Cheaper Color-Changing Window

Stained glass: These photos show the two electrodes that make up the color-changing part of an electrochromic window. The clear electrode on the left has has been impregnated with lithium. The dark electrode on the right been drained of ions.   Credit: NREL

Thin, battery-like films change color when the weather changes.

By Katherine Bourzac

Thirty percent of the energy used by buildings in the United States is spent making up for heat loss or gain through windows. That adds up to about $40 billion in electricity costs each year. Windows that change color in response to changes in the weather can help save on electricity costs by absorbing sunlight in the winter and reflecting it in the summer. Such windows have existed for awhile, but they are expensive and not widely used. Now researchers are developing cheap printing methods for making these electrochromic systems, and hope to make electrochromic films that can be cut to fit existing windows.

Electrochromic windows sandwich materials that change color when a small electrical field is applied across them. This change is triggered by changes in light or temperature measured by sensors. “With electrochromic windows, everything happens dynamically–you don’t have to think about it,” says Anne Dillon, senior scientist at the National Renewable Energy Laboratory (NREL). “The problem is, they’re too expensive.”

This week at the Materials Research Society meeting in Boston, Dillon and research scientist Robert Tenent at NREL presented their new and potentially cheaper method for making electrochromic windows.

Typical electrochromic systems are made up of two electrodes separated by an electrolyte that shuttles ions between them. The electrode materials, usually oxidized metals, change color when an ion such as lithium moves into and out of them.

The NREL systems are based on electrodes made of nickel oxide and tungsten oxide and are the first electrochromic systems to be made by spraying down cheap precursors and then heating them. NREL has tested the systems using a liquid electrolyte, and is currently developing systems that rely on solid ion conductors. When a voltage is applied across the NREL system, lithium ions move out of the nickel oxide and into the electrolyte; on the other side, lithium ions move into the tungsten oxide. The movement of the ions causes the two electrodes to color.

Spraying the films is not only a cheaper alternative, says Tenent, it also provides some advantages in performance. The NREL team found that adding a small amount of lithium to the nickel-oxide ink solution before it’s printed made for a film that changes color much faster and within a wider range. In 29 seconds, as lithium leaves the nickel electrode and it darkens in color, the electrode goes from transmitting 80 percent of incident light to transmitting just 30 percent. Adding a small amount of lithium using conventional manufacturing techniques would be much more difficult, Tenent says.

There are other ways to make color-changing windows–by using materials that undergo a chemical change in response to light, for example. But these materials are prone to degradation. The NREL group is developing the metal-oxide electrodes in the hopes that these materials, which are robust and don’t degrade in response to light, will have long lifetimes.

So far, the NREL system has been tested on glass substrates. To make a truly affordable window coating, the group is working to make electrochromic films based on flexible, transparent plastics. The group is talking to DuPont, which makes plastics, about collaborating to fabricate electrochromic films sandwiched between one of the company’s heat-tolerant polymers. The nickel-oxide precursor must be heated to about 300 ºC in order to form the electrode material, a temperature many plastics can’t tolerate.

http://www.technologyreview.com/energy/24049/

Innovation Puts Next-Generation Solar Cells on the Horizon

Scientists have developed an innovative way to boost the output of the next generation of solar cells. (Credit: iStockphoto/Tamara Kulikova)

In a world first, a Monash University-led international research team has developed an innovative way to boost the output of the next generation of solar cells.

Scientists at Monash University, in collaboration with colleagues from the universities of Wollongong and Ulm in Germany, have produced tandem dye-sensitised solar cells with a three-fold increase in energy conversion efficiency compared with previously reported tandem dye-sensitised solar cells.

Lead researcher Dr Udo Bach, from Monash University, said the breakthrough had the potential to increase the energy generation performance of the cells and make them a viable and competitive alternative to traditional silicon solar cells.

Dr Bach said the key was the discovery of a new, more efficient type of dye that made the operation of inverse dye-sensitised solar cells much more efficient.

When the research team combined two types of dye-sensitised solar cell — one inverse and the other classic — into a simple stack, they were able to produce for the first time a tandem solar cell that exceeded the efficiency of its individual components.

“The tandem approach — stacking many solar cells together — has been successfully used in conventional photovoltaic devices to maximise energy generation, but there have been obstacles in doing this with dye-sensitised cells because there has not been a method for creating an inverse system that would allow dye molecules to efficiently pass on positive charges to a semiconductor when illuminated with light,” Dr Bach said.

