#Unlocking nanofiberspotential Prototype boosts production of versatile fibers fourfold, while cutting energy consumption by 92 percent.
Nanofibers-polymer filaments only a couple of hundred nanometers in diameter have a huge range of potential applications, from solar cells to water filtration to fuel cells.
But so far, their high cost of manufacture has relegated them to just a few niche industries.
In the latest issue of the journal Nanotechnology, MIT researchers describe a new technique for producing nanofibers that increases the rate of production fourfold
while reducing energy consumption by more than 90 percent, holding out the prospect of cheap, efficient nanofiber production. e have demonstrated a systematic way to produce nanofibers through electrospinning that surpasses the state of the art,
says Luis Fernando Velásquez-García, a principal research scientist in MIT Microsystems Technology Laboratories, who led the new work. ut the way that it done opens a very interesting possibility.
Our group and many other groups are working to push 3-D printing further, to make it possible to print components that transduce,
that actuate, that exchange energy between different domains, like solar to electrical or mechanical. We have something that naturally fits into that picture.
We have an array of emitters that can be thought of as a dot matrix-printer printer where you would be able to individually control each emitter to print deposits of nanofibers. angled talenanofibers are useful for any application that benefits from a high ratio of surface area to volume solar cells, for instance,
which try to maximize exposure to sunlight, or fuel cell electrodes, which catalyze reactions at their surfaces.
Nanofibers can also yield materials that are permeable only at very small scales, like water filters,
or that are remarkably tough for their weight, like body armor. The standard technique for manufacturing nanofibers is called electrospinning,
and it comes in two varieties. In the first a polymer solution is pumped through a small nozzle,
and then a strong electric field stretches it out. The process is slow, however, and the number of nozzles per unit area is limited by the size of the pump hydraulics. The other approach is to apply a voltage between a rotating drum covered by metal cones and a collector electrode.
The cones are dipped in a polymer solution, and the electric field causes the solution to travel to the top of the cones,
where it emitted toward the electrode as a fiber. That approach is erratic however, and produces fibers of uneven lengths;
it also requires voltages as high as 100,000 volts. Thinking smallvelásquez-García and his co-authors Philip Ponce de Leon, a former master student in mechanical engineering;
Frances Hill, a former postdoc in Velásquez-García group who now at KLA-Tencor; and Eric Heubel, a current postdoc adapt the second approach,
but on a much smaller scale, using techniques common in the manufacture of microelectromechanical systems to produce dense arrays of tiny emitters.
The emitterssmall size reduces the voltage necessary to drive them and allows more of them to be packed together, increasing production rate.
At the same time, a nubbly texture etched into the emitterssides regulates the rate at which fluid flows toward their tips,
yielding uniform fibers even at high manufacturing rates. e did all kinds of experiments, and all of them show that the emission is uniform,
Velásquez-García says. To build their emitters, Velásquez-García and his colleagues use a technique called deep reactive-ion etching.
and a dissolved polymer. When an electrode is mounted opposite the sawteeth and a voltage applied between them,
the water-ethanol mixture streams upward, dragging chains of polymer with it. The water and ethanol quickly dissolve, leaving a tangle of polymer filaments opposite each emitter, on the electrode.
The researchers were able to pack 225 emitters, several millimeters long, on a square chip about 35 millimeters on a side.
At the relatively low voltage of 8, 000 volts, that device yielded four times as much fiber per unit area as the best commercial electrospinning devices.
The work is n elegant and creative way of demonstrating the strong capability of traditional MEMS microelectromechanical systems fabrication processes toward parallel nanomanufacturing
says Reza Ghodssi, a professor of electrical engineering at the University of Maryland. Relative to other approaches, he adds,
there is n increased potential to scale it up while maintaining the integrity and accuracy by
which the processing method is applied. mage: A scanning electron micrograph of the new microfiber emitters, showing the arrays of rectangular columns etched into their sides.
