Graphene competitor molybdenum disulfide easier to make

February 20, 2015 // By Jean-Pierre Joosting
A potential replacement for silicon, graphene is a single-atom-thick lattice of carbon atoms that features high conductivity and is essentially 2D. However, it is not the only 2D material that could replace silicon, there is competition — molybdenum disulfide — which unlike graphene has an energy band gap, meaning its conductivity can be turned on and off. Such a trait is critical for semiconductor devices used in computing.

Another difference is that molybdenum disulphide emits light, meaning it could be used in applications like LEDs, self-reporting sensors and optoelectronics.

To this end, University of Pennsylvania researchers have advanced manufacturing molybdenum disulphide by growing flakes of the material around "seeds" of molybdenum oxide, — making it easier to control the size, thickness and location of the material.

The study was led by A. T. Charlie Johnson, professor in the Department of Physics & Astronomy in Penn's School of Arts & Sciences, and includes members of his lab, Gang Hee Han, Nicholas Kybert, Carl Naylor and Jinglei Ping. Also contributing to the study was Ritesh Agarwal, professor of materials science and engineering in Penn's School of Engineering and Applied Science; members of his lab, Bumsu Lee and Joohee Park; and Jisoo Kang, a master's student in Penn's nanotechnology program. They collaborated with researchers from South Korea's Sungkyunkwan University, Si Young Lee and Young Hee Lee.

"Everything we do with regular electronics we'd like to be able to do with two-dimensional materials," Johnson said. "Graphene has one set of properties that make it very attractive for electronics, but it lacks this critical property, being able to turn on and off. Molybdenum disulphide gives you that."

Graphene's ultra-high conductivity means that it can move electrons more quickly than any known material, but that is not the only quality that matters for electronics. For the transistors that form the basis for modern computing technology, being able to stop the flow of electrons is also critical.

"Molybdenum disulphide is not as conductive as graphene," Naylor said, "but it has a very high on/off ratio. We need 1's and 0's to do computation; graphene can only give us 1's and 0.5's."