Modification of surface morphology and lattice order in nanocrystalline ZnO thin films prepared by spin-coating sol–gel method

The surface morphology and structure of zinc oxide thin films play a key role in many applications such as chemical sensors and photocatalysts. In this study, ZnO thin films are prepared on Si/SiO2 substrates by spin-coating sol–gel technique. New element in the films preparation is the application of drying with hot air flow (Th= 90–95 °C), as first step of the drying procedure, followed by furnace drying as second step. It is shown that hot air drying has significant influence on the films properties. It reduces the internal stress, strongly affects the films surface morphology, gives assistance to the effusion of organic remains and results in a better crystallinity and lower defect density in the as-prepared films when compared with the films prepared by furnace drying only. Besides, first data on the modification of sol–gel ZnO films by post-deposition irradiation with a nanosecond infrared laser are obtained, giving an alternative to the standard furnace annealing. They indicate that laser irradiation of as-prepared ZnO films gives rise to certain improvement in crystal structure and slight increase in crystallite size, followed by the increase of micro-strain. It also reduces the number of defects playing role of non-radiative recombination centers, as well as the size and density of small cracks and pores on the surface of as-prepared films.