Researchers at RMIT University and the University of Adelaide have joined forces to create a stretchable nano-scale device to manipulate light.

The device manipulates light to such an extent that it can filter specific colours while still being transparent and could be used in the future to make smart contact lenses.

                                                             

 nanoscale glass structures that filter or manipulate light
credit: RMIT/The University of Adelaide

Using the technology, high-tech lenses could one day filter harmful optical radiation without interfering with vision – or in a more advanced version, transmit data and gather live vital information or even show information like a head-up display.

The light manipulation relies on creating tiny artificial crystals termed  “dielectric resonators”, which are a fraction of the wavelength of light – 100-200 nanometers, or over 500 times thinner than a human hair.

The research combined the University of Adelaide researchers’ expertise in interaction of light with artificial materials with the materials science and nanofabrication expertise at RMIT University.

Dr Withawat Withayachumnankul, from the University of Adelaide’s School of Electrical and Electronic Engineering, said: “Manipulation of light using these artificial crystals uses precise engineering.

“With advanced techniques to control the properties of surfaces, we can dynamically control their filter properties, which allow us to potentially create devices for high data-rate optical communication or smart contact lenses.

“The current challenge is that dielectric resonators only work for specific colours, but with our flexible surface we can adjust the operation range simply by stretching it.”

Associate Professor Madhu Bhaskaran, Co-Leader of the Functional Materials and Microsystems Research Group at RMIT, said the devices were made on a rubber-like material used for contact lenses.

“We embed precisely-controlled crystals of titanium oxide, a material that is usually found in sunscreen, in these soft and pliable materials,” she said.

“Both materials are proven to be bio-compatible, forming an ideal platform for wearable optical devices.

“By engineering the shape of these common materials, we can create a device that changes properties when stretched. This modifies the way the light interacts with and travels through the device, which holds promise of making smart contact lenses and stretchable colour changing surfaces.”

Lead author and RMIT researcher Dr. Philipp Gutruf said the major scientific hurdle overcome by the team was combining high temperature processed titanium dioxide with the rubber-like material, and achieving nanoscale features.

“With this technology, we now have the ability to develop light weight wearable optical components which also allow for the creation of futuristic devices such as smart contact lenses or flexible ultrathin smartphone cameras,” Gutruf said.

source ; RMIT news release link : click here

This post is copied from the materials in the RMIT website(news)

UW scientists create ultrathin semiconductor heterostructures for new technological applications...............

Heterostructures formed by different three-dimensional semiconductors form the foundation for modern electronic and photonic devices. Now, University of Washington scientists have successfully combined two different ultrathin semiconductors — each just one layer of atoms thick and roughly 100,000 times thinner than a human hair — to make a new two-dimensional heterostructure with potential uses in clean energy and optically-active electronics. The team, led by Boeing Distinguished Associate Professor Xiaodong Xu, announced its findings in a paper published Feb. 12 in the journal Science.

                                                               

An illustration of the strong valley exciton interactions and transport in a 2-D semiconductor heterostructure.Pasqual Rivera, Kyle Seyler

              Senior author Xu and lead authors Kyle Seyler and Pasqual Rivera, both doctoral students in the UW physics department, synthesized and investigated the optical properties of this new type of semiconductor sandwich.

“What we’re seeing here is distinct from heterostructures made of 3-D semiconductors,” said Xu, who has joint appointments in the Department of Physics and the Department of Materials Science and Engineering. “We’ve created a system to study the special properties of these atomically thin layers and their potential to answer basic questions about physics and develop new electronic and photonic technologies.”

When semiconductors absorb light, pairs of positive and negative charges can form and bind together to create so-called excitons. Scientists have long studied how these excitons behave, but when they are squeezed down to the 2-D limit in these atomically thin materials, surprising interactions can occur.

While traditional semiconductors manipulate the flow of electron charge, this device allows excitons to be preserved in “valleys,” a concept from quantum mechanics similar to the spin of electrons. This is a critical step in the development of new nanoscale technologies that integrate light with electronics.

“It was already known that these ultrathin 2-D semiconductor have these unique properties that you cannot find in other 2-D or 3-D arrangements,” said Xu. “But as we show here, when we put these two layers together — one on top of the other — the interface between these sheets becomes the site of even more new physical properties, which you don’t see in each layer on its own or in the 3-D version.”

Xu and his team wanted to create and explore the properties of a 2-D semiconductor heterostructure made up of two different layers of material, a natural expansion of their previous studies on atomically thin junctions, as well as nanoscale lasers based on atomically thin layers of semiconductors. By studying how laser light interacts with this heterostructure, they gathered information about the physical properties at the atomically sharp interface.

“Many groups have studied the optical properties of single 2-D sheets,” said Seyler. “What we do here is carefully stack one material on top of another, and then study the new properties that arise at the interface.”

The team obtained two types of semiconducting crystals, tungsten diselenide (WSe2) and molybdenum diselenide (MoSe2), from collaborators at Oak Ridge National Laboratory. They used facilities developed in-house to precisely arrange two layers, one derived from each crystal, a process that took a few years to fully develop.

“But now that we know how to do it properly, we can make new ones in one or two weeks,” said Xu.

Getting these devices to emit light posed a unique challenge, due to the properties of electrons in each layer.

“Once you have these two sheets of material, an essential question is how to position the two layers together,” said Seyler. The electrons in each layer have unique spin and valley properties, and “how you position them — their twist angle — affects how they interact with light.”

By aligning the crystal lattices, the authors could excite the heterostructure with a laser and create optically active excitons between the two layers.

“These excitons at the interface can store valley information for orders of magnitude longer than either of the layers on their own,” said Rivera. “This long lifetime allows for fascinating effects which may lead to further optical and electronic applications with valley functionality.”

Now that they can efficiently make a semiconductor heterostructure out of 2-D materials, Xu and his team would like to explore a number of fascinating physical properties, including how exciton behavior varies as they change angles between the layers, the quantum properties excitons between layers and electrically driven light emission.

