Nanoclast iconNanoclast

Inventors Claim Graphene Hybrid Could Revolutionize Electronics Industry

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.

IBM Researchers Build Multi-Layer Graphene for Photonics Applications

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.

FDA Invites Industry Collaboration on Nanotech Safety in Food and Cosmetics

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.

Read More

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.

Advertisement

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
Load More