Small Particles Show Big Promise In Beating Unpleasant Odors

There should be an image here!Scientists are reporting development of a new approach for dealing with offensive household and other odors — one that doesn’t simply mask odors like today’s room fresheners, but eliminates them at the source. Their research found that a deodorant made from nanoparticles — hundreds of times smaller than peach fuzz — eliminates odors up to twice as effectively as today’s gold standard. A report on these next-generation odor-fighters appears in ACS’ Langmuir, a bi-weekly journal.

Brij Moudgil and colleagues note that consumers use a wide range of materials to battle undesirable odors in clothing, on pets, in rooms, and elsewhere. Most common household air fresheners, for instance, mask odors with pleasing fragrances but do not eliminate the odors from the environment. People also apply deodorizing substances that absorb smells. These materials include activated carbon and baking soda. However, these substances tend to have only a weak ability to absorb the chemicals responsible for the odor.

The scientists describe development of a new material consisting of nanoparticles of silica (the main ingredient in beach sand) — each 1/50,000th the width of a human hair — coated with copper. That metal has well-established antibacterial and anti-odor properties, and the nanoparticles gave copper a greater surface area to exert its effects. Tests of the particles against ethyl mercaptan, the stuff that gives natural gas its unpleasant odor, showed that nanoparticles were up to twice as effective as the gold standard — activated carbon — at removing the material’s foul-smelling odor. In addition to fighting odors, the particles also show promise for removing sulfur contaminants found in crude oil and for fighting harmful bacteria, they add.

[Photo above by Steven Depolo / CC BY-ND 2.0]

Michael Bernstein @ American Chemical Society

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Batteries Smaller Than A Grain Of Salt

There should be an image here!Lithium-ion batteries have become ubiquitous in today’s consumer electronics — powering our laptops, phones, and iPods. Research funded by DARPA is pushing the limits of this technology and trying to create some of the tiniest batteries on Earth, the largest of which would be no bigger than a grain of sand.

These tiny energy storage devices could one day be used to power the electronics and mechanical components of tiny micro- to nano-scale devices.

Jane Chang, an engineer at the University of California, Los Angeles, is designing one component of these batteries: the electrolyte that allows charge to flow between electrodes. She presents her results today at the AVS 57th International Symposium & Exhibition, which takes place this week at the Albuquerque Convention Center in New Mexico.

“We’re trying to achieve the same power densities, the same energy densities as traditional lithium ion batteries, but we need to make the footprint much smaller,” says Chang.

To reach this goal, Chang is thinking in three dimensions in collaboration with Bruce Dunn other researchers at UCLA. She’s coating well-ordered micro-pillars or nano-wires — fabricated to maximize the surface-to-volume ratio, and thus the potential energy density — with electrolyte, the conductive material that allows current to flow in a battery.

Using atomic layer deposition — a slow but precise process that allows layers of material only an atom thick to be sprayed on a surface — she has successfully applied the solid electrolyte lithium aluminosilicate to these nanomaterials.

The research is still in its early stages: other components of these 3D microbatteries, such as the electrodes, have also been developed, but they have yet to be assembled and integrated to make a functioning battery.

[Photo above by Kevin Dooley / CC BY-ND 2.0]

Jason Socrates Bardi @ American Institute of Physics

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Way Paved For Graphene-Based Spin Computer

There should be an image here!Physicists at the University of California, Riverside have taken an important step forward in developing a “spin computer” by successfully achieving “tunneling spin injection” into graphene.

An electron can be polarized to have a directional orientation, called “spin.” This spin comes in two forms — electrons are said to be either “spin up” or “spin down” — and allows for more data storage than is possible with current electronics.

Spin computers, when developed, would utilize the electron’s spin state to store and process vast amounts of information while using less energy, generating less heat and performing much faster than conventional computers in use today.

Tunneling spin injection is a term used to describe conductivity through an insulator. Graphene, brought into the limelight by this year’s Nobel Prize in physics, is a single-atom-thick sheet of carbon atoms arrayed in a honeycomb pattern. Extremely strong and flexible, it is a good conductor of electricity and capable of resisting heat.

“Graphene has among the best spin transport characteristics of any material at room temperature,” explained Roland Kawakami, an associate professor of physics and astronomy, who led the research team, “which makes it a promising candidate for use in spin computers. But electrical spin injection from a ferromagnetic electrode into graphene is inefficient. An even greater concern is that the observed spin lifetimes are thousands of times shorter than expected theoretically. We would like longer spin lifetimes because the longer the lifetime, the more computational operations you can do.”

To address these problems, in the lab Kawakami and colleagues inserted a nanometer-thick insulating layer, known as a “tunnel barrier,” in between the ferromagnetic electrode and the graphene layer. They found that the spin injection efficiency increased dramatically.

“We found a 30-fold increase in the efficiency of how spins were being injected by quantum tunneling across the insulator and into graphene,” said Kawakami, who is also a member of UC Riverside’s Center for Nanoscale Science and Engineering. “Equally interesting is that the insulator was operating like a one-way valve, allowing electron flow in one direction — from the electrode to graphene — but not the other. The insulator helps to keep the injected spin inside the graphene, which is what leads to high spin injection efficiency. This counterintuitive result is the first demonstration of tunneling spin injection into graphene. We now have world record values for spin injection efficiency into graphene.”

Study results appear this week in Physical Review Letters.

In their experiments, the Kawakami lab also made an unexpected discovery that explains short spin lifetimes of electrons in graphene that have been reported by other experimental researchers.

