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Dendrites growing in a lithium-metal battery

Video Microscopy Technique Reveals How Battery-Killing Dendrites Grow

While the exact cause of the recent fires experienced with Samsung’s Galaxy Note 7 smartphones have not yet been precisely determined, it appears that these incidents are in some way related to the batteries.

One known problem for both the lithium-ion (Li-ion) batteries used in today’s mobile phones as well as next-generation lithium metal batteries is that they are susceptible to the growth of finger-like deposits of lithium called dendrites inside the battery. These dendrites grow so long that they pierce the barrier between the two sides of the battery and cause a short circuit, possibly leading to a fire.

Now researchers at the University of Michigan—inspired by the potential of next-generation lithium metal batteries to store 10 times more charge than conventional Li-ion batteries—have peered into lithium metal batteries to observe the growth of dendrites. They leveraged a novel microscopy tool that enables them to watch how the lithium changes inside the battery during cycling to create conditions conducive to dendrite growth.

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Reflection spectra in air of the red, green, and blue samples for different angles

Flexible and Colorful Electronic Paper Promises a New Look for E-books

Plasmonic nanostructures leverage the oscillations in the density of electrons that are generated when photons hit a metal surface. Researchers have used these structures for applications including increasing the light absorption of solar cells and creating colors without the need for dyes. As a demonstration of how effective these nanostructures are as a replacement for color dyes, a the technology has been used to produce a miniature copy of the Mona Lisa in a space smaller than the footprint taken up by a single pixel on an iPhone Retina display.

It has also been shown that if you combine these plasmonic nanostructures with electrochromic polymers that change color when a voltage is applied—the kind used in windows that can be turned from clear to opaque with a flip of a switch—you can make a display.

Now researchers at Chalmers University of Technology, in Göteborg, Sweden, have used these plasmonic nanostructures in combination with a electrochromic polymer to create a micrometer-thin display capable of rendering all the colors of traditional light-emitting diode (LED) displays. What’s more, it does so on one-tenth the energy needed to run a Kindle.

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Three gold nanoparticles supported by a DNA scaffold

DNA Scaffold Self-Assembles Into Single-Electron Device

To organize nanoparticles into structures that are useful in electronics, researchers have turned to DNA scaffolds that self-assemble into patterns and attract the nanoparticles into functional arrangements.

Now researchers at the Nanoscience Center (NSC) of the University of Jyväskylä and BioMediTech (BMT) of the University of Tampere, both in Finland, have used these DNA scaffolds to organize three gold nanoparticles into a single-electron transistor. DNA scaffolds have previously been used to organize gold nanoparticles into patterns. But this work represents the first time that these DNA scaffolds have been used to construct precise, controllable DNA-based assemblies that are fully electrically characterized for use in single-electron nanoelectronics. The immediate benefit: There’s no longer a need to keep these structures at cryogenic temperatures in order for them to work.

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Mirkó Palla (left) and P. Benjamin Stranges (right) who performed the work at the Wyss Institute

Personalized Medicine Draws Closer With Cheap and Accurate DNA Sequencer

Sequencing-by-synthesis (SBS) technology currently dominates the gene sequencing market. The process involves dividing a DNA molecule into many pieces of single-stranded templates that are put into millions of tiny wells on a substrate inside a machine that washes them through millions of cycles. Even though prices have dropped five orders of magnitude in the last decade for this technology, it’s still complicated and expensive. 

Many experts thought the key to cheaper DNA sequencers was going to be performing the SBS process in nanopore-based DNA sequencers. Here, the strands of the DNA are pulled through nanometer-scale pores in a membrane and the electric field variations of the four nucleic acids—A, C, G, T—are measured. While a number of companies have launched businesses around this technology, it remains costly enough to delay the revolution in medical care known as personalized medicine.

Now researchers at Wyss Institute for Biologically Inspired Engineering at Harvard University believe that they have developed a way to make these nanopore-SBS DNA sequencers fast, accurate, and, most importantly, cheaper than what is currently on the market. The trick was to biologically engineer the nanopore structure. If they can further develop the technology, they could enable doctors to quickly discern changes in your specific DNA sequence signaling a disease.

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Microscope image of a quantum LED device shows bright quantum emitter generating a stream of single photons.

