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A molybdenum disulfide tube wired together with carbon nanotubes for use as an electrode in a lithium ion battery

Molybendum Disulfide and Carbon Nanotubes Join Forces for a Super Li-ion Battery

The initial high hopes surrounding molybdenum disulfide’s (MoS2) potential in electronic applications were tempered somewhat when it was revealed that MoS2 contained traps—impurities or dislocations that can capture an electron or hole—that limit its electronic properties. Since then the two-dimensional material has been investigated for other applications, one of the most promising of which has been for use on the electrodes of lithium-ion (Li-ion) batteries where some research has indicated that it has three times the theoretical capacity of graphite.

However, even here MoS2 does not come without some challenges. Most notable among the problems with MoS2 anodes is the speed at which they begin to degrade and the low rate at which they discharge.

Now researchers at Nanyang Technological University in collaboration with a team at Hanyang University in South Korea have developed a solution that addresses these issues by using tubular structures of MoS2 that have been wired together by carbon nanotubes to enhance conductivity.

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NASA Eyes First Carbon Nanotube Mirrors for CubeSat Telescope

Some have dubbed NASA’s CubeSats "nanosatellites" because of their relatively small dimensions that are based on the size of a Beanie Baby box one of their inventors found in a store. The CubeSats are small, weighing in at just 1 to 10 kilograms, but they’re not nanoscale small.

While the CubeSats are not going to be shrunk down to the nanoscale any time soon, they now at least contain some nanotechnology. For the first time, researchers at NASA’s Goddard Space Flight Center have used carbon nanotubes in an epoxy resin to fabricate a mirror for a lightweight telescope on a CubeSat.

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Pores in a lithium-ion battery electrode align in a magnetic field

Magnetic Field Makes a Better Lithium-Ion Battery for Electric Vehicles

Researchers at MIT have developed a manufacturing approach for the electrode material of lithium-ion (Li-ion) batteries that should lead to a threefold higher area capacity for conventional electrodes. In the devices that they have fabricated thus far they have measured 12 milliamp hours per square centimeter (mAh cm2) versus the 4 mAh cm2 seen in conventional electrodes at normal charge-discharge rates.

The technique the MIT team developed involves using an external magnetic field to align pores in the electrode material in a particular way to achieve these much higher capacity numbers. And because of some of the unique properties of the resulting material, these Li-ion batteries may be far better suited for the requirements of electric vehicles (EVs).

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Atomically Thin Circuits Made From Graphene and Molybdenite

Atomically thin transistors and circuits made of graphene and molybdenum disulfide (molybdenite) can now be chemically assembled on a large scale, researchers say. Previous attempts to build circutis from 2-D materials involved placing materials precisely instead of growing them where they’re needed.

Researchers hope such atomically-thin devices will allow Moore’s Law to continue once it becomes impossible to make further progress using silicon. "A big drive for nanotechnology has been the search for new materials to replace silicon to meet Moore's law," says study senior author Xiang Zhang, a materials scientist at the University of California Berkeley.

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Graphene-Silicon Photodetector Could Enable the Internet of Things

While graphene has faced challenges in the field of digital logic because of its lack of an inherent band gap, it has been that very weakness that has attracted many researchers to exploring its use in optoelectronics. This lack of a band gap makes graphene an extreme broadband absorber, enabling photodetection for visible, infrared, and terahertz frequencies.

Now, in research supported by the European Commission’s €1 billion ($1.3 billion) 10-year project, the Graphene Flagship, a group of universities—including the University of Cambridge in the UK, The Hebrew University in Israel, and John Hopkins University in the United States—has successfully combined graphene with silicon on a chip to make “high-responsivity” Schottky barrier photodetectors

Such photodetectors are formed by a junction between metal and a semiconductor. Since photodetectors are a key building block of optoelectronic links, the result of this research could lead to far less energy being consumed to process and move information, a key achievement in realizing the potential of the Internet of Things (IoT), say the researchers.

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Compound 2-D Material Leads to a Practical Electronic Device

Researchers have found it effective to combine different two-dimensional (2D) materials to create compound materials that have properties that no single 2D material would have on its own.  For instance, hexagonal boron nitride with its enormous band gap—which gives it pseudo-insulator characteristics—has been combined with a pure conductor like graphene to create a semiconductor material for a host of applications, especially in flexible electronics.

Now researchers at the University of California, Riverside and the University of Georgia have taken this practice one step further and added a third 2D material to boron nitride and graphene: tantalum sulfide. The result is a compound material that the researchers used to make a voltage-controlled oscillator (VCO). These VCOs are ubiquitous, and are found in applications such as clocks, radios, and computers.

In research described in the journal Nature Nanotechnology, the researchers fabricated for the first time a practical device that exploits charge-density waves to modulate an electrical current through a 2D material. A charge-density wave is an ordered array of electrons in either a linear chain compound or layered crystal.

The VCO that the researchers made could be used as an ultralow power alternative to conventional devices that are now based on silicon. Because this VCO is flexible, it could be also used in wearables.

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Map of crystal facets in a perovskite photovoltaic.

