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When it comes to reducing the toxins released by burning gasoline, coal, or other such fuels, the catalyst needs to be reliable. Yet, a promising catalyst, cerium dioxide (CeO2), seemed erratic. The catalyst’s three different surfaces behaved differently. For the first time, researchers got an atomically resolved view of the three structures, including the placement of previously difficult-to-visualize oxygen atoms. This information may provide insights into why the surfaces have distinct catalytic properties (“Probing the Surface Sites of CeO2 Nanocrystals with Well-Defined Surface Planes via Methanol Adsorption and Desorption”).
cubic CeO2 nanoparticles
The image on the left shows the general shape of a cubic CeO2 nanoparticle. The images on the right show edge-on views of three exposed surfaces at atomic resolution. The atomic models are overlaid on the simulated images to illustrate atom positions. (Image courtesy of Northwestern University)
The Impact
Solving the three different atomic surface structures of CeO2 nanoparticles provides insight into how to potentially control the morphology of the nanoparticles to improve catalytic selectivity, activity and stability. This knowledge provides an opportunity to potentially improve the catalytic properties of CeO2 nanoparticles in catalytic converters in vehicles and other applications.
Summary
Cerium oxide (CeO2) nanoparticles are widely used in chemical catalysis. Typical CeO2 catalytic nanoparticles have three main surfaces exposed: (100), (110) and (111).
Previous studies show that the differing catalytic properties of each surface are closely related to the atomic structure of the surface. Unfortunately, scientists had difficulties in visualizing the oxygen atoms that pack these surfaces. The challenge was overcome by a team of researchers at Northwestern University, Oak Ridge National Laboratory, and Argonne National Laboratory. The researchers determined the surface structures using the most advanced chromatic and spherical aberration-corrected electron microscope at Argonne National Laboratory. The microscope enables clear imaging of both cerium and oxygen atoms. For the high energy (100) surface, the presence of cerium, oxygen, and reduced cerium oxide terminations on the outermost surface as well as the partially occupied lattice sites in the near-surface region (~1 nm from the surface) were directly observed.
The disordered surface demonstrates that the previous understanding of the (100) surface was oversimplified. For the (110) surface, a combination of reduced flat CeO2-x surface layers and “sawtooth-like” (111) nanofacets exist. The (111) surface is terminated by an oxygen layer, precisely as anticipated from previous models, and consistent with its high stability. Further, the surface structures derived from the microscopy study are consistent with results from a macroscopic infrared spectroscopy investigation.
The variation in surface defect density between these three facets appears to be responsible for their differences in catalytic activity and potentially opens options to modify faces of CeO2 nanoparticles to develop face selective catalysts.
Source: U.S. Department of Energy, Office of Science

