Characterization of the surfaces of hydrogen-passivated silicon by STM

Hydrogen-passivated silicon (amorphous, microcrystalline or crystalline sil icon) is characterized by a low density of surface states. Thus, standard t unnelling theory, which relies on tunnelling at the Fermi energy, may not b e 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 loc al apparent barrier height, phi(A), 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 al low the characterization of inhomogeneities related to both local roughness and chemical composition. (C) 2000 Elsevier Science S.A. All rights reserv ed.