Zinc Oxide Thin Films Characterization, AFM, XRD and X-ray Reflectivity

Abstract

In this study, surface structures of two zinc oxide (ZnO) thin films, prepared by sol-gel spin and dip-coating methods, were investigated. Ex situ Atomic Force Microscopy (AFM), X-ray diffraction (XRD), and X-ray reflectivity measurements were carried out in order to study the surface structure. XRD measurements showed nanostructured ZnO thin films with well-defined orientations. Fractal analysis was applied on the AFM data to illustrate the surface morphology of thin films. Fractal analysis provided a precious depiction of irregularities found in ZnO thin films and revealed that both interface width W and lateral correlation length ξ are strongly affected by coating method. Calculations showed that the film that was prepared by dip-coating had correlation length, interface width and fractal dimension of 56.2, 2.3, and 2.2 nm, respectively. These parameters for spin-coated sample were 354.8, 8.5, and 2.64 nm, respectively. Optimization of X-ray reflectivity by Genetic Algorithm optimization revealed structural parameters of thin films such as surface and interface roughness and thickness of the films. These calculations showed that dip-coated thin film has a smooth surface, whereas spin-coated thin film has a rough surface.