Molecular Layering of Titanium Oxide Coatings on Morphologically Various Polycrystalline α-Al2O3 Wafers

The effect of the surface roughness (160 or 45 nm) of polycrystalline α-Al2O3 wafers on the composition, structure, and properties of titanium oxide coatings formed on the wafers upon chemical assembly in a set number (up to 600) of molecular layering (ML) cycles comprising an alternating exposure of the substrate to titanium tetrachloride and water vapor was studied. X-ray fluorescence analysis and scanning electron microscopy (SEM) showed that the titanium concentration was higher in samples with the higher initial surface roughness. The coordination states of titanium in the oxide coatings according to UV–Vis diffuse reflectance (UV–Vis DRS) spectra correspond to aluminotitanate, tetrahedral, and anatase-like structures, the ratio between which depends both on the coating thickness and on the substrate surface roughness. Atomic force microscopy (AFM) showed that layers consisting of larger particles were formed on substrates of higher roughness. At the same time, as the thickness of the coating increased, its roughness increased, too, and the oxygen gas sensitivity in the sensors increased.