Tunable Synthesis of Single-Crystalline ZnO Hexagonal Microtubes and Nanowires

Here we report the tuning of growth morphology of ZnO structures from nanowire to microtubes by using Si substrate with and without gold coating. The growth of single crystalline ZnO hexagonal microtubes was obtained on bare Si substrate whereas nanowires obtained on gold coated Si substrate in similar growth environment by using simple chemical vapor deposition system (CVD). The as-synthesized ZnO microtubes are crystalline in nature with lattice fringes spacing d =0.26 nm. The growth of ZnO nanowires follows V L S mechanism whereas ZnO microtubes grow via self templated method followed by oxidation and re-sublimation process. The carbothermly reduced Zinc rich reactive species preferred to grow in hexagonal rod having facets with lower energy. The oxidation of faces results in walls of microtubes and re-sublimation of Zn-rich core left hollow cavity at center of microtubes. The photoluminescence spectra of ZnO microtubes and nanowires measured at room temperature show UV peak at 381 nm and green peak at 523 nm. The ratio of peak intensities of UV and green emission (I-uv:I-GR) in the PL spectra of microtubes and nanowires is 22.8 and 0.87, respectively, implying that microtubes are of subsequently higher crystalline quality.