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Silicon Photonics id39403 Researchers at the University of Rochester have shown that defects on an atomically thin semiconductor can produce light-emitting quantum dots. The quantum dots serve as a source of single photons and could be useful for the integration of quantum photonics with solid-state electronics — a combination known as integrated photonics.

Scientists have become interested in integrated solid-state devices for quantum information processing uses. Quantum dots in atomically thin semiconductors could not only provide a framework to explore the fundamental physics of how they interact, but also enable nanophotonics applications, the researchers say.

Quantum dots are often referred to as artificial atoms. They are artificially engineered or naturally occurring defects in solids that are being studied for a wide range of applications. Nick Vamivakas, assistant professor of optics at the University of Rochester and senior author on the paper, adds that atomically thin, 2D materials, such as graphene, have also generated interest among scientists who want to explore their potential for optoelectronics. However, until now, optically active quantum dots have not been observed in 2D materials.

In a paper published in Nature Nanotechnology this week, the Rochester researchers show how tungsten diselenide (WSe2) can be fashioned into an atomically thin semiconductor that serves as a platform for solid-state quantum dots. Perhaps most importantly the defects that create the dots do not inhibit the electrical or optical performance of the semiconductor and they can be controlled by applying electric and magnetic fields.

Vamivakas explains that the brightness of the quantum dot emission can be controlled by applying the voltage. He adds that the next step is to use voltage to “tune the color” of the emitted photons, which can make it possible to integrate these quantum dots with nanophotonic devices.

A key advantage is how much easier it is to create quantum dots in atomically thin tungsten diselenide compared to producing quantum dots in more traditional materials like indium arsenide.

“We start with a black crystal and then we peel layers of it off until we have an extremely thin later left, an atomically thin sheet of tungsten diselenide,” said Vamivakas.1-nano devices howtomakemob

The researchers take two of these atomically thin sheets and lay one over the other one. At the point where they overlap, a quantum dot is created. The overlap creates a defect in the otherwise smooth 2D sheet of semiconductor material. The extremely thin semiconductors are much easier to integrate with other electronics.

The quantum dots in tungsten diselenide also possess an intrinsic quantum degree of freedom — the electron spin. This is a desirable property as the spin can both act as a store of quantum information as well as provide a probe of the local quantum dot environment.

COMING ~ JUNE 2015 ~ WATCH OUR NEW VIDEO ~ Genesis Nanotechnology ~ “Great Things from Small Things”

“What makes tungsten diselenide extremely versatile is that the color of the single photons emitted by the quantum dots is correlated with the quantum dot spin,” said first author Chitraleema Chakraborty. Chakraborty added that the ease with which the spins and photons interact with one another should make these systems ideal for quantum information applications as well as nanoscale metrology.


Story Source:

The above story is based on materials provided by University of Rochester. Note: Materials may be edited for content and length.

Difference engine

Graphene’s lightbulb moment

Can the “wonder material” live up to all the hype?

PHYSICISTS Andre Geim and Kostya Novoselev have been rightly feted for their isolation, in 2003, of graphene—sheets of pure carbon a single atom thick—whose existence had been pondered for decades, but which theory suggested was too unstable to survive. The two Soviet-born researchers won the Nobel physics prize in 2010 for their groundbreaking work, carried out at Manchester University, which involved peeling layers of graphene from blocks of graphite. Both men, now British citizens, were knighted in 2012 for their contribution to science. Their work has won generous support from the British government and the European Union—in particular, the construction, at a cost of £61m ($92m), of the National Graphene Institute, which was opened by George Osborne, Chancellor of the Exchequer, in March.

The researchers now have another distinction to their credit: their discovery is about to become a commercial product. A graphene-based lightbulb, said to be longer-lasting, more efficient and cheaper to make than today’s domestic LED lamps, will go on sale in a few months’ time. Though graphene flakes have already been incorporated into tennis racquets, skis and conductive ink, the new lightbulb is claimed by its manufacturer—Graphene Lighting Plc, a spin-out from the National Graphene Institute and Manchester University—to be the first commercially viable consumer product based on the material.

