Nanoclast iconNanoclast

Engineering of Graphene Gives it Piezoelectric Properties

Researchers at Stanford University are extending the capabilities of graphene by engineering piezoelectric capabilities into the material.

"The physical deformations we can create are directly proportional to the electrical field applied and this represents a fundamentally new way to control electronics at the nanoscale," says Evan Reed, head of the Materials Computation and Theory Group at Stanford and senior author of the study. "This phenomenon brings new dimension to the concept of 'straintronics' for the way the electrical field strains—or deforms—the lattice of carbon, causing it to change shape in predictable ways."

The concept of ‘straintronics’ in Graphene was demonstrated at least as far back as 2010 when Lawrence Berkeley National Laboratory research, led by Michael Crommie, professor of physics at UC Berkeley and a faculty researcher at LBNL, serendipitously discovered that when graphene was grown on platinum a strain pattern was created.

It should be noted that the Stanford research, which was published in the journal ACS Nano,  was conducted within modeling and simulation software. Nonetheless the researchers achieved their piezoelectric effect quite deliberately in the models by depositing lithium, hydrogen, potassium and fluorine atoms on one side of the graphene lattice. They expected this to generate a piezoelectric effect, but not on the scale they witnessed in the models.

“We thought the piezoelectric effect would be present, but relatively small. Yet, we were able to achieve piezoelectric levels comparable to traditional three-dimensional materials," said Reed. "It was pretty significant."

While the level of the piezoelectric effect was unexpected, the real breakthrough here may be that they were able to control the effect by depositing the atoms in specific locations within the graphene.

"We were further able to fine tune the effect by pattern doping the graphene—selectively placing atoms in specific sections and not others," said Mitchell Ong, a post-doctoral scholar in Reed's lab and first author of the paper. "We call it designer piezoelectricity because it allows us to strategically control where, when and how much the graphene is deformed by an applied electrical field with promising implications for engineering."

It should be interesting to see if anyone takes on these simulations and starts running physical experiments. If it can be duplicated in physical experiments, it could open the possibility for this kind of doping to be used on other nanomaterials that could open their use in a number of application areas, ranging from energy harvesting to chemical sensing and high-frequency acoustics.

Carbon Nanofibers Improve Silicon Electrodes for Li-ion Batteries, But Is It Enough?

For the last couple of years the big news for lithium-ion (Li-ion) batteries has been the replacement of graphite in the anodes with silicon.

This move from graphite to silicon has been eagerly pursued in order to address one of the fundamental operations of Li-ion batteries: the movement of lithium ions from the cathode to the anode and their storage there. The more lithium ions that the anode can store, the longer the battery will stay charged. The charge can be increased by a factor of ten by replacing the graphite with silicon.

But there is a drawback with these silicon electrodes. They swell to three times their original size when charged and the charging and discharging of the battery soon renders the silicon useless as an electrode in a battery. For this reason, researchers have been working with various nanostructured silicon materials that take advantage of the superior storage capacity of silicon but are not as susceptible to the deterioration caused by charge-discharge cycles.

Now researchers at Pacific Northwest National Laboratory (PNNL) are taking a closer look at why these nanostructured silicon electrodes perform better than the graphite variety. "The electrodes expand as they get charged, and that shortens the lifespan of the battery," lead researcher Chongmin Wang at the Department of Energy's Pacific Northwest National Laboratory, was quoted as saying. "We want to learn how to improve their lifespan, because silicon-carbon nanofiber electrodes have great potential for rechargeable batteries."

The research, which was published in the journal Nano Letters, first tested how much lithium the electrodes could hold and how long they would last by putting the electrodes—which were made from carbon nanofibers wrapped by a thin layer of silicon—into a half-cell.

The researchers were initially impressed by the results, which showed that material maintained a very good capacity of about 1000 milliAmp-hours per gram of material after 100 charge-discharge cycles, five to 10 times the capacity of conventional electrodes in lithium ion batteries. However, they remained skeptical that the material would withstand continued charge-discharge cycles.

