Aluminum as catalyst for ZnO nanostructures growth

• The efficiency of aluminum as catalyst to grow ZnO nanostructures is proved.
• Aluminum as a new catalyst is proposed due to its reduced economic cost.
• VSS growth mechanism is the main mechanism using Al as catalyst.
• Abrupt diameter change of NWs is discussed due to Al-assisted growth.

We report the growth of Al-catalyzed ZnO nanowires (NWs) using a thermal evaporation technique. Before the growth, the substrates were covered with a distribution of Al nano-island that act as seeds. We found that the density of NWs increases as the density of seeds is increased, confirming the catalyst properties of Al. The critical parameters of growth are the substrate temperature, oxygen partial pressure and the thickness of the initial Al layer from which the seeds are formed. The results showed that the oxygen pressure has a strong influence on the structural characteristics: the nanowires exhibit a preferential orientation in the (0 0 l)-planes when they are grown at low oxygen flow, and they become polycrystalline when a high concentration of oxygen in the flow is used. We consider that the growth occurs via a vapor-solid-solid (VSS) process as the predominant growth mechanism.