Nanoclast

Professor Zhong Lin Wang at Georgia Tech has been championing his work in exploiting the piezoelectric qualities of zinc oxide nanowires for years now with his so-called "nanogenerators".

Now researchers at the Korea Advanced Institute of Science and Technology  (KAIST) have taken up the mantle of Wang’s work by creating a piezoelectric “nanogenerator” more easily and cheaply than ever before.

The research, which was initially published in the Wiley journal Advanced Materials, produced a piezoelectric nanocomposite through relatively simple processes such as spin-casting and the bar-coating method. So this new generation of “nanogenerators” is not restricted by a complicated and high-cost process or even size.

Even Wang himself is impressed by this work. “This exciting result first introduces a nanocomposite material into the self-powered energy system, and therefore it can expand the feasibility of nanogenerator in consumer electronics, ubiquitous sensor networks, and wearable clothes," says Wang.

The lead researcher on this project, Keon Jae Lee, a Professor at the Department of Materials Science and Engineering at KAIST, has a comprehensive website that covers much of the work.

One of the videos from that website (below) manages to demonstrate just how uncomplicated the process is to create this nanocomposite and shows how it works in generating an electric charge from the movement of a finger.

While Wang has been expert at getting this research into the media, it hasn't yet found itself in commercial products. It should be interesting to see if these manufacturing simplifications and cost reductions will help push this technology into consumer electronics where Wang always envisioned it could be.

The example of the Lycurgus Cup, as a paradigm of nanotechnology, has always bothered me. Yes, the glass of the cup changes colors depending on the light because of the presence of nanoparticles, but it's not really nanotechnology. While the  Romans knew the process that would make this glass, they didn’t know why it performed the way it did. Without that kind of knowledge—and the concomitant ability to manipulate an effect—what you have is at most craft, and not science.

That's the reason many trace the real beginning of nanotechnology to the development of microscopy tools like the scanning tunneling microscope (STM). Without the array of tools we have for seeing, measuring and manipulating the world on the scale of atoms and molecules, there would have been little to no advancement in nanotechnology. In other words, nanotechnology is not just the world of the very small but having the tools to know what we’re doing at that scale and setting about to do it.

Now researchers at the National Institute of Standards & Technology (NIST) have added a new tool to the arsenal that should allow researchers to better user lasers in manipulating nanoparticles inside biological cells without damaging them. The researchers have developed a control and feedback system that lets the laser nudge nanoparticles to exactly where they are needed for analysis.

In the NIST press release covering the technology, Thomas LeBrun, one of the researchers on the project, explains: "You can think of it like attracting moths in the dark with a flashlight. A moth is naturally attracted to the flashlight beam and will follow it even as the moth flutters around apparently at random. We follow the fluttering particle with our flashlight beam as the particle is pushed around by the neighboring molecules in the fluid. We make the light brighter when it gets too far off course, and we turn the light off when it is where we want it to be. This lets us maximize the time that the nanoparticle is under our control while minimizing the time that the beam is on, increasing the particle's lifetime in the trap."

The researchers report two key results:

• 100-nanometer gold particles remained trapped 26 times longer than had been seen in previous experiments
• Silica particles 350 nanometers in diameter lasted 22 times longer, but with the average beam power reduced by 33 percent.

LeBrun characterizes this development as pushing the field an order of magnitude further than it was before. He says the researchers will now begin work in building complex nanoscale devices and testing nanoparticles as sensors and drugs in living cells.

Earlier this year, I was teased by news that graphene could be ‘tattooed’ to one’s tooth to detect harmful bacteria. I say teased because the bacteria that could be detected was not the Streptococcus mutans bacteria that causes tooth decay. Instead the device could detect just about every other bacteria except that one. So, what appeared to be a story that might be able to redeem me in the eyes of the dental community—after I echoed others’ doubts about the efficacy of a nanofilm in promoting cell growth in decayed teeth—just wasn’t the opportunity I had hoped for.

This week, however, researchers at the University of Maryland have offered up a technology that should be of keen interest to the dentists of the world, and those who visit them. The researchers have developed a nanocomposite that can be used not only as a filling for the cavity, but also can kill any remaining bacteria in the tooth and regenerate that tooth’s structure that had been lost due to the decay. You can access a PDF file that offers up a poster presentation of the research here.

The basis of the nanocomposite are calcium phosphate nanoparticles that regenerate tooth minerals. The ingredient that kills off the remaining bacteria in the tooth is made up of silver nanoparticles and quaternary ammonium along with a high pH. According to the news release, the alkaline pH is the feature that limits the acid production by the bacteria. This begs the question: why not just develop a mouthwash with these ingredients so you don’t need the cavity filling in the first place?

