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Illustration of the nanoscale semiconductor structure used for demonstrating the ultralow-threshold nanolaser. A single nanorod is placed on a thin silver film (28 nm thick). The resonant electromagnetic field is concentrated at the 5-nm-thick silicon dioxide gap layer sandwiched by the semiconductor nanorod and the atomically smooth silver film. (Image Credit: University of Texas)

Physicists at The University of Texas at Austin, in collaboration with colleagues in Taiwan and China, have developed the world’s smallest semiconductor laser, a breakthrough for emerging photonic technology with applications from computing to medicine. Miniaturization of semiconductor lasers is key for the development of faster, smaller and lower energy photon-based technologies, such as ultrafast computer chips; highly sensitive biosensors for detecting, treating and studying disease; and next-generation communication technologies. Such photonic devices could use nanolasers to generate optical signals and transmit information, and have the potential to replace electronic circuits. But the size and performance of photonic devices have been restricted by what’s known as the three-dimensional optical diffraction limit. “We have developed a nanolaser device that operates well below the 3-D diffraction limit,” said Chih-Kang “Ken” Shih, professor of physics at The University of Texas at Austin. “We believe our research could have a large impact on nanoscale technologies.” The device is constructed of a gallium nitride nanorod that is partially filled with indium gallium nitride. Both alloys are semiconductors used commonly in LEDs. The nanorod is placed on top of a thin insulating layer of silicon that in turn covers a layer of silver film that is smooth at the atomic level. It’s a material that the Shih lab has been perfecting for more than 15 years. That “atomic smoothness” is key to building photonic devices that don’t scatter and lose plasmons, which are waves of electrons that can be used to move large amounts of data.

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Atomic force microscopy images of artificial ion channels created by scientists. The images are of the same sample, with increasing magnification. (Image Credit: Bing Gong, University at Buffalo)

Inspired by nature, an international research team has created synthetic pores that mimic the activity of cellular ion channels, which play a vital role in human health by severely restricting the types of materials allowed to enter cells. The pores the scientists built are permeable to potassium ions and water, but not to other ions such as sodium and lithium ions. This kind of extreme selectivity, while prominent in nature, is unprecedented for a synthetic structure, said University at Buffalo chemistry professor Bing Gong, PhD, who led the study. The project's success lays the foundation for an array of exciting new technologies. In the future, scientists could use such highly discerning pores to purify water, kill tumors, or otherwise treat disease by regulating the substances inside of cells. To create the synthetic pores, the researchers developed a method to force donut-shaped molecules called rigid macrocycles to pile on top of one another. The scientists then stitched these stacks of molecules together using hydrogen bonding. The resulting structure was a nanotube with a pore less than a nanometer in diameter. "This nanotube can be viewed as a stack of many, many rings," said Xiao Cheng Zeng, University of Nebraska-Lincoln Ameritas University Professor of Chemistry, and one of the study's senior authors. "The rings come together through a process called self-assembly, and it's very precise. It's the first synthetic nanotube that has a very uniform diameter. It's actually a sub-nanometer tube. It's about 8.8 angstroms." (One angstrom is one-10th of a nanometer, which is one-billionth of a meter.) The next step in the research is to tune the structure of the pores to allow different materials to selectively pass through, and to figure out what qualities govern the transport of materials through the pores, Gong said.

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Researchers from the University of Toronto (Canada) and King Abdullah University of Science & Technology (Saudi Arabia) have made a breakthrough in the development of colloidal quantum dot (CQD) films, leading to the most efficient CQD solar cell ever. The researchers created a solar cell out of inexpensive materials that was certified at a world-record 7.0% efficiency. Quantum dots are semiconductors only a few nanometres in size and can be used to harvest electricity from the entire solar spectrum -- including both visible and invisible wavelengths. Unlike current semiconductor growth techniques, CQD films can be created quickly and at low cost, similar to paint or ink. This research paves the way for solar cells that can be fabricated on flexible substrates in the same way newspapers are rapidly printed in mass quantities. The U of T cell represents a 37% increase in efficiency over the previous certified record. In order to improve efficiency, the researchers needed a way to both reduce the number of “traps” for electrons associated with poor surface quality while simultaneously ensuring their films were very dense to absorb as much light as possible. 

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The researchers’ designed structure, left, was inspired by natural viruses, such as the tobacco mosaic virus, right. (Image Credit: University of Pennsylvania)

Engineering structures on the smallest possible scales — using molecules and individual atoms as building blocks — is both physically and conceptually challenging. An interdisciplinary team of researchers at theUniversity of Pennsylvania has now developed a method of computationally selecting the best of these blocks, drawing inspiration from the similar behavior of proteins in making biological structures. The team set out to design proteins that could wrap around single-walled carbon nanotubes. Consisting of a cylindrical pattern of carbon atoms tens of thousands of times thinner than a human hair, nanotubes are enticing to nanoengineers as they are extraordinarily strong and could be useful as platform for other nano-structures. The hurdle in making such scaffolds isn’t a lack of information, but a surfeit of it: researchers have compiled databases that list hundreds of thousands of actual and potential protein structures in atomic detail. Picking the building materials for a particular structure from this vast array and assuring that they self-assemble into the desired shape was beyond the abilities of powerful computers, much less humans. The researchers’ algorithm works in three steps, which, given the parameters of the desired scaffolding, successively eliminate proteins that will not produce the right shape. The elimination criteria were based on traits like symmetry, periodicity of binding sites and similarity to protein “motifs” found in nature. After separating the wheat from the chaff, the result is a list of thousands of candidate proteins. While still a daunting amount, the algorithm makes the protein selection process merely difficult, rather than impossible.

