A novel process was reported for preparing zinc oxide (ZnO) nanowires almost vertically well-aligned on various planes of silicon substrates by using polyvinyl alcohol (PVA) as self-assembling complex polymer to control nucleation and crystal growth via polymer complexation and low-temperature oxidizing-sintering. Highly regular Zn(OH)₂ nanodots on the Si substrate were first synthesized via complexing the homogeneous polar hydroxy groups —OH on PVA side-chains with Zn²⁺ ions in zinc salt solution when the pH value of the solution was adjusted to 8.5±0.1 by addition of a concentrated aqueous ammonia. Then the synthesized Zn(OH)₂ nanodots decomposed into ZnO nanodots at about 125 ℃ by thermal hydrolysis. Subsequently the ZnO nanodots grew gradually up into the well-oriented ZnO nanowires on the substrate at sintering temperature of 420 ℃. In the early stage of sintering, the carbonized PVA grid backbones were formed, which confined the ZnO nanowire's diameter and enhanced the absorption of ZnO at the tips of nanowires. At the presence of carbonized PVA, part of ZnO reduced to Zn through carbothermal reduction and in oxygen Zn was further oxidized to ZnO, forming the catalytically active site at the tips of nanowires. All the polymers were removed after sintering. The analytical results of FE-SEM, TEM, HR-TEM and XRD indicated that the ZnO nanowires are evenly distributed on Si substrate and possess a hexagonal wurtzite structure with preferred orientation along the [0001] direction of ZnO, and their diameter varies from 20 to 80 nm and the length from 0.5 to several μm. A polymer-controlled crystallization and morphogenesis by polymer grid backbone localization model was proposed to explain the growth behavior of ZnO nanowires.

Key words: ZnO nanowire, self-assembling, polymer induced, oriented growth, coordinate complexation