Nitrogen plasma-induced conductivity enhancement of a single CuO nanowire

Isolated single CuO nanowires (NWs) with different lengths and diameters were synthesized from thermally oxidized Cu. These NWs were exposed to radio frequency (100 W) nitrogen plasma for varying durations to investigate the effect of reactive nitrogen species on their electronic conductivity. The results obtained were correlated with the physical and chemical property changes at the surface of the NWs. It has been observed that, upon plasma exposure for up to 7 min, the conductance per unit volume of small-diameter NWs (d = 102, 118, 120 nm), measured in a two-terminal configuration, increases by up to five times (e.g., from 62.17 to 276 nS μm−3 for d = 102 nm) compared to that of the pristine NWs. Plasma exposure for longer durations lowered the conductance due to the domination of the effect of surface defects over that of doping-induced chemical modification, as validated by the data from Raman spectroscopy, EDX, and HRTEM measurements. Four-terminal conductivity measurements on thicker NWs, with contacts fabricated using photolithography and e-beam lithography, also showed an increase in conductivity (e.g., from 7.82 to 73.92 S m−1 for d = 150 nm). In addition, the contact resistance of the CuO NW|Cr|Ag junction, calculated from the low voltage linear range of the I–V characteristics by the transfer length method, was 74.52 MΩ.