Polyethylenimine-guided self-twin zinc oxide nanoarray assemblies

Well-oriented and twin ZnO nanoarray assemblies have been fabricated using the aqueous solution deposition technique at low temperature. Polyethylenimine was added to the zinc nitrate hexahydrate-hexamethylenetetramine aqueous solution during the deposition processes at 88 °C. The formation mechanism of twin ZnO nanoarray assemblies was clarified by X-ray diffraction, a field emission scanning electron microscope and high-resolution transmission electron microscope. The addition of polyethylenimine resulted in the formation of zinc hydroxide and zinc hydroxide nitrate dihydrate (Zn₅ (OH) ₈ (NO₃)₂ ·2H₂O) as the intermediate phases. In situ forced hydrolysis of the cloudlike intermediate phase Zn ₅ (OH) ₈ (NO₃)₂ ·2H ₂O effectively provided nucleation sites and reduced the interface energy barrier for ZnO crystal growth, and promoted preferential growth along the [0001] direction by heterogeneous nucleation through the dissolution-reprecipitation of zinc hydroxide. The formation of twin ZnO assemblies should be attributed to kinetic confinement and thermodynamic motivation.