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New Method Developed for Making a Transistor from Graphene

 

Researchers from Germany and Sweden have developed a new method for creating a transistor from graphene, according to an artlcle at Phys.org.

The headline, "Researchers devise a way to create a graphene transistor," is a bit misleading. Researchers have been making transistors out of graphene for some time now,  and have been using a process based on silicon carbide, like the German-Swedish research. 

The real breakthrough for this latest line of research, which was published 17 July in the journal Nature Communications (“Tailoring the graphene/silicon carbide interface for monolithic wafer-scale electronics”),  appears to be how they engineered all the constituent parts of the transistor.

To be honest, I am not entirely clear on how even their process diverges drastically from the IBM research. After a year of trying to figure out how to connect all the parts of the graphene-based transistor without damaging it, the IBM team used electron beam lithography and a resist that was sensitive to electrons.The German-Swedish researchers used electron beam lithography too.

Maybe the difference between the two is the use of oxygen plasma etching, which converted the middle channel on the transistor from a contact into a gate. This could be the “tailoring the graphene/silicon carbide interface” of which the paper title speaks.

An important caveat to the research is that because the researchers had to scale up dramatically their transistor they don’t really know how much faster the transistor might be than the current variety. Furthermore, they’re not even sure how fast it might be when they scale the transistor down.

I am sure this work is helpful and evolutionary research in the development of graphene transistors, but I think maybe the Phys.org article has perhaps overstated its case when it says that this research “is the breakthrough computer engineers have been waiting for.”

Nanoparticle Completely Eradicates Hepatitis C Virus

 

Researchers at the University of Florida (UF) have developed a nanoparticle that has shown 100 percent effectiveness in eradicating the hepatitis C virus in laboratory testing. 

The nanoparticle, dubbed a nanozyme, consists of a backbone made from gold nanoparticles and a surface with two biological components. One biological component is an enzyme that attacks and destroys the mRNA, which provides the recipe for duplicating the protein that causes the disease. The other biological part is the navigator, if you will. It is a DNA oligonucleotide that identifies the disease-related protein and sends the enzyme on course to destroy it.

Y. Charles Cao, a UF associate professor of chemistry, and Dr. Chen Liu, a professor of pathology at the UF College of Medicine published their research online this week in the Proceedings of the National Academy of Sciences ("Nanoparticle-based artificial RNA silencing machinery for antiviral therapy"). 

The basis of the work is mimicking the biological process of RNA interference, which researchers in the past have used effectively in the laboratory for treating HIV. In the UF research the nanoparticle mimics the function of RNA-induced silencing complex (RISC), which mediates the RNA interference process.

Current hepatitis C treatments do attack the replication process of the virus but they are not entirely effective and only help about 50 percent of the patients treated with them. Cao and Liu along with their team wanted to see if they could improve upon that percentage. The researchers claim that their treatment (in cell culture and mice) led to a near 100 percent eradication of the hepatitis C virus without bringing on any side effects caused by the immune system attacking the treatment.

Of course, this is a long way from becoming a treatment anytime soon. A major caveat is that the use of nanotreatments for the targeting and destroying of abnormal cells like cancer cells is always problematic since those cells are “still us” as George Whitesides noted some time back.  It’s always a bit of a tricky business to make sure that nanoparticles are targeting those biological processes within us that we want stopped and not the ones we want to keep.

Further complicating this particular line of research is some of the terminology that is part of the press release. They have decided to use the term “nanorobots” to describe the nanoparticles, apparently because that can really excite the general public about what might otherwise be a fairly niche story.  That’s fine, I suppose. Whatever manages to get the public interested in what is genuinely ground breaking research. The problem is that it creates confusion in some terribly misguided people who are convinced that we are about to be overrun by ‘nanobots’ that will render the planet into nothing but “gray goo”.   Can’t we just retire the term “nano robots” for the sake of human life?

Nanomaterial Duplicates Self-Regulation of Living Organisms

Bio-inspired nanomaterials seem to be the rage this week, at least on this blog.  Adding to the furor, researchers at Harvard University have developed a nanomaterial that can actively self-regulate depending on environmental changes. 

