Wednesday, July 25, 2012

Clothing the Body Electric: Cotton T-Shirt Fabric Can Store Electricity, Maybe Keep Your Cell Phone Charged

Over the years, the telephone has gone mobile, from the house to the car to the pocket. The University of South Carolina's Xiaodong Li envisions even further integration of the cell phone -- and just about every electronic gadget, for that matter -- into our lives.
He sees a future where electronics are part of our wardrobe.

"We wear fabric every day," said Li, a professor of mechanical engineering at USC. "One day our cotton T-shirts could have more functions; for example, a flexible energy storage device that could charge your cell phone or your iPad."

Li is helping make the vision a reality. He and post-doctoral associate Lihong Bao have just reported in the journal Advanced Materials how to turn the material in a cotton T-shirt into a source of electrical power.

Starting with a T-shirt from a local discount store, Li's team soaked it in a solution of fluoride, dried it and baked it at high temperature. They excluded oxygen in the oven to prevent the material from charring or simply combusting.

The surfaces of the resulting fibers in the fabric were shown by infrared spectroscopy to have been converted from cellulose to activated carbon. Yet the material retained flexibility; it could be folded without breaking.

"We will soon see roll-up cell phones and laptop computers on the market," Li said. "But a flexible energy storage device is needed to make this possible."

The once-cotton T-shirt proved to be a repository for electricity. By using small swatches of the fabric as an electrode, the researchers showed that the flexible material, which Li's team terms activated carbon textile, acts as a capacitor. Capacitors are components of nearly every electronic device on the market, and they have the ability to store electrical charge.

Moreover, Li reports that activated carbon textile acts like double-layer capacitors, which are also called a supercapacitors because they can have particularly high energy storage densities.

But Li and Bao took the material even further than that. They then coated the individual fibers in the activated carbon textile with "nanoflowers" of manganese oxide. Just a nanometer thick, this layer of manganese oxide greatly enhanced the electrode performance of the fabric. "This created a stable, high-performing supercapacitor," said Li.

This hybrid fabric, in which the activated carbon textile fibers are coated with nanostructured manganese oxide, improved the energy storage capability beyond the activated carbon textile alone. The hybrid supercapacitors were resilient: even after thousands of charge-discharge cycles, performance didn't diminish more than 5 percent.

"By stacking these supercapacitors up, we should be able to charge portable electronic devices such as cell phones," Li said.

Li is particularly pleased to have improved on the means by which activated carbon fibers are usually obtained. "Previous methods used oil or environmentally unfriendly chemicals as starting materials," he said. "Those processes are complicated and produce harmful side products. Our method is a very inexpensive, green process."


Highly Transparent Solar Cells for Windows That Generate Electricity

UCLA researchers have developed a new transparent solar cell that is an advance toward giving windows in homes and other buildings the ability to generate electricity while still allowing people to see outside. Their study appears in the journal ACS Nano.

The UCLA team describes a new kind of polymer solar cell (PSC) that produces energy by absorbing mainly infrared light, not visible light, making the cells nearly 70% transparent to the human eye. They made the device from a photoactive plastic that converts infrared light into an electrical current.

"These results open the potential for visibly transparent polymer solar cells as add-on components of portable electronics, smart windows and building-integrated photovoltaics and in other applications," said study leader Yang Yang, a UCLA professor of materials science and engineering, who also is director of the Nano Renewable Energy Center at California NanoSystems Institute (CNSI).

Yang added that there has been intense world-wide interest in so-called polymer solar cells. "Our new PSCs are made from plastic-like materials and are lightweight and flexible," he said. "More importantly, they can be produced in high volume at low cost."

Polymer solar cells have attracted great attention due to their advantages over competing solar cell technologies. Scientists have also been intensely investigating PSCs for their potential in making unique advances for broader applications. Several such applications would be enabled by high-performance visibly transparent photovoltaic (PV) devices, including building-integrated photovoltaics and integrated PV chargers for portable electronics.

Previously, many attempts have been made toward demonstrating visibly transparent or semitransparent PSCs. However, these demonstrations often result in low visible light transparency and/or low device efficiency because suitable polymeric PV materials and efficient transparent conductors were not well deployed in device design and fabrication.

A team of UCLA researchers from the California NanoSystems Institute, the UCLA Henry Samueli School of Engineering and Applied Science and UCLA's Department of Chemistry and Biochemistry have demonstrated high-performance, solution-processed, visibly transparent polymer solar cells through the incorporation of near-infrared light-sensitive polymer and using silver nanowire composite films as the top transparent electrode. The near-infrared photoactive polymer absorbs more near-infrared light but is less sensitive to visible light, balancing solar cell performance and transparency in the visible wavelength region.

