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New Germanium-Based Material Could Replace Silicon for Electronics

The old adage “what goes around comes around” is now being applied in electronics. Before silicon ruled the roost as the electronics material of choice, the first transistors were fashioned out of germanium.

Now researchers at Ohio State University (OSU) are bringing germanium back to electronics in a way that they believe could displace silicon. To achieve its new role the researchers have manipulated the germanium down into a one-atom-thick material that gives it a two-dimensional structure not unlike graphene, thereby joining a growing list of 2-D materials targeted for electronic applications.

The researchers say that electrons conduct through their germanium-based material ten times faster than through silicon and five times faster than in traditional germanium.

Joshua Goldberger, assistant professor of chemistry at Ohio State, was attracted to the material because of the more than half century that has gone into characterizing and developing electronics around germanium, such as germanium MOSFETs.

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Will the Sequester Derail U.S. Nanotech R&D?

Analysts are still trying to determine the impact of the US budget sequestration, which went into effect on 1 March.The sequester—as it has been dubbed—requires across-the-board mandatory federal budgets cuts.

Some programs are already feeling the pinch and now one of the premier U.S. nanotechnology scientists, A. Paul Alivisatos, in comments he made at the National Meeting & Exposition of the American Chemical Society (ACS) in New Orleans this week expressed concern about the budget cuts imposed by the sequester on nanotechnology funding.

“The National Science Foundation announced that they will issue a thousand fewer new grants this year because of sequestration,” said Alivisatos, in an ACS press release. “What it means in practice is that an entire generation of early career scientists, some of our brightest and most promising scientists, will not have the funding to launch their careers and begin research properly, in the pathway that has established the United States as leader in nanotechnology research. It will be a setback, perhaps quite serious, for our international competitiveness in this key field.”

If Alivisatos is correct, this would be an unfortunate way to make cuts in federal funding of nanotechnology research. Of course, this has been the concern about the sequester from the time it was first proposed: It would make cuts indiscriminately, leaving wasteful programs largely intact while hacking into useful ones.

To give some context, US government funding of nanotechnology research through the National Nanotechnology Initiative (NNI) has been on a fairly steady yearly increase since 2001 (except for a brief hiccup in 2010),  cumulatively accounting for US $14 billion in spending between 2001-2011.

The timing is indeed unfortunate. Much of the initial funding was used to build out the laboratory infrastructure to support the new line of research. So far, this has mainly enriched the construction industry and the microscopy companies that equip these facilities, investments that inevitably take time to bear fruit in terms of nanotechnology research and products. Now that the funding can actually go to supporting research projects, the crunch is on and the new labs will likely run below their full capacity.

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Combining Nanowires and Memristors Could Lead to Brain-like Computing

For decades now, researchers have been trying to get computers to behave like artificial brains instead of merely binary data crunchers. One of the obstacles in creating this capability has been that computers are based on silicon CMOS chips rather than the dendrites and synapses found in the human brain. One of the drawbacks with silicon chips is that they lack what is known  as "plasticity" in which the brain's neurons adapt in order to learn and remember.

To overcome such limitations, nanotechnology has been offering alternatives to silicon chip architecture that will more closely resemble the human brain. DARPA’s SyNAPSE project is one example.

Now researchers at the Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN) at Trinity College in Dublin are pursuing a new nanomaterial-based approach to neural networks that combines work in nanowires and memristors. The aim of the project, for which the researchers have just received a  €2.5 million research grant from the European Research Council (ERC), is to develop a new computing paradigm that mimics the neural networks of the human brain.  A video describing the CRANN research can be seen below.

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Any Mobile Device Can Display Glasses-Free 3-D Images With This Novel Plastic Film

Glasses-free 3D imaging on mobile devices is nothing new; the Nintendo 3DS has been around since 2010 impressing users with its 3D graphics sans spectacles. Since that breakthrough, ensuing generations have seen incremental improvements.

The latest development comes via a plastic film produced through nanoimprinting technology that enables mobile devices to display 3D content without using 3D glasses in both portrait and landscape mode. And because it is a film, it can be put on the screens of mobile devices with normal screens to enable them to produce 3D imaging.

The thin film technology was jointly developed at Temasek Polytechnic (TP) and A*STAR’s Institute of Materials Research and Engineering’s (IMRE), both located in Singapore. The start-up Nanoveu Pte Ltd. film will commercialize and market the technology.

The film is basically a lenticular lens, which is a series of tiny lens elements that direct light to each eye.  The nanoimprinting technology developed at IMRE makes it possible to create this type of lens on a plastic film.

