Single-crystal, Al-catalyzed Si nanowires (SiNWs) were grown under atmospheric pressure using the dimpled feature of Al metal that remained after the removal of an anodic aluminum oxide (AAO) template directly formed on a Si substrate. During the H-2 preannealing prior to growth, the dimpled surface morphology of the remaining Al changed as the Al formed agglomerations with each other and subsequently formed Al-Si alloy islands on the silicon surface. Silicon nanowires were found to only grow on these islands, resulting in the final hedgehog-shaped morphology. The amount of Al agglomeration which controlled the overall size of the alloy islands was determined by varying the H-2/Ar flow ratio during preannealing. High-density growth of SiNWs was observed at a lower ratio of the H-2/Ar flow rates. (C) 2009 Elsevier B.V. All rights reserved.