That may be splitting hairs. Even so, going from discovery to commercialisation in little more than a decade is quick. Many entrepreneurial companies find turning an invention into a successful innovation can take 20 years or more.

Graphene is composed of a single layer of carbon atoms arranged in the form of a hexagonal lattice. This means there is a world of difference between it and a three-dimensional crystalline structure like graphite. The electrons associated with carbon atoms in graphite can interact with other carbon atoms in the layers above and below them. In a sheet, this electron-coupling effect disappears, and the electrons are free to behave in entirely different ways.

The most striking consequence of this is that those electrons are thus able to move great distances at close to the speed of light, resulting in a material that has exceptionally low resistance. Because graphene can transport electricity 200 times faster than silicon, it seems a good candidate to replace that element as the semiconductor material used in computer chips.

Hype aside, graphene has not been called a “wonder material” for nothing. Apart from its remarkable electrical properties (and also, thermal and acoustical properties), it is the thinnest and lightest substance known, as well as being the strongest (more than 100 times stronger than high-strength steel). As if all that were not enough, graphene is also extremely flexible and almost totally transparent, absorbing only a minuscule amount of the light falling on it.

As such, potential applications of graphene appear myriad. Some of the more obvious ones include rapid-charging lithium-ion batteries, better solar cells, compact supercapacitors, printable electronics, foldable LED touchscreens, tunable sensors, ultrafast molecular sieves, improved DNA sequencers, corrosion-resistant coatings, a replacement for Kevlar, terahertz wave generators for extremely fast wireless communication, and, of course, more efficient lightbulbs. The list of proposals for future graphene products goes on and on, as researchers cozy up to potential sponsors.

There is little, save lack of money and consumer interest, to stop a good number of these suggestions reaching the market in the not-too-distant future. But the one graphene application that could turn the whole of electronics on its head—a replacement for silicon-based semiconductors—remains tantalisingly over the horizon.

Big computer, wireless and electronics firms—including such research powerhouses as IBM, Intel and Samsung—have been racing to create a field-effect transistor that uses graphene instead of silicon. They have a big incentive to do so. After 50 years of success, Moore’s Law (that the processing power of semiconductor devices doubles every 18 months or so) appears to be coming to an end, at least as far as silicon is concerned. Another material is needed to take its place.

Despite the billions poured into finding an alternative, attempts to make graphene work as a semiconductor have been disappointing. The problem is that the material has no “band gap”—the property that makes a solid an insulator (large band gap), a conductor (tiny or no band gap) or something in between—ie, a semiconductor (small band gap). Having no band gap at all is why graphene is such an excellent conductor. Making it into a semiconductor is tricky.

That is not all. A transistor works by flipping between two states—one insulating and the other conductive—in the presence of an electric field. These two states (off and on) represent the digital zeros and ones of computerspeak. By its nature, a graphene gate (switch) is on all the time. Getting it to turn off, let alone flip on and off billions of times a second, is the stumbling block.

There have been various attempts to open a band gap in graphene. One approach has been to dope it with compounds like silicon carbide or boron nitride that have matching crystalline lattice structures. Unfortunately, creating a band gap big enough to turn graphene into a usable semiconductor destroys the very properties—especially the high electron mobility—that made the material so attractive in the first place.

Older and wiser, researchers have turned to building hybrid chips that are fabricated, layer by layer, using conventional silicon epitaxy for everything except the final graphene transistor channels on the top of the device. These delicate structures are added at the end, so as not to get damaged during fabrication. So far, only analogue chips have been built this way. Even IBM has failed to create a band gap in graphene that would result in a digital device capable of challenging silicon’s preeminence. Transistors made entirely from graphene appear to be decades away.

So, where does that leave graphene’s prospects? While a replacement for silicon may be a long shot, many applications that do not rely on a band gap have a better chance of success. That said, not all graphene proposals being hyped at present can expect to survive the inevitable shake-out.

Had Gartner, an information-technology consultancy in Connecticut, included graphene-based processes as a stand-alone entry in its latest Emerging Technologies Hype Cycle, such processes would be over two-thirds the way up the slope to its “peak of inflated expectations”,which comes before the tip-over into the “trough of disillusionment” (see “Divining reality from hype”, August 27th 2014). Experience suggests that only those innovations which show genuine commercial value manage to crawl out of the trough and up the subsequent slope of enlightenment towards the plateau of productivity and market acceptance. Venture capitalists reckon no more than one in seven, at this stage of development, manages such a feat. It is too early to say whether graphene lightbulbs will be among them.

