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Georgia Tech researchers pose with a computer model of graphene oxide’s structure and the chemical species that become part of it. Shown are (l-r, first row) Elisa Riedo and Suenne Kim, (l-r, second row) Angelo Bongiorno, Claire Berger and Si Zhou. Credit: Gary Meek, Georgia Tech.

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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.

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Georgia Tech researchers display samples of materials on which ferroelectric nanostructures have been fabricated by thermochemical nanolithography. Graduate research assistant Yaser Bastani (left) with silicon, assistant professor Nazanin Bassiri-Gharb with polyimide and postdoctoral fellow Suenne Kim with glass. (Credit: Gary Meek, Georgia Tech.)

“We can directly create piezoelectric materials of the shape we want, where we want them, on flexible substrates,” says Nazanin Bassiri-Gharb in a Georgia Tech press release. ”This is the first time that structures like these have been directly grown with a CMOS-compatible process at such a small resolution. Not only have we been able to grow these ferroelectric structures at low substrate temperatures, but we have also been able to pattern them at very small scales.”

Bassiri-Gharb, a mechanical engineering assistant professor at the Georgia Institute of Technology, and others at the school have been learning how to successfully use thermochemical nanolithography to make nanometer-scale ferroelectric structures directly on bendable plastic substrates. From an applications viewpoint, this means manufacturers can now use TCNL on a substrate that would typically be ruled out because it would be unable to withstand normal processing temperatures.

The TCNL efforts are described in recent paper in Advanced Materials (doi:10.1002/adma.201101991).

TCNL, itself, isn’t novel and apparently was developed around 2007 at Georgia Tech. In general, it involves the use of a heated atomic force microscope tip to produce patterns. Since then, investigators have been perfecting where its use might be most beneficial.  Because the polarization of ferroelectrics can easily be toggled they are of interest for random access memory elements.

In this new paper, investigators report they have produced wires approximately 30 nanometers wide and spheres with diameters of approximately 10 nanometers using the patterning technique. According to Suenne Kim, the paper’s first author and a postdoctoral fellow in GT’s School of Physics, ”Spheres with potential application as ferroelectric memory were fabricated at densities exceeding 200 gigabytes per square inch, currently the record for this perovskite-type ferroelectric material.”

According to a GT news release, the group hopes their work demonstrates how TCNL could lead to high-density, low-cost production of complex ferroelectric structures. The types of applications they have in mind are energy-harvesting arrays, sensors and actuators in nanoelectromechanical systems and microelectromechanical systems.

Image shows the topography (by atomic force microscope) of a ferroelectric PTO line array crystallized on a 360-nanometer thick precursor film on polyimide. Bar corresponds to one micron. (Credit: Suenne Kim, Georgia Tech.)

The problem is that normal ferroelectric crystallization processes require temperatures that exceed 600°C. Typically, ferroelectric structures first had to be grown on a single-crystal substrate and then transferred to a flexible substrate for use in energy-harvesting. But, by using an AFM tip on amophous precursor materials, TCNL leads to only “extremely localized heating” that is more on the order of 250°C, Then, it’s only a matter of matter of using computer controls to draw patterns of crystallized material, for example, lines of ferroelectric nanowires drawn along the direction in which strain would be applied.

The GT group says it has created lead titanate and lead zirconate titanate structures on polyimide, glass and silicon substrates. In general, however, the researchers say the only substrate requirement is that it be able to withstand the 250” heating step.

Next, the group says it plans on assembling arrays of AFM tips to produce larger patterned areas, and also get a handle on the growth thermodynamics of ferroelectric materials at the nanoscale.

Pztlines-sem: Scanning electron microscope image shows a large PZT line array crystallized on a 240-nanometer thick precursor film on a platinized silicon wafer. (Credit: Yaser Bastani, Georgia Tech.)

“We are really addressing the problem caused by the existing limitations of photolithography at these size scales,” says GT physics professor Elisa Riedo, in the news release. “We can envision creating a full device based on the same fabrication technique without the requirements of costly clean rooms and vacuum-based equipment. We are moving toward a process in which multiple steps are done using the same tool to pattern at the small scale.”

The research was sponsored by NSF and the DOE, and also involved scientists from the University of Illinois Urbana-Champaign and the University of Nebraska Lincoln.

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President Barack Obama announces Advanced Manufacturing Initiative at Carnegie Mellon University. Credit: Pete Souza; Official White House Photo.

Last week President Obama unveiled a new initiative to invest in emerging technologies and create new manufacturing jobs and increase the nation’s global competitiveness. During a visit to Carnegie Mellon University in Pittsburgh, Pa., Obama introduced the Advanced Manufacturing Partnership, which, according to the White House press release, will invest more than $500 million to leverage existing programs and proposals to meet these goals.

The press release said that AMP’s initial investments will target manufacturing for critical national security industries, advanced materials development, robotics, improving energy efficiency of manufacturing processes and accelerating the product development timeline for manufactured goods.

“Today, I’m calling for all of us to come together- private sector industry, universities, and the government- to spark a renaissance in American manufacturing and help our manufacturers develop the cutting-edge tools they need to compete with anyone in the world,” said Obama in the press release. “With these key investments, we can ensure that the United States remains a nation that ‘invents it here and manufactures it here’ and creates high-quality, good paying jobs for American workers.”

AMP is a response to the first of four recommendations made by the President’s Council of Advisors on Science and Technology in their just-released report, “Ensuring Leadership in Advanced Manufacturing (pdf).” The report cites an erosion of domestic leadership in manufacturing and the heavy investment of other nations to fill that void, the advantages of having R&D and manufacturing located in the United States, the essential role of an advanced manufacturing competence in national security and that, historically, federal investment in new technologies has cleared the way for fledglings to become major new industries.

