Physicists have used almost every superlative they can think of to describe graphene. This gossamer, one-atom-thick sheet of carbon is flexible, transparent, stronger than steel, more conductive than copper and so thin that it is effectively two-dimensional (2D). No sooner was it isolated in 2004 than it became an obsession for researchers around the world.
But not for Andras Kis. As miraculous as graphene was, says Kis, “I felt there had to be more than carbon.” So in 2008, when he got the chance to start his own research group in nanoscale electronics at the Swiss Federal Institute of Technology in Lausanne (EPFL), Kis focused his efforts on a class of super-flat materials that had been languishing in graphene's shadow.
These materials had an ungainly name — transition-metal dichalcogenides (TMDCs) — but a 2D form that was quite simple. A single sheet of transition-metal atoms such as molybdenum or tungsten was sandwiched between equally thin layers of chalcogens: elements, such as sulfur and selenium, that lie below oxygen in the periodic table. TMDCs were almost as thin, transparent and flexible as graphene, says Kis, but “somehow they got a reputation as not that interesting. I thought they deserved a second chance.”
He was right. Work by his team and a handful of others soon showed that different combinations of the basic ingredients could produce TMDCs with a wide range of electronic and optical properties. Unlike graphene, for example, many TMDCs are semiconductors, meaning that they have the potential to be made into molecular-scale digital processors that are much more energy efficient than anything possible with silicon.To read more, click here.