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Spintastic Nanorods Rotate at 150,000 RPM

Recent research has demonstrated that triggering nanoparticles to spin after being injected into the bloodstream can provide some remarkable medical benefits. Just this week, we reported on work out of the University of Georgia in which nanorods that were stimulated to spin by rotating magnets provided greater efficacy for the blood-thinning drug recombinant tissue plasminogen activator, or t-PA, used in stroke treatment. Earlier this year, researchers at Penn State University got nanorods to spin in response to both magnets and ultrasonic waves to churn cancer cells into mush.

While these have been promising results, nobody really knew how fast these nanorods were spinning—that is until now. Researchers at the National Institute of Standards and Technology (NIST) in cooperation with the Penn State researchers discovered that these nanorods were spinning so quickly that they believe that their application may extend beyond medical uses.

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Nanoparticles Improve Stroke Treatment

Currently there is just one drug that has been approved for treatment of acute stroke—recombinant tissue plasminogen activator, or t-PA. Essentially it works by thinning blood clots. Researchers at the University of Georgia (UGA) announced last week that they have developed a magnetic nanoparticle that when combined with t-PA can make the drug significantly more effective.

The Georgia researchers injected magnetic nanorods into the bloodstream. When stimulated by rotating magnets the nanorods act as a kind of mixing tool that shakes up blood clots that have already been thinned by t-PA.

The injected nanorods "act like stirring bars to drive t-PA to the site of the clot," said Yiping Zhao, professor of physics at UGA, in a press release. "Our preliminary results show that the breakdown of clots can be enhanced up to twofold compared to treatment with t-PA alone."

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Mechanical Properties of Nanoantennas Explored for First Time

Researchers have been leveraging the field of plasmonics—which takes advantage of the surface plasmons that are generated when photons hit a metal structure—to enable arrays of nanoantennas to manipulate light in ways that make possible a number of optoelectronic applications including optoelectronic circuits and for producing hydrogen gas through artificial photosynthesis.

Recent experiments have shown that placing these plasmonic nanoantennas on top of glass pillars enhances their power for sensor applications, such as fluorescence enhancement in biochemical sensing. Now researchers at the University at Illinois have discovered that this high perch for the nanoantennas introduces mechanical properties into the system that can be tuned and manipulated.

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Nanoporous Silicon Oxide Is Back in the Race for Resistive Memory

Resistive random-access memory (RRAM) has promised a new generation of computer memory by decreasing the size of memory cells through the storage of data as resistance rather than charge.  With RRAM, a dielectric material is sandwiched between two electrodes so that when a voltage is applied ions are pulled from one of the electrodes, forming conductive filaments that lower the cell’s resistance.

Research has focused on finding the best material for the dielectric, and a wide variety of materials are being pursued, including paper.

Since 2010, James Tour and his colleagues at Rice University have been pursuing silicon dioxide as the dielectric material for a RRAM cell after they discovered conductive filament pathways can be formed in the material.  Now Tour and his colleagues have taken another step in making silicon oxide the basis for high-density, next-generation computer memory.

The Rice team has refined the production of the memory cells to make it possible to fabricate the devices at room temperature with conventional production methods.

Companies are looking to win at RRAM using a variety of materials, such as Panasonic’s use of tantalum oxide and others the development of hafnium oxide. But Tour and his colleagues recently published a paper in the journal Nano Letters that makes the case that nanoporous silicon oxide is superior to the other technologies.

“Our technology is the only one that satisfies every market requirement, both from a production and a performance standpoint, for nonvolatile memory,” Tour said in a press release. “It can be manufactured at room temperature, has an extremely low forming voltage, high on-off ratio, low power consumption, nine-bit capacity per cell, exceptional switching speeds and excellent cycling endurance.”

Tour comes to this conclusion after the latest version of silicon oxide produced by the Rice researchers exceeded previous versions in a number of important performance parameters. The Rice team used a nanoporous version of silicon dioxide that reduced the amount of voltage needed to create the conductive pathways down to less than two volts. This represents a 13-fold improvement over the team’s previous best. And it brings silicon oxide right back into the running against competing materials.