Two-Dimensional Materials Combined to Produce “Quantum LED”

One of the many scientific and engineering challenges to realizing the prospects of quantum computing—which involves the use of quantum phenomena, like entanglement, to perform complex calculations—is  creating a device that can electrically generate a single photon to be used for carrying data in a quantum network. One method for producing these single photons is the use of complex multiple laser arrangements that have been precisely set up with optical components to produce these single photons. Lately, layered materials that serve as quantum emitters have begun to show a way forward. But even these layered materials require some kind of light source to trigger the emission of a single photon.

Now researchers at the University of Cambridge in England have constructed devices made from thin layers of graphene, boron nitride, and transition metal dichalcogenides (TMDs) that generate a single photon entirely electrically.  The combination of these three types of two-dimensional (2D) materials produces devices that are essentially all-electrical ultrathin quantum light-emitting diodes (LEDs).

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Schematic of a transistor with a molybdenum disulfide channel and 1-nanometer carbon nanotube gate.

One-Nanometer Gate Dimensions for Transistors Have Been Achieved

While there may be some quibbling about what really is the smallest transistor ever fabricated, an all-star lineup of U.S.-based researchers has laid a legitimate claim to having fabricated one that is at, or at least very near, the top of the list. And this one enjoys the relatively rare quality of having the potential to become more than just a lab curiosity.

With a physical gate length of only one nanometer, this latest transistor, made from a combination of molybdenum disulfide and carbon nanotubes, not only shatters the 20-nm gate length of state-of-the-art transistors currently on the market, but also surpasses the theoretical limit of five nanometers for the gate length of silicon-based transistors. While silicon transistors may stop shrinking by 2021, this research shows that transistors based on nanomaterials may still have some way to go in their miniaturization journey.

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Jean-Pierre Sauvage, Fraser Stoddart and Bernard Feringa have been awarded the Nobel chemistry prize.

Molecular Machine Makers Win Nobel Prize in Chemistry

In what seems to have come both as a shock to some of the recipients and a confirmation to all those who envision molecular nanotechnology as the true future of nanotechnology, Bernard Feringa, Jean-Pierre Sauvage, and Sir J. Fraser Stoddart have been awarded the 2016 Nobel Prize in Chemistry for their development of molecular machines.

The Nobel Prize was awarded to all three of the scientists based on their complementary work over nearly three decades. First, in 1983, Sauvage (currently at Strasbourg University in France) was able to link two ring-shaped molecules to form a chain. Then, eight years later, Stoddart, a professor at Northwestern University in Evanston, Ill., demonstrated that a molecular ring could turn on a thin molecular axle. Then, eight years after that, Feringa, a professor at the University of Groningen, in the Netherlands, built on Stoddardt’s work and fabricated a molecular rotor blade that could spin continually in the same direction.

The world of molecular nanotechnology is probably most familiar with Feringa’s work. He’s the one credited with being the first person to develop an actual molecular motor. In fact, IEEE Spectrum covered some of Feringa’s more recent work in 2011, when he and his team constructed a molecule that looks and seems to move like a four-wheeled car.

Of course, these molecular machines are far from having any practical, real-world applications. Despite nods in the press to nanoparticles moving through someone’s blood stream to deliver drugs, the nanogears, nanocars, and nanomachines developed by this year’s Nobel Laureates in Chemistry remain a long way from bringing to reality the primary hope of molecular nanotechnology (MNT): that these machines will work in unison to build macroscale devices. However, this Nobel Prize is as much a spur to future research as it is a recognition of what has already been achieved.

Speaking of the Nobel committee’s selection, Donna Nelson, a chemist and president of the American Chemical Society told Scientific American: “I think this topic is going to be fabulous for science. When the Nobel Prize is given, it inspires a lot of interest in the topic by other researchers. It will also increase funding.” Nelson added that this line of research will be fascinating for kids. “They can visualize it, and imagine a nanocar. This comes at a great time, when we need to inspire the next generation of scientists.”

Indeed, nanomachines do capture our imagination and have played a role in an increasing number of sci-fi movies and novels. However, experimental research in adapting these nanogears and nanomachines into the kind of MNT manufacturing that is envisioned in these works of fiction seems to still be lacking. MNT supporters have identified a lack of funding as one of the main obstacles. Whether this latest Nobel Prize will spur some funding bodies to open up the purse strings to realize the broader potential that this initial work seems to promise remains a question that only time can answer.

he graphene superlattice in which Stanford researchers measured conduction behaviors. Two-dimensional material is shown in green.