What they discovered while looking at the electrode through a transmission electron microscope confirmed some previous research and revealed some new phenomena. The research observed, as previous work has shown, that charging the battery does cause lithium ions to flow into the silicon. But what this research discovered was that the addition of the carbon to the silicon speeds up this process considerably—as much as 60 times faster than silicon alone.

It also turns outjust as expectedthat the silicon nanocomposite electrode does swell to three times its size just as its silicon cousin, but it does so evenly avoiding the imperfections that are caused by the uneven expansion of silicon alone.

Another interesting discovery from this research builds on previous work that discovered that once the ratio of lithium to silicon reached 15 to 4 in these electrodes the material crystallizes. The PNNL research discovered that the crystallization happens all at once rather than gradually—it ‘snaps’ into its crystallized form—a phenomenon known as congruent phase transition.

The key determination though was to find out how this charging and discharging affected the electrode. The results were not encouraging. It turns out the charge-discharge process leaves the surface of the electrode looking like a potholed stretch of road.

"We can see the electrode's surface go from smooth to rough as we charge and discharge it. We think as it cycles, small defects occur, and the defects accumulate," said Wang.

While this may not sound like good news, there is the positive side in that the thin silicon reacts better than thicker silicon and is more durable. “"In the current design, because the silicon is so thin, you don't get bigger cavities, just like little gas bubbles in shallow water come up to the surface. If the water is deep, the bubbles come together and form bigger bubbles," says Wang.

The researchers will next be looking into optimizing the bonding between the carbon nanofibers and the silicon to improve both the performance and the lifetime of the electrodes.

HyperSolar's Zero-carbon Process for Hydrogen Gas Production

Last week, I covered nanotechnology research that mimics photosynthesis to split water molecules into hydrogen gas. The resulting gas could be used for powering fuel cells.

Despite the comments being led off into an odd tangent about this development depriving the earth of its water resources, the aim of this line of research is to find sustainable and environmentally friendly methods for producing hydrogen gas.

In keeping with this spirit, Santa Barbara, CA-based HyperSolar, Inc. has announced this week that they have plans for producing “the world’s first nanotechnology-based, zero-carbon process for the production of renewable hydrogen and natural gas.”

I suppose in anticipation of some concern that potable water would be used in the proposed process, Tim Young, CEO of HyperSolar, made it clear in the press release that waste water would be used in the hydrogen production.

“Our research and development to date gives us a high degree of confidence that our innovative process can achieve commercial viability,” said Young. “Starting with a negative value feedstock in the form of wastewater and operating in low cost reactors, we believe that our artificial photosynthesis process of extracting hydrogen from water will be cost effective.”

There are not a lot of details about the process that Hypersolar is planning to adopt. We know from the quote above that it will be an “artificial photosynthesis process” like those I blogged on last week. And we know that nanoparticles will be used to detoxify the wastewater to “produce clean water and pure hydrogen in the presence of sunlight.” But we don’t know what nanoparticles will be used—except that they will be made from low-cost semiconducting materials—nor how they will be used in the process. Nonetheless Hypersolar has said that they expect to have a robust prototype of its process by 2013.

This year they will be attempting to meet the following milestones:

1.      A proof-of-concept microparticle for hydrogen production using conventional photovoltaic elements

2.      Analysis of the feedstock potential of multiple wastewater sources

3.      A complete photoreactor prototype for sustained hydrogen production

4.      Design of nanoparticles using low-cost semiconducting materials

I am pleased to see a company make such a grand proposal and I wish them luck. However, if they are successful in finding a cheap and environmentally friendly method for producing hydrogen gas for fuel cells, maybe they can turn their attention to finding a cheap and safe way of creating an infrastructure to distribute the hydrogen to cars powered by fuel cells.

