Catalyst-free synthesis of macro-scale ZnO nanonail arrays on Si substrate by simple physical vapor deposition

Macro-scale ZnO nanonail arrays have been synthesized on silicon wafer by a simple physical vapor deposition approach without any catalyst. These synthesized ZnO nanonails grow vertically on the substrate with their caps upside. This probably results from the crowding effect. Each ZnO nanonail has a large hexagonal cap and a thinner shaft of several microns in length. Most of the nanonails are perfect single crystals with wurtzite structure and their preferred growth orientation is along [001] direction. The growth mechanism is VS mechanism and the detailed growth process is also proposed. The macro-scale nanonail arrays on Si substrate could offer novel opportunities for both fundamental research and technological applications. (C) 2007 Elsevier B.V. All rights reserved.