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Light Could Become the Dominant Form of Heat Transfer

We know that when you touch a hot cup of tea it can warm your hands. That’s heat conduction: Two surfaces of different temperatures make physical contact and heat is transferred from one to the other. We are also pretty aware of convective heat transfer, though it may not be quite as simple. In convection, the heat transfer occurs when a fluid—this can be air, some other gas, or even a liquid—is caused to move away from a source of heat and in the process carries energy with it. For instance, above the hot surface of a stove, the air being warmed expands, becomes less dense than the surrounding cold air, and rises.

The reason for this elementary explanation of heat transfer is to set them apart from another means of thermal energy transfer. Objects can also transfer heat to their surroundings using light, but that method of heat exchange has always been thought to be very weak compared with conduction and convection. Now, in collaborative research among researchers at Columbia, Cornell, and Stanford, they discovered that we just weren’t doing it right. Their conclusion: light could become the most dominant form of heat exchange between objects.

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Silicon and Graphene Combo Finally Achieve Lithium-Ion Battery Greatness

Silicon, graphene, and sometimes the two of them combined together have all been suggested as potential replacements for graphite in the electrodes of lithium-ion batteries.

While all three of these options bring attractive properties to the table—most importantly, a very high theoretical capacity—those properties are lost in the real world. Silicon electrodes crack and break after just a short number of charge/discharge cycles. Meanwhile, the use of graphene on electrodes is limited because graphene’s attractive surface area is only possible in single stand-alone sheets, which don’t provide enough volumetric capacitance. Layer the graphene sheets on top of each other to gain that volumetric capacity, and you begin to lose that attractive surface area.

Now researchers at Kansas State University (KSU) claim to have developed a technique that uses silicon oxycarbide that makes the combination of silicon and graphene achieve its expected greatness as an electrode material.

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UK's National Graphene Institute Kerfuffle Gets the PR Treatment

Earlier this month, the UK newspaper The Sunday Times broke a story  claiming that researchers at the University of Manchester and the National Graphene Institute (NGI) were reluctant to occupy the NGI’s new $71 million research building. Their reason: fear that the work they produce there would be taken by a foreign company.

Since that news story broke, damage control from the NGI, the University of Manchester, and BGT Materials, the company identified in the Times article, has been coming fast and furious. Even this blog’s coverage of the story has gotten comments from representatives of BGT Materials and the University of Manchester.

There was perhaps no greater effort in this coordinated defense than getting Andre Geim, a University of Manchester researcher who was a co-discoverer of graphene, to weigh in. Geim, typically reluctant to speak with the press, offered a full-throated defense of his employer and its partners, saying that the UK has not lost out on graphene-related tech jobs, nor is the new research institute close to empty.

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Nanocones Funnel Light So Solar Cells Soak Up More Sun

Researchers at the Royal Melbourne Institute of Technology (RMIT University) in Australia have created an entirely new nanostructure they have dubbed a “nanocone”. It combines the upside-down physics of topological insulators with the easier-to-explain process of plasmonics. The result is a nanomaterial that can be used with silicon-based photovoltaics to increase their light absorption properties.

Topological insulators have the peculiar property of behaving as insulators on the inside but conductors on the outside and plasmonics exploits the oscillations in the density of electrons that are generated when photons hit a metal surface. What the RMIT researchers have done by bringing these worlds together is create a plasmonic nanostructure that has a core-shell structure that lends itself to being topological insulator.

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Crumpling Graphene Repeatedly Adds a New Wrinkle

Over the last year, research is increasingly showing that if you crumple graphene so that it has wrinkles, the material takes on attractive new properties. For instance, researchers at RIKEN in Japan discovered last year that by forming wrinkles in graphene you can restrict the movements of electrons to create a junction-like structure that changes from a zero-gap conductor to a semiconductor and back to zero-gap conductor.

This Japanese research and others like it that have looked at creating wrinkles in graphene have only examined the potential of wrinkling the material once.

Now research out of Brown University has looked to see what happens when you wrinkle graphene repeatedly.

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Atomic "Sandblaster" Could Write, Edit 2-D Circuits

The dominance of resist-based lithography in nanoscale fabrication is being slowly eclipsed by the growing emergence of physical-probe methods, such as electron beam induced deposition  or focused ion beam milling.

Now researchers at Oak Ridge National Laboratory (ORNL) have tested the capabilities of one of these physical probe methods, known as helium ion microscopy (HIM), to see whether it may be the way forward in fabricating a next generation of two-dimensional electronic devices.

HIM is similar to other focused-ion-beam techniques in that it uses a scanning beam of helium ions to mill and cut samples. What sets HIM apart is its cleanliness. Milling or imaging with helium or neon is preferred to other ion-beam methods, since these two noble gases aren’t reactive and don’t induce any chemical side effects during the fabrication process. Imaging and milling resolution are also hugely important factors. The helium beam can be strongly collimated offering smaller features—and as a result smaller devices.