“There’s a whole industry that wants to use these 2-D semiconductors to make new electronic and photonic devices,” said Xu. “So we’re trying to study the fundamental properties of these new heterostructures for things like efficient laser technology, light-emitting diodes and light-harvesting devices. These will hopefully be useful for clean energy and information technology applications. It is quite exciting but there’s a lot work to do.”

Other co-authors are Hongyi Yu and Wang Yao at the University of Hong Kong; Jiaqiang Yan and David Mandrus at Oak Ridge National Laboratory and the University of Tennessee; and UW physics postdoctoral researcher John Schaibley. The UW authors were primarily funded by the U.S. Department of Energy, with additional support from the UW’s Clean Energy Institute and the National Science Foundation.

source: UW TODAY  link: click here

Technical University of Denmark (DTU) researchers from DTU Nanotech and DTU Fotonik have reproduced a colour image of Mona Lisa which is less than one pixel on an iPhone Retina display.

A nanotechnology breakthrough from DTU revolutionizes laser printing technology, allowing you to print high-resolution data and colour images of unprecedented quality and microscopic dimensions.

Researchers from DTU Nanotech and DTU Fotonik have succeeded in printing a microscopic Mona Lisa. She is 50 micrometres long or about 10,000 times smaller than the real Mona Lisa in the Louvre in Paris.

credit: DTU

                                                                                                                                                                    Using this new technology, DTU researchers from DTU Nanotech and DTU Fotonik have reproduced a colour image of Mona Lisa which is less than one pixel on an iPhone Retina display. The laser technology allows printing in a mind-blowing resolution of 127,000 DPI. In comparison, weekly or monthly magazines are normally printed in a resolution equivalent to 300 DPI.

Printing the microscopic images requires a special nanoscale-structured surface. The structure consists of rows with small columns with a diameter of merely 100 nanometres each. This structured surface is then covered by 20 nanometres of aluminium. When a laser pulse is transmitted from nanocolumn to nanocolumn, the nanocolumn is heated locally, after which it melts and is deformed. The temperature can reach up to 1,500°C, but only for a few nanoseconds, preventing the extreme heat from spreading.

The intensity of the laser beam determines which colours are printed on the surface, since the extent of column deformation decides which colour is reflected. Low-intensity laser pulses lead to a minor deformation of the nanocolumn, resulting in blue and purple colour tone reflections. Strong laser pulses create a drastic deformation, which gives the reflection from the nanocolumn an orange and yellow colour tone.

The DTU researchers believe that there is considerable scope for application of the new laser printing technology. Professor Anders Kristensen from DTU Nanotech elaborates: "It will be possible to save data invisible to the naked eye. This includes serial numbers or bar codes of products and other information. The technology can also be used to combat fraud and forgery, as the products will be labelled in way that makes them very difficult to reproduce. It will be easier to determine whether the product is an original or a copy."

The new laser printing technology can also be used on a larger scale to personify products such as mobile phones with unique decorations, names, etc. Foreign companies producing parts for cars, such as instrument panels and buttons, are already taking a keen interest in the technology as it can simplify the production. Today, the large number of different instrument panels must be adapted to the various accessories that the car has, including airconditioning, USB, cigarette lighters, etc.

The technology has been patented, and the researchers will now focus on developing the technology, so that it can replace the conventional laser printers that we have at our offices and in our homes.

SOURCE: Technical University of Denmark (DTU) link : click here

Super-elastic Conducting Nano Fibers for Artificial Muscles, Sensors , robots and exoskeletons

An international research team based at The University of Texas at Dallas has made electrically conducting fibers that can be reversibly stretched to over 14 times their initial length and whose electrical conductivity increases 200-fold when stretched.

                                                 

UT Dallas scientists have constructed novel fibers by wrapping sheets of tiny carbon nanotubes to form a sheath around a long rubber core. This illustration shows complex two-dimensional buckling, shown in yellow, of the carbon nanotube sheath/rubber-core fiber. The buckling results in a conductive fiber with super elasticity and novel electronic properties.credit:ut dellas

           

The research team is using the new fibers to make artificial muscles, as well as capacitors whose energy storage capacity increases about tenfold when the fibers are stretched. Fibers and cables derived from the invention might one day be used as interconnects for super-elastic electronic circuits; robots and exoskeletons having great reach; morphing aircraft; giant-range strain sensors; failure-free pacemaker leads; and super-stretchy charger cords for electronic devices.

In a study published in the July 24 issue of the journal Science, the scientists describe how they constructed the fibers by wrapping lighter-than-air, electrically conductive sheets of tiny carbon nanotubes to form a jelly-roll-like sheath around a long rubber core.

The new fibers differ from conventional materials in several ways. For example, when conventional fibers are stretched, the resulting increase in length and decrease in cross-sectional area restricts the flow of electrons through the material. But even a “giant” stretch of the new conducting sheath-core fibers causes little change in their electrical resistance, said Dr. Ray Baughman, senior author of the paper and director of the Alan G. MacDiarmid NanoTech Institute at UT Dallas.

One key to the performance of the new conducting elastic fibers is the introduction of buckling into the carbon nanotube sheets. Because the rubber core is stretched along its length as the sheets are being wrapped around it, when the wrapped rubber relaxes, the carbon nanofibers form a complex buckled structure, which allows for repeated stretching of the fiber.

“Think of the buckling that occurs when an accordion is compressed, which makes the inelastic material of the accordion stretchable,” said Baughman, the Robert A. Welch Distinguished Chair in Chemistry at UT Dallas.

“We make the inelastic carbon nanotube sheaths of our sheath-core fibers super stretchable by modulating large buckles with small buckles, so that the elongation of both buckle types can contribute to elasticity. These amazing fibers maintain the same electrical resistance, even when stretched by giant amounts, because electrons can travel over such a hierarchically buckled sheath as easily as they can traverse a straight sheath.”

