Structural Analysis of Vertically-Aligned Single Crystalline ZnO Nanorods Grown on Different Seed Layers with Chemical Solution Deposition

We report the structural properties of the vertically-oriented ZnO nanorods fabricated on various ZnO seed layers with chemical solution deposition (CSD) technique. The ZnO nanorods were prepared using an aqueous solution with Zinc nitrate (Zn(NO₃)₂ ·6H₂O, Aldrich) and hexamethylenetetramine (HMT, Aldrich) in a convection oven. A-plane sapphire substrates with a deposited ZnO thin film were placed upside down in a quartz holder to avoid any micro-crystalline contamination. Especially, our hydro-thermal syntheses are automatically processed on precision pump drive systems (Masterflex) to accurately control the pH of the aqueous solution. The [002] crystal orientation of the ZnO seed layer was observed by the X-ray diffraction pattern. Structural features of ZnO nanorods were systematically analyzed by scanning electron microscopy and tunneling electron microscopy, together with selective area electron diffraction patterns. Experimental observations clearly demonstrated the dependence of the growth direction of the ZnO nanorods on the crystal structures of the ZnO seed layers.