In research described in the journal Applied Materials and Interfaces,  the ORNL scientists used the HIM technique to serve as a kind of atomic-scale “sandblaster” on bulk copper indium thiophosphate (CITP). CITP is a ferroelectric material, and the HIM beam was used to introduce localized defects that effect its ferroelectric properties.

While this research only worked with bulk CITP (2-D versions will come later), ferroelecriticy in CITP is very special because this behavior is completely unexpected in a 2-D material. CITP is a layered van der Waals crystal ferroelectric—part of a family of thiophosphate molecules capable of a huge variety of metal substitutions. Besides ferroelectricity, the thiophosphate family offers a number of useful properities including semiconductivity, magnetism, anti-ferroelectricity, and piezoresponse.

By introducing localized defects into the CITP, the researchers discovered it served as a way to manipulate the properties of the material. In particular, the researchers discovered that they could control the distribution of ferroelectric domains in the material as well as enhance its conductivity.

The main point of the research was to look at what properties can be particularly appealing in novel 2-D materials and see how can they be incorporated into the next generation of devices, according to Oak Ridge staff scientist Alex Belianinov.

To this end, the ORNL researchers tested the capabilities of HIM in conjunction with a suite of scanning probe microscopy (SPM) techniques, specifically atomic force microscopy (AFM) band excitation (BE-AFM). What they discovered was that HIM is attractive for nanofabrication because it combines imaging and patterning without poisoning the surface of whatever is being studied with gallium, or other metals typically used in FIB techniques. HIM also offers imaging quality (resolution, field of view, and enhanced channeling effects) that rivals and perhaps exceeds that of scanning electron microscopy (SEM), the workhorse in the field.

“This opens a host of opportunities in clean, direct manufacturing where surfaces can be imaged and modified without a multi-step chemical preparation process,” said Belianinov, in an e-mail interview with IEEE Spectrum. “Additionally, HIM is compatible with direct-write technologies using gas precursors, and in-situ liquid work; both approaches are under intense investigation in the area of electron microscopy to expand material processing arsenal.”

Belianinov added: “HIM is an exceptionally good tool for working with 2-D materials because it can image them, cleanly cut them, (no chemical processing or metal poisoning) and locally induce defects that drastically change material’s properties—as illustrated with the bulk CITP work.”

In future research, the ORNL team will look at tuning the material and synthesizing related compounds with a host of other properties, incorporating the existing materials into functional devices, and continuing to explore the HIM characterization and processing approaches to push novelty and scalability.


Direct Control of Nanowire Self-Assembly Leads to New Devices

Researchers at IBM’s T. J. Watson Research Center have developed a technique for achieving greater control over the self-assembly of nanowires. The team claims that the nanowires fabricated in this way can be tuned to have properties that would make them attractive for a new generation of transistors.

To accomplish this, the IBM researchers have combined so-called top-down manufacturing techniques—like lithography—with bottom-up techniques that “grow” electronics through self-assembly to create a single approach that produces nanowires with specific electrical properties. Having control over the properties of nanowires makes it possible to better target them for various devices, like single-electron transistors.

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UK's National Graphene Institute in Revolt After Foreign Tech Grab

A technology that, a year ago, was being lauded as the “first commercially viable consumer product” using graphene now appears to be caught up in an imbroglio over who owns its intellectual property rights. The resulting controversy has left the research institute behind the technology in a bit of a public relations quagmire.

The venerable UK publication The Sunday Times reported this week on what appeared to be a mutiny occurring at the National Graphene Institute (NGI) located at the University of Manchester. Researchers at the NGI had reportedly stayed away from working at the institute’s gleaming new $71 million research facility over fears that their research was going to end up in the hands of foreign companies, in particular a Taiwan-based company called BGT Materials.

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Chemoelectronics: Nanoparticle Diodes and Devices That Work When Wet

Whether they’re for sensors in artificial skin that demands flexibility or for wearable electronics where the circuits must withstand our sweat, silicon-based chips aren’t always up to the task.

Now, an international research team has developed a way to fabricate flexible, water-loving logic circuits and sensors without the need of semiconductors. Instead, what the researchers have done is coat gold nanoparticles with charged organic molecules to create a system that they’ve dubbed a “chemoelectronic circuit”.

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Reconfigurable Nanopatterning Technique Promises New Generation of Metamaterials

Metamaterials are moving on from being merely laboratory curiosities in which objects can be made invisible. They are now reaching the commercial-applications stage—in one example, as the basis of new antenna technologies for mobile phones that are much smaller than earlier generations, but still provide the same signal coverage.

There is a subset of metamaterials known as magnetic metamaterials; these exploit the propagation of electromagnetic radiation, surface plasmons, and spin waves, all of which are properties critical to a new generation of electronics. The development of these materials has been somewhat limited by the fact that the magnetic nanopatterns on them must be fabricated through conventional lithography or ion radiation processes, both of which are irreversible.

Now an international research team led by researchers from the CUNY Advanced Science Research Center (ASRC) in New York City, and the Politecnico of Milan, in Italy, has developed a new process for fabricating these magnetic nanopatterns that allows them to be reconfigured so that their properties can be programmed and reprogrammed on demand.

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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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