Study of structural and surface morphological properties of Tb doped ZnO nanoparticles using XRD, XPS and fractal analysis

A systematic study was performed on Tb³⁺ doped ZnO nanoparticles of different mole-fraction using Atomic Force Microscopy (AFM), X-ray Diffraction (XRD) and X-ray Photoemission Spectroscopy (XPS) measurements. XRD studies confirm that all the samples are in wurtzite phase. XRD analysis suggests a compressive lattice strain as doping concentration increases. The strain generated in the doped samples is found to be more as compared to pure nanoparticle samples. XPS result indicates the presence of several oxygen species adsorbed on the surface. Furthermore, the effect of incorporation of Tb³⁺ ions into ZnO nanoparticles was explored using fractal analysis approach to extract the quantitative surface parameters. The fractal dimension is a scale invariant technique for representation and understanding of surface morphology of nanostructures. Fractal dimension provides a clear distinction between vertical and horizontal properties of the surfaces and their correlation. This technique could be very useful in selecting the suitable substrate for various technological applications. The lateral correlation length was estimated by auto-correlation function. While, the roughness exponent and fractal dimension were calculated from height-height correlation function. Moreover, this study reveals that the complexity of surface increases with doping. Moreover, as doping increases, the surface becomes more and more zagged as compared to pure samples. (paper)