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Nanodot Memory Leaves Charge-Storage Memory in the Dust

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."

Nanocoating Encourages Bone Growth in Hip Replacements

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.

Graphene Electronics Applications Get One Step Closer with New Semiconducting Variety

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.

Nanoparticle Could Recapture Water Lost at Power Plants

I have covered the role that nanotechnology can play in providing clean drinking water numerous times in this blog over the years, going as far back as 2007 and as recently as February this year.  But over the years the various nanotechnologies I have covered have been related to desalination processes--like those I linked to above--or improved filters to provide clean drinking water in remote regions of the world.

The latest nano-related development for water comes from Argonne National Laboratory. It is completely different from what I have seen before and addresses a huge issue: water waste at nuclear- and coal-powered power plants.

Approximately 40 percent of the US’s freshwater withdrawals and 3 percent of overall freshwater consumption goes to simply feeding the steam generators at power plants. Because the power plants use partially condensed high-temperature steam to run the turbines, a significant amount of water is lost due to evaporation and cannot be recaptured.

The technology the Argonne researchers are developing to address this issue and reduce the amount of fresh water lost is a nanoparticle based on a “core-shell” configuration, which basically means that the nanoparticles have a core made of one type of material and the coating of that core is another type of material. In this case, the outer coating protects an inner core that melts above a certain temperature.

The nanoparticles are dispersed in the plant’s water supply so that they absorb heat during the thermal cycle of the process. This causes the nanoparticles to melt partially, but they totally solidify again once they reach the cooling tower. Apparently, water is conserved because the outer coating bonds with the water molecules.

This is very preliminary research and they are still experimenting with the chemistry at the boundary between the metal nanoparticles and the water molecules. But it is such a large issue that the project looks like it’s getting fast-tracked. There are plans to have a proof of concept this year and a full-scale commercial deployment in four years.

“It’s practically unheard of for industry to seek to deploy a new technology so quickly,” said Argonne associate division director Thomas Ewing. “However, water consumption is a major issue that limits the expansion of power. If we want to solve the energy crisis, we’ll have to move boldly.”

Formula 1 to Restrict Use of Nanotechnology

Back in 2010, it was becoming clear that Formula 1 auto racing was taking note of nanotechnologies--ranging from nanomaterials to microscopy--but the variety of nanotechnologies that were actually finding their way into the cars still seemed pretty limited. Nanotech seemed destined, though, to play an even bigger role.

While to some people Formula 1 may conjure up Monte Carlo and the Jet-Set lifestyle, in fact it's populated with material scientists and engineers and more than its fair share of microscopy tools. In terms of advanced technologies, Formula 1 is really in a class by itself compared to other motoring sports.

Despite technology playing such a key in Formula 1 cars, the teams and cars need to abide by an ever-evolving list of rules that govern what technology can and can't be used. So, before anyone can jump ahead and start adopting the latest methods for reinforcing composites with carbon nanotubes, they’ll have to do some digging into F1 regulations.

Cientifica and the Motorsport Industry Association have launched a new website that looks at the issue of nanotechnology in motor sports. One of the first pieces put up on its website raises the issue of whether nanotech in Formula 1 is even legal.

In the interest of full disclosure, I do work for Cientifica, but I have not been involved in this particular project. So when the article poses the question of why the Federation Internationale de l'Automobile (FIA, the governing body of Formula 1) has turned its attention back to nanofiber composites, it’s the first time I’ve heard the question posed. And I think the answer may very well be the news I covered last year in which Applied NanoStructured Solutions LLC (ANS, Baltimore, Md.), a Lockheed Martin subsidiary, and Owens Corning (Toledo, Ohio) have developed a way to use carbon nanotubes in composites that actually strengthens and lightens the material.

I think with the Lockheed Martin/Owens Corning development carbon nanotubes are no longer just a very expensive resin filler that makes for good marketing copy, but something that can change the strength-to-weight ratio of composites to the point where FIA has to take notice.

Carbon Nanotubes Have Strange New "Remote Heating" Property

The world of the nanoscale phenomenon offers us a wide range of surprises. For instance, the yellow color we expect to see with gold turns to red or purple on the nanoscale.

