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Oxygen frees silicene from its metal substrate

Breakthrough in Silicene Production

In the expanding universe of two-dimensional materials, perhaps none have been more tempting than silicon and its 2D version, known as silicene. The attraction is obvious: Silicon is the boat on which the computer age has floated for more than 50 years. And its proximity on the periodic table to carbon, whose 2D version is the wonder material graphene, has led researchers to investigate whether it might have the same attractive properties.

If researchers can overcome more of the obstacles standing in the way of silicene production, it has some pretty attractive qualities. First, unlike graphene, it has an intrinsic bandgap, which makes it attractive for digital electronics to stop and start the flow of electrons. Its semiconductor nature also comes with many of the same properties that make graphene so attractive—including, potentially, superconductivity.

While silicene is indeed tempting, it has proven frustratingly difficult to produce. Now researchers at the University of Wollongong, in Australia, have overcome one of the main obstacles: separating it from its substrate.

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A hexagon-shaped silicon-based virus sorter

IBM Making Silicon to Sort Viruses and Other Nanoscale Biological Targets

It’s long been understood that early disease detection is the key to successful treatments. But annual checkups with a doctor might not be frequent enough to help. So imagine if you could forego a trip to the doctor’s office and detect any disease with a simple urine or saliva test at home.

Of course this has been the aim of lab-on-a-chip technologies for years now, but now scientists at IBM Research may have tipped the scales in the technology that could make such at-home tests real.

In cross-disciplinary research described in the journal Nature Nanotechnology, a team at IBM led by research scientist Joshua Smith and Gustavo Stolovitzky, program director of IBM Translational Systems Biology and Nanobiotechnology, has been able to retool silicon-based technologies to create a diagnostic device that can separate viruses, DNA, and other nanoscale-size biological targets from saliva or urine. This could enable the device to detect the presence of diseases before any physical symptoms are visible.

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Turn printer paper into a flexible electronic display by slapping on a coat of graphene

Graphene-Enabled Paper Makes for Flexible Display

Graphene has been building quite a reputation for itself in flexible displays. Among the ways graphene has been used in this field is as an alternative to the relatively scarce indium tin oxide (ITO), a transparent conductor that controls display pixels. Graphene has also been used in a display’s pixel electronics, or backplane, where a solution-processed graphene is used as an electrode.

Now researchers at Bilkent University in Ankara, Turkey, have demonstrated that an ordinary sheet of paper that is sandwiched between two films of multilayer graphene can act as a rudimentary flexible electronic display.

In an interview with Nature Photonics, the corresponding author, Coskun Kocabas, says that this system could serve as a framework for turning ordinary printing paper into an optoelectronic display.

Kocabas explained:

We would like to fabricate a display device that can reconfigure the displayed information electronically on a sheet of printing paper. Several technologies based on electrophoretic motion of particles, thermochromic dyes and electrowetting of liquids have been developed to realize electronic paper, or e-paper, which has great potential for consumer electronics. Contrasting with the primary aim of e-paper, these technologies, however, are not compatible with conventional cellulose-based printing papers.

The researchers described their device in the journal ACS Photonics. It operates by applying a bias voltage to the graphene to trigger an intercalation of ions so that the optical absorption of the graphene layers is altered. That turns them from transparent to dark and back again. (Intercalation is the reversible inclusion of a molecule or ions between two other molecules in multilayered structures or compounds.)

In the experiments, the display’s transition to transparent takes a bit of time— about 4 seconds; reverting to its darker form takes under half a second. While this may be suitable for signs that don’t need to change their images that often, the lapse is still too long for display applications that require quick refresh times.

The multilayer graphene was produced through chemical vapor deposition in which the graphene is grown on a metal surface inside a furnace. After it’s removed from the furnace, the metal is etched away, leaving a thin film of graphene on the surface of the water in which the etching occurs. Then the paper is simply submersed into the liquid, which transfers the thin film of graphene onto the paper.

While the initial experiments showed that there were some issues with oxidation of the doped graphene layers, the researchers believe that this hiccup can be overcome with the addition of a simple polymer coating.

In future research, Kocabas and his colleagues are planning to make a fully functional sheet of e-paper with pixels and an integrated driving circuit. They would like to see the process they have developed adapted into a roll-to-roll-compatible manufacturing process.

Examples of handheld devices that could benefit from a new oxide compound for power electronics.

New Material Offers a Revolutionary Approach to Power Electronics

Researchers at the University of Utah and the University of Minnesota have discovered that when two oxide compounds—strontium titanate (STO) and neodymium titanate (NTO)—are joined together, they make an extraordinary conductive material that could vastly improve power transistors.  The researchers have shown that these two materials—which on their own operate as insulators—are up to five times more conductive than silicon.

In research described in the journal APL Materials, scientists found that the bonds between the atoms from the oxide compounds arrange themselves in a way that generates 100 times more free electrons than conventional semiconductors, which means the new material can transport more electrical current.

