New method uses heat flow to levitate variety of objects

Although scientists have been able to levitate specific types of material, a pair of UChicago undergraduate physics students helped take the science to a new level. Third-year Frankie Fung and fourth-year Mykhaylo Usatyuk led a team of UChicago researchers who demonstrated how to levitate a variety of objects -- ceramic and polyethylene spheres, glass bubbles, ice particles, lint strands and thistle seeds -- between a warm plate and a cold plate in a vacuum chamber. "They made lots of intriguing observations that blew my mind," said Cheng Chin, professor of physics, whose ultracold lab in the Gordon Center for Integrative Science was home to the experiments. Usatyuk and Fung In their work, researchers achieved a number of levitation breakthroughs, in terms of duration, orientation and method: The levitation lasted for more than an hour, as opposed to a few minutes; stability was achieved radially and vertically, as opposed to just vertically; and it used a temperature gradient rather than light or a magnetic field. Their findings appeared Jan. 20 in Applied Physics Letters. "Magnetic levitation only works on magnetic particles, and optical levitation only works on objects that can be polarized by light, but with our first-of-its-kind method, we demonstrate a method to levitate generic objects," said Chin. In the experiment, the bottom copper plate was kept at room temperature while a stainless steel cylinder filled with liquid nitrogen served as the top plate. The upward flow of heat from the warm to the cold plate kept the particles suspended indefinitely. "The large temperature gradient leads to a force that balances gravity and results in stable levitation," said Fung, the study's lead author. "We managed to quantify the thermophoretic force and found reasonable agreement with what is predicted by theory. This will allow us to explore the possibilities of levitating different types of objects." (Thermophoresis refers to the movement of particles by means of a temperature gradient.) "Our increased understanding of the thermophoretic force will help us investigate the interactions and binding affinities between the particles we observed," said Usatyuk, a study co-author. "We are excited about the future research directions we can follow with our system." The key to obtaining high levitation stability is the geometrical design of the two plates. A proper ratio of their sizes and vertical spacing allows the warm air to flow around and efficiently capture the levitated objects when they drift away from the center. Another sensitivity factor is that the thermal gradient needs to be pointing upward -- even a misalignment of one degree will greatly reduce the levitation stability. "Only within a narrow range of pressure, temperature gradient and plate geometric factors can we reach stable and long levitation," Chin said. "Different particles also require fine adjustment of the parameters." The apparatus offers a new ground-based platform to investigate the dynamics of astrophysical, chemical and biological systems in a microgravity environment, according to the researchers. Levitation of macroscopic particles in a vacuum is of particular interest due to its wide applications in space, atmospheric and astro-chemical research. And thermophoresis has been utilized in aerosol thermal precipitators, nuclear reactor safety and the manufacturing of optical fibers through vacuum deposition processes, which apply progressive layers of atoms or molecules during fabrication. The new method is significant because it offers a new approach to manipulating small objects without contacting or contaminating them, said Thomas Witten, the Homer J. Livingston Professor Emeritus of Physics. "It offers new avenues for mass assembly of tiny parts for micro-electro-mechanical systems, for example, and to measure small forces within such systems. "Also, it forces us to re-examine how 'driven gases,' such as gases driven by heat flow, can differ from ordinary gases," he added. "Driven gases hold promise to create new forms of interaction between suspended particles." Levitation of materials in ground-based experiments provides an ideal platform for the study of particle dynamics and interactions in a pristine isolated environment, the paper concluded. Chin's lab is now looking at how to levitate macroscopic substances greater than a centimeter in size, as well as how these objects interact or aggregate in a weightless environment. "There are ample research opportunities to which our talented undergraduate students can contribute," Chin said.   Story Source:   Materials provided by University of Chicago. Original written by Greg Borzo. Note: Content may be edited for style and length.

