Single-crystalline ZnO microtubes formed by coalescence of ZnO nanowires using a simple metal-vapor deposition method

Single-crystalline ZnO microtubes were synthesized by a simple metal-vapor deposition method. The ZnO microtubes, which had outer diameters in the range of 0.3-2 mu m and wall thickness in the range of 100-500 nm, indicated a faceted hexagonal shape. In addition, it was found that there were many incomplete ZnO microtubes, which indicate the morphology assembled with several nanowires at the tip part of the microtubes and prismatic tubular morphology at the bottom part of the microtubes. It is suggested that the ZnO microtubes were formed by the coalescence of ZnO nanowires due to a high reaction temperature of 950 degrees C and optimized oxygen supplement when ZnO nanowires were grown on a large ZnO grain. We discuss the growth mechanism of the ZnO microtubes in detail.