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Graphene-based Microbattery Ushers in New Age for Biotelemetry

There's no denying that building the world’s smallest battery is a notable achievement. But while they may lay the groundwork for future battery technologies, today such microbatteries are mostly laboratory curiosities.

Developing a battery that's no bigger than a grain of rice—and that's actually useful in the real world—is quite another kind of achievement. Researchers at Pacific Northwest National Laboratory (PNNL) have done just that, creating a battery based on graphene that has successfully been used in monitoring the movements of salmon through rivers.

The microbattery is being heralded as a breakthrough in biotelemetry and should give researchers never before insights into the movements and the early stages of life of the fish.

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Nanotechnology Helps 3-D TV Make a Comeback Without Glasses

At this year’s Consumer Electronics Show (CES), it became clear that the much-ballyhooed age of 3-D TV was coming to a quiet and uncelebrated end. One of the suggested causes of its demise was the cost of the 3D glasses. If you wanted to invite a group over to watch the big sporting event, you had better have a lot of extra pairs on hand, which might cost you a small fortune.

Eliminating the glasses from the experience has been proposed from the first moment 3-D TVs were introduced to the marketplace. In 2010, Toshiba and Nintendo shared their plans to bring glasses-free 3-D to portable devices.

There have been a number of approaches proposed for accomplishing the feat. Now researchers at the University of Central Florida (UCF) are leveraging nanomanufacturing techniques to do the job.

Jayan Thomas, an assistant professor at UCF’s NanoScience Technology Center, has received a US $400 000 grant from the National Science Foundation to pursue the use of nanoprinting techniques for turning polymers into displays whose images appear in 3-D to the naked eye. The kind of 3-D displays Thomas envisions conjure images of the holograms used to display messages in the Star Wars movies.

“The TV screen should be like a table top,” Thomas said. “People would sit around and watch the TV from all angles, like sitting around a table. Therefore, the images should be like real-world objects. If you watch a football game on this 3-D TV, you would feel like it is happening right in front of you. A holographic 3-D TV is a feasible direction to accomplish this without the need of glasses.”

The nanomanufacturing techniques Thomas uses are similar to the printing process he developed for creating nanomaterials to be used in supercapacitors—a process that we covered last year. That technique involved printing polymer nanostructures on a substrate that served as a scaffold upon which electrode material made of manganese dioxide is deposited. That technique is a variation on the simple spin-on nanoprinting (SNAP) technique.

With these nanomanufacturing techniques, Thomas has developed a polymer composite that improves the process of making the 3-D images in the first place. When you are watching 3-D television, what you are really seeing is two perspectives of an image, so it is actually not very close to a real world object.  The 3-D glasses help to provide a 3-D appearance of the image. 

"Our technology uses multiple cameras positioned above and around an object to photograph it from multiple perspectives," explains Thomas. "We are then doing a couple of new things; we need to make the recording process so fast that the human eye will not see the images refreshing from the multiple perspectives. This requires new materials options—a new plastic type display on which to play what are ultimately holographic images."

Whether this technique proves to be any more successful than those offered by MIT and other research groups, remains to be seen. In any case, we may not yet have seen the end of 3D TV, as long as it doesn't require glasses.

Illustration: Randi Klett; Photos: iStockphotos

Nanomotors Could Churn Inside of Cancer Cells to Mush

Researchers at Penn State University have placed nanoparticles inside living human cells and been able to direct the movement of the particles through the use of both ultrasonic waves and magnetic forces. While similar demonstrations have been conducted in a test tube (in vitro), this marks the first time that this kind of work has succeeded inside a live human cell.

Once the nanoparticle motors start moving about inside them, the researchers observed that the cells begin to react in ways not previously observed.

"As these nanomotors move around and bump into structures inside the cells, the live cells show internal mechanical responses that no one has seen before," Tom Mallouk, a professor of materials chemistry and physics at Penn State, said in a press release.

(A video showing how the nanomotors move around inside the cells is below.)

