Butterfly wings behind anti-counterfeiting technology

(PhysOrg.com) -- Imagine a hole so small that air can't go through it, or a hole so small it can trap a single wavelength of light. Nanotech Security Corp., with the help of Simon Fraser University researchers, is using this type of nano-technology– 1,500 times thinner than a human hair and first of its kind in the world– to create unique anti-counterfeiting security features.

The technology is first being applied to banknotes but it also has many more practical applications, such as authenticating legal documents, retail merchandise, concert tickets, stock certificates, visas, passports, and pharmaceuticals.

SFU applied sciences grad Clint Landrock started the initial research into nanoholes under the guidance of SFU engineering science professor Bozena Kaminska. When the pair pitched their idea to Doug Blakeway, SFU Venture Connection’s entrepreneur in residence and also CEO and chairman of Nanotech, he was immediately intrigued by the technology’s potential.

“I love nanotechnology but I really have not seen a commercialization of it that can make you money in the near term,” said Blakeway.“When this was initially presented to me by Bozena and Clint, I immediately saw their vision and they were only after one application– creating anti-counterfeiting features for banknotes. I felt this could be the first commercial application of nanotechnology in the world. I kept thinking of applications for it and how it could be used; the technologies and potential astound me.”

Landrock and Kaminska both continue their work as part of Nanotech’s scientific team. The company’s Nano-Optic Technology for Enhanced Security (NOtES) product stems from an idea originating in the purest form of nature– insects using colorful markings to identify themselves.

How this works is microscopic gratings composed of nanostructures interact withlightto produce the shimmering iridescence seen on the Costa Rican morpho butterfly. The nanostructures act to reflect and refract light waves to produce the morpho’s signature blue wings and absorb other unwanted light.

The highly advanced wing structures are the result of many millennia of evolution, and only recently have Nanotech's scientists discovered how to reproduce these structures reliably. While others have talked about the possibility of re-creating it, Nanotech has made this a reality.

The U.S. Treasury, which produces up to 11 billion banknotes annually, is a potential customer for Nanotech’s product. The new U.S. $100 bill, designed with state-of-the art security features, was supposed to be introduced in February 2011 but it’s been delayed due to some manufacturing issues.

Banknotes contain several security features– some that you can plainly see and some that only machines can read– such as hologram strips, security threads woven into the paper, watermarks, color-shifting inks, raised type, and UV inks.

According to Blakeway, Nanotech’s product– which has attracted the attention of treasuries internationally– is superior to holograms and can’t be duplicated.

“Nobody has ever done this,” he said.“We have succeeded while everybody is still trying to duplicate or imitate a butterfly’s wing because it absorbs light and gives off the color. There’s no color pigment– there’s nothing like a dye or anything else. It’s a hole that traps light and releases color.

“You can’t copy or scan it in, you can’t inkjet it on paper, you can’t do any of these things. It’s extremely sophisticated and expensive to make the shims and dyes to produce, but very inexpensive to produce it at the end. Anywhere you can think of where a hologram is being used today, our technology can replace it. It’s more secure than a hologram. You can’t lift it off– we can put it onto metal, plastic, or paper.”

SFU Venture Connections offers training and support programs for SFU entrepreneurs. It links students, faculty and local entrepreneurs with experienced advisors and funding opportunities.

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Researchers develop unique combination of elements for thermal nanotape

Semiconductor Research Corporation (SRC) and researchers from Stanford University have developed a novel combination of elements that yields a unique nanostructure material for packaging. This advance should allow longer life for semiconductor devices while costing less than current state-of-the-art materials. In addition to chip manufacturers, several other industries could also gain greater product efficiencies from related thermal energy management technology.

Forsemiconductors, the improvement will come in the form of packaging for devices. Presently, manufacturers must rely on tiny pins or thick solder to bond sections of the semiconductor in order for the device to perform. However, current solder materials tend to degrade and fail due to heat andmechanical stress. In order to continue the scaling ofintegrated circuits, SRC and Stanford have researched materials that provide a high thermal connectivity— comparable to copper— with the flexible compliance of foam. The answer has been created through a nanostructured thermal tape that conducts heat like a metal while allowing the neighboring materials to expand and contract with temperature changes (metals are too stiff to allow this). This ability to reduce chip temperatures while remaining compliant is a key breakthrough for electronic packaging.