World's thinnest lightbulb developed Led by Young Duck Kim, a postdoctoral research scientist in James Hone's group at Columbia Engineering, a team of scientists from Columbia, Seoul National University (SNU),
and Korea Research Institute of Standards and Science (KRISS) reported today that they have demonstrated-for the first time-an on-chip visible light source using graphene, an atomically thin and perfectly crystalline form of carbon,
They attached small strips of graphene to metal electrodes, suspended the strips above the substrate,
right Visible light Emission from Graphene, is published in the Advance Online Publication (AOP) on Nature Nanotechnology's website on June 15."
what is essentially the world's thinnest light bulb, "says Hone, Wang Fon-Jen Professor of Mechanical engineering at Columbia Engineering and co-author of the study."
"This new type of'broadband'light emitter can be integrated into chips and will pave the way towards the realization of atomically thin, flexible,
and transparent displays, and graphene-based on-chip optical communications.""Creating light in small structures on the surface of a chip is crucial for developing fully integrated'photonic'circuits that do with light
what is now done with electric currents in semiconductor integrated circuits. Researchers have developed many approaches to do this, but have not yet been able to put the oldest and simplest artificial light sourcehe incandescent light bulbnto a chip.
This is primarily because light bulb filaments must be extremely hothousands of degrees Celsiusn order to glow in the visible range
and micro-scale metal wires cannot withstand such temperatures. In addition, heat transfer from the hot filament to its surroundings is extremely efficient at the microscale
making such structures impractical and leading to damage of the surrounding chip. By measuring the spectrum of the light emitted from the graphene,
the team was able to show that the graphene was reaching temperatures of above 2500 degrees Celsius,
hot enough to glow brightly. he visible light from atomically thin graphene is so intense that it is visible even to the naked eye,
without any additional magnification, explains Kim, first and co-lead author on the paper. Interestingly, the spectrum of the emitted light showed peaks at specific wavelengths,
or the metal electrodes is due to another interesting property: as it heats up, graphene becomes a much poorer conductor of heat.
so that less energy is needed to attain temperatures needed for visible light emission, Myung-Ho Bae, a senior researcher at KRISS and co-lead author,
Yun Daniel Park, professor in the Department of physics and Astronomy at Seoul National University and co-lead author,
dison originally used carbon as a filament for his light bulb and here we are going back to the same element,
#Chemists devise technology that could transform solar energy storage The materials in most of today's residential rooftop solar panels can store energy from the sun for only a few microseconds at a time.
A new technology developed by chemists at UCLA is capable of storing solar energy for up to several weeks-an advance that could change the way scientists think about designing solar cells.
The new design is inspired by the way that plants generate energy through photosynthesis. iology does a very good job of creating energy from sunlight
a UCLA professor of chemistry and one of the senior authors of the research. lants do this through photosynthesis with extremely high efficiency. n photosynthesis,
plants that are exposed to sunlight use carefully organized nanoscale structures within their cells to rapidly separate charges pulling electrons away from the positively charged molecule that is left behind,
To capture energy from sunlight, conventional rooftop solar cells use silicon, a fairly expensive material. There is currently a big push to make lower-cost solar cells using plastics
rather than silicon, but today plastic solar cells are relatively inefficient, in large part because the separated positive and negative electric charges often recombine before they can become electrical energy. odern plastic solar cells don have well-defined structures like plants do
because we never knew how to make them before, Tolbert said. ut this new system pulls charges apart
and keeps them separated for days, or even weeks. Once you make the right structure,
you can vastly improve the retention of energy. The two components that make the UCLA-developed system work are a polymer donor and a nanoscale fullerene acceptor.
The polymer donor absorbs sunlight and passes electrons to the fullerene acceptor; the process generates electrical energy.
The plastic materials, called organic photovoltaics, are organized typically like a plate of cooked pasta a disorganized mass of long, skinny polymer paghettiwith random fullerene eatballs.