One answer may be the use of silver nanoparticles, which are not without some controversy when associated with anything that might be consumed by humans. Sure enough, just a quick perusal to see how this story was being covered turned up a blog called “Beyond Pesticides” that offered up this headline: “New Dental Fillings Utilize Controversial Nanotechnology to Kill Bacteria”. The blog goes into some detail about the potential risks of silver nanoparticles.

The researchers are continuing with their animal and human testing with the nanocomposite. Given that some sectors of the public are concerned about the potential risks of silver nanoparticles, they should probably take a look at the issue as part of their research.

Just four months after the National Nanotechnology Initiative (NNI) responded to the President’s Council of Advisors on Science and Technology’s (PCAST) 2010 report on the status of nanotechnology, PCAST has offered up a new assessment.

While the PCAST report on the NNI in 2010 wanted to see greater efforts towards commercialization and some attempt to address environmental, health and safety (EHS) concerns, this time they just wanted to see how well the NNI had done in meeting their previous recommendations.

In the Whitehouse.gov blog covering the announcement it seems PCAST are satisfied:

“PCAST found that the Federal agencies in the NNI have made substantial progress in addressing many of the 2010 recommendations that were aimed at maintaining U.S. leadership in nanotechnology… The PCAST assessment particularly commends the expanded efforts of the NNCO in the area of commercialization and coordination with industry, and the NNCO’s release of a focused research strategy for addressing environmental, health, and safety (EHS) implications of nanotechnology.”

Okay, pat on the back, job well done…uh, wait, there are still some new recommendations that PCAST would like to see addressed.  You can find them in the PDF of the full report on page vii. They fall into the areas of strategic planning, program management, metrics for assessing nanotechnology’s commercial and societal impacts, and…wait for it…increased support for EHS research.

Additional support for EHS research might be a required element for every PCAST report in the future. More interesting to me, however, is this continued emphasis on improved “metrics for assessing nanotechnology’s commercial and societal impacts.”

It seems to me that this is an area in which everyone from governments to corporations wants a formula that will churn out a sense of what kind of impact nanotechnology is really having. While nobody is satisfied with the metrics that we have,  I would suggest that there are few number-counting options that will really be able to sort out the full impact of nanotechnology. But again, it should be interesting to see what they come up with.

The latest flavor of graphene is something the researchers who invented it are calling GraphExeter. While the name itself is not big on originality—just combining the words graphene with Exeter (the name of the University where the researchers are affiliated)—it does seem to have some superlative characteristics.

The researchers, led by University of Exeter Engineer Monica Craciun, claim that the material is the most transparent, lightweight and flexible material ever for conducting electricity. GraphExeter is actually two layers of graphene sandwiching molecules of ferric chloride. The ferric chloride increases the electrical conductivity of the graphene without compromising its transparency.

“GraphExeter could revolutionize the electronics industry,” says Craciun in the university press release. “It outperforms any other carbon-based transparent conductor used in electronics and could be used for a range of applications, from solar panels to ‘smart’ teeshirts. We are very excited about the potential of this material and look forward to seeing where it can take the electronics industry in the future.”

Craciun and her colleagues initially published their work in the Wiley journal Advanced Materials where the description is not quite as bold as the university press release. Nonetheless the abstract does say that GraphExeter “outperforms the current limit of transparent conductors such as indium tin oxide, carbon-nanotube films, and doped graphene materials.”

It seems that the material’s capability as a superior transparent conductor makes it an ideal candidate for optoelectronic devices. So this latest news represents quite a recent run for graphene in optoelectronics applications following IBM’s announcement earlier in the week.

The researchers say that potential applications include photovoltaics and wearable electronics among many others. An ambitious list to say the least, but the researchers do point out that looming bottleneck of using indium tin oxide (ITO) for transparent conducting electrodes provides a strong motivation to find an alternative.

Whether a shortage of ITO will be enough to get the electronics industry to adopt a material that has just been invented remains to be seen. So I think we will see some evolutions to this material’s development before we see any revolution occur to the electronics industry.

While new breakthroughs continue to come in using graphene (or cousins of graphene) for electronics applications, research in the area of using graphene for photonics applications is growing.

The latest use of graphene for photonics comes from IBM where researchers have created a graphene/insulator superlattice capable of serving as a terahertz frequency notch filter and linear polarizer, according to an article in EE Times.

IBM has certainly been a trailblazer in using graphene for electronics applications over the years, such as their graphene transistor work and then later an integrated circuit.  But IBM—along with other researchers outside of Big Blue—has also been hard at work looking at how graphene could be used in optoelectronics.