While living organisms have developed sophisticated systems for responding to the external environment, the Harvard team believe this to be the first instance in which artificial materials have been able to self-regulate themselves in response to external factors, such as temperature or pH.

The research, which was published in the July 12th issue of Nature, aimed initially at making the material regulate itself based on temperature. But the researchers believe in principle that the material can be made to regulate itself according to pH, pressure or some other parameter. This ability to self-regulate itself according to a variety of external factors is one of the features that distinguish it from something like photochromic eyeglasses, which can only react to a single stimulus and cannot self-regulate.

The material itself is fairly simple. Dubbed SMARTS (Self-regulated Mechano-chemical Adaptively Reconfigurable Tunable System), it consists of nanofibers that have been embedded into a hydrogel. When set up for temperature regulation, the hydrogel swells in the presence of colder temperatures causing the nanofibers to stand upright; and it contracts in warmer temperatures causing the nanofibers to lie down.

“Think about how goosebumps form on your skin,” explains lead author Joanna Aizenberg, and Professor of Materials Science at the Harvard School of Engineering and Applied Sciences (SEAS) in the university press release covering the research. “When it is cold out, tiny muscles at the base of each hair on your arm cause the hairs to stand up in an insulating layer. As your skin warms up, the muscles contract and the hairs lie back down to keep you from overheating. SMARTS works in a similar way.”

This is clearly early stage research, but the researchers have suggested applications in medical implants and buildings that could react to the outside temperatures. Added to these fairly specific applications are the broad fields of robotics, computing and healthcare.

“Whether it is the pH level, temperature, wetness, pressure, or something else, SMARTS can be designed to directly sense and modulate the desired stimulus using no external power or complex machinery, giving us a conceptually new robust platform that is customizable, reversible, and remarkably precise,” co-lead author Ximin He noted.

Tightening Graphene Like a Drumhead Changes Its Electrical Properties

 

The main preoccupation with graphene research has been trying to impart a band gap to the wonder material. Researchers at the University of Wisconsin-Milwaukee were able to get graphene to behave like a semiconductor earlier this year by making a new variety of graphene dubbed “graphene monoxide”. But now researchers at National Institute of Standards and Technology (NIST) and the University of Maryland discovered they could do it by just treating graphene like a drumhead

The research was published in the journal Science under the title “Electromechanical Properties of Graphene Drumheads”  and is available with a subscription.

Initially the aim of the NIST and University of Maryland team was to see if they could just slow electrons down with the use of a substrate. So they suspended a layer of graphene over a substrate of silicon dioxide that contained shallow holes. When the graphene was laid on top of these holes, it formed a kind of graphene drumhead.

The next step, of course, was to measure their new graphene drumhead. It was then that they discovered when the tip of the scanning probe microscope (SPM) approached the graphene, it rose up to meet the tip. The attraction of the graphene to the SPM tip was caused by van der Waal force, in which a weak electrical force is created that attracts objects together. 

"While our instrument was telling us that the graphene was shaped like a bubble clamped at the edges, the simulations run by our colleagues at the University of Maryland showed that we were only detecting the graphene's highest point," says NIST scientist Nikolai Zhitenev in the NIST press release covering the research. "Their calculations showed that the shape was actually more like the shape you would get if you poked into the surface of an inflated balloon, like a teepee or circus tent."

The researchers then tinkered with the graphene drumhead a little more and soon discovered that they could tighten the graphene like one would with the skin on a real drum. But instead of changing the sound as with the real drum, the tightening of the graphene drumhead resulted in changing the electrical properties of the graphene.

If you tightened the graphene drumhead enough so that it actually went into the shallow hole and created a kind of tent like shape, the graphene started to behave like a quantum dot.

This result could open up an entirely new avenue of research in which by simply altering the shape of graphene you can maintain its high conductivity but create a band gap as well.

Zhitenev further noted in the release: "Normally, to make a graphene quantum dot, you would have to cut out a nanosize piece of graphene," says NIST fellow Joseph Stroscio. "Our work shows that you can achieve the same thing with strain-induced pseudomagnetic fields. It's a great result, and a significant step toward developing future graphene-based devices."

