Direct growth of comet-like superstructures of Au–ZnO submicron rod arrays by solvothermal soft chemistry process

The synthesis, characterization and proposed growth process of a new kind of comet-like Au–ZnO superstructures are described here. This Au–ZnO superstructure was directly created by a simple and mild solvothermal reaction, dissolving the reactants of zinc acetate dihydrate and hydrogen tetrachloroaurate tetrahydrate (HAuCl4·4H2O) in ethylenediamine and taking advantage of the lattice matching growth between definitized ZnO plane and Au plane and the natural growth habit of the ZnO rods along [001] direction in solutions. For a typical comet-like Au–ZnO superstructure, its comet head consists of one hemispherical end of a central thick ZnO rod and an outer Au–ZnO thin layer, and its comet tail consists of radially standing ZnO submicron rod arrays growing on the Au–ZnO thin layer. These ZnO rods have diameters in range of 0.2–0.5 μm, an average aspect ratio of about 10, and lengths of up to about 4 μm. The morphology, size and structure of the ZnO superstructures are dependent on the concentration of reactants and the reaction time. The HAuCl4·4H2O plays a key role for the solvothermal growth of the comet-like superstructure, and only are ZnO fibers obtained in absence of the HAuCl4·4H2O. The UV–vis absorption spectrum shows two absorptions at 365–390 nm and 480–600 nm, respectively attributing to the characteristic of the ZnO wide-band semiconductor material and the surface plasmon resonance of the Au particles.