Secret Hidden in Grains of Perovskite Could Boost Solar Cell Efficiency

The rise of the crystal perovskite as a potential replacement for silicon in photovoltaics has been impressive over the last decade, with its conversion efficiency improving from 3.8 to 22.1 percent over that time period. Nonetheless, there has been a vague sense that this rise is beginning to peter out of late, largely because when a solar cell made from perovskite gets larger than 1 square centimeter the best conversion efficiency had been around 15.6 percent. This figure has been improved recently in the work of Michael Grätzel to an average of 19.6 percent.  However, the bright prospects for perovskite have dimmed in eyes of some.

Now researchers at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) may have discovered something hidden in perovskite crystals that could boost the conversion efficiency of this material to as high as 31 percent.

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Microscope image of a carbon nanobrush

Nanobrushes: A New Carbon Material to Boost Batteries and Capacitors

NEC says it has produced a new addition to its portfolio of nanomaterial discoveries—the carbon nanobrush. The company says the new material will boost the performance of batteries, sensors, and capacitors among other devices.

The nanobrush is a fibrous aggregate of single-walled carbon nanohorns measuring several microns in length. These thimble-shaped nanohorns measure 2 to 5 nm in diameter, and between 40 to 50 nm in length.

Like nanohorns, which NEC discovered in 1998, nanobrushes have disperse well in water and allow other molecules to stick to their surface, which makes them suitable for use as conductive additives and compounds. Despite the similarities between the two materials, the nanobrush boasts more than 10 times the electrical conductivity of spherical aggregate of nanohorns of the same length.

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A red octopus floats underwater, with two rows of white suckers on the underside of each tentacle

Octopus-Inspired Smart Adhesive Boosts Flexible Electronics

Octopuses are widely admired for their intelligence, their skill as escape artists, and their extraordinary ability to camouflage themselves. Materials scientists are also taken by the adhesive properties of their tentacles. By controlling the pressure in their suckers, the cephalopods can rapidly grab onto and then release themselves from just about any surface they come across as they make their way along the ocean floor.

Now researchers led by materials scientist Hyunhyub Ko at the Ulsan National Institute of Science and Technology (UNIST) in South Korea have made octopus-inspired adhesives. Described online in Advanced Materialsthe adhesives can be used in the transfer printing of nanomaterials to make flexible electronics and compound-semiconductor devices on silicon: adhesive pads can pick-and-place a broad range of nanomaterials, including as indium gallium arsenide nanoribbons, and place them on a wafer or flexible substrate.

Nature has long offered many examples of adhesives that put chemical engineers to shame—including tree-frog toes and the gecko’s foot. Attempts to mimic them have yielded flurries of research papers. But in just about every case, engineers have trouble matching the natural adhesives’ high on/off strength ratio, says Ko, who came into this area through his work on electronic skin.

Flexible pressure sensors, circiuts, and other electronics might give future prosthetics and robots a better sense of touch. But they can be a pain to build. Making such flexible electronics involves a lot of laborious transferring of nano- and microribbons of inorganic semiconductor materials onto polymer or rubber sheets. In search of an easier way to do this transfer printing, Ko turned to the octopus for inspiration.

Each of the animal’s suckers contains a cavity whose pressure is controlled by surrounding muscles. When one set of muscles contracts, the wall of the sucker thins. This increases the volume of the cavity, reducing the pressure in the sucker relative to the surroundings and creating suction. When it's time to let go, other muscles contract to thicken the wall, increasing the pressure and releasing the sucker.

To mimic this approach, Ko made an array of microscale “suckers” using the rubbery material PDMS. Sheets of PDMS riddled with pores are coated with a thermally responsive polymer to create sucker-like walls. At ambient temperatures, the polymer is hydrophilic, swollen up with water. When a pad of the material is heated to 32 degrees Celsius, the polymer undergoes a phase transition, becoming hydrophobic. It shrinks dramatically, creating suction. The adhesive strength spikes from .32 kilopascals to 94 kilopascals at high temperature.

“This temperature control makes it very easy to transfer semiconductor nanoribbons,” says Ko. “We can transfer any nanomaterial to any substrate.” (Transfer printing is pretty much the only way to get high quality, inorganic semiconducting materials like silicon or gallium arsenide onto flexible or stretchy substrates. Typically, matching the material, the stamp, and the substrate can be tricky.)

So far Ko has used this universal smart adhesive to make indium gallium arsenide transistors on a silicon dioxide substrate. They’ve also transferred nanomaterials to flexible polymers. And they’ve made stacks of crossed silicon ribbons, and silicon criss-crossed on compound semiconductor ribbons—something that’s quite laborious to do with traditional adhesive stamps, which adhere weakly using van der Waals forces.

Ko says these adhesives could also be used as the substrate for wearable health sensors, eliminating the need for any extra glues. The adhesive is very sticky at body temperature, 37 degrees; it could be removed by rinsing under cold water—with no painful band-aid tear. 

An illustration styled to look like a semiconductor micrograph. A sheet of hexagons with an electrode on either side is stretched over a circular depression.

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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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
New York City
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