Semi-circular shaped ZnO nanowhiskers assemblies were fabricated on a substrate by a simple bottom-up approach using an aqueous solution at 88 degrees C. The substrate was coated with ZnO seeds derived from the thermal decomposition of zinc nitrate hexahydrate at 350 degrees C. A 200-mL aqueous solution of 0.1 mol/L zinc nitrate hexahydrate, 0.1 mol/L hexamethylenetetramine, and 0.02 mol/L polyethylenimine was used for depositing ZnO nanowhiskers. X-ray diffraction (XRD) and a field emission scanning electron microscope (FE-SEM) were used to characterize phase and orientation, and morphology and microstructure, respectively. The pre-existing aggregated ZnO nanosheets on the substrate promoted heterogeneous nucleation and growth of ZnO nanowhiskers assemblies preferentially orientated along the c-axis direction, resulting in the formation of the semi-circular shape. (C) 2008 Elsevier B. V. All rights reserved.