“A big roadblock to increasing the performance of modern chips is hot spots, or millimeter-sized regions of high power generation. This advance in nanostructured materials and methods will allow us to better cool these spots and serves as a key enabler for densification of computational circuitry,” said Professor Ken Goodson, lead researcher for SRC at Stanford University.“This can help packaging to withstand the demands of Moore’s Law.”

In addressing the challenges of miniaturization, the first line of defense for hot spots is the interface material. Incorporating nearly two decades of advanced research and simulations for problems at the packaging level— much of it funded by SRC— the Stanford team ultimately arrived at their unique combination of binder materials surrounding carbon nanotubes. This innovation is expected to facilitate the highest thermal conduction and the most desirable level of elasticity of any known packaging solutions.

“Researchers love to create useful materials and structures that we’ve never seen before, and this new thermal nanotape revolutionizes the chip’s heat sink contact,” said Jon Candelaria, director of Interconnect and Packaging Sciences at SRC.“Instead of being forced to rely upon the properties of just a single material, this combination gives the integrated circuits industry an opportunity to circumvent severe performance limitations and continue to improvepackagingwithout adding cost.”

While the research was funded by members of SRC to enhance computer chips, demand for applications of this kind of thermal interface also is rising in other industries. For instance, several automotive-related companies hope to recover electrical power from hot exhaust gases in cars and trucks using thermoelectric energy converters— enabling better fuel economy— but reliable interfaces are a problem for this technology. Professor Goodson leads a major grant from the National Science Foundation-Department of Energy Partnership on Thermoelectric Devices for Vehicle Applications, with the goal of transferring the SRC-funded interface work to vehicles.

Patents for the technology are pending. The next step in the research is to license the new methods and materials to advanced thermal-interface companies for perfection of the application. End users are expected to benefit from the technology by 2014.

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High-performance capacitor could lead to better rechargeable batteries

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(PhysOrg.com) -- In order to develop next-generation electric vehicles, solar energy systems, and other clean energy technologies, researchers need an efficient way to store the energy. One of the key energy storage devices for these applications and others is a supercapacitor, also called an electric double-layer capacitor. In a recent study, scientists have investigated the possibility of using a material called zeolite-templated carbon for the electrode in this type of capacitor, and found that the material’s unique pore structure greatly improves the capacitor's overall performance.

The researchers, Hiroyuki Itoi, Hirotomo Nishihara, Taichi Kogure, and Takashi Kyotani, from Tohoku University in Sendai, Japan, have published their results on the high-performance electric double-layer capacitor in a recent issue of theJournal of the American Chemical Society.

To store energy, the electric double-layer capacitor is charged by ions that migrate from a bulk solution to an electrode, where they are adsorbed. Before reaching the electrode’s surface, the ions have to travel through narrow nanopores as quickly and efficiently as possible. Basically, the quicker the ions can travel down these paths, the quicker the capacitor can be charged, resulting in a high rate performance. Also, the greater the adsorbed ion density in the electrode, the greater the charge that the capacitor can store, resulting in a high volumetric capacitance.

Recently, scientists have been testing materials with pores of various sizes and structures to try to achieve both quick ion transport and high adsorption ion density. But the two requirements are somewhat contradictory, since ions can travel more quickly through larger nanopores, but large nanopores make the electrode density low and thus decrease the adsorbed ion density.

“In this work, we have successfully demonstrated that it is possible to meet the two seemingly contradictory requirements, high power density and high volumetric capacitance, with zeolite-templated carbon,” Nishihara toldPhysOrg.com.

The zeolite-templated carbon consists of nanopores that are 1.2 nm in diameter (smaller than most electrode materials) and that have a very ordered structure (whereas other pores can be disordered and random). The nanopores’ small size makes the adsorbed ion density high, while the ordered structure– described as a diamond-like framework– allows the ions to quickly pass through the nanopores. In a previous study, the researchers showed that zeolite-templated carbon with nanopores smaller than 1.2 nm cannot enable fast ion transport, suggesting that this size may provide the optimal balance between high rate performance and high volumetric capacitance.

