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Could Tin be the Two-Dimensional Material of the Future?

For the better part of a decade, researchers have been theorizing and calculating about a mysterious new class of materials called topological insulators. In computer models, scientists have been able to reveal that these topological insulators possess the odd property of insulating on the inside and conducting on the outside. It was even demonstrated last year that topological insulators could be produced from heavy metals like uranium and plutonium that could work at room temperature.

Now researchers at U.S. Department of Energy’s (DOE) SLAC National Accelerator Laboratory and Stanford University have simulated what would happen if you whittled a topological insulator down to a single atomic layer—a two-dimensional material like graphene. The result is that the edges of the material become conductors and rest behaves as an insulator.

The researchers have dubbed their new material “Stanene”, which is the combining of the Latin word for tin (stannum) with the suffix used in graphene. They believe that it could be a “wonder material” every bit as fascinating as its carbon cousin, graphene. Initial calculations indicate that it could be the world’s first material to conduct electricity with 100 percent efficiency at the temperatures that computer chips operate.

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Nanoparticles Enable Novel Loudspeaker Design

While technological developments in personal computing always seem to be eagerly received, it seems that developments in our personal entertainment—like TVs and stereos—get us most excited.

Along these lines, there is now a completely new way to build loudspeakers thanks in large part to nanoparticles. Researchers at Sweden’s KTH Royal Institute of Technology have found a way to eliminate the need for a permanent magnet in stereo speakers by adding metallic nanoparticles to a speaker's membrane.

“This is, to our knowledge, the first reported magnetic speaker membrane,” said Richard Olsson, a KTH researcher, in a press release.

The design of the speaker, which is detailed in the journal of the Royal Society of Chemistry (“Cellulose nanofibers decorated with magnetic nanoparticles--synthesis, structure and use in magnetized high toughness membranes for a prototype loudspeaker”) employs cellulose nanofibers that have had ferrite nanoparticles dispersed evenly throughout the membrane.

The result is a speaker that does not need a permanent magnet to drive the membrane and yet produces a sound quality the researchers argue is as good as, if not better than, traditional speaker designs because of the even distribution of forces within the membrane.

In traditional speaker designs, a voice coil is wrapped around a permanent magnet. The voice coil drives the speaker cone’s movements, which produces the sounds that we hear.

In the speaker design resulting from this latest advance, there is still a voice coil but it is obviously not wrapped around a permanent magnet nor is it directly attached to the cone. Instead, sound is produced solely by the movement of air.

This isn't the first time that nanotechnology has been offered as a possible solution to loudspeaker design.  Five years ago, researchers in China demonstrated how carbon nanotubes could be used to create a transparent loudspeaker film. I have not heard whether anything ultimately ever came of that research.

But if KTH's new speaker technology doesn’t get off the ground, the researchers believe that it has alternative applications in sound cancellation and in one of our other favorite technologies: the automobile.

“We want to look at applications for the material that are driven by magnetic fields. It may, for example, be a form of active damping for cars and trains,” says Olsson in the press release.

Photo: Richard Anderssson

Graphene Comes to Nanopore Gene Sequencing

Nanopore sequencing—the ability to sequence a strand of DNA by reading its electronic signature as it slithers through a nanoscale pore in a membrane— has always held great promise, but it has been frustratingly difficult to realize its full potential. There have been attempts to boost the faint signal produced as the DNA passes through the nanopore. Other research has aimed to slow the speed at which the DNA passes through the nanopore to improve the measurement. Some researchers have even created a molecular motor that doesn’t just slow the DNA down but controls it’s movement through the nanopore.

Now researchers at the Ecole Polytechnique Fédérale de Lausanne (EPFL) in Switzerland have turned to the wonder material graphene as the membrane.

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New Path to Big Crystals of Graphene

While stock market mavens try to find an angle for making a buck on graphene,  researchers are just trying to find a way to manufacture the material in a way that could work at industrial scale while maintaining high quality. It’s proving much more difficult than expected.

Now researchers at the University of Texas at Austin have developed a new method by which very large flakes of single-crystal graphene can be produced that exhibit excellent electrical properties. The Austin engineers claim that these graphene crystals are 10 000 times larger than the largest crystals they could produce only four years ago.

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Nanowires and Viruses Combine to Create High-Capacity Batteries

While lithium-ion (Li-ion) batteries have managed to elevate hybrid vehicles into a significant segment of the automotive market, all-electric vehicles using that same battery technology have languished as a niche product. Li-ion batteries just don’t have the long charge life or short recharging capabilities that would make all-electric vehicles a good fit for most people’s driving habits. (It also doesn’t help the marketing image of automakers when these all-electric vehicles burst into flames.)

Marketing considerations aside, the recent demise of a few high-profile nanotech companies that tried to make Li-ion batteries for all-electric vehicles may indicate fundamental problems with the current approach. Maybe we need a different battery technology to make all-electric vehicles mainstream.