But this arrangement makes it difficult to get current out of the cell because the electrons sometimes hop back to the polymer spaghetti
and are lost. The UCLA technology arranges the elements more neatly like small bundles of uncooked spaghetti with precisely placed meatballs.
Some fullerene meatballs are designed to sit inside the spaghetti bundles, but others are forced to stay on the outside.
The fullerenes inside the structure take electrons from the polymers and toss them to the outside fullerene
which can effectively keep the electrons away from the polymer for weeks. hen the charges never come back together,
the system works far better, said Benjamin Schwartz, a UCLA professor of chemistry and another senior co-author. his is the first time this has been shown using modern synthetic organic photovoltaic materials.
In the new system, the materials self-assemble just by being placed in close proximity. e worked really hard to design something
so we don have to work very hard, Tolbert said. The new design is also more environmentally friendly than current technology,
because the materials can assemble in water instead of more toxic organic solutions that are used widely today. nce you make the materials,
Schwartz said. o there no additional work. The researchers are already working on how to incorporate the technology into actual solar cells.
Yves Rubin, a UCLA professor of chemistry and another senior co-author of the study, led the team that created the uniquely designed molecules. e don have these materials in a real device yet;
this is all in solution, he said. hen we can put them together and make a closed circuit,
#Chemists devise technology that could transform solar energy storage The materials in most of today's residential rooftop solar panels can store energy from the sun for only a few microseconds at a time.
A new technology developed by chemists at UCLA is capable of storing solar energy for up to several weeks-an advance that could change the way scientists think about designing solar cells.
The new design is inspired by the way that plants generate energy through photosynthesis. iology does a very good job of creating energy from sunlight
a UCLA professor of chemistry and one of the senior authors of the research. lants do this through photosynthesis with extremely high efficiency. n photosynthesis,
plants that are exposed to sunlight use carefully organized nanoscale structures within their cells to rapidly separate charges pulling electrons away from the positively charged molecule that is left behind,
To capture energy from sunlight, conventional rooftop solar cells use silicon, a fairly expensive material. There is currently a big push to make lower-cost solar cells using plastics
rather than silicon, but today plastic solar cells are relatively inefficient, in large part because the separated positive and negative electric charges often recombine before they can become electrical energy. odern plastic solar cells don have well-defined structures like plants do
because we never knew how to make them before, Tolbert said. ut this new system pulls charges apart
and keeps them separated for days, or even weeks. Once you make the right structure,
you can vastly improve the retention of energy. The two components that make the UCLA-developed system work are a polymer donor and a nanoscale fullerene acceptor.
The polymer donor absorbs sunlight and passes electrons to the fullerene acceptor; the process generates electrical energy.
The plastic materials, called organic photovoltaics, are organized typically like a plate of cooked pasta a disorganized mass of long, skinny polymer paghettiwith random fullerene eatballs.
But this arrangement makes it difficult to get current out of the cell because the electrons sometimes hop back to the polymer spaghetti
and are lost. The UCLA technology arranges the elements more neatly like small bundles of uncooked spaghetti with precisely placed meatballs.
Some fullerene meatballs are designed to sit inside the spaghetti bundles, but others are forced to stay on the outside.
The fullerenes inside the structure take electrons from the polymers and toss them to the outside fullerene
which can effectively keep the electrons away from the polymer for weeks. hen the charges never come back together,
the system works far better, said Benjamin Schwartz, a UCLA professor of chemistry and another senior co-author. his is the first time this has been shown using modern synthetic organic photovoltaic materials.
In the new system, the materials self-assemble just by being placed in close proximity. e worked really hard to design something
so we don have to work very hard, Tolbert said. The new design is also more environmentally friendly than current technology,
because the materials can assemble in water instead of more toxic organic solutions that are used widely today. nce you make the materials,
Schwartz said. o there no additional work. The researchers are already working on how to incorporate the technology into actual solar cells.
