some strong X-rays. One researcher even made an X-ray image of one of their fingers. The ability of some tapes to unleash visible light when being peeled has been known for sometime and it was always a little bit of a concern to those of us who - in the old days - opened cans of 35 mm film in darkrooms. But it turns out that Russian scientists reported evidence of X-rays from peeling sticky tape off glass a half-century ago.

The new work takes this old research a step further by documenting the strength of the X-rays. “We were very surprised,” said Juan Escobar, a UCLA grad student and one of the authors of the Nature report. “The power you could get from just peeling tape was enormous.” Is there any practicality to this property? Escobar thinks it could be used to make inexpensive and/or portable X-ray machines running with only human power. Escobar and his colleagues have even applied for a patent covering such devices. Escobar says the tape-produced X-rays only occur in a vacuum, so the rest of us are safe when wrapping packages or mending our glasses. “If you’re going to peel tape in a vacuum, you should be extra careful,” he said. “I will continue to use Scotch tape during my daily life, and I think it’s safe to do it in your office.” But, it is a little unnerving that he quickly added, “No guarantees.”

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