Kawakami explained that spin lifetimes are typically investigated through an experiment, known as a Hanle measurement, which uses a ferromagnetic spin detector to monitor the electron spins in graphene as they change direction in an external magnetic field. When his team placed a tunnel barrier in between the ferromagnetic spin detector and the graphene, the spin lifetime from the Hanle measurement jumped up to about 500 picoseconds (compared to typical values of 100 picoseconds) even though the researchers did nothing different to the graphene itself.

“People usually assume that the Hanle measurement accurately measures the spin lifetime, but this result shows that it severely underestimates the spin lifetime when the ferromagnet is touching the graphene,” said Wei Han, the first author of the research paper and a graduate student in Kawakami’s lab. “This is good news because it means the true spin lifetime in graphene must be longer than reported previously — potentially a lot longer.”

Kawakami explained that, theoretically, graphene has the potential for extremely long spin lifetimes.

“This lifetime could be microseconds long,” he said. “A long lifetime is a special property of graphene, making it a very attractive material for a spin computer.”

Growing insulating barriers on graphene is neither a simple nor easy process. The insulator tends to form clumps on the graphene sheet, due in part to graphene’s reluctance to form strong bonds with materials. To circumvent the problem of clumping, in their experiments the Kawakami team layered the graphene sheet with titanium (about half an atom thick) using a method called molecular beam epitaxy. The titanium layer, the researchers found, prevented the insulator from clumping on graphene or sliding off it.

Next in the research, the Kawakami lab plans to demonstrate a working spin logic device

Han, a recipient of the Leo Falicov Award from the American Vacuum Society, and Kawakami were joined in the study by Kyle Pi, Kathy McCreary, Yan Li, Jared Wong, and Adrian Swartz of UCR. Grants to Kawakami from the National Science Foundation and the Office of Naval Research supported the study.

Iqbal Pittalwala @ UC Riverside

Tiny Generators Turn Waste Heat Into Power

There should be an image here!The second law of thermodynamics is a big hit with the beret-wearing college crowd because of its implicit existential crunch. The tendency of a closed systems to become increasingly disordered if no energy is added or removed is a popular, if not depressing, “things fall apart” sort-of-law that would seem to confirm the adolescent experience.

Now a joint team of Ukrainian and American scientists has demanded more work and less poetry from the second law of thermodynamics, proposing a novel “pyroelectric” method to power tiny devices using waste heat.

Using tiny structures called ferroelectric nanowires, they can rapidly generate an electrical current in response to any change in the ambient temperature, harvesting otherwise wasted energy from thermal fluctuations. Their report appears in the Journal of Applied Physics, which is published by the American Institute of Physics.

Explains lead researcher Anna Morozovska of the National Academy of Sciences of Ukraine, “The second law of thermodynamics rules modern life: Through all kinds of industry, humans consistently produce an enormous amount of waste heat. However, the laws of thermodynamics do not exclude rescuing some of this energy by harvesting the thermal fluctuations to produce electricity.”

Pyroelectrictricity can play key role in consumer electronics, says Morozovska, and recovering this heat in the form of pyroelectric energy may bring about a new era of “tiny energy.” Pyroelectric nanogenerators could be extremely useful for powering specific tasks in biological applications, medicine and nanotechnology, particularly in space because they perform well in low temperatures.

In an investigation of the pyroelectric properties of ferroelectric nanowires, the team analyzed how the pyroelectric coefficient corresponds to the radius of the wire and its coupling. They found that the smaller the wire radius, the more the pyroelectric coefficient diverges until a critical radius at which the response changes to paraelectric (above the Curie temperature). This so-called “size effect” could be used to tune the phase transition temperatures in ferroelectric nanostructures, thus enabling a system with a large, tunable, pyroelectric response.

In theory, the use of rectifying contacts could enable the polarized ferroelectric nanowire to generate a giant, pyroelectric, direct current and voltage in response to temperature fluctuations that could be harvested and detected using a bolometric detector. Such a nanoscale device would not contain any moving parts and could be suitable for long-term operation in ambient applications such as in-vitro biological systems and outer space. The researchers calculate that these little nanogenerators would have very high efficiency at low temperatures, decreasing at warmer temperatures.

The article, “Pyroelectric response of ferroelectric nanowires: Size effect and electric energy harvesting” by Anna N. Morozovska, Eugene A. Eliseev, George S. Svechnikov, and Sergei V. Kalinin appears in the Journal of Applied Physics.

[Photo above by benmckune / CC BY-ND 2.0]

Jason Bardi @ American Institute of Physics

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Caltech Researchers Design A New Nanomesh Material

There should be an image here!Computers, light bulbs, and even people generate heat — energy that ends up being wasted. With a thermoelectric device, which converts heat to electricity and vice versa, you can harness that otherwise wasted energy. Thermoelectric devices are touted for use in new and efficient refrigerators, and other cooling or heating machines. But present-day designs are not efficient enough for widespread commercial use or are made from rare materials that are expensive and harmful to the environment.

Researchers at the California Institute of Technology (Caltech) have developed a new type of material — made out of silicon, the second most abundant element in Earth’s crust — that could lead to more efficient thermoelectric devices. The material — a type of nanomesh — is composed of a thin film with a grid-like arrangement of tiny holes. This unique design makes it difficult for heat to travel through the material, lowering its thermal conductivity to near silicon’s theoretical limit. At the same time, the design allows electricity to flow as well as it does in unmodified silicon.

“In terms of controlling thermal conductivity, these are pretty sophisticated devices,” says James Heath, the Elizabeth W. Gilloon Professor and professor of chemistry at Caltech, who led the work. A paper about the research will be published in the October issue of the journal Nature Nanotechnology.

A major strategy for making thermoelectric materials energy efficient is to lower the thermal conductivity without affecting the electrical conductivity, which is how well electricity can travel through the substance. Heath and his colleagues had previously accomplished this using silicon nanowires — wires of silicon that are 10 to 100 times narrower than those currently used in computer microchips. The nanowires work by impeding heat while allowing electrons to flow freely.