Yves Rubin, a UCLA professor of chemistry and another senior co-author of the study, led the team that created the uniquely designed molecules. e don have these materials in a real device yet;
this is all in solution, he said. hen we can put them together and make a closed circuit,
When the new iphone came out, customers complained that it could be bent-but what if you could roll up your too big 6 Plus to actually fit in your pocket?
That technology might be available sooner than you think, based on the work of USC Viterbi engineers.
For many decades, silicon has been the heart of modern electronics but as a material, it has its limits.
As our devices get smaller and smaller, the basic unit of these devices, a transistor,
the size of the silicon transistor is reaching its physical limit. As silicon devices are based on
Consumers also demand phones to be lighter, faster, smaller, more flexible, wearable, bendable, etc. Yet silicon is also rigid one can bend your smart phone or computer.
These physical limitations have driven the race for new materials that can be used as semiconductors in lieu of silicon.
The demand for a silicon material aided the discovery of graphene, a single layer of graphite
which won the Nobel prize in Physics in 2010. Since this time scientists and engineers have developed many two-dimensional (2d) material innovations layered materials with the thickness of only one atom or a few atoms.
This method demands less energy and is cheaper, and the synthesized materials have some incredible new properties.
Ahamad Abbas, graduate student; Han Wang, assistant professor; Rohan Dhall, graduate student; Stephen B. Cronin, associate professor; Mingyuan Ge, research assistant;
Xin Fang, graduate student; and Professor Chongwu Zhou of the Ming Hsieh Department of Electrical engineering, in concert with their collaborators, is documented in a paper titled lack Arsenic-Phosphorus:
Layered Anisotropic Infrared Semiconductors with Highly Tunable Compositions and Properties. The paper appeared in Advanced Materials on June 25, 2015.
What the researchers are excited most about is the ability to adjust the electronic and optical properties of these materials to a range that cannot be achieved by any other 2d materials thus far.
This includes manipulating the materialschemical compositions during materials synthesis and the materialsability to sense long wavelength infrared (LWIR) waves due to their small energy gaps.
This particular electromagnetic spectral range of LWIR is important for a range of applications such as LIDAR (light radar) systems
basically because LWIR waves are highly transparent in earth atmosphere. This wave range also has great application for the soldiers in the military who rely on infrared thermal imaging technology and for flexible night vision glasses.
Another intriguing aspect of these new layeredsemiconductors is their anisotropic electronic and optical properties, which means the materials have different properties along x and y direction in the same plane.
The researchers believe these are marked improvement from existing materials and devices and would lead to unique applications.
In addition, the researchers anticipate that it could also lead to important improvement for devices that monitor the environment. e believe these materials are important members in a large family of 2d materials
we anticipate there is lots of exciting fundamental physics research as well as engineering work to be Done for example,
Atomic force microscope image of a black arsenic-phosphorus field-effect transistor. Image courtesy of Chongwu Zhou and Bilu Liu y
The results demonstrate a powerful operando technique-from the Latin for"in working condition"-that may revolutionize research on catalysts
batteries, fuel cells, and other major energy technologies.""We tracked the dynamic transformations of a working catalyst,
including single atoms and larger structures, during an active reaction at room temperature,"said study coauthor and Brookhaven Lab scientist Eric Stach."
"This gives us unparalleled insight into nanoparticle structure and would be impossible to achieve without combining two complementary operando techniques."
To prove the efficacy of this new mosquito-sized reaction chamber-called a micro-reactor-the scientists tracked the performance of a platinum catalyst during the conversion of ethylene to ethane, a model reaction relevant to many industrial synthesis processes.
They conducted x-ray studies at the National Synchrotron Light source (NSLS) and electron microscopy at the Center for Functional Nanomaterials (CFN), both DOE Office of Science User Facilities."
and distribution of catalysts affect their efficiency and durability,"said study coauthor Ralph Nuzzo of the University of Illinois at Urbana-Champaign."
"Now that we can track those parameters throughout the reaction sequence, we can better determine the ideal design of future catalysts-especially those that drive energy-efficient reactions without using expensive and rare materials like platinum."
