Carbon nanotubes find real world applications

But, like other 'great technologies of the the future', are we over hyping nanotubes? Are they near passing the real test – that of widespread practical use? The answer is a qualified yes. Qualified, because there are two distinct kinds of nanotube – single wall and multiwall (SWNT and MWNT). A carbon nanotube is a seamless cylinder of either one or many layers of graphene, hence the term single or multiwall. Typically, MWNTs are being used in practical applications. SWNTs are mostly much more expensive, although they hold out huge potential for the future.

The success of MWNTs is proved by a surprising statistic: worldwide commercial production capacity presently exceeds several thousand tons per year, according to Dr Michael De Volder, previously with imec, but now a lecturer in nanomanufacturing and engineering design at Cambridge University's Institute or Manufacturing. But it's a level of production that has taken around 20 years to achieve.

"The beginning of widespread carbon nanotube research was preceded in the 1990s by the first scientific report of MWNTs, although hollow carbon was reported as early as the 1950s," Dr De Volder says. "However, carbon nanotube related commercial activity has grown most substantially during the past decade. Since 2006, worldwide carbon nanotube production capacity has increased at least tenfold."

A summary of some carbon nanotube applications now available commercially gives a flavour of just how widespread a real impact the technology is starting to make. Take water and oil purifiers, for example. the size, surface area (500m2/g) and adsorption properties of carbon nanotubes make them an ideal membrane for filtering toxic chemicals, dissolved salts and biological contaminants from water. That makes them a potential technology for producing clean water and drinking water from the sea.

US company Seldon Technologies has developed the MineralWater System using its Nanomesh Purification Technology – a carbon nanotube filtration system – to do just that. It says its system delivers drinking water without the use of chemicals, heat, or power: vital for use in developing countries where it is most needed.
Nanomesh removes pathogens and contaminants such as viruses, bacteria, cysts and spores, delivering water that meets or exceeds the USEPA Drinking Water Standard. It is suitable for use in homes, offices, schools, clinics, and other commercial environments, Seldon says.

The huge surface area of carbon nanotubes is also being exploited when they are used as the electrodes in capacitors to provide more current and better electrical and mechanical stability than other materials. Their large surface area means energy is stored all along them, not just at the ends as in conventional capacitors. Research labs at Stanford and MIT have been working to create carbon nanotube based ultracapacitors that would rival batteries in cars. Bringing them to market is FastCAP Systems of Boston, using carbon nanotube to create ultracapacitors that it claims offer long life spans, durability, and recharge times and power levels beyond the traditional batteries and other capacitors. They also contain no lithium and carry no risk of thermal explosions.

The properties of carbon nanotubes make them ideal for supporting different kinds of structures – for example, sports equipment, body armour, vehicles, rockets and building materials, where they are being widely used. The nanotubes create networks within the composite material to bear the load of the weight and strain placed upon it. This can apply to medical areas as well: the University of Delaware's Center for Composite Materials is researching carbon nanotube as a 'smart skin' to sense changes in a structure's integrity.

There are many other medical uses for carbon nanotubes, including: bone scaffolding; cell therapy – achieved by delivering drugs or silencing genes, with modified carbon nanotubes recently used to control the damage caused by a stroke; synthetic muscles; biosensors; and dental implants.

"Microelectronics is one area where carbon nanotubes have been studied for some time and where work is being done towards using carbon nanotubes for flexible electronics," Dr De Volder says. "Companies like IBM are looking to make the smallest possible transistors consisting of only one nanotube, but they are also aiming to create slightly larger transistors containing many nanotubes for use in applications like flexible mobile phones and for integration in textiles.

"You could call such applications traditional, but I have been happily surprised to see other very interesting and promising applications of carbon nanotubes, for example the portable water filtration devices developed by Seldon Technologies for use in developing countries."

The growing use of carbon nanotubes is coming as a result of improvements in the production of nanotube materials – prices have come down significantly as volumes increase, vital for applications like water filtration, which have to be very affordable.

Another use of carbon nanotubes that is already quite well established is their addition to polymer composites to enhance stiffness and improve damping. Sports manufacturers use them in tennis and badminton rackets, and bicycle frames as with BMC Switzerland.

But while carbon nanotubes are being used in practical applications, it doesn't imply their more widespread use will not be problem free.