Nanowire Forest Splits Water with Sunlight

Nanotechnology has a checkered past in improving fuel cell technology. I have cataloged some of the missteps previously. At the time, the areas in which researchers were attempting to apply nanotechnology to fuel cells—namely improved catalysts and hydrogen storage—didn’t address the real problems that have prevented fuel cells from receiving wider adoption.

One of the fundamental problems with fuel cells has been the cost of producing hydrogen. While hydrogen is, of course, the most abundant element, it attaches itself to other elements like nitrogen or fluorine, and perhaps most ubiquitously to oxygen to create the water molecule. The process used to separate hydrogen out into hydrogen gas for powering fuel cells now relies on electricity produced from fossil fuels, negating some of the potential environmental benefits. So in the last few years, a new line of research has emerged that uses nanomaterials to imitate photosynthesis and break water down into hydrogen and oxygen thereby creating a more cost-effective and environmentally-friendly method for producing hydrogen.

Angela Belcher at MIT reported on just such a method two years ago when she used man-made viruses to serve as a scaffold to attract molecules of the catalyst iridium oxide and a biological pigment (zinc porphyrins). Once these two molecules attached themselves to the scaffold, the viruses would become “wire-like,” which enabled them to split the water molecules into hydrogen and oxygen because of the precise spacing in the wire.

Now researchers at University of California, San Diego have developed a quite different approach to mimicking photosynthesis for splitting water molecules by using a 3D branched nanowire array that looks like a forest of trees.

According to Deli Wang, professor in the Department of Electrical and Computer Engineering at the UC San Diego Jacobs School of Engineering, this tree-like structure enables both trees and the nanowire arrays to capture the maximum amount of solar energy. To illustrate what he means, Wang points to satellite imagery in which flat surfaces like oceans or deserts simply reflect the light back and forests remain dark because they are absorbing the light.

The nanowire forest that Wang and his colleagues have created uses the process of photoelectrochemical water-splitting to produce hydrogen gas. The method used by the researchers, which was published in the journal Nanoscale, found that the forest structure of the nanowires, which has a massive amount of surface area, not only captured more light than flat planar designs, but also produced more hydrogen gas.

“With this structure, we have enhanced, by at least 400,000 times, the surface area for chemical reactions,” said Ke Sun, a PhD student in electrical engineering who led the project.

While it appears from the press release that the researchers are more interested in pursuing the photosynthesis aspect of this research to expand its use into capturing carbon dioxide, it could be a cost-effective way for producing hydrogen gas.

Nokia and Cambridge Look at Applying Nanotechnology to Super-Hydrophobic Phones

Mobile phone giant Nokia and Cambridge University have been working for a number of years on  nanotechnology applications for cell phones. In 2008, they announced the much-ballyhooed Morph phone that featured plastic electronics; the flexible circuits allowed the handset, which I like to call it the Dick Tracy phone, to wrap around your wrist like a watch.

I guess it’s impressive to duplicate a tech gadget used by a comic book character developed in the 1930s, but I never could see the point. Adding to the head scratching on that one was their admission that they didn’t expect to commercialize that phone for another 20 years.

As a marketing tool—as I’ve heard the Morph phone described—it was effective in that it got a lot of press coverage. But it left me thinking: Does Nokia really have a handle on what nanotechnology can do for mobile phones?

It seems the researchers there did. In fact, Nokia published an entire book on the subject back in 2010 called “Nanotechnologies for Future Mobile Devices.” So there remained considerable hope that Nokia would focus its attention on the technologies that would really make a difference in cell phones, namely longer lasting batteries.

So, when news came out this week that the big breakthrough it had made in pairing cellular telephony  with nanotechnology was to make handsets waterproof, I couldn’t help but be disappointed.

Okay, I'll admit that waterproofing is a good feature—and sure is a step up from a Dick Tracy phone. But really, Nokia? Five years of collaboration with Cambridge University and this is the result? I have ‘water-resistant’ nanotechnology on my cycling apparel. At this point, water resistance is just not one of those added features made available by nanotechnology that I can get too excited about anymore, even if it is the super-hydrophobic variety.

