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Resonating Drums Made Out of Graphene Could Lead to Better Sensors

Researchers at Cornell University have fabricated graphene membranes into micrometer-scale drums that can be stimulated by a voltage to transfer one type of mechanical vibration into another. The researchers believe this capability can lead to new applications in telecommunications where graphene-based mechanical resonators could be used as frequency mixers, which are often used, for example, to modulate carrier waves with signals.

In research described in the journal Nature Nanotechnology, the researchers found that graphene could produce three different frequencies of vibration in circular drums made of graphene. Each frequency, or mode, of vibration was coupled to the other and could exchange energy.

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Nanophotonic Crystals Separate Real Luxury Watches From the Fakes

Researchers at Ecole Polytechnique Fédérale de Lausanne (EPFL) in Switzerland have developed a technique for embedding nanoscale photonic crystals into the glass face of a watch so that when it is exposed to UV light, the design made by the crystals becomes visible. The team at Nanoga, a new startup that has been spun off to market this research, believes that this technology can be used to offer luxury watch makers an anti-counterfeiting method that is quick and easy to adopt.

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Nanowires Offer Real-Time Monitoring and Control of Heart Tissue

A key treatment for heart disease is a procedure known as myocardial resection, wherein a section of diseased or damaged heart tissue is removed. Researchers have been trying to figure out the best way to fill the void where the tissue has been removed. There has been research into creating 3-D scaffolds made from the patient’s own skin cells—structures on which the heart muscle can be regenerated. However, this approach doesn’t provide for a way to continuously monitor and control the development of these tissue patches.

Now, researchers out of Harvard University, led by Charles Lieber, may have found a way to create tissue scaffolds that can be controlled and monitored. The Harvard researchers added this capability by mimicking 3-D nanoelectronic arrays; the results show a way towards real-time mapping and control of electrophysiology in tissues.

In research described in the journal Nature Nanotechnology, Lieber and his team employed a bottom-up approach that started with the fabrication of doped p-type silicon nanowires. Lieber has been spearheading the use of silicon nanowires as a scaffold for growing nerve, heart, and muscle tissue for years now.

In this latest work, Lieber and his team fabricated the nanowires, applied them onto a polymer surface, and arranged them into a field-effect transistor (FET). The researchers avoided an increase in the device’s impedance as its dimensions were reduced by adopting this FET approach as opposed to simply configuring the device as an electrode. Each FET, along with its source-drain interconnects, created a 4-micrometer-by-20-micrometer-by-350-nanometer pad. Each of these pads was, in effect, a single recording device.

“Our latest work shows for the first time a nanoelectronics-enabled scaffold with both size scale and mechanical properties on the same order of magnitude as conventional cardiac tissue scaffold made of FDA-approved biomaterials,” said Lieber in an email interview with IEEE Spectrum. “Compared to previous work, we have reduced the device dimensions by 10x and [made it, mechanically] 1000x softer—which is critical for being matched to the tissue.”

Each tissue scaffold consists of four layers, each of which contains a four-by-four array of the pads described above, along with four circular palladium-platinum microelectrodes that provide electrical stimulation. Sandwiched between each of the four layers are polymer fibers that led to the final scaffold having bending stiffness on par with current technology.

“Our latest work demonstrates an array of more than 100 incorporated sensing devices (64 of which act as monitors), versus only 3 previously,” explained Lieber. “This larger-scale integration of active devices allows for true 3-D mapping of action potentials. Due to the fast response time of nanoelectronics, such 3-D activity mapping has sub-millisecond single-shot time resolution, which greatly exceeds capabilities of optical methods.”

In tests, the researchers put the scaffold into a petri dish containing ventricular cardiomyocyte cells taken from rats. Over the subsequent eight days, the scaffold was able to monitor the electrical activity of the cells.

“Thanks to the 3-D mapping capability, we are now able to use our nanoelectronics-innervated cardiac tissues to study critical problems, including 3-D tissue development, arrhythmia, and drug effectiveness,” said Lieber. “We have also achieved simultaneous mapping and regulation of cardiac activity by incorporating both sensor and stimulating devices, which allows us to ‘smartly’ control the abnormal cardiac activities with continuous feedback from the tissues.”

While the researchers were impressed that the scaffold layout they developed displayed only a 10 percent failure rate in the FET sensors over a two-week period, they concede that the silicon nanowires will eventually fail. In order to overcome this time limitation, the strategy would be to perform a metal passivation of the silicon nanowires in which a light coating of a an oxide is applied as a protective shell that would allow them to provide stable recordings for several months.

This work is best described as proof-of-principal research. However, it does offer huge potential impact in the fields of regenerative medicine and electronic therapeutics.

Lieber added: “The next steps towards implantation would be validation of the capabilities of the smart cardiac patch through implantation in animal models of myocardial infarction.”

Lithium-Sulfur Batteries Overcome Another Limitation: High Temperatures

Lithium-sulfur (Li-S) batteries have been pursued as an alternative to lithium-ion (Li-ion) batteries for powering electric vehicles due to their ability to hold up to four times as much energy per unit mass as Li-ion. However, Li-S batteries don’t come without some problems. For instance, the sulfur in the electrode can become depleted after just a few charge-discharge cycles, or polysulfides can pass through the cathode and foul the electrolyte.