That’s unusual, but researchers at University of Maryland (UMD) have discovered a phenomenon when passing an electrical current through carbon nanotubes that is so strange they have had to coin a new term for it: “Remote Joule heating”.

Joule heating is when an electric current passes through a conductor, like a metal wire, and releases heat. At the nanoscale, joule heating involves electrons bouncing off atoms in the conductor, causing the atoms to vibrate. In turn, these vibrations generate heat.

So fundamental is the understanding of Joule heating that you need never have heard the term to know that it exists. With your electric stove, you send electricity through the stove’s heating element, it heats up and then passes that heat onto your tea kettle. However, imagine, if you will, that you sent current through your stove but the heating element remained cold to the touch. While the heater may be cold, your tea kettle got hot enough to boil water.

That’s a bit like what the UMD researchers discovered when they sent current through carbon nanotubes (CNTs). CNTs are conductors like metal wires so when researchers started sending electricity through them they expected that nanotubes would heat up, but they didn’t. Instead they remained cool while the materials close to them—a silicon nitride substrate—got hot.

“This is a new phenomenon we're observing, exclusively at the nanoscale, and it is completely contrary to our intuition and knowledge of Joule heating at larger scales—for example, in things like your toaster," says Kamal Baloch, who conducted the research while a graduate student at the University of Maryland. "The nanotube's electrons are bouncing off of something, but not its atoms. Somehow, the atoms of the neighboring materials—the silicon nitride substrate—are vibrating and getting hot instead."

The research, which was published in the journal Nature Nanotechnology took a CNT and attached it to metal contacts and laid it on top of a silicon-nitride substrate. They passed electricity through the CNTs and observed the process using electron thermal microscopy.

They observed the same phenomenon over and over again. Every time the metal nanoparticles in the substrate would melt from the heat but the CNTs would remain cold.

While the researchers have been able to duplicate this phenomenon repeatedly, they haven’t absolutely nailed down how it happens that the substrate’s atoms are made to vibrate from a distance when those in the CNT are not.

“We believe that the nanotube's electrons are creating electrical fields due to the current, and the substrate's atoms are directly responding to those fields," says John Cumings, an assistant professor in the Department of Materials Science and Engineering who oversaw the research. "The transfer of energy is taking place through these intermediaries, and not because the nanotube's electrons are bouncing off of the substrate's atoms."

The implications for this phenomenon in computing could be huge. Keeping transistors cool remains one of the biggest obstacles for advancing computing power. This phenomenon could provide a path to a new solution.

"This new mechanism of thermal transport would allow you to engineer your thermal conductor and electrical conductor separately, choosing the best properties for each without requiring the two to be the same material occupying the same region of space," says Baloch.

E-nosy Phone Sniffs Out Danger

In the sometimes baffling array of proposed applications for nanotechnology in mobile phones,  we have a new addition with which your mobile phone can detect harmful, airborne substances.

The nanotechnology developed by the University of California (UC) Riverside researchers, led by Nosang Myung, professor and chair of the Department of Chemical and Environmental Engineering, uses nanowires made with functionalized carbon nanotubes in a sensor array to detect dangerous substances in a portable device.

While these proposed applications for mobile phones using nanotechnology are often as much marketing spin as real-world, commercial possibilities, in this case it appears that Riverside, CA-based Innovation Economy Corporation (IE Corp) has plans to commercialize the research. IE Corp is handling the commercialization through the start-up it created and funded, Nano Engineering Applications, Inc.

Nonetheless once again the mobile phone tie-in seems as though it might just be a bit of a marketing ploy. Developed using functionalized carbon nanotubes, the sensor has a broad range of applications from agriculture—where it would detect concentrations of pesticides—to military applications for detecting chemical warfare agents.

All of these are worthwhile applications, but I suppose if you want any chance of getting in the mainstream press, you have to couch your technology in terms of people’s smart phone. Detecting pesticides just doesn’t have the same appeal.