Readers with long memories may have noticed how the trajectory graphene is following resembles the one blazed by carbon fibre back in the 1960s. Then, as now, the new material was seen as a wonder product that would have numerous applications. Then, as now also, the British government felt it had a sacred duty to protect and promote what it perceived to be a home-grown invention—with the promise of jobs and exports.

If truth be told, the first hank of pyrolysed nylon (a carbon-fibre precursor) was snaffled from a Japanese textile factory and flown back to Britain in a diplomatic bag. At the time, British officials involved considered the super-strength material ideal for making gas centrifuges for enriching uranium. But samples that landed up at the Royal Aircraft Establishment in Farnborough led to the first carbon-fibre composite (Hyfil) being made available to select industrial partners, including the aeroengine manufacturer Rolls-Royce.

Of the many applications touted for carbon fibre, its promise to revolutionise air travel captured the most attention. With stronger, lighter fan blades, made from Hyfil instead of aluminium alloy or titanium, in a fan-jet’s first compressor stage, Rolls-Royce’s latest aircraft engine at the time, the RB211, would have had a significant weight-saving advantage—and thus better fuel economy—over rivals from General Electric and Pratt & Whitney.

The outcome was rather different. While turbine blades made from Hyfil had all the tensile strength, and more, to withstand the centrifugal forces of a big fan engine at full power, their shear strength left much to be desired. The story of how compressor blades shattered when a frozen chicken was fired at them to simulate bird impact contributed to carbon fibre’s fall from grace.

Meanwhile, the cost and delay involved in replacing the RB211’s Hyfil blades with titanium ones plunged Rolls-Royce into bankruptcy. Britain’s proudest engineering firm then had to be rescued at taxpayer expense. So much for governments picking winners. Hopefully, graphene is spared a similar fate.

1-california-drought-farmsNano-Filtration and the Water Crisis

Abstract: Adam Alonzi
The approaching water crisis will be solved by devices made possible by nanotechnology.

Since its conception concerns have been raised about nanotechnology’s potentially deleterious impact on the environment, but at this point it looks as though it will do more good than harm. From water remediation to solar cells to pollutant monitoring, nanotechnology, as I wrote in a recent blog entry, presents humanity with a “bevy of Black Swans.” The world’s fresh water supply is dwindling. Nanotech devices can empower governments and individuals around the world to use otherwise untapped sources through desalination and reclamation.

Zhang calls the scale of groundwater pollution “enormous” and the complexity “seemingly intractable.” Of the hundreds of thousands of sites in the United States identified by environmental agencies over the last three decades less than one third have been restored. Old mining areas, factories, landfills and dumping grounds continue to increase. As well as obvious undesirables like pathogens and heavy metals, more modern toxins, like endocrine disruptors and pharmaceuticals, must also be removed. While infrastructure improvements are necessary and inevitable in many places, nanotech research will accelerate, and be expedited by, the decentralization of water treatment.

 

Lockheed simulated-nanoporous-graphene-filtering-salt-ions

Nanofiltration involves using membranes with tiny pores (1-10 NM across) to remove specific molecules from a solution. Among other applications they are used to separate whey from the other constituents of milk and antibiotics from salty waste products. The major advantage they have over their competitors is the amount of pressure needed to pass liquid through them. Carbon nanotube membranes can remove an assortment of contaminants and aluminum based nanostructures are good at dismantling negatively charged baddies like viruses and bacteria, as well as some organic and inorganic compounds. Biomagnetite removes chlorinated organic molecules, silver slays bacteria and titanium dioxide, which is already used in a variety of consumer and industrial products, can break down organic compounds.