This realization already began to sink in with the research communities a few years back, and I started noticing more research into Lithium-air batteries.  Lithium-air batteries use the oxidation of lithium at the anode and the reduction of oxygen at the cathode to create a current. This battery design has promised up to 10 times as much energy as a lithium-ion battery at the same weight, giving them an energy density equal to that of gasoline.

Greater storage capacity certainly helps solve one EV limitation, but if a battery technology is going to displace fossil fuels, it also needs to recharge as quickly as—or on par with—filling up a car at gas station. Earlier this year, researchers at Massachusetts Institute of Technology (MIT) and Sandia National Laboratory peered into the lithium oxidation process of Li-air batteries and saw a possible way to speed up battery recharging.

Now researchers—again from MIT—have made progress on both fronts. They took nanowires made of manganese oxide (which is often used as the material for the cathode of Li-air batteries) and coated them with man-made viruses. These viruses create a larger surface area that improves the reaction between the lithium and oxygen, resulting in a greater storage capacity and a faster rate of recharging. A video describing the technology can be seen below.

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Flexible Mobile Devices Get a Flexible Battery Made From Nanotubes

After years of promises that mobile phones were going to become flexible, Samsung announced plans last month to release its flexible phone.

While the Samsung Galaxy Round is not flexible to the extent you can bend it to your heart’s content, it does offer a display that is flexible enough for the manufacturer to curve it. The move has also spurred other mobile device manufacturers to announce their intentions to market similar devices.

With the age of flexible devices seemingly upon us, one of the primary challenges for their development has been the power source. Samsung’s new phone is more or less powered by a standard rigid battery. But both LG and Samsung acknowledged that they are on a quest to develop a flexible battery that will enable a truly flexible phone.

Researchers, who anticipated that the launch of flexible mobile devices would require a flexible power source, have steadily pursued the flexible battery. There have been a few commercial efforts using printed electronics, and some thin-film technologies that have made a splash.

Now researchers at the New Jersey Institute of Technology (NJIT) have developed a flexible battery made from carbon nanotubes that is aimed at powering flexible devices. 

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Tricorder-like Mobile Phones Enabled by Nanotechnology

Your typical mobile phone user—who may be cursing his or her smart phone because the battery runs out after just a few hours of normal usage—may not be thinking: What this phone really needs is a spectrometer built into it. But if they knew what spectrometers could do, they might change their minds.

How about a smart phone that you could wave over the fruit and vegetables at the grocery store in order to determine whether they are ripe? That’s the kind of Star Trek Tricorder, gee-whiz technology that gets people to buy a smart phone.

Researchers at the Technische Universität Dresden and the Fraunhofer Institute for Electron Beam and Plasma Technology in Germany have developed a technology that could enable exactly that kind of capability. The German researchers have created a novel, miniature spectrometer, enabled by metallic nano-antennas, small enough to fit onto a mobile phone.

In addition to checking on the ripeness of produce, it could also serve in a more critical role as a tool for diabetes patients to monitor their blood-sugar levels. Of course, using nanotechnology to make your mobile phone into a portable medical monitor is not a new concept. But what distinguishes this latest research out of Germany is that the thin-film manufacturing technique employed makes the spectrometer sensor compatible with mass production.

Even if you could shrink a spectrometer—which measures light over a specific portion of the electromagnetic spectrum—to its smallest physical dimensions using conventional techniques and have it still work, it would not fit onto a mobile phone. The trick employed by the German researchers is the use of metallic nanowires that serve as nano-antennas to absorb, amplify and redirect the light onto the light detector—a CCD/CMOS chip that houses the antenna array. This makes it possible to miniaturize the spectrometer to a scale never conceived of before. The only limit to the size of the spectrometer is how small you could make the CCD/CMOS chip.

The three-year-long research project, dubbed "nanoSPECS", began in August of this year. Naturally, it is still at a preliminary stage, but the researchers expect that by the end of the project, they will be able to manufacture the graded antenna-array to the 8”-wafer size.

If the German researchers are successful, at that point you will have a smart phone that you can wave over a plum or canteloupe to pick the best, and you might even have a way to power the phone so that it would last as long as a Tricorder.

Image: Fraunhofer

Nanotechnology Offers Potential to Predict Football Concussions

American football is a collision sport. And one consequence of repeated collisions between players is concussions. Science is starting to draw a link between these so-called mild brain injuries and the long-term effects they have on the players—namely the onset of chronic traumatic encephalopathy (CTE), a degenerative condition believed to be caused by head trauma and linked to depression and dementia. Recently, the issue has come to a head with the deaths of several former star players and the broadcast of the Frontline report “League of Denial,” which chronicles scientists' long struggle to convince NFL officials to recognize a link between concussions and CTE.