“The filter is essentially a piece of plastic film with about half a million perfectly shaped lenses engineered onto its surface using IMRE’s proprietary nanoimprinting technology,” said Jaslyn Law, the IMRE scientist who worked with TP on the nanoimprinting R&D since 2010, in a press release.

The Singapore team apparently recognized that a stronger business model is to sell products rather than just a nanomaterial. So in addition to the plastic film, the researchers developed a few applications that will operate on both Apple iOS and Android. The applications will make it possible to convert 2D images into 3D content. They will also provide a software development kit to help game developers convert their existing games into 3D.

“The team’s expertise in both hardware and software development in 3D technology has enabled high quality 3D to be readily available to consumers,” said Mr. Frank Chan, the TP scientist who led the overall NRF-funded project, in the press release. “We have taken age-old lenticular lens technology that has been around for the last hundred years, modernized it, and patented it, using nanotechnology.”

Image: A*Star

Nanostructures of Butterfly Wings Lead to Anti-counterfeiting Technique

Nanotechnology is being used in a number of anti-counterfeiting techniques. There are those that are still at a fairly preliminary stage of their development and others that are well-established commercial interests.

Now a new company, Vancouver, Canada-based NanoTech Security Corp., is bringing a nanotech-based, anti-counterfeiting technology to market that operates on the same principle as the iridescent wings of the Blue Morpho butterfly.

Researchers have mimicked the Morpho wing structure as the basis for developing nanostructures before. In at least one case, it involved removing the actual scales from the butterfly wing and doping them with carbon nanotubes for improved thermal imaging.

NanoTech Security’s approach merely mimics the Morpho and forgoes the removal of the wing’s scales. The technique they developed involves using an electron beam to engrave nanoscale inscriptions into a material that are smaller than a wavelength of visible light. At this size, the light is captured in the same way that the Morpho’s iridescent wings operate.

In actual operation, when a product has been marked in this way it will produce a bright flickering image—like a hologram—whenever the light striking it changes, such as when someone walks between a light source and the object.

In addition to being difficult to duplicate, as are some quantum cash proposals, anti-counterfeiting marks have to be mass produced. Unfortunately, using an electron beam to carve out nanostructures in purse clasps doesn’t seem to lend itself to economies of scale.

However, the team at NanoTech Security argues that only creating the initial master is difficult and time consuming. After the master has been created, the pattern can be duplicated in a roll-to-roll process. But the roll-to-roll process cannot be executed without the master, thwarting any other duplication attempts.

The Vancouver-based company has been spent the last several years refining their processes to the point where the company has shipped its first masters and expects to see products using the technique in 2013.

The key for any counterfeiting technology is finding the price point at which their added-value technique does not add so much to the product’s cost that it scares away buyers. Based on that understanding, it should be interesting to see the value of the products that first adopt the technology.

Photo: Didier Descouens/Wikipedia

Nanoparticles Combined with Light Reverses Rusting

Research out of the University of Michigan may have developed a method for reversing the process of rusting. But perhaps the more important potential for the development, which involves exposing copper nanoparticles to high-intensity light, will be its ability to create propylene oxide, a precursor for making many plastics.

Researchers have frequently been turning to nanomaterials to serve as catalysts for speeding up a number of industrial chemical processes—as well as other smaller scale reactions, such as those found in fuel cells—because the nanoscale of the particles creates more surface area and therefore makes them more reactive. It’s similar to cubes of sugar compared to granulated sugar. If you put two cubes of sugar on a table and then place the equivalent amount of the granulated version next to it, the latter would take up much more surface area on your table—and mix into your tea and coffee much more quickly.

For this reason, there’s been a fair amount of research into developing nanocatalysts that will improve the petrochemical process of producing plastic precursors. Just last year researchers at Utrecht University and Dow Chemical Company developed a nanocatalyst for creating the lower olefins ethylene and propylene at large petrochemical plants, both precursors in the production of plastics.

The work of the University of Michigan researchers was in this vein, but a little bit different. They were trying to develop a catalyst that would get propylene and oxygen to form propylene oxide in a direct reaction. Attempts to develop such a catalyst were falling into that unattainable-quest category of a “Holy Grail”. But sometimes the knights find the Holy Grail.

The researchers started by looking at the frustratingly promising use of metallic copper. While metallic copper did possess the electronic structure that would create the pathways for forming propylene oxide, it also tended to react with oxygen creating copper oxide, which is a poor catalyst.

To overcome this, the Michigan team structured the metallic copper into nanoparticles and dusted them with clear silica while combining them with propylene and oxygen gas. The results were encouraging, but still only capable of converting 20 percent of the gas into propylene oxide.

The eureka moment came when they exposed the reaction to high intensity light and suddenly they were able to convert 50 percent of the gas into propylene oxide.