“Inverse dye-sensitised solar cells are the key to producing dye-sensitised tandem solar cells, but the challenge has been to find a way to make them perform more effectively. By creating a way of making inverse dye-sensitised solar cells operate very efficiently we have opened the way for dye-sensitised tandem solar cells to become a commercial reality.”

Although dye-sensitised solar cells have been the focus of research for a number of years because they can be fabricated with relative simplicity and cost-efficiency, their effectiveness has not been on par with high-performance silicon solar cells.

Dr Bach said the breakthrough, which is detailed in a paper published in Nature Materials, was an important milestone in the ongoing development of viable and efficient solar cell technology.

“While this new tandem technology is still in its early infancy, it represents an important first step towards the development of the next generation of solar cells that can be produced at low cost and with energy efficient production methods,” he said.

“With this innovation we are one step closer to the creation of a cost-efficient and carbon-neutral energy source.”

Story Source:

Adapted from materials provided by Monash University.

http://www.sciencedaily.com/releases/2009/12/091201100553.htm

Shape Shifters: Researchers Create New Breed of Antennas

The antenna consists of liquid metal injected into elastomeric microchannels. The antennas can be deformed (twisted and bent) since the mechanical properties are dictated by the elastomer and not the metal. (Credit: Image courtesy of North Carolina State University)

Antennas aren’t just for listening to the radio anymore. They’re used in everything from cell phones to GPS devices. Research from North Carolina State University is revolutionizing the field of antenna design — creating shape-shifting antennas that open the door to a host of new uses in fields ranging from public safety to military deployment.

Modern antennas are made from copper or other metals, but there are limitations to how far they can be bent — and how often — before they break completely. NC State scientists have created antennas using an alloy that “can be bent, stretched, cut and twisted — and will return to its original shape,” says Dr. Michael Dickey, assistant professor of chemical and biomolecular engineering at NC State and co-author of the research.

The researchers make the new antennas by injecting an alloy made up of the metals gallium and indium, which remains in liquid form at room temperature, into very small channels the width of a human hair. The channels are hollow, like a straw, with openings at either end — but can be any shape. Once the alloy has filled the channel, the surface of the alloy oxidizes, creating a “skin” that holds the alloy in place while allowing it to retain its liquid properties.

“Because the alloy remains a liquid,” Dickey says, “it takes on the mechanical properties of the material encasing it.” For example, the researchers injected the alloy into elastic silicone channels, creating wirelike antennas that are incredibly resilient and that can be manipulated into a variety of shapes. “This flexibility is particularly attractive for antennas because the frequency of an antenna is determined by its shape,” says Dickey. “So you can tune these antennas by stretching them.”

While the alloy makes an effective antenna that could be used in a variety of existing electronic devices, its durability and flexibility also open the door to a host of new applications. For example, an antenna in a flexible silicone shell could be used to monitor civil construction, such as bridges. As the bridge expands and contracts, it would stretch the antenna — changing the frequency of the antenna, and providing civil engineers information wirelessly about the condition of the bridge.

Flexibility and durability are also ideal characteristics for military equipment, since the antenna could be folded or rolled up into a small package for deployment and then unfolded again without any impact on its function. Dickey thinks these new applications are the most likely uses for the new antennas, since the alloy is more expensive than the copper typically used in most consumer electronics that contain antennas.

Dickey’s lab is performing further research under a National Science Foundation grant to better understand the alloy’s properties and means of utilizing it to create useful devices.

The research is co-authored by Dickey, NC State doctoral students Ju-Hee So, Amit Qusba and Gerard Hayes, NC State undergraduate student Jacob Thelen, and University of Utah professor Dr. Gianluca Lazzi, who participated in the research while a professor at NC State. The research is published in Advanced Functional Materials.

Story Source:

Adapted from materials provided by North Carolina State University.

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Journal Reference:

1. Ju-Hee So, Jacob Thelen, Amit Qusba, Gerard J. Hayes, Gianluca Lazzi, Michael D. Dickey. Reversibly Deformable and Mechanically Tunable Fluidic Antennas. Advanced Functional Materials, 2009; 19 (22): 3632 DOI: 10.1002/adfm.200900604

http://www.sciencedaily.com/releases/2009/12/091201100545.htm

Carbon Capture with Nanotubes

Startup Porifera is developing membranes to separate greenhouse gases from smokestacks.