While the over-exuberant press release likened the work to the 1960s sci-fi movie “Fantastic Vogage”, it does not involve anything remotely close to plot details of that movie. (It’s time to put aside this misleading comparison once and for all.)  However, this research does invite comparisons to a proposal out of Stanford University back in 2012 in which small antennas on a microchip could receive magnetic fields that propel the chip through the blood stream.

The new nanomotor research, which was published in the 10 February international edition of the journal Angewandte Chemie ("Acoustic Propulsion of Nanorod Motors Inside Living Cells"), used HeLa cells, a type of human cervical cancer cells. The HeLa cells ingest the nanoparticles. Once a high level of ultrasonic waves is focused on the nanoparticles, they begin to move about. If the level is too low, the nanoparticle will not react to the ultrasonic waves.

If a cancer cell were to ingest these nanoparticles, they could be moved around fast enough so that they acted as a sort of high-tech food processor, making a homogenized mix of the cell’s contents.

But Mallouk also sees a more refined role for them. “We might be able to use nanomotors to treat cancer and other diseases by mechanically manipulating cells from the inside,” said Mallouk in the release. “Nanomotors could perform intracellular surgery and deliver drugs noninvasively to living tissues."

It is through the combination of the ultrasonic waves and the magnetic forces that the researchers have been able to make the nanoparticles move autonomously from each other. The ultrasonic waves manage to move the nanoparticles forward or spin them around. But the magnetic forces are used to actually steer them.

"Autonomous motion might help nanomotors selectively destroy the cells that engulf them," Mallouk said. "If you want these motors to seek out and destroy cancer cells, for example, it's better to have them move independently. You don't want a whole mass of them going in one direction."

Image: Mallouk Lab/Penn State University

Graphene Sandwich Enables Clear Images of Biomolecules

Electron microscopy and spectroscopy are great tools for peering into matter on the molecular scale. But they’re not terribly effective if that matter happens to be biological.

Researchers at the University of Illinois in Chicago (UIC) may have changed that with a novel use of graphene in which a biomolecule is sandwiched between two sheets of graphene, making it possible to create much higher resolution images than in previous methods.

“We found a way to encapsulate a liquid sample in two very thin layers of graphene — sheets of carbon that are only one atom thick,” said Canhui Wang, UIC graduate student in physics and first author of the study, in a press release.

In the research, which was published in the journal Advanced Materials (“High-Resolution Electron Microscopy and Spectroscopy of Ferritin in Biocompatible Graphene Liquid Cells and Graphene Sandwiches”), the molecule ferritin was imaged. Ferritin is an iron-storage protein, and itself has been proposed for developing magnetic nanoparticles to enable forward osmosis for water purification.

Prior to this research, if you wanted to image a biomolecule like ferritin with an electron microscope, you would need to use a container known as a “liquid stage” that is wedged between two thick windows of silicon nitrate to protect the sample from the vacuum.

Robert Klie, the senior investigator on the study, likened the difference between the liquid stage approach and the graphene sandwich as “…the difference between looking through Saran Wrap and thick crystal.”

The better resolution produced by the graphene sandwich is not just because of graphene’s superior transparency. The graphene sandwich also provides better protection from the electron beam that is fired at a sample during microscopy. Wang says that some have calculated that to visualize a sample requires 10 times the amount of radiation one would be exposed to from a 10-megaton hydrogen bomb when standing just 30 meters away.

To mitigate the deleterious effect of the electron beam, most electron microscopes use a low-energy beam that results in a fuzzy picture that has to be corrected by imaging algorithms. Because of graphene’s high thermal and electrical conductivity the material removes both the heat and electrons generated by the beam as it passes through the sample. So higher energy electron beams can be used on the sample, resulting in higher resolution images.

In their experiments with the ferritin, the researchers were able to image for the first time iron oxide in the core of ferritin changing its electric charge, leading to the release of iron. The imaging of this process could lead to a better understanding of some human disorders.