Dr. Zunfeng Liu, lead author of the study and a research associate in the NanoTech Institute, said the structure of the sheath-core fibers “has further interesting and important complexity.” Buckles form not only along the fiber’s length, but also around its circumference.

“Shrinking the fiber’s circumference during fiber stretch causes this second type of reversible hierarchical buckling around its circumference, even as the buckling in the fiber direction temporarily disappears,” Liu said. “This novel combination of buckling in two dimensions avoids misalignment of nanotube and rubber core directions, enabling the electrical resistance of the sheath-core fiber to be insensitive to stretch.”

By adding a thin overcoat of rubber to the sheath-core fibers and then another carbon nanotube sheath, the researchers made strain sensors and artificial muscles in which the buckled nanotube sheaths serve as electrodes and the thin rubber layer is a dielectric, resulting in a fiber capacitor. These fiber capacitors exhibited a capacitance change of 860 percent when the fiber was stretched 950 percent.

“No presently available material-based strain sensor can operate over nearly as large a strain range,” Liu said.

Adding twist to these double-sheath fibers resulted in fast, electrically powered torsional — or rotating — artificial muscles that could be used to rotate mirrors in optical circuits or pump liquids in miniature devices used for chemical analysis, said Dr. Carter Haines BS’11 PhD’15, a research associate in the NanoTech Institute and an author of the paper.

  In the laboratory, Nan Jiang, a research associate in the NanoTech Institute, demonstrated that the conducting elastomers can be fabricated in diameters ranging from the very small — about 150 microns, or twice the width of a human hair — to much larger sizes, depending on the size of the rubber core. “Individual small fibers also can be combined into large bundles and plied together like yarn or rope,” she said.

“This technology could be well-suited for rapid commercialization,” said Dr. Raquel Ovalle-Robles MS’06 PhD’08, an author on the paper and chief research and intellectual properties strategist at Lintec of America’s Nano-Science & Technology Center.

“The rubber cores used for these sheath-core fibers are inexpensive and readily available,” she said. “The only exotic component is the carbon nanotube aerogel sheet used for the fiber sheath.”

Last year, UT Dallas licensed to Lintec of America a process Baughman’s team developed to transform carbon nanotubes into large-scale structures, such as sheets. Lintec opened its Nano-Science & Technology Center in Richardson, Texas, less than 5 miles from the UT Dallas campus, to manufacture carbon nanotube aerogel sheets for diverse applications.

The Science research was supported by the Air Force Office of Scientific Research, the Robert A. Welch Foundation, the U.S. Army, the National Institutes of Health, the National Science Foundation and the Office of Naval Research. Several funding sources from China and Brazil also contributed.

In addition to Baughman, Liu, Haines, Jiang and Ovalle-Robles, paper authors based at UT Dallas’ NanoTech Institute are research scientists Dr. Shaoli Fang and Dr. Márcio Lima, and research associates Dr. Xavier Lépro and Dr. Jiangtao Di. Contributors based in the UT Dallas Department of Mechanical Engineering include Dr. Hongbing Lu, professor; Dr. Dong Qian, associate professor; and Xuemin Wang, research assistant. Researchers also contributed from universities in Florida, China and Brazil. 

source: UT Dellas News centre,July 23, 2015 press release  link : clickhere

recyclable and cleanable chip

A light-triggered cleanable, recyclable chip makes fabrication feasible for all

Throw away the detergent and forgo the elbow grease: pesky proteins can now be removed from surfaces by simply exposing them to light, thanks to a reusable titania template developed by A*STAR researchers1.
                                                             

From left to right: Mark Moxey, Karen Chong and MSM Saifullah from the A*STAR Institute of Materials Research and Engineering.

credit :© 2015 A*STAR Institute of Materials Research and Engineering

Biologists have many reasons to pattern surfaces with proteins, from creating highly selective biosensors to studying fundamental processes such as tissue formation. What they don’t want, however, is for the proteins to stay on the surface indefinitely. Unfortunately, ridding a surface of proteins is a complicated and time-consuming task, which means that the majority of biologists typically throw away their substrates after a single use — leading to a high cost for consumables. Moreover, due to the complexity of fabrication systems, biologists usually outsource their chip manufacturing to engineers, which introduces delays and further exacerbates cost.

Karen Chong and her team at the A*STAR Institute of Materials Research and Engineering in Singapore recognized that these delays and costs could be avoided by designing a fabrication technique that non-engineers could use. “We wanted to demonstrate that fabrication and patterning techniques could move away from the traditional domains of microelectronics,” she recalls. “Specifically, we wanted to create fabrication techniques that could easily be adopted and replicated by biologists.”

Chong notes that to be practical, fabrication techniques must be either easy to use or have the potential to be scaled up to produce commercial quantities. Consequently, she and the team focused on two techniques: interferometric lithography for the former and nanoimprint lithography for the latter.

“Interferometric lithography techniques can be easily replicated by biologists without the need for a very complex or costly set-up in their laboratories,” she explains. “While nanoimprinting is not practical for smaller labs, it does allow us to scale up these samples into larger-area substrates.”

Both approaches yielded surfaces with titania nanostructures (see image) that were then covered with protein-resistant silanes. Exposure to ultraviolet light degrades the silanes, which allows proteins to adhere to the selected regions. After the protein-patterned substrates have served their purpose, Chong describes how “the proteins on the chips can be quickly removed, by just exposing the used substrates to ultraviolet light, without the need for elaborate cleaning methods.” The substrates can then be immediately reused without the need for further preparation.

“With the recyclable chip and the technique that we have demonstrated, fabrication techniques are no longer the exclusive domain of engineers,” remarks Chong.

source:A*STAR research  link : click here

A Most Singular Nano-Imaging Technique : Berkeley Lab’s SINGLE Provides Images of Individual Nanoparticles in Solution

                                                                    

SINGLE uses in situ TEM imaging of platinum nanocrystals freely rotating in a graphene liquid cell to determine the 3D structures of individual colloidal nanoparticles.