Read more: One nanocrystal, many faces

Wearable Nano Heat Cool 061015 id40246 Imagine a fabric that will keep your body at a comfortable temperature—regardless of how hot or cold it actually is. That’s the goal of an engineering project at the University of California, San Diego, funded with a $2.6M grant from the U.S. Department of Energy’s Advanced Research Projects Agency – Energy (ARPA-E). Wearing this smart fabric could potentially reduce heating and air conditioning bills for buildings and homes.
The project, named ATTACH (Adaptive Textiles Technology with Active Cooling and Heating), is led by Joseph Wang, distinguished professor of nanoengineering at UC San Diego.
By regulating the temperature around an individual person, rather than a large room, the smart fabric could potentially cut the energy use of buildings and homes by at least 15 percent, Wang noted.
“In cases where there are only one or two people in a large room, it’s not cost-effective to heat or cool the entire room,” said Wang. “If you can do it locally, like you can in a car by heating just the car seat instead of the entire car, then you can save a lot of energy.”
Garment-based printable electrodes developed
Garment-based printable electrodes developed in the lab of Joseph Wang, distinguished professor of nanoengineering at UC San Diego, and lead principal investigator of ATTACH. (Image: Jacobs School of Engineering/UC San Diego)
The smart fabric will be designed to regulate the temperature of the wearer’s skin—keeping it at 93° F—by adapting to temperature changes in the room. When the room gets cooler, the fabric will become thicker. When the room gets hotter, the fabric will become thinner. To accomplish this feat, the researchers will insert polymers that expand in the cold and shrink in the heat inside the smart fabric.
“Regardless if the surrounding temperature increases or decreases, the user will still feel the same without having to adjust the thermostat,” said Wang.
“93° F is the average comfortable skin temperature for most people,” added Renkun Chen, assistant professor of mechanical and aerospace engineering at UC San Diego, and one of the collaborators on this project.
Chen’s contribution to ATTACH is to develop supplemental heating and cooling devices, called thermoelectrics, that are printable and will be incorporated into specific spots of the smart fabric. The thermoelectrics will regulate the temperature on “hot spots”—such as areas on the back and underneath the feet—that tend to get hotter than other parts of the body when a person is active.
“This is like a personalized air-conditioner and heater,” said Chen.
Saving energy
“With the smart fabric, you won’t need to heat the room as much in the winter, and you won’t need to cool the room down as much in the summer. That means less energy is consumed. Plus, you will still feel comfortable within a wider temperature range,” said Chen.
The researchers are also designing the smart fabric to power itself. The fabric will include rechargeable batteries, which will power the thermoelectrics, as well as biofuel cells that can harvest electrical power from human sweat. Plus, all of these parts—batteries, thermoelectrics and biofuel cells—will be printed using the technology developed in Wang’s lab to make printable wearable devices. These parts will also be thin, stretchable and flexible to ensure that the smart fabric is not bulky or heavy.
“We are aiming to make the smart clothing look and feel as much like the clothes that people regularly wear. It will be washable, stretchable, bendable and lightweight. We also hope to make it look attractive and fashionable to wear,” said Wang.
In terms of price, the team has not yet concluded how much the smart clothing will cost. This will depend on the scale of production, but the printing technology in Wang’s lab will offer a low-cost method to produce the parts. Keeping the costs down is a major goal, the researchers said.
The research team
Professor Joseph Wang, Department of NanoEngineering
Wang, the lead principal investigator of ATTACH, has pioneered the development of wearable printable devices, such as electrochemical sensors and temporary tattoo-based biofuel cells. He is the chair of the nanoengineering department and the director for the Center for Wearable Sensors at UC San Diego. His extensive expertise in printable, stretchable and wearable devices will be used here to make the proposed flexible biofuel cells, batteries and thermoelectrics.
Assistant Professor Renkun Chen, Department of Mechanical and Aerospace Engineering
Chen specializes in heat transfer and thermoelectrics. His research group works on physics, materials and devices related to thermal energy transport, conversion and management. His specialty in these areas will be used to develop the thermal models and the thermoelectric devices.
Associate Professor Shirley Meng, Department of NanoEngineering
Meng’s research focuses on energy storage and conversion, particularly on battery cell design and testing. At UC San Diego, she established the Laboratory for Energy Storage and Conversion and is the inaugural director for the Sustainable Power and Energy Center. Meng will develop the rechargeable batteries and will work on power integration throughout the smart fabric system.
Professor Sungho Jin, Department of Mechanical and Aerospace Engineering
Jin specializes in functional materials for applications in nanotechnology, magnetism, energy and biomedicine. He will design the self-responsive polymers that change in thickness based on changes in the surrounding temperature.
Dr. Joshua Windmiller, CEO of Electrozyme LLC
Windmiller, former Ph.D. student and postdoc in Wang’s nanoengineering lab, is an expert in printed biosensors, bioelectronics and biofuel cells. He co-founded Electrozyme LLC, a startup devoted to the development of novel biosensors for application in the personal wellness and healthcare domains. Electrozyme will serve as the industrial partner for ATTACH and will lead the efforts to test the smart fabric prototype and bring the technology into the market.
Source: UC San Diego

 

