Microstructural and optical properties of ZnO nanowires synthesized on Si substrates without a catalyst

Catalyst-free ZnO nanowires were formed on an n-Si substrate by using metal-vapor deposition. The scanning electron microscopy and the high-resolution transmission electron microscopy (HRTEM) images showed that the ZnO nanowires had diameters of about 120 nm, relatively uniform rod-like shapes, and a uniform size distribution. Selected-area electron diffraction patterns and HRTEM images showed that the ZnO nanowires had a preferentially c-axis-orientation wurzite structure. Cathodoluminescence spectra showed two peaks, one around 380 nm and the other around 500 nm, that corresponded to ultraviolet and green emission. The microstructural and optical properties of ZnO nanowires synthesized on Si and sapphire substrates were compared. These results can help improve understanding of the microstructural and optical properties of ZnO nanowires synthesized on Si substrates without a catalyst.