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Rendering of the ultra-flexible probe in neural tissue

Flexibility Gives Nanothread Brain Probes Long-Term Durability

For over two decades, electrodes implanted in the brain have made it possible to electrically measure the activity of individual neurons. While the technology has continued to progress over the years, the implanted probes have continued to suffer from poor recording ability brought on by biocompatibility issues, limiting their efficacy over the long term.

It turns out that size matters: In this case, the smaller the better. Researchers at the University of Texas at Austin have developed neural probes made from a flexible nanoelectronic thread (NET). These probes are so thin and tiny that when they are implanted, they don’t trigger the human body to create scar tissue, which limits their recording efficacy. Without that hindrance, the threadlike probes can work effectively for months, making it possible to follow the long-term progression of such neurovascular and neurodegenerative diagnoses as strokes and Parkinson’s and Alzheimer’s diseases.

In research described in the journal Science Advances, UT researchers fabricated the multilayered nanoprobes out of five to seven nanometer-scale functional layers with a total thickness of around 1 micrometer.

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A nanoelectrode array and its CMOS control chip sit at the bottom of a shallow well where a network of cells will grow.

Nanoelectrode Array Sees Signals From Inside a Network of Cells

Researchers at Harvard University have developed a nanoelectrode array capable of imaging the electrical signals within the living cells. While other technologies have been able to measure these signals, this new complimentary metal oxide semiconductor nanoelectrode array (called a CNEA) can measure these signal across an entire network of cells.

“It’s similar to an imager combining the light signal from each detector in a pixel array to form a picture; the CNEA combines the electrical signals from within each cell to map the network level electrical activities of the entire cell culture,” explained Donhee Ham, a professor at Harvard involved in the research, in an e-mail interview with IEEE Spectrum.

This network-level intracellular recording capability can be used, for example, to examine the effect of pharmaceuticals on a network of heart muscle tissue, enabling tissue-based screening of drug candidates. It could also help better understand how cells communicate with each other across a network.

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A laser stylus writes on a small array of multifunction pixels made by dual-function LEDs than can both emit and respond to light.

Nanorods Emit and Detect Light, Could Lead to Displays That Communicate via Li-Fi

Ever since the 2015 Consumer Electronics Show, quantum dots have been in a market struggle to displace light-emitting diodes (LEDs) as a backlight source for liquid crystal displays (LCDs).

Now an advance by a team of researchers from the University of Illinois at Urbana–Champaign, the Electronics and Telecommunications Research Institute in South Korea, and Dow Chemical may turn the display market on its head by eliminating the need for backlights in LCD devices. They have produced a LED pixel out of nanorods capable of both emitting and detecting light.

In the video below, you can get a further description of how the nanorods manage to both detect and emit light as well as some pretty attractive future applications, like mobile phones that can “see” without the need of a camera lens or communicate with each other using Light Fidelity (Li-Fi) technology.

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Top view of the experimental set-up used in the paper.

Scientists Measure Single Quantum of Heat

IBM researchers have established experimental proof of a previously difficult-to-prove law of physics, and in so doing may have pointed to a way to overcome many of the heat management issues faced in today’s electronics. Researchers at IBM Zurich have been able to take measurements of the thermal conductance of metallic quantum point contacts made of gold. No big deal, you say? They conducted measurements at the single-atom level, at room temperature—the first time that’s ever been done.

The first measurement of a quantum of thermal conductance was achieved back in 1999 by researchers at the California Institute of Technology. This latest research differs in that it was able to make measurements at room temperature as opposed to very low temperatures.

These latest measurements provide further confirmation of the Wiedemann–Franz law, which predicts that the smallest amount of heat that can be carried across a metallic junction—a single quantum of heat—is directly proportional to the quantum of electrical conductance through the same junction. By experimentally confirming this law, it can now be used with confidence to predict and to explore nanoscale thermal and electrical phenomena affecting materials down to the size of few atoms or a single molecule.

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image of a device with lateral pads patterned as electrically connected finger-like structures

Graphene Infrared Eye Needs No Signal Amplification

An international team of researchers under the umbrella of the EU-funded Graphene Flagship have taken a significant step in thermal infrared (IR) photodetctors with the development of the most sensitive uncooled graphene-based thermal detector yet fabricated.  These new photodetectors, known as bolometers, are so sensitive that they can register the presence of a scant few nanowatts of radiation. That level of radiation is about a thousandth of what would be given off by a hand waving in front of the detector.

In the research described in the journal Nature Communications, scientists from the University of Cambridge, UK; the Institute of Photonic Sciences (ICFO), Spain; the University of Ioannina, Greece; and from Nokia and Emberion found that the combination of graphene and pyroelectric materials—which generate a voltage when they are heated or cooled—yields a unique synergy that boosts the performance of thermal photodetectors.

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water-based two-dimensional crystal inks

Biocompatible Inks for Printed Medical Devices Just Got Easier to Make

Researchers at the University of Manchester in the UK have built photosensors and programmable logic memory devices with inkjet printers using biocompatible, water-based 2D crystal inks that are highly concentrated for improved electrical performance.

The Manchester research, described in the journal Nature Nanotechnology,  represents a significant development over current ink formulations that are typically toxic and difficult to process. While this new formulation is easier to produce, biocompatibility may be its most attractive feature, opening up potential applications in medical devices.

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Smoltek's chip packaging process

Nanomaterials Enable Smaller Chip Packaging

Overwhelmingly, the focus for applying nanomaterials to electronics has been to meet the demands of Moore’s Law by continuing the seemingly inexorable shrinking of transistor dimensions.