“Defects in ferritin are associated with many diseases and disorders, but it has not been well understood how a dysfunctional ferritin works towards triggering life-threatening diseases in the brain and other parts of the human body,” said Tolou Shokuhfar, assistant professor of mechanical engineering-engineering mechanics at Michigan Technological University and adjunct professor of physics at UIC, in a press release.

Illustration: Celia Gorman; Image: iStockphoto

Graphene Nanoribbons Get Electrons to Behave Like Photons

An international team of researchers has developed a novel way to produce graphene nanoribbons that enables electrons to travel though it without resistance at room temperature, a property known as ballistic transport. The ballistic transport properties measured by the researchers exceeds previous theoretical limits for graphene by a factor of ten, opening up the potential in the opinion of the researchers for graphene to usher in a new era in electronics despite the material's lack of a band gap. 

The team of researchers, including those at Georgia Institute of Technology along with others from Leibniz Universität Hannover in Germany, the Centre National de la Recherche Scientifique (CNRS) in France and Oak Ridge National Laboratory in the United States, has developed a process for producing graphene nanoribbons on a silicon wafer that results in such high electron mobility that the electrons behave more like photons do when in an optical fiber.

The lack of inherent band gap in graphene—its inability to effectively stop and start the flow of electrons—has remained a major stumbling block in developing it for use in electronics. Of course, there have been various approaches to engineering a band gap into graphene, such as applying a strong electrical field to bilayer graphene. However, Walt de Heer, a Regent's professor in the School of Physics at the Georgia Institute of Technology, believes that we should stop trying to get graphene to behave like silicon, and instead design a new type of electronics that exploits graphene’s unique properties. This is along the lines of what Samsung proposed 18 months ago by developing new switches to exploit graphene’s electron mobility.

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Graphene Circuit Competes Head-to-Head With Silicon Technology

IBM has built on their previous graphene research and developed what is being reported as the best graphene-based integrated circuit (IC) built to date, with 10 000 times better performance than previously reported efforts.

This graphene-based IC serves as a radio frequency receiver that performs signal amplification, filtering and mixing. In tests, the IBM team was able to use the circuit to send text messages (in this case, “IBM”) without any distortion.

“This is the first time that someone has shown graphene devices and circuits to perform modern wireless communication functions comparable to silicon technology,” IBM Research director of physical sciences Supratik Guha said in a release.

The IC, which is fully described in the journal Nature Communications (“Graphene radio frequency receiver integrated circuit”), overcomes major problems previously encountered with graphene-based ICs that cause the transistor performance to degrade.

The key to overcoming this issue was a new manufacturing method. Simply put, the graphene is added late in the process to prevent it from being damaged during other manufacturing steps.

Despite the improved manufacturing method for the IC, the IBM researchers still depended on a costly method for producing the graphene that was used. They believe that if a high-quality graphene could be produced in a roll-to-roll process, the IC would become easier and cheaper to produce.

This latest circuit builds on the first integrated circuit built from graphene—developed by IBM in 2011—that was a broadband radio-frequency mixer, a fundamental component of radios that processes signals by finding the difference between two high-frequency wavelengths.

While others have judged the odds that graphene will yield benefits in electronic applications as slim to none because it lacks an inherent band gap, IBM has stayed on a steady course to test those assumptions. In early 2010, Big Blue researchers engineered a band gap into graphene large enough to pursue the use of graphene in infrared (IR) and terahertz (THz) detectors and emitters. Then a year later, IBM followed up with a graphene transistor capable of operating at 100 gigahertz that has the same gate length as silicon chips with speeds of 40 GHz.  Of course, a transistor on its own can’t do much of anything, so about six months later, IBM reported building the first integrated graphene circuit that was the precursor to this latest version.

In describing the impact of the research, Shu-Jen Han of IBM Research said in an IBM blog:

“Our demonstration has the potential to improve today’s wireless devices’ communication speed, and lead the way toward carbon-based electronics device and circuit applications beyond what is possible with today’s silicon chips. Integrating graphene radio frequency (RF) devices into today’s low-cost silicon technology could also be a way to enable pervasive wireless communications allowing such things as smart sensors and RFID tags to send data signals at significant distances.”

