Microstructural analysis and transport properties of MoO and MoC nanostructures prepared by focused electron beam-induced deposition

By electron-beam-induced deposition, we have succeeded in the direct fabrication of nanowires of molybdenum oxide (MoO_x) and molybdenum carbide (MoC) on a SiO₂ substrate set in a scanning electron microscope. In order to prepare MoO_x specimens of high purity, a precursor gas of molybdenum hexacarbonyl [Mo(CO)₆] is used, mixed with O_xygen gas. On the other hand, MoC is grown by mixing H2O gas with the precursor gas. The electrical transport properties of the nanowires are investigated by the DC four-terminal method. A highly resistive MoO_x nanowire prepared from an as-deposited specimen by annealing in air shows nonlinear current-voltage characteristics and a high photoconductivity. The resistivity ρ of an as-deposited amorphousMoC (a-MoC) nanowire takes its maximum at a temperature T ≈ 10 K and decreases to ≈ 0 with decreasing temperature. This behavior of ρ(T) indicates the possible occurrence of superconductivity in a-MoC nanowires. The characteristic of ρ(T) below the superconducting transition temperature T_c ≈ 4 K can be well explained by the quantum phase-slip model with a coherence length ξ(0) ≈ 8 nmat T=0.