Dr. Sujoy Das assembled a silica-silver nanocomposite via biosynthesis. In other words, its production is cheap and green. The proteins covering the nanoparticles prevent them from leaching into the water. They also function as both reducing and protective agents for the silver nanoparticles. The nanocomposite removes dyes and microorganisms quickly. Moreover, the material can be reused several times.The LifeSaver bottle, invented shortly after hurricane Katrina, removes objects larger than 15 nanometers and works well for up to 1,500 gallons. It does not take out salt or some metals, however. This is unfortunate as in many regions the ocean is the only option.

Yet desalination is costly. It requires approximately 12 times the electricity needed to prepare fresh water for consumption. There is also the large initial investment of 200 million dollars or more to build a plant. Although for a glass of water 3 kilowatt hours is not bad at all, desalination is unfeasible on a large scale. Perforene, a graphene nanomembrane developed by Lockheed-Martin, was originally touted as being 100 times more efficient than other methods, but this estimate was later lowered to 20%. Thus, the enthusiasm was massively excessive and woefully premature. Yet this should not discourage. Every boom, or potential boom industry, has its share of exaggerated but stock boosting announcements, and does not mitigate the promise held by the technology in question.

Graphene, a hydrophobic material almost synonymous with nanotech, creates ultrafine capillaries through which water can pass. The pores can be extremely selective and the water can pass through them as easily as through a coffee filter, thus eliminating the need for energy-intensive high pressure systems. However, as Dr. Cohen cautions, a membrane that is five hundred times more permeable than its predecessor will not translate into proportional savings. Dr. Nair, one of the researchers working with this material says it “is as fast and as precise as one could possibly hope for such narrow capillaries. Now we want to control the graphene mesh size and reduce it below nine Angstroms to filter out even the smallest salts like in seawater. Our work shows that it is possible.”

Baines, Lawrence. “The Fight for Water.” Project-Based Writing in Science. SensePublishers, 2014. 81-89.

Cohen-Tanugi, David, and Jeffrey C. Grossman. “Water desalination across nanoporous graphene.” Nano letters 12.7 (2012): 3602-3608.

Inderscience Publishers. “Nanotechnology for water purification.” ScienceDaily. ScienceDaily, 28 July 2010. .

R. K. Joshi, P. Carbone, F. C. Wang, V. G. Kravets, Y. Su, I. V. Grigorieva, H. A. Wu, A. K. “Precise and Ultrafast Molecular Sieving through Graphene Oxide Membranes” Geim and R. R. Nair, Science, 2014.

Qu, Xiaolei, Pedro JJ Alvarez, and Qilin Li. “Applications of nanotechnology in water and wastewater treatment.” water research 47.12 (2013): 3931-3946.

Fuel Cells 0426 116806119How can nanotechnology improve fuel cells?

 *** From UnderstandingNano.com ***

Catalysts are used with fuels such as hydrogen or methanol to produce hydrogen ions. Platinum, which is very expensive, is the catalyst typically used in this process. Companies are using nanoparticles of platinum to reduce the amount of platinum needed, or using nanoparticles of other materials to replace platinum entirely and thereby lower costs.

Fuel cells contain membranes that allow hydrogen ions to pass through the cell but do not allow other atoms or ions, such as oxygen, to pass through. Companies are using nanotechnology to create more efficient membranes; this will allow them to build lighter weight and longer lasting fuel cells.

Small fuel cells are being developed that can be used to replace batteries in handheld devices such as PDAs or laptop computers. Most companies working on this type of fuel cell are using methanol as a fuel and are calling them DMFC’s, which stands for direct methanol fuel cell. DMFC’s are designed to last longer than conventional batteries. In addition, rather than plugging your device into an electrical outlet and waiting for the battery to recharge, with a DMFC you simply insert a new cartridge of methanol into the device and you’re ready to go.

Fuel cells that can replace batteries in electric cars are also under development. Hydrogen is the fuel most researchers propose for use in fuel cell powered cars. In addition to the improvements to catalysts and membranes discussed above, it is necessary to develop a lightweight and safe hydrogen fuel tank to hold the fuel and build a network of refueling stations. To build these tanks, researchers are trying to develop lightweight nanomaterials that will absorb the hydrogen and only release it when needed. The Department of Energy is estimating that widespread usage of hydrogen powered cars will not occur until approximately 2020.