Battery New LI 061015 id40374 Many of us would be hard-pressed to spend a day without using a lithium-ion battery, the technology that powers our portable electronics. And with electric vehicles (EVs) and energy storage for the power grid around the corner, their future appears pretty bright.
So bright that the iconic California-based upstart Tesla Motors stated that their newly announced residential Powerwall battery is sold out until mid-2016 and that the strong market demand could meet the capacity of their upcoming battery “gigafactory” of 35 gigawatt-hours per year – the daily electrical energy needs of 1.2 million US households.
When released by Sony in the early 1990s, many considered lithium-ion batteries to be a breakthrough in rechargeable batteries: with their high operating voltage and their large energy density, they outclassed the then state-of-the-art nickel metal hydride batteries (NiMH). The adoption of the lithium-ion technology fueled the portable electronic revolution: without lithium-ion, the battery in the latest Samsung Galaxy smartphones would weigh close to four ounces, as opposed to 1.5 ounces, and occupy twice as much volume.
Yet, in recent years lithium-ion batteries have gathered bad press. They offer disappointing battery life for modern portable devices and limited driving range of electric cars, compared to gasoline-powered vehicles. Lithium-ion batteries also have safety concerns, notably the danger of fire.
This situation raises legitimate questions: What is coming next? Will there be breakthroughs that will solve these problems?
Better lithium chemistries
Before we attempt to answer these questions, let’s briefly discuss the inner mechanics of a battery. A battery cell consists of two distinct electrodes separated by an insulating layer, conveniently called a separator, which is soaked in an electrolyte. The two electrodes must have different potentials, or a different electromotive force, and the resulting potential difference defines the cell’s voltage. The electrode with the largest potential is referred to as the positive electrode, the one with the lowest potential as the negative electrode.
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Next-generation batteries could improve on energy density, allowing for longer run-time on electronics and driving range on EVs. (Image: Author and Wikipedia, Author provided)
During discharge, electrons flow through an external wire from the negative electrode to the positive electrode, while charged atoms, or ions, flow internally to maintain a neutral electrical charge. With rechargeable batteries, the process is reversed during charging.
Lithium-ion batteries’ energy density, or the amount of energy stored per weight, has increased steadily by about 5% every year, from 90 watt-hours/kilogram (Wh/kg) to 240 Wh/kg over 20 years, and this trend is forecast to continue. It’s due to incremental refinements in electrodes and electrolyte compositions and architectures, as well as increases in the maximum charge voltage, from 4.2 volts conventionally to 4.4 volts in the latest portable devices.
Picking up the pace of energy density improvements would require breakthroughs on both the electrodes’ materials and the electrolyte fronts. The biggest awaited leap would be to introduce elemental sulfur or air as a positive electrode and use metallic lithium as a negative electrode.
In the labs
Lithium-sulfur batteries could potentially bring a twofold improvement over the energy density of current lithium-ion batteries to about 400 Wh/kg. Lithium-air batteries could bring a tenfold improvement to approximately 3,000 Wh/kg, mainly because using air as an off-board reactant – that is, oxygen in the air rather than an element on a battery electrode – would greatly reduce weight.
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A lithium air battery uses oxygen from the air to drive an electrochemical reaction – if it would work outside the lab. (Image: Na9234/wikimedia, CC BY)
Both systems are intensively studied by the research community, but commercial availability has been elusive as labs struggle to develop viable prototypes. During the discharge of the sulfur electrodes, the sulfur can be dissolved in the electrolyte, disconnecting it from the electronic circuit. This reduces the amount of lithium that could be removed from the sulfur during the charge and hurts the overall reversibility of the system.
To make this technology viable, critical milestones must be reached: improve the positive electrode architecture to better retain the active material or develop new electrolytes in which the active material is not soluble.
The lithium-air battery, too, suffers from this difficulty of being repeatedly recharged as a result of problems caused by reactions between the electrolyte and air. Also, with both technologies, protection of the lithium electrode is an issue that needs to be solved.
Savior in sodium?
For all of the aforementioned batteries, lithium is an essential component of the battery. Lithium is a fairly abundant element around the world but unfortunately only at trace levels, which prevents its worldwide commercial extraction. Although it is found in harvestable conditions in a few ores that could be mined, most of the production of lithium comes from brines of high-altitude salt lakes, mostly in the Andes in South America.
Despite this relatively difficult extraction, lithium carbonate can be found at around US$6 per kilogram, and since an electric vehicle battery pack requires only about three kilograms of lithium carbonate, its cost is not a major concern to date.
The concern here is more about geopolitics: every country seeks energy independence, and replacing oil with lithium batteries as a transportation fuel simply shifts the dependence from the Middle East to South America.
One possible solution would be to replace lithium with the element sodium, which is 2,000 times more abundant.
Electrochemically speaking, sodium is almost comparable to lithium, which makes it an extremely good candidate for batteries. Sodium-ion batteries research has exploded in recent years, and their performance, once commercialized, could be on par with their lithium-ion counterparts.
While sodium-ion batteries might not bring any significant cost or performance advantage over lithium-ion technology, it could offer a path for every country to manufacture their own batteries with readily available resources.
No cure-all
No matter what, all of these emerging technologies are likely to suffer from the same safety concerns as the current lithium-ion cells. The threat comes from the flammable solvent-based electrolyte which makes it possible to operate at voltages above two volts.
Indeed, because water splits into oxygen and hydrogen above two volts, it cannot be used in three volt-class lithium or sodium batteries and has been replaced by expensive flammable carbonate solvents. Alternatives such as solvent-free electrolytes do not provide a good enough conductivity for ions at room temperature to handle high-power applications, such as powering a car, and are therefore not used in commercial cells.
Fortunately, with the current lithium-ion technology, it has been estimated that only one in 40 million cells undergoes dramatic failure, of a fire. Although the risk cannot be fully suppressed, engineering controls and conservative designs can keep it in check.
In sum, the current lithium-ion batteries offer fairly good performances. Emerging chemistries such as lithium-sulfur or lithium-air have the potential to revolutionize portable energy storage applications, but they are still at the lab research stage with no guarantee of becoming a viable product.
For stationary energy storage applications such as storing wind and solar energy, other types of batteries, including high-temperature sodium-sulfur batteries or the redox flow batteries, might prove more sustainable and cost-effective candidates than lithium-ion batteries, but that could be a story for another article.
Source: By Matthieu Dubarry, Assistant Researcher in Electrochemistry and Solid State Science at University of Hawaii, and Arnaud Devie, Postdoctoral Research Fellow at University of Hawaii, via The Conversation

