Catalyst-Free Growth of Vertical Alignment ZnO Nanowire Arrays by a Two-Stage Process

We successfully synthesized well aligned ZnO nanowire (ZnO NW) arrays on Si (100) and indium tin oxide (ITO) glass substrates at the low temperature of 500 °C by a two-stage growth process without metal catalyst. The synthesized ZnO NWs had diameters in the range of 50−100 nm and lengths in the range of 5−8 μm. X-ray diffraction showed that ZnO NW arrays had single-crystal wurtzite structures and grew along the c-axis. Photoluminescence spectra revealed that the ZnO NWs showed a strong UV band at 3.2 eV and a broad green band at 2.3 eV at room temperature. We also observed that the alignment situation and UV band emission of the ZnO NW arrays was enhanced with an increased O2 flow rate in the first stage. In addition, various O2 gas flow rates affected the morphologies of the ZnO nanomaterials. We present a detailed discussion regarding the growth behavior and mechanism of the ZnO NW arrays in this study.