The researchers were also able to eliminate the need to fabricate so-called device edge structures. “That means we can take a sheet of porous silicon oxide and just drop down electrodes without having to fabricate edges,” Tour said. “When we made our initial announcement about silicon oxide in 2010, one of the first questions I got from industry was whether we could do this without fabricating edges. At the time we could not, but the change to porous silicon oxide finally allows us to do that.”

The advantages of switching to a nanoporous variety of silicon oxide didn’t end there. The new porous version allows the cell to endure 100 times as many write-erase cycles as the previous version. Additionally, the porous silicon oxide cell's capacity to hold up to nine bits is the highest number among oxide-based memories, the Rice team claims.

The research team reports that they have already received overtures from companies interested in licensing the technology.

IBM Pours $3 Billion Into Future of Nanoelectronics

We have been hearing the obituaries for complimentary metal-oxide-semiconductor (CMOS) for twenty years now. But it’s still here and holding out to the bitter end it seems. Despite needing ever more ingenious engineering twists to keep it going, CMOS will eventually fall victim to Moore’s Law as it continues its march towards ever smaller transistor dimensions.

IBM has stepped up to face this growing issue with the announcement this week that it will be spending US $3 billion over the next five years on a project it has dubbed “7nm and Beyond”.  Big Blue’s aim will be to pursue ways to bring traditional silicon-based technologies to ever smaller dimensions and simultaneously develop alternative materials, namely carbon nanotubes, graphene, and other nanomaterials.

The $3 billion is equivalent to half of all IBM's R&D expenditure last year, but others have pointed out that this amount of funding spread out over five years essentially maintains IBM's current chip research spending levels.

Nonetheless, for a company that has reportedly been trying to sell off its hardware business, this is a significant investment—whether it’s aimed at boosting the slumping hardware unit to achieve its old glory or polishing it up for a sale.

While this may be a matter of fascinating speculation for investors, the impact on nanotechnology development  is going to be significant. To get a better sense of what it all means, I was able to talk to some of the key figures of IBM’s push in nanotechnology research.

I conducted e-mail interviews with Tze-Chiang (T.C.) Chen, vice president science & technology, IBM Fellow at the Thomas J. Watson Research Center and Wilfried Haensch, senior manager, physics and materials for logic and communications, IBM Research.

Silicon versus Nanomaterials

First, I wanted to get a sense for how long IBM envisioned sticking with silicon and when they expected the company would permanently make the move away from CMOS to alternative nanomaterials. Unfortunately, as expected, I didn’t get solid answers, except for them to say that new manufacturing tools and techniques need to be developed now.

“We anticipate that in order to scale to 7 nanometers and perhaps below for the industry, we will need to have the semiconductor architectures and new manufacturing tools and techniques in place by the end of the decade,” said Chen in an e-mail interview. “That's why it is critical for us to make the significant investment now into the research and early stage development to demonstrate what 7nm innovations will be useful before it can even be commercialized.”

Top-Down versus Bottom-Up Manufacturing Techniques

I was particularly interested in the “beyond” part of the project, which implied dimensions below 7nm and where things start to get really tricky for traditional top-down manufacturing techniques, like lithography.  Despite all the continued advances, some have argued that once you get below 3nm top-down manufacturing techniques are just not viable.

I didn’t get a clear response as to whether IBM agreed with the assessment that at the 3-nm threshold top-down manufacturing fails to be effective for large scale manufacturing, but I did get the answer that IBM is pursuing both top-down and bottom-up manufacturing techniques. That’s apparent by the body of research they’ve published, but what we still don’t know is how far they intend to push lithography below 7 nm for large-scale chip production.

Carbon Nanotubes versus Graphene

In the press release, IBM provides details on two of the favored nanomaterials of the last decade: carbon nanotubes and graphene.

With carbon nanotubes (CNTs), points out its recent success at producing the material with 99.99 percent purity. To clarify, Wilfried Haensch explained: “The 99.9 percent refers to the purity with respect to semiconductor tools. It means that out of 10,000 tubes 1 is metallic and this is what you want if you want to build devices. But we need to reach 999,999 and that is part of our current focus.”