Just as proteins are one of the basic building blocks of biology, nanoparticles can serve as the basic building blocks for next generation materials. In keeping with this parallel between biology and nanotechnology, a proven technique for determining the three dimensional structures of individual proteins has been adapted to determine the 3D structures of individual nanoparticles in solution.

A multi-institutional team of researchers led by the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab), has developed a new technique called “SINGLE” that provides the first atomic-scale images of colloidal nanoparticles. SINGLE, which stands for 3D Structure Identification of Nanoparticles by Graphene Liquid Cell Electron Microscopy, has been used to separately reconstruct the 3D structures of two individual platinum nanoparticles in solution.

“Understanding structural details of colloidal nanoparticles is required to bridge our knowledge about their synthesis, growth mechanisms, and physical properties to facilitate their application to renewable energy, catalysis and a great many other fields,” says Berkeley Lab director and renowned nanoscience authority Paul Alivisatos, who led this research. “Whereas most structural studies of colloidal nanoparticles are performed in a vacuum after crystal growth is complete, our SINGLE method allows us to determine their 3D structure in a solution, an important step to improving the design of nanoparticles for catalysis and energy research applications.”

     Alivisatos, who also holds the Samsung Distinguished Chair in Nanoscience and Nanotechnology at the University of California Berkeley, and directs the Kavli Energy NanoScience Institute at Berkeley (Kavli ENSI), is the corresponding author of a paper detailing this research in the journal Science. The paper is titled “3D Structure of Individual Nanocrystals in Solution by Electron Microscopy.” The lead co-authors are Jungwon Park of Harvard University, Hans Elmlund of Australia’s Monash University, and Peter Ercius of Berkeley Lab. Other co-authors are Jong Min Yuk, David Limmer, Qian Chen, Kwanpyo Kim, Sang Hoon Han, David Weitz and Alex Zettl.

      

Colloidal nanoparticles are clusters of hundreds to thousands of atoms suspended in a solution whose collective chemical and physical properties are determined by the size and shape of the individual nanoparticles. Imaging techniques that are routinely used to analyze the 3D structure of individual crystals in a material can’t be applied to suspended nanomaterials because individual particles in a solution are not static. The functionality of proteins are also determined by their size and shape, and scientists who wanted to image 3D protein structures faced a similar problem. The protein imaging problem was solved by a technique called “single-particle cryo-electron microscopy,” in which tens of thousands of 2D transmission electron microscope (TEM) images of identical copies of an individual protein or protein complex frozen in random orientations are recorded then computationally combined into high-resolution 3D reconstructions. Alivisatos and his colleagues utilized this concept to create their SINGLE technique.

                                                           

The Berkeley Lab GLC improves the resolution of TEM imaging with a viewing window made from a graphene sheet that is only a single atom thick.

“In materials science, we cannot assume the nanoparticles in a solution are all identical so we needed to develop a hybrid approach for reconstructing the 3D structures of individual nanoparticles,” says co-lead author of the Science paper Peter Ercius, a staff scientist with the National Center for Electron Microscopy (NCEM) at the Molecular Foundry, a DOE Office of Science User Facility.

         “SINGLE represents a combination of three technological advancements from TEM imaging in biological and materials science,” Ercius says. “These three advancements are the development of a graphene liquid cell that allows TEM imaging of nanoparticles rotating freely in solution, direct electron detectors that can produce movies with millisecond frame-to-frame time resolution of the rotating nanocrystals, and a theory for ab initio single particle 3D reconstruction.”

The graphene liquid cell (GLC) that helped make this study possible was also developed at Berkeley Lab under the leadership of Alivisatos and co-author Zettl, a physicist who also holds joint appointments with Berkeley Lab, UC Berkeley and Kavli ENSI. TEM imaging uses a beam of electrons rather than light for illumination and magnification but can only be used in a high vacuum because molecules in the air disrupt the electron beam. Since liquids evaporate in high vacuum, samples in solutions must be hermetically sealed in special solid containers – called cells – with a very thin viewing window before being imaged with TEM. In the past, liquid cells featured silicon-based viewing windows whose thickness limited resolution and perturbed the natural state of the sample materials. The GLC developed at Berkeley lab features a viewing window made from a graphene sheet that is only a single atom thick.

“The GLC provides us with an ultra-thin covering of our nanoparticles while maintaining liquid conditions in the TEM vacuum,” Ercius says. “Since the graphene surface of the GLC is inert, it does not adsorb or otherwise perturb the natural state of our nanoparticles.”

  Working at NCEM’s TEAM I, the world’s most powerful electron microscope, Ercius, Alivisatos and their colleagues were able to image in situ the translational and rotational motions of individual nanoparticles of platinum that were less than two nanometers in diameter. Platinum nanoparticles were chosen because of their high electron scattering strength and because their detailed atomic structure is important for catalysis.

“Our earlier GLC studies of platinum nanocrystals showed that they grow by aggregation, resulting in complex structures that are not possible to determine by any previously developed method,” Ercius says. “Since SINGLE derives its 3D structures from images of individual nanoparticles rotating freely in solution, it enables the analysis of heterogeneous populations of potentially unordered nanoparticles that are synthesized in solution, thereby providing a means to understand the structure and stability of defects at the nanoscale.”

The next step for SINGLE is to recover a full 3D atomic resolution density map of colloidal nanoparticles using a more advanced camera installed on TEAM I that can provide 400 frames-per-second and better image quality.

“We plan to image defects in nanoparticles made from different materials, core shell particles, and also alloys made of two different atomic species,” Ercius says.