State-of-the-art motion control and electronics for sorting line

The sorting and packaging of small, medium and large ceramic formats represent a crucial phase in the manufacturing process. System Group has developed Multigecko Special, a fully automated system with high-end technologies designed from a mechatronic approach. The hardware is merged with the software to give life to an interconnected process, where technology guarantees flexibility and speed for small and medium formats. Design and production of Multigecko Special was managed and completed by the End-of-Line Research and Development department, together with the Electronics Department, by virtue of a methodological approach based on mechatronics. The international market requires increasing flexibility and systems able to dialogue between one another for improved efficiency and productive optimisation. System Group adopts a multidisciplinary approach in which the hardware merges with the software, and the role of the latter is destined to play an increasingly crucial role given that developments in software will enable systems to meet the demands of a constantly changing manufacturing world. The packaging and wrapping processes are applicable to a host of industrial sectors, enhanced with additional functions besides that of containment, becoming essential means also for purposes of communication. Multigecko Special find its place in this scenario, claiming to have high performance automation solutions that guarantee higher product quality, optimal levels of flexibility and impressive speed. The System Group’s packaging process is a system designed also for those needing to pack special parts, and small- to medium-sized components, such as strips, hexagons, ribbed tiles and skirting panels. The tiles are transported on the belt conveyor on infeed to the sorting bench, where the quality is graded by means of powerful vision, measurement and quality systems specially developed by System (Qualitron, Liner 2000, Red Line). The data obtained is processed by Multigecko Special, which selects the optimal box composition accordingly. In this way the material enters the machine along the infeed conveyor and is collected by the pick-up device to form uniform stacks. Once stacks are complete, the gripper picks them up and positions them in the packaging area. One of the special features consists in the four-axis gripper that is driven by a brushless motor, while 90-degree rotation is completed by a pneumatic drive. A feature of the Multigecko Special lies in the double suction cup, which enables the pick-up of two parts at a time, depositing them onto an independent stacker that processes two stacks simultaneously. Double axes and double suction cups resulting in a high-speed process for special parts. The sorter manages two stacks at a time, and a 4-jaw gripper picks up the stacks to ensure delivery intact to the packaging line, without losing any parts, regardless of size. Movement is on two axes to manage “back and forth journeys”. The pack can be created from pre-formed blanks or from neutral carton customisable on the machine. As regards the motors, Multigecko Special is equipped with stepper motors with drives developed by System Electronics. In particular, the technical staff in the department of electronic engineering of System had the task of designing the robotic movement of the machine. The hardware and software have been designed to best respond to the application requirements, such as in the drives, that can operate at high voltages and deliver high currents. Another distinguishing factor is the highly evolved diagnostics system. The added value in this unit is the possibility of using operating voltages and currents according to the needs for machine movement. What’s more, the power elements of the drives are equipped with temperature sensors to ensure constant monitoring of work conditions. The data are read by special software that emits specific warnings when certain thresholds are reached. This operation has a dual purpose: on the one hand it enables the user to check that the machine is appropriately sized, and on the other the user can intervene and run diagnostics as required. Management of current is digital, thus enabling the elimination of unpleasant noise levels that traditionally accompany conventional analogue controls. The drive by System Electronics can also receive commands from a non-real-time network, such as Ethernet. This is a smart system, the function of which does not only depend on the PLC but also a local movement profiler.     Source:electronicsnews.com