Nanostructures Modeled on the Moth Eye Reduce Radiation in Medical Imaging

Typically it’s the butterfly that serves as the bio-inspiration for nanotechnology advances.  But now the butterfly’s modest cousin, the moth, is serving as the model.

Yasha Yi, a physics professor at the City University of New York, has attempted to duplicate the moth’s anti-reflective eyes with a nanostructured material that should improve medical imaging

This is not the first time that the anti-reflective qualities of moth eyes have been used as models for devices. Researchers have attempted to duplicate this feature to create more efficient coatings for solar panels and some military devices. But Yi and his research team, which published their work in the journal Optics Letters,  were looking at improving “scintillation” materials used in medical imaging technologies. These scintillation materials absorb incoming X-rays and reemit the energy as light of wavelengths that can be picked up by a detector.

If you want the detector to pick up more light, the technique has usually been to increase the intensity of the X-rays. But this obviously has associated health risks. Yi and his team believed that if they could improve the scintillation material so that it reemitted more light from the same amount of X-rays, then they could create safer medical imaging devices.

To do this, the researchers needed to create a new class of materials. What they came up with is based on a thin film made from cerium-doped lutetium oxyorthosilicate crystals. They were then able to cover these crystals with pyramid-shaped bumps made of silicon nitride. It is these bumps that make the scintillator appear like the moth’s eye and give the structures its ability to extract more light.

The results have been pretty dramatic. Yi and his team measure that adding their moth-eye-inspired thin film to the scintillator of an X-ray mammographic unit increases the amount of reemitted light by 175 percent.

“The moth eye has been considered one of the most exciting bio structures because of its unique nano-optical properties,” Yi says in Nanomagazine article. “Our work further improved upon this fascinating structure and demonstrated its use in medical imaging materials, where it promises to achieve lower patient radiation doses, higher-resolution imaging of human organs, and even smaller-scale medical imaging. And because the film is on the scintillator,” he adds, “the patient would not be aware of it at all.”

We shouldn’t expect to see this scintillator material on the market in the near future. Yi expects that it will be another three to five years to evaluate and perfect the film.

Nanoscale Vacuums Speed Semiconductors

When you want to make the point of how far electronics and computer technology have come in the last sixty years, you likely refer to the old computers that used vacuum tubes for circuitry.

So, it’s a bit counterintuitive to see the latest research that suggests vacuums may be the way forward to help semiconductor electronics keep pace with Moore’s law. Researchers at the University of Pittsburgh have developed a method for generating a vacuum within a semiconductor device to transport electrons more efficiently through it. 

“Physical barriers are blocking scientists from achieving more efficient electronics,” said Hong Koo Kim, principal investigator on the project and Bell of Pennsylvania/Bell Atlantic Professor in the University of Pittsburgh’s Swanson School of Engineering, in a press release. “We worked toward solving that road block by investigating transistors and its predecessor—the vacuum.”

Of course, there already exist vacuum electronic devices, but these require high voltage. The researchers, who published their findings in the journal Nature Nanotechnology, designed an entirely new vacuum electronic device that requires minimal voltage to operate.

The key to the design was the discovery by Kim's team that it was fairly easy to pull electrons out into the air when they are trapped at the interface of an oxide or metal layer inside a semiconductor. These trapped electrons form a two-dimensional electron gas.

The researchers exploited the phenomenon known as Coulombic Repulsion--the repulsive force between two positive or negative charges--to emit the electrons from this electron gas layer. By then applying a small voltage of  1V to the silicon structure, the electrons were extracted into the air, which made it possible for them to travel ballistically in a nanometer-scale vacuum channel without the scattering typically seen in conventional devices.

Kim further noted in the release, “The emission of this electron system into vacuum channels could enable a new class of low-power, high-speed transistors, and it’s also compatible with current silicon electronics, complementing those electronics by adding new functions that are faster and more energy efficient due to the low voltage."

Analysis of Nanosilver Risk Reaching Point of Diminished Return?

It's been clear for several years that we need to move beyond merely conducting more studies on nanotechnology and risk and start looking at how regulation of nanotechnologies should be established, something I first wrote about nearly three years ago.

