Synthesis and characterization of mixed phase anatase TiO2 and sodium-doped TiO2(B) thin films by low pressure chemical vapour deposition (LPCVD)

Abstract

TiO₂ thin films were synthesized using Low Pressure Chemical Vapour Deposition (LPCVD) onto glass substrates. Titanium isopropoxide (TTIP) and N₂ gas were used as the precursor and carrier gas respectively. The effects of reaction temperature, carrier gas flow rate and deposited area were studied. SEM, TEM, powder XRD and UV-Vis and Raman spectroscopy were employed to characterize the phase and morphology of the synthesized materials. The results show that a dual phase (sodium-doped TiO₂(B) and anatase) nanocrystalline thin film was successfully prepared by LPCVD with needle- and polygonal plate-shape crystallites respectively. At the interface with the substrate, the thin film deposit exhibited a preferred orientation of TiO₂(B) needles in