Four-stroke engine cycle produces hydrogen from methane, captures carbon dioxide

When is an internal combustion engine not an internal combustion engine? When it's been transformed into a modular reforming reactor that could make hydrogen available to power fuel cells wherever there's a natural gas supply available. By adding a catalyst, a hydrogen separating membrane and carbon dioxide sorbent to the century-old four-stroke engine cycle, researchers have demonstrated a laboratory-scale hydrogen reforming system that produces the green fuel at relatively low temperature in a process that can be scaled up or down to meet specific needs. The process could provide hydrogen at the point of use for residential fuel cells or neighborhood power plants, electricity and power production in natural-gas powered vehicles, fueling of municipal buses or other hydrogen-based vehicles, and supplementing intermittent renewable energy sources such as photovoltaics. Known as the CO2/H2 Active Membrane Piston (CHAMP) reactor, the device operates at temperatures much lower than conventional steam reforming processes, consumes substantially less water and could also operate on other fuels such as methanol or bio-derived feedstock. It also captures and concentrates carbon dioxide emissions, a by-product that now lacks a secondary use -- though that could change in the future. Unlike conventional engines that run at thousands of revolutions per minute, the reactor operates at only a few cycles per minute -- or more slowly -- depending on the reactor scale and required rate of hydrogen production. And there are no spark plugs because there's no fuel combusted. "We already have a nationwide natural gas distribution infrastructure, so it's much better to produce hydrogen at the point of use rather than trying to distribute it," said Andrei Fedorov, a Georgia Institute of Technology professor who's been working on CHAMP since 2008. "Our technology could produce this fuel of choice wherever natural gas is available, which could resolve one of the major challenges with the hydrogen economy." A paper published February 9 in the journal Industrial & Engineering Chemistry Research describes the operating model of the CHAMP process, including a critical step of internally adsorbing carbon dioxide, a byproduct of the methane reforming process, so it can be concentrated and expelled from the reactor for capture, storage or utilization. Other implementations of the system have been reported as thesis work by three Georgia Tech Ph.D. graduates since the project began in 2008. The research was supported by the National Science Foundation, the Department of Defense through NDSEG fellowships, and the U.S. Civilian Research & Development Foundation (CRDF Global). Key to the reaction process is the variable volume provided by a piston rising and falling in a cylinder. As with a conventional engine, a valve controls the flow of gases into and out of the reactor as the piston moves up and down. The four-stroke system works like this: Natural gas (methane) and steam are drawn into the reaction cylinder through a valve as the piston inside is lowered. The valve closes once the piston reaches the bottom of the cylinder. The piston rises into the cylinder, compressing the steam and methane as the reactor is heated. Once it reaches approximately 400 degrees Celsius, catalytic reactions take place inside the reactor, forming hydrogen and carbon dioxide. The hydrogen exits through a selective membrane, and the pressurized carbon dioxide is adsorbed by the sorbent material, which is mixed with the catalyst. Once the hydrogen has exited the reactor and carbon dioxide is tied up in the sorbent, the piston is lowered, reducing the volume (and pressure) in the cylinder. The carbon dioxide is released from the sorbent into the cylinder. The piston is again moved up into the chamber and the valve opens, expelling the concentrated carbon dioxide and clearing the reactor for the start of a new cycle. "All of the pieces of the puzzle have come together," said Fedorov, a professor in Georgia Tech's George W. Woodruff School of Mechanical Engineering. "The challenges ahead are primarily economic in nature. Our next step would be to build a pilot-scale CHAMP reactor." The project was begun to address some of the challenges to the use of hydrogen in fuel cells. Most hydrogen used today is produced in a high-temperature reforming process in which methane is combined with steam at about 900 degrees Celsius. The industrial-scale process requires as many as three water molecules for every molecule of hydrogen, and the resulting low density gas must be transported to where it will be used. Fedorov's lab first carried out thermodynamic calculations suggesting that the four-stroke process could be modified to produce hydrogen in relatively small amounts where it would be used. The goals of the research were to create a modular reforming process that could operate at between 400 and 500 degrees Celsius, use just two molecules of water for every molecule of methane to produce four hydrogen molecules, be able to scale down to meet the specific needs, and capture the resulting carbon dioxide for potential utilization or sequestration. "We wanted to completely rethink how we designed reactor systems," said Fedorov. "To gain the kind of efficiency we needed, we realized we'd need to dynamically change the volume of the reactor vessel. We looked at existing mechanical systems that could do this, and realized that this capability could be found in a system that has had more than a century of improvements: the internal combustion engine." The CHAMP system could be scaled up or down to produce the hundreds of kilograms of hydrogen per day required for a typical automotive refueling station -- or a few kilograms for an individual vehicle or residential fuel cell, Fedorov said. The volume and piston speed in the CHAMP reactor can be adjusted to meet hydrogen demands while matching the requirements for the carbon dioxide sorbent regeneration and separation efficiency of the hydrogen membrane. In practical use, multiple reactors would likely be operated together to produce a continuous stream of hydrogen at a desired production level. "We took the conventional chemical processing plant and created an analog using the magnificent machinery of the internal combustion engine," Fedorov said. "The reactor is scalable and modular, so you could have one module or a hundred of modules depending on how much hydrogen you needed. The processes for reforming fuel, purifying hydrogen and capturing carbon dioxide emission are all combined into one compact system."     Story Source:   Materials provided by Georgia Institute of Technology. Original written by John Toon. Note: Content may be edited for style and length.