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Organic nanowires bound for supramolecular electronics

Promise of Nanowires in Optoelectronics Realized By Getting Them Connected

Supramolecular electronics has been solidifying as the bridge between molecular electronics—in which molecules become the basic building blocks of electronics—and the use polymers for the fabrication of nanoscale circuitry. A supramolecule is actually a number of different molecules that are fused together to act as a single molecule and carry out a particular programmed function. These supramolecules are used, for instance, in block copolymer-based supramolecular solutions that direct the self-assembly of nanoparticles.

Now researchers at the University of Strasbourg and the Le Centre National de la Recherche Scientifique (CRNS) in France, along with collaborators from the University of Nova Gorica in Slovenia, have buoyed the prospects of supramolecular electronics by addressing one of the chief problems of supramolecular organic nanowires for optoelectronics: getting them connected.

In research described in the journal Nature Nanotechnology, the international team of researchers fabricated a photovoltaic device in which they managed to connect and integrate hundreds of organic nanowires.

This is a significant achievement, because supramolecular organic nanowires have long tantalized researchers in the field of optoelectronics. Their highly efficient generation of excitons—essentially energized electrons that are formed when light hits a semiconductor—make devices like solar cells very sensitive to light and boost their light absorption coefficient.

While this is indeed tempting, the rub has been that you couldn’t harvest that photocurrent from the supramolecular nanowires unless they were connected to nanoelectrodes (anodes and cathodes) that carry out different functions. And the best anyone had previously been able to do was connect just a few. Thus, these nanowires were limited to use in very rudimentary devices.

To the rescue is this new approach: a nanomesh scaffold that supports and connects the supramolecular nanowires between two nanoelectrodes with different work functions.

The researchers were able to fabricate this nanomesh scaffold using a technique known as nanosphere lithography, in which nanoscale spheres are used as a mask to fabricate nanoparticle arrays. The result is a nanomesh comprising millions of hole-shaped nanoelectrodes patterned into a hexagonal array with channel lengths less than 100 nanometers.

By using a commercially available n-type organic semiconductor that self-assembles into supramolecular nanowires in combination with the nanomesh scaffold so that the nanowires become connected to the nanoelectrodes, the researchers have been able to fabricate a photovoltaic device with very promising characteristics.

One of the attractive properties of the device is that the polymer/nanowire p-n junction provides a fast photoresponse because the anode and cathode are quite close together. Another feature of this device is that it is possible to chemically modify the anode and cathode separately. This enables tailoring of interfaces that, in turn, makes it possible to replace calcium and aluminum cathodes. It also makes the use of transparent electrodes such as indium tin oxide unnecessary.

In future research, the team intends to optimize the device in a number of different areas, such as using polymer thin films to impart flexibility . The researchers are also considering the use of thinner dielectric layers to increase the photocurrent.

Porous silicon nanoparticles offer harmless theraphy and diagnostic solution for many types of cancer

Silicon Nanoparticles Provide Biocompatible Solution to Cancer Detection and Treatment

When it comes to cancer treatment and nanoparticles, the preference has been to use gold nanoparticlesSilicon nanoparticles, on the other hand, have been limited mainly to the realm of electronics applications.

Now researchers at Lomonosov Moscow State University and the Leibniz Institute of Photonic Technology in Germany have demonstrated that silicon nanoparticles can be applied to the diagnosis and treatment of cancer. The researchers claim that this work represents the first time nanoparticles have penetrated into diseased cells and completely dissolved after delivering their cancer treatment drug payload.

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Professor Shubhra Gangopadhyay of the University of Missouri holding plasmonic gratings.

Plasmonics Enable Optical Microscopes to Perform Like Electron Microscopes

Optical microscopes are  a key tool in biological studies. But because they are limited by approximately half the wavelength of light used (200 to 400 nanometers), they can’t resolve molecules that are typically much smaller than these dimensions. While electron microscopes can reach resolutions far below an optical microscope, they are large, expensive pieces of equipment that require a vacuum to operate, limiting the ability to examine live samples.

Now researchers at the University of Missouri have developed a way to make an optical microscope resolve images down to 65 nanometers. In the process, they may have extended access to high resolution imaging to a much larger group of scientists who may not have access to electron microscopes.

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Smart Sutures Integrate Microfluidics and Nanosensors

The role of nanomaterials in textiles has evolved from comparatively simple hydrophobic materials to the creation of textile electrodes that leverage graphene and the weaving of nanowires into t-shirts to make them into supercapacitors.

Now researchers at Tufts University have taken nanomaterials for wearable systems to a new level with the development of a “smart” thread consisting of nanoscale sensors and microfluidics. The thread could be used in sutures, providing critical information in medical treatments.

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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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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
 
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Rachel Courtland
Associate Editor, IEEE Spectrum
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