Possibility of selective and morphology-controlled growth of CuO and Cu2O films

Possibility of selective growth of polycrystalline CuO and Cu2O films on the Au/SiO2/Si(100) substrates by chemical bath deposition (CBD) based technique using Cu(NO3)2·3H2O (abbreviated as “CuNit”) as a Cu precursor was investigated. The CuO films synthesized from the aqueous solutions of CuNit with pH adjusted to be in the range from 6.0 to 11 were composed of the corncob-like nanorods whose average diameter increased with increasing pH. For the CuO films synthesized from the CuNit aqueous solutions with pH > 10.5, the corncob-like nanorods were self-organized in the caddis clew-like shapes. The Cu2O films were synthesized mainly from the mixed aqueous solutions of CuNit and C6H12N4 (denoted by “HMT”) with the assistance of a piece of iron (Fe) plate immersed in the solution but without applying any electric field (denoted by “Fe-assisted CBD” as distinguished from the usual CBD). Oxidation-reduction potential measurements revealed that the mixed aqueous solutions of CuNit and HMT in which the Fe plate was immersed had high concentration of electrons, contributing to the reduction of Cu2 + ions to Cu+ ions. At the beginning of the deposition, the Cu2O film composed of the triangular grains was oriented towards the [111] direction. The increase in growth time resulted in the enhancement of the contribution of the pyramidal grains oriented towards the [100] direction. By increasing the concentration of the mixed aqueous solution of CuNit and HMT, the preferential growth direction was changed continuously from the [111] direction to the [100] direction, accompanied with the change in grain shape from the triangle to the four-sided pyramid. It was also confirmed that the Cu2O films can be synthesized from the CuNit solutions by the Fe-assisted CBD when the pH value of the solution is adjusted to be in the range pH 4.7 to 5.1. However, the use of the CuNit solution with pH higher than 6.2 led to the coexistence of Cu2O and Cu(OH)2 or the appearance of the single phase CuO in the film.