In any material, heat travels via phonons — quantized packets of vibration that are akin to photons, which are themselves quantized packets of light waves. As phonons zip along the material, they deliver heat from one point to another. Nanowires, because of their tiny sizes, have a lot of surface area relative to their volume. And since phonons scatter off surfaces and interfaces, it is harder for them to make it through a nanowire without bouncing astray. As a result, a nanowire resists heat flow but remains electrically conductive.

But creating narrower and narrower nanowires is effective only up to a point. If the nanowire is too small, it will have so much relative surface area that even electrons will scatter, causing the electrical conductivity to plummet and negating the thermoelectric benefits of phonon scattering.

To get around this problem, the Caltech team built a nanomesh material from a 22-nanometer-thick sheet of silicon. (One nanometer is a billionth of a meter.) The silicon sheet is converted into a mesh — similar to a tiny window screen — with a highly regular array of 11- or 16-nanometer-wide holes that are spaced just 34 nanometers apart.

Instead of scattering the phonons traveling through it, the nanomesh changes the way those phonons behave, essentially slowing them down. The properties of a particular material determine how fast phonons can go, and it turns out that — in silicon at least — the mesh structure lowers this speed limit. As far as the phonons are concerned, the nanomesh is no longer silicon at all. “The nanomesh no longer behaves in ways typical of silicon,” says Slobodan Mitrovic, a postdoctoral scholar in chemistry at Caltech. Mitrovic and Caltech graduate student Jen-Kan Yu are the first authors on the Nature Nanotechnology paper.

When the researchers compared the nanomesh to the nanowires, they found that — despite having a much higher surface-area-to-volume ratio — the nanowires were still twice as thermally conductive as the nanomesh. The researchers suggest that the decrease in thermal conductivity seen in the nanomesh is indeed caused by the slowing down of phonons, and not by phonons scattering off the mesh’s surface. The team also compared the nanomesh to a thin film and to a grid-like sheet of silicon with features roughly 100 times larger than the nanomesh; both the film and the grid had thermal conductivities about 10 times higher than that of the nanomesh.

Although the electrical conductivity of the nanomesh remained comparable to regular, bulk silicon, its thermal conductivity was reduced to near the theoretical lower limit for silicon. And the researchers say they can lower it even further. “Now that we’ve showed that we can slow the phonons down,” Heath says, “who’s to say we can’t slow them down a lot more?”

The researchers are now experimenting with different materials and arrangements of holes in order to optimize their design. “One day, we might be able to engineer a material where you not only can slow the phonons down, but you can exclude the phonons that carry heat altogether,” Mitrovic says. “That would be the ultimate goal.”

Kathy Svitil @ California Institute of Technology

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Nano-Architectured Aluminum Has Steely Strength

There should be an image here!A North Carolina State University researcher and colleagues have figured out a way to make an aluminum alloy, or a mixture of aluminum and other elements, just as strong as steel.

That’s important, says Dr. Yuntian Zhu, professor of materials science and engineering and the NC State researcher involved in the project, because the search for ever lighter — yet stronger — materials is crucial to devising everything from more fuel-efficient cars to safer airplanes.

In a paper published in the journal Nature Communications, Zhu and his colleagues describe the new nanoscale architecture within aluminum alloys that have unprecedented strength but also reasonable plasticity to stretch and not break under stress. Perhaps even more importantly, the technique of creating these nanostructures can be used on many different types of metals.

Zhu says the aluminum alloys have unique structural elements that, when combined to form a hierarchical structure at several nanoscale levels, make them super-strong and ductile.

The aluminum alloys have small building blocks, called “grains,” that are thousands of times smaller than the width of a human hair. Each grain is a tiny crystal less than 100 nanometers in size. Bigger is not better in materials, Zhu says, as smaller grains result in stronger materials.

Zhu also says the aluminum alloys have a number of different types of crystal “defects.” Nanocrystals with defects are stronger than perfect crystals.

Now, Zhu plans on working on strengthening magnesium, a metal that is even lighter than aluminum. He’s collaborating with the Department of Defense on a project to make magnesium alloys strong enough to be used as body armor for soldiers.

Zhu’s colleagues on the Nature Communications paper are affiliated with the University of Sydney in Australia; the University of California, Davis; and Ufa State Aviation Technical University in Russia.

The Department of Materials Science and Engineering is part of NC State’s College of Engineering.

[Photo above by EraPhernalia Vintage / CC BY-ND 2.0]

Dr. Yuntian Zhu @ North Carolina State University

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High-Speed Filter Uses Electrified Nanostructures To Purify Water At Low Cost

There should be an image here!By dipping plain cotton cloth in a high-tech broth full of silver nanowires and carbon nanotubes, Stanford researchers have developed a new high-speed, low-cost filter that could easily be implemented to purify water in the developing world.

Instead of physically trapping bacteria as most existing filters do, the new filter lets them flow on through with the water. But by the time the pathogens have passed through, they have also passed on, because the device kills them with an electrical field that runs through the highly conductive “nano-coated” cotton.

In lab tests, over 98 percent of Escherichia coli bacteria that were exposed to 20 volts of electricity in the filter for several seconds were killed. Multiple layers of fabric were used to make the filter 2.5 inches thick.

“This really provides a new water treatment method to kill pathogens,” said Yi Cui, an associate professor of materials science and engineering. “It can easily be used in remote areas where people don’t have access to chemical treatments such as chlorine.”

Cholera, typhoid and hepatitis are among the waterborne diseases that are a continuing problem in the developing world. Cui said the new filter could be used in water purification systems from cities to small villages.