"There are a number of obstacles we have been working on which we haven't solved yet," Dr De Volder says. "Particularly in high end targets, like the search for better transistors, the exact morphology of the nanotube and the orientation of the graphene lattice with respect to the tube axis – referred to as its chirality – is really important. At this moment, we have little ability to synthesise carbon nanotubes with very specific types of chirality and it is this that determines the semiconducting versus conducting properties of the carbon nanotubes.

"One of the interesting things happening is the improvement in computer simulations of how carbon nanotubes are synthesised, which will hopefully enable us to tweak the fabrication process. And electron microscopy is making it possible to look at the carbon nanotubes while they are being formed, which is helping increase the deep understanding of the process."

Dr De Volder himself is working on the challenge of mass producing devices featuring hundreds of thousands of nanotubes.

"Unfortunately, when you bring them together in large numbers, the figures of merit for their properties are often disappointing compared with what you get from an individual carbon nanotube. I am trying to develop techniques for bringing particles together in more efficient ways, or looking at new emerging properties of the materials depending on how you bring the carbon nanotubes together."

Nevertheless, progress is now happening with SWNTs, with UK company Thomas Swan being a world leader in making SWNTs with its Elicarb material, now being used in areas like advanced composites, electronics, energy storage, print, paper and packaging and fuel cells.

Another recent development in SWNTs – announced in June by Linde Electronics – is the development of a carbon nanotube ink for use in displays, sensors and other electronic devices. Potential applications include smartphones with a roll up screen and a see through GPS device embedded in the windshield of a c

"Linde is now making its nanotube inks available to developers," says Dr Sian Fogden, market and technology development manager for Linde's nanomaterials unit. "These inks contain single walled carbon nanotubes and are produced without damaging or shortening the nanotubes and therefore they preserve the unique nanotube properties."

Linde claims this is a landmark development that drastically improves the performance of transparent conductive thin films made from the inks and opens the door for the development of carbon nanotube applications in not only consumer electronics, but also the healthcare and sensor manufacturing sectors.

Because nanotubes are long and thin, they have high van der Waals forces between them and they stick together. The standard way to separate them is by using high powered sound waves. But this can damage the nanotubes and affect their properties.

"With our inks, we use a process called Salt Enhanced Electrostatic Repulsion (SEER) that doesn't require sonication but which produces solutions of individual carbon nanotubes while maintaining the length of the nanotube," Dr Fogden says. "Only very recently have products such as touch screens begun to be produced which contain single walled carbon nanotubes and these devices have yet to be launched into the full consumer market. Only when the raw carbon nanotube material can be fully processed in a reliable and repeatable manner will they be used in consumer electronics on a large scale."

Another recent intriguing development in electronics and computing comes from US company Nantero, which says it is commercialising carbon nanotube based semiconductor devices, including memory, logic and others.

"We have developed NRAM, a high density nonvolatile RAM and the aim is for it to serve as a universal memory technology," says ceo Greg Schmergel. "NRAM can be manufactured for both standalone and embedded memory applications and samples have already been shipped to selected customers and are under development at several production cmos fabs by Nantero and its licensees. These samples are multimegabit arrays that demonstrate high yield, high speeds, reliability and low power consumption."

Nantero claims it is the first company to actively develop semiconductor products using carbon nanotubes suitable for production in a standard cmos fab.

"The main obstacle in the past has been the fact that carbon nanotubes have not been compatible with existing semiconductor fabs," Schmergel says. "At Nantero, we have solved that by developing a cmos compatible carbon nanotube material that can be accepted into any fab in the world and manufacturing processes compatible with existing semiconductor manufacturing equipment. So our memory and other carbon nanotube devices can be made in any cmos fab at high volumes.

Using existing processes means reliability and reproducibility is far higher." Nantero's microelectronic grade carbon nanotube material is now available commercially through licensee Brewer Science.

This could be a pointer to the longer term future, involving mainstream computing. At Stanford University recently, a team announced the first functioning computer built from carbon nanotubes. Despite featuring just 178 transistors and running at 1kHz, the computer is nevertheless 'Turing complete', meaning it can do anything today's machines can do, just much slower.

But, in a few years time, billions of carbon nanotubes may be on our desks and in our pockets.