Sure, duplicating the lotus effect and other biomimicry on the nanoscale is a worthy feature for a score of products, but some of these products have already been on the market for nearly a decade now.

While I know people who have ruined their phones by dropping it in water, when Chris Bower, the principal scientist at Nokia Research Center in Cambridge, claimed in the video that a coating of the super-hydrophobic material could manage to help a phone dropped in water survive, he seemed less than certain and I was less than impressed.  Don’t get me wrong. Keeping a phone from becoming waterlogged is a big deal. I suppose I just expected an even bigger one. Worse still for Nokia, at least one news report seems to have contradicted Bower's claim, pointing out that because of all the openings on a cell phone, water would still find its way into the electronics.

I'll give the researchers their due: The graphene sensor they rigged up to help them film the water droplet falling on the coating in super slow motion is quite impressive. But it seems I’m still going to have to wait for Nokia and Cambridge to announce a mobile phone that will operate for a month without recharging .

China Surges ahead of India in Nanotechnology: Does it Matter?

I am not certain why there is this hullabaloo about the so-called nanotech race. To me it just seems as though scientists around the world are working on their research, they publish it in journals, other scientists read it and then build on that research and so it goes. I don’t see how that translates into a competition between countries, but it seems to be a matter for which some are enormously preoccupied.

The latest news is that China is “soaring ahead” of India in nanotechnology research.  China and India are nearly always discussed in this great nanotechnology race. This is to be expected. These two countries represent two of the fastest growing economies in the world, and much of that growth has been leveraged upon technology.

However, it’s not always clear that these countries’ efforts in the field of nanotechnology should give Europe, North America or any other advanced OECD countries in nanotechnology any reason for alarm. One day it seems one of these countries (China, in this instance) has a lead and then the next it doesn’t.

In this latest study published in Scientometrics, once you get past the quantification of the race (i.e. how many articles are published, how many times they are cited, etc.), you discover the interesting bit. It seems China is focusing its efforts in nanotechnology research on “nanomaterials and their applications” whereas India is focusing their work on addressing their developmental problems, such as clean drinking water.

To be honest though, I’m not clear on how this makes China more “sophisticated” than India in its nanotechnology development. Further there seems to be a distinction here without much difference: India’s aim of developing nanotechnology solutions for clean drinking water will clearly require “nanomaterials and their applications”. I think what the study is trying to say is that  China is approaching nanomaterials development in a more systematic way.

Nonetheless when all is said and done, what matters is the impact nanotechnology can have on a country or life in that country. Cientifica has its measuring stick for this impact. But ultimately perhaps the impact that comes to China and India from nanotechnology may not originate from research in those countries, but from somewhere else entirely, which still leaves me wondering why all of this measuring of which country publishes what matters.

Nanotechnology’s Threat to Privacy Over-Hyped

The field of nanotechnology has been on the defensive for reasonable causes, such as the safety of workers that handle certain nanomaterials. But it also finds itself under attack from the purely fanciful, like charges of nanotechnology compromising our privacy.

The latest misleading screed on this particular avenue of inquiry comes from the International Business Times (IBT) in which we are told that personal privacy is not only "dead but getting deadlier with nanotechnology."

I have noted previously the rather imaginative approach the publication IBT takes to nanotechnology, and I know that I probably should just ignore them. But these stories keep ending up in my hopper and I suppose I am not the only one for whom this occurs. So I am taking it upon myself to call this publication out again for their less than accurate reporting on the subject.

First off, whatever personal privacy people think nanotechnology is taking away from them has long since disappeared with the existing potent combination of information technology, basic telecommunication technology and a video camera at every street corner. But this is ignored because the idea of an invisible nanorobot spying on you is just too seductive for these reporters.

What we get from IBT is: “Just imagine a spy invisible to your eye trace out your name, address, passport, driving license, SSN, health conditions, shopping or net surfing habits and just about everything else that governs your life in a day. All this is possible with the use of nanotechnology.” Umh…I though we got all of that with the Internet?