Faster filtering by letting bacteria through

Filters that physically trap bacteria must have pore spaces small enough to keep the pathogens from slipping through, but that restricts the filters’ flow rate.

Since the new filter doesn’t trap bacteria, it can have much larger pores, allowing water to speed through at a more rapid rate.

“Our filter is about 80,000 times faster than filters that trap bacteria,” Cui said. He is the senior author of a paper describing the research that will be published in an upcoming issue of Nano Letters. The paper is available online now.

The larger pore spaces in Cui’s filter also keep it from getting clogged, which is a problem with filters that physically pull bacteria out of the water.

Cui’s research group teamed with that of Sarah Heilshorn, an assistant professor of materials science and engineering, whose group brought its bioengineering expertise to bear on designing the filters.

Silver has long been known to have chemical properties that kill bacteria. “In the days before pasteurization and refrigeration, people would sometimes drop silver dollars into milk bottles to combat bacteria, or even swallow it,” Heilshorn said.

Cui’s group knew from previous projects that carbon nanotubes were good electrical conductors, so the researchers reasoned the two materials in concert would be effective against bacteria. “This approach really takes silver out of the folk remedy realm and into a high-tech setting, where it is much more effective,” Heilshorn said.

Using the commonplace keeps costs down

But the scientists also wanted to design the filters to be as inexpensive as possible. The amount of silver used for the nanowires was so small the cost was negligible, Cui said. Still, they needed a foundation material that was “cheap, widely available and chemically and mechanically robust.” So they went with ordinary woven cotton fabric.

“We got it at Wal-mart,” Cui said.

To turn their discount store cotton into a filter, they dipped it into a solution of carbon nanotubes, let it dry, then dipped it into the silver nanowire solution. They also tried mixing both nanomaterials together and doing a single dunk, which also worked. They let the cotton soak for at least a few minutes, sometimes up to 20, but that was all it took.

The big advantage of the nanomaterials is that their small size makes it easier for them to stick to the cotton, Cui said. The nanowires range from 40 to 100 billionths of a meter in diameter and up to 10 millionths of a meter in length. The nanotubes were only a few millionths of a meter long and as narrow as a single billionth of a meter. Because the nanomaterials stick so well, the nanotubes create a smooth, continuous surface on the cotton fibers. The longer nanowires generally have one end attached with the nanotubes and the other end branching off, poking into the void space between cotton fibers.

“With a continuous structure along the length, you can move the electrons very efficiently and really make the filter very conducting,” he said. “That means the filter requires less voltage.”

Minimal electricity required

The electrical current that helps do the killing is only a few milliamperes strong – barely enough to cause a tingling sensation in a person and easily supplied by a small solar panel or a couple 12-volt car batteries. The electrical current can also be generated from a stationary bicycle or by a hand-cranked device.

The low electricity requirement of the new filter is another advantage over those that physically filter bacteria, which use electric pumps to force water through their tiny pores. Those pumps take a lot of electricity to operate, Cui said.

In some of the lab tests of the nano-filter, the electricity needed to run current through the filter was only a fifth of what a filtration pump would have needed to filter a comparable amount of water.

The pores in the nano-filter are large enough that no pumping is needed – the force of gravity is enough to send the water speeding through.

Although the new filter is designed to let bacteria pass through, an added advantage of using the silver nanowire is that if any bacteria were to linger, the silver would likely kill it. This avoids biofouling, in which bacteria form a film on a filter. Biofouling is a common problem in filters that use small pores to filter out bacteria.

Cui said the electricity passing through the conducting filter may also be altering the pH of the water near the filter surface, which could add to its lethality toward the bacteria.

Cui said the next steps in the research are to try the filter on different types of bacteria and to run tests using several successive filters.

“With one filter, we can kill 98 percent of the bacteria,” Cui said. “For drinking water, you don’t want any live bacteria in the water, so we will have to use multiple filter stages.”

Cui’s research group has gained attention recently for using nanomaterials to build batteries from paper and cloth.

[Photo above by Snap / CC BY-ND 2.0]

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"Greening" Your Flat Screen TV

There should be an image here!Electronic products pollute our environment with a number of heavy metals before, during and after they’re used. In the U.S. alone, an estimated 70% of heavy metals in landfill come from discarded electronics. With flat screen TVs getting bigger and cheaper every year, environmental costs continue to mount.

To counter this, a new Tel Aviv University solution applies a discovery in nano-technology, based on self-assembled peptide nanotubes, to “green” the optics and electronics industry. Researchers Nadav Amdursky and Prof. Gil Rosenman of Tel Aviv University’s Department of Electrical Engineering say their technology could make flat screen TV production green and can even make medical equipment — like subcutaneous ultrasound devices — more sensitive.

Inspired by a biomaterial involved in Alzheimer’s disease research discovered by Prof. Ehud Gazit of the university’s Department of Microbiology and Biotechnology, the scientists developed a new nano-material, applying the scientific disciplines of both biology and physics. This biological material is the basis for their new, environmentally-friendly variety of light-emitting diodes (LED) used in both consumer and medical electronics.

TV in a test tube?

Their new invention is more than a clean, green way to create light, the researchers say. It also generates a strong signal that can be used in other applications in the nano-world of motors, actuators and ultrasound.

“We are growing our own light sources,” says Amdursky, a doctoral student working under Prof. Rosenman’s supervision. The organic nano-lightsticks he and his supervisors have developed using organic chemistry are made from carbon, making them cheap as well as environmentally friendly.

Unlike conventional light sources, the biologically-derived light source has a nano-scale architecture, easing the integration into light-emitting devices such as LED TVs and improving the resolution of the picture as well. The Tel Aviv University team has recently written a patent to cover their “organic LED” lights.