Fuel Cells: Nanotechnology Applications

Researchers at the University of Copenhagen have demonstrated the ability to significantly reduce the amount of platinum needed as a catalyst in fuel cells.  The researchers found that the spacing between platinum nanoparticles affected the catalytic behavior, and that by controlling the packing density of the platinum nanoparticles they could reduce the amount of platinum needed.

Researchers at Brown University are developing a catalyst that uses no platinum. The catalyst is made from a sheet of graphene coated with cobalt nanoparticles. If this catalyst works out for production use with fuel cells it should be much less expensive than platinum based catalysts.

Researchers at Ulsan National Institute of Science and Technology have demonstrated how to produce edge-halogenated graphene nanoplatelets that have good catalytic properties. The researchers prepared the nanoplatelets by ball-milling graphene flakes in the presence of chlorine, bromine or iodine. They believe these halogenated nanoplatelets could be used as a replacement for expensive platinum catalystic material in fuel cells.

Researchers at Cornell University have developed a catalyst using platinum-cobalt nanoparticles that produces 12 times more catalytic activity than pure platinum. In order to achieve this performance the researchers annealed the nanoparticles so they formed a crystalline lattice which reduced the spacing between platinum atoms on the surface, increasing their reactivity.

Researchers at the University of Illinois have developed a proton exchange membrane using a silicon layer with pores of about 5 nanometers in diameter capped by a layer of porous silica. The silica layer is designed to insure that water stays in the nanopores. The water combines with the acid molecules along the wall of the nanopores to form an acidic solution, providing an easy pathway for hydrogen ions through the membrane. Evaluation of this membrane showed it to have much better conductivity of hydrogen ions (100 times better conductivity was reported) in low humidity conditions than the membrane normally used in fuel cells.

Researchers at Rensselaer Polytechnic Institute have investigated the storage of hydrogen in graphene (single atom thick carbon sheets). Hydrogen has a high bonding energy to carbon, and the researchers used annealing and plasma treatment to increase this bonding energy. Because graphene is only one atom thick it has the highest surface area exposure of carbon per weight of any material. High hydrogen to carbon bonding energy and high surface area exposure of carbon gives graphene has a good chance of storing hydrogen. The researchers found that they could store14% by weight of hydrogen in graphene.

Researchers at Stony Brook University have demonstrated that gold nanoparticles can be very effective at using solar energy to generate hydrogen from water. The key is making the nanoparticles very small. They found that  nanoparticles containing less than a dozen gold atoms are very effective photocatalysts for the generation of hydrogen.goldstand

Researchers at the SLAC National Accelerator Laboratory have developed a way to use less platinum for the cathode in a fuel cell, which could significantly reduce the cost of fuel cells. They alloyed platinum with copper and then removed the copper from the surface of the film, which caused the platinum atoms to move closer to each other (reducing the lattice space). It turns out that platinum with reduced lattice spacing is more a more effective catalyst for breaking up oxygen molecules into oxygen ion. The difference is that the reduced spacing changes the electronic structure of the platinum atoms so that the separated oxygen ions more easily released, and allowed to react with the hydrogen ions passing through the proton exchange membrane.

Another way to reduce the use of platinum for catalyst in fuel cell cathodes is being developed by researchers at Brown University. They deposited a one nanometer thick layer of platinum and iron on spherical nanoparticles of palladium. In laboratory scale testing they found that an catalyst made with these nanoparticles generated 12 times more current than a catalyst using pure platinum, and lasted ten times longer. The researchers believe that the improvement is due to a more efficient transfer of electrons than in standard catalysts.

Increasing catalyst surface area and efficiency by depositing platinum on porous alumina

Allowing the use of lower purity, and therefore less expensive, hydrogen with an anode made made of platinum nanoparticles deposited on titanium oxide.

Replacing platinum catalysts with less expensive nanomaterials

Using hydrogen fuel cells to power cars

Using nanostructured vanadium oxide in the anode of solid oxide fuel cells. The structure forms a battery, as well a fuel cell, therefore the cell can continue to provide electric current after the hydrogen fuel runs out.

