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NanoMRI Gets Real

Many of us are acquainted with magnetic resonance imaging (MRI), but you may not have heard of nanoMRI a technology that can image viruses and cells for in-depth analysis.

Up until now, nanoMRI has been a long and laborious process, in which a single scan can take up to two weeks to complete. Now researchers at the Swiss Federal Institute of Technology in Zurich (ETH Zurich) have dramatically reduced this scanning time to a couple of days by developing a system that can perform in parallel the measurements that used to have to be done sequentially—a process known as multiplexing.

"As a loose analogy, think of how your eyes register green, red, and blue information at the same time using different receptors—you're measuring different colors in parallel," Alexander Eichler, a postdoctoral researcher in the physics department at ETH Zurich said in a press release.

Fundamentally, MRI exploits the fact that particular atoms have nuclei that are like tiny magnets. When these atoms come under the influence of a magnetic field, they start to rotate around the axis of that magnetic field.

This rotation is called precession.  The precession generates its own frequency of electromagnetic radiation known as the Larmor frequency. The Larmor frequency depends on the type of atoms and the strength of the magnetic field. So an MRI determines the positions of the atoms based on frequencies of their precession.

This standard MRI process works pretty well until you get down to nanoscale objects like cells where the strength of around 1000 atoms is not robust enough to be detected.

"Clinical MRI is only possible because a single 3-D pixel—a ‘voxel’—contains about 1018 atoms," Eichler explained in the press release. "With nanoMRI, we want to detect voxels with only a thousand atoms or less, meaning that we need a sensitivity at least a quadrillion [1015, or a million billion] times better."

In the research published in the journal Applied Physics Letters, the ETH Zurich team developed their technique around a magnetic resonance force microscopy (MRFM) apparatus, which has been the standard piece of equipment for previous nanoMRI methods.

With the MRFM apparatus, the nuclei of the atoms are exposed to a small magnetic force that is transferred to a micro-scale cantilever. The force on the cantilever causes it to vibrate, and that vibration can then be measured in a way that forms an image.

This process used to have to be done one measurement at a time but the ETH researchers have developed a technique to do make these measurements in parallel across six data points. This parallel measurement, known as multiplexing, involves encoding different bits of information in the detector using different phases.

"The term 'phase' refers to a lag in a periodic signal,” said Eichler. “The phase can be used to differentiate between periodic signals in a way similar to how color is used to differentiate between light signals in the eye."

Eichler added: “With commercial applications in mind, this time gain is crucial because it makes a huge difference to a pharmaceutical company if a virus can be characterized within three days rather than a month."

Supercapacitors Take Huge Leap in Performance

The Economist has published an article this week highlighting the work of Lu Wu at the Gwangju Institute of Science and Technology in South Korea in which he and his colleagues have developed a process for producing graphene that could lead to better supercapacitors.

While The Economist article makes some pretty incredible claims, such as that the graphene-based supercapacitors produced by the Korean researchers can store more energy per kilogram than lithium-ion (Li-ion) batteries, the actual research paper in the Journal of Power Sciences offers a less-hyped but nonetheless impressive list of achievements from the research.

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Molecular Electronics Takes Large Stride Forward

Molecular electronics has long promised a day when individual molecules would serve as the basic building blocks for electronics.

That day has moved a bit closer thanks to research out of the Columbia University School of Engineering and Applied Science. Researchers there have developed a new technique that makes it possible to produce a diode from a single molecule.

In research published in the journal Nature Nanotechnology,  the researchers claim that they have not only produced a single-molecule diode, but that it greatly outperforms all previous designs.

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Graphene Overcomes Achilles' Heel of Artificial Muscles

In the world of biomimetic robotics, so-called artificial muscles have promised everything from the ability to make fish-like fins for underwater vehicles to devices to help the disabled in their rehabilitation.

These ionic polymer composites are attractive for their sheer simplicity. You just put two electrodes on the polymer and when you switch on the voltage, the ions migrate, deforming the polymer.

However, there was a problem with the metal electrodes. After being exposed to air and current, the electrodes would begin to crack, leaking ions and diminishing the muscle’s performance.

Scientists at the Korea Advanced Institute of Science and Technology (KAIST) have come up with a solution to that problem, and it involves graphene.

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Graphene Composites Go Big

Graphene is a wonder material — flexible, transparent, light, strong, and electrically and thermally conductive, qualities that have led to research worldwide into weaving these atom-thick layers of carbon into advanced devices. Now scientists have demonstrated what they say is the first large-scale fabrication of a graphene composite—a material that combines graphene with another substance to form something with new properties.

Until now, labs could only incorporate tiny flakes of graphene or graphene-like materials into composites. The mechanical and electrical capabilities of these composites were never as good as scientists would have liked because of weak links between the flakes, and the flakes often clumped together, leading to irregularities across the composites.

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New Memristors Could Usher in Bionic Brains

Last month we saw researchers in the US push the envelope of non-volatile memory devices based on resistance switching to the point where they are now capable of mimicking the neurons in the human brain.