"To our knowledge, this is the first time anyone has shown that light can be used to switch the oxidation state from an oxide to a metallic state," said Michigan's Marimuthu Andiappan in a press release.

It is unlikely that this research foretells of a future in which we can reverse the rust forming on our cars. However, it does promise to alter an array of industrial processes beyond propylene oxide production that involve changing the oxidation state, such as the production of compact discs or in electrochemical cells.

Photo: Joseph Xu/Michigan Engineering Communications & Marketing

Graphene Hybrid Material Comes to the Rescue of Li-ion Battery-Powered Vehicles

Researchers at Rice University believe a hybrid material they have developed combining vanadium oxide (VO2) and graphene could revitalize the use of lithium-ion (Li-ion) batteries for powering all-electric vehicles.

While Li-ion batteries for hybrid vehicles have enabled that car segment to grow rapidly over the years, the all-electric vehicle has languished as a niche market. This is in large part because Li-ion batteries just don’t have the charge life or short recharging capabilities for them to make sense for most people’s driving habits.  The demise of companies that have developed nanomaterials for Li-ion batteries in all-electric vehicles, like A123 Systems and Ener1, underscores just how difficult it has been to get Li-ion batteries to perform at levels necessary to make electric vehicles to take a stronger foothold in the market.

To address this shortcoming, Pulickel Ajayan, professor of engineering at Rice, and his team turned to the well-characterized use of VO2 for cathodes because of their high energy and power density. While vanadium pentoxide has been used in Li-ion batteries, oxides have not been so readily adopted because they have a low electrical conductivity that translates into slow charge and discharge rates.

Ajayan and his team overcame this problem by essentially baking graphene into the VO2, a process that imparted graphene’s high electrical conductivity into the ribbon-like hybrid material that makes up the cathodes. The graphene is able to pass its conductivity to the hybrid material even though the VO2 accounts for 84 percent of the cathode’s overall weight.

The challenge for the researchers was finding the right method for "baking" the graphene into the VO2. In a process described in the journal Nano Letters, the researchers suspended graphene oxide nanosheets along with vanadium pentoxide in water and then heated the suspension for hours in an autoclave. The result was that the vanadium pentoxide had been reduced into vanadium oxide and had taken the form of crystallized ribbons, and the graphene oxide had been reduced to graphene. When characterized, the VO2 ribbons had a web-like coating of graphene and were about 10 nanometers thick, 600 nanometers wide, and tens of micrometers in length.

"These ribbons were the building blocks of the three-dimensional architecture," said Shubin Yang, lead author of the research, in a press release. "This unique structure was favorable for the ultrafast diffusion of both lithium ions and electrons during charge and discharge processes. It was the key to the achievement of excellent electrochemical performance."

As far as performance, the cathodes are capable of holding 204 milliamp hours of energy per gram and remained stable after 200 cycles even at high temperatures (75 degrees Celsius).

"We think this is real progress in the development of cathode materials for high-power lithium-ion batteries," Ajayan said in the press release. "This is the direction battery research is going, not only for something with high energy density but also high power density. It’s somewhere between a battery and a supercapacitor."

Image: Rice University/Ajayan Group

Nanowires Could Enable Solar Cells to Surpass the Shockley-Queisser Limit

Researchers at the Nano-Science Center at the Niels Bohr Institut in Denmark and the Ecole Polytechnique Fédérale de Lausanne in Switzerland have developed a single nanowire prototype device that can concentrate sunlight up to 15 times its normal intensity.  The researchers believe that if the technology can be further developed, it could lead to photovoltaics (PVs) that can surpass what's known as the Shockley-Queisser limit.

The Shockley-Queisser limit has developed into a Holy-Grail quest for conversion efficiency of PVs.  As Hans J. Queisser commented on this blog: “Exactly on October 30, 1960, Shockley and I published this paper, which initially nobody quoted. Now, merely 50 years later, twice a week.”

As the term “limit” implies, the theory posited that only 33.7 percent of all the sun’s energy hitting a solar cell could be converted into electricity for solar cells with a single p-n junction.

Achieving, or even surpassing, the Shockley-Queisser limit would overcome one of the commercial problems PVs have faced in competing with fossil fuel energy: higher conversion efficiency. While PVs have seen their costs decrease by a factor of 20 between 1978 and 2008, the efficiencies have not risen quite as dramatically. Commercially available silicon crystal-based PVs are still stuck with conversion efficiencies only in the high teens.

