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By compressing layers of boron nitride and graphene, researchers were able to enhance the material's band gap, bringing it one step closer to being a viable semiconductor for use in today's electronic devices.

Engineered Band Gap Pushes Graphene Closer to Displacing Silicon

Graphene might be the best conductor of electrons we know. However, as a pure conductor it can’t stop the flow of electrons like a semiconductor such as silicon can. Silicon’s ability to create an on/off state for the flow of electrons makes it possible to create the “0” and “1” of binary digital logic for computing.

While many believe this has pretty much taken graphene out of the running for digital logic applications that depend on turning the flow of electrons on and off, it hasn’t stopped researchers from looking to see if there’s a way to engineer a band gap into it that will make graphene behave like a semiconductor. The pressure of Moore’s Law on silicon is too much not to look for a solution from every corner.

The problem with these engineered band gaps is that they come at the cost of compromising the electronic properties of graphene that were so attractive in the first place—most notably its high conductivity.

Now a team of researchers at Columbia University has developed a graphene-based material that has a signifcant band gap without coming at the cost of sacrificing its attractive electronic properties.

In research described in the journal Nature, the Columbia researchers have created what’s known as a van der Waal (vdW) heterostructure—a combination of different two-dimensional (2D) materials held together by atomic scale forces known van der Waal forces. The researchers have provided a new level of understanding about why band gaps emerge in these vdW heterostructures, and how to modify the stacking between the 2D layers to open a much larger band gap, potentially even without pressure.

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The first quantum drum test.

A Quantum Drum Brings Quantum Mechanics to the Macroscale

One of the basic principles of quantum mechanics is that objects can act both as waves and particles. Also, these objects can be in a “superposition” in which they are in two different places at the same time.

One of the more elegant explanations of this quantum phenomenon is Schrödinger's Cat. In this thought experiment, a cat is put into box and a vial of poison is suspended in the box. The poison is released when the decay of a radioactive atom in the box is detected. The decay of the radioactive atom is a quantum mechanical process, leading to a level of uncertainty about when the atom decays. In this system, the atom has both decayed and not decayed. So, in essence, the cat is both dead and alive; the system is said to be in a state of superposition.

This quantum effect has always been talked about in terms of the atomic or molecular scale, never for macroscale objects. Now, a team of researchers led by scientists at the Imperial College London has described, in the New Journal of Physics, their ability to measure this quantum effect in a small—yet visible to the naked eye—drum. In the experiment, the drum is essentially struck by a drumstick of light—a few photons. The result: the skin of the drum has been made to vibrate and not vibrate at the same time.

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An artist’s impression of a robot, powered by artificial intelligence, in the process of fabricating a van der Waals heterostructure

Robotic System Leads to Mass Assembly of Nanostructures

In the sci-fi addled popular imagination, the term “nanotechnology” conjures an image of nanobots assembling macroscale objects atom-by-atom. Whether these nanobots end up being the soft, biological variety or the hard, diamondoid version, the prevailing wisdom remains that it’s all still pretty far off.

Last month in the journal Nature Communications, we got a real-world glimpse into what nanoscale robotic assembly might look like—and it’s pretty close to being commercially available.

Japanese researchers have fabricated a system consisting of an automated optical microscope, a chip transfer robotic arm and a stamping apparatus that is capable of stacking two-dimensional (2D) materials known as van der Waal (vdW) heterostructures much more rapidly than humans can.  These vdW heterostructures get their name because van der Waal forces  hold the layers together. The unique property of these nanostructures is that by alternating the layers between conductors (like graphene) and insulators (like hexagonal boron nitride) it’s possible to give them tailored electronic properties, like specific band gaps were no electron states can exist.

This week in the journal Nature Nanotechnology, Riccardo Frisenda, a researcher at the Madrid Institute for Advanced Studies (IMDEA) and Andres Castellanos-Gomez,  also a researcher at IMDEA, penned an analysis piece about this research that indicates this robotic system could not only be a game changer for nanotechnology research but also improve the prospects of large-scale nanotechnology manufacturing.

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Crossbar's demo unit.

Crossbar Pushes Resistive RAM into Embedded AI

Resistive RAM technology developer Crossbar says it has inked a deal with aerospace chip maker Microsemi allowing the latter to embed Crossbar’s nonvolatile memory on future chips. The move follows selection of Crossbar’s technology by a leading foundry for advanced manufacturing nodes. Crossbar is counting on resistive RAM (ReRAM) to enable artificial intelligence systems whose neural networks are housed within the device rather than in the cloud.

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Illustration showing a flexible optically transparent photodetector

Silicon Nanowires Could Enable Smart Solar Windows

Transparent photodetectors are at the heart of how today’s touch-screen displays function. The material indium tin oxide (ITO) has kept that heart beating over the years by serving as a transparent conductor for controlling display pixels. While nanomaterials such as carbon nanotubes and graphene have been tapped as potential replacements for ITO, the old king has held its throne.

Now an international group of researchers from India and Ireland have developed a new approach based on transparent nanowire networks made from silicon-on-insulator (SOI) that appears it could finally take the crown from ITO.

In research described in the journal ACS Nano, researchers from the Indian Association for the Cultivation of Science (IACS) and the Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN) in Ireland have for the first time fabricated silicon (Si) nanowire networks with seamless junctions.

The major breakthrough was not simply fabricating a Si nanowire network with seamless junctions, but also transferring that network onto a flexible polymer substrate, according to according to K. Mallikarjuna Rao, a scientist at IACS and co-author of the study. This process should open up avenues to fabricating transparent and flexible devices for all materials.