IBM Fellow Phaedon Avouris told EE Times that "In addition to its good electrical properties, graphene also has exceptional optical properties. In particular, it absorbs light from the far-infrared to the ultra-violet."

It is in the terahertz frequency that graphene’s optical properties were of particular interest to the IBM team. Tunable notch filters have become fairly ubiquitous in optoelectronics, but they didn’t really operate at the terahertz frequency. The new application seemed that a good way to take advantage of graphene's terahertz frequency capabilities.

“Unfortunately, today there are very few ways of manipulating terahertz waves such as polarizing and filtering it, but because graphene operates well at terahertz frequencies we have concentrating on creating these types of devices," said Avouris.

As good as graphene is at operating at terahertz frequencies, when single-layer graphene is used carrier concentration and resonant frequency are too weak for it to be used in photonics applications. This is where the IBM researchers' work began and they developed a multi-layer graphene/insulator superlattice that improved the carrier density and the resonant frequency.

“We have found that graphene interaction with electromagnetic radiation is particularly strong in the terahertz range, however with a single layer of graphene the interaction was still not strong enough," Hugen Yan, a member of the Nanoscale Science and Technology Group at IBM's T. J. Watson Research Lab (Yorktown Heights, N.Y.) was quoted as saying. "But by using a multi-layer stack structure in microdisk arrays we achieved frequency selectivity in the terahertz range, allowing us to tune the desired resonant frequency."

The devices that IBM have developed could find their way into future mid- and far-infrared photonic devices, such as detectors and modulators. The next step for the researchers will be to tune the devices for infrared frequencies typically used in optical communications equipment.

Last Friday the US Food & Drug Administration (FDA) issued draft guidance documents on the use of nanotechnology by food and cosmetics industries.  Since then the reports covering this story have characterized it as “FDA opts for stricter role on nanotechnology”  or “FDA proposes new rules for nanotechnology.”

While "draft guidance documents" may not garner as much interest as these more confrontational headlines, the guidelines come closer to the FDA's invitation to industry on how together they can look at the issue of nanomaterials in food and cosmetics. And from someone who has been accused of being too dismissive of government attempts at regulation of nanotech, I believe this to be a sensible way to approach the issue.

A misconception that has circulated in a number of the stories covering this news is that the guidelines are limited to food packaging. This is not true. The guidelines cover food ingredients and additives in addition to packaging as the blog Frogheart rightly points out.

But getting back to why I believe this collaborative approach makes sense: Both the food and cosmetics industries could quite easily retreat into silence about their use of nanotechnology in their products if a more hard-line approach was taken. This reticence has made sense to me considering the hyped up rhetoric that seemed to preclude the possibility for a reasoned, balanced and scientific discussion of nanotechnology in food as well as cosmetics.

The latest entry into the nano-enabled nonvolatile memory sweepstakes comes from a team of researchers from Taiwan and the University of California Berkeley. The multinational research team claims it has developed a new electronic memory using silicon quantum dots that is 10-100 times faster in writing and erasing data than charge-storage memory.

While nanoribbons promise greater storage density and carbon nanotubes look to be able to make resistive random-access memory and phase-change memory realities, it seems the metal-gate silicon quantum-dot nonvolatile memory the researchers described in Applied Physics Letters is just ultrafast. There doesn’t seem to be any information on what kind of storage density the memory is capable of.

Nonetheless the researchers believe that metal-gate structures—like the one that was used in this memory—are on a path to realizing nanoscale complementary metal-oxide-semiconductor (CMOS) memory. "Our system uses numerous, discrete silicon nanodots for charge storage and removal. These charges can enter (data write) and leave (data erase) the numerous discrete nanodots in a quick and simple way," explains Jia-Min Shieh, a researcher with the National Nano Device Laboratories in Taiwan.

The memory is designed around a non-conducting material in which discrete quantum dots have been fixed. Each one of these quantum dots serves as a single memory bit. After the quantum dots have been affixed to the non-conducting material, a metallic layer is laid on top, which serves as the metal gate providing the “on” and “off” function of the transistor.

The extreme speed of the device is the result of using ultra-short bursts of green laser light to stimulate specific areas of the metal layer. What the researchers discovered was that the green laser was able to create gates over each individual quantum dot.

It’s not clear what kind of commercialization track this research may be on, but the researchers seem to feel that because it’s compatible with CMOS processes commercial aspirations should be achievable.

"The materials and the processes used for the devices are also compatible with current main-stream integrated circuit technologies," explains Shieh. "This technology not only meets the current CMOS process line, but can also be applied to other advanced-structure devices."