While the NFL has tried to institute rules aimed at limiting the number of concussions that players suffer, the new regulations don’t seem to have stemmed the tide of brain injuries. Each week, a slew of player concussions are reported.

Another avenue being pursued in the hopes of limiting player concussions is the engineering of better helmets to improve head protection. An IEEE Spectrum article published last year, “Ratings for Football Helmets Help Improve Player Safety—But Not Before Another Tragedy,” reported on efforts to measure the effectiveness of different football helmets in reducing head trauma and categorize them based on their efficacy.

Now researchers at Brigham Young University have taken this measurement of helmet impact one step further with immediate, real-time measurements of each hit that a player endures. From those measurements, which are communicated immediately to a hand-held device, coaches know whether a collision is capable of inducing a concussion, even if the player denies any problem. A description of the technology is provided in the video below.

“A coach will know within seconds exactly how hard their player just got hit,” said Jake Merrell, a student at BYU who developed the technology, in a press release. “Even if a player pops up and acts fine, the folks on the sidelines will have data showing that maybe he isn’t OK.”

The heart of the technology is smart foam enabled by nanoparticles, which Merrell has dubbed “ExoNanoFoam.” The nano-enabled foam behaves as a piezoelectric in which pressure on the material produces an electrical voltage. A microcontroller sensor in the helmet reads the electrical voltage produced by the foam, and sends a signal to a handheld tablet equipped with a program that interprets it and delivers  real-time information on the seriousness of the hit sustained by the player.

Since the foam is actually in contact with the player's head, it provides a more accurate measurement of the forces upon the player’s head than the accelerometers that have been used previously to measure these impacts. The drawback with accelerometers is that they measure only of the acceleration or deceleration of the player’s helmet.

Merrell intends to submit his prototype to the upcoming Head Health Challenge, which aims to develop new technologies for measuring impacts in real-time in order to improve player safety.

Photo: Brigham Young University

Nanoparticle Enables Cheap and Easy Test for Blood Clots

Despite the wide range of diseases and conditions that can be diagnosed through a urine test, these tests have failed up till now in being able to detect blood clots. The terrible effects of blood clots include death so a cheap and easy detection method could save lives.

Now researchers at MIT have developed a simple urine test that can detect blood clots.The test centers around an iron oxide nanoparticle that is coated with peptides (short proteins) capable of detecting the enzyme thrombin, which is an indicator of blood clots.

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Engineers Make Electrical Contact to Graphene on It's 1-Atom-Thick Edge

Graphene has presented all sorts of barriers for efforts to apply the material to electronics. It lacks a band gap, so research has focused on engineering one into it. Then even if you could engineer a band gap into the material, its challenging to manufacture at a high quality and high volume.

Another big obstacle is that graphene does not lend itself to being stacked with other materials, something that could be important to making graphene ICs. The reason is that electrical contacts have to be placed on the top surface of the graphene, making the layering of another material on top of those contacts complicated.

Now researchers at Columbia University have developed a way to contact 2-D graphene from its 1-D side.

"No other group has been able to successfully achieve a pure edge-contact geometry to 2-D materials such as graphene," said Columbia electrical engineering professor Ken Shepard in a press release. "This is an exciting new paradigm in materials engineering where instead of the conventional approach of layer by layer growth, hybrid materials can now be fabricated by mechanical assembly of constituent 2-D crystals."

In a research published this week in the journal Science (“One-Dimensional Electrical Contact to a Two-Dimensional Material”), the Shepard and his colleagues created a stack of graphene with boron nitride (which is itself an intensively studied 2-D material, especially in combination with graphene).  After they created a boron-nitride-graphene-boron-nitride sandwich, they etched the stack to expose the edge of the graphene. They then evaporated metal onto those graphene edges to make an electrical contact.

While there was some concern that the electrical contact between the 3-D metal electrode and the one dimensional edge of the graphene would result in high contact resistance, it didn’t happen. Instead the researchers report that contact resistance was in fact lower than what can currently be achieved by making those contacts at the top of the graphene surface.

"Our novel edge-contact geometry provides more efficient contact than the conventional geometry without the need for further complex processing. There are now many more possibilities in the pursuit of both device applications and fundamental physics explorations,” said Shepard in the press release.

To start pursuing those new possibilities, the researchers are applying the techniques they developed for creating new hybrid materials of all the 2D materials that are gaining such interest of late.

"We are taking advantage of the unprecedented performance we now routinely achieve in graphene-based devices to explore effects and applications related to ballistic electron transport over fantastically large length scales," Cory Dean, who led the research as a postdoc at Columbia, said in the press release. "With so much current research focused on developing new devices by integrating layered 2D systems, potential applications are incredible, from vertically structured transistors, tunneling based devices and sensors, photoactive hybrid materials, to flexible and transparent electronics."

Illustration: Cory Dean/Columbia Engineering

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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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