Polymer mold makes perfect silicon nanostructures
For this to work, the mold needs to be stable while the hot liquid material hardens into shape. In a breakthrough for nanoscience, Cornell polymer engineers have made such a mold for nanostructures that can shape liquid silicon out of an organic polymer material. This paves the way for perfect, 3-D, single crystal nanostructures.
The advance is from the lab of Uli Wiesner, the Spencer T. Olin Professor of Engineering in the Department of Materials Science and Engineering, whose lab previously has led the creation of novel materials made of organic polymers. With the right chemistry, organic polymers self-assemble, and the researchers used this special ability of polymers to make a mold dotted with precisely shaped and sized nano-pores.
The research is published in Science July 3.
Normally, melting amorphous silicon, which has a melting temperature of about 2,350 degrees, would destroy the delicate polymer mold, which degrades at about 600 degrees. But the scientists, in collaboration with Michael Thompson, associate professor of materials science and engineering, got around this issue by using extremely short melt periods induced by a laser.
The researchers found the polymer mold holds up if the silicon is heated by laser pulses just nanoseconds long. At such short time scales, silicon can be heated to a liquid, but the melt duration is so short the polymer doesn't have time to oxidize and decompose. They essentially tricked the polymer mold into retaining its shape at temperatures above its decomposition point.
When the mold was etched away, the researchers showed that the silicon had been perfectly shaped by the mold. This could lead to making perfect, single-crystal silicon nanostructures. They haven't done it yet, but their Science paper shows it's possible. In work published in 2010, Wiesner and colleagues showed the pathway for this process, using an oxide mold.