One-molecule thick material promises electronics revolution
By David Szondy
August 28, 2012
Imagine a world where rooms are lit by their walls, clothes are smartphones and windows turn into video screens. That may seem like a bit of science fiction, but not for long. Researchers at MIT are using a two-dimensional version of molybdenum disulfide (MoS2) to build electrical circuits that may soon revolutionize consumer electronics.
We've heard a great deal about graphene in recent years. A two-dimensional version of graphite, graphene has proven to be something of a wonder substance. It’s tremendously hard, highly heat conductive, is possessed of unique optical qualities ... and that’s just scratching the surface as engineers discover new uses for it in everything from solar panels to space elevators.
By comparison molybdenum disulfide is a humble substance used largely for lubricant or as a catalyst in petroleum refining. That, however, is changing. Last year, Swiss scientists described a version of molybdenum disulfide that had the same 2D-style structure as graphene and now researchers at MIT are using it to build electrical circuits.
Until recently, MIT had been trying with little success to make electrical circuits out of graphene, but the wonder material turned out to be harder to use than thought. It’s a natural conductor, probably the best ever discovered, which makes it great for some applications, but not for electronics. To make a transistor out of graphene, for example, requires some very clever and problematic doping with various elements. Even, then, the results are often disappointing.
Molybdenum disulfide, on the other hand, is a natural semiconductor, which makes turning it into transistors very easy. This was especially the case when Yi-Hsien Lee, a postdoctoral student, learned how to use a chemical vapor deposition process to make large sheets of molybdenum disulfide. These sheets and mechanically-produced flakes of the material formed the basis for the circuits described recently in the journal Nano Letters.
The list of circuits that the MIT team have produced so far is impressive. Molybdenum disulfide has been used to create NAND gates, an inverter circuit, a memory device and a ring oscillator composed of twelve transistors.
Tomás Palacios, the Emmanuel E. Landsman Associate Professor of MIT's Department of Electrical Engineering and Computer Science (EECS), and graduate student Han Wang, say that the ready availability of molybdenum disulfide and the MIT method of manufacturing sheets opens up whole new applications for two-dimensional materials. Television screens, for example, could be built with transistors only a few molecules thick and make today’s flat screens look like stone slabs in comparison - not to mention the savings in energy. They also see light-emitting walls that would make the incandescent vs fluorescent light bulb debate moot, mobile phones and other devices that could be woven into the fabric of clothing and optical displays so thin that they’d be transparent and could be sprayed on any surface.
It may not be very long before windows, mirrors, table tops or even drinking glasses will become an interactive digital display and where your shirts keep you permanently connected to the Web. When or if that day comes, you’ll have a bottomless pit of data to tap anytime and anywhere.