Low-temperature, catalyst-free vapor–solid growth of ultralong ZnO nanowires

The ultralong ZnO nanowires have been obtained by using ZnO and graphite as the mixture source via the catalyst-free vapor–solid (VS) process at 917 °C. The ZnO nanowires are over 100 μm in length and ∼100–300 nm in diameter with uniform hexagonal cross section. The single ultralong ZnO nanowire grows on the top of one ZnO nanotower with the length of ∼5 μm and the diameter of ∼600 nm. The formation of a ZnO hard layer on the surface of the mixture source is responsible for the abrupt morphology change and the growth of the ultralong nanowires. The local concentration of the Zn vapor and the oxygen are found to be critical for the formation of the ultralong ZnO nanowires. The catalyst-free growth of the ultralong ZnO nanowire was carried out with good repeatability in a low-cost quartz tube electric resistance furnace with the temperature lower than 1000 °C, showing a promising potential for the development of the ZnO based nanodevices and nanocircuits.