Shape controlled growth of ZnO nanorods and fabrication of ZnO/CuO heterojunctions by chemical bath deposition using zinc nitrate hexahydrate and copper (III) nitrate trihydrate

• Zinc nitrate hexahydrate was used for chemical bath deposition (CBD) of ZnO.
• Vertically aligned ZnO nanorods (NRs) were grown on Au/glass substrates by CBD.
• Heterojunctions of ZnO NRs/CuO were successfully fabricated by CBD.
• The shapes of the NRs depended on the configuration of the substrate in the solution.

Vertically aligned zinc oxide (ZnO) nanorods (NRs) were successfully grown on Au/alkali-free glass substrates by chemical bath deposition (CBD) using the mixed aqueous solution of zinc nitrate hexahydrate [Zn(NO3)2 · 6H2O] and hexamethylenetetramine (HMT) (denoted by “ZnNit solution”). Even if both the growth time and growth temperature were constant, both the diameter and length of the NRs increased with increasing the concentration of the ZnNit solution. The ZnO NRs grown from the ZnNit solutions with the high concentrations exhibited a strong near-band-edge emission on their PL spectra, indicating their high crystalline quality. Using two different types of substrate holders realizing the different substrate configurations in the ZnNit solution, ZnO NRs standing perpendicular to the CuO surface or inclined with respect to the normal of the CuO surface were obtained on the CuO films prepared by CBD using the aqueous solution of copper (II) nitrate trihydrate [Cu(NO3)2 · 3H2O]. The CBD experiments of ZnO NRs/CuO heterostructures were performed by using the ZnNit solutions with different concentrations in the range of 0.01–0.1 M. Remarkable differences between the NRs grown using the two different substrate holders can be observed on the densities and the average diameters of the NRs, but not on the average lengths of the NRs. This finding suggests that the configuration of the substrate in the ZnNit solution during the deposition process is one of the important factors for controlling the shapes of the NRs as well as the concentration of the solution.