This research was primarily supported by the DOE Office of Science.

source: Berkely labs   link: click here

‘White graphene’ structures can take the heat

Rice University scientists find 3-D boron nitride structures will excel at thermal management for electronics .Three-dimensional structures of boron nitride might be the right stuff to keep small electronics cool, according to scientists at Rice University.
                                                                       

A 3-D structure of hexagonal boron nitride sheets and boron nitride nanotubes could be a tunable material to control heat in electronics, according to researchers at Rice University. Courtesy of the Shahsavari Group 

Rice researchers Rouzbeh Shahsavari and Navid Sakhavand have completed the first theoretical analysis of how 3-D boron nitride might be used as a tunable material to control heat flow in such devices.
                                                           

Rice researchers Rouzbeh Shahsavari (left) and Navid Sakhavand calculated the flow of heat across simulated structures of hexagonal boron nitride and boron nitride nanotubes. Photo by Jeff Fitlow 

Their work appears this month in the American Chemical Society journal Applied Materials and Interfaces.

In its two-dimensional form, hexagonal boron nitride (h-BN), aka white graphene, looks just like the atom-thick form of carbon known as graphene. One well-studied difference is that h-BN is a natural insulator, where perfect graphene presents no barrier to electricity.
But like graphene, h-BN is a good conductor of heat, which can be quantified in the form of phonons. (Technically, a phonon is one part — a “quasiparticle” – in a collective excitation of atoms.) Using boron nitride to control heat flow seemed worthy of a closer look, Shahsavari said.

“Typically in all electronics, it is highly desired to get heat out of the system as quickly and efficiently as possible,” he said. “One of the drawbacks in electronics, especially when you have layered materials on a substrate, is that heat moves very quickly in one direction, along a conductive plane, but not so good from layer to layer. Multiple stacked graphene layers is a good example of this.”

Heat moves ballistically across flat planes of boron nitride, too, but the Rice simulations showed that 3-D structures of h-BN planes connected by boron nitride nanotubes would be able to move phonons in all directions, whether in-plane or across planes, Shahsavari said.

The researchers calculated how phonons would flow across four such structures with nanotubes of various lengths and densities. They found the junctions of pillars and planes acted like yellow traffic lights, not stopping but significantly slowing the flow of phonons from layer to layer, Shahsavari said. Both the length and density of the pillars had an effect on the heat flow: more and/or shorter pillars slowed conduction, while longer pillars presented fewer barriers and thus sped things along.

While researchers have already made graphene/carbon nanotube junctions, Shahsavari believed such junctions for boron nitride materials could be just as promising. “Given the insulating properties of boron nitride, they can enable and complement the creation of 3-D, graphene-based nanoelectronics.

“This type of 3-D thermal-management system can open up opportunities for thermal switches, or thermal rectifiers, where the heat flowing in one direction can be different than the reverse direction,” Shahsavari said. “This can be done by changing the shape of the material, or changing its mass – say one side is heavier than the other – to create a switch. The heat would always prefer to go one way, but in the reverse direction it would be slower.”

Shahsavari is an assistant professor of civil and environmental engineering and of materials science and nanoengineering. Sakhavand is a former graduate student at Rice.

The National Science Foundation and the Rice Department of Civil and Environmental Engineering supported the research. The researchers used the National Science Foundation-supported DAVinCI supercomputer administered by Rice’s Ken Kennedy Institute for Information Technology. They also used computing resources supported by the National Institutes of Health, IBM, CISCO, Qlogic and Adaptive Computing.


source : rice university    link: click here

University of Toronto researchers successfully combine two different materials to create new hyper-efficient light-emitting crystal

                                                                     

Researchers in The Edward S. Rogers Sr. Department of Electrical & Computer Engineering used this insight to invent something totally new: they’ve combined two promising solar cell materials together for the first time, creating a new platform for LED technology.
                                                                     

A glowing quantum dot seamlessly integrated into a perovskite crystal matrix (Image: Ella Marushchenko).

The team designed a way to embed strongly luminescent nanoparticles called colloidal quantum dots (the chocolate chips) into perovskite (the oatmeal cookie). Perovskites are a family of materials that can be easily manufactured from solution, and that allow electrons to move swiftly through them with minimal loss or capture by defects.

The work is published today in the international journal Nature.

“It’s a pretty novel idea to blend together these two optoelectronic materials, both of which are gaining a lot of traction,” says Xiwen Gong (ECE), one of the study’s lead authors and a PhD candidate working with Professor Ted Sargent (ECE). “We wanted to take advantage of the benefits of both by combining them seamlessly in a solid-state matrix.”

                                                                        

(Image: Ella Marushchenko).

The result is a black crystal that relies on the perovskite matrix to ‘funnel’ electrons into the quantum dots, which are extremely efficient at converting electricity to light. Hyper-efficient LED technologies could enable applications from the visible-light LED bulbs in every home, to new displays, to gesture recognition using near-infrared wavelengths.

“When you try to jam two different crystals together, they often form separate phases without blending smoothly into each other,” says Dr. Riccardo Comin, a post-doctoral fellow in the Sargent Group. “We had to design a new strategy to convince these two components to forget about their differences and to rather intermix into forming a unique crystalline entity.”

The main challenge was making the orientation of the two crystal structures line up, called heteroexpitaxy. To achieve heteroepitaxy, Gong, Comin and their team engineered a way to connect the atomic ‘ends’ of the two crystalline structures so that they aligned smoothly, without defects forming at the seams. “We started by building a nano-scale scaffolding ‘shell’ around the quantum dots in solution, then grew the perovskite crystal around that shell so the two faces aligned,” explained coauthor Dr. Zhijun Ning, who contributed to the work while a post-doctoral fellow at UofT and is now a faculty member at ShanghaiTech.

The resulting heterogeneous material is the basis for a new family of highly energy-efficient near-infrared LEDs. Infrared LEDs can be harnessed for improved night-vision technology, to better biomedical imaging, to high-speed telecommunications.

