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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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Researchers Seek Source of Frequency Fluctuations in Nanoresonators

The expectation has been that nanoelectromechanical systems (NEMS) will replace its technological predecessor microelectromechanical systems (MEMS) in the varied range of applications for which MEMS are currently used. However, the emergence of the usurper technology has not been without some struggles.

There have been durability issues with NEMS devices and there has also been the nagging issue that they never seem to perform quite up to their theoretical limits.

Now in joint research between the Commissariat a l'Energie Atomique (the French Atomic Energy and Alternative Energies Commission or CEA) and the University of Grenbole-Alpes, researchers have taken on the challenge of addressing this shortfall in performance for NEMS devices—in particular nanoresonators—by looking for better ways to measure their performance.

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New Measurement Technique Tests Nanomaterials During Production

The addition of nanomaterials such as graphene and carbon nanotubes to polymers and other materials in order to impart conductivity or mechanical strength is fairly commonplace at this point. It is now possible to buy a nanomaterial for a specific application and know the kind of functionalization that the nanomaterial needs, as well all the dispersion parameters required to extract the full effect of the nanomaterial’s properties in the polymer.

While the growing maturity of this value chain would seem to indicate that all is clear to start churning out materials that are either conductive or super strong or both (and in large part it is), it has still remained difficult to perform non-destructive testing of these materials during production operations such as roll-to-roll processing.

Now researchers at the U.S. National Institute of Standards and Technology (NIST) have developed a non-destructive measurement technique to ensure that nano-enabled materials are reaching their specified technical properties while being mass-produced in a roll-to-roll process.

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Graphene and Quantum Dots Turn a Mobile Device Into a Heart-Rate Monitor

The Mobile World Congress (MWC) held in Barcelona, Spain, last week hosted a Graphene Pavilion that included a number of research institutes operating under the umbrella of the Graphene Flagship, the European Commission’s €1 billion ($1.1 billion) investment aimed at centralizing graphene research throughout Europe. There were some other companies at the event that are not directly tied to the Graphene Flagship, such as Haydale and Zap&Go. (I visited both booths and posted videos that described their technologies.)

Another booth I visited while at the MWC was that of the Institute of Photonic Sciences (ICFO) in Barcelona, Spain. While this blog has covered a fair amount of the research coming out of ICFO over the years, our coverage has mostly followed the more long-range research projects that have attempted to leverage two-dimensional materials and plasmonics for the creation of a new generation of integrated circuits based around photons rather than electrons.

The prospect of integrated photonic circuits based on plasmonics remains firmly in the future. But ICFO was demonstrating what it has been able to fabricate based on its work with graphene and quantum dots. Essentially, what researchers there have built and demonstrated (see the video, below) is a transparent and flexible photodetector.

Last year, we reported on other research out of ICFO in which they developed a graphene-based photodetector that was capable of converting absorbed light into an electrical voltage in less than 50 femtoseconds, bringing switching to the brink of terahertz speeds. And, four years ago, we covered ICFO’s work in combining graphene and quantum dots, which, at the time, they believed would be ideal for automotive night-vision technologies.

We can only speculate on how this latest technology ties into that previous research. When asked if a description of the underlying technology had been published anywhere, the researchers explained that it hadn’t and that they could not provide any further details until it has. 

Nonetheless, the demonstration of the technology did capture the imagination of many folks visiting the booth. One of the applications that ICFO has devised for the transparent, flexible photodetector was as a heart rate monitor. You can see the demonstration of the technology in the video.

Basically what happens is that when a finger is placed on the photodetector, the digit acts as an optical modulator, changing the amount of light hitting the photodetector as your heart beats and sends blood through your fingertip. This change in signal is what generates a pulse rate on the screen of the mobile device.

It was a nifty application of the technology and certainly inspired a lot of gee-whizzes from those who saw it. However, the ICFO researchers didn’t really envision this as a shot at a viable commercial technology, but more of a demonstration of what is possible. I wasn’t quite so sure that they should have been so dismissive. It seemed to me like it would be cool little technology to have on one’s mobile device. We’ll have to see what they publish, maybe they envision a better application potential.

Scanning Probe Thermometry: A New Tool That Can Take the Temperature of Nanoelectronics

If you were to point to one invention that triggered what has come to be known as the field of nanotechnology, then you would be on pretty safe ground to cite the work of IBM Zurich scientists in creating first the scanning tunneling microscope (STM)  and later the atomic force microscope (AFM).  Both of these were the first tools to give us the capabilities to investigate, characterize and manipulate matter on the nanoscale.

Now, once again, scientists at IBM Zurich have provided us with a new tool to see the nanoscale world: They’ve developed a technique that uses an AFM to measure the temperature of an object on the nanoscale. The resulting device could provide a greater understanding of the capabilities of nanoscale devices, such as a new generation of transistors based on nanomaterials.

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New 2-D Material Hits the Goldilocks "Just Right" Button

Most of the so-called flatlands, the universe of two-dimensional (2-D) materials, is reminiscent of the beds and bowls of porridge sampled by Goldilocks during her short stay at the home of the three bears. Some 2-D materials, like silicene, are unable to remain two-dimensional for very long. Others, like graphene or boron nitride, remain stable but can’t be pressed into service as anything other than metallic conductors or insulators. (Another group of materials tick the stability box and behave as semiconductors, but are not one-atom-thick.)

Now researchers at the University of Kentucky, in collaboration with scientists from Daimler in Germany and the Institute for Electronic Structure and Laser (IESL) in Greece, may have found a formulation that is just right: a 2-D material that is both stable at high temperatures and under mechanical stress and easily fashioned into a semiconductor.

In research described in the journal Physical Review B, Rapid Communications, the researchers discovered that a combination of silicon, boron and nitrogen—all of which are cheap and abundant elements—led to the formation of an extremely stable one-atom-thick material.

In a phone interview, Madhu Menon, the physicist at the University of Kentucky who led the research, said that the stability was created by the fact that silicon and nitrogen form strong double bonds in 2-D form. This stands in contrast to silicene, the two-dimensional form of silicon.

“Silicene is not stable because the silicon atoms do not like to stay as a two-dimensional system,” Menon told IEEE Spectrum. “Silicon likes to have more than three neighbors, so that is why the surface gets puckered. And if you wait long enough, it will go into its 3-D silicon form.”

He added: “This proposed material is quite unique. The double bond between the silicon and nitrogen that leads to its stability in 2-D form was quite a revelation for me. This is unusual for this to happen.”

In the video below, Menon describes the new material and its potential electronic applications.

This new material is like graphene in that it too is a metallic conductor and must be functionalized in order to behave as a semiconductor. However, because its surface is made up of silicon atoms, it’s possible to functionalize the surface to gain a band gap. But with graphene, you cannot easily dope the surface but only the edges—a more complicated and expensive process.

One of the more interesting properties of the proposed silicon-boron-nitrogen material, according to Menon, is that when it is made into nanotubes it always acts as a metallic conductor. Nanotubes made from graphene can be semiconductors or metallic conductors. The prospect of having a material that will consistently form microscopic one-dimensional conductors is very attractive for electronic applications that depend on the availability of conducting channels.

Menon and his colleagues are eager to make the material in the lab, but they will need additional funding to proceed with that work. In the meantime, Menon will continue to characterize the material in simulations, examining its thermal properties and figuring out whether it can form n-type or p-type semiconductors.

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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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