Characterization of the surfaces of hydrogen-passivated silicon by STM

Hydrogen-passivated silicon (amorphous, microcrystalline or crystalline silicon) is characterized by a low density of surface states. Thus, standard tunnelling theory, which relies on tunnelling at the Fermi energy, may not be applicable to this class of materials and it may be difficult to optimize scanning tunnelling microscopy. We performed simultaneous measurements of topography (by constant-current imaging) and of the distribution of the local apparent barrier height, ΦA, as a function of the tunnelling voltage on hydrogen-passivated, misoriented Si(111) samples that were prepared by etching with NH4F solution. Tunnelling conditions were identified, which allow the characterization of inhomogeneities related to both local roughness and chemical composition.