Combining the two materials in this way also solves the problem of self-absorption, which occurs when a substance partly re-absorbs the same spectrum of energy that it emits, with a net efficiency loss. “These dots in perovskite don’t suffer reabsorption, because the emission of the dots doesn’t overlap with the absorption spectrum of the perovskite,” explains Comin.

Gong, Comin and the team deliberately designed their material to be compatible with solution-processing, so it could be readily integrated with the most inexpensive and commercially practical ways of manufacturing solar film and devices. Their next step is to build and test the hardware to capitalize on the concept they have proven with this work.

“We’re going to build the LED device and try to beat the record power efficiency reported in the literature,” says Gong.

This work was supported by the Ontario Research Fund Research Excellence Program, the Natural Sciences and Engineering Research Council of Canada (NSERC), and the King Abdullah University of Science & Technology (KAUST).

source: U of T engineering news   link : click here

Rice University lab calculates unique electronic qualities of double-walled carbon nanotubes

Rice University researchers have determined that two walls are better than one when turning carbon nanotubes into materials like strong, conductive fibers or transistors.

                                                            

Researchers at Rice University are working to determine the electronic properties of double-walled carbon nanotubes. In this example, the team analyzed a nanotube with two zigzag components. The individual nanotubes have band gaps and are semiconductors, but when combined, the band gaps overlap and make the double-walled a semimetal. Click image for larger version. Illustration by Matías Soto 

Rice materials scientist Enrique Barrera and his colleagues used atomic-level models of double-walled nanotubes to see how they might be tuned for applications that require particular properties. They knew from others’ work that double-walled nanotubes are stronger and stiffer than their single-walled cousins. But they found it may someday be possible to tune double-walled tubes for specific electronic properties by controlling their configuration, chiral angles and the distance between the walls.

       Carbon nanotubes, grown by various methods, come in two basic varieties: single-walled and multiwalled (those with two or more walls). But double-walled tubes hold a special place in the hierarchy because, the researchers wrote, they behave somewhat like single-walled tubes but are stronger and better able to survive extreme conditions.

     The Rice team found there’s even more to them when they started looking at how the inner and outer walls match up using tubes with zigzag chirality. Because the electrical properties of single-walled tubes depend on their chirality – the angles of their hexagonal arrangement of atoms – the researchers thought it would be interesting to learn more about those properties in double-walled tubes.

“We saw that the interwall interaction could affect the electronic properties of double-walled carbon nanotubes and decided to study this effect in a more systematic way using computational simulations,” Soto said.

      It turned out that both the distance between the walls — as small as a fraction of a nanometer — and the individual chirality of the tubes impact the double-walls’ electrical properties. In addition, the researchers found the diameter of the tube — especially the inner one, with its more pronounced curvature — has a small but significant impact on the structure’s semiconducting properties.

    Breaking it down further, they determined that semiconducting nanotubes wrapped around metallic, highly conductive nanotubes could be the best candidates for tuning the band gap, the property that defines the value of a semiconductor.

  “The most interesting thing we found was that when you combine a metallic with a semiconductor, the band gap depends on the distance between them,” Soto said.

It’s not yet possible to do so, but the ability to adjust the distance between walls may lead to nanotube transistors, he said.

Other nanotube configurations may be best for turning into macroscopic carbon nanotube conducting wires, particularly with metallic-metallic nanotubes, the researchers found.

Co-authors of the paper are Rice graduate students Travis Boyer and postdoctoral researchers Santoshkumar Biradar and Liehui Ge; Robert Vajtai, a senior faculty fellow at Rice; Alex Elías-Zúñiga, a professor at Tecnológico de Monterrey, Mexico; and Pulickel Ajayan, Rice’s Benjamin M. and Mary Greenwood Anderson Professor in Engineering and a professor of materials science and nanoengineering and of chemistry. Barrera is a professor of materials science and nanoengineering.

The Department of Energy’s Research Partnership to Secure Energy for America, the Mexican government’s CONACyT program and the state of Nuevo León funded the research. The researchers utilized the National Science Foundation-supported DAVinCI supercomputer administered by Rice’s Ken Kennedy Institute for Information Technology.

source: rice university press release  link: click here

New control method for future quantum computers.

A UNSW-led research team has encoded quantum information in silicon using simple electrical pulses for the first time, bringing the construction of affordable large-scale quantum computers one step closer to reality.

Lead researcher, UNSW Associate Professor Andrea Morello from the School of Electrical Engineering and Telecommunications, said his team had successfully realised a new control method for future quantum computers.

Unlike conventional computers that store data on transistors and hard drives, quantum computers encode data in the quantum states of microscopic objects called qubits.

The UNSW team, which is affiliated with the ARC Centre of Excellence for Quantum Computation & Communication Technology, was first in the world to demonstrate single-atom spin qubits in silicon, reported in Nature in 2012 and 2013.

The team has already improved the control of these qubits to an accuracy of above 99% and established the world record for how long quantum information can be stored in the solid state, as published in Nature Nanotechnology in 2014.

It has now demonstrated a key step that had remained elusive since 1998.

"We demonstrated that a highly coherent qubit, like the spin of a single phosphorus atom in isotopically enriched silicon, can be controlled using electric fields, instead of using pulses of oscillating magnetic fields," explained UNSW's Dr Arne Laucht, post-doctoral researcher and lead author of the study.

Associate Professor Morello said the method works by distorting the shape of the electron cloud attached to the atom, using a very localized electric field.

"This distortion at the atomic level has the effect of modifying the frequency at which the electron responds.

"Therefore, we can selectively choose which qubit to operate. It's a bit like selecting which radio station we tune to, by turning a simple knob. Here, the 'knob' is the voltage applied to a small electrode placed above the atom."

                                                                             

CAPTION

This is an eectron wave in a phosphorus atom, distorted by a local electric field.

CREDIT

Dr. Arne Laucht

The findings suggest that it would be possible to locally control individual qubits with electric fields in a large-scale quantum computer using only inexpensive voltage generators, rather than the expensive high-frequency microwave sources.