Now researchers at the Royal Melbourne Institute of Technology (RMIT) in Australia have built on their previous work developing ultra-fast nano-scale memories. They used a functional oxide ultra-thin film to create one of the world’s first electronic multi-state memory cells. The researchers claim that the memristive devices they have developed mimic the brain’s ability to simultaneously process and store multiple strands of information.

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Plasmonic Nanostructures Could Change the Landscape of Optoelectronics

Scientists have high hopes that the emerging field of plasmonics can improve technologies such as photovoltaicsLEDs, and other optoelectronics. It’s a natural fit: Plasmonics exploits the oscillations in the density of electrons that are generated when photons hit a metal surface.

However, it’s been studied in a bit too much isolation. Scientists have only looked at the phenomenon in isloated metal nanostructures and not the metal adhesion layer that glued the nanostructures to a metal substrate.

Now researchers at Rice University have expanded the understanding of plasmonics beyond just the nanostructure itself and down into the metal substrate. They expect that their increased ability to characterize and manipulate the plasmonic effect could make plasmonic devices viable alternatives for highly complex optoelectronic devices like optomechnical oscillators, which couple photons into mechanical resonators and are used in photonic and wireless communications applications.

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Graphene Enables First Example of a Textile Electrode

Wearable electronics has been a hotly pursued research area for years now, but there has been precious little to show for all that effort in terms of electronic garments appearing on people’s backs. The reason for this is not entirely clear. Maybe it’s because the technologies that would enable fabric makers to weave in electronic components have been unwieldy, or maybe people just don’t feel that compelled to wear their electronic devices.

In any case, researchers have recently been able to leverage the properties of graphene to bring the long-promised future of wearable electronics closer to the present. We’ve already seen graphene woven into a yarn-like material that acts as a supercapacitor to power wearable electronics both here and here.

Now, an international research team from the University of Exeter in the U.K. and the Institute for Systems Engineering and Computers, Microsystems and Nanotechnology (INESC-MN) in Lisbon, the Universities of Lisbon and Aveiro in Portugal and the Belgian Textile Research Centre (CenTexBel) has managed to coat textile fibers with graphene in a way that turns them into electrodes.

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Perovskite Transistors Made for First Time

The last couple of years have seen the emergence of a new “wonder material” in photovoltaics: perovskite. Recently, we’ve seen that perovskite’s wonders are not limited to just solar cells; they can create 100-percent efficient lasers and can be manipulated to carry both electric and magnetic polarization.

Even without any particular manipulation, perovskites are a class of material with attractive PV properties such as high charge-carrier mobility, long diffusion lengths, and low cost. With these as motivation, research has pushed perovskite energy conversion efficiency up from 5 percent to 20 percent in just a few years.

Despite its spectacular development in photovoltaics, there has been no way to directly measure perovskits charge-transport properties for other applications. Now a team of researchers from both Wake Forest University and the University of Utah has overcome this limitation. The researchers have shown that it’s possible to make a field-effect transistor (FET) out of perovskite, showing for the first time that anyone can directly measure the material’s electronic properties at room temperature.

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2-D Materials Produce Optically Active Quantum Dots for First Time

Tungsten diselenide (WSe2), which belongs to a class of 2-D crystals known as transition metal dichalcogenides, is proving to be an attractive platform for producing solid-state quantum dots for emitting light.

While graphene has become increasingly used for optoelectronic applications, researchers at the University of Rochester claim that the work they have done with tungsten diselenide represents the first time that 2-D materials have produced optically active quantum dots.

The researchers believe that this research, details of which were published in the journal Nature Nanotechnology, could serve as a basis for integrating quantum photonics with solid-state electronics. The result could be a new way to produce so-called integrated photonics.

In the research, the Rochester team laid atomically thin sheets of the semiconductor tungsten diselenide one on top of the next, creating defects in the semiconducting material. These defects are what create the quantum dots: nanoscale semiconductor crystals that are sometimes described as “artificial atoms” because, like atoms, when they absorb the right amount of energy they subsequently give off energy as colored light.

The researchers discovered that the quantum dots they created by engineering the tungsten diselenide defects did not impact the electrical or optical performance of the semiconductor. Further, they found that they could control the electrical and optical properties of the quantum dots by applying either an electrical or magnetic field.

In this way, the researchers were able to control the brightness of the quantum dot’s light emissions simply by applying a voltage. In future iterations of the technology, the researchers believe they will also be able to tune the color of the emitted photons using a voltage, which will open up these quantum dots to applications including nanophotonic devices.

Another possibility opened up by the quantum dots having been produced in this way is a potential use in “spintronics,” where the spin of an electron is used to encode information rather than a charge.

"What makes tungsten diselenide extremely versatile is that the color of the single photons emitted by the quantum dots is correlated with the quantum dot spin," said Chitraleema Chakraborty, one of the authors of the Nature Nanotechnology paper, in a press release.

The researchers believe that the easy interaction between the spin and the photons should make them attractive for quantum information applications.

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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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