Synthetic batteries for the energy revolution

Jena (Germany) Sun and wind are important sources of renewable energy, but they suffer from natural fluctuations: In stormy weather or bright sunshine electricity produced exceeds demand, whereas clouds or a lull in the wind inevitably cause a power shortage. For continuity in electricity supply and stable power grids, energy storage devices will become essential. So-called redox-flow batteries are the most promising technology to solve this problem. However, they still have one crucial disadvantage: They require expensive materials and aggressive acids. A team of researchers at the Friedrich Schiller University Jena (FSU Jena), in the Center for Energy and Environmental Chemistry (CEEC Jena) and the JenaBatteries GmbH (a spin-off of the University Jena), made a decisive step towards a redox-flow battery which is simple to handle, safe and economical at the same time: They developed a system on the basis of organic polymers and a harmless saline solution. "What's new and innovative about our battery is that it can be produced at much less cost, while nearly reaching the capacity of traditional metal and acid containing systems," Dr. Martin Hager says. The scientists present their battery technology in the current edition of the scientific journal Nature. In contrast to conventional batteries, the electrodes of a redox-flow battery are not made of solid materials (e.g., metals or metal salts) but they come in a dissolved form: The electrolyte solutions are stored in two tanks, which form the positive and negative terminal of the battery. With the help of pumps the polymer solutions are transferred to an electrochemical cell, in which the polymers are electrochemically reduced or oxidized, thereby charging or discharging the battery. To prevent the electrolytes from intermixing, the cell is divided into two compartments by a membrane. "In these systems the amount of energy stored as well as the power rating can be individually adjusted. Moreover, hardly any self-discharge occurs," Martin Hager explains. Traditional redox-flow systems mostly use the heavy metal vanadium, dissolved in sulphuric acid as electrolyte. "This is not only extremely expensive, but the solution is highly corrosive, so that a specific membrane has to be used and the life-span of the battery is limited," Hager points out. In the redox-flow battery of the Jena scientists, on the other hand, novel synthetic materials are used: In their core structure they resemble Plexiglas and Styrofoam (polystyrene), but functional groups have been added enabling the material to accept or donate electrons. No aggressive acids are necessary anymore; the polymers rather 'swim' in an aqueous solution. "Thus we are able to use a simple and low-cost cellulose membrane and avoid poisonous and expensive materials," Tobias Janoschka, first author of the new study, explains. "This polymer-based redox-flow battery is ideally suited as energy storage for large wind farms and photovoltaic power stations," Prof. Dr. Ulrich S. Schubert says. He is chair for Organic and Macromolecular Chemistry at the FSU Jena and director of the CEEC Jena, a unique energy research center run in collaboration with the Fraunhofer Institute for Ceramic Technologies and Systems Hermsdorf/Dresden (IKTS). In first tests the redox-flow battery from Jena could withstand up to 10,000 charging cycles without losing a crucial amount of capacity. The energy density of the system presented in the study is ten watt-hours per liter. Yet, the scientists are already working on larger, more efficient systems. In addition to the fundamental research at the University, the chemists develop their system, within the framework of the start-up company JenaBatteries GmbH, towards marketable products.   Story Source:   Materials provided by Friedrich-Schiller-Universitaet Jena. Note: Content may be edited for style and length.