Long-Theorized Material Poised to Close the Terahertz Gap

Electronic devices are designed around how electrons travel through different kinds of solids. This movement of electrons can determine the material’s conductivity, its band gap, and its optical properties.

Nobel Laureate and one-time Stanford University professor Felix Bloch  theorized decades ago that it should be possible to get electrons to travel through a material in a very particular way that scientists hadn’t previously considered. Bloch predicted that it should be possible to structure a material in a way that causes electrons to oscillate in the terahertz band of the electromagnetic spectrum

This terahertz region has become known as the terahertz gap, because it has been so difficult to access even though it sits right between the radio wave and infrared radiation bands that we’ve been able to exploit in myriad ways.

Now, researchers at Stanford have realized Bloch’s theorized material. They’ve created heterostructures made of graphene and hexagonal-boron nitride that form a periodic lattice pattern of atoms known as a superlattice. In the process, they may have put us on a path to making a wide range of electronic devices including better airport scanners and solar cells.

In research described in the journal Science, the Stanford researchers demonstrated that layering graphene-hexagonal-boron nitride heterostructures in this superlattice structure makes it possible for the electrons to travel relatively long distances through the material before they are deflected by anything such as small impurities. The superlattice structure also ensured that the electrons were restricted to very narrow energy bands. This confinement, combined with their long-distance travel, cause the electrons oscillate at the frequencies they do.

It should be noted that this research did not actually produce a so-called Bloch oscillator. But it did yield a material that makes it possible for an electron to maintain its momentum and velocity over long periods—a key to eventually making a terahertz oscillator device.

What benefits would such a material provide? In the case of a solar cell, when a photon hits the superlattice material at a p-n junction, instead of the photon pushing out one electron, it could cause several several electrons to be emitted. If this material can eventually be made into a terahertz oscillator, it could eventually lead to the replacement of microwave-based scanners at airport security checkpoints. The shorter wavelength of terahertz-based scanner could reveal non-metal objects that can’t be detected currently.

Interestingly, while all of this comports perfectly with Bloch’s theory, the researchers discovered something new: another property of the material that turns the understanding of how electrons behave in semiconductors upside down.

“In semiconductors, like silicon, we can tune how many electrons are packed into this material,” said David Goldhaber-Gordon, a professor at Stanford and co-author of the paper, in a press release. “If we put in extra, they behave as though they are negatively charged. If we take some out, the current that moves through the system behaves as if it’s instead composed of positive charges, even though we know it’s all electrons.”

The graphene–hexagonal boron nitride offers a twist on this property: When more electrons are added to this material, it produces particles of positive charge; removing electrons has the opposite effect.

This reversal in the way electrons behave as they are added or subtracted from the material could lead to more efficient p-n junctions, the points at which p-type and n-type semiconductors are joined together to form the basis of many of the electronic devices we are familiar with. Menyoung Lee, a collaborator on the study who conducted the research as a graduate student in the Goldhaber-Gordon Group, believes that this nano-engineered material offers a very clear application of Bloch’s theory of solid-state physics.

Goldhaber-Gordon further envisions this work leading to a better understanding of how electrons travel through a material, and plans to leverage that understanding to create extremely narrow beams of electrons that are then send through superlattices. He believes that this could open up an entirely new field that he has dubbed “electron optics in 2-D materials.” The beams of electrons would travel in straight lines like a beam of light following the laws of refraction.

Goldhaber-Gordon added: “This is going to be an area that opens up a lot of new possibilities, and we’re just at the start of exploring what we can do.”

Visual representation of a fractal pattern

Mimicking the Veins in a Leaf, Scientists Hope to Make Super-Efficient Displays and Solar Cells

If you take a close look at a leaf from a tree and you’ll notice the veins that run through it. The structure these veins take are what’s called a quasi-fractal hierarchical networks. Fractals are geometric shapes in which each part has the same statistical character of the whole. Fractal science is used to model everything from snowflakes and the veins of leaves to crystal growth.

Now an international team of researchers led by Helmholtz-Zentrum Berlin have mimicked leaves’ quasi-fractal structure and used it to create a network of nanowires for solar cells and touch screen displays.

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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
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