From living rooms to hospital rooms

According to Amdursky, the light emitted by the new light sticks is not appreciably different than that which emanates from today’s inorganically engineered LED lights.

“We don’t need a special plant, bacterium or a big machine to grow these structures in,” says Amdursky, who says the applications of the technology are wider than the widest screen television. The core technology and structures, described in Advanced Materials, Nano Letters, and ACS Nano, exhibit “piezoelectric characteristics,” necessary for the development of tiny nano-ultrasound machines that could scan cells from inside the body. Piezoelectric motors or actuators are only dozens of nanometers wide, which can lead to their application in energy harvesting systems as super-capacitors — large energy storage devices, necessary for the solar energy and wind energy business.

George Hunka @ American Friends of Tel Aviv University

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The Nano World Of Shrinky Dinks

There should be an image here!The magical world of Shrinky Dinks — an arts and crafts material used by children since the 1970s — has taken up residence in a Northwestern University laboratory. A team of nanoscientists is using the flexible plastic sheets as the backbone of a new inexpensive way to create, test and mass-produce large-area patterns on the nanoscale.

“Anyone needing access to large-area nanoscale patterns on the cheap could benefit from this method,” said Teri W. Odom, associate professor of chemistry and Dow Chemical Company Research Professor in the Weinberg College of Arts and Sciences. Odom led the research. “It is a simple, low-cost and high-throughput nanopatterning method that can be done in any laboratory.”

Details of the solvent-assisted nanoscale embossing (SANE) method are published by the journal Nano Letters. The work also will appear as the cover story of the journal’s February 2011 issue.

The method offers unprecedented opportunities to manipulate the electronic, photonic and magnetic properties of nanomaterials. It also easily controls a pattern’s size and symmetry and can be used to produce millions of copies of the pattern over a large area. Potential applications include devices that take advantage of nanoscale patterns, such as solar cells, high-density displays, computers and chemical and biological sensors.

“No other existing nanopatterning method can both prototype arbitrary patterns with small separations and reproduce them over six-inch wafers for less than $100,” Odom said.

Starting with a single master pattern, the simple yet potentially transformative method can be used to create new nanoscale masters with variable spacings and feature sizes. SANE can increase the spacing of patterns up to 100 percent as well as decrease them down to 50 percent in a single step, merely by stretching or heating (shrinking) the polymer substrate (the Shrinky Dinks material). Also, SANE can reduce critical feature sizes as small as 45 percent compared to the master by controlled swelling of patterned polymer molds with different solvents. SANE works from the nanoscale to the macroscale.

Biologists, chemists and physicists who are not familiar with nanopatterning now can use SANE for research at the nanoscale. Those working on solar energy, data storage and plasmonics will find the method particularly useful, Odom said.

For example, in a plasmonics application, Odom and her research team used the patterning capabilities to generate metal nanoparticle arrays with continuously variable separations on the same substrate.

SANE offers a way to meet three grand challenges in nanofabrication from the same — and a single — master pattern: (1) creating programmable array densities, (2) reducing critical feature sizes, and (3) designing different and reconfigurable lattice symmetries over large areas and in a massively parallel manner.

[Photo above by bandita / CC BY-ND 2.0]

Megan Fellman @ Northwestern University

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Shape-Shifting Sheets Automatically Fold Into Multiple Shapes

There should be an image here!“More than meets the eye” may soon become more than just a tagline for a line of popular robotic toys.

Researchers at Harvard and MIT have reshaped the landscape of programmable matter by devising self-folding sheets that rely on the ancient art of origami.

Called programmable matter by folding, the team demonstrated how a single thin sheet composed of interconnected triangular sections could transform itself into a boat- or plane-shape — all without the help of skilled fingers.

Published in the online Early Edition of the Proceedings of the National Academy of Sciences (PNAS) during the week of June 28, lead authors Robert Wood, associate professor of electrical engineering at the Harvard School of Engineering and Applied Sciences (SEAS) and a core faculty member of the Wyss Institute for Biologically Inspired Engineering, and Daniela Rus, a professor in the Electrical Engineering and Computer Science department at MIT and co-director of the CSAIL Center for Robotics, envision creating “smart” cups that could adjust based upon the amount of liquid needed or even a “Swiss army knife” that could form into tools ranging from wrenches to tripods.

“The process begins when we first create an algorithm for folding,” explains Wood. “Similar to a set of instructions in an origami book, we determine, based upon the desired end shapes, where to crease the sheet.”

The sheet, a thin composite of rigid tiles and elastomer joints, is studded with thin foil actuators (motorized switches) and flexible electronics. The demonstration material contains twenty-five total actuators, divided into five groupings. A shape is produced by triggering the proper actuator groups in sequence.

To initiate the on-demand folding, the team devised a series of stickers, thin materials that contain the circuitry able to prompt the actuators to make the folds. This can be done without a user having to access a computer, reducing “programming” to merely placing the stickers in the appropriate places. When the sheet receives the proper jolt of current, it begins to fold, staying in place thanks to magnetic closures.

“Smart sheets are Origami Robots that will make any shape on demand for their user,” says Rus. “A big achievement was discovering the theoretical foundations and universality of folding and fold planning, which provide the brain and the decision making system for the smart sheet.”

The fancy folding techniques were inspired in part by the work of co-author Erik Dermaine, an associate professor of electrical engineering and computer science at MIT and one of the world’s most recognized experts on computational origami.

While the Harvard and MIT engineers only demonstrated two simple shapes, the proof of concept holds promise. The long-term aim is to make programmable matter more robust and practical, leading to materials that can perform multiple tasks, such as an entire dining utensil set derived from one piece of foldable material.