- See more at: http://www.newelectronics.co.uk/electronics-technology/carbon-nanotubes-find-real-world-applications/58278/#sthash.caMfgtR5.dpuf

Electronic Article Surveillance

Security experts say the most effective anti-shoplifting tools these days are CCTV and the tag-and-alarm systems, better known as electronic article surveillance (EAS) systems. Separately, these are good options. Used together, experts say, they're almost unbeatable. EAS is a technology used to identify articles as they pass through a gated area in a store. This identification is used to alert someone that unauthorized removal of items is being attempted. According to the Association of Automated Identification Manufacturers, over 800,000 EAS systems have been installed worldwide, primarily in the retail arena. EAS systems are useful anywhere there is an opportunity for theft of items of any size. Using an EAS system enables the retailer to display popular items on the floor, where they can be seen, rather than putting them in locked cases or behind the counter.

Loss prevention expert Robert L. DiLonardo, says new EAS technologies are being produced -- not only to reduce shoplifting -- but also to help increase sales, lower labor costs, speed inventory, improve stockroom logistics and, one day, to replace inventory record-keeping. But for now, we'll stick to the role of EAS in battling shoplifting in your imaginary store!

Three types of EAS systems dominate the retail industry. In each case, an EAS tag or label is attached to an item. The tag is then deactivated, or taken from an active state where it will alarm an EAS system to an inactive state where it will not flag the alarm. If the tag is a hard, reusable tag, a detacher is used to remove it when a customer purchases the item it's attached to. If it's a disposable, paper tag, it can be deactivated by swiping it over a pad or with a handheld scanner that "tells" the tag it's been authorized to leave the store. If the item has not been deactivated or detached by the clerk, when it is carried through the gates, an alarm will sound.

The use of EAS systems does not completely eliminate shoplifting. However, experts say, theft can be reduced by 60 percent or more when a reliable system is used. Even when a shoplifter manages to leave the store with a tagged item, the tag still must be removed -- something that is no longer as easy as it once was. For example, some EAS tags contain special ink capsules, which will damage the stolen item when forcibly, and illegally, removed. (This type of device is known in the industry as benefit denial -- we'll discuss it more later!). Other popular EAS components today include source tagging, whereby an inexpensive label is integrated into the product or its packaging by the manufacturer.

The type of EAS system dictates how wide the exit/entrance aisle may be, and the physics of a particular EAS tag and technology determines which frequency range is used to create a surveillance area. EAS systems range from very low frequencies through the radio frequency range (see How Radio Scanners Work). These EAS systems operate on different principles, are not compatible and have specific benefits and disadvantages. That's why the Consumer Products Manufacturers Association is encouraging a "tower-centric" EAS approach that can "read" multiple tag technologies rather than the "tag-centric" models that exist today.

Art Could Help Create a Better 'STEM' Student

Science, technology, engineering and mathematics (STEM) have become part of educational vernacular, as colleges, universities and other institutions strive to raise the profile of the areas of study and the number of graduates in each field.

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Now a project from the University of Houston College of Education Urban Talent Research Institute encourages the incorporation of creative endeavors to attract more and better STEM students.
"There is not a unanimous consensus on what STEM is and there is little research on what it means to support STEM," said Jay Young, a University of Houston College of Education Ph.D. student specializing in educational psychology and individual differences. Young, whose own academic studies were in physics and who taught high school math, does not doubt the need to encourage more STEM students. He does, however, doubt the methods for getting there.
"The federal government considers STEM natural sciences, while the National Science Foundation includes social sciences," he said. "Supporting STEM education should also mean increasing the quality of the graduate. That is where STEAM comes in."
STEAM takes STEM efforts and incorporates art (the "A" in STEAM is for "Art"). Young's research focuses on how to incorporate creativity into STEM education with the implication that doing so will increase the quality of STEM graduates. He says STEM studies are about problem solving, and creative endeavors are exercises in problem solving.
"When an artist is painting, he is trying to solve a problem -- how to express what is being felt. He experiments with colors, technique and images the same way a scientist or engineer experiments with energy and signals," he said. "There is more than one way information can be taught just like there is more than one way problems can be solved."
Young is a recipient of a Fellowship in Education Evaluation, Assessment and Research (FEEAR) sponsored by UH and U.S. Department of Education. Through an internship at the Children's Museum of Houston, Young is evaluating an afterschool program at the museum which integrates art and STEM.
"Creative thinking and problem solving are essential in the practice of math and science," he said. "Incorporating art into math and science will not only help students become more creative and better problem solvers, it will help them understand math and science better."
Young's research is guided by faculty adviser and Interim Associate Provost for Faculty Development and Faculty Affairs Rick Olenchak,. He directs the UH Urban Talent Research Institute and studies issues surrounding talent development and giftedness, as well as mentoring and creativity.
Recently, Young and eight others associated with the Urban Talent Research Institute presented research findings to the National Association of Gifted Children conference in Indianapolis

