Model analysis of anomalies in highly oriented pyrolytic graphite images by scanning tunneling microscope in air

The atomic corrugations of highly oriented pyrolytic graphite (HOPG) were measured in the constant current mode using a scanning tunneling microscope (STM) in air. The apparent corrugations depend on the angular frequency of the vertical vibrational motion of the tip. The tip motion resulted in a forced vibration of the sample surface through the aid of the contact of the tip with the sample surface. In our previous work, we managed to analyze constant height mode images with a simple model of the tunneling current, and reported that the apparent current modulations corresponding to the atomic corrugation are strongly influenced by the elastic deformation of the sample surface [Jpn. J. Appl. Phys. 34 (1995) 578]. In the present paper, a model for the constant current mode is presented taking additionally into consideration the one-dimensional spring deformation model to explain the forced vibration. From this model, well-known anomalies of atomic corrugations in HOPG images can be explained.