By Kevin Bullis

Membranes made with carbon nanotubes could reduce the amount of energy needed to capture carbon-dioxide emissions from smokestacks, and therefore cut costs, according to a company that will receive $1 million from the new advanced-research projects agency for energy, Arpa-e, to develop the technology.

The company, Hayward, CA-based Porifera, claims that its carbon-nanotube membranes could capture one billion to three billion tons of carbon dioxide a year and save $10 billion a year compared to existing CO₂ capture technology. At this point, however, the work is at an early stage, says Olgica Bakajin, Porifera’s chief technology officer. She expects that it will be another year before the first prototype is ready.

The company hopes to make use of some peculiar properties of nanotubes to capture carbon dioxide. Membranes for capturing CO₂ from smokestacks need to have two features. They need to be selective, allowing carbon dioxide to pass through and not the other exhaust gases. This produces a concentrated stream of carbon dioxide that can then be compressed and stored. The membranes also need to be highly permeable–allowing CO₂ to pass through freely to minimize the energy needed to pump it.

Carbon nanotube membranes are particularly good for this second property. Gases can move through the interior of nanotubes extremely quickly–at rates 100 times as fast as through conventional membrane materials, according to experiments Bakajin led at Lawrence Livermore National Laboratory. Those results were published in the journal Science in 2006. As a result, membranes based on nanotubes would require far less energy than conventional membranes.

The challenge with carbon nanotube membranes is selectively transporting carbon dioxide and not the other gases in a smokestack. This is particularly difficult because the main component of flue gas, nitrogen has many properties that are very similar to CO₂, says Karl Johnson, professor of chemical and petroleum engineering at the University of Pittsburgh. One approach to selecting the carbon dioxide is to bind compounds to the ends of the carbon nanotubes that chemically attract carbon dioxide but not other gases. Attracting the CO₂ would create high concentrations of it near the membrane, increasing the amount of carbon dioxide that gets transported through relative to the nitrogen and other flue gases. Attaching these compounds is particularly easy because the ends of nanotubes have open locations for binding with such molecules, Bakajin says.

Article Continues - http://www.technologyreview.com/energy/24021/

A Cancer-Fighting Implant

Cancer killer: A cross section of a polymer matrix designed to prime the immune system against cancer. Immune cells crawl through the pores and are activated by chemical signals and tumor molecules.  Credit: Edward Doherty, Omar Ali and Microvision Labs

A polymer disc shrinks tumors in rodents by eliciting an immune attack.

By Emily Singer

In a new approach to fighting cancer, scientists from Harvard University have engineered an implantable disc designed to attract immune cells and prep them to attack tumors. Mice with melanoma tumors were much more likely to survive if they’d been implanted with the device, and tumors disappeared in up to half of the vaccinated animals, according to research published today in the journal Science Translational Medicine. Researchers believe that the implant elicits a broader immune response than traditional vaccines, and may therefore prove more effective. A startup called InCytu, based in Lincoln, RI, is now developing the technology for human testing.

A number of vaccines for treating different types of cancer are currently being tested in clinical trials, though none has yet been approved by the U.S. Food and Drug Administration. Unlike traditional vaccines, therapeutic cancer vaccines are designed to halt or reverse the course of the disease after it has developed. Gardasil, Merck’s vaccine against the human papillomavirus, is considered a preventative cancer vaccine and acts in a similar way to traditional vaccines. It helps prevent the development of cervical cancer by stopping viral infection–but it cannot treat existing cervical cancer.

While cancer vaccines come in several variations, the general approach is to trigger the immune system to recognize and destroy cells bearing a cancer-specific marker. The immune system can be tuned to cancer cells by injecting patients with specific molecules linked to different types of cancer, or by injecting irradiated cancer cells. Scientists have also tried to enhance this process by training the immune cells in a controlled environment outside the body–the cells are isolated from the patient’s blood and exposed to cancer-specific molecules. The primed immune cells are then injected back into the patient, where they travel to the lymph nodes and trigger an immune response against the cancer.

A number of vaccines for treating different types of cancer are currently being tested in clinical trials, though none has yet been approved by the U.S. Food and Drug Administration. Unlike traditional vaccines, therapeutic cancer vaccines are designed to halt or reverse the course of the disease after it has developed. Gardasil, Merck’s vaccine against the human papillomavirus, is considered a preventative cancer vaccine and acts in a similar way to traditional vaccines. It helps prevent the development of cervical cancer by stopping viral infection–but it cannot treat existing cervical cancer.