In tests, the zeolite-templated carbon’s properties exceeded those of other materials, demonstrating its potential to be used as an electrode for high-performance electric double-layer capacitors.

“We are now trying to further increase the energy density of the zeolite-templated carbon up to the same level of secondary batteries,” Nishihara said.“If such an electric double layercapacitoris developed and used for mobile devices, such as cellular phones, their charging time can be shortened to only a few minutes. Another important future application of electric double layer capacitors is a support of secondary batteries inelectric vehiclesto prolong the battery's lifetime. Also for this purpose, achieving a higherenergydensity is one of the key issues.”

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Atom-thick sheets unlock future technologies

(PhysOrg.com) -- A new way of splitting layered materials, similar to graphite, into sheets of material just one atom thick could lead to revolutionary new electronic and energy storage technologies.

An international team, led by Oxford University and Trinity College Dublin scientists, has invented a versatile method for creating these one-atom thick 'nanosheets' from a range of materials using mild ultrasonic pulses, like those generated by jewellery cleaning devices, and common solvents. The new method is simple, fast, and inexpensive, and could be scaled up to work on an industrial scale.

The team publish a report of the research in this week'sScience.

Each one-millimetre-thick layer of graphite is made up of around three million layers of graphene– a flat sheet of carbon one atom thick– stacked one on top of the other.

'Because of its extraordinary electronic properties graphene has been getting all the attention, including a recent Nobel Prize, as physicists hope that it might, one day, compete with silicon in electronics,' said Dr Valeria Nicolosi of Oxford University’s Department of Materials, who led the research with Professor Jonathan Coleman of Trinity College Dublin. 'But in fact there are hundreds of other layered materials that could enable us to create powerful new technologies.'

Professor Coleman, of Trinity College Dublin, said: 'These novel materials have chemical and electronic properties which are well suited for applications in new electronic devices, super-strong composite materials and energy generation and storage. In particular, this research represents a major breakthrough towards the development of efficient thermoelectric materials.'

There are over 150 of these exotic layered materials– such as Boron Nitride, Molybdenum disulfide, and Tungsten disulfide– that have the potential to be metallic, semi-metallic or semiconducting depending on their chemical composition and how their atoms are arranged.

For decades researchers have tried to create nanosheets of these kind of materials as arranging them in atom-thick layers would enable us to unlock their unusual electronic and thermoelectric properties. However, all previous methods were extremely time consuming and laborious and the resulting materials were fragile and unsuited to most applications.

'Our new method offers low-costs, a very high yield and a very large throughput: within a couple of hours, and with just 1 mg of material, billions and billions of one-atom-thick graphene-like nanosheets can be made at the same time from a wide variety of exotic layered materials,' said Dr Nicolosi.

Nanosheets created using this method can be sprayed onto the surface of other materials, such as silicon, to produce‘hybrid films’ which, potentially, enable their exotic abilities to be integrated with conventional technologies. Such films could be used to construct, among other things, new designs of computing devices, sensors or batteries.

A report of the research, 'Two-dimensional nanosheets produced by liquid exfoliation of layered materials', is published in the 4 February edition of the journalScience.

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Nano research fit for a king: Scientists test strength of composite bonds one nanotube at a time

(PhysOrg.com) -- Arthur pulled a sword from a stone, proving to a kingdom that right beats might. Researchers at Rice University are making the same point in the nanoscale realm.

In this case, the sword is a multiwalledcarbon nanotubeand the stone is a bead of epoxy.

Knowing precisely how much strength is needed to pull the nanotube from the bead is essential to materials scientists’ advancing the art of making stronger, lighter composites for everything from sporting goods to spacecraft.

A team led by Jun Lou, an assistant professor of mechanical engineering and materials science at Rice, and first author Yogeeswaran Ganesan, who recently earned his doctorate in Lou's lab, has published a paper in the American Chemical Society journal Applied Materials and Interfaces describing its work to measure the interface toughness of carbon nanotube-reinforced epoxy composites.

Lou, Ganesan and their colleagues have a second new paper inACS Nanoon using the same technique to measure the effect of nitrogen doping on the mechanical properties of carbon nanotubes.

