Producing energy from the sun, wind or chemical reactions is only half of the answer to global energy problems, according to Drs. Jon-Paul Maria and Zlatko Sitar. To be useful, they say, the energy must be able to be stored until needed and then efficiently delivered to power vehicles, homes, and factories. “You can produce as much energy as you want,” Sitar says, “but much of it is wasted if you can’t store what you don’t need immediately for later use.”

So, the two NC State materials science professors are trying to build a better storage technology. They are part of a three-year study, funded by the Office of Naval Research, to design long-lasting, nanoscale capacitors. Although the Navy envisions the capacitors in military applications like ship propulsion and weapons systems, Maria and Sitar are also revved up by the commercial potential in fuel-cell vehicles. “It’s exciting to be involved in something that could have a major impact on people’s lives,” says Maria, who was recently recognized by the National Science Foundation as a rising star in engineering with a Faculty Early Career Development Award. “Energy research will be important for at least the next 20, 30, or 40 years.”

The electrolytic capacitor banks now used in gas-electric hybrid cars are so bulky, Maria says, it’s like hauling a few cases of soda wherever you go. Further, the capacitors can’t withstand the high temperatures that occur when electric power is discharged rapidly. For their nanoscale capacitors, Maria and Sitar are developing materials based on diamond, aluminum nitride, and rare earth oxide films. The goal is to find a material that can store charges well, is a good thermal conductor, and works well at high operating temperatures.

Using a sputtering process in a clean room environment, they layer thin films of the insulator materials alternately with layers of tantalum into stacks measuring about 100 nanometers—a tenth of the width of a human hair. “The thinner we can make the sandwich,” Maria says, “the higher the electric field, which means more power is generated.”

The challenge is to consistently make the layers uniform and smooth—as well as thin—and then to demonstrate their performance over hundreds of hours, says Sitar, who also is testing aluminum nitride as a substrate for semiconductors and other electronic devices. “Cutting-edge research like this,” he says, “will help us create an energy-conscious culture.”