While cancer vaccines come in several variations, the general approach is to trigger the immune system to recognize and destroy cells bearing a cancer-specific marker. The immune system can be tuned to cancer cells by injecting patients with specific molecules linked to different types of cancer, or by injecting irradiated cancer cells. Scientists have also tried to enhance this process by training the immune cells in a controlled environment outside the body–the cells are isolated from the patient’s blood and exposed to cancer-specific molecules. The primed immune cells are then injected back into the patient, where they travel to the lymph nodes and trigger an immune response against the cancer.

The polymer is also packed with small fragments of genetic material designed to mimic bacterial DNA. These fragments signal to the dendritic cells that a foreign invader is present. Also present are ground-up pieces of the patient’s tumor, which show the cells what to attack. The dendritic cells pick up these molecules as they move through the scaffold. The cells then travel to the lymph nodes, where they introduce the target molecules and generate an immune response. “When the implant is in the body, the immune system sees it as dangerous material and attacks it,” says Tarek Fahmy, a bioengineer at Yale University who was not involved in the research.

In mice with established melanoma tumors, the vaccine significantly slowed the growth of the tumors and increased animals’ survival time. In addition, tumors completely disappeared in 20 to 50 percent of animals given two vaccinations, depending on how long the tumors had been growing. Researchers say this is significant, given that most cancer vaccines considered to be effective in rodents have been shown to prevent formation of tumors rather than to diminish established tumors. However, it’s difficult to compare different rodent models of cancer, which can vary widely.

The implant’s effectiveness may lie in the immune response that it triggers, says Mooney. It appears to generate the formation of different types of dendritic cells, which may make the immune response more potent. It also appears to dampen a part of the immune system that typically neutralizes the response once it’s been activated–maintaining an activated immune system might be important in preventing tumors from recurring. “That is very novel and extremely important for cancer immunotherapy,” says Fahmy.

As is often the case with new cancer treatments, it’s difficult to predict how well the findings will translate to humans. A number of cancer vaccines have shown success in animal models and then failed in human clinical trials.

http://www.technologyreview.com/biomedicine/24013/

Vaccine disc: The disc-shaped implant is smaller than a dime.  Credit: InCytu

Nuclear Waste Reduction: Polymers Designed to Mop Up Radioactive Isotopes

Nuclear power could solve our energy problems but it has rather nasty by-products: radioactive waste. Not only the disposal of the old core rods but also reactor operation results in a large amount of low-level waste, especially contaminated cooling water.

Together with his colleague Sevilimendu Narasimhan from the Bhabha Atomic Research Center in Kalpakkam, India, the chemist PD Dr. Börje Sellergren from the Institute of Environmental Research at Technische Universität Dortmund has developed a new method to reduce the amount of this radioactive waste considerably. His approach: small beads consisting of a special polymer which “fishes” the radioactivity out of the water.

In pressurized-water reactors, the most common reactor, hot water circulates at high pressure through the steel pipes, dissolving metal ions from the walls of the pipes. When the water is pumped through the reactor’s core, these ions are bombarded by neutrons.

Because the pipes are steel pipes, most of the ions are common iron-isotopes (56 Fe), which don’t become radioactive when bombarded by neutrons. But the steel in the pipes is usually alloyed with cobalt. And when this cobalt absorbs neutrons, an instable cobalt-isotope (60 Co) emerges which is radioactive with a half-life of more than five years.

Usually the water is cleaned with ion exchangers. But this technique has a crucial disadvantage, because it doesn’t differentiate between non-radioactive iron-ions and radioactive cobalt-ions.

To overcome this problem, Sellergren and Narasimhan were looking for a material which binds cobalt and not iron. They developed a special polymer which is made through a procedure called “molecular imprinting.” This polymer is made in an environment containing cobalt. Then the cobalt-ions are extracted with hydrochloric acid, meaning that they are virtually “washed out.” The resulting cobalt-sized holes — the imprinting — are able to trap cobalt — and just cobalt — in other environments. The result: a small amount of this polymer can mop up a large amount of radioactive isotopes.

The team is now forming the polymer into small beads that can pass through the cooling system of a nuclear-power station. They expect that it would be more economical and environment-friendly to concentrate radioactivity into such beads than to dispose of large amounts of low-level waste. There obviously is a demand. Some 40 new nuclear-power stations are being built around the world. And the International Atomic Energy Agency estimates that a further 70 will be built in the next 15 years.