Small Size Enhances Charge Transfer in Quantum Dots

Quantum dots -- tiny semiconductor crystals with diameters measured in billionths of a meter -- have enormous potential for applications that make use of their ability to absorb or emit light and/or electric charges. Examples include more vividly colored light-emitting diodes (LEDs), photovoltaic solar cells, nanoscale transistors, and biosensors. But because these applications have differing -- sometimes opposite -- requirements, finding ways to control the dots' optical and electronic properties is crucial to their success.

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In a study just published in the journal Chemical Communications, scientists at the U.S. Department of Energy's Brookhaven National Laboratory, Stony Brook University, and Syracuse University show that shrinking the core of a quantum dot can enhance the ability of a surrounding polymer to extract electric charges generated in the dot by the absorption of light.
"Photovoltaic cells made of quantum dots paired with plastic materials like conductive polymers are far easier to make and less expensive than conventional silicon-based solar cells," said Mircea Cotlet, a physical chemist at Brookhaven's Center for Functional Nanomaterials (CFN), who led the research team. "These kinds of materials are inexpensive, easy to synthesize, and their assembly would be relatively easy."
The downside is that, right now, solar devices based on silicon can't be beat in terms of efficiency. But research aimed at understanding the photovoltaic process at the nanoscale could change that.
"The ability to make and study single particles at the CFN allows us to observe and test properties that would be blurred, or averaged out, in larger samples," said Huidong Zang, a postdoctoral research fellow working with Cotlet and first author on the paper.
In a solar cell, the ideal material would absorb a lot of light and efficiently convert that energy into electric charges that can be easily extracted as a current. To study the details of this process, the scientists used quantum dots composed of a light-absorbing cadmium-selenium core encased in a protective zinc-sulfide shell and surrounded by a conductive polymer. They tested the ability of the polymer to extract electric charges generated when the quantum dots absorbed light, and conducted experiments using quantum dots with cores of different sizes.
"We knew from theoretical predictions that particle size should have an effect on the charge transfer with the polymer, but no one had done this as an experiment until now, and in particular at the single-particle level," Cotlet said.
When they varied the size of the quantum dot's core, the scientists found that the smaller the diameter, the more efficient and more consistent the charge transfer process.
"By using a smaller core, we increased the efficiency of the charge transfer process and narrowed the distribution of the charge-transfer rate so it was closer to the ideal with less variability," Zang said.
The scientists were exploring a particular type of charge transfer created by the movement of "holes" -- areas of positive charge created by the absence of negatively charged electrons. In electronic devices, holes can be channeled just like electrons to create electric current. And in this case extracting holes had an added benefit -- it increased the time that quantum dots, which turn on and off in a blinking pattern, remained in the "on" condition.
"Hole transfer inhibits blinking," Cotlet said. "It keeps the quantum dot optically active longer, which is better for the photovoltaic process, because charges can only be extracted when the quantum dot is on."
"It would be impossible to see this effect with bulk samples because you can't see the 'on' and 'off' states. When lots of quantum dots are mixed together, the signals average out. You can only see it by looking at the single nanoparticles."
Cotlet's group had previously conducted a similar study pairing quantum dots with carbon-rich buckyballs. In that study, they found the opposite effect: Buckyballs decreased the dots "on" time while enhancing the transfer of electrons.
In other applications combing dots and polymers, such as LEDs or biosensors, scientists are looking for ways to suppress charge transfer as this process becomes detrimental.
"Knowing these fundamentals and how to control these processes at the nanoscale should help us optimize the use of quantum dots for a wide range of applications," Cotlet said.
This research was funded by the DOE Office of Science and by the Air Force Office of Scientific Research.