The origin of opto-functional enhancement in ZnO/CuO nanoforest structure fabricated by submerged photosynthesis

Semiconductor hetero-nanostructures are of great interest for practical industry use. In this report, we demonstrated ZnO/CuO nanoforest (NFRs) fabricated by galvanic submerged photo-synthesis (G-SPSC) method, which utilizes light illumination in pure water without additives. For the first time, we elucidated the origin of its enhanced opto-functional properties. At the hetero-epitaxial interface, ZnO(001)/CuO(001) planes linkage were established, even though with 13.62 - 28.15% local lattice discrepancies along the c axis. Formed under Zn rich condition and photo-induced {110} ZnO surface, the NFRs exhibited photoluminescence emissions at 450 nm and 650 nm, due to zinc interstitial (I-Zn) and oxygen vacancies (V-O). Ternary oxide of ZnCuO2 was discovered. The interface exhibited significant emission at 650 - 700 nm and absorbance at 450 - 500 nm. On the basis of STEM-VEELS spectra and ab initio calculations, electrons occupancy at Cu 3p was responsible for 2.0 eV peak of the interface absorption coefficient. In particular, an interface dipole under interface-induced gap states (IFIGS) was clarified, caused by quasi defects zinc antisite (Zn-O). This led to an incommensurate charge density (ICCD) for a coherent ZnO(001)/CuO(001) interface. This is the origin for the opto-functional enhancement of the ZnO/CuO NFRs, where a maximum 12% IPCE at 550 nm, a 20% increase from similar NFRs morphology was demonstrated. Our results indicated a promising method and strategy for novel hetero-epitaxial nanostructures fabrication in the field of optoelectrical devices. (C) 2021 The Author(s). Published by Elsevier Ltd.