A comparative study on the growth of ZnO nanorods by annealing method in different environments

• A detail comparative study of the growth of ZnO nanorods by annealing method was done.
• Comparison between air, oxygen and water loaded oxygen annealing ambient was carried out.
• Temperature and ambient were found to critically affect the density and aspect ratio.
• It was found that water vapor enhances the density of nanorods greatly by 1–2 order (∼109/cm2).
• A stress–diffusion based growth mechanism and a simple and efficient synthesis method was proposed.

A detailed comparative study of zinc oxide (ZnO) nanorods (NRs) grown by thermal annealing method in air, oxygen and water loaded oxygen environments was carried out. The number density, diameter and length of the NRs were studied as a function of annealing temperature and duration of anneal in all the three environments. Scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and photo-luminescence spectroscopy (PL) were used for the characterizations. The growth in water loaded oxygen environment was best and led to a very high density, good aspect ratio NRs of very good optical quality as compared to the other two environments. The environment and annealing temperature critically influenced the density and aspect ratio whereas the duration of annealing affected mainly the aspect ratio of NRs. It was also found that water vapor increased the density of NRs growth by an order. It has been proposed that the growth of NRs takes place due to the relaxation of stress accumulated in oxide film during the process of oxidation and annealing.