Density Controlled Growth of ZnO Nanowall–Nanowire 3D Networks

This paper presents the synthesis of wafer scale 3D ZnO nanoarchitectures composed of an array of 1D nanowires (NWs) embedded in 2D nanowalls by the vapor−liquid−solid (VLS) method. The effects of oxygen concentration and growth temperature on the density of nanostructures were studied. The 3D ZnO nanostructures were synthesized on c-plane GaN-on-sapphire substrate utilizing high purity ZnO powder and oxygen (O2) as source materials, and argon (Ar) as carrier gas. ZnO materials were also grown on c-plane sapphire and Si (111) substrates for comparison. Transmission electron microscopy (TEM) diffraction pattern showed the nanostructures are high quality single crystals having wurtzite crystal structure. High resolution transmission electron microscopy (HRTEM) showed the growth direction of ZnO nanowires is along ⟨0001⟩ c-plane orientation. The growth mechanism of such 3D nanostructures was proposed. The understanding of the formation mechanism of the unique ZnO 3D nanostructures will provide guidance for controlled growth of other semiconductor-based nanostructures suitable for surface related applications such as sensing, energy harvesting, and catalyzing.