 

MIT- Graph RolltoRoll 061015-1

Copper substrate is shown in the process of being coated with graphene. At left, the process begins by treating the copper surface, and, at right, the graphene layer is beginning to form. Upper images are taken using visible light microscopy, and lower images using a scanning electron microscope.

Courtesy of the researchers

New manufacturing process could take exotic material out of the lab and into commercial products.

Graphene is a material with a host of potential applications, including in flexible light sources, solar panels that could be integrated into windows, and membranes to desalinate and purify water. But all these possible uses face the same big hurdle: the need for a scalable and cost-effective method for continuous manufacturing of graphene films.

That could finally change with a new process described this week in the journal Scientific Reports by researchers at MIT and the University of Michigan. MIT mechanical engineering Associate Professor A. John Hart, the paper’s senior author, says the new roll-to-roll manufacturing process described by his team addresses the fact that for many proposed applications of graphene and other 2-D materials to be practical, “you’re going to need to make acres of it, repeatedly and in a cost-effective manner.”

Making such quantities of graphene would represent a big leap from present approaches, where researchers struggle to produce small quantities of graphene — often pulling these sheets from a lump of graphite using adhesive tape, or producing a film the size of a postage stamp using a laboratory furnace. But the new method promises to enable continuous production, using a thin metal foil as a substrate, in an industrial process where the material would be deposited onto the foil as it smoothly moves from one spool to another. The resulting sheets would be limited in size only by the width of the rolls of foil and the size of the chamber where the deposition would take place.

Because a continuous process eliminates the need to stop and start to load and unload materials from a fixed vacuum chamber, as in today’s processing methods, it could lead to significant scale-up of production. That could finally unleash applications for graphene, which has unique electronic and optical properties and is one of the strongest materials known.

The new process is an adaptation of a chemical vapor deposition method already used at MIT and elsewhere to make graphene — using a small vacuum chamber into which a vapor containing carbon reacts on a horizontal substrate, such as a copper foil. The new system uses a similar vapor chemistry, but the chamber is in the form of two concentric tubes, one inside the other, and the substrate is a thin ribbon of copper that slides smoothly over the inner tube.

Gases flow into the tubes and are released through precisely placed holes, allowing for the substrate to be exposed to two mixtures of gases sequentially. The first region is called an annealing region, used to prepare the surface of the substrate; the second region is the growth zone, where the graphene is formed on the ribbon. The chamber is heated to approximately 1,000 degrees Celsius to perform the reaction.

The researchers have designed and built a lab-scale version of the system, and found that when the ribbon is moved through at a rate of 25 millimeters (1 inch) per minute, a very uniform, high-quality single layer of graphene is created. When rolled 20 times faster, it still produces a coating, but the graphene is of lower quality, with more defects.

Some potential applications, such as filtration membranes, may require very high-quality graphene, but other applications, such as thin-film heaters may work well enough with lower-quality sheets, says Hart, who is the Mitsui Career Development Associate Professor in Contemporary Technology at MIT.

So far, the new system produces graphene that is “not quite [equal to] the best that can be done by batch processing,” Hart says — but “to our knowledge, it’s still at least as good” as what’s been produced by other continuous processes. Further work on details such as pretreatment of the substrate to remove unwanted surface defects could lead to improvements in the quality of the resulting graphene sheets, he says.

