is grown around individual nanoparticles. “Such control is crucial for a wide range of applications,” he said, “including using nanoparticles for cancer treatment, as tiny light emitters for use in more efficient lighting and displays, or as lightweight solid fuels for rocket propulsion.”
Uwe Kortshagen Creating bright ideas
Silicon is one of the natural world’s miracle substances. As the second most abundant element in the Earth’s crust, it is non-toxic. Even better, it has long been known for its electrical properties, which is why it is used in a host of electronic devices, from iPods to computers. Broken down into nanoparticles, silicon will emit electromagnetic waves in the visible spectrum when it is electrically charged. Uwe Kortshagen, the new head of the Department of Mechanical Engineering, is one of the lead researchers of a team that includes faculty members from chemical engineering, materials science, and physics. Using silicon nanoparticles, the team is developing low-cost, high-efficiency solar photo-
voltaic cells—solar cells that can transform sunlight into electricity. If successful, Kortshagen and his colleagues will have invented a critical key to producing a part of the estimated 15 terawatts (15 million megawatts) of carbon-free energy the world will need if it is to achieve a balance between economic growth and climate stabilization. Subjecting silane molecules (consisting of one silicon and four hydrogen atoms) to a plasma jet, Kortshagen and his colleagues are able to break up the silane molecules and allow the silicon atoms to form nanoparticles small enough to incorporate into inks. These silicon nanoparticle inks can be sprayed or printed onto the surfaces to be processed into solar cells at low temperatures—the smaller the nanoparticles, the lower their melting point. In addition, the process enables the researchers to electrically dope the inkjet stream— implant impurities that improve electrical conductivities of the films. The printing at low temperatures and atmospheric pressure may potentially vastly reduce production costs of such solar cells. “The lower temperature and atmospheric pressure both contribute to lower costs,” Kortshagen said.
Uwe Kortshagen, a professor of mechanical engineering and physics, works with silicon, the second most abundant element on Earth, and a substance well-known for its electrical properties. Kortshagen has developed an efficient way to make silicon nanocrystals which involves putting a gas that contains silicon and hydrogen (silane) into a reactor.
fall/winter 2008-09 INVENTING TOMORROW 11