Story Source:

Adapted from materials provided by Technische Universitaet Dortmund, via AlphaGalileo.

http://www.sciencedaily.com/releases/2009/11/091127123921.htm

24-Carat Gold ‘Snowflakes’ Improve Graphene’s Electrical Properties

The above image shows the way in which snowflake-shaped gold nanostars cluster on a graphene sheet. (Credit: Kansas State University, Department of Chemical Engineering)

In an effort to make graphene more useful in electronics applications, Kansas State University engineers made a golden discovery — gold “snowflakes” on graphene.

Vikas Berry is a K-State assistant professor of chemical engineering who works with graphene, a carbon material only a single atom thick and discovered just five years ago. To functionalize graphene with gold — thus controlling its electronics properties — Berry and Kabeer Jasuja, a K-State doctoral student in chemical engineering, imbedded gold on graphene.

To do this, the engineers placed the graphene oxide sheets in a gold ion solution that had a growth catalyst. Here, the atomically thick sheets swim and bathe in a pool of chemicals.

“Graphene-derivatives act like swimming molecular carpets when in solution and exhibit fascinating physiochemical behavior,” Berry said. “If we change the surface functionality or the concentration, we can control their properties.”

They found that rather than distributing itself evenly over graphene, the gold formed islands on the sheets’ surfaces. They named these islands snowflake-shaped gold nanostars, or SFGNs.

“So we started exploring how these gold nanostars are formed,” Berry said. “We found out that nanostars with no surface functionality are rather challenging to produce by other chemical processes. We can control the size of these nanostars and have characterized the mechanism of nucleation and growth of these nanostructures. It’s similar to the mechanism that forms real snowflakes.”

Berry said the presence of graphene is critical for the formation of the gold nanostars. “If graphene is absent, the gold would clump together and settle down as big chunks,” he said. “But the graphene helps in stabilizing the gold. This makes the nanostars more useful for electronic applications.”

In July, Jasuja and Berry published their work in the journal ACS-Nano.

The discovery of these gold “snowflakes” on graphene shows promise for biological devices as well as

electronics. Berry is attaching DNA to these gold islands to make DNA sensors. He is joined by Nihar Mohanty, a doctoral student in chemical engineering, and undergraduate researcher Ashvin Nagaraja, a senior in electrical engineering. Nagaraja is a 2004 Manhattan High School graduate.

Berry said graphene-gold based DNA sensors will have enhanced sensitivity. Chemically reducing graphene oxide to obtain graphene requires harsh chemicals that destroy the DNA.

“Now we can use the harsh chemicals on graphene oxide imbedded with gold to obtain graphene with gold islands. Then we can use these gold islands to functionalize DNA.”

Berry also is using graphene in conjunction with microwaves. He and Jasuja are “cooking” the graphene sheets as another way to produce particles on the material’s surface.

Some of Berry’s other graphene research involves using the modified graphene sheets to compartmentalize a coagulating solution, thus stabilizing it. His group has recently used hydrides to reduce graphene oxide to produce reduced graphene oxide in the matter of a few seconds. The graphene produced in this way can remain stable in the solution for several days. Further results will shortly appear in the journal Small

Discovered only five years ago, graphene has captured the attention of a large number of researchers who are studying its exceptional electrical, mechanical and optical properties, Berry said. His research group is among the few studying the material’s interfacial properties and biological applications.

“We’re entering a new era,” Berry said. “From the zero-dimensional or one-dimensional molecular or polymer solutions, we are now venturing into the two-dimensional graphene solutions, which have fascinating new properties.”

Story Source:

Adapted from materials provided by Kansas State University.

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Journal Reference:

1. Kabeer Jasuja and Vikas Berry. Implantation and Growth of Dendritic Gold Nanostructures on Graphene Derivatives: Electrical Property Tailoring and Raman Enhancement. ACS Nano, 2009; 3 (8): 2358 DOI: 10.1021/nn900504v

http://www.sciencedaily.com/releases/2009/10/091013112521.htm

Bioengineers Succeed in Producing Plastics Without the Use of Fossil Fuels

Computer rendering of E. coli bacteria. A newly developed E. coli strain is capable of efficiently producing unnatural polymers, through a one-step fermentation process. (Credit: iStockphoto/Sebastian Kaulitzki)

A team of pioneering South Korean scientists have succeeded in producing the polymers used for everyday plastics through bioengineering, rather than through the use of fossil fuel based chemicals. This groundbreaking research, which may now allow for the production of environmentally conscious plastics, is published in two papers in the journal Biotechnology and Bioengineering.