 

Fuel Cells: Nanotechnology Company Directory

Company Product Advantage
QuantumSphere Non-platinum catalyst Reduces cost
MTI Micro DMFC’s Minimizes moving parts, reduces cost, size and weight
UltraCell DMFC’s that uses an extra catalyst to convert methanol to hydrogen before reaching the core of the fuel cell Increases power density and cell voltage
EDC Ovonics Hydrogen fuel tanks using metal hydrides as the storage media Reduce size, weight and pressure for storing hydrogen
Unidym Carbon nanotube based electrodes Improve efficiency of fuel cells by reducing resistive and mass transfer losses
GridShift Hydrogen generation using nanoparticle coated electrodes Improve efficiency of hydrogen generation by electrolysis
Aerogel Composite Catalyst with platinum nanoparticles embedded in a carbon aerogel Reduces platinum usage

Fuel Cell Resources

Hydrogen, Fuel Cells & Infrastructure Technologies Program at DOE

National Hydrogen Energy Roadmap

National Fuel Cell Research Center

California Fuel Cell Partnership

Department of Energy Hydrogen Permitting Web site

Listing of Hydrogen Fueling Station Location Worldwide

 

Given that less than 1 percent of the water on the planet is drinkable, a process to remove minerals, like salt, from water could help to alleviate many problems for the global community.
In the U.S., a research group based at the Department of Energy’s Oak Ridge National Laboratory have been working on a low-energy efficient desalination process. The newly devised method deploys a porous membrane made of graphene.

Graphene is a very strong, low weight material. It is 100 times stronger than steel and it conducts heat and electricity with great efficiency. The material is being investigated for many potential applications, including water purification.

The graphene membrane is, according to the researchers, more effective and uses less energy compared with current polymeric membranes, which work on the basis of reverse osmosis. With reverse osmosis an applied pressure is used to overcome osmotic pressure; this allows water to pass through a membrane whilst at the same time particles are retained.

With the new method the most important aspect is making the pores in the graphene. The size here is important: large enough to allow water molecules to pass through but sufficiently small to stop salt molecules from traversing the mesh.

The reason that the graphene process is more energy efficient comes down to the size of the mesh. Graphene is considerably thinner (just one atom in thickness) than the plastic polymers and the result of this is that less energy is required to push the fluid through.

The graphene structure was manufactured by passing methane gas through a tube furnace at 1,000 degrees C over a copper foil. This decomposed the methane into carbon and hydrogen. The carbon then assembled into a hexagonal configuration of one atom thick molecules. The graphene was then mounted onto a silicon nitride support. Small pores in the graphene are created using a plasma (an ionized gas.) Pores were created at the rate of one pore for every 100 square nanometers of graphene.

In experimental runs the graphene filter was used to remove salt from sea water in order to create water of drinking water quality. The test runs were effective with almost 100 percent of the salt removed.

The research has been published in the journal Nature Nanotechnology. The title of the paper is “Water Desalination Using Nanoporous Single-Layer Graphene.”

Read more: http://www.digitaljournal.com/science/graphene-technology-used-to-desalinate-water/article/429594#ixzz3Y4AR4wTh

Silicon Photonics id39403 Real or counterfeit? Northwestern Univ. scientists have invented sophisticated fluorescent inks that one day could be used as multicolored barcodes for consumers to authenticate products that are often counterfeited. Snap a photo with your smartphone, and it will tell you if the item is real and worth your money.

Counterfeiting is very big business worldwide, with $650 billion per year lost globally, according to the International Chamber of Commerce. The new fluorescent inks give manufacturers and consumers an authentication tool that would be very difficult for counterfeiters to mimic.

These inks, which can be printed using an inkjet printer, are invisible under normal light but visible under ultraviolet light. The inks could be stamped as barcodes or QR codes on anything from banknotes and bottles of whisky to luxury handbags and expensive cosmetics, providing proof of authenticity.

A key advantage is the control one has over the color of the ink; the inks can be made in single colors or as multicolor gradients. An ink’s color depends on the amounts and interaction of three different “ingredient” molecules, providing a built-in “molecular encryption” tool. (One of the ingredients is a sugar.) Even a tiny tweak to the ink’s composition results in a significant color change.