In any case, a mobile phone that can detect dangerous airborne substances is similar to the recent research out of Princeton and Tufts Universities in which a graphene nanosensor could be placed on your teeth for detecting dangerous bacteria.  It's not clear whether the UC Riverside researchers and their commercial partner IE Corp will continue to purse the portable health monitoring aspect of the technology, but it should keep the technology in the press while they pursue the various other applications.

Getting a Handle on the EU’s Definition of Nanomaterials

Last year, I covered some of the European Union's (EU) machinations in trying to arrive at a definition for nanotechnology. The EU ultimately published a definition in October last year.

There was a fair amount of surprise at some aspects of the definition, in particular its inclusion of not only manufactured nanoparticles but also the natural and incidental varieties.  This made the definition of nanomaterials so broad that industries that may never had given a second thought to nanotechnology found that they too were swept up into this regulatory framework.

The UK-based Nanosight, whose nanoparticle measurement instruments I covered back in 2007,  decided to offer a webinar that would try to bring some clarity to a definition that seemed to lack it.

In the webinar, Jeremy Warren, CEO of Nanosight, expresses his initial dismay at finding that the EU was including both natural and incidental nanoparticles in its definition for nanomaterials.

“We’ve met people recently who work on the legal side within large chemical organizations, who up until October last year didn’t know anything about nanotechnology and suddenly they’re going to be caught within legislation, which is quite a shock to them,” says Warren in the webinar.

Warren put the question of why the definition was made so broad to Dr. Denis Koltsov, a leading international expert in nanotechnology legislation and control. According to Koltsov, it seems that it was just impossible to determine whether a nanoparticle that had found its way into a nanomaterial matrix was deliberately manufactured or was a naturally occurring nanoparticle. In other words, since a regulator can’t differentiate between the various origins of the nanoparticles they just included them all.

You don’t have to extrapolate too much to conclude that companies that have been making things for years—maybe decades—without the slightest inkling that nature had put nanoparticles into their products are now part of this regulation. It got even more complicated in February of this year when the French government issued Decree # 2012-232, which ordered that anybody producing or transporting these nanomaterials in amounts of 100 grams or more would have to make a report to the French government.

While this webinar’s aim was to clarify the EU nanomaterial definition—which it largely succeeds in doing—I think more than anything I found its clarifications alarming. I joked back in October that the EU had succeeded in turning the idea of a definition on its head and offered something that broadened the definition of a nanomaterial to the nearly infinite. But now it appears that governments are now going to take this absence of a definition as an opportunity to place an entirely new layer of regulations on products and industries that seem remote from the world of nanomaterials. I don’t think it’s so funny any more.

Does Lifecycle Analysis Make Sense for Nanotechnology?

Last week, at the International Symposium on Assessing the Economic Impact of Nanotechnology held in Washington, D.C., researchers from the Georgia Institute of Technology presented a paper about using lifecycle analysis to gauge the impact of nanotechnology.

In their presentation, Philip Shapira and Jan Youtie emphasized that any assessment of nanotechnology’s impact—economic or otherwise—must take into account the full lifecycle of the product.

It seems sensible to perform a lifecycle assessment to determine how nanotechnology will add or subtract from our lives (and it rounds out the myriad other attempts at measuring its impact). But as the researchers themselves concede, it's extremely difficult to assess and make forecasts about nanotechnology, because it underlies so many different industries.

“Compared to information technology and biotechnology, for example, nanotechnology has more of the characteristics of a general technology such as the development of electric power,” said Youtie, director of policy research services at Georgia Tech’s Enterprise Innovation Institute. “That makes it difficult to analyze the value of products and processes that are enabled by the technology.”

I couldn’t agree more and it’s a point myself and others have been making for years, initially to widespread skepticism: nanotechnology is not an industry; it’s an enabling technology. If that is understood, it begs the question why continue to assess it as though it were a monolithic entity, or condemn it as one?

I think the answer is hidden in the press release for this new report when Youtie comments: “Scientists, policy-makers and other observers have found that some of the promise of prior rounds of technology was limited by not anticipating and considering societal concerns prior to the introduction of new products. For nanotechnology, it is vital that these issues are being considered even during the research and development stage, before products hit the market in significant quantities.”