The PCAST report concludes that individual companies cannot go it alone: “Private investment must be complemented by public investment to overcome market failures. Key opportunities include investing in the advancement of new technologies with transformative potential, supporting shared infrastructure, and accelerating the manufacturing process through targeted support for new methods and approaches.”

To create an environment conducive to innovation and to overcome market failures, the PCAST report recommended a four-point plan:

• Launch an advanced manufacturing initiative;
• Improve tax policy;
• Support research; and
• Strengthen the workforce.

AMP is the administration’s response to the first of these, and as recommended by PCAST, is a government, industry and academic partnership. It will be led by Andrew Liveris, CEO of Dow Chemical and Susan Hockfield, president of MIT, and will work closely with the White House’s National Economic Council, Office of Science and Technology Policy, as well as with PCAST.

The first team has been picked already. From industry it will be Allegheny Technologies, Caterpillar, Corning, Dow Chemical, Ford, Honeywell, Intel, Johnson & Johnson, Northrop Grumman, Proctor & Gamble and Stryker. Participating universities are MIT, Carnegie Mellon, Georgia Tech, Stanford, UC-Berkeley and University of Michigan. Government players are DARPA, DOE, DOD, and the Commerce Department.

The White House press release gives examples of how several partnerships that are in place will modify their programs to support AMP goals. Several of the named agencies have a long history as important, strategic investors in materials science and engineering such as NSF, NASA and NIST. For example, NIST, a Commerce Department agency, issued a press release outlining its programs that will support the AMP initiative including robotics, nanomanufacturing, advanced materials design through the Materials Genome Initiative and an advanced manufacturing technology consortium scheduled for launch in FY2010.

The PCAST report recommended that AMP funding should rise from $500 million to $1 billion over the course of four years. While touring Carnegie Mellon and seeing demonstrations of several cutting-edge technologies developed at the university, Obama said that it was important for ideas to have a place to incubate and become products that can be made in the US and sold worldwide. “And that’s in our blood. That’s who we are. We are inventors, and we are makers, and we are doers.”

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Regents professor Meilin Liu (right) and postdoctoral researcher Mingfei Liu examine a button fuel cell used to evaluate a new self-cleaning anode material based on barium oxide. The self-cleaning technique could allow fuel cells to be powered by coal gas. Credit: Georgia Tech Photo, Gary Meek.

The nation’s energy spotlight has drifted away from solid oxide fuel cells over the last year or so (the last big splash being the Bloom Energy media fest), but that doesn’t mean researchers aren’t still working to figure out how to overcome the barriers to making SOFCs commercially successful.

One of the main engineering barriers is operating temperature. The problem is that when SOFCs operate above 850 °C, the materials or other workarounds that have to be used to prevent performance problems are either expensive or require fuel dilution. Either way, they make these fuel cells cost prohibitive under current circumstances. Go below 850 °C and coking (carbon buildup) on traditional anode materials, such as Ni-yttrium-stabilized zirconia, causes deactivation and creates sharp drop offs in fuel-to-energy conversion. It’s a pity because these fuel cells could be fueled with waste hydrocarbon sources, such as municipal wastes and biomass, or could double the energy output of coal (gasified) and consequently cut CO₂ emissions in half.

But, a workgroup led by ACerS member Meilin Liu believes it has found a new way to make an SOFC anode, which can operate effectively and efficiently with carbonaceous fuels at 750 °C, using a nanostructured barium oxide/nickel interface. A paper about the group’s achievements was recently published in Nature Communications (doi:10:1038/ncomms1359). Liu, professor of MSE at Georgia Tech, and his research group collaborated with researchers at the Brookhaven National Lab, the New Jersey Institute of Technology and Oak Ridge National Lab.

The BaO possibilities were interesting to the group because the oxide is known to have been used as a promoter for reforming catalysts (the catalysts that breakdown hydrocarbon fuels into hydrogen and a byproduct). The challenge was to come up with a way of using the material that would not create a block to electrons but absorb water that would be used to remove carbon and combat coking. Their solution was to deposit (by evaporation) BaO onto Ni-YST. According to the authors, “In this process, BaO reacts with the surfaces of NiO, producing a thin film of NiO-BaO compounds on the NiO surface. On exposure to fuel, the thin film of NiO–BaO compounds is reduced to nanosized islands distributed on the Ni surface.”

Button-type test cells were made with the new anode structures. When fueled with dry C₃H₈, the cells attained a power density of ~0.88 Wcm^-2 at 750 °C (more than 50 percent higher that traditional SOFCs operated under the same conditions). Further, cells were able to produce a stable current of 500 mA cm^-2 for 100 hours, indicating the absence of coking.

Researchers also tested the new cells tolerance to CO. They used a wet (~3 v%) CO fuel stream and attained a power density of ~0.70 Wcm^-2 (again, higher than what has been reported for other SOFC under the same conditions).

Finally, they used a fluidized carbon bed–SOFC arrangement to test the anode’s possible performance with something like gasified coal. They formed the fuel stream using a wet CO₂ gasification technique. Here, they attained a peak power density of ~1.08 Wcm^-2 at 850 °C, twice that of other SOFCs. When they lowered the temperature to 750 °C, the cell peak power density was still remarkable: ~0.65 Wcm^-2 . Although cells cannot operate for long at this lower temperature, the the new anode delivered stable performance for 1000 hours.

The researchers say the performance and resistance to coking demonstrated using BaO/Ni interface “represent a vital step towards a cost-effecitve fuel cell for direct conversion of hydrocarbons and gasified carbonaceous solid fuels to electricity.”

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