Electrical conductivities of nanosheets studied by conductive atomic force microscopy

The electrical conductivities of single nanosheets of titanium oxide (TiO(2)), manganese oxide (MnO(2)), double-layered titanium perovskite oxide (GdEuTiO), niobium oxide (NbO), and graphite oxide (GO) adsorbed on HOPG were studied by conductive atomic force microscopy (C-AFM) with a Pt-Ir tip. The conduction mechanism for different types of nanosheets could be clarified by using electrodes (HOPG and Pt-Ir tip) having different work functions. While the TiO(2), GdEuTiO, and NbO nanosheets showed asymmetric (rectifying) current/voltage (I/V)-profiles, those for the MnO(2) and GO nanosheets; were symmetric (nonrectifying). The differences in the I/V-profile indicated that the dominant electron transfer mechanism in case of TiO(2), GdEuTiO, and NbO nanosheets was tunneling under reverse bias like an n-type semiconductor and that for MnO(2) and GO nanosheets, having a defected structure, was hopping. Among all these nanosheets, MnO(2) exhibited the highest conductivity. (C) 2009 Elsevier B.V. All rights reserved.