Moreover, this specific type of quantum bit can be manufactured using a similar technology to that employed for the production of everyday computers, drastically reducing the time and cost of development.

The device used in this experiment was fabricated at the NSW node of the Australian National Fabrication Facility, in collaboration with the group led by UNSW Scientia Professor Andrew Dzurak.

Key to the success of this electrical control method is the placement of the qubits inside a thin layer of specially purified silicon, containing only the silicon-28 isotope.

"This isotope is perfectly non-magnetic and, unlike those in naturally occurring silicon, does not disturb the quantum bit," Associate Professor Morello said.

The purified silicon was provided through collaboration with Professor Kohei Itoh from Keio University in JapAN

Associate Professor Morello is at the School of Electrical Engineering & Telecommunications, UNSW Australia. He is a team leader at the ARC Centre of Excellence for Quantum Computation and Communication Technology, headquartered at UNSW.

The quantum bit device was constructed at UNSW at the Australian National Fabrication Facility, with support from researchers at the University of Melbourne and the Australian National University. The research was funded by the Australian Research Council, the US Army Research Office, the NSW Government, UNSW Australia and the University of Melbourne.

source ; eurekaalert  link : click here

Cost-effective production of magnetic sensors:cost half, and production time is reduced by 50 percent

They are found wherever other measurement methods fail: magnetic sensors. They defy harsh environmental conditions and also function in fluids. A new procedure is now revolutionizing the production of two-dimensional magnetic sensors: They now only cost half, and production time is reduced by 50 percent.

                                                                       

View from above of the prototype of a two-dimensional magnetic sensor. 
© Fraunhofer ENAS

Where did you have to go? Turn right here – or was it the next turn? A glance at the smart-phone helps: Various apps provide maps and turn them in the right direction, adjusting them to north. Navigation devices are equally »clever«: They too show the right direction even before the car sets off. This is made possible by a magnetic sensor. It establishes how the device is being held in relation to the earth’s magnetic field. The market is highly competitive: Every cent counts in the price of the sensors. Until now, manufacturers have relied on several cheap one-dimensional sensors. The disadvantage: They are less sensitive and do not work as accurately as two-dimensional models.

In future however, compact two-dimensional sensors could find their way into smart-phones. Researchers from the Fraunhofer Institute for Electronic Nano Systems ENAS, in Chemnitz have optimized the corresponding manufacturing process. »The costs and manufacturing time for two-dimensional magnetic field sensors drop by half«, says Dr. Olaf Ueberschär, group manager at the ENAS.

Sensors  from one piece

The reason for this drop in costs lies in the method of production: The scientists produce the sensors from one piece of material – hence in a totally different way than ever before. Because even a one-dimensional sensor needs two microelectronic half-bridges, whose applied magnetic fields point in opposite directions. As the basic materials specify a magnetization direction, meaning that the magnetic field within them is already aligned, two different pieces of material used to have to be joined – an elaborate and also expensive procedure. Two half-bridge sensors or four pieces of material were required for two-dimensional sensors.

»For the first time we are able to produce not only the full bridges, but also the two-dimensional sensors monolithically – from one piece«, Ueberschär adds. For this purpose, the researchers separate a layer of material off a wafer and etch the desired structure out. The trick lies in the subsequent laser treatment: This enables the scientists to adjust the preferred magnetic directions at will.

As small as the dot on the “i”

Another advantage: The new sensor is not even quite a square millimeter in size, thus being only about half the size as former models. The smaller the mini-chips are, the more applications they are suitable for. For example for magnetic field cameras, containing numerous sensors in several lines and columns, recording magnetic data. If a high resolution is to be achieved, the sensors must be as small as possible – only then do they fit in close proximity to one another and do not mutually interfere.

Magnetic sensor technology is not restricted to smart-phones. It is used wherever adverse ambient conditions prevail and other measurement methods would fail – for instance in fluids or hot oil baths. They are also found in cars, for example in fully electronic gear levers such as are installed in newer vehicles in the center console or on the steering wheel. And in medical diagnostics they are used to trace tropical diseases and other viruses and bacteria.

Experts will present prototypes of the two-dimensional sensors at the Sensor + Test trade fair from May 19 to 21, 2015 in Nuremberg (Hall 12, Booth 12-531 / 12-537). It will however take about another year before the sensors can actually be used in products.

source: Fraunhofer-Gesellschaft. link: click here

nanomechanical plasmonic phase modulator : Nanoscale Speed Bump Could Regulate Plasmons for High-Speed Data Flow

The name sounds like something Marvin the Martian might have built, but the “nanomechanical plasmonic phase modulator” is not a doomsday device. Developed by a team of government and university researchers, including physicists from the National Institute of Standards and Technology (NIST), the innovation harnesses tiny electron waves called plasmons. It’s a step towards enabling computers to process information hundreds of times faster than today’s machines.

                                                    

The plasmonic phase modulator is an inverted, nanoscale speed bump. Gold strands are stretched side by side across a gap just 270 nanometers above the gold surface below them. Incoming plasmons travel though this air gap between the bridges and the bottom gold layer. Lowering the "bump" with a control voltage squeezes the gap and makes the device function like a plasmon switch. Credit: Dennis/Rutgers and Dill/NIST

                  Computers currently shuttle information around using electricity traveling down nanoscale metal wires. Although inexpensive and easy to miniaturize, metal wires are limited in terms of speed due to the resistance in the metal itself. Fiber optics use light to move information about 10,000 times faster, but these and other nonmetallic waveguides are constrained by pesky physical laws that require critical dimensions to be at least half the wavelength of the light in size; still small, but many times larger than the dimensions of current commercial nanoscale electronics.

Plasmonics combines the small size and manufacturability of electronics with the high speeds of optics. When light waves interact with electrons on a metal’s surface, strong fields with dimensions far smaller than the wavelength of the original light can be created—plasmons. Unlike light, these plasmons are free to travel down nanoscale wires or gaps in metals.

