Characterization of SnO2 thin films grown from aqueous solutions

Nanocrystalline SnO2 thin films with the cassiterite structure and grains 5–10 nm in size were deposited from precipitating aqueous solutions of SnCl4×5H2O and HCl at 80°C. The substrates were single-crystal {100} silicon wafers, either with or without sulfonate-functionalized self-assembled monolayer (SAM) coatings. Films, 60–70 nm thick, were obtained in 12 h from a medium of 2 mM SnCl4/0.4 M HCl. These films grew at a rate of approximately 9 nm h−1 during the first 4 h. Thicker films, 160 nm thick, containing cassiterite grains 5–10 nm in size were obtained by continuously flowing a solution of 2 mM SnCl4/0.2 M HCl past the substrates. The as-deposited films were uniform and adherent. They contained ∼2–3 at.% Cl and excess oxygen (2<O/Sn<3). A detailed X-ray photoelectron spectroscopy (XPS) analysis of the oxygen content of the films indicates that the additional oxygen may be present in an amorphous tin oxyhydroxide phase.