The team is studying these details, Hart adds, and learning about tradeoffs that can inform the selection of process conditions for specific applications, such as between higher production rate and graphene quality. Then, he says, “The next step is to understand how to push the limits, to get it 10 times faster or more.”

Hart says that while this study focuses on graphene, the machine could be adapted to continuously manufacture other two-dimensional materials, or even to growing arrays of carbon nanotubes, which his group is also studying.

“This is high-quality research that represents significant progress on the path to scalable production methods for large-area graphene,” says Charlie Johnson, a professor of physics and astronomy at the University of Pennsylvania who was not involved in this work. “I think that the concentric tube approach is very creative. It has the potential to lead to significantly lower production costs for graphene, if it can be scaled to larger copper-foil widths.”

The research team also included Erik Polsen and Daniel McNerny of the University of Michigan and postdocs Viswanath Balakrishnan and Sebastian Pattinson of MIT. The work was supported by the National Science Foundation and the Air Force Office of Scientific Research.

At near absolute zero, molecules may start to exhibit exotic states of matter.

MIT News Office
June 10, 2015

MIT-SuperCoolMolecules-1The air around us is a chaotic superhighway of molecules whizzing through space and constantly colliding with each other at speeds of hundreds of miles per hour.

Such erratic molecular behavior is normal at ambient temperatures.

But scientists have long suspected that if temperatures were to plunge to near absolute zero, molecules would come to a screeching halt, ceasing their individual chaotic motion and behaving as one collective body. This more orderly molecular behavior would begin to form very strange, exotic states of matter — states that have never been observed in the physical world.

Now experimental physicists at MIT have successfully cooled molecules in a gas of sodium potassium (NaK) to a temperature of 500 nanokelvins — just a hair above absolute zero, and over a million times colder than interstellar space. The researchers found that the ultracold molecules were relatively long-lived and stable, resisting reactive collisions with other molecules. The molecules also exhibited very strong dipole moments — strong imbalances in electric charge within molecules that mediate magnet-like forces between molecules over large distances.

Martin Zwierlein, professor of physics at MIT and a principal investigator in MIT’s Research Laboratory of Electronics, says that while molecules are normally full of energy, vibrating and rotating and moving through space at a frenetic pace, the group’s ultracold molecules have been effectively stilled — cooled to average speeds of centimeters per second and prepared in their absolute lowest vibrational and rotational states.

“We are very close to the temperature at which quantum mechanics plays a big role in the motion of molecules,” Zwierlein says. “So these molecules would no longer run around like billiard balls, but move as quantum mechanical matter waves. And with ultracold molecules, you can get a huge variety of different states of matter, like superfluid crystals, which are crystalline, yet feel no friction, which is totally bizarre. This has not been observed so far, but predicted. We might not be far from seeing these effects, so we’re all excited.”

Zwierlein, along with graduate student Jee Woo Park and postdoc Sebastian Will — all of whom are members of the MIT-Harvard Center of Ultracold Atoms — have published their results in the journal Physical Review Letters.

Sucking away 7,500 kelvins

Every molecule is composed of individual atoms that are bonded together to form a molecular structure. The simplest molecule, resembling a dumbbell, is made up of two atoms connected by electromagnetic forces. Zwierlein’s group sought to create ultracold molecules of sodium potassium, each consisting of a single sodium and potassium atom.

However, due to their many degrees of freedom — translation, vibration, and rotation — cooling molecules directly is very difficult. Atoms, with their much simpler structure, are much easier to chill. As a first step, the MIT team used lasers and evaporative cooling to cool clouds of individual sodium and potassium atoms to near absolute zero. They then essentially glued the atoms together to form ultracold molecules, applying a magnetic field to prompt the atoms to bond — a mechanism known as a “Feshbach resonance,” named after the late MIT physicist Herman Feshbach.

“It’s like tuning your radio to be in resonance with some station,” Zwierlein says. “These atoms start to vibrate happily together, and form a bound molecule.”

The resulting bond is relatively weak, creating what Zwierlein calls a “fluffy” molecule that still vibrates quite a bit, as each atom is bonded over a long, tenuous connection. To bring the atoms closer together to create a stronger, more stable molecule, the team employed a technique first reported in 2008 by groups from the University of Colorado, for potassium rubidium (KRb) molecules, and the University of Innsbruck, for non-polar cesium­ (Ce) molecules.