This overcomes one of the big obstacles in carbon nanotube production: ensuring you get semiconducting or metallic versions. But what about the other obstacle: aligning the CNTs?

It turns out that the two are problems are related. “There are two approaches,” says Haensch. “One is to grow the nanotubes on a wafer and then transfer them. The challenge is you loose purity for semiconductor tubes.  One-third are metallic and two-thirds are semiconductor, so the metallic ones need to be burned and then you have randomness. We take the tubes and purify them first to remove the metallic, and use a self-assembly method to place them in the positions we would like to have them.”

Finally, with graphene I wanted to know what IBM saw as the material's role in electronics, especially because it lacks an inherent band gap and must have that property engineered into the material. For this, Haensch was direct and to the point: “We see an opportunity with graphene in RF electronics. We have shown that RF circuits can be manufactured on the back end of an existing CMOS process.” Not exactly a broad set of applications for graphene in electronics.

"Nanojuice" Could Diagnose Gastrointestinal Illnesses

Researchers at the University of Buffalo (UB) have developed what they're calling a "nanojuice", which when ingested enables doctors to see clear images of the small intestine in real time.

The novel medical imaging technique promises better diagnosis of a variety of gastrointestinal illnesses, including Crohn’s disease and celiac disease. Other medical imaging techniques used to examine the small intestine, such as X-rays, magnetic resonance imaging, and ultrasound, have drawbacks in terms of safety, accessibility to the organ, and an inability to produce clear images. 

Perhaps the biggest breakthrough of this technique is that unlike other imaging techniques it is capable of monitoring what’s happening in the small intestine in real time.

“Conventional imaging methods show the organ and blockages, but this method allows you to see how the small intestine operates in real time,” said Jonathan Lovell, assistant professor of biomedical engineering at UB in a press release. “Better imaging will improve our understanding of these diseases and allow doctors to more effectively care for people suffering from them.”

The key to the technique is the ingestion of a liquid with nanoparticles suspended in it, thus the name "nanojuice." The basis of the nanoparticles is a family of dyes known as napthalcyanines. While these molecules are great for absorbing light that make them ideal as a contrasting agent, alone they are unsuitable for use in the human body. First, they don’t disperse in a liquid; and, secondly, they could be absorbed in the intestine and transferred into the blood stream.

To counteract this, the UB researchers developed nanoparticles they dubbed “nanonaps” that contain the dye molecules inside them, imparting the ability to both disperse in liquid and pass through the intestine without problems.

In the research, which was published in the journal Nature Nanotechnology, the UB team gave the nanojuice to mice orally and then used photoacoustic tomography—a kind of ultrasound imaging that uses light-induced pressure waves. The result was that nanoparticles in the intestine could be visualized with low background and a high resolution.

This technique enables for the first time the visualization of peristalsis, which involves the contraction of muscles that moves food through the small intestine. The ability to observe this process in patients could not only help in the diagnosis of gastrointestinal illnesses but also help determine the link between peristalsis dysfunction and ranges of disorders, including diabetes and Parkinson’s disease.

The researchers plan to take this work to the next step, human trials, and test the technique in other areas of the gastrointestinal tract.

Start-up Puts the Carbon on the Cathode of Li-ion Batteries

The approach of many researchers seeking to improve the ubiquitous lithium-ion (Li-ion) battery has been to replace the graphite typically used for the battery's anode. Now, in work that originated at the University of Alberta in Canada, the focus has moved to the cathode. The result, claims lead researcher Xinwei Cui, is a battery that can deliver an energy output five to eight times that of the Li-ion batteries currently available.

So confident is Cui, whose research was published in the journal Nature Scientific Reports, that he has co-founded AdvEn Solutions, which is manufacturing the batteries for use in electronic devices and plans to have something on the market by the end of this year.

“What we’ve done is develop a new electrochemistry technology that can provide high energy density and high power density for the next generation,” said Cui in a press release.