Nanotubes are finding their way into products as manufacturers bank on their reputation for strength and lightness. One can buy baseball bats, tennis rackets and high-priced bicycles reinforced with nanotubes.

"Carbon nanotubes are so small (a strand of hair is 50,000 times wider) that in order to use them on the human scale, you have to do something to make them bigger,"Lou said.

One such way is to mix them into composites, an imperfect science that involves much trial and error since the possible strength of the interface between every type of nanotube and every type of base material is not well understood. Lou and his team intend to eliminate the guesswork with a way to measure important properties of a composite before the first batch is mixed.

"You don't want to spend a lot of time and money on a fancy chemical treatment without knowing what's happening at the critical interface,"Lou said.

Single-fiber pullout tests have been used since the early days of composite manufacturing to measure not only the strength of a bond but when, why and how it will break. That's hard on the nanoscale. Others have used atomic force microscopes as part of the pulling mechanism, but the method has its limitations, Lou said.

The Rice team has built a better device: a spring-loaded, push-pull micromechanical assembly on a silicon chip that allows researchers to string a multiwalled nanotube to a blanket of epoxy on one side while the other is held firmly in place with a platinum anchor. Pressing down on the spring applies equal force to both sides, allowing researchers to see just how much is needed to pull the tube from the epoxy.

The team reported in the first paper that forces binding multiwalled nanotubes to a general-purpose epoxy called Epon 828 were actually weaker than they expected."We have started to understand that adding nanotubes to bulk material doesn't always give you better properties,"Lou said."You have to be very careful about how you add them in and what kind interface they form."

Because batches of nanotubes tend to stick together, some manufacturers functionalize their surfaces to disperse them before mixing into a material."But that can disrupt the outer wall, and that's a bad thing,"Lou said."If you do something to make nanotubes easily dispersible but decrease their intrinsic strength, you're shooting yourself in the foot."

On the other hand, he said,"If manufacturers need a tough material that absorbs energy without breaking, a weaker interface may not be a bad thing. During this pullout process, there's a lot of friction at the interface of the nanotube and the matrix, and friction is effectively a way to dissipate energy."

Sometimes the end product is better if the nanotube stretches before it breaks. In theACS Nanopaper, the team compared the tensile strength of pristine versus nitrogen-doped multiwalled carbon nanotubes. They found the pristine tubes tend to snap in a brittle fashion, while nitrogen-doped tubes exhibit signs of plasticity --"necking"before they break.

That may be desirable for certain materials, Lou said."You don't build a bridge out of ceramic. You build it out of steel because of its plasticity.

"If we can develop a nanotube composite with room-temperature plasticity, it's going to be fantastic,"he said."It will find many, many uses."

Lou said Rice's versatile technique for carrying out nanomechanical experiments is poised to find many long-sought answers."Developing an ability to engineering nanocomposites with mechanical properties tailored for specific applications is the proverbial holy grail of all structural nanocomposite research,"Ganesan said."The technique essentially takes us one step closer to achieving this goal."

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Stanford scientists see the solar future, and it's all about 'nanodomes' and 'plasmonics'

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(PhysOrg.com) -- Stanford engineers have succeeded in harnessing plasmonics -- an emerging branch of science and technology -- to more effectively trap light within thin solar cells. As a result, we're one step closer to thin, inexpensive solar cells.

Researchers in solar energy speak of a day when millions of otherwise fallow square meters of sun-drenched roofs, windows, deserts and even clothing will be integrated with inexpensive solar cells that are many times thinner and lighter than the bulky rooftop panels familiar today.

So, when your iPod is on the nod, you might plug it into your shirt to recharge. Lost in the Serengeti with a sapped cell phone? No problem; rolled in your backpack is a lightweight solar pad. Sailing the seven seas and your GPS needs some juice? Hoist a solar sail and be one with the gods of geosynchronous orbit.

It is not hard to envision a time when such technologies will be ubiquitous in our increasingly energy-hungry lives. That day may come a bit sooner thanks to a multidisciplinary team of Stanford engineers led by Mike McGehee, Yi Cui and Mark Brongersma, and joined by Michael Graetzel at theÉcole Polytechnique Fédérale de Lausanne (EPFL).