Hip replacement surgery seems commonplace, what with 1 million Americans receiving the procedure each year. Yet while it may seem routine at this point, the truth is that 17 percent of patients experience some kind of problem with the implant requiring an earlier than expected replacement.

Now researchers at MIT have developed a nanomaterial that could avoid the need for a large portion of these replacements. The research, which was initially published in the Wiley journal Advanced Materials, was able to create a nanocoating that would replace the bone cement typically used in these procedures.

The nanocoating uses hydroxyapatite nanoparticles that not only initially secures the implant to the bone, but also encourages faster bone tissue growth. The bone cement currently used, to fix the replacement hip to the femur, can harden to a consistency like glass—and, like glass, sometimes cracks and detaches from the implant, leaving the patient in chronic pain.

“Typically, in such a case, the implant is removed and replaced, which causes tremendous secondary tissue loss in the patient,” says Nisarg Shah in a news release by MIT News. Shah is a graduate student in Paula Hammond’s lab (which we previously wrote about in the context of lithium ion batteries) and one of the author’s of the research. “Our idea is to prevent failure by coating these implants with materials that can induce native bone that is generated within the body. That bone grows into the implant and helps fix it in place.”

The hydroxyapatite nanoparticles are in fact a natural component of bone and attract mesenchymal stem cells from the bone marrow. The material is also made up of thin layers of other materials that encourage the mesenchymal stem cells to become bone producing cells known as osteoblasts. Together this mix of materials stimulates the production of bone tissue that fills in the space around the implant.

“When bone cement is used, dead space is created between the existing bone and implant stem, where there are no blood vessels. If bacteria colonize this space they would keep proliferating, as the immune system is unable to reach and destroy them. Such a coating would be helpful in preventing that from occurring,” Shah says.

This is not the first time attempts have been made to use hydroxyapatite for orthopedic implants. But previously it has always resulted in coatings that are too thick and suffer the same demise of the bone cement, breaking away from the implant.

The MIT team has been able to control the thickness of the material by using layer-by-layer assembly.

“This is a significant advantage because other systems so far have really not been able to control the amount of growth factor that you need. A lot of devices typically must use quantities that may be orders of magnitude more than you need, which can lead to unwanted side effects,” Shah says.

The research is currently still at the point of animal studies, but the results thus far have been very encouraging, according to the researchers.

Because graphene lacks an inherent band gap, some critics have claimed that it is a dead-end line of research for electronics. But it's important to note that graphene comes in several varieties.

At the University of Wisconsin-Milwaukee (UWM) researchers have developed a new form of graphene they have dubbed “graphene monoxide (GMO).” With GMO, the UWM researchers believe they have brought graphene electronics applications one-step closer to reality. Instead of merely behaving as a conductor or insulator, the new material is capable of acting like a semiconductor. As a bonus, it also can be mass produced inexpensively.

“A major drive in the graphene research community is to make the material semiconducting so it can be used in electronic applications,” says Junhong Chen, professor of mechanical engineering and a member of the research team. “Our major contribution in this study was achieved through a chemical modification of graphene.”

The research, which was initially published in the journal ACS Nano in November of last year,  didn’t really start off as graphene research at all. Instead it was based around graphene’s forgotten cousin, carbon nanotubes (CNTs).  Chen and his UWM colleagues had developed a hybrid material based around CNTs that they mixed with tin oxide nanoparticles to create sensors.

The researchers wanted to be able to image this hybrid material as it was in the process of sensing. In order to do this they approached Carol Hirschmugl, who had developed an infrared imaging technique. But in order to see more molecules attaching themselves to the CNT, Chen and his colleague Marija Gajdardziska realized that they needed to unroll the CNT, thereby making it graphene.

Once the researchers had made the hybrid material into graphene, they decided to experiment with another cousin of graphene—graphene oxide (GO). GO is essentially layers of graphene that have been stacked on top of one another in an unaligned orientation. One of the experiments they undertook with GO was to put it in a vacuum to reduce the oxygen and heat it. Quite unexpectedly, instead of the material being damaged or even destroyed the unaligned orientation suddenly became aligned. With the addition of heat and a vacuum, GO had become the semiconducting GMO.

“We thought the oxygen would go away and leave multilayered graphene, so the observation of something other than that was a surprise,” says Eric Mattson, a doctoral student of Hirschmugl’s.

While this material they stumbled upon sounds quite promising for further development, it should be noted that the researchers plan to be focusing their attention on determining what the actual trigger mechanism was for the self-ordering of the GMO. In other words, there seems to be a good deal more science to be done before the engineering can begin.