An artefact in scanning tunneling microscopy images of highly oriented pyrolytic graphite

An artefact with a structure that appears as an ordered array of chains, several 1000 Å long and with distances of between 10 Å and 30 Å in STM images of HOPG is reported. The artefact, which emerges from a too low point density in the scanning grid during data aquisition in the scanning tunneling microscope, is explained using the atomically resolved image, the orientation of the substrate in the STM, the sequential character of data acquisition in scanning tunneling microscopy together with the limited number of data points for the reconstruction of STM images and related image-processing problems, and the specific noise spectrum of the tunneling current. The identification of the artefact is verified by a computer simulation of the STM images, which reproduces the experimental data in detail.