Then we get this bit that manages to get a number of matters mixed up: “For instance, the Defense Advanced Research Projects Agency (DARPA) is pouring funds into nanocomputing because National Security Agency (NSA) is looking for faster ways to break codes. Till now, the NSA could break only up to 140 or so prime number encryptions and each set of decryption needed to be done serially.”

My first question when I read this was: What could the reporter possibly be thinking of when he uses the term “nanocomputing”? I can only guess that they have confused quantum encryption and quantum computing with something they call “nanocomputing”.

From there it gets even sloppier. We get two ideas brought together in the same paragraph that have absolutely no connection to one another: “Scientists from MIT, Carnegie Mellon University have already replicated Quantum Computing with light in 2001 which made computing applications far easier. Nanotubes and nanowires are already developed and are racing to industrial fabrication.” I can only guess how these two sentences might be related to one another in the reporter’s mind, and my guesses scare me.

I suppose I should just dismiss articles like this and not even bring them to people’s attention. But I’ve seen before how these fear-mongering articles lead to more ignorance and misunderstanding. And that ignorance and misunderstanding actually can turn deadly as evidenced by the attacks of a terrorist group in Mexico last year.

In that case, the terrorists were attempting to defend the world from "grey goo"  by sending letter bombs to researchers they suspected of conducting nanotechnology research. Perhaps they would haven't been motivated to carry out their senseless act if more news stories covered how the theoretical grey goo resulting from nanobots devouring the world around them was a concept that had long been abandoned by the originator of the idea.

One can't help but think that this confusing of speculation with fact in relation to nanotechnology's postulated infringement on our privacy could result in the same dire consequences.

Carbon Nanotube-enabled "Power Felt" Could Eventually Power Your Cell Phone

Researchers at the Wake Forest University Center for Nanotechnology and Molecular Materials have developed an inexpensive thermoelectric material that could be a solution for powering small electronic devices, like cell phones.The new material can convert differences in temperature into electrical energy more efficiently and inexpensively than existing solutions.

As reported in the journal Nano Letters, the material is a thin film made from a combination of multi-walled carbon nanotubes and polyvinylidene fluoride. While carbon nanotube/polymer composites are known to exhibit thermoelectric effects, the researchers discovered that they could generate more voltage by layering the film: the thermoelectric voltage generated was the sum of contributions from each layer, which considerably boosted the thermoelectric conversion efficiency.

The resulting material resembles humble felt in appearance and texture, which led the researchers to call it “Power Felt.”

Until now, thermoelectrics have been a tantalizing technology for powering all sorts of devices, but has remained largely untapped in commercial markets because of a lack of suitable materials. Existing materials either displayed poor thermoelectric conversion efficiency or were prohibitively expensive for commercial use. For instance, bismuth telluride, one of the materials most often used in commercial thermoelectric products like mobile refrigerators and CPU coolers, can cost as much as $1000 per kilogram.  In contrast, the Wake Forest researchers expect that Power Felt would only cost $1 to add to a cell phone cover.

“Imagine it in an emergency kit, wrapped around a flashlight, powering a weather radio, charging a prepaid cell phone,” says David Carroll, director of the Center for Nanotechnology and Molecular Materials and head of the team leading this research. “Literally, just by sitting on your phone, Power Felt could provide relief during power outages or accidents.”

It seems there still is some question as to whether the Power Felt can actually generate enough current to power some of the items they’ve put on their list of potential applications. At present, seventy-two stacked layers of the carbon nanotube/polymer thin film can produce 140 nanowatts of power. So the researchers are looking into ways of adding more layers to the material to generate more.

Perhaps the answer is not just in boosting the power output of the thermoelectric material, but reducing the power consumption of the devices.

Last year I reported on work at the University of Illinois’s Beckman Institute for Advanced Science and Technology in developing a system that uses carbon nanotubes to control bits and lower power switching in phase change materials. At the time, one of the expected results of that work was that cell phones could be manufactured so that they consumed so little energy they could be powered by merely harvesting the thermal or mechanical energy from the environment.

