Local surface morphology and chemistry of SnO₂ thin films deposited by rheotaxial growth and thermal oxidation method for gas sensor application

In this paper experimental results of a comparative X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS) study of the crystalline structure, the local morphology, and the surface and in-depth chemistry of SnO₂ thin films obtained by Rheotaxial Growth and Thermal Oxidation (RGTO) method are presented. XRD rules out even a minor presence of a coexisting SnO phase. AFM and SEM show a fractal like morphology of nanograins (20 nm typical size) agglomerated in clusters of crystallites with a bimodal size distribution. XPS shows that the surface of the SnO₂ crystallites is slightly under-stoichiometric as expected from the oxygen deficient termination of their facets. Noteworthy, as evidenced by XPS depth profiles, there are no significant changes of the surface chemistry of the RGTO film with argon ion sputtering.