“The Shape-Shifting Sheets demonstrate an end-to-end process that is a first step towards making everyday objects whose mechanical properties can be programmed,” concludes Wood.

Michael Patrick Rutter @ Harvard University

[awsbullet:Creative Leaps That Shaped the World]

Using Carbon Nanotubes In Lithium Batteries Can Dramatically Improve Energy Capacity

There should be an image here!Batteries might gain a boost in power capacity as a result of a new finding from researchers at MIT. They found that using carbon nanotubes for one of the battery’s electrodes produced a significant increase — up to tenfold — in the amount of power it could deliver from a given weight of material, compared to a conventional lithium-ion battery. Such electrodes might find applications in small portable devices, and with further research might also lead to improved batteries for larger, more power-hungry applications.

To produce the powerful new electrode material, the team used a layer-by-layer fabrication method, in which a base material is alternately dipped in solutions containing carbon nanotubes that have been treated with simple organic compounds that give them either a positive or negative net charge. When these layers are alternated on a surface, they bond tightly together because of the complementary charges, making a stable and durable film.

The findings, by a team led by Associate Professor of Mechanical Engineering and Materials Science and Engineering Yang Shao-Horn, in collaboration with Bayer Chair Professor of Chemical Engineering Paula Hammond, are reported in a paper published June 20 in the journal Nature Nanotechnology. The lead authors are chemical engineering student Seung Woo Lee PhD ’10 and postdoctoral researcher Naoaki Yabuuchi.

Batteries, such as the lithium-ion batteries widely used in portable electronics, are made up of three basic components: two electrodes (called the anode, or negative electrode, and the cathode, or positive electrode) separated by an electrolyte, an electrically conductive material through which charged particles, or ions, can move easily. When these batteries are in use, positively charged lithium ions travel across the electrolyte to the cathode, producing an electric current; when they are recharged, an external current causes these ions to move the opposite way, so they become embedded in the spaces in the porous material of the anode.

In the new battery electrode, carbon nanotubes — a form of pure carbon in which sheets of carbon atoms are rolled up into tiny tubes — “self-assemble” into a tightly bound structure that is porous at the nanometer scale (billionths of a meter). In addition, the carbon nanotubes have many oxygen groups on their surfaces, which can store a large number of lithium ions; this enables carbon nanotubes for the first time to serve as the positive electrode in lithium batteries, instead of just the negative electrode.

This “electrostatic self-assembly” process is important, Hammond explains, because ordinarily carbon nanotubes on a surface tend to clump together in bundles, leaving fewer exposed surfaces to undergo reactions. By incorporating organic molecules on the nanotubes, they assemble in a way that “has a high degree of porosity while having a great number of nanotubes present,” she says.

Lithium batteries with the new material demonstrate some of the advantages of both capacitors, which can produce very high power outputs in short bursts, and lithium batteries, which can provide lower power steadily for long periods, Lee says. The energy output for a given weight of this new electrode material was shown to be five times greater than for conventional capacitors, and the total power delivery rate was 10 times that of lithium-ion batteries, the team says. This performance can be attributed to good conduction of ions and electrons in the electrode, and efficient lithium storage on the surface of the nanotubes.

In addition to their high power output, the carbon nanotube electrodes showed very good stability over time. After 1,000 cycles of charging and discharging a test battery, there was no detectable change in the material’s performance.

The electrodes the team produced had thicknesses up to a few microns, and the improvements in energy delivery only were seen at high-power output levels. In future work, the team aims to produce thicker electrodes and extend the improved performance to low-power outputs as well, they say. In its present form, the material might have applications for small, portable electronic devices, says Shao-Horn, but if the reported high power capability were demonstrated in a much thicker form — with thicknesses of hundreds of microns rather than just a few — it might eventually be suitable for other applications such as hybrid cars.

While the electrode material was produced by alternately dipping a substrate into two different solutions — a relatively time-consuming process — Hammond suggests that the process could be modified by instead spraying the alternate layers onto a moving ribbon of material, a technique now being developed in her lab. This could eventually open the possibility of a continuous manufacturing process that could be scaled up to high volumes for commercial production, and could also be used to produce thicker electrodes with a greater power capacity. “There isn’t a real limit” on the potential thickness, Hammond says. “The only limit is the time it takes to make the layers,” and the spraying technique can be up to 100 times faster than dipping, she says.

Lee says that while carbon nanotubes have been produced in limited quantities so far, a number of companies are currently gearing up for mass production of the material, which could help to make it a viable material for large-scale battery manufacturing.

Jennifer Hirsch @ Massachusetts Institute of Technology

[Photo above by evelynishere / CC BY-ND 2.0]

[awsbullet:Henry Schlesinger]

Researchers Capture First Images Of Sub-Nano Pore Structures

There should be an image here!Moore’s law marches on: In the quest for faster and cheaper computers, scientists have imaged pore structures in insulation material at sub-nanometer scale for the first time. Understanding these structures could substantially enhance computer performance and power usage of integrated circuits, say Semiconductor Research Corporation (SRC) and Cornell University scientists.

To help maintain the ever-increasing power and performance benefits of semiconductors — like the speed and memory trend described in Moore’s law — the industry has introduced very porous, low-dielectric constant materials to replace silicon dioxide as the insulator between nano-scaled copper wires. This has sped up the electrical signals sent along these copper wires inside a computer chip, and at the same time reduced power consumption.

“Knowing how many of the molecule-sized voids in the carefully-engineered Swiss cheese survive in an actual device will greatly affect future designs of integrated circuits,” said David Muller, Cornell University professor of applied and engineering physics, and co-director of Kavli Institute for Nanoscale Science at Cornell. “The techniques we developed look deeply, as well as in and around the structures, to give a much clearer picture so complex processing and integration issues can be addressed.”