“We have introduced a level of complexity not seen before in tools to combat counterfeiters,” said Sir Fraser Stoddart, the senior author of the study. “Our inks are similar to the proprietary formulations of soft drinks. One could approximate their flavor using other ingredients, but it would be impossible to match the flavor exactly without a precise knowledge of the recipe.”

Sir Fraser is the Board of Trustees Professor of Chemistry in the Weinberg College of Arts and Sciences.

“The rather unusual relationship between the composition of the inks and their color makes them ideal for security applications where it’s desirable to keep certain information encrypted or to have brand items with unique labels that can be authenticated easily,” Stoddart said.

With a manufacturer controlling the ink’s “recipe,” or chemical composition, counterfeiters would find it virtually impossible to reverse engineer the color information encoded in the printed barcodes, QR codes or trademarks. Even the inks’ inventors would not be able to reverse engineer the process without a detailed knowledge of the encryption settings.

Details of the fluorescent inks, which are prepared from simple and inexpensive commodity chemicals, are published in Nature Communications.

Stoddart’s research team, led by Xisen Hou and Chenfeng Ke, stumbled across the water-based ink composite serendipitously. A series of rigorous follow-up investigations unraveled the mechanism of the unique behavior of the inks and led the scientists to propose an encryption theory for security printing.

Hou, a third-year graduate student, and Ke, a postdoctoral fellow, are co-first authors of the paper.

The researchers developed an encryption and authentication security system combined with inkjet-printing technology. In the study, they demonstrated both a monochromic barcode and QR code printed on paper from an inkjet printer. The information, invisible under natural light, can be read on a smartphone under UV light.

As another demonstration of the technology, the research team loaded the three chemical components into an inkjet cartridge and printed Vincent Van Gogh’s “Sunflowers” painting with good color resolution. Like the barcodes and QR codes, the printed image is only visible under UV light.

The inks are formulated by mixing a simple sugar (cyclodextrin) and a competitive binding agent together with an active ingredient (a molecule known as heterorotaxane) whose fluorescent color changes along a spectrum of red to yellow to green, depending upon the way the components come together. An infinite number of combinations can be defined easily.

Although the sugar itself is colorless, it interacts with the other components of the ink, encapsulating some parts selectively, thus preventing the molecules from sticking to one another and causing a change in color that is difficult to predict. This characteristic presents a formidable challenge to counterfeiters.

Hou and Ke were trying to prevent fluorophore aggregation by encircling a fluorescent molecule with other ring-shaped molecules, one being cyclodextrin. Unexpectedly, they isolated the compound that is the active ingredient of the inks. They found that the compound’s unusual arrangement of three rings trapped around the fluorescent component affords the unique aggregation behavior that is behind the color-changing inks.

“You never know what Mother Nature will give you,” Hou said. “It was a real surprise when we first isolated the main component of the inks as an unexpected byproduct. The compound shows a beautiful dark-red fluorescence under UV light, yet when we dissolve it in large amounts of water, the fluorescent color turns green. At that moment, we realized we had discovered something that is quite unique.”

The fluorescent colors can be tuned easily by adding the sugar dissolved in water. As more cyclodextrin is added, the fluorescent color changes from red to yellow and then green, giving a wide range of beautiful colors. The fluorescent color can be reversed, by adding another compound that mops up the cyclodextrin.

The researchers also discovered that the fluorescent ink is sensitive to the surface to which it is applied. For example, an ink blend that appears as orange on standard copy paper appears as green on newsprint. This observation means that this type of fluorescent ink can be used to identify different papers.

“This is a smart technology that allows people to create their own security code by manually setting all the critical parameters,” Hou said. “One can imagine that it would be virtually impossible for someone to reproduce the information unless they knew exactly all the parameters.”

The researchers also have developed an authentication mechanism to verify the protected information produced by the fluorescent security inks. Simply by wiping some wet authentication wipes on top of the fluorescent image causes its colors to change under UV light.

“Since the color changing process is dynamic, even if counterfeiters can mimic the initial fluorescent color, they will find it impossible to reproduce the color-changing process,” Ke emphasized.

Source: Northwestern Univ.