Another issue Li-S batteries face is the difficulty of ensuring that they operate safely at high temperatures due to their low boiling and flash temperatures. Now, researchers at the University of Western Ontario, in collaboration with a team from the Canadian Light Source, have leveraged a relatively new coating technique dubbed molecular layer deposition (MLD) that promises to lead to safe and durable high-temperature Li-S batteries.

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Nanocones Boost Efficiency of Solar-based Water Splitting

The long list of attempts to use the sun to split water, and thus isolate hydrogen, has always had one big issue: energy conversion efficiency. Sure, solar-based water-splitting processes don’t yield carbon dioxide byproducts like those based on natural gas. But their conversion efficiencies are so notoriously low that many have never seen a way for them to make economic sense as a replacement for those based on natural gas. While headlines heralded tenfold increases in solar splitting efficiency, the result was only conversion efficiencies of 2.9 percent.

That is, until now. Researchers at Stanford University have made what they believe to be a significant step in realizing the kind of photovoltaic energy conversion efficiencies that will eventually make solar water-splitting economically competitive with natural gas processes. If they can realize their lofty ambitions for the technique, it could lead to the emission-free hydrogen economy that has for so long been promised.

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Flexible Nanogenerators Offer Dependable Energy Source for Flexible Electronics

Ever since 2012, when Zhong Lin Wang and his colleagues at Georgia Tech developed the first triboelectric nanogenerator (TENG), Wang and his team have been making continual progress in updating the technology so it can better deliver power to small electronic devices. TENGs essentially harvest static electricity from friction.

TENGs consist of two different materials that are rubbed together. In this way, materials that like to give off electrons, such as glass or nylon, will donate them to materials that like to absorb them, such as silicon or teflon. Since rubbing generally results in wear, what Wang and his Georgia Tech colleagues did back in 2012 was arrange the component materials so that they generate electricity when they are pressed together. By corrugating the contact surfaces of the materials, and by pressing them together, the structures enmesh, causing the friction that leads to electricity generation.

Such devices have impressive energy conversion efficiency, but they have thus far been limited to use with rigid electronics. Now Wang and his team have adapted them for use in flexible electronics, thus providing a dependable energy source for bendable, stretchable gadgets that has been sorely lacking.

In research described in the journal Science Advances, the Georgia Tech researchers adapted the TENG device by combining a conductive liquid electrode and a flexible, rubber elastic cover. So successful have the researchers been at making the nanogenerator flexible that they have given it a new name: shape-adaptive TENG, or “saTENG”.

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Ultrahigh Density Data Storage Could Get Faster and Easier to Produce

Data storage density has doubled every three years since magnetic storage was first developed in the mid-1950s. Key technological innovations along the way such as giant magneto resistance (GMR), perpendicular magnetic recording (PMR) and heat-assisted magnetic recording (HAMR) have fueled that enormous growth in capacity. Despite this continually increasing storage density, there is a growing sense that this upward trend is beginning to lose steam.

Now researchers at the Helmholtz Zentrum Berlin (HZB) have developed a new technique with a new kind of material that could move magnetic storage technology beyond the current state-of-the-art HAMR technology and lead to faster and more energy efficient ultrahigh density data storage.

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DNA Structures Coordinate Nanoparticle Self-Assembly

The aim of nanoparticle self-assembly research has been to get the particles to organize themselves into structures arrangment is largely controlled by us. However, the level of control we have sought has sometimes left a little bit to be desired.

Now, researchers at the U.S. Department of Energy's (DOE’s) Brookhaven National Laboratory have demonstrated that polyhedral structures made from DNA can serve as a framework for ensuring that the nanoparticles self-assemble in the exact arrangement their minders intended.  In these DNA structures, the nanoparticles can be assembled into crystalline and open 3-D frameworks that themselves can be interconnected, making possible a wide variety of different structures.

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On-Chip Supercapacitors Dump Carbon in Favor of Silicon

Tiny supercapacitors that can fit right on a chip have been hotly pursued for at least the last half decade. We’ve seen the usual suspects—graphene, titanium carbide and porous carbon—proposed for making the electrode material for these on-chip supercapacitors.

Now researchers at the VTT Technical Research Centre of Finland have turned to an unlikely material for producing these pint-sized energy storage devices: porous silicon.  What have the researchers done to turn this notoriously weak electrode material into a powerhouse? They have found that topcoating it with a nanometer-thick layer of titanium nitride makes all the difference.

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Now Graphene Can Have a Tunable, Stable Bandgap

The knock against using graphene in digital electronics has been that it lacks an inherent band gap. However, over the years there have been a number of approaches that have been able to engineer a band gap into the material.

One of the most promising methods has been nitrogen doping, which actually increases the material’s conductivity rather than reduces it.

Now researchers at the U.S. Naval Research Laboratory (NRL) have developed a new technique for nitrogen doping of graphene that can control exactly where the dopants are placed in the graphene lattice. This precise localizing of the dopants reduces defects and provides greater material stability.

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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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