Power felt may provide just such a cost-effective method for harvesting that thermal energy.

IBM Scientists Image Charge Distribution within a Molecule for First Time

IBM Zurich has achieved another breakthrough at the nanoscale by demonstrating for the first time the ability to "see" the charge distribution within a single molecule.

To measure the charge distribution, the IBM scientists, who published their work in the jorunal Nature Nanotechnology, used an offspring of Atomic Force Microscopy (AFM) called Kelvin probe force microscopy (KPFM). 

Observers say they expect this development to have a significant impact on a range of applications.

"This work demonstrates an important new capability," says Michael Crommie, Professor in the Department of Physics at the University of California, Berkeley. "Understanding this kind of charge distribution is critical for understanding how molecules work in different environments. I expect this technique to have an especially important future impact on the many areas where physics, chemistry, and biology intersect."

“This technique provides another channel of information that will further our understanding of nanoscale physics," explains Fabian Mohn, a member of the research team that made the breakthrough. "It will now be possible to investigate at the single-molecule level how charge is redistributed when individual chemical bonds are formed between atoms and molecules on surfaces. This is essential as we seek to build atomic and molecular scale devices.”

Among the hoped-for results from this work is a new method for understanding charge separation and charge transport in charge-transfer, or CT, complexes. These CT complexes, which exist at the places where two or more molecules meet and at junctures connecting parts of one large molecule, are where a fraction of the electronic charge is transferred between the molecules, or parts. Gaining a better understanding of how these CT complexes work could aid in the design of molecular-sized transistors that are more energy efficient.

IBM Zurich has been on a bit of a run lately with AFM-related breakthroughs, announcing earlier this month a new ultrasharp silicon carbide tip for an atomic force microscope that is thousands of times more wear-resistant at the nanoscale than previous designs.

In addition to these developments, it was IBM Zurich researchers who in 2009 developed a method for measuring the amount of electric charge in an atom without it being on the surface of a conducting material.  And in the same year, researchers there were the first to make an image of a molecule.

In a sense, this most recent work, which was conducted by the same team of researchers—Mohn, Leo Gross, Nikolaj Moll and Gerhard Meyer—is a combination of both of those earlier developments.



MIT Researchers Able to Control Properties of Nanowires as They Grow

Researchers at MIT have developed a method by which they can control the growth process of nanowires and thereby control the composition, structure, and even their resulting properties.

The MIT research team, led by Silvija Gradečak, assistant professor of materials science and engineering, followed the usual method of growing nanoparticles by using “seed” particles (metal nanoparticles), but in their experiments the researchers closely controlled the amount of gases used in the growth process.

The results, which were published in the journal Nano Letters, demonstrated that by controlling the gases interacting with the seed particles, the researchers were able to control the width and composition of the resulting nanowires.

Gradečak's team used an electron microscope to observe the effects that the gases were having on the growth process, and then the researchers adjusted the amount of gases to get the characteristics they wanted in terms of both structure and composition.

While the research team restricted their seed particles to indium nitride and indium gallium nitride, they say that the process will work with a variety of different materials.

Naturally, the goal of controlling the size and composition of nanowires is to change their properties. If you could fine tune the exact properties you wanted in a nanowire, you could use it in applications for which they are best suited.

The application that seems to be at the top of the list for the nanowires created by the MIT team is LED light bulbs. In this case, the nanowires would be used as a substrate replacing the expensive sapphire or silicon carbide typically used. Not only could the nanowires be a less expensive substrate, but they could also prove to be more efficient, according to Gradečak.

The varying diameters and structures could also make the nanowires useful in thermoelectric devices, in which waste heat can be turned into electricity. By changing the structure and thickness of the nanowires along their length, it’s possible to make them good conductors of electricity but bad conductors of heat, a much-desired property for thermoelectric power systems.



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
Load More