Various nanomaterials have  promised both lower costs and higher efficiencies and in some cases the ability to surpass the Shockley-Queisser limit. However, some of these approaches have centered on the somewhat controversial ideas of electron multiplication and hot carrier cells. Electron multiplication involves making multiple electron-hole pairs for each incoming photon while with hot carrier cells the extra energy supplied by a photon that is usually lost as heat is exploited to make in higher-energy electrons which in turn leads to a higher voltage.

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Carbon Aerogel Supersponge Could Soak Up Oil Spills

Researchers in China claim to have produced the world’s lightest aerogel. The feather-like aerogel is synthesized from a combination of carbon nanotubes and graphene and weighs in at 0.16 milligrams per cubic centimeter, a sixth that of air.

Carbon nanotubes have been applied to the production of aerogels previously. However, instead of enabling an “invisibility cloak” as in previous research, the researchers at Zhejiang University in Hangzhou, China believe this aerogel, which they have dubbed “carbon aerogel," could be used as an environmental remediation tool for cleaning up oil spills.

While aerogels have long been proposed as a solution to cleaning up oil spills, actual commercial offerings of any nanotech-based method have been few and far between.

But it’s hard to dismiss the incredible capability of this latest aerogel to absorb organic solvents. Whereas current commercial oil-absorbent products are capable of soaking up to 10 times their own weight, this carbon aerogel is reported to be capable of absorbing 900 times its own weight. This translates into 1 gram of carbon aerogel absorbing 68.8 grams of organics per second, according to the researchers.

"Carbon aerogel is expected to play an important role in pollution control such as oil spill control, water purification and even air purification," said Professor Professor Gao Chao, one of the lead researchers in the project, in a press release.

The researchers have reported the development of their carbon aerogel in the journal Advanced Materials ("Multifunctional, Ultra-Flyweight, Synergistically Assembled Carbon Aerogels").

The Chinese scientists were able to reduce the weight of their aerogel to previous carbon-nanotube versions by using freeze-dried solutions to create the carbon aerogel. This eliminated any moisture that may have been on the carbon nanotubes and graphene, but still managed to maintain the characteristics that were needed for creating the aerogel.

In addition to reducing the weight of the aerogel, the freeze-dried approach lends itself more readily to mass production, according to Gao.

Despite improved avenues to mass production and significantly improved absorption capabilities, it’s easy to be skeptical about whether this technology will be available the next time there’s a catastrophic oil spill. Let’s hope commercialization efforts start sooner rather than later.

Photo:  Imaginechina/AP Photo

Graphene and Molybdenite Join Forces for a New Flash Memory

As noted here earlier this week, yet another attempt has been mounted to overthrow the non-volatile memory king: flash. It's easy to be skeptical; the landscape of non-volatile memory is littered with pretenders to the throne. One of the biggest reasons for this carnage has been flash memory's ability to consistently evolve into a more powerful memory storage medium than it had been originally.

Now researchers at École polytechnique fédérale de Lausanne (EPFL) in Switzerland have combined graphene, which has already been shown to be effective as a basis for flash memory, with molybdenum disulfide (MoSor molybdenite), which is developing into graphene’s biggest two-dimensional material rival, into a flash memory prototype with improved performance.

The research, which was published in the journal ACS Nano (“Nonvolatile Memory Cells Based on MoS2/Graphene Heterostructures”), builds on the work EPFL had done in using molybdenite to create a working transistor. Since the development of a working transistor, the EPFL team has continued to focus its attention on the two-dimensional material to explore its potential applications.

To demonstrate the versatility of molybdenite, the Swiss researchers have combined it with graphene to create a flash memory prototype that is at least theoretically capable of being faster and with greater power efficiency than conventional silicon designs.

"Combining these two materials enabled us to make great progress in miniaturization, and also using these transistors we can make flexible nanoelectronic devices," says Andras Kis, author of the study, in a press release.

The flash memory prototype was built around field-effect geometry that forms the basis of field-effect transistors (FETs) used in complementary metal-oxide semiconductor (CMOS) electronics. In this case, the Swiss researchers replaced the silicon that would make up the middle layer of the sandwich-like device with the molybdenite. Graphene electrodes reside beneath this layer of molybdenite to transmit electricity into the molybdenite. The top layer of the device is several layers of graphene, which capture electrical charge and thereby stores memory.

The researchers believe this architecture should make for a more efficient flash memory design. The graphene is a much better at conducting electricity than silicon and the molybdenite is more sensitive to charge because it is far thinner than silicon.

This is all pretty early-stage at this point, so it's understandable that reports on this research seem to lack any discussion of its potential for commercialization. It’s not clear that marrying graphene and molybdenum will keep flash memory the king of the hill, but at a minimum, the king may have enlisted some new allies.

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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.

 
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Dexter Johnson
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