Electrical conductivities of nanosheets studied by conductive atomic force microscopy

摘要

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.