Surface Science 408 (1998) 86–94 Formation of superperiodic patterns on highly oriented pyrolytic graphite by manipulation of nanosized graphite sheets with the STM tip T.M. Bernhardt, B. Kaiser *, K. Rademann Walther-Nernst-Institut fu¨r Physikalische und Theoretische Chemie der Humboldt-Universita¨ t zu Berlin, Bunsenstraße 1, 10117 Berlin, Germany Received 13 November 1997; accepted for publication 11 February 1998 Abstract 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 a ect 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 A ˚ . 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. © 1998 Elsevier Science B.V. All rights reserved. Keywords: Graphite; Scanning tunneling microscopy; Surface structure 1. Introduction patterns [1–12] and their major findings are: (1) The superstructures appear as giant hexagonal lattices superimposed on the atomic lattice of The (0001) basal plane of graphite is one of the graphite, (2) the periodicities of the observed giant most often investigated substrates in scanning tun- lattices show a large variety of values ranging from neling microscopy, mainly because of its versatility 7.4 [3] to 440 A ˚ [7], (3) the vertical amplitudes of as a weakly interacting substrate for molecular the superstructures are considerably larger than imaging and deposition experiments. On this sur- the atomic corrugation of graphite (up to 15 A ˚ face regular superlattices with periodicities on the [4,8]), (4) the superlattices can extend over thou- order of tens or hundreds of A ˚ ngstrøms can be sands of A ˚ ngstrøms and they are usually termi- observed occasionally. Several authors have con- nated by sharp boundaries [10]. ducted closer investigations of these superperiodic It has been noted [3,4] that these hexagonal superperiodic structures strongly resemble rota- * Corresponding author. Fax: (+49 ) 30 20935559; e-mail: bernd@rad01.chemie.hu-berlin.de tional moire´ patterns. Moire´ patterns are generally 0039-6028/98/$19.00 © 1998 Elsevier Science B.V. All rights reserved. PII: S0039-6028(98)00152-6