"Hidden behind the curtainin transmission electron microscopy (TEM), a focused electron beam passes through the sample and captures images of the nanoparticles within.
This is usually performed in a pristine environment-often an inactive, low-pressure vacuum-but the micro-reactor allowed the TEM to operate in the presence of an atmosphere of reactive gases."
"With TEM, we take high-resolution pictures of the particles to directly see their size and distribution,"said Stach,
who leads CFN's Electron microscopy Group.""But with the micro-reactor, some signals were too small to detect.
Particles smaller than a single nanometer were hidden behind what we call the resolution curtain of the technique."
"Another technique was needed to peer behind the curtain and reveal the full reaction story: x-ray absorption spectroscopy (XAS.
In XAS, a beam of x-rays bombards the catalyst sample and deposits energy as it passes through the micro-reactor.
The sample then emits secondary x-rays, which are measured to identify its chemical composition-in this instance, the distribution of platinum particles."
"The XAS and TEM data, analyzed together, let us calculate the numbers and average sizes of not one,
but several different types of catalysts,"said coauthor and Yeshiva University scientist Anatoly Frenkel, who led the x-ray experiments."
"Versatile micro-reactorthe new micro-reactor was designed specifically and built to work seamlessly with both synchrotron x-rays and electron microscopes."
"Everything was controlled exquisitely at both NSLS and CFN, including precise measurements of the progress of the catalytic reaction,
"For the first time, the operando approach was used to correlate data obtained by different techniques at the same stages of the reaction."
"A relatively straightforward mathematical approach allowed them to deduce the total number of ultra-small particles missing in the TEM data."
"We took the full XAS data, which incorporates particles of all sizes, and removed the TEM results covering particles larger than one nanometer-the remainder fills in that crucial subnanometer gap in our knowledge of catalyst size
and distribution during each step of the reaction, "Frenkel said. Added Stach,"In the past, scientists would look at data before and after the reaction under model conditions, especially with TEM,
and make educated guesses. Now we can make definitive statements.""Brighter, faster experimentsthe collaboration has extended already this operando micro-reactor approach to incorporate two additional techniques-infrared
and Raman spectroscopy-and plans to introduce other complex and complementary x-ray and electron probe techniques over time.
"Each round of data collection took six hours at NSLS, but will take just minutes at NSLS-II,
"Through Laboratory Directed Research and development funding, we will be part of the initial experiments at the Submicron Resolution X-ray (SRX) Spectroscopy beamline this summer,
but other new micro-reactors can operate at up to 800 degrees Celsius-more than hot enough for most catalytic reactions
In the near future, this same micro-reactor approach will be used to explore other crucial energy frontiers,
including batteries and fuel cells.""We are seeing the emergence of a very powerful and versatile technique that leverages both NSLS-II
who was named recently Special Assistant for Operando Experimentation for Brookhaven's Energy Sciences Directorate.""This approach complements the many facilities being developed at Brookhaven Lab for operando energy research.
Our goal is to be world leaders in operando science.""Image: Series of scanning transmission electron microscopy (STEM) images of platinum nanoparticles, tracking their changes under different atmospheric pressure reaction conditions.
Source: http://www0. bnl. gov/newsroom
#New method for cheaper solar-energy storage Building on a unique idea, scientists have developed a cost-effective new method for converting
and storing solar energy into hydrogen. Storing solar energy as hydrogen is a promising way for developing comprehensive renewable energy systems.
To accomplish this, traditional solar panels can be used to generate an electrical current that splits water molecules into oxygen and hydrogen,
However, the cost of producing efficient solar panels makes water-splitting technologies too expensive to commercialize.
unconventional method to fabricate high-quality, efficient solar panels for direct solar hydrogen production with low cost. The work is published in Nature Communications.
Many different materials have been considered for use in direct solar-to-hydrogen conversion technologies but"2-D materialshave recently been identified as promising candidates.
