Photoelectrochemical Fabrication of CuO-Cu2O Nanocomposite Semiconductors by High-Frequency Potential-Switching in Copper(II)-Tartrate Complex Aqueous Solution and the Energy Band Structures

P-type CuO-Cu2O nanocomposite semiconductors composed of Cu2O-embedded CuO aggregations and Cu2O aggregation consisting of space-filling CuO grains have been fabricated by photoelectrochemical high-frequency potential-switching of 100 to 1000 cycles in an aqueous solution containing copper(II) sulfate hydrate, tartaric acid, and sodium hydroxide, and the size of both the CuO and Cu2O grains decreased from 40-44 nm to approximately 10 nm remaining the characteristic monoclinic and cubic lattices with an increase in cycle numbers. The bandgap energy of CuO components was almost a constant value of 1.5 eV, and the Cu2O components showed a decrease in bandgap energy from 2.05 eV to 1.85 eV with an increase in cycle number due to the Cu2+ state incorporation, and the CuO-Cu2O nanocomposites possessed an ionization energy of approximately 5.2 eV and work function of approximately 4.6 eV respectively, and were close to those for single CuO and Cu2O layers.