Electrical transport properties of single ZnO nanorods

Abstract

Single ZnO nanorods with diameters of $\sim 130\mathrm{nm}$ were grown on Au-coated ${\mathrm{Al}}_2{\mathrm{O}}_3$ substrates by catalyst-driven molecular beam epitaxy. Individual nanorods were removed from the substrate and placed between Ohmic contact pads and the current–voltage characteristics measured as a function of temperature and gas ambient. In the temperature range from $25\text{to}150°\mathrm{C}$ , the resistivity of nanorods treated in ${\mathrm{H}}_2$ at $400°\mathrm{C}$ prior to measurement showed an activation energy of $0.089\pm 0.02\mathrm{eV}$ and was insensitive to the ambient used (${\mathrm{C}}_2{\mathrm{H}}_4,{\mathrm{N}}_2\mathrm{O},{\mathrm{O}}_2$ or 10% ${\mathrm{H}}_2$ in ${\mathrm{N}}_2$ ). By sharp contrast, the conductivity of nanorods not treated in ${\mathrm{H}}_2$ was sensitive to trace concentrations of gases in the measurement ambient even at room temperature, demonstrating their potential as gas sensors.