The scientists understand that the detailed structure and connectivity of these nanopores have profound control on the mechanical strength, chemical stability and reliability of these dielectrics. With today’s announcement, researches now have a nearly atomic understanding of the three-dimensional pore structures of low-k materials required to solve these problems.

Welcome to the atomic world: SRC and Cornell researchers were able to devise a method to obtain 3-D images of the pores using electron tomography, leverages imaging advances used for CT scans and MRIs in the medical field, says Scott List, director of interconnect and packaging sciences at SRC, at Research Triangle Park, N.C. “Sophisticated software extracts 3-D images from a series of 2-D images taken at multiple angles. A 2-D picture is worth a thousand words, but a 3-D image at near atomic resolution gives the semiconductor industry new insights into scaling low-k materials for several additional technology nodes.”

Blaine Friedlander @ Cornell University

[Photo above by Père Ubu / CC BY-ND 2.0]

[awsbullet:Nanotechnology For Dummies]

How Nature's Colors Could Cut Bank Fraud

There should be an image here!Scientists have discovered a way of mimicking the stunningly bright and beautiful colours found on the wings of tropical butterflies. The findings could have important applications in the security printing industry, helping to make bank notes and credit cards harder to forge.

The striking iridescent colours displayed on beetles, butterflies and other insects have long fascinated both physicists and biologists, but mimicking nature’s most colourful, eye-catching surfaces has proved elusive.

This is partly because rather than relying on pigments, these colours are produced by light bouncing off microscopic structures on the insects’ wings.

Mathias Kolle, working with Professor Ullrich Steiner and Professor Jeremy Baumberg of the University of Cambridge, studied the Indonesian Peacock or Swallowtail butterfly (Papilio blumei), whose wing scales are composed of intricate, microscopic structures that resemble the inside of an egg carton.

Because of their shape and the fact that they are made up of alternate layers of cuticle and air, these structures produce intense colours.

Using a combination of nanofabrication procedures — including self-assembly and atomic layer deposition — Kolle and his colleagues made structurally identical copies of the butterfly scales, and these copies produced the same vivid colours as the butterflies’ wings.

According to Kolle: “We have unlocked one of nature’s secrets and combined this knowledge with state-of-the-art nanofabrication to mimic the intricate optical designs found in nature.”

“Although nature is better at self-assembly than we are, we have the advantage that we can use a wider variety of artificial, custom-made materials to optimise our optical structures.”

As well as helping scientists gain a deeper understanding of the physics behind these butterflies’ colours, being able to mimic them has promising applications in security printing.

“These artificial structures could be used to encrypt information in optical signatures on banknotes or other valuable items to protect them against forgery. We still need to refine our system but in future we could see structures based on butterflies wings shining from a £10 note or even our passports,” he says.

Intriguingly, the butterfly may also be using its colours to encrypt itself — appearing one colour to potential mates but another colour to predators.

Kolle explains: “The shiny green patches on this tropical butterfly’s wing scales are a stunning example of nature’s ingenuity in optical design. Seen with the right optical equipment these patches appear bright blue, but with the naked eye they appear green.

“This could explain why the butterfly has evolved this way of producing colour. If its eyes see fellow butterflies as bright blue, while predators only see green patches in a green tropical environment, then it can hide from predators at the same time as remaining visible to members of its own species.”

The results are published today in Nature Nanotechnology.

Becky Allen @ University of Cambridge

[Photo above by Vicki’s Nature / CC BY-ND 2.0]

[awsbullet:Q. David Bowers]

Applied Physicists Create Building Blocks For A New Class Of Optical Circuits

There should be an image here!Imagine creating novel devices with amazing and exotic optical properties not found in Nature — by simply evaporating a droplet of particles on a surface.

By chemically building clusters of nanospheres from a liquid, a team of Harvard researchers, in collaboration with scientists at Rice University, the University of Texas at Austin, and the University of Houston, has developed just that.

The finding, published in the May 28 issue of Science, demonstrates simple scalable devices that exhibit customizable optical properties suitable for applications ranging from highly sensitive sensors and detectors to invisibility cloaks. Using particles consisting of concentric metallic and insulating shells, Jonathan Fan, a graduate student at the Harvard School of Engineering and Applied Sciences (SEAS), his lead co-author Federico Capasso, Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at SEAS, and Vinothan Manoharan, Associate professor of Chemical Engineering and Physics at SEAS and Harvard’s Physics Department, devised a bottom-up, self-assembly approach to meet the design challenge.

“A longstanding challenge in optical engineering has been to find ways to make structures of size much smaller than the wavelength that exhibit desired and interesting properties,” says Fan. “At visible frequencies, these structures must be nanoscale.”

In contrast, most nanoscale devices are fabricated using top-down approaches, akin to how computer chips are manufactured. The smallest sizes that can be realized by such techniques are severely constrained by the intrinsic limits of the fabrication process, such as the wavelength of light used in the process. Moreover, such methods are restricted to planar geometries, are expensive, and require intense infrastructure such as cleanrooms.

“With our bottom-up approach, we mimic the way nature creates innovative structures, which exhibit extremely useful properties,” explains Capasso. “Our nanoclusters behave as tiny optical circuits and could be the basis of new technology such as detectors of single molecules, efficient and biologically compatible probes in cancer therapeutics, and optical tweezers to manipulate and sort out nano-sized particles. Moreover, the fabrication process is much simpler and cheaper to carry out.”

The researcher’s self-assembly method requires nothing more than a bit of mixing and drying. To form the clusters, the particles are first coated with a polymer, and a droplet of them is then evaporated on a water-repellent surface. In the process of evaporation, the particles pack together into small clusters. Using polymer spacers to separate the nanoparticles, the researchers were able to controllably achieve a two nanometer gap between the particles — far better resolution than traditional top-down methods allow.

