Surface properties of SnO<sub>2</sub> nanolayers prepared by spin-coating and thermal oxidation
Monika Kwoka, Barbara Lyson-Sypien, Elisabetta Comini, Maciej Krzywiecki, K. Waczyński, J. Szuber
Abstract
Abstract In this work, comparative studies of the surface morphology and surface chemistry of SnO 2 nanolayers prepared by spin coating with subsequent thermal oxidation (SCTO) in the temperature range of 400–700 °C using scanning electron microscopy (SEM), atomic force microscopy (AFM) and x-ray photoelectron spectroscopy (XPS) methods, are presented. The SEM images show that SCTO SnO 2 nanolayers contain partly connected irregular structures strongly dependent on the final oxidation temperature, with interconnected single grains of longitudinal shape and size, resulting in a flatter surface morphology with respect to the commonly used three-dimensional (3D) SnO 2 thin films. In turn, AFM studies additionally confirm that SCTO SnO 2 nanolayers after post-oxidation annealing at higher temperatures contain isolated grains of average lateral dimensions in the range of 20–50 nm having a rather flat surface morphology of average surface roughness defined by the root mean square factor at the level of ∼2 nm. From the XPS experimental research it can be concluded that, for our SCTO SnO 2 samples, a slight surface nonstoichiometry defined by the relative [O]/[Sn] concentration at the level of 1.8–1.9 is observed, also depending on the final post-oxidation temperature, being an evident contradiction to recently published literature using x-ray diffraction data. Moreover, XPS experiments show that there is also a permanent small amount of carbon contamination present at the surface of internal grains of our SCTO SnO 2 nanolayers, creating an undesired potential barrier for interactions with gaseous species when they are used as the active materials for gas sensing devices.