Chemicals hitch a ride onto new protein for better compounds

Chemists have developed a powerful new method of selectively linking chemicals to proteins, a major advance in the manipulation of biomolecules that could transform the way drugs are developed, proteins are probed, and molecules are tracked and imaged. The new technique, called redox activated chemical tagging (ReACT), is described in the Feb. 10 issue of the journal Science. Developed at the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab), it could fundamentally change the process of bioconjugation, the process by which chemicals and tags are attached to biomolecules, particularly proteins. "We've essentially invented a new type of chemical Swiss army knife for proteins, the first that can be used for the essential and naturally occurring amino acid methionine," said study principal investigator Christopher Chang. "This ReACT method can be incorporated into a variety of different tools depending on what you need it to do. You can mix-and-match different reagents for a variety of applications." Chang and fellow Berkeley Lab faculty scientist F. Dean Toste led this work as part of the Catalysis Program at Berkeley Lab's Chemical Sciences Division. Chang is also a Howard Hughes Medical Institute Investigator. Hitching a ride onto a new protein Toste compared the process of bioconjugation to hitching cargo onto the back of a pickup truck. "That cargo can be used for many purposes," he said. "It can deliver drugs to cancerous cells, or it can be used as a tracking device to monitor the truck's movements. We can even modify the truck and change it to an ambulance. This change can be done in a number of ways, like rebuilding a truck or putting on a new hitch." Bioconjugation traditionally relies upon the amino acid cysteine, which is highly reactive. Cysteine is often used as an attachment point for tags and chemical groups because it is one of two amino acids that contain sulfur, providing an anchor for acid-base chemistry and making it easy to modify. But cysteine is often involved in the actual function of proteins, so "hitching cargo" to it creates instability and disrupts its natural function. For this reason, people have been looking for ways to circumvent cysteine, and they naturally turned to methionine, the only other sulfur amino acid available. However, methionine has an extra carbon atom attached to its sulfur, which blocks most hitches. The researchers developed a new hitch using a process called oxidation-reduction chemistry that allows cargo to be attached to the methionine sulfur with this extra carbon still attached. The potential of a chemical Swiss army knife A key benefit to methionine is that it is a relatively rare amino acid, which allows researchers to selectively target it with fewer side effects and less impact on the biomolecule. They put ReACT to the test by synthesizing an antibody-drug conjugate to highlight its applicability to biological therapeutics. They also identified the metabolic enzyme enolase as a potential therapeutic target for cancer, showing that the tool could help home in on new targets for drug discovery. In the long term, the researchers say, this new bioconjugation tool could be used in: Nanotechnology, where protein conjugation can help make nanomaterials compatible with air and water, reducing toxicity. The creation of artificial enzymes that can be recycled, have better stability, and have improved activity and selectivity through chemical protein modification. Synthetic biology, where it can be used to selectively make new proteins or augment the function of existing ones. "This method could also add to the functionality of living organisms by directly modifying natural proteins to improve their stability and activity without making a genetically modified organism that relies on gene editing," said Chang. "It could have implications for the sustainable production of fuels, food, or medicines, as well as in bioremediation."   Story Source:   Materials provided by DOE/Lawrence Berkeley National Laboratory. Note: Content may be edited for style and length.

New device harnesses sun and sewage to produce hydrogen fuel

A novel device that uses only sunlight and wastewater to produce hydrogen gas could provide a sustainable energy source while improving the efficiency of wastewater treatment. A research team led by Yat Li, associate professor of chemistry at the University of California, Santa Cruz, developed the solar-microbial device and reported their results in a paper published in the American Chemical Society journal ACS Nano. The hybrid device combines a microbial fuel cell (MFC) and a type of solar cell called a photoelectrochemical cell (PEC). In the MFC component, bacteria degrade organic matter in the wastewater, generating electricity in the process. The biologically generated electricity is delivered to the PEC component to assist the solar-powered splitting of water (electrolysis) that generates hydrogen and oxygen. Either a PEC or MFC device can be used alone to produce hydrogen gas. Both, however, require a small additional voltage (an "external bias") to overcome the thermodynamic energy barrier for proton reduction into hydrogen gas. The need to incorporate an additional electric power element adds significantly to the cost and complication of these types of energy conversion devices, especially at large scales. In comparison, Li's hybrid solar-microbial device is self-driven and self-sustained, because the combined energy from the organic matter (harvested by the MFC) and sunlight (captured by the PEC) is sufficient to drive electrolysis of water. In effect, the MFC component can be regarded as a self-sustained "bio-battery" that provides extra voltage and energy to the PEC for hydrogen gas generation. "The only energy sources are wastewater and sunlight," Li said. "The successful demonstration of such a self-biased, sustainable microbial device for hydrogen generation could provide a new solution that can simultaneously address the need for wastewater treatment and the increasing demand for clean energy." Microbial fuel cells rely on unusual bacteria, known as electrogenic bacteria, that are able to generate electricity by transferring metabolically-generated electrons across their cell membranes to an external electrode. Li's group collaborated with researchers at Lawrence Livermore National Laboratory (LLNL) who have been studying electrogenic bacteria and working to enhance MFC performance. Initial "proof-of-concept" tests of the solar-microbial (PEC-MFC) device used a well-studied strain of electrogenic bacteria grown in the lab on artificial growth medium. Subsequent tests used untreated municipal wastewater from the Livermore Water Reclamation Plant. The wastewater contained both rich organic nutrients and a diverse mix of microbes that feed on those nutrients, including naturally occurring strains of electrogenic bacteria. When fed with wastewater and illuminated in a solar simulator, the PEC-MFC device showed continuous production of hydrogen gas at an average rate of 0.05 m3/day, according to LLNL researcher and coauthor Fang Qian. At the same time, the turbid black wastewater became clearer. The soluble chemical oxygen demand--a measure of the amount of organic compounds in water, widely used as a water quality test--declined by 67 percent over 48 hours. The researchers also noted that hydrogen generation declined over time as the bacteria used up the organic matter in the wastewater. Replenishment of the wastewater in each feeding cycle led to complete restoration of electric current generation and hydrogen gas production. Qian said the researchers are optimistic about the commercial potential for their invention. Currently they are planning to scale up the small laboratory device to make a larger 40-liter prototype continuously fed with municipal wastewater. If results from the 40-liter prototype are promising, they will test the device on site at the wastewater treatment plant. "The MFC will be integrated with the existing pipelines of the plant for continuous wastewater feeding, and the PEC will be set up outdoors to receive natural solar illumination," Qian said. "Fortunately, the Golden State is blessed with abundant sunlight that can be used for the field test," Li added. Qian and Hanyu Wang, a graduate student in Li's lab at UC Santa Cruz, are co-first authors of the ACS Nano paper. The other coauthors include UCSC graduate student Gongming Wang; LLNL researcher Yongqin Jiao; and Zhen He of Virginia Polytechnic Institute & State University. This research was supported by the National Science Foundation and Department of Energy.   Story Source:   Materials provided by University of California - Santa Cruz. Original written by Tim Stephens. Note: Content may be edited for style and length.