Because we now have the social science capability to do this sort of thing, it seems like we're willing to apply it to a field that defies quantification of any kind.

I'm also nonplussed by another of the researcher's observations. Youtie implies that nanotechnology began with large companies and is now migrating toward an ever increasing number of small companies. I suppose a statement like this probably should be couched in all sorts of definitions of terms, which might color one’s interpretation of what it was intended to mean, but to me it seems that the trend has been almost the opposite of this.

Sure, the IBMs of the world did have the research money to develop the key tools that enabled us to work on the nanoscale. But I remember back in 2001-2003 that there were a lot of small companies that discovered that they could produce a nanomaterial and believed that this somehow would miraculously constitute a business. They soon discovered that large chemical companies could quickly produce the same material in bulk and had the supply chain connections to make sure that the material got into products. As a result, we have seen a number of small companies that were initially exhilarated they could produce carbon nanotubes in their garage get swept up into the great consolidation of nanomaterials companies.

But let’s get back to the primary point of the paper, which seems to be that we need to not only look at the great things nanotechnology can enable but also at the costs it creates. This echoes one of the most cogent arguments that the Friends of the Earth (FoE) have raised thus far. Essentially, the FoE points out that nanotechnology has not yet delivered on its claims to enable cheap solar, hydrogen and wind power, but even if it could, the energy used to create the nanomaterials would result in a net energy loss.

In an example of how quickly things change in the field of nanotechnology, a week after I covered the FoE’s report I reported on research from MIT that demonstrated a process for producing carbon nanotubes that reduced emissions of harmful byproducts by at least ten-fold and could cut energy use in half. One week you have a cogent argument, and the next you’re behind the times.

While it may be difficult to predict nanotechnology's impact without conducting lifecycle analysis, trying to include those lifecycle considerations will be far more difficult, and make their accuracy short-lived.

Image: Georgia Tech Photo (Gary Meek)

Graphene Nanosensor Tattooed to Teeth Detects Bacteria

A couple of years ago I covered research into developing a nanomaterial that could end the need for root canals. I took some criticism at the time for suggesting in that blog that root canals were unpleasant. So, despite some reluctance on my part to cover dental-related nanotechnologies, let's look once again at the latest nanotechnology being used with teeth.

The technology involves a nanosensor made out of graphene that can detect bacteria in our mouths when the sensor is in a sense tattooed to our teeth. Oddly, it seems that the bacteria that the nanosensor detects is not the Streptococcus mutans bacteria that is the principal cause of tooth decay.

While the research, which was initially published in the journal Nature Communications, may not combat tooth decay, it holds some promise as method for on-body health monitoring. The researchers from Tufts University and Princeton University have developed a method for placing wireless graphene nanosensors onto biomaterials via silk absorption.

“In our paper, we demonstrate that graphene can be printed onto water-soluble silk, says Manu S Mannoor, a graduate student at Princeton University and the paper’s first author. “This in turn permits intimate biotransfer and direct interfacing of graphene nanosensors with a variety of substrates including biological tissues and hospital IV bags to provide in situ monitoring and detection of bacterial contamination and infection."

The key to the technology seems to be the use of silk thin films. "First, we printed graphene nanosensors onto water-soluble silk thin-film substrates,” explains Mannoor in the Nanowerk piece. “The graphene is then contacted by interdigitated electrodes, which are simultaneously patterned with an inductive coil antenna. Finally, the graphene/electrode/silk hybrid structure is transferred to biomaterials such as tooth enamel or tissue, followed by functionalization with bifunctional graphene–AMP biorecognition moeities."

The researchers expect that this technology could serve as a first-generation platform of in situ monitoring for bacterial contamination in environments ranging from hospital sanitation to food safety analysis.

This new nanosensor may not alert you to the buildup of bacteria that would cause tooth decay, but it might be of interest those who like to decorate their teeth and be alerted to other types of bacteria.

Image: McAlpine Group, Princeton University



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

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