Abstract
Vertically aligned ZnO nanorods were grown at 700°C for 2 h on sapphire substrates with catalysts in bilayer configurations of Sn (top)/Ni (bottom) and Sn/In, where the top layer is formed by sputtering and the bottom one is deposited by spin coating. The effects of bilayer catalysts on growth kinetics of nucleation and growth, growth micromechanism, and vertical alignment of growing ZnO nanorods have been investigated. The vertical alignment of the Sn/Ni‐catalyzing ZnO nanorods is determined at the initial nucleation stage, where the nuclei are formed as regular candlestick‐like platforms. The reason for the formation of the candlestick‐like nuclei is due to the contribution of strain energy built in the underlying catalyst bilayers. The variations of axial and radial dimensions with growth duration for the growth of ZnO rods were explained and data fitting with the aids of kinetic growth equations, which are based upon the well‐known ledge model for crystal growth from vapor and diffusion kinetics.
Highlights
Zinc oxide (ZnO) is a direct bandgap semiconductor with a wide bandgap of 3.37 eV and large exciton binding energy (60 meV)
The most uniform and vertically aligned (VA) ZnO nanorods with a diameter of 50–150 nm have been grown by using the carbothermal reaction above 850◦C on Au catalystpatterned sapphire substrates with the aids of submicrometer sized polystyrene balls [1] and laser-hardening lithography technology [2, 3] or by using the Zn source at 750◦C on sapphire substrates covered with a c axis-oriented ZnO buffer layer [4]
There is no difference for ZnO from the Sn catalyst, which can be attributed to its melt state at different catalyst size
Summary
Zinc oxide (ZnO) is a direct bandgap semiconductor with a wide bandgap of 3.37 eV and large exciton binding energy (60 meV). This semiconductor has been attractive for optoelectronic applications in light-emitting diodes and laser diodes at room temperature. The vapor-phase growth of 1D ZnO has been widely conducted with Zn and (ZnO + graphite) powders as reactants. Because no droplets on the tips of flat-ended nanorods have been observed, the self-catalytic growth mechanism or the vapor-solid mechanism is used to explain the growth behaviors. The self-catalytic mechanism needs to consider the oxidation of catalysts during the growth period. The vapor-liquid-solid growth mechanism has been applied for nanowires with dome-shaped droplets on its tips. The formation of catalyst droplets and its durability through the growth process without oxidation or nitridation are the major concerns
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