Bacteria fed synthetic iron-containing molecules turn into electrical generators

The bacterial world is rife with unusual talents, among them a knack for producing electricity. In the wild, "electrogenic" bacteria generate current as part of their metabolism, and now researchers at the University of California, Santa Barbara (UCSB), have found a way to confer that ability upon non-electrogenic bacteria. This technique could have applications for sustainable electricity generation and wastewater treatment, the researchers report February 9 in the journal Chem. "The concept here is that if we just close the lid of the wastewater treatment tank and then give the bacteria an electrode, they can produce electricity while cleaning the water," says co-first author Zach Rengert, a chemistry graduate student at UCSB. "And the amount of electricity they produce will never power anything very big, but it can offset the cost of cleaning water." The bacteria that inspired this study, Shewanella oneidensis MR-1, live in oxygen-free environments and can breathe in metal minerals and electrodes -- instead of air -- via current-conducting proteins in their cell membranes. Most bacterial species, however, do not have such proteins and therefore naturally do not produce current. Taking inspiration from S. oneidensis' membrane-spanning conductive proteins, the team hypothesized that with the right kind of bio-compatible molecular additive, this electrogenesis might be conferred to bacteria that have not evolved to do so. The researchers, under the guidance of senior author Guillermo Bazan at UCSB, built a molecule called DFSO+, which contains an iron atom at its core. To add the DFSO+ to bacteria, the researchers dissolved a small amount of the rust-colored powder into water and added that solution to bacteria. Within a few minutes, the synthetic molecule found its way into the bacteria's cell membranes and began conducting current through its iron core, providing a new pathway for the bacteria to shuttle electrons from inside to outside the cell. Because the DFSO+ molecule's shape mirrors the structure of cell membranes, it can quickly slip into the membranes and remain there comfortably for weeks. The approach might need some tweaking before being applied to long-term power generation, the researchers say, but it's an encouraging initial finding. This chemical approach to changing bacteria's capabilities will most likely be cheaper than bacteria genetically engineered to do the same job. "It's a totally different strategy for microbial electrical energy generation," says the other co-first author, Nate Kirchhofer (@natekirchhofer), formerly a grad student at UCSB and now a postdoctoral researcher at Asylum Research in Santa Barbara, CA. "Before, we were building these devices, and we were limited to optimizing them by changing reactor materials and architectures or using genetic engineering techniques." The researchers call the DFSO+ molecule a "protein prosthetic" because it is a non-protein chemical that does a protein's job. "It's sort of analogous to a prosthetic limb, where you're using a plastic limb that's not actually made out of someone else's body," says Rengert. Understanding how electrogenic bacteria consume organic fuels and use their metabolic processes to generate electric currents could lead to more efficient biological electricity-generating technology. "It's useful to have a well-defined, well-understood molecule that we can interrogate," says Kirchhofer. "We know how it's interfaced with the bacteria, so it gives us very precise electrochemical control over the bacteria. While this molecule might not be the best one that will ever exist, it's the first generation of this kind of molecule."   Story Source:   Materials provided by Cell Press. Note: Content may be edited for style and length.