For this technique, the newly created NaK molecules were exposed to a pair of lasers, the large frequency difference of which exactly matched the energy difference between the molecule’s initial, highly vibrating state, and its lowest possible vibrational state. Through absorption of the low-energy laser, and emission into the high-energy laser beam, the molecules lost all their available vibrational energy.

With this method, the MIT group was able to bring the molecules down to their lowest vibrational and rotational states — a huge drop in energy.

“In terms of temperature, we sucked away 7,500 kelvins, just like that,” Zwierlein says.

Chemically stable

In their earlier work, the Colorado group observed a significant drawback of their ultracold potassium rubidium molecules: They were chemically reactive, and essentially came apart when they collided with other molecules. That group subsequently confined the molecules in crystals of light to inhibit such chemical reactions.

Zwierlein’s group chose to create ultracold molecules of sodium potassium, as this molecule is chemically stable and naturally resilient against reactive molecular collisions.

“When two potassium rubidium molecules collide, it is more energetically favorable for the two potassium atoms and the two rubidium atoms to pair up,” Zwierlein says. “It turns out with our molecule, sodium potassium, this reaction is not favored energetically. It just doesn’t happen.”

In their experiments, Park, Will, and Zwierlein observed that their molecular gas was indeed stable, with a relatively long lifetime, lasting about 2.5 seconds.

“In the case where molecules are chemically reactive, one simply doesn’t have time to study them in bulk samples: They decay away before they can be cooled further to observe interesting states,” Zwierlein says. “In our case, we hope our lifetime is long enough to see these novel states of matter.”

By first cooling atoms to ultralow temperatures and only then forming molecules, the group succeeded in creating an ultracold gas of molecules, measuring one thousand times colder than what can be achieved by direct cooling techniques.

To begin to see exotic states of matter, Zwierlein says molecules will have to be cooled still a bit further, to all but freeze them in place. “Now we’re at 500 nanokelvins, which is already fantastic, we love it. A factor of 10 colder or so, and the music starts playing.”

This research was supported in part by the National Science Foundation, the Air Force Office of Scientific Research, the Army Research Office, and the David and Lucile Packard Foundation.

Bio Computer Chip 053015 uploaded_1076

Portable electronics — typically made of non-renewable, non-biodegradable and potentially toxic materials — are discarded at an alarming rate in consumers’ pursuit of the next best electronic gadget.

In an effort to alleviate the environmental burden of electronic devices, a team of University of Wisconsin-Madison researchers has collaborated with researchers in the Madison-based U.S. Department of Agriculture Forest Products Laboratory (FPL) to develop a surprising solution: a semiconductor chip made almost entirely of wood.
The research team, led by UW-Madison electrical and computer engineering professor Zhenqiang “Jack” Ma, described the new device in a paper published today (May 26, 2015) by the journal Nature Communications. The paper demonstrates the feasibility of replacing the substrate, or support layer, of a computer chip, with cellulose nanofibril (CNF), a flexible, biodegradable material made from wood.
“The majority of material in a chip is support. We only use less than a couple of micrometers for everything else,” Ma says. “Now the chips are so safe you can put them in the forest and fungus will degrade it. They become as safe as fertilizer.”
Zhiyong Cai, project leader for an engineering composite science research group at FPL, has been developing sustainable nanomaterials since 2009.
“If you take a big tree and cut it down to the individual fiber, the most common product is paper. The dimension of the fiber is in the micron stage,” Cai says. “But what if we could break it down further to the nano scale? At that scale you can make this material, very strong and transparent CNF paper.”
“You don’t want it to expand or shrink too much. Wood is a natural hydroscopic material and could attract moisture from the air and expand,” Cai says. “With an epoxy coating on the surface of the CNF, we solved both the surface smoothness and the moisture barrier.”Working with Shaoqin “Sarah” Gong, a UW-Madison professor of biomedical engineering, Cai’s group addressed two key barriers to using wood-derived materials in an electronics setting: surface smoothness and thermal expansion.
Gong and her students also have been studying bio-based polymers for more than a decade. CNF offers many benefits over current chip substrates, she says.
“The advantage of CNF over other polymers is that it’s a bio-based material and most other polymers are petroleum-based polymers. Bio-based materials are sustainable, bio-compatible and biodegradable,” Gong says. “And, compared to other polymers, CNF actually has a relatively low thermal expansion coefficient.”
The group’s work also demonstrates a more environmentally friendly process that showed performance similar to existing chips.
The majority of today’s wireless devices use gallium arsenide-based microwave chips due to their superior high-frequency operation and power handling capabilities. However, gallium arsenide can be environmentally toxic, particularly in the massive quantities of discarded wireless electronics.
Yei Hwan Jung, a graduate student in electrical and computer engineering and a co-author of the paper, says the new process greatly reduces the use of such expensive and potentially toxic material.
“I’ve made 1,500 gallium arsenide transistors in a 5-by-6 millimeter chip. Typically for a microwave chip that size, there are only eight to 40 transistors. The rest of the area is just wasted,” he says. “We take our design and put it on CNF using deterministic assembly technique, then we can put it wherever we want and make a completely functional circuit with performance comparable to existing chips.”
While the biodegradability of these materials will have a positive impact on the environment, Ma says the flexibility of the technology can lead to widespread adoption of these electronic chips.
“Mass-producing current semiconductor chips is so cheap, and it may take time for the industry to adapt to our design,” he says. “But flexible electronics are the future, and we think we’re going to be well ahead of the curve.”
Source: http://www.news.wisc.edu/23805