Polymers are molecules found in everyday life in the form of plastics and rubbers. The team, from the KAIST University and the Korean chemical company LG Chem, led by Professor Sang Yup Lee focused their research on polylactic acid (PLA), a bio-based polymer which holds the key to producing plastics through natural and renewable resources.

“The polyesters and other polymers we use everyday are mostly derived from fossil oils made through the refinery or chemical process,” said Lee. “The idea of producing polymers from renewable biomass has attracted much attention due to the increasing concerns of environmental problems and the limited nature of fossil resources. PLA is considered a good alternative to petroleum based plastics as it is both biodegradable and has a low toxicity to humans.”

Until now PLA has been produced in a two-step fermentation and chemical process of polymerization, which is both complex and expensive. Now, through the use of a metabolically engineered strain of E.coli, the team has developed a one-stage process which produces polylactic acid and its copolymers through direct fermentation. This makes the renewable production of PLA and lactate-containing copolymers cheaper and more commercially viable.

“By developing a strategy which combines metabolic engineering and enzyme engineering, we’ve developed an efficient bio-based one-step production process for PLA and its copolymers,” said Lee. “This means that a developed E. coli strain is now capable of efficiently producing unnatural polymers, through a one-step fermentation process,”

This combined approach of systems-level metabolic engineering and enzyme engineering now allows for the production of polymer and polyester based products through direct microbial fermentation of renewable resources.

“Global warming and other environmental problems are urging us to develop sustainable processes based on renewable resources,” concluded Lee. “This new strategy should be generally useful for developing other engineered organisms capable of producing various unnatural polymers by direct fermentation from renewable resources”.

Story Source:

Adapted from materials provided by Wiley-Blackwell, via EurekAlert!, a service of AAAS.

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Journal References:

1. Taek Ho Yang, Tae Wan Kim, Hye Ok Kang, Sang-Hyun Lee, Eun Jeong Lee, Sung-Chul Lim, Sun Ok Oh, Ae-Jin Song, Si Jae Park, Sang Yup Lee. Biosynthesis of polylactic acid and its copolymers using evolved propionate CoA transferase and PHA synthase. Biotechnology and Bioengineering, 2010; 105 (1): 150 DOI: 10.1002/bit.22547
2. Yu Kyung Jung, Tae Yong Kim, Si Jae Park, Sang Yup Lee. Metabolic engineering of Escherichia coli for the production of polylactic acid and its copolymers. Biotechnology and Bioengineering, 2010; 105 (1): 161 DOI: 10.1002/bit.22548

http://www.sciencedaily.com/releases/2009/11/091123083702.htm

Origami Solar Cells

Fold-up silicon: In these images, three thin films of silicon fold up into 3-D shapes under the force of surface tension as water droplets placed in their centers evaporate. The top row depicts the first step, when the water droplets are large, and the images below it show a time progression as the water droplets shrinks.   Credit: PNAS

Silicon sheets self-assemble into spheres to capture more light.

By Katherine Bourzac

One way to squeeze more power out of sunlight is to ensure that it always hits a solar panel at the ideal angle. This means either tracking the sun and maneuvering a panel to face it, or using complex optics to redirect the sun’s rays to hit the panel’s surface from above.

Researchers at the University of Illinois have now come up with self-assembling spherical solar cells capable of capturing more sunlight than flat ones. The shape is a simpler way to make more use of the sun’s rays, but has been difficult to realize in a solar cell. These new microscale solar cells are made using conventional lithography combined with self-assembly. If they prove practical, the devices could be wired up into large arrays that have the same power output as conventional cells, but that save on materials costs by using less silicon.

“Instead of a big slab of semiconductor fitted with concentrating lenses and motors to move it around, we want to make compact cells that still have a significant power output,” says Ralph Nuzzo, professor of chemistry at the University of Illinois at Urbana-Champaign.

Curved surfaces capture more light than flat ones because they have a greater surface area. But making solar cells that are curved or spherical is challenging, says Nuzzo, because the techniques used to process semiconducting materials such as silicon work best on flat surfaces. Nuzzo’s group has overcome this problem by making microscale 3-D structures that self-assemble from flat sheets.