Thin, flexible, light-absorbent material for energy and stealth applications

Transparent window coatings that keep buildings and cars cool on sunny days. Devices that could more than triple solar cell efficiencies. Thin, lightweight shields that block thermal detection. These are potential applications for a thin, flexible, light-absorbing material developed by engineers at the University of California San Diego. The material, called a near-perfect broadband absorber, absorbs more than 87 percent of near-infrared light (1,200 to 2,200 nanometer wavelengths), with 98 percent absorption at 1,550 nanometers, the wavelength for fiber optic communication. The material is capable of absorbing light from every angle. It also can theoretically be customized to absorb certain wavelengths of light while letting others pass through. Materials that "perfectly" absorb light already exist, but they are bulky and can break when bent. They also cannot be controlled to absorb only a selected range of wavelengths, which is a disadvantage for certain applications. Imagine if a window coating used for cooling not only blocked infrared radiation, but also normal light and radio waves that transmit television and radio programs. By developing a novel nanoparticle-based design, a team led by professors Zhaowei Liu and Donald Sirbuly at the UC San Diego Jacobs School of Engineering has created a broadband absorber that's thin, flexible and tunable. The work was published online on Jan. 24 in Proceedings of the National Academy of Sciences. "This material offers broadband, yet selective absorption that could be tuned to distinct parts of the electromagnetic spectrum," Liu said. The absorber relies on optical phenomena known as surface plasmon resonances, which are collective movements of free electrons that occur on the surface of metal nanoparticles upon interaction with certain wavelengths of light. Metal nanoparticles can carry a lot of free electrons, so they exhibit strong surface plasmon resonance -- but mainly in visible light, not in the infrared. UC San Diego engineers reasoned that if they could change the number of free electron carriers, they could tune the material's surface plasmon resonance to different wavelengths of light. "Make this number lower, and we can push the plasmon resonance to the infrared. Make the number higher, with more electrons, and we can push the plasmon resonance to the ultraviolet region," Sirbuly said. The problem with this approach is that it is difficult to do in metals. To address this challenge, engineers designed and built an absorber from materials that could be modified, or doped, to carry a different amount of free electrons: semiconductors. Researchers used a semiconductor called zinc oxide, which has a moderate number of free electrons, and combined it with its metallic version, aluminum-doped zinc oxide, which houses a high number of free electrons -- not as much as an actual metal, but enough to give it plasmonic properties in the infrared. The materials were combined and structured in a precise fashion using advanced nanofabrication technologies in the Nano3 cleanroom facility at the Qualcomm Institute at UC San Diego. The materials were deposited one atomic layer at a time on a silicon substrate to create an array of standing nanotubes, each made of alternating concentric rings of zinc oxide and aluminum-doped zinc oxide. The tubes are 1,730 nanometers tall, 650 to 770 nanometers in diameter, and spaced less than a hundred nanometers apart. The nanotube array was then transferred from the silicon substrate to a thin, elastic polymer. The result is a material that is thin, flexible and transparent in the visible. "There are different parameters that we can alter in this design to tailor the material's absorption band: the gap size between tubes, the ratio of the materials, the types of materials, and the electron carrier concentration. Our simulations show that this is possible," said Conor Riley, a recent nanoengineering Ph.D. graduate from UC San Diego and the first author of this work. Riley is currently a postdoctoral researcher in Sirbuly's group. Those are just a few exciting features of this particle-based design, researchers said. It's also potentially transferrable to any type of substrate and can be scaled up to make large surface area devices, like broadband absorbers for large windows. "Nanomaterials normally aren't fabricated at scales larger than a couple centimeters, so this would be a big step in that direction," Sirbuly said. The technology is still at the developmental stage. Liu and Sirbuly's teams are continuing to work together to explore different materials, geometries and designs to develop absorbers that work at different wavelengths of light for various applications.   Story Source:   Materials provided by University of California - San Diego. Note: Content may be edited for style and length.
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