However, harvesting usable amounts of solar energy requires large areas of solar panels, and it is notoriously difficult and expensive to fabricate thin films of 2-D materials at such a scale
which is much less expensive than a traditional solar panel. The thin film produced like this was tested
this represents an important advance towards economical solar-to-fuel energy conversion
#A stretchy mesh heater for sore muscles If you suffer from chronic muscle pain a doctor will likely recommend for you to apply heat to the injury.
But how do you effectively wrap that heat around a joint? Korean Scientists at the Center for Nanoparticle Research, Institute for Basic Science (IBS) in Seoul,
along with an international team, have come up with an ingenious way of creating therapeutic heat in a light, flexible design.
Other teams have come up with similar devices before, although no one was able to create something that didn't rely on exotic materials or a complex fabrication process, factors which both carry hefty price tags.
Unlike their predecessors, the team at IBS stayed away from things like carbon nanotubes and gold and looked at a more utilitarian option for their build material:
thin slivers of silver nanowires. The silver nanowires are tiny, averaging#150 nm in diameter and#30 m in length (a human hair ranges from 17 to 181 m). The nanowires were mixed into a liquid elastic material
which is both soft and stretchy when dry. To ensure that the material remains tight on the target area while heating,
the team devised a 2-D interlocking coil pattern for the mesh structure. To make the mesh,
while deformed and under stress on knee and wrist joints. It is lightweight, breathable and generates heat over the entire surface area of the material.
Commercially available electric heating pads are sufficient for applying heat to an injured area but their cords need to be attached to an A c outlet to work.
This is where the new technology trumps the old. The mesh maintains a constant temperature instead of cooling down during use
and is powered battery so it doesn't need an outlet. Beyond thermotherapy the applications are endless.
or as a hyper-efficient seat warmer in a car. Although only flat mesh connected into a tube has been made so far,
it isn a stretch to imagine creating more intricate designs like the shape of a hand with detailed fingers d
When a duck paddles across a pond or a supersonic plane flies through the sky, it leaves a wake in its path.
For the first time, Harvard researchers have created similar wakes of light-like waves moving on a metallic surface, called surface plasmons,
The discovery, published today in the journal Nature Nanotechnology, was made in the lab of Federico Capasso, the Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical engineering at the Harvard John A. Paulson School of engineering and Applied science (SEAS)."
"The ability to control light is a powerful one, "said Capasso.""Our understanding of optics on the macroscale has led to holograms, Google glass and LEDS,
just to name a few technologies. Nano-optics is a major part of the future of nanotechnology and this research furthers our ability to control
and harness the power of light on the nanoscale.""The creation and control of surface plasmon wakes could lead to new types of plasmonic couplers
and lenses that could create two-dimensional holograms or focus light at the nanoscale. Surface plasmons are confined to the surface of a metal.
In order to create wakes through them, Capasso's team designed a faster-than-light running wave of charge along a one-dimensional metamaterialike a powerboat speeding across a lake.
The metamaterial, a nanostructure of rotated slits etched into a gold film, changes the phase of the surface plasmons generated at each slit relative to each other
increasing the velocity of the running wave. The nanostructure also acts like the boat's rudder, allowing the wakes to be steered by controlling the speed of the running wave.
The team discovered that the angle of incidence of the light shining onto the metamaterial provides an additional measure of control
and using polarized light can even reverse the direction of the wake relative to the running waveike a wake traveling in the opposite direction of a boat."
"Being able to control and manipulate light at scales much smaller than the wavelength of the light is said very difficult
and graduate student in the Capasso lab."It's important that we not only observed these wakes
as"surface plasmons are not visible to the eye or cameras,"said co-lead author Antonio Ambrosio of SEAS and the Italian Research Council (CNR)."
we used an experimental technique that forces plasmons from the surface, collects them via fiber optics and records the image."
"This work could represent a new testbed for wake physics across a variety of disciplines."
An artistic rendition of the superluminal running wave of charge that excites the surface plasmon wakes.
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