On the STM imaging contrast of graphite: towards a "true'' atomic resolution

Different phenomena observed in the high-resolution images of graphite by s canning tunneling microscopy (STM) or atomic force microscopy (AFM) such as the asymmetry in the charge density of neighboring carbon atoms in a hexag on, the high corrugation amplitudes and the apparent absence of point defec ts has led to a controversial discussion since the first published STM imag es of graphite. Different theoretical concepts and hypotheses have been dev eloped to explain these phenomena. Despite these efforts a generally accept ed interpretation is still lacking. In this paper we discuss a possible ima ging mechanism based on mechanical considerations. Forces acting between ti p and sample are taken into account to explain the image contrast. We prese nt for the first time a direct atomic resolution of the graphite hexagonal structure by transmission electron microscopy (HRTEM), revealing the expect ed hexagonal array of atoms and the existence of several types of defects. We discuss the possibility that the STM image of graphite is a result of co nvolution of the electronic properties and the atomic hardness of graphite.