Growth of ultra-thin TiO2 films by spray pyrolysis on different substrates

In the present study TiO₂ films were deposited by spray pyrolysis method onto ITO covered glass and Si (1 0 0) substrates. The spray solution containing titanium(IV) isopropoxide, acetylacetone and ethanol was sprayed at a substrate temperature of 450 °C employing 1-125 spray pulses (1 s spray and 30 s pause). According to AFM, continuous coverage of ITO and Si substrates with TiO₂ layer is formed by 5-10 and below 5 spray pulses, respectively. XPS studies revealed that TiO₂ film growth on Si substrate using up to 4 spray pulses follows 2D or layer-by-layer-growth. Above 4 spray pulses, 3D or island growth becomes dominant irrespective of the substrate. Only 50 spray pulses result in TiO₂ layer with the thickness more than XPS measurement escape depth as any signal from the substrate could not be detected. TiO₂ grain size remains 30 nm on ITO and increases from 10-20 nm to 50-100 nm on Si substrate with the number of spray pulses from 1 to 125.