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This artistic rendering magnifies a switch researchers have developed within a computer chip to control for loss of photons when light is reduced to a nanoscale. 

Plasmonics Takes a Step Closer to Real-World Applications

While the field of plasmonics may sound esoteric, it is based on some fairly straightforward physics and, when applied to devices, could alter photonics dramatically. It involves exploiting the waves of electrons—known as surface plasmons—that are triggered when light (photons) strikes a metal surface. The length of these plasmon waves is much shorter than the wavelengths of light, making it possible to use light indirectly in the very small dimensions of today’s integrated circuits.

By transforming wavelengths of light into waves of electrons, it has become possible for scientists to merge the speed of optics with the dimensions of electronic devices. However, plasmonics has remained mired in a proof-of-concept state despite many practical devices having been experimentally demonstrated for on-chip circuitry.

Now, an international team of researchers has developed a switch for plasmonic devices that could eventually lead to a CMOS-compatible material platform for making practical plasmonic circuits.

In research described in the journal Nature, researchers at Purdue University in collaboration with those from ETH Zürich, the University of Washington, and Virginia Commonwealth University, have created a switch in the form of a ring modulator for a plasmonic-based circuit that uses resonance—or a vibration—to control whether photons interact with surface plasmons, or not. This switch should overcome a key problem for these circuits: the light used within them can be absorbed by surface plasmons—a property known as “loss.”

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Photographic image of ultrathin AM-OLED display on the human wrist

Stick-on Displays: Bendy 2D Semiconductor is Fast Enough to Drive OLED Pixels

One of the great things about 2D semiconductors like molybdenum disulfide is that they bend easily. They also allow electrons to zip through them pretty quickly. And, unsurprisingly, since they are only about an atom thick, they are transparent. That combination makes them perfect for flexible OLED displays.

However, if display makers try to build MoS2 into transistors needed to control OLED pixels, the resistance between the MoS2 and the transistors’ source and drain electrodes is so high that it puts the 2D wonder material out of contention for the job.

But now, engineers in South Korea have come up with a way to build MoS2 transistors that can work in bendable OLED displays. They used the transistors to construct a simple 6 x 6-pixel array on a 7 micrometer-thick plastic sheet you can stick on your skin. The display is so flexible it could be repeatedly bent to a radius smaller than one millimeter without breaking.

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“Experiment (left) and simulation (right) of a diamond nanoneedle being bent by the side surface of a diamond tip, showing ultralarge and reversible elastic deformation.”

How to Bend Diamonds

It’s commonly known that diamonds are the hardest natural material. However, with that hardness comes brittleness: they may be hard but they’re not very flexible.

Now an international team of researchers has demonstrated that diamonds, which are commonly believed to be inflexible, can be bent and stretched significantly. The researchers showed that the maximum tensile elastic strain of a diamond can reach nearly 9 percent, close to the theoretical limit of the material.

The researchers believe that these enhanced mechanical properties make nanodiamonds much more durable than expected, and therefore could lead to applications that involve mechanical loading, making them candidates for applications such as diamond needle-based intracellular delivery. But it is what this flexiblity does to diamonds’ optical and electrical properties may prove to be the most significant in the long run.

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Magnified images revealing the internal structure of nanoporous graphene.

Graphene Is Grown With the Same Bandgap as Silicon

For all of graphene’s amazing electronic capabilities, it has not made much of an impact as a replacement for silicon in digital logic applications. This shortcoming is largely due to its lack of an inherent bandgap that’s needed in computing applications to start and stop the flow of electrons.

While methods for engineering a bandgap into graphene have been around for years, these approaches have been recognized as imperfect solutions. They have added critical costs and complications to using the material and compromised the attractive electronic properties that made graphene a desirable replacement for silicon in the first place.

Now researchers in Spain have devised an inexpensive way to grow graphene with the same bandgap that exists in silicon (1 electron volt), and in so doing, may have reopened graphene’s potential as an alternative to silicon for digital logic.

In research described in the journal Science, a team from throughout Spain and led by the Catalan Institute of Nanoscience and Nanotechnology (ICN2) has employed bottom-up manufacturing techniques to assemble nanoporous graphene in such a way that the pores have the size, density, and morphology to create a perfect bandgap for digital electronics. The researchers then made a field-effect transistor (FET) device using this material.

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Schematic structure of the 2D SFG memory

"Quasi-Non-Volatile" Memory Looks to Fill Gap Between Volatile and Non-Volatile Memory

Researchers at Fudan University in Shanghai, China have leveraged two-dimensional (2D) materials to fabricate a relatively new gate design for transistors that may fill the gap between volatile and non-volatile memory.

The result is what the researchers are dubbing a “quasi-non-volatile” device that combines the benefits of static random access memory (SRAM) and dynamic random access memory (DRAM). The new device will make up for DRAM’s limited data retention ability and its need to be frequently refreshed and SRAM’s high cost.

In research described in Nature Nanotechnology, the Chinese researchers leveraged a gate design that has been gaining popularity, recently called semi-floating gate (SFG) memory technology. The SFG gate design is similar to a typical field effect transistor except that SFG transistor can “remember” the applied voltage from the gate.

The researchers have shown that the 2D SFG memory they have fabricated has 156 times longer refresh time (10 seconds) than DRAM (64 milliseconds), which saves power, and ultrahigh-speed writing operations on nanosecond timescales (15 nanoseconds), which puts it on par with DRAM (10 nanoseconds). This new device also boosts the writing operation performance to approximately 106 times faster than other memories based on 2D materials.

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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
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