Abstract
One-dimensional nanostructures, such as nanorods, nanowires and nanotubes, have attracted great attention because of their peculiar optical, electrical and mechanical properties. Tapered ZnO nanorod, herein called nanoneedle, arrays have been grown on ZnO-coated silicon substrate by a hydrothermal downward growth process. The ZnO seeds layer facilitated the growth of aligned nanorods. The nanoneedles were grown with the substrate placed flush with the surface of the reaction solution and facing downward. The correlation between the depletion of solution and reaction temperature was exploited to control the length of the tapered portion of ZnO nanoneedles for the same solution. The ZnO nanoneedle arrays exhibit very strong and sharp ultraviolet emission from band gap transition and almost no green emission attributed to singly ionized oxygen vacancies in the cathodoluminescence spectrum. Self-assembled 2D inverse opal ZnO nanorod networks have been grown on silicon. The 488 nm PS nanospheres monolayers were used as the mold to grow the ZnO nanorod networks through the steps of self-assembly of monolayer PS nanospheres, deposition of Au buffer layer, catalytic growth of ZnO seeds layer on Au, growth of ZnO nanorods on ZnO seeds layer and removal of PS nanospheres. The work represents the successful growth of 2D ZnO photonic crystal with band gap at the green light emission region for the first time. The combination of nanosphere lithography and aqueous chemical growth provides a large-scale, facile and low cost fabrication method at low temperature, which shall be of tremendous value in practical applications of the grown photonic crystals. Aligned ZnO nanopagoda arrays have been grown on the silicon substrate with ZnO nanorod arrays by a hydrothermal and downward growth process. The concentration of bid-friendly ascorbic acid (vitamin C) was used to control the growth direction and the degree of lamination of ZnO nanostructure with vastly reduced reaction time (from 24 to 2 hrs). Low turn-on and threshold fields indicate that ZnO nanopagodas are promising for applications in field emission devices. The ZnO nanopagodas exhibit very prominent blue shift (10 nm) of UV emission and almost no green emission attributed to singly ionized oxygen vacancies at room temperature. The enhancement in deep-UV optical properties shall be advantageous in applications for nanoscale light-emitting devices. The polar surface concept can be useful to understand the ZnO growth mechanism of nanopagodas. The appropriate substrate and reaction condition lead to the growth of ZnO nanopagoda arrays with wafer-scale production. The large-scale ZnO nanopagoda arrays shall be very useful in fabricating the novel devices, such as field emitter, ultraviolet laser and dye-sensitized solar cells.