In the intervening years, serious observers have expressed concern on how such regulations would be enacted. Then the European Union (EU) further fueled that concern by their awkward process of defining nanotechnology in order to establish its regulatory policy. Creating regulatory policy is never an elegant process.

But this is the way of governments, I suppose. When in doubt about what course of action to take, establish a committee, or, better yet, a public outreach project

Now this grinding pace of governance has worn thin the patience of some scientists. In a recent editorial piece in the journal Nature Nanotechnology, entitled “When Enough is Enough,”  authors Steffen Foss Hansen and Anders Baun, both of Technical University of Denmark's Department of Environmental Engineering, have reached their breaking point. In the editorial, they explain their frustration with a request from the European Commission (EC) for another study on the environmental, health and safety considerations of nanosilver.

If you don’t have a Nature Nanotechnology subscription, Nanowerk has a story on the editorial and an interview with the two authors. They do not hide their irritation with the EC and its “paralysis by analysis,” as Nanowerk calls it.

"Most of these questions—and possibly all of them—have already been addressed by no less than 18 review articles in scientific journals, the oldest dating back to 2008, plus at least seven more reviews and reports commissioned and/or funded by governments and other organizations" Hansen tells Nanowerk. "Many of these reviews and reports go through the same literature, cover the same ground and identify many of the same data gaps and research needs."

What may make the matter even worse is that we may already have a pretty substantial framework—in the US, at least—on which to base nanosilver regulations, which dates back to the 1950s. It concerned what was called at the time collodial silver, which is essentially what today is called nanosilver.

But getting back to current stagnant state of affairs, it’s hard to know exactly what’s causing the paralysis. It could be concern over implementing regulations in a depressed economy, or just a fear of taking a position. But in both these instances, the lack of action is making the situation worse. Investment is scared off by a market that appears ripe for regulation but none have been implemented. Taking no action may seem politically expedient now, but it will come back to haunt the timid bureaucrats. Surely, we can base regulations on what we know now about nanosilver risk, and amend them later, if the situation demands it.

Nanoporous Graphene Promises Affordable Water Desalination

For some parts of the world desalination of seawater is an important option for accessing fresh drinking water. In 2007 the estimates were that worldwide desalination reached 30 billion liters a day.  But the cost of that desalination was at the exorbitant levels of $0.50 to $0.85 per cubic meter.

Because of this huge expense, most desalination production remains in the oil-producing countries of the Persian Gulf, where they can afford the huge energy costs of running the multi-stage flash (MSF) processes. But outside of the Middle East, the predominant method for desalination is Reverse Osmosis (RO), which is only slightly less energy consuming and expensive than MSF processes. 

Researchers at MIT are looking to replace the membrane materials used now in RO with nanoporous graphene

Currently, RO depends on comparatively thick membranes that effectively block the salt ions when water molecules are hydraulically pushed through them. In the process envisioned by the MIT researchers, which was published in the journal Nano Letters, one-atom-thick grapheme with nanometer-sized pores would replace those membranes. Because the graphene is a thousand times thinner than the traditional membrane materials it requires far less force—and therefore energy—to push the water molecules through it. A video describing the benefits can be seen below.

The key to making nanoporous graphene work in this desalination process is getting the size of the pores just right. If the pores are too big, the salt can pass right through; and, conversely, if the they are too small, the water will be blocked. According to Jeffrey Grossman, the Carl Richard Soderberg Associate Professor of Power Engineering in MIT’s Department of Materials Science and Engineering, the ideal size range is extremely limited and looks to be 1 nanometer. If the pores are slightly smaller, 0.7 nanometers, the water won’t pass through the membrane at all.

At this point, the research seems largely centered around computer modeling of an RO process using the nanoporous graphene. And in the MIT press release Joshua Schrier, an assistant professor of chemistry at Haverford College, points out that translating this research from computer models to the real world will not be an easy step.

“Manufacturing the very precise pore structures that are found in this paper will be difficult to do on a large scale with existing methods,” he says. However, he also believes that “the predictions are exciting enough that they should motivate chemical engineers to perform more detailed economic analyses of … water desalination with these types of materials.”

