Edited by T. Maurice Rice, Swiss Federal Institute of Technology, Zurich, Switzerland (received for review April 6, 2005)
We report free-standing atomic crystals that are strictly 2D and can be viewed as individual atomic planes pulled out of bulk crystals or as unrolled single-wall nanotubes. By using micromechanical cleavage, we have prepared and studied a variety of 2D crystals including single layers of boron nitride, graphite, several dichalcogenides, and complex oxides. These atomically thin sheets (essentially gigantic 2D molecules unprotected from the immediate environment) are stable under ambient conditions, exhibit high crystal quality, and are continuous on a macroscopic scale.
↵ ‡ To whom correspondence may be addressed. E-mail: geim{at}man.ac.uk.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations: AFM, atomic force microscopy; HRTEM, high-resolution transmission electron microscopy.
↵ § In the case of HRTEM studies [we used an FEI (Eindhoven, The Netherlands) Tecnai F30], the cleaved material was deposited directly on holey carbon films, which made the described route of preliminary identification of 2D crystallites in an optical microscope impossible. To find them on top of holey carbon among thicker flakes, a different procedure was developed. First, we used scanning electron microscopy imaging at low acceleration voltages (FEI Sirion at 500 V). Then, the flakes that were found most transparent in scanning electron microscopy were studied by AFM (i.e., directly on top of holey carbon) to define their thickness and select single-layer crystals.
