Texture vs morphology in ZnO nano-rods: On the x-ray diffraction characterization of electrochemically grown samples

Abstract

Texture characterization in thin films from standard powder x-ray diffraction (XRD) rely on the comparison between observed peak relative intensities with those of powder diffraction standards of the same compound, trough the so-called texture coefficient (TC). While these methods apply for polycrystalline materials with isotropic grains, they are less accurate—and even wrong—for anisotropic materials like ZnO oriented single-crystal nano-rods, which would require the use of dedicated XRD texture setups. By using simple geometrical considerations, we succeed in discriminating between texture and morphology contributions to the observed intensity ratios in powder diffraction patterns. On this basis, we developed a method that provides a quantitative determination of both texture (polar distribution) and morphology (aspect ratio of nano-rods), using simple x-ray powder diffraction. The method is illustrated on a typical sample from a series of Zinc oxide (ZnO) nano-rod arrays grown onto a gold thin film sputtered onto a F:SnO2-coated glass substrate (FTO) by using cathodic electro-deposition. In order to check the consistency of our method, we confronted our findings with scanning electron microscope (SEM) images, grazing incidence diffraction (GID), and XRD pole-figures of the same sample. Nevertheless, the proposed method is self-consistent and only requires the use of a standard powder diffractometer, nowadays available in most solid-state laboratories.