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The honeycomb material structure allows selective adsorption of carbon dioxide while allowing other gases such as nitrogen, methane, and hydrogen to pass back through. (Image Credit: University of Nottingham)

A novel porous material that has unique carbon dioxide retention properties has been developed through research led by The University of Nottingham in the UK. The findings form part of ongoing efforts to develop new materials for gas storage applications and could have an impact in the advancement of new carbon capture products for reducing emissions from fossil fuel processes. It focuses on the metal organic framework NOTT-202a, which has a unique honeycomb-like structural arrangement and can be considered to represent an entirely new class of porous material. Most importantly, the material structure allows selective adsorption of carbon dioxide — while other gases such as nitrogen, methane and hydrogen can pass back through, the carbon dioxide remains trapped in the materials nanopores, even at low temperatures. NOTT-202a consists of a tetra-carboxylate ligands — a honeycomb like structure made of a series of molecules or ions bound to a central metal atom — and filled with indium metal centres. This forms a novel structure consisting of two interlocked frameworks. State-of-the-art X-ray powder diffraction measurements at Diamond Light Source and advanced computer modelling were used to probe and gain insight into the unique carbon dioxide capturing properties of the material.

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Vienna Printer Distance between the towers: 90 µm (credit: Klaus Cicha). Photo courtesy Vienna University of Technolog

Printing three dimensional objects with incredibly fine details is now possible using “two-photon lithography”. With this technology, tiny structures on a nanometer scale can be fabricated. Researchers at theVienna University of Technology (TU Vienna) have now made a major breakthrough in speeding up this printing technique: The high-precision-3D-printer at TU Vienna is orders of magnitude faster than similar devices. This opens up completely new areas of application, such as in medicine. The 3D printer uses a liquid resin, which is hardened at precisely the correct spots by a focused laser beam. The focal point of the laser beam is guided through the resin by movable mirrors and leaves behind a polymerized line of solid polymer, just a few hundred nanometers wide. This high resolution enables the creation of intricately structured sculptures as tiny as a grain of sand. “Until now, this technique used to be quite slow”, says Professor Jürgen Stampfl from the Institute of Materials Science and Technology at the TU Vienna. “The printing speed used to be measured in millimeters per second – our device can do five meters in one second.” In two-photon lithography, this is a world record. Researchers all over the world are working on 3D printers today – at universities as well as in industry. “Our competitive edge here at the Vienna University of Technology comes from the fact that we have experts from very different fields, working on different parts of the problem, at one single university”, Jürgen Stampfl emphasizes. In materials science, process engineering or the optimization of light sources, there are experts working together and coming up with mutually stimulating ideas. Because of the dramatically increased speed, much larger objects can now be created in a given period of time. This makes two-photon-lithography an interesting technique for industry. At the TU Vienna, scientists are now developing bio-compatible resins for medical applications. They can be used to create scaffolds to which living cells can attach themselves facilitating the systematic creation of biological tissues. The 3d printer could also be used to create tailor made construction parts for biomedical technology or nanotechnology.

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The University of Texas at Tyler has created a student chapter of the Institute of Electrical and Electronics Engineers, Dr. Harold Doty, College of Business and Technology dean, announced. The UT Tyler IEEE Nanotechnology Student Branch Chapter is the first of its kind in Texas and only the second one worldwide. "I wanted to create an interest in nanotechnology for students in the industrial technology program. The chapter is a perfect platform to get students involved,” said Dr. Dominick Fazarro, UT Tyler associate professor and chapter adviser. “Nanotechnology is considered the new industrial revolution, and students need to know the future implications and impact in society.” Nanotechnology is the engineering science of creating materials at the atomic and molecular level. It has many applications in a variety of industries including medicine, energy, electronics and computers. One of the 15 campuses of the UT System, UT Tyler offers excellence in teaching, research, artistic performance and community service. More than 80 undergraduate and graduate degree programs are available at UT Tyler, which has an enrollment of almost 7,000 high-ability students at its campuses in Tyler, Longview and Palestine.

