Alignment Growth Mechanisms of Rod-like ZnO on Zinc Substrates

Discontinuous films of ZnO particles were prepared on zinc substrates by air pre-oxidation process. The arrays of rod-like ZnO nano-/micro- crystals on zinc substrates were synthesized through hydrothermal processing with N2H4·H2O solution. It is found that the rod-like ZnO nano-/micro-crystals align well on the substrate surface with a unique crystallographic orientation. The experimental results suggest a free alignment growth mechanism for rod-like ZnO nano-/micro-crystals on zinc substrates. The crystallization habit of ZnO nano-/micro-crystals is to grow along with the c axis fast under hydrothermal conditions, thus the well alignment of rod-like ZnO nano-/micro-crystals only depends on the state of ZnO nuclei on the substrate surface. The states of ZnO nuclei on the substrate surface with a unique crystallographic orientation well agree with others, which regulates the alignment of rod-like ZnO nano-/micro-crystals. In temperature-dependent photoluminescence spectra, the "negative thermal quenching" phenomenon of near band-gap edge excitons is observed in the temperature ranging from 30 K to 60 K, which identify two non-radiative processes and one negative thermal quenching process.