“…HOPG is an ordered form of pyrolytic graphite with a high degree of crystallographic orientation of the c -axis. Polycrystalline HOPG consists of micrometer-sized grains and has been widely used as a substrate in STM studies [1–3] due to its high conductivity, atomic flatness and chemical inertness [4]. The surface also contains various defects such as cleavage steps, graphite strands, wrinkles/ridges, fiber-like entities, folded-over flakes, broken graphite pieces and other carbon aggregates [5–10].…”