Diodes 053015 diodes-are-fundamental-building-blocks-of-integrated-circuits-they-allow-current-to-flow-in-only-one-directionResearchers created a single-molecule diode, which has been sought after since the 1970s.

Scientists have designed a new way to create a single-molecule diode that performs 50 times better than past models.

These single-molecule diodes are the first that could be used for real-world applications in nanoscale devices, Columbia University School of Engineering and Applied Sciencereported. The idea of creating a single-molecule diode was first proposed in the 1970s by Arieh Aviram and Mark Ratner, who theorized that a molecule could act as a “rectifier” to conduct one-way currents.

Molecular electronics ever since its inception with Aviram and Ratner’s 1974 seminal paper, represents the ultimate in functional miniaturization that can be achieved for an electronic device,” said Latha Venkataraman, associate professor of applied physics at Columbia Engineering.

Since the 1974 paper, scientists have determined single-molecules attached themselves to metal electrodes, and act as a number of circuit elements such as switches, resistors, and diodes. A diode works as an “electricity valve,” and requires an asymmetrical structure in order to create different environments for electricity flowing in each direction.

Diodes 053015 diodes-are-fundamental-building-blocks-of-integrated-circuits-they-allow-current-to-flow-in-only-one-direction

“While such asymmetric molecules do indeed display some diode-like properties, they are not effective,” said Brian Capozzi, a PhD student working with Venkataraman and lead author of the paper. “A well-designed diode should only allow current to flow in one direction-the ‘on’ direction-and it should allow a lot of current to flow in that direction. Asymmetric molecular designs have typically suffered from very low current flow in both ‘on’ and ‘off’ directions, and the ratio of current flow in the two has typically been low. Ideally, the ratio of ‘on’ current to ‘off’ current, the rectification ratio, should be very high.”

To remedy this, the researchers worked to develop asymmetry in the environment around the molecular junction. They accomplished this by surrounding the active molecule with an ionic solution and employed the use of gold metal electrodes that differed in size to contact the molecule. The method led to rectification ratios as high as 250, which is 50 times higher than earlier designs.

“It’s amazing to be able to design a molecular circuit, using concepts from chemistry and physics, and have it do something functional,” Venkataraman said. “The length scale is so small that quantum mechanical effects are absolutely a crucial aspect of the device. So it is truly a triumph to be able to create something that you will never be able to physically see and that behaves as intended.”

The findings were published in a recent edition of the journal Nature Nanotechnology.

http://engineering.columbia.edu/news-archive

QDOT imagesCA1L02JV 5 Just as alchemists always dreamed of turning common metal into gold, their 19th century physicist counterparts dreamed of efficiently turning heat into electricity, a field called thermoelectrics. Such scientists had long known that, in conducting materials, the flow of energy in the form of heat is accompanied by a flow of electrons. What they did not know at the time is that it takes nanometric-scale systems for the flow of charge and heat to reach a level of efficiency that cannot be achieved with larger scale systems. Now, in a paper published in EPJ B Barbara Szukiewicz and Karol Wysokiński from Marie Curie-Skłodowska University, in Lublin, Poland have demonstrated the importance of thermoelectric effects, which are not easily modelled, in nanostructures.

Since the 1990s, scientists have looked into developing efficient energy generation from nanostructures such as quantum dots. Their advantage: they display a greater energy conversion efficiency leading to the emergence of nanoscale thermoelectrics. The authors evaluate the thermoelectric performance of models made of two quantum dots—which are coupled electrostatically—connected to two electrodes kept at a different temperature and a single quantum dot with two levels. First, they using the theoretical approach based on approximations to calculate the so-called thermoelectric figure of merit, expected to be high for systems with high energy conversion efficiency. Then, they calculated the charge and heat fluxes as a means to define the efficiency of the system.

