Spray pyrolysis deposition of zinc oxide nanostructured layers

Highly structured ZnO layers comprising well-shaped hexagonal rods were prepared by spray pyrolysis deposition of zinc chloride aqueous solutions in the temperature range of 490-560 °C. The layers were characterised by SEM, XRD and SAED. A flat ZnO film evolves into the structured layer consisting of single crystalline hexagonal elongated prisms at growth temperatures close to 500 °C and above. The rise of both the growth temperature and solution concentration increases rod dimensions. The deposition of the 0.1 mol/l solution at ∼500 °C results in crystals with a diameter of 200-300 nm and length of 800 nm. However, the rods grown at 560 °C indicate a width in the range of 400-600 nm and a length of up to 2500 nm. The deposition of the 0.05 mol/l solution at 560 °C results in the rods with a diameter of 100-300 nm and a length of 1500 nm. The increase of the concentration up to 0.2 mol/l results in branched crystals, mainly tripods with a similar leg size of 600-700 nm in width and 3000 nm in length. According to XRD, the ZnO layers grown from the 0.1 mol/l solution in the temperature range of 450-560 °C are c-axis-oriented, independent of morphology. The XRD peaks intensities ratio (I₀₀₂/I₁₀₁) of the samples deposited at 560 °C changes from 9 to 1.3 by an increase in the solution concentration from 0.05 to 0.2 mol/l and indicates that c-axis orientation vanishes at higher concentrations. We showed that ZnO nanorods with the length to diameter ratio of 30 can be prepared by spray technique using indium tin oxide-covered glass substrates instead of bare glass.