Monolayers of graphite rotated by a defined angle:: hexagonal superstructures by STM

For understanding the STM imaging contrast on layered materials on the atomic scale, it is of great interest to perform STM studies on single monolayers of graphite put onto a graphite surface at a defined rotation angle. Here, we report first STM results on monolayers of graphite spread on a graphite surface and rotated by a known angle. The layers were obtained by folding back during cleavage, and the rotation angle relative to the substrate was determined directly by STM. Whereas the area of the rotated layers was homogeneously covered with hexagonal superstructures (lattice constant 3.5 nm), no such superstructures were found on the surrounding substrate area. The periodicity of the superstructures is consistent with their explanation as a Moire pattern induced by the two interacting rotated layers. The observed giant corrugations of the superstructures could be explained as an effect of elastic tip-sample interaction.