While there have been some remarkable achievements in that regard—among them, getting dimensions down as low as 1 nanometer in the laboratory—the drive towards putting systems on chips (SoC) and systems in packages (SiP) is causing a shift in focus from smaller transistors to smaller packaging. This shift appears to be opening up a new use for nanomaterials that could expand the focus of nanomaterials in chip manufacturing.

The Swedish company Smoltek AB, a spinout from Chalmers University, sees chip packaging as the new frontier in nanoelectronics. It has been positioning itself at the forefront of this new movement over the last five years with its development of a variation on chemical vapor deposition (CVD) technology it has dubbed SMOLTEK TigerTM.

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Nantero NRAM nonvolatile memory chip

Carbon Nanotube Memory Company's Ship May Finally Come In

To many, the sell-by date on the carbon nanotube-based non-volatile random access memory (NRAM) developed by Nantero has long since passed. IEEE Spectrum characterized the technology as a “loser” nearly a decade ago after several of the company’s launch dates came and went with hardly a whimper.

The technology’s promise was that it could lend itself to easy mass production because it relies on a group of nanotubes deposited randomly on a substrate rather than individual nanotubes precisely placed. By eliminating the need for individual placement, Nantero hoped to sidestep the main bugbear of nanotubes in electronics: purity. It turns out purity could not be sidestepped to the degree originally believed, and a decade-and-half of disappointment ensued.

But a new analyst report published by BCC Research asserts that NRAM’s ship may have finally come in. The upshot: It (and a host of other non-volatile memory approaches) may be poised to dislodge flash from its long-held throne.

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Schematic diagram showing the structure of a carbon nanotube transistor

Scientists: Carbon Nanotubes Would Outperform Silicon Transistors at the Same Scale

The end appears nigh for scaling down silicon-based complementary metal-oxide semiconductor (CMOS) transistors, with some experts seeing the cutoff date as early as 2020

While carbon nanotubes (CNTs) have long been among the nanomaterials investigated to serve as replacement for silicon in CMOS field-effect transistors (FETs) in a postsilicon future, they have always been bogged down by some frustrating technical problems. But, with some of the main technical showstoppers having been largely addressed—like sorting between metallic and semiconducting carbon nanotubes—the stage has been set for CNTs to start making their presence felt a bit more urgently in the chip industry.

Peking University scientists in China have now developed carbon-nanotube field-effect transistors (CNT FETs) having a critical dimension—the gate length of just 5 nanometers—that would outperform silicon-based CMOS FETs at the same scale. The researchers claim in the journal Science that this marks the first time that carbon-nanotube CMOS FETs under 10 nanometers have been reported.

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Super-thin graphene-based health monitor is mechanically invisible

Graphene Temporary Tattoo Tracks Vital Signs

A graphene health sensor that goes on the skin like a temporary tattoo takes measurements with the same precision as bulky medical equipment. The graphene tattoos, presented in December at the International Electron Devices Meeting in San Francisco, are the thinnest epidermal electronics ever made. They can measure electrical signals from the heart, muscles, and brain, as well as skin temperature and hydration.

Researchers at the University of Texas at Austin who are developing the sensors hope to develop them for consumer cosmetic use. They also hope the ultrathin sensors will provide a more comfortable replacement for existing medical equipment.

Today, if your doctor wants to monitor your heart rate over an extended period of time to help diagnose some cardiac irregularity, you’ll be sent home with a bulky EKG monitoring harness to wear for 24 hours. The Texas researchers hope to make a system that can take measurements of the same quality or better, but that’s unobtrusive. Deji Akinwande, an electrical engineer who specializes in 2D materials, is collaborating on the project with Nanshu Lu, who works on epidermal electronics.

Materials scientists have for years sung the praises of graphene’s electrical properties and mechanical toughness. What’s been underappreciated, says Akinwande, is that this single-atom-thick stuff is mechanically invisible. When it goes on the skin, it doesn’t just stay flat—it conforms to the microscale ridges and roughness of the epidermis. “You don’t feel it because it’s so compliant,” says Akinwande.

The Texas researchers start by growing single-layer graphene on a sheet of copper. The 2D carbon sheet is then coated with a stretchy support polymer, and the copper is etched off. Next, the polymer-graphene sheet is placed on temporary tattoo paper, the graphene is carved to make electrodes with stretchy spiral-shaped connections between them, and the excess graphene is removed. Now the sensor is ready to be applied by placing it on the skin and wetting the back of the paper.

In their proof-of-concept work, the researchers used the graphene tattoos to take five kinds of measurements, and compared the data with results from conventional sensors. The graphene electrodes can pick up changes in electrical resistance caused by electrical activity in the tissue underneath. When worn on the chest, the graphene sensor detected faint fluctuations that were not visible on an EKG taken by an adjacent, conventional electrode. The sensor readouts for electroencephalography (EEG) and electromyography (EMG, which can be used to register electrical signals from muscles and is being incorporated into next-generation prosthetic arms and legs) were also of good quality. And the sensors could measure skin temperature and hydration, something cosmetics companies are interested in, says Akinwande.

Graphene’s conformity to the skin might be what enables the high-quality measurements. Air gaps between the skin and the relatively large, rigid electrodes used in conventional medical devices degrade these instruments’ signal quality. Newer sensors that stick to the skin and stretch and wrinkle with it have fewer airgaps, but because they’re still a few micrometers thick, and use gold electrodes hundreds of nanometers thick, they can lose contact with the skin when it wrinkles. The graphene in the Texas researchers’ device is 0.3-nm thick. Most of the tattoo’s bulk comes from the 463-nm-thick polymer support.

The next step is to add an antenna to the design so that signals can be beamed off the device to a phone or computer, says Akinwande.

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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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