Israeli 0422 flexible-screen-811x497

Imagine an electronic screen that looks and feels like paper that could connect to your smartphone. You can shift your longer readings and video viewing to this bendable screen, then roll it up and throw it in your bag when you arrive at your subway stop. This may sound like sci-fi, but Israeli researchers have actually found a way to develop such thin, flexible screens you can use on the go.

A new Tel Aviv University study suggests that a novel DNA nanotechnology could produce a structure that can be used to produce ultra-thin, flexible screens. The research team’s building blocks are three molecules they’ve synthesized, which later self-assembled into ordered structures. Essentially, the team has built the molecular backbone of a super-slim, bendable digital display. In the field of bio-nanotechnology, scientists utilize these molecular building blocks to develop cutting-edge technologies with properties not available for inorganic materials such as plastic and metal.

DNA

This could provide a solution to roughly 2 billion smartphone users who may not want the content they view to be confined to a pocket-sized screen. That’s because currently the size of smartphone screens makes it particularly hard to read more than a few hundred words at a time or watch videos without feeling like you’re on the tilt-a-whirl at Six Flags.

The number of people using mobile devices to view media is on the rise. According to Pew Research Center, 68 percent of smartphone owners use their phone occasionally to follow breaking news stories, and 33 percent do it frequently. Moreover, YouTube reports that 50 percent of its 4 billion video views per month are watched on a mobile device.

SEE ALSO: CES 2015: The Best Of Israeli Tech

[youtube https://www.youtube.com/watch?v=IXVHEox0d50&w=560&h=315]

The structures formed by the researchers were found to emit light in every color, as opposed to other fluorescent materials that shine only in one specific color. Moreover, light emission was observed in response to electric voltage — which makes this technology a perfect candidate for display screens.

The TAU researchers, who recently published their findings in the scientific journal Nature Nanotechnology, are currently building a prototype of the screen and are in talks with major consumer electronics companies regarding the technology, which they’ve patented. “Our material is light, organic and environmentally friendly,” TAU’s Prof. Ehud Gazit said in a statement. “It is flexible, and its single layer emits the same range of light that requires several layers today.” Moreover, fewer layers are better for consumers, he says: “By using only one layer, you can minimize production costs dramatically, which will lead to lower prices.”

lg g flex

Back to the good old newspaper display? 

It’s important to mention that this technology is still in its early stages and a price tag for these screens remains unknown. What is clear, however, is that the desire to consume content on portable, large screens isn’t going away and consumer preferences are trending more and more toward bigger screens.

Ironically, people seem to be drawn back to the old newspaper display – thin, flexible, and capable of being rolled up; now, all of these features are turning digital.

Regardless of flexibility, the tendency to enlarge mobile screens was already evident last year. It is widely believed that sales of Apple and Samsung (500 million smartphone in 2014) were buoyed by their newest smartphone iterations which boast larger screens than past versions. Apple especially took note of this trend, releasing the iPhone 6 (4.7 inch screen) and iPhone 6 Plus (5.5 inches) simultaneously.

newspaper

 

nanotech20concept
Published on Mar 24, 2015

Dr. Christoph Deneke, Scientific Head at the Laboratory for Surface Science, Brazilian Nanotechnology National Laboratory (LNNano)/CNPEM, Brazil, delivered a WIN seminar entitled “Nanometer Thick Membranes as Substrates for InAs Growth”.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

nanotech20concept“Harnessing the transformational POWER of Nanotechnology will usher our world into the age of the ‘2nd Great Industrial Revolution’. Nanotechnology  will impact almost every aspect of our daily lives, from clean abundant Renewable Energy, Wearable-Sensory Textiles, Displays & Electronics to Bio-Medical, Diagnostics, Life-Saving Drug Therapies, Agriculture, Water Filtration, Waste Water Remediation and Desalination.south-africa-ii-nanotechnology-india-brazil_261.jpg GNT is very excited to be a part of this Revolution’. Bringing together leading ‘Nano-University Research Programs’ with Marketplace & Industry Leaders , engaging our Proprietary Business Model, fostering in a new paradigm in nanotechnology innovation.”

~ Bruce W. Hoy, C.E.O. of Genesis Nanotechnology, Inc. ~


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