Formation of superperiodic patterns on highly oriented pyrolytic graphite by manipulation of nanosized graphite sheets with the STM tip

Scanning tunneling microscopy investigations of superperiodic lattices on graphite (0001) are reported. The origin of these superperiodic features is still uncertain. In this investigation particular attention is paid to unusual superstructures with a spatially varying periodicity, because this sort of superstructures refers to the presence of in plane bending forces which affect the topmost graphite layer. We use the tip of the scanning tunneling microscope to manipulate single weakly bound nanometer-sized sheets on the graphite surface in order to directly induce intralayer strain and interlayer mismatch. By this means it has been possible to fold a graphite sheet onto a step or a boundary region and thus create superstructures with hexagonal symmetry. The observed lattice constants in the stressed area varied continuously between 50 and 80 Angstrom. The giant pattern vanished as the topmost layer was forced to break up. These observations also point to the important role of intralayer strain in the formation of the observed superstructures on graphite surfaces and are discussed in terms of the rotational moire pattern hypothesis and a dislocation network model. (C) 1998 Elsevier Science B.V. All rights reserved.