Waves of energy

In an article published inAdvance Energy Materials, the Stanford/EPFL team announced a new type of thin solar cell that could offer a new direction for the field. They succeeded in harnessing plasmonics– an emerging branch of science and technology– to more effectively trap light within thin solar cells to improve performance and push them one step closer to daily reality.

"Plasmonics makes it much easier to improve the efficiency of solar cells,"said McGehee, an associate professor of materials science and engineering at Stanford.

McGehee is the director of CAMP– the Center for Advanced Molecular Photovoltaics– a multidisciplinary, multi-university team tackling the challenges of thin-film solar cells.

"Using plasmonics we can absorb the light in thinner films than ever before,"McGehee said."The thinner the film, the closer the charged particles are to the electrodes. In essence, more electrons can make it to the electrode to become electricity."

Plasmonics is the study of the interaction of light and metal. Under precise circumstances, these interactions create a flow of high-frequency, dense electrical waves rather than electron particles. The electronic pulse travels in extremely fast waves of greater and lesser density, like sound through the air.

A perfect solar waffle

The lightbulb moment for the team came when they imprinted a honeycomb pattern of nanoscale dimples into a layer of metal within the solar cell. Think of it as a nanoscale waffle, only the bumps on the waffle iron are domes rather than cubes– nanodomes to be exact, each only a few billionths of a meter across.

To fashion their waffle, McGehee and team members spread a thin layer of batter on a transparent, electrically conductive base. This batter is mostly titania, a semi-porous metal that is also transparent to light. Next, they use their nano waffle iron to imprint the dimples into the batter. Next, they layer on some butter– a light-sensitive dye– which oozes into the dimples and pores of the waffle. Lastly, the engineers add some syrup– a layer of silver, which hardens almost immediately.

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Titania within the solar cell is imprinted by the silicon nanodomes like a waffle imprinted by the iron.

When all those nanodimples fill up, the result is a pattern of nanodomes on the light-ward side of the silver.

This bumpy layer of silver has two primary benefits. First, it acts as a mirror, scattering unabsorbed light back into the dye for another shot at collection. Second, the light interacts with the silver nanodomes to produce plasmonic effects. Those domes of silver are crucial. Reflectors without them will not produce the desired effect. And any old nanodomes won't do either; they must be just the right diameter and height, and spaced just so, to fully optimize the plasmonics.

If you imagine your nanoself observing one of these solar cells in slow motion, you would see photons enter and pass through the transparent base and the titania (the waffle), at which point some photons would be absorbed by the light-sensitive dye (the butter), creating an electric current. Most of the remaining photons would hit the silver back reflector (the hardened syrup) and bounce back into the solar cell. A certain portion of the photons that reach the silver, however, will strike the nanodomes and cause plasmonic waves to course outward. And there you have it– the first-ever plasmonic dye-sensitized solar cell.

Trapping the light fantastic

It is easy to see why researchers are focused on thin-film solar technology. In recent years, much hope has been directed toward these lightweight, flexible cells that use photosensitive dyes to generate electricity. These cells have many advantages: They are less energy intensive and less costly to produce, flowing like newsprint off huge roll presses. They are thinner even than other"thin"solar cells. They are also printable on flexible bases that can be rolled up and taken virtually anywhere. Many use non-toxic, abundantly available materials, as well– a huge plus in the push for sustainability.

Dye-sensitized solar cells are not without challenges, however. First off, the very best convert only a small percentage of light into electricity– about 8 percent. The bulkier commercial technologies available today have reached 25 percent efficiency, and certain advanced applications have topped 40 percent. And then there is durability. The latest thin solar cell will last about seven years under continuous exposure to the elements. Not bad until you consider that 20 to 30 years is the commercial standard.

Both efficiency and reliability will have to improve. Nonetheless, engineers like McGehee believe that if they can convert just 15 percent of the light into electricity– a figure that is not out of reach– and tease the lifespan to a decade, we might soon find ourselves in the age of personal solar cells. An advance likeplasmonicsjust might provide the spark necessary to take the field down a new and exciting path.

