Growth mechanism and optical properties of ZnO nanotube by the hydrothermal method on Si substrates

Well-faceted hexagonal ZnO nanotubes have been synthesized on Si substrates by a simple hydrothermal method and the subsequent aged process at relative low temperature without any catalysts or templates. The samples have been characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) measurement. XRD pattern confirmed that the as-prepared ZnO was the single-phase wurtzite structure. SEM results showed that the samples were tubular textures, with the average lengths of 3-5 mu m, inner diameters of 300-350 nm. The surface-related optical properties have been investigated by photoluminescence (PL) spectrum and Raman spectrum. The PL implied that fairly high surface state density existed in ZnO nanotubes. And the green emission in Raman measurement might be related to surface states. A possible growth mechanism on the formation of crystalline ZnO nanotubes has been presented. (C) 2008 Elsevier B.V. All rights reserved.