The Illinois researchers start by treating the surface of a thin, high-quality silicon wafer and using conventional lithography to etch out a thin, two-dimensional shape. To make a sphere, the researchers cut the silicon into a flower shape. They then use an adhesive to secure a small piece of glass inside. The glass helps the structure maintain its shape once it is assembled. Finally, as a drop of water placed in the center of the flower shape evaporates, surface tension pulls its petals up, eventually bringing them together to form a sphere.

“The challenge in this is, how do you get things to follow the necessary sequence of steps to fold into the desired shape?” says Nuzzo. The Illinois group came up with mathematical models to help predict the mechanical properties of silicon sheets of different shapes and thicknesses, as well as how they interact with water, which can be tuned by chemically treating their surfaces.

Article Continues – http://www.technologyreview.com/biomedicine/24012/

Hydrogen-Economy on the Way? New Hydrogen-Storage Method Discovered

This schematic shows the structure of the new material, Xe(H₂)₇. Freely rotating hydrogen molecules (red dumbbells) surround xenon atoms (yellow). (Credit: Image courtesy of Nature Chemistry)

Scientists at the Carnegie Institution have found for the first time that high pressure can be used to make a unique hydrogen-storage material. The discovery paves the way for an entirely new way to approach the hydrogen-storage problem.

The researchers found that the normally unreactive, noble gas xenon combines with molecular hydrogen (H₂) under pressure to form a previously unknown solid with unusual bonding chemistry. The experiments are the first time these elements have been combined to form a stable compound. The discovery debuts a new family of materials, which could boost new hydrogen technologies.

The paper is published in the November 22, 2009, advanced online publication of Nature Chemistry.

Xenon has some intriguing properties, including its use as an anesthesia, its ability to preserve biological tissues, and its employment in lighting. Xenon is a noble gas, which means that it does not typically react with other elements.

As lead author Maddury Somayazulu, research scientist at Carnegie’s Geophysical Laboratory, explained: “Elements change their configuration when placed under pressure, sort of like passengers readjusting themselves as the elevator becomes full. We subjected a series of gas mixtures of xenon in combination with hydrogen to high pressures in a diamond anvil cell. At about 41,000 times the pressure at sea level (1 atmosphere), the atoms became arranged in a lattice structure dominated by hydrogen, but interspersed with layers of loosely bonded xenon pairs. When we increased pressure, like tuning a radio, the distances between the xenon pairs changed-the distances contracted to those observed in dense metallic xenon.”

The researchers imaged the compound at varying pressures using X-ray diffraction, infrared and Raman spectroscopy. When they looked at the xenon part of the structure, they realized that the interaction of xenon with the surrounding hydrogen was responsible for the unusual stability and the continuous change in xenon-xenon distances as pressure was adjusted from 41,000 to 255,000 atmospheres.

Why was the compound so stable? “We were taken off guard by both the structure and stability of this material,” said Przemek Dera, the lead crystallographer who looked at the changes in electron density at different pressures using single-crystal diffraction. As electron density from the xenon atoms spreads towards the surrounding hydrogen molecules, it seems to stabilize the compound and the xenon pairs.

“Xenon is too heavy and expensive to be practical for use in hydrogen-storage applications,” remarked Somayazulu. “But by understanding how it works in this situation, researchers can come up with lighter substitutes.”

“It’s very exciting to come up with new hydrogen-rich compounds, not just for our interest in simple molecular systems, but because such discoveries can be the foundation for important new technologies,” commented Russell Hemley, director of the Geophysical Laboratory and a co-author. “This hydrogen-rich solid represents a new pathway to forming novel hydrogen storage compounds and the new pressure-induced chemistry opens the possibility of synthesizing new energetic materials.”

This research was funded by the Department of Energy, Basic Energy Sciences hydrogen storage, and the National Science Foundation, Division of Materials Research.

Story Source:

Adapted from materials provided by Carnegie Institution, via EurekAlert!, a service of AAAS.

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Journal Reference:

 

1. Maddury Somayazulu, Przemyslaw Dera, Alexander F. Goncharov, Stephen A. Gramsch, Peter Liermann, Wenge Yang, Zhenxian Liu, Ho-kwang Mao & Russell J. Hemley. Pressure-induced bonding and compound formation in xenon-hydrogen solids. Nature Chemistry, 2009; DOI: 10.1038/nchem.445

http://www.sciencedaily.com/releases/2009/11/091122161751.htm