Vertically well-aligned ZnO nanowires with a high density were successfully grown on Si (100) substrates without a catalyst by conventional thermal evaporation. The grown ZnO nanowires are relatively uniform in diameter of about 180 nm and length of about 4 μm. They exhibit the morphological features of faceted planes at the tips of hexagonal columns and are preferentially oriented along the [001] direction. The optimum growth condition was obtained from the experimental result that the degree of vertical alignment of the ZnO nanowires depends sensitively on the distance between the substrate and the Zn source. The PL characteristics of the grown ZnO nanowires reveal a strong and sharp UV emission at 380 nm and a broad green emission in the region of 500 nm, indicating excellent optical properties.

Keywords: ZnO nanowires, thermal evaporation, photoluminescence, nanostructure.