Seed-free electrochemical growth of ZnO nanotube arrays on single-layer graphene

Dense and vertical ZnO nanotubes were directly grown on single-layer graphene by convenient electrochemical deposition method, without ZnO seed layer, O ₂ bubbling, electrolyte assistance, or additional etching process. The formation of the ZnO nanotubes was governed by the self-etching process with H ⁺ generated during the growth process. The hole depth of the nanotubes can be controlled by adjusting deposition time. The nanotubes have weak visible luminescence intensity in photoluminescence spectrum, indicating excellent crystalline properties. The transmittance of the nanotubes on graphene/glass electrode was above 75% over entire visible range.