Simple Process Turns T-Shirt into a Supercapacitor

The idea of combing electronics with our clothing has been around for a while, but, so far, it has produced mixed results. Nanotechnology has often been mentioned as an ingredient to add to the electronics-textile mix, to help push concept beyond mere novelty.

One way to bring nanotechnology into electronic textiles is to make the textile itself into a big battery for powering our personal electronics. Two years ago, researchers at the University of California Berkeley pursued this line of research. Their approach was to weave nanowires into the textile and to rely on the piezoelectric properties of the nanowires to develop power. While I have not followed up to see where that research ended up, it did seem a bit complicated—weaving nanowires into a textile sounded like a daunting task.

Now, researchers at University of South Carolina (USC), led by Xiaodong Li, a professor of mechanical engineering, has developed what appears to be a much easier way to make a cotton t-shirt into a supercapacitor

The technique, which was described in the Wiley journal Advanced Materials, started by soaking a regular cotton t-shirt a in a solution of fluoride. After dying it, the researchers examined the material with infrared spectroscopy and discovered that the cellulose of the cotton t-shirt had been converted into activated carbon. Not only had they made it into activated carbon, but also the t-shirt still maintained its flexibility and could be rolled and folded without breaking.

While the activated carbon now could serve as a capacitor and store electrical charge, Li and post-doctoral associate Lihong Bao decided to take it a step further. They took the individual fibers from the treated t-shirt and coated them with “nanoflowers” of manganese oxide. The result was a “stable, high-performing supercapacitor,” said Li in the USC press release. "By stacking these supercapacitors up, we should be able to charge portable electronic devices such as cell phones."

While Li makes mention of the environmentally friendly chemicals used to impart this capability to a t-shirt, it is perhaps the simplicity of the process that will likely be the most intriguing aspect to manufacturers.

World Smallest Optical Cavities Lead to Most Intense Nanolaser Beams

Metamaterials can produce astounding effects. They possess quite different electromagnetic properties from conventional materials that allow them—among other things—to make objects appear invisible. Physics as magic, if you will.

If you manipulate the structure of a metamaterial, it will change how it interacts with electromagnetic waves. Researchers with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) Berkeley have taken advantage of this phenomenon at the nanoscale to create “the world’s smallest three-dimensional optical cavities with the potential to generate the world’s most intense nanolaser beams.” 

The development of the “world’s smallest optical cavities” should have applications across a number of optical fields, including LEDs, optical sensing, nonlinear optics, quantum optics and photonic integrated circuits. It seems that metamaterials are on a bit of a roll when it comes to optoelectronics applications as evidenced by research coming out of the UK and Spain earlier this year.

Key to this technology’s operation is the optical property known as negative refraction, which makes it possible for some kinds of metamaterials to bend light in the opposite direction from what we would expect based on typical refraction. Achieving this negative refraction involves reversing the electrical component (permittivity) and the magnetic component (permeability) of a material’s refractive index. This is accomplished by constructing the material so that it has structures with dimensions smaller than the wavelengths of the light it is intended to refract.

“Due to the unnaturally high refractive index supported in the metamaterials, our 3D cavities can be smaller than one tenth of the optical wavelength,” says Xiaodong Yang, lead author of the Nature Photonics paper,  in a Berkeley Lab press release. “At these nanoscale dimensions, optical cavities compress the optical mode into a tiny space, increasing the photon density of states and thereby enhancing the interactions between light and matter.”

Xiang Zhang, a principal investigator with Berkeley Lab’s Materials Sciences Division and director of UC Berkeley’s Nano-scale Science and Engineering Center (SINAM), believes this research should make possible a new generation of high-performance photonic devices.

“Our work opens up a new approach for designing a truly nano-scale optical cavity,” Zhang says in the Berkeley Lab press release. “By using metamaterials, we show intriguing cavity physics that counters conventional wisdom. For example, the quality factor of our optical mode rapidly increases with the decrease of cavity size. The results of this study provide us with a tremendous opportunity to develop high performance photonic devices for communications.”

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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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