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Gold nanoparticles created by the Rice University lab of Eugene Zubarev take on the shape of starfruit in a chemical bath with silver nitrate, ascorbic acid and gold chloride. Photo courtesy Zubarev Lab/Rice University

They look like fruit, and indeed the nanoscale stars of new research at Rice University have tasty implications for medical imaging and chemical sensing.  Starfruit-shaped gold nanorods synthesized by chemist Eugene Zubarev and Leonid Vigderman, a graduate student in his lab at Rice’s BioScience Research Collaborative, could nourish applications that rely on surface-enhanced Raman spectroscopy (SERS). The researchers found their particles returned signals 25 times stronger than similar nanorods with smooth surfaces. That may ultimately make it possible to detect very small amounts of such organic molecules as DNA and biomarkers, found in bodily fluids, for particular diseases. “There’s a great deal of interest in sensing applications,” said Zubarev, an associate professor of chemistry. “SERS takes advantage of the ability of gold to enhance electromagnetic fields locally. Fields will concentrate at specific defects, like the sharp edges of our nanostarfruits, and that could help detect the presence of organic molecules at very low concentration.” SERS can detect organic molecules by themselves, but the presence of a gold surface greatly enhances the effect, Zubarev said. “If we take the spectrum of organic molecules in solution and compare it to when they are adsorbed on a gold particle, the difference can be millions of times,” he said. The potential to further boost that stronger signal by a factor of 25 is significant, he said. Zubarev and Vigderman grew batches of the star-shaped rods in a chemical bath. They started with seed particles of highly purified gold nanorods with pentagonal cross-sections developed by Zubarev’s lab in 2008 and added them to a mixture of silver nitrate, ascorbic acid and gold chloride.

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This illustration shows lithium atoms (red) adhered to a graphene lattice that will produce electricity when bent, squeezed or twisted. Conversely, the graphene will deform when an electric field is applied, opening new possibilities in nanotechnology. (Image Credit: Mitchell Ong / Stanford School of Engineering)

To the long list of exceptional physical properties of graphene, engineers atStanford Universityhave added yet another: piezoelectricity, the property of some materials to produce an electric charge when bent, squeezed or twisted. In what became known as the "Scotch tape technique," researchers first extracted graphene with a piece of adhesive in 2004. Graphene is a single layer of carbon atoms arranged in a honeycomb, hexagonal pattern. Under a microscope, it looks like chicken wire.  In 2010, the researchers who first isolated it shared the Nobel Prize. Graphene is a wonder material. It is a hundred times better at conducting electricity than silicon. It is stronger than diamond. And, at just one atom thick, it is so thin as to be essentially a two-dimensional material. Such promising physics have made graphene the most studied substance of the last decade, particularly in nanotechnology. Yet, while graphene is many things, it is not piezoelectric. Perhaps most valuably, piezoelectricity is reversible. When an electric field is applied, piezoelectric materials change shape, yielding a remarkable level of engineering control. Piezoelectrics have found application in countless devices from watches, radios and ultrasound to the push-button starters on propane grills, but these uses all require relatively large, three-dimensional quantities of piezoelectric materials. The Stanford team's engineered graphene has, for the first time, extended such fine physical control to the nanoscale. "The physical deformations we can create are directly proportional to the electrical field applied and this represents a fundamentally new way to control electronics at the nanoscale," said Evan Reed, head of the Materials Computation and Theory Group at Stanford. "This phenomenon brings new dimension to the concept of  'straintronics' for the way the electrical field strains — or deforms — the lattice of carbon, causing it to change shape in predictable ways." "Piezoelectric graphene could provide an unparalleled degree of electrical, optical or mechanical control for applications ranging from touchscreens to nanoscale transistors," said Mitchell Ong, a post-doctoral scholar in Reed's lab. Using a sophisticated modeling application running on high-performance supercomputers, the engineers simulated the deposition of atoms on one side of a graphene lattice – a process known as doping – and measured the piezoelectric effect. They modeled graphene doped with lithium, hydrogen, potassium and fluorine, as well as combinations of hydrogen and fluorine and lithium and fluorine, on either side of the lattice. Doping just one side of the graphene, or doping both sides with different atoms, is key to the process as it breaks graphene's perfect physical symmetry, which otherwise cancels the piezoelectric effect. The results surprised both engineers. "We thought the piezoelectric effect would be present, but relatively small. Yet, we were able to achieve piezoelectric levels comparable to traditional three-dimensional materials," said Reed. "It was pretty significant."

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In this graphic, clockwise from top: the glue can be printed in a pattern on a surface, treated to make it sticky (red) and then a new layer stuck on top. The background is a patterned nanoglue on a surface.(Tingrui Pan/UC Davis photo)

Engineers at the University of California, Davis, have invented a superthin “nanoglue” that could be used in new-generation microchip fabrication. “The material itself (say, semiconductor wafers) would break before the glue peels off,” said Tingrui Pan, professor of biomedical engineering. He and his fellow researchers have filed a provisional patent. Conventional glues form a thick layer between two surfaces. Pan’s nanoglue, which conducts heat and can be printed, or applied, in patterns, forms a layer the thickness of only a few molecules. The nanoglue is based on a transparent, flexible material called polydimethylsiloxane, or PDMS, which, when peeled off a smooth surface usually leaves behind an ultrathin, sticky residue that researchers had mostly regarded as a nuisance. Pan and his colleagues realized that this residue could instead be used as glue, and enhanced its bonding properties by treating the residue surface with oxygen. The nanoglue could be used to stick silicon wafers into a stack to make new types of multilayered computer chips. Pan said he thinks it could also be used for home applications — for example, as double-sided tape or for sticking objects to tiles. The glue only works on smooth surfaces and can be removed with heat treatment.

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