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Wafer-scale Nanotube Film Is Finally Here

Single-walled carbon nanotubes (SWCNTs) used to be the darling of those who were looking for an alternative to silicon in digital electronics. The first SWCNT-based transistors were fashioned almost twenty years ago, but scaling up the use of SWCNTs since then to very large scale integration (VLSI) processes has remained elusive.

There were two persistent problems with SWCNTs that led to much of the research community pursuing graphene instead of SWCNTs as the next great post-silicon hope: an inconsistency between semiconducting and metallic nanotubes and the frustration of trying to get all of the nanotubes to align on a wafer.

Now researchers at Rice University claim that they have struck upon a method that produces a uniform and wafer-scale film of highly aligned and densely packed SWCNTs that may finally deliver on the long-promised potential of SWCNTs.

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2-D Boron Is an Intrinsic Superconductor

Just as we were getting confirmation that graphene could be coaxed into behaving as a superconductor, we now get research out of Rice University indicating that the two-dimensional version of boron may be the only flatlands material that is an intrinsic superconductor.

Researchers at Rice, led by Boris Yakobson, have used computer calculations to determine that boron is a natural low-temperature superconductor, and may, in fact, be the only 2-D material with this intrinsic property.

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World's Smallest Diode Is Made of DNA

Scientists have now created what they say is the world's smallest diode, one the size of a single (rather short) molecule of a DNA. This work could help spur development of DNA components for molecular electronics, its creators claim.

Diodes—also known as rectifiers—allow electric current to flow in just one direction. More than 40 years ago, scientists proposed miniaturizing diodes and other electronic components down to the size of single molecules, an idea that eventually helped give birth to the field of molecular electronics, which could help push computing beyond the limits of conventional silicon devices. [See “Whatever Happened to the Molecular Computer?IEEE Spectrum, October 2015]

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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.

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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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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
 
Contributor
Rachel Courtland
Associate Editor, IEEE Spectrum
New York, NY
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