The new electrochemistry involves using fluorinated carbon nanotubes in the cathode. Earlier attempts at using carbon and fluorine in the cathode had produced non-rechargeable batteries. Research instead focused on lithium-sulfur, or lithium-air based cathodes. But using flourinated carbon nanotubes allowed for a rechargeable battery that also overcomes some of the issues associated with the lithum-sulfur and lithium-air cathodes, such as large volume expansion when the cathode fills up with ions that shortens a battery's life span.

Batteries using the fluorinated carbon nanotubes in their cathode demonstrated a maximum discharging capacity of 2174 milliamp-hours per gram (mAh/g) and a specific energy density of 4113 Watt-hours per kilogram (Wh/kg), compared to  an average Li-ion battery that has a discharging capacity of 372mAh/g and a specific energy of around 100 to 265 Wh/kg.

AdvEn Solutions plans to produce three types of batteries based on fluorinated carbon nanotube architecture. One of the batteries will have a high power output and long-life cycle, the second will provide high energy and quick charging rates and the third will have a super-high energy storage capacity.

“We have a long way to go, but we’re on the right track. It’s exciting work and we want everyone to know about it and that it’s very young but promising,” said Cui.

Carbon Nanotubes Unzip Into Nanoribbons When Smashed

Researchers have "unzipped" carbon nanotubes into graphene nanoribbons using a variety of methods since the feat was demonstrated over five years ago.

But there has always been one unifying characteristic about those methods: they involved a chemical solution to get the tubes to transform into sheets. Now researchers at Rice University have discovered that if carbon nanotubes are shot at a target and hit it broadside, they unzip into the graphene nanoribbons.

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Three-Atom Thick Material Switches Between a Conductor and an Insulator When Tugged

As chip dimensions have decreased to match the demands of Moore’s Law, insulating materials separating the transistor gate from the channel below it have had to be thinned down so much that keeping current from leaking through has been difficult. In fact, chipmakers are no longer thinning the gate oxide, and it stands now at 1 nanometer in thickness because to go thinner would allow too much current to flow through the channel when the transistor is supposed to be turned off.

Researchers at Stanford University have been running simulations with some two-dimensional materials that when sandwiched together can switch the material between conducting and insulating just by tugging on its edges.  If physical experiments on the material are successful, it could provide a way to completely shut down the leakage of current in chips and still go to smaller chip dimensions.

The researchers believe that if the material could be used in today's smart phone processors it could reduce their power consumption considerably.

The work, which was published in the journal Nature Communications, represents a growing body of knowledge on so-called transition dichalcogenide metals, which are materials that combine one of 15 transition metals with one of three members of the chalcogen family: sulfur, selenium, or tellurium.

In the computer models, the Stanford researchers took one atomic layer of molybdenum atoms and sandwiched it between two atomic layers of tellurium atoms. In the video below, you can see the three-atom thick structure switch between conductor and an insulator as it us pulled.

It does make an attractive computer model. However, whether it can be translated into an actual physical material remains to be seen. Even if they can produce the three-atom-thick sandwich, it’s not clear whether it could really be developed for large-scale production. While physical experiments have successfully demonstrated single-atom transistors, many are questioning whether such a device could ever be be made by the millions or billions.

It’s not clear that a now three-year-old challenge of Professor Mike Kelly at Cambridge University has ever been sufficiently answered. In the challenge he argues that devices with dimensions less than three nanometers cannot be mass produced using a top-down manufacturing technique. Until that question is adequately addressed, we may have here just another computer model that could lead to a physical material but not one that could be used in the mass production of electronic devices.

US Government Regulators Take on Nanomaterials

Besides a big funding gap that has prevented many nascent nanotechnologies from reaching the marketplace, two major obstacles to nanotech's advance are a seeming lack of a regulatory framework, especially in food and drugs, and environmental, health and safety (EHS) concerns.

This week, in what appears to be a coincidence, the US Food & Drug Administration (FDA) and the National Nanotechnology Initiative (NNI) have both issued formal announcements that should have an impact on both regulations and EHS concerns. The FDA has outlined a policy for overseeing nanomaterials in food, drugs and even cosmetics. Yesterday, the NNI provided an overview of progress on the implementation of the 2011 NNI Environmental, Health and Safety (EHS) Research Strategy.

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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
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