The team, which included researchers from Rutgers, the University of Colorado at Colorado Springs, and Argonne National Laboratory, fabricated their device using commercial nanofabrication equipment at the NIST NanoFab. Small enough to serve in existing and future computer architectures, this technology may also enable electrically tunable and switchable thin optical components.

        The plasmonic phase modulator is effectively an inverted, nanoscale speed bump. Eleven gold strands are stretched side by side like footbridges across a 23-micrometer gap just 270 nanometers above the gold surface below them. Incoming plasmons, created by laser light at one end of the array, travel though this air gap between the bridges and the bottom gold layer.

When a control voltage is applied, electrostatic attraction bends the gold strands downwards into a U shape. At a maximum voltage—close to the voltages used in today’s computer chips—the gap narrows, slowing the plasmons. As the plasmons slow, their wavelength becomes shorter, allowing more than an extra half of a plasmonic wave to fit under the bridge. Because it’s exactly out of phase with the original wave, this additional half wavelength can be used to selectively cancel the wave, making the bridge an optical switch.

At 23 micrometers, the prototype is relatively large, but according to NIST researcher Vladimir Aksyuk, their calculations show that the device could be shortened by a factor of 10, scaling the device’s footprint down by a factor of 100. According to these calculations, the modulation range can be maintained without increase in the optical loss, as the length and the size of the gap are reduced. 

“With these prototypes, we showed that nanomechanical phase tuning is efficient,” says Aksyuk. “This effect can be generalized to other tunable plasmonic devices that need to be made smaller. And as they get smaller, you can put more of them on the same chip, bringing them closer to practical realization.”

source: NIST ,Nature Photonics  LINK: click here

Wound Healing Promoted by Novel Nanoparticle Therapy developed by researchers at Albert Einstein College of Medicine

An experimental therapy developed by researchers at Albert Einstein College of Medicine of Yeshiva University cut in half the time it takes to heal wounds compared to no treatment at all. Details of the therapy, which was successfully tested in mice, were published online in the Journal of Investigative Dermatology.

“We envision that our nanoparticle therapy could be used to speed the healing of all sorts of wounds, including everyday cuts and burns, surgical incisions, and chronic skin ulcers, which are a particular problem in the elderly and people with diabetes,” said study co-leader David J. Sharp, Ph.D., professor of physiology & biophysics at Einstein.

                                                       

Imaging of burns indicates that those treated with the FL2 inhibitor nanotechnology experienced collagen deposition and hair follicle formation. (2-photo confocal microscopy) credit:Vera DesMarais/Albert Einstein College of Medicine

Dr. Sharp and his colleagues had earlier discovered that an enzyme called fidgetin-like 2 (FL2) puts the brakes on skin cells as they migrate towards wounds to heal them. They reasoned that the healing cells could reach their destination faster if their levels of FL2 could be reduced. So they developed a drug that inactivates the gene that makes FL2 and then put the drug in tiny gel capsules called nanoparticles and applied the nanoparticles to wounds on mice. The treated wounds healed much faster than untreated wounds.

FL2 belongs to the fidgetin family of enzymes, which play varying roles in cellular development and function. To learn more about FL2’s role in humans, Dr. Sharp suppressed FL2’s activity in human cells in tissue culture. When those cells were placed on a standard wound assay (for measuring properties like cell migration and proliferation), they moved unusually fast. “This suggested that if we could find a way to target FL2 in humans, we might have a new way to promote wound healing,” said Dr. Sharp.

Dr. Sharp and project co-leader Joshua Nosanchuk, M.D., professor of medicine at Einstein and attending physician, infectious diseases at Montefiore Medical Center, developed a wound-healing therapy that uses molecules of silencing RNA (siRNAs) specific for FL2. The siRNAs act to silence genes. They do so by binding to a gene’s messenger RNA (mRNA), preventing the mRNA from being translated into proteins (in this case, the enzyme FL2). However, “siRNAs on their own won’t be effectively taken up by cells, particularly inside a living organism” said Dr. Sharp. “They will be quickly degraded unless they are put into some kind of delivery vehicle.”

To find a way to deliver siRNAs for curbing FL2, Dr. Sharp collaborated with Joel Friedman, M.D., Ph.D., professor of physiology & biophysics and of medicine at Einstein, and study co-leader Adam Friedman, M.D., director of dermatologic research at Einstein and Montefiore, who together had developed nanoparticles that protect molecules such as siRNA from being degraded as they ferry the molecules to their intended targets.

The nanoparticles with their siRNA cargoes were then tested by topically applying them to mice with either skin excisions or burns. In both cases, the wounds closed more than twice as fast as in untreated controls. “Not only did the cells move into the wounds faster, but they knew what to do when they got there,” said Dr. Sharp. “We saw normal, well-orchestrated regeneration of tissue, including hair follicles and the skin’s supportive collagen network.”

Dr. Sharp plans to start testing the therapy on pigs, whose skin closely resembles that of humans, within months.

       The research presented in this manuscript was funded by grants from the National Institute of Health (R01 GM109909) and the Telemedicine and Advanced Technology Research Center (TATRC) at the U.S. Army Medical Research and Materiel Command (USAMRMC) through award W81XWH1210379. Support was also granted by the Women’s Dermatologic Society academic grant program.

David Sharp and Rabab Charafeddine are co-inventors on U.S. Patent #20130022667, “Fidgetin-like 2 as a target to enhance wound healing,” which has been licensed by MicroCures Inc. Dr. Sharp is currently chief scientific officer of MicroCures. Dr. Sharp, Dr. Joel Friedman, Dr. Adam Friedman and Dr. Nosanchuk all have equity in the company. The other authors declare no conflicts of interest.

source: Albert Einstein College of Medicine of Yeshiva University  link: click here