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Metastable material: Study shows availability of hydrogen controls chemical structure of graphene oxide

A new study shows that the availability of hydrogen plays a significant role in determining the chemical and structural makeup of graphene oxide. The study also found that after the material is produced, its structural and chemical properties continue to evolve for more than a month as a result of continuing chemical reactions with hydrogen. The Georgia Tech researchers began their studies with multilayer epitaxial graphene grown atop a silicon carbide wafer. Their samples included an average of ten layers of graphene. After oxidizing the thin films of graphene using the established Hummers method, the researchers examined their samples using XPS. Over about 35 days, they noticed the number of epoxide functional groups declining while the number of hydroxyl groups increased slightly. After about three months, the ratio of the two groups finally reached equilibrium. “We found that the material changed by itself at room temperature without any external stimulation,” said Suenne Kim, a postdoctoral fellow in Riedo’s laboratory. “The degree to which it was unstable at room temperature was surprising.”

Slip-and-slide power generators

Researchers from Vestfold University College in Norway have created a simple, efficient energy-harvesting device that uses the motion of a single droplet to generate electrical power. The new technology could be used as a power source for low-power portable devices, and would be especially suitable for harvesting energy from low frequency sources such as human body motion, write the authors in a paper accepted to the American Institute of Physics’ journal Applied Physics Letters. The harvester produces power when an electrically conductive droplet (mercury or an ionic liquid) slides along a thin microfabricated material called an electret film, which has a permanent electric charge built into it during deposition. Cyclic tilting of the device causes the droplet to accelerate across the film’s surface; the maximum output voltage (and power) occurs when the sliding droplet reaches its maximum velocity at one end of the film. A prototype of the fluidic energy harvester demonstrated a peak output power at 0.18 microwatts, using a single droplet 1.2 millimeters in diameter sliding along a 2-micrometer-thick electret film.

Reversible doping: Hydrogen flips switch on vanadium oxide

If vanadium oxide had its own TV infomercial, you’d already know: “It’s a metal. It’s an insulator. It’s a window coating and an optical switch.” And thanks to a new study by Rice University physicists – there’s more! The study shows how to reversibly alter VO₂′s quirky electronic properties by treating it with the simplest of substances-hydrogen. When oxygen reacts with vanadium to form VO₂, the atoms form crystals that look like long rectangular boxes. The vanadium atoms line up along the four edges of the box in regularly spaced rows. A single crystal of VO₂ can have many of these boxes lined up side by side, and the crystals conduct electricity like wire as long as they are kept warm. “The weird thing about this material is that if you cool it, when you get to 67°C, it goes through a phase transition that is both electronic and structural. When the phase changes, and these pairings take place, the material changes from being a electrical conductor to an electrical insulator,” says Rice’s Douglas Natelson, lead co-author of the study in this week’s Nature Nanotechnology. In 2010, Natelson and postdoctoral research associate Jiang Wei began to systematically study the phase changes in VO₂. Wei and graduate student Heng Ji began by using a process called vapor deposition to grow VO₂ wires that were about 1,000 times smaller than a human hair. One set of experiments on wires that had been baked in the presence of hydrogen gas returned particularly odd readings. Wei, Ji and Natelson determined that the hydrogen was apparently modifying the VO2 nanowires, but only those in contact with metal electrodes.

Utah-led group gets $15M from Army to design new materials

US soldiers are increasingly weighed down by batteries to power weapons, detection devices and communications equipment. So the Army Research Laboratory has awarded a University of Utah-led consortium almost $15 million to use computer simulations to help design materials for lighter-weight, energy efficient devices and batteries. “We want to help the Army make advances in fundamental research that will lead to better materials to help our soldiers in the field,” says computing Professor Martin Berzins, principal investigator among five University of Utah faculty members who will work on the project. “One of Utah’s main contributions will be the batteries.” Of the five-year Army grant of $14,898,000, the University of Utah will retain $4.2 million for research plus additional administrative costs. The remainder will go to members of the consortium led by the University of Utah, including Boston University, Rensselaer Polytechnic Institute, Pennsylvania State University, Harvard University, Brown University, the University of California, Davis, and the Polytechnic University of Turin, Italy. The new research effort is based on the idea that by using powerful computers to simulate the behavior of materials on multiple scales – from the atomic and molecular nanoscale to the large or “bulk” scale—new, lighter, more energy efficient power supplies and materials can be designed and developed. Improving existing materials also is a goal. “We want to model everything from the nanoscale to the soldier scale,” Berzins says. “It’s virtual design, in some sense.”

Zinc oxide solar reactor could be a renewable source of hydrogen

Producing hydrogen from non-fossil fuel sources is a problem that continues to elude many scientists but University of Delaware’s Erik Koepf thinks he may have discovered a solution. Koepf, a doctoral candidate in mechanical engineering, has designed a novel reactor that employs highly concentrated sunlight and zinc oxide powder to produce solar hydrogen, a truly clean, sustainable fuel with zero emissions. The reactor, which resembles a large cylinder, is comprised of layers of advanced, ultrahigh temperature insulation and ceramic materials. The conical geometry of the reactor’ design uses gravity to feed zinc oxide powder (the reactant) into the system through 15 hoppers perched on top of the device using special gears and a custom built control assembly Koepf developed at UD. Cooling blocks embedded in the structure keep the motors, a quartz window and the aperture ring, where the sunlight enters, cool. “The idea is to create a small, well-insulated cavity and subject it to highly concentrated sunlight from above,” explains Koepf. Once hot, the hoppers will feed zinc oxide powder (a benign substance resembling baking soda) onto the ceramic layer, causing a reaction that decomposes the powder into pure zinc vapor. In a subsequent step, the zinc will be reacted with water to produce solar hydrogen. “Essentially, we take zinc oxide powder and thermochemically store the energy of the sun in it, then bottle it,” explains Koepf.

Fraunhofer: Feel-good glass for windows

Daylight acts on our body clock and stimulates the brain. Fraunhofer researchers have made use of this knowledge and worked with industry partners to develop a coating for panes of glass that lets through more light. Above all, it promotes the passage through the glass of those wavelengths of light that govern our hormonal balance. Most people prefer to live in homes that are airy and flooded with light. Nobody likes to spend much time in a dark and dingy room. That’s no surprise, since daylight gives us energy and has a major impact on our sense of wellbeing. It is a real mood lifter. Anti-reflective glass that is more transmissive overall to daylight is reserved for certain special applications, such as in glass covers for photovoltaic modules or in glazing for shop windows. The aim with this new kind of glass is to avoid nuisance reflections and to achieve maximum light transmission at the peak emission wavelength of sunlight. This is the wavelength at which the human retina is also most sensitive to light. “However, our biorhythms are not affected by the wavelengths that brighten a room the most, but rather by blue light,” explains graduate engineer Walther Glaubitt, a researcher at the Fraunhofer Institute for Silicate Research ISC in Würzburg. That is why he and his team have developed glass that is designed to be particularly transmissive to light in the blue part of the spectrum. The secret is a special, long-lasting and barely perceptible inorganic coating that is only 0.1 micrometers thick. “Nobody’s ever made glass like this before. It makes you feel as if the window is permanently open,” says Glaubitt. One reason the glass gives this impression is that it exhibits maximum transmission at wavelengths between 450 and 500 nanometers—which is exactly where the effects of blue light are at their strongest.