We report on the synthesis of elemental zinc nanowires by physical vapor deposition in high vacuum. In contrast to conventional vapor transport setups using tube furnaces, our growth system allows to control the substrate temperature independently from the vapor source. The physical vapor is generated by evaporation of pure zinc from resistively heated crucibles under high vacuum conditions. The evaporation rate and the total amount of zinc deposited on the substrate during the growth run are monitored using a quartz crystal microbalance. As substrates, silicon wafers are sputter-coated with gold, forming nanocrystalline islands as metal seeds. The work pressure is adjusted by the partial pressure of argon or oxygen flow gas.
One-dimensional nanostructures of serpentine and wire morphologies are obtained at substrate temperatures of 100-200°C. Scanning electron microscopy reveals that the nanowires gradually dominate over the serpentine nanostructures with increasing temperatures. The nanowires are several tens of micrometers long and have diameters of 30-200nm. The average growth rate is determined to be 1µm/min. Transmission electron micrographs show that the nanowires consist of single crystalline zinc covered with a thin native oxide. The growth direction of the nanowires is <11-20>. The growth mechanism follows the Vapor-Solid process since no catalyst particles are found on top of the nanowires. We also present a model to derive the surface diffusion length of zinc adatoms on the wire sidewalls.
This demonstration of zinc metal nanowire growth opens up a route for low-temperature synthesis of zinc oxide, which is highly attractive for photonic and sensor applications, by adding a subsequent oxidation step.
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