Sustainable Energy

The Year in Materials

New materials harnessed hamster power, and researchers made carbon nanotubes practical.

For years now, people have been talking up carbon nanotubes and their potential to be used for far-out applications including strong space-elevator cables, robust electrical transmission lines, and high-performance nanotube computers. These things may still be a decade off, but several advances this year make them sound less like fantasies.

Researchers at Rice University refined methods for spinning acid solutions of carbon nanotubes into fibers hundreds of meters long (“Making Carbon Nanotubes into Long Fibers”). Their process, which could be used industrially (it’s similar to how Kevlar is made), is the culmination of eight years of work begun by the late Richard Smalley, who shared the Nobel Prize in chemistry in 1996 for the discovery of carbon nanomaterials (“Wires of Wonder”). In order to make electrical transmission lines, researchers still need to perfect a process for growing pure batches of metallic nanotubes. Today they come out mixed with semiconducting tubes, and the two must be separated. Still, the Rice demonstration of making nanotubes into large structures is a major accomplishment.

On the nanotube electronics front, the year started out strong. The company Unidym, which makes transparent electrodes from carbon nanotubes, demonstrated its products, and companies including Samsung tested them in displays (“Clear Carbon-Nanotube Films”). Unidym’s nanotube films could be incorporated into flexible displays and replace the expensive, brittle materials currently used to make display electrodes.

The year also brought major accomplishments in making more sophisticated nanotube devices for displays, including the integrated circuits that drive them (“Practical Nanotube Electronics”). One of the major advantages of nanotube display circuits is that they could be printed like newspaper, which should bring down costs. And this month at the International Electron Devices Meeting, researchers at Stanford presented the first three-dimensional nanotube circuits (“Complex Integrated Circuits Made of Carbon Nanotubes”). The processes their nanotube circuits can carry out, like adding and storing numbers, are about as sophisticated as what silicon could do in the mid-1960s.

Meanwhile, researchers at Cornell made an interesting basic science demonstration: single nanotubes can be wired up to make extremely efficient solar cells (“Superefficient Solar from Nanotubes”). While conventional solar materials can only produce one electron per striking photon, carbon nanotubes can produce two if the photon has enough energy.

Nanomaterials, Big Energy

Activity in academic labs and companies this year showed that energy-storage materials structured on the nanoscale have a greater capacity than their conventional counterparts. This concept launched two startups that received government funding. FastCAP Systems of Cambridge, MA, is developing ultracapacitors based on carbon nanotubes, which can store a large amount of electrical charge because of their huge surface area (“Ultracapacitor Startup Gets a Big Boost”). The company received an ARPA-E grant for $5.35 million over two-and-a-half years. And Amprius of Menlo Park, CA, received $3 million from the National Institute of Standards and Technology to develop high-performance lithium-ion battery anodes made from silicon nanowires (“More Energy in Batteries”). Both companies are aiming for the electric-car market, hoping to make energy-storage devices that will allow cars to run longer between charges.

Nanomaterials continued to prove their promise in solar cells. Researchers determined that solar cells patterned with nanoscale pillars can convert more energy than smooth ones. The upshot: the performance of cheap materials can be boosted without adding expense, and it’s possible to make them on aluminum foil (“Nanopillar Solar Cells”). This work was done at the University of California, Berkeley, by one of Technology Review’s 35 young innovators of 2009, Ali Javey. Another Berkeley researcher on our young innovators list, Cyrus Wadia, analyzed the abundance and properties of unconventional solar materials and then made strides in developing them. One of the materials is pyrite, also known as fool’s gold, which Wadia is growing as nanocrystals (“Mining Fool’s Gold for Solar”). The advantage of nanocrystals for solar cells is that they can be made into inks and cheaply printed. Meanwhile, one of Wadia’s mentors, Paul Alivisatos, interim director of the Lawrence Berkeley National Laboratory, founded a company to develop high-efficiency, low-cost solar cells based on nanomaterials. Solexant of San Jose, CA, hopes to sell printed nanocrystal solar cells with 10 percent efficiencies for $1 per watt (“Thin-Film Solar with High Efficiency”).

Harvesting Energy from Strange Sources

Cheap, yet efficient, solar cells could help wean us from dirty electricity sources. But that’s not what Zhong Lin Wang at Georgia Tech has in mind. Technology Review recognized his work on nanopiezotronics, nanowires and other structures that convert mechanical stress into electrical currents, in our special section on the 10 emerging technologies of the year. Zinc-oxide nanowires that produce an electrical current when stressed could provide a power source for implantable diagnostics and stress sensors embedded in buildings and bridges. These materials could also be woven into an iPod-charging jacket that harvests the small amount of energy produced by the rustling of fabric as you walk. A series of papers produced by Wang throughout the year further established the concept, showing that nanopiezotronics could harness the energy produced by a running hamster (“Harnessing Hamster Power with a Nanogenerator”), that they could act as stress sensors (“Nanosensing Transistors Controlled by Stress”), and that they could be combined with solar cells in a hybrid nanogenerator (“A Hybrid Nano-Energy Harvester”).

Optical Materials Advance

Part of the 2009 Nobel Prize in physics went to a researcher whose work formed the basis of modern telecommunications. Charles Kuo figured out why optical fibers that had been made in the lab in the 1960s weren’t working: the material contained impurities that attenuated the signal. Based on this finding, Kuo determined that pure glass could realize the potential of optical data transmission to speed the flow of information (“Nobel for Revolutionary Optical Technologies”). Modern optical fibers are even better than what Kao predicted, losing just 5 percent of the light over a distance of a kilometer; today there are over one billion kilometers of optical fiber around the world, with more being added each day.

And this year Intel announced its intention to replace copper wires used to carry data between your MP3 player, laptop, and other devices with optical fiber (“Intel’s Plan to Replace Copper Wires”). In 2010, the company will ship Light Peak data cables that will zip 10 gigabits of data per second between gadgets using light, which is much faster than electrons.

A fundamental advance in optics this year was the fabrication of an extremely small laser that may eventually be developed into a compact light source for optical computers (“The Smallest Laser Ever Made”). Optical devices can operate at hundreds of terahertz, compared to the 10 gigahertz speeds of the best consumer electronics. But optical devices are difficult to miniaturize. The “nano laser,” made by researchers at Cornell, Purdue, and Norfolk State universities, helps overcome this problem.

Ultradense Data Storage and Biodegradable Electronics

The year also brought innovative materials for storing more data for longer periods of time. Layers of gold nanorods that polarize light and reflect different colors can store data in five dimensions (“Five-Dimensional Data Storage”); optical antennas that focus light to tiny, intense spots to heat bits could extend the lifetime of magnetic data storage (“Heating Up Magnetic Memory”); and researchers at HP looked to magnetic nanowires to make racetrack memory (“TR10: Racetrack Memory”).

Meanwhile, researchers in Japan demonstrated the first plastic, flexible flash memory device, which might be incorporated into unconventional electronics such as disposable sensors (“Cheap, Plastic Memory for Flexible Devices”). Researchers in Illinois worked wonders with silicon to make electronics that took strange forms, including flexible LED arrays (“Cheaper LEDs”) and biocompatible electronics (“Implantable Silicon-Silk Electronics”) that could drive medical implants. These projects were led by John Rogers, who invented a stretchable silicon technology we recognized in 2006 (“Stretchable Silicon”). And at Stanford, researchers made the first fully biodegradable transistors, which might control drug delivery in future medical implants (“Biodegradable Transistors”).

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