Thinnest Crystals

MATERIALS

The first stable crystalline materials confirmed to be but a single atom thick have been prepared and characterized. The materials--whose compositions range from boron nitride, graphite, and dichalcogenides to complex oxides--exhibit properties that could be useful for a range of advanced materials applications.

Andre K. Geim of the Centre for Mesoscience & Nanotech nology at the University of Manchester, in England, and coworkers created the materials by a rubbing technique and successfully visualized them by an optical phase-contrast method. Some materials exhibited conductivity and others showed resistivity, among other properties the researchers found (Proc. Natl. Acad. Sci. USA 2005, 102, 10451).

The work "demonstrates that single layers can be obtained by mechanically working layered materials--something that many others, including my group, have been searching for," says chemistry professor Richard B. Kaner of the University of California, Los Angeles.

In earlier work, chemical peeling of layered graphite led only to multilayer sheets, and mechanical cleavage of graphite gave materials with a few layers at best.

Geim and coworkers have now extended mechanical cleavage to its ultimate limit, creating single-atom-thick materials. To obtain these "2-D" materials, they released flakes from layered materials by rubbing them against other surfaces, a method they compare with using chalk on a blackboard. They visualized the crystals by optical microscopy on oxidized silicon wafers and characterized them by atomic force microscopy and scanning and transmission electron microscopy.

"A synthetic breakthrough would be needed to scale up the process for industrial applications," Kaner says. If that is achieved, many applications could ensue, he adds. "For now, the technique should lead to interesting studies in the physics and chemistry of truly 2-D systems."