Density improvement of the sol–gel dip-coated SnO2 films by chemical surface modification

We compare the effect of organic (Tiron®) and inorganic (Mn(II)) additives on the low temperature (<600 °C) densification of the sol–gel dip-coated SnO2 films. The structural and compositional properties of the samples were investigated by X-ray reflectometry (XRR), X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS). The results suggest that the replacement of hydroxyl groups at the particle surface by Tiron® reduces the level of agglomeration of the sol, increasing the particles packing and the apparent density of the coatings. Undoped and Mn-doped films drawn from a Tiron® containing suspension show after firing at 500 °C a porosity reduction of 12 and 8.6%, respectively. The porosity decrease is less pronounced (4.3%) for the film without additives. Both XAS and XPS data show the presence of trivalent manganese. The formation of a non-homogeneous solid solution characterised by the presence of Mn(III) replacing tin atom near to the crystallite surface was evidenced by XAS. Additionally, XPS results reveal the presence of metallic Sn at the surface of films containing Tiron®.