With IBM's apparent relentless pursuit of an IC for a radio frequency receiver, it would seem that seeing these devices in our telephones at some point in the future could be a realistic prospect.

Photo: IBM Research - Zurich

Graphene Composite Offers Critical Fix for Sodium-ion Batteries

Sodium-ion batteries offer an attractive alternative to Li-ion batteries not because they outperform Li-ion batteries, but mainly because of lower costs due to the the nearly unlimited supply of sodium. They are also an attractive alternative in part because unlike their sodium-sulfur battery cousins they can be made in similar sizes to Li-ion batteries.

However, the commercial development of sodium-ion batteries has been hampered by the materials used in the negative electrodes. These swell to as much as 400 to 500 percent their original size, leading to mechanical damage and loss of electrical contact.

Now researchers at Kansas State University have developed a composite, paper-like material made from two 2-dimensional materials—molybdenum disulfide and graphene nanosheets—that has been shown to overcome this shortcoming.

In research published in the journal ACS Nano (“MoS2/Graphene Composite Paper for Sodium-Ion Battery Electrodes”),  the 2-D composite material developed proved resistant to the “alloying” reaction that electrode materials typically suffer when in contact with sodium.

The research also marks the first time that the flexible paper electrode was used in an anode for sodium-ion battery that operates at room temperature.

The Kansas State researchers began their work by looking for better ways to synthesize 2-D materials for rechargeable battery applications. This led them to create the large-area composite paper that they used for negative electrodes.

The paper is a composite of acid-treated layered molybdenum disulfide and chemically modified graphene in an interleaved structured. “The interleaved and porous structure of the paper electrode offers smooth channels for sodium to diffuse in and out as the cell is charged and discharged quickly,” said Gurpreet Singh, an assistant professor at Kansas State and one of the authors of the paper, in a press release. “This design also eliminates the polymeric binders and copper current collector foil used in a traditional battery electrode.”

While the researchers are looking for opportunities to commercialize their technology for rechargeable battery applications, they also feel that they have contributed to the fundamental understanding of how to synthesize 2-D materials.

"This method should allow synthesis of gram quantities of few-layer-thick molybdenum disulfide sheets, which is very crucial for applications such as flexible batteries, supercapacitors, and polymer composites,” Singh said.

Image: Gurpreet Singh

Can Graphene Enable Thermal Transistors?

One of the critical functions for electronic devices is a process known as rectification in which an electrical current can be forced to move in one direction and then the opposite one. Rectification makes possible electronics devices such as transistors, diodes and memory circuits.

Now researchers at Purdue University's School of Mechanical Engineering and Birck Nanotechnology Center have determined that a material based on graphene is capable of producing this rectification effect not on electric current but on heat flow.

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‘Borophene’ Might Be Joining Graphene in the 2-D Material Club

The world of two-dimensional (2-D) materials has just gotten a little more crowded. If graphene, boron nitride, molybendum disulfide and silicene weren’t quite enough, we now may have something to join the mix in the 2-D universe that will go by the name “borophene.”

In experiments and simulations based at Brown University, in Providence, R.I., researchers took a big step toward a long theorized material made up of single-atom sheets of boron. The researchers haven’t actually produced borophene, but they did make a needed precursor structure that proves that the material is possible.

In research that was published in the journal Nature Communications (“Planar hexagonal B36 as a potential basis for extended single-atom layer boron sheets”)  a cluster of 36 boron atoms were formed into a structure that resembles theoretical predictions for borphene: a symmetrical, one-atom thick disc with a perfect hexagonal hole in the middle.

The prediction was that boron, which has one fewer electron than carbon, wouldn’t be able to form into the honeycomb-lattice pattern that graphene takes. Instead it would likely form into a triangular lattice and a hexagonal hole would form in the middle of the sheet. That prediction pretty closely resembles what the researchers were able to produce in the lab.