A matter of economics

Cheaper and cleaner will be the keys. Coal-based power is plentiful and cheap, but also comes at a steep environmental cost in gouged landscapes and polluted skies. At today's commercial rates, however, even the best solar alternatives cost five times more per kilowatt-hour than coal. It is clear that economics, and not technology, is what stands between us and our solar future.

But McGehee and others are confident they can make thinsolar cellsmore attractive.

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A nanoscale rope, and another step toward complex nanomaterials that assemble themselves

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(PhysOrg.com) -- Scientists at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have coaxed polymers to braid themselves into wispy nanoscale ropes that approach the structural complexity of biological materials.

Their work is the latest development in the push to develop self-assembling nanoscale materials that mimic the intricacy and functionality of nature’s handiwork, but which are rugged enough to withstand harsh conditions such as heat and dryness.

Although still early in the development stage, their research could lead to new applications that combine the best of both worlds. Perhaps they’ll be used as scaffolds to guide the construction of nanoscale wires and other structures. Or perhaps they’ll be used to develop drug-delivery vehicles that target disease at the molecular scale, or to develop molecular sensors and sieve-like devices that separate molecules from one another.

Specifically, the scientists created the conditions for synthetic polymers called polypeptoids to assemble themselves into ever more complicated structures: first into sheets, then into stacks of sheets, which in turn roll up into double helices that resemble a rope measuring only 600 nanometers in diameter (a nanometer is a billionth of a meter).

“This hierarchichal self assembly is the hallmark of biological materials such as collagen, but designing synthetic structures that do this has been a major challenge,” says Ron Zuckermann, who is the Facility Director of the Biological Nanostructures Facility in Berkeley Lab’s Molecular Foundry.

In addition, unlike normal polymers, the scientists can control the atom-by-atom makeup of the ropy structures. They can also engineer helices of specific lengths and sequences. This“tunability” opens the door for the development of synthetic structures that mimicbiological materials’ ability to carry out incredible feats of precision, such as homing in on specific molecules.

“Nature uses exact length and sequence to develop highly functional structures. An antibody can recognize one form of a protein over another, and we’re trying to mimic this,” adds Zuckermann.

Zuckermann and colleagues conducted the research at The Molecular Foundry, which is one of the five DOE Nanoscale Science Research Centers premier national user facilities for interdisciplinary research at the nanoscale. Joining him were fellow Berkeley Lab scientists Hannah Murnen, Adrianne Rosales, Jonathan Jaworski, and Rachel Segalman. Their research was published in a recent issue of theJournal of the American Chemical Society.

The scientists worked with chains of bioinspired polymers called a peptoids. Peptoids are structures that mimic peptides, which nature uses to form proteins, the workhorses of biology. Instead of using peptides to build proteins, however, the scientists are striving to use peptoids to build synthetic structures that behave like proteins.

The team started with a block copolymer, which is a polymer composed of two or more different monomers.

“Simple block copolymers self assemble intonanoscalestructures, but we wanted to see how the detailed sequence and functionality of bioinspired units could be used to make more complicated structures,” says Rachel Segalman, a faculty scientist at Berkeley Lab and professor of Chemical and Biomolecular Engineering at University of California, Berkeley.

With this in mind, the peptoid pieces were robotically synthesized, processed, and then added to a solution that fosters self assembly.

The result was a variety of self-made shapes and structures, with the braided helices being the most intriguing. The hierarchical structure of the helix, and its ability to be manipulated atom-by-atom, means that it could be used as a template for mineralizing complex structures on a nanometer scale.

“The idea is to assemble structurally complex structures at the nanometer scale with minimal input,” says Hannah Murnen. She adds that the scientists next hope is to capitalize on the fact that they have minute control over the structure’s sequence, and explore how very small chemical changes alter the helical structure.

Says Zuckermann,“These braided helices are one of the first forays into making atomically defined block copolymers. The idea is to take something we normally think of as plastic, and enable it to adopt structures that are more complex and capable of higher function, such as molecular recognition, which is what proteins do really well.”

X-ray diffraction experiments used to characterize the structures were conducted at beamlines 8.3.1 and 7.3.3 of Berkeley Lab’s Advanced Light Source, a national user facility that generates intense x-rays to probe the fundamental properties of substances. This work was supported in part by the Office of Naval Research.

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