They found that the outcomes of the direct calculations giving the actual—as opposed to theoretical—performance of the system were less optimistic. For most parameters with an excellent performance, calculated predictions turned out to be surprisingly poor. These findings reveal that effects that are not easily formalized using equations are important at the nanoscale. This, in turn, calls for new ways to optimize the structures before they can be used for nanoscale energy harvesting.

KAIST-emissive-graphene-quantum-dots-img_assist-400x257 From Scopii News

Ground-breaking research has successfully created the world’s first truly electronic textile, using the wonder material Graphene. An international team of scientists, including Professor Monica Craciun from the University of Exeter, have pioneered a new technique to embed transparent, flexible graphene electrodes into fibers commonly associated with the textile industry.

The discovery could revolutionize the creation of wearable electronic devices, such as clothing containing computers, phones and MP3 players, which are lightweight, durable and easily transportable.
Graphene Exeter 051115 1431364300347

The international collaborative research, which includes experts from the Centre for Graphene Science at the University of Exeter, the Institute for Systems Engineering and Computers, Microsystems and Nanotechnology (INESC-MN) in Lisbon, the Universities of Lisbon and Aveiro in Portugal and the Belgian Textile Research Centre (CenTexBel), is published in the leading scientific journal Scientific Reports.
Professor Craciun, co-author of the research said: “This is a pivotal point in the future of wearable electronic devices. The potential has been there for a number of years, and transparent and flexible electrodes are already widely used in plastics and glass, for example. But this is the first example of a textile electrode being truly embedded in a yarn. The possibilities for its use are endless, including textile GPS systems, to biomedical monitoring, personal security or even communication tools for those who are sensory impaired.  The only limits are really within our own imagination.”

At just one atom thick, graphene is the thinnest substance capable of conducting electricity. It is very flexible and is one of the strongest known materials. The race has been on for scientists and engineers to adapt graphene for the use in wearable electronic devices in recent years.
This new research has identified that ‘monolayer graphene’, which has exceptional electrical, mechanical and optical properties, make it a highly attractive proposition as a transparent electrode for applications in wearable electronics. In this work graphene was created by a growth method called chemical vapor deposition (CVD) onto copper foil, using a state-of-the-art nanoCVD system recently developed by Moorfield.

The collaborative team established a technique to transfer graphene from the copper foils to a polypropylene fibre already commonly used in the textile industry.
Dr Helena Alves who led the research team from INESC-MN and the University of Aveiro said: “The concept of wearable technology is emerging, but so far having fully textile-embedded transparent and flexible technology is currently non-existing. Therefore, the development of processes and engineering for the integration of graphene in textiles would give rise to a new universe of commercial applications. “
Dr Ana Neves, Associate Research Fellow in Prof Craciun’s team from Exeter’s Engineering Department and former postdoctoral researcher at INESC added: “We are surrounded by fabrics, the carpet floors in our homes or offices, the seats in our cars, and obviously all our garments and clothing accessories. The incorporation of electronic devices on fabrics would certainly be a game-changer in modern technology.

“All electronic devices need wiring, so the first issue to be address in this strategy is the development of conducting textile fibers while keeping the same aspect, comfort and lightness. The methodology that we have developed to prepare transparent and conductive textile fibers by coating them with graphene will now open way to the integration of electronic devices on these textile fibers.”

Dr Isabel De Schrijver,an expert of smart textiles fromCenTexBel said: “Successful manufacturing of wearable electronics has the potential for a disruptive technology with a wide array of potential new applications. We are very excited about the potential of this breakthrough and look forward to seeing where it can take the electronics industry in the future.”

Professor Saverio Russo, co-author and also from the University of Exeter, added: “This breakthrough will also nurture the birth of novel and transformative research directions benefitting a wide range of sectors ranging from defense to health care. “
In 2012 Professor Craciun and Professor Russo, from the University of Exeter’s Centre for Graphene Science, discovered GraphExeter – sandwiched molecules of ferric chloride between two graphene layers which makes a whole new system that is the best known transparent material able to conduct electricity.  The same team recently discovered that GraphExeter is also more stable than many transparent conductors commonly used by, for example, the display industry.

Source: University of Exeter

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

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

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

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

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

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

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

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

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

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


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


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