Two types of resulting optical circuits are of considerable interest. A trimer, comprising three equally-spaced particles, can support a magnetic response, an essential property of invisibility cloaks and materials that exhibit negative refractive index.

“In essence, the trimer acts as a nanoscale resonator that can support a circulating loop of current at visible and near-infrared frequencies,” says Fan. “This structure functions as a nanoscale magnet at optical frequencies, something that natural materials cannot do.”

Heptamers, or packed seven particle structures, exhibit almost no scattering for a narrow range of well-defined colors or wavelengths when illuminated with white light. These sharp dips, known as Fano resonances, arise from the interference of two modes of electron oscillations, a “bright” mode and a non-optically active “dark” mode, in the nanoparticle.

“Heptamers are very efficient at creating extremely intense electric fields localized in nanometer-size regions where molecules and nanoscale particles can be trapped, manipulated, and detected. Molecular sensing would rely on detecting shifts in the narrow spectra dips,” says Capasso.

Ultimately, all of the self-assembled circuit designs can be readily tuned by varying the geometry, how the particles are separated, and the chemical environment. In short, the new method allows a “tool kit” for manipulating “artificial molecules” in such a way to create optical properties at will, a feature the researchers expect is broadly generalizable to a host of other characteristics.

Looking ahead, the researchers plan to work on achieving higher cluster yields and hope to assemble three-dimensional structures at the macroscale, a “holy grail” of materials science.

“We are excited by the potentially scalability of the method,” says Manoharan. “Spheres are the easiest shapes to assemble as they can be readily packed together. While we only demonstrated here planar particle clusters, our method can be extended to three-dimensional structures, something that a top-down approach would have difficulty doing.”

Michael Patrick Rutter @ Harvard University

[Photo above by Joost J. Bakker IJmuiden / CC BY-ND 2.0]

[awsbullet:Nanotechnology For Dummies]

New Spintronics Material Could Help Usher In Next Generation Of Microelectronics

As the electronics industry works toward developing smaller and more compact devices, the need to create new types of scaled-down semiconductors that are more efficient and use less power has become essential.

In a study to be published in the April issue of Nature Materials (currently available online), researchers from UCLA’s Henry Samueli School of Engineering and Applied Science describe the creation of a new material incorporating spintronics that could help usher in the next generation of smaller, more affordable and more power-efficient devices.

While conventional complementary metal-oxide semiconductors (CMOS), a technology used today in all types of electronics, rely on electrons’ charge to power devices, the emerging field of spintronics exploits another aspect of electrons — their spin, which could be manipulated by electric and magnetic fields.

“With the use of nanoscaled magnetic materials, spintronics or electronic devices, when switched off, will not have a stand-by power dissipation problem. With this advantage, devices with much lower power consumption, known as non-volatile electronics, can become a reality,” said the study’s corresponding author, Kang L. Wang, Raytheon Professor of Electrical Engineering at UCLA Engineering, whose team carried out the research. “Our approach provides a possible solution to address the critical challenges facing today’s microelectronics industry and sheds light on the future of spintronics.”

“We’ve built a new class of material with magnetic properties in a dilute magnetic semiconductor (DMS) system,” said Faxian Xiu, a UCLA senior researcher and lead author of the study. “Traditionally, it’s been really difficult to enhance the ferromagnetism of this material above room temperature. However in our work, by using a type of quantum structure, we’ve been able to push the ferromagnetism above room temperature.”

Ferromagnetism is the phenomenon by which certain materials form permanent magnets. In the past, the control of magnetic properties has been accomplished by applying an electric current. For example, passing an electric current will generate magnetic fields. Unfortunately, using electric currents poses significant challenges for reducing power consumption and for device miniaturization.

“You can think of a transformer, which passes a current to generate a magnetic field. This will have huge power dissipation (heat),” Xiu said. “In our study, we tried to modulate the magnetic properties of DMS without passing the current.”

Ferromagnetic coupling in DMS systems, the researchers say, could lead to a new breed of magneto-electronic devices that alleviate the problems related to electric currents. The electric field–controlled ferromagnetism reported in this study shows that without passing an electric current, electronic devices could be operated and functioning based on the collective spin behavior of the carriers. This holds great promise for building next-generation nanoscaled integrated chips with much lower power consumption.

To achieve the ferromagnetic properties, Kang’s group grew germanium dots on a silicon p-type substrate, creating quantum dots on top of the substrate. Silicon and germanium are ideal candidates because of their excellent compatibility and ability to be incorporated within conventional CMOS technology. The quantum dots, which are themselves semiconductors, would then be utilized in building new devices.

“To demonstrate possible applications of these fantastic quantum dots, we fabricated metal-oxide semiconductor devices and used these dots as the channel layer. By applying an electric field, we are able to control the hole concentration inside the dots and thus modulate their ferromagnetism,” Xiu said.

“This finding is significant in the sense that it opens up a completely new paradigm for next-generation microelectronics, which takes advantage of the spin properties of carriers, in addition to the existing charge transport as envisaged in the conventional CMOS technology.”

The key is to be able to use this material at room temperature.

“The material is not very useful if it doesn’t work at room temperature,” Wang said. “We want to be able to use it anywhere. In this work, we’ve achieved success on electric field–controlled ferromagnetism at 100 degrees Kelvin and are moving towards room temperature. We feel strongly that we’ll be able to accomplish this. Once we’ve achieved room-temperature controllability, we’ll be able to start building real devices to demonstrate its viability in non-volatile electronic devices.”

[Wileen Wong Kromhout @ University of California – Los Angeles]

[awsbullet:spintronics technology]