Another breakthrough is the transparent conductor made of a mixture of silver nanowire and titanium dioxide nanoparticles, which was able to replace the opaque metal electrode used in the past. This composite electrode also allows the solar cells to be fabricated economically by solution processing. With this combination, 4% power-conversion efficiency for solution-processed and visibly transparent polymer solar cells has been achieved.

"We are excited by this new invention on transparent solar cells, which applied our recent advances in transparent conducting windows (also published in ACS Nano) to fabricate these devices," said Paul S.Weiss, CNSI director and Fred Kavli Chair in NanoSystems Sciences.

Study authors also include Weiss; materials science and engineering postdoctoral researcher Rui Zhu; Ph.D. candidates Chun-Chao Chen, Letian Dou, Choong-Heui Chung, Tze-Bin Song and Steve Hawks; Gang Li, who is former vice president of engineering for Solarmer Energy, Inc., a startup from UCLA; and CNSI postdoctoral researcher Yue Bing Zheng.


Tuesday, July 10, 2012

ZPlasma: Plasma Startup Creates High-Energy Light to Make Smaller Microchips

A University of Washington lab has been working for more than a decade on fusion energy, harnessing the energy-generating mechanism of the sun. But in one of the twists of scientific discovery, on the way the researchers found a potential solution to a looming problem in the electronics industry.
To bring their solution to market two UW engineers have launched a startup, Zplasma, that aims to produce the high-energy light needed to etch the next generation of microchips.

"In order to get smaller feature sizes on silicon, the industry has to go to shorter wavelength light," said Uri Shumlak, a UW professor of aeronautics and astronautics. "We're able to produce that light with enough power that it can be used to manufacture microchips."

The UW beam lasts up to 1,000 times longer than competing technologies and provides more control over the million-degree plasma that produces the light.

For more than four decades the technology industry has kept up with Moore's Law, a prediction that the number of transistors on a computer chip will double every two years. This trend has allowed ever-smaller, faster, lighter and less energy-intensive electronics. But it's hit a roadblock: the 193-nanometer ultraviolet light now being used cannot etch circuits any smaller.

The industry has determined that the future standard for making microchips will be 13.5-nanometer light, a wavelength less than 1/14 the current size that should carry the industry for years to come. Such extreme ultraviolet light can be created only from plasmas, which are high-temperature, electrically charged gases in which electrons are stripped from their nuclei.

The electronics industry is trying to produce this extreme ultraviolet light in various ways. One takes a droplet of tin and shoots it with a laser to make plasma that releases a brief spark of light. But so far this spark is too brief. Chip manufacturers use a $100 million machine to bounce light off a series of mirrors and eventually project the light onto a silicon wafer; each step absorbs some of the light's energy.

"Over the past decade, the primary issue with these extreme ultraviolet light sources is they just can't produce enough power," Shumlak said. "It's a stumbling block for the whole semiconductor industry."

Fusion scientists, it turns out, are plasma experts. The hydrogen plasma in the sun is so hot that hydrogen nuclei fuse together and release energy. Scientists around the world, including at the UW, are working to replicate this on Earth. A fusion reactor would use hydrogen as its fuel and emit helium as a waste product, a technically challenging but clean source of energy.

The UW group's specialty is a lower-cost version of a fusion reactor that uses currents flowing through the material, rather than giant magnets, to contain the million-degree plasma. Their method also produces plasma that is stable and long-lived.

"It's a completely different way to make the plasma that gives you much more control," said Brian Nelson, a UW research associate professor of electrical engineering.

The first time they triggered the experiment in 1999, an engineer looking through the glass said, "That was really bright!" That was when the proverbial light bulb went off, Nelson said, and the team began to explore applications for bright high-energy light.

They may have found that application in the microchip industry. Light produced through techniques now being considered by the chip industry generate a spark that lasts just 20 to 50 nanoseconds. Zplasma's light beam lasts 20 to 50 millionths of a second, about 1,000 times longer.

"That translates directly into more light output, more power depositing on the wafer, such that you can move it through in some reasonable amount of time," Shumlak said.

An initial grant from the UW's Center for Commercialization allowed the team to verify that it could produce 13.5-nanometer light. A gift last fall from the Washington Research Foundation helped the team shrink the equipment from the size of a broomstick to a new version the size of a pin, which can produce a sharp beam.

The company was established last year with help from the UW's Center for Commercialization and Henry Berg, a technology entrepreneur who met the researchers through the center's Entrepreneurs in Residence program. Berg is now CEO of Zplasma.

The company is seeking "smart money" from corporate investors who can integrate the new technology with existing industrial processes.

"I hope this gets implemented into the industry and has an impact," Shumlak said.

The group will continue its fusion research project funded by the U.S. Department of Energy. Raymond Golingo, a UW research scientist in aeronautics and astronautics, is co-author of the patent for the technology issued in 2008.