"It’s beautiful,” said Lai-Sheng Wang, professor of chemistry at Brown, in a press release. “It has exact hexagonal symmetry with the hexagonal hole we were looking for. The hole is of real significance here. It suggests that this theoretical calculation about a boron planar structure might be right.”

Producing the boron structure was not anything like using the “Scotch Tape” method for producing graphene. The researchers were able to make the cluster of 36 boron atoms by first shooting a laser at bulk boron to vaporize it into boron atoms. They then shot the vapor of boron atoms with a jet of helium that froze the atoms into clusters. After being frozen, they were zapped again with a laser. This second laser kicks an electron out, which is funneled down a tube of sorts. By measuring the speed of the electron, they can determine how strongly the cluster holds onto its electrons, which is known as the electron binding energy spectrum. This spectrum is distinct, like a fingerprint, to the cluster’s structure.

Based on this binding energy spectrum, which indicated that it was very low energy compared to other boron clusters, certain structures were possible—3000 possible structures in fact. By using a supercomputer the researchers could go through each possibility. When Wang saw that one of the possibilities was a planar disc with the hexagonal hole, he knew that was the structure to investigate.

The researchers plowed on investigating all 3000 structures with a supercomputer and finally concluded that the B36 structure was the one that most closely matched the spectrum measured in the physical experiments.

While theoretically borophene should have even more interesting electronic characteristics than graphene, it’s not clear from this work whether anyone will ever be able to make it.

Image: Wang Lab/Brown University

Two-Dimensional Materials Get Into Hydrogen Gas Production

One of the inconvenient truths about fuel cells for powering automobiles—a key to the establishment of the so-called hydrogen economy—is that it is extremely costly and energy intensive to isolate hydrogen gas.

The last couple of years have produced research using different nanomaterials that can do the job. Last year, University of Buffalo researchers created silicon nanoparticles that generated hydrogen gas nearly instantaneously when water was added to them. In that process, the nanomaterial didn’t need light or electricity to produce the hydrogen. Of course, the downside was that producing the silicon nanoparticles required a fair amount of energy itself, so it wasn’t clear whether this was a viable solution to overcoming the energy costs of hydrogen production.

The main push in nanomaterials for hydrogen gas separation has been artificial photosynthesis approaches in which sunlight rather than electricity is used to split the hydrogen from a water molecule. These efforts stood in contrast to other nanomaterial solutions that entailed simply replacing the platinum catalyst in the standard electrocatalytic process with a nanomaterial.

Now researchers at North Carolina State University (NCSU) have demonstrated that molybdenum sulfide (MoS2) can be used as an effective catalyst for producing hydrogen gas in a solar water-splitting process.

In research published in the journal Nano Letters (“Layer-Dependent Electrocatalysis of MoS2 for Hydrogen Evolution”), the NCSU team demonstrated that while MoS2 it is not as effective a catalyst as platinum, its relative low cost could make it an attractive alternative.

“We found that the thickness of the thin film is very important,” says Dr. Linyou Cao, an assistant professor of materials science and engineering at NCSU, in a press release. “A thin film consisting of a single layer of atoms was the most efficient, with every additional layer of atoms making the catalytic performance approximately five times worse.”

The researchers also have indicated that MoS2 thin films have an ideal band gap for solar water splitting. In a Q&A with an NCSU blog, Cao said:

"The band gap of monolayer MoS2 spans over the redox potentials of water. Its valence band is lower than the potential of water oxidation, and the conduction band is higher than that of water reduction. Additionally, its band gap, about 1.8eV, nicely matches the spectrum of solar radiation."

It should be interesting to see if this discovery that MoS2 makes for an ideal material in solar water splitting compares favorably to other nanomaterials used in artificial photosynthesis approaches.

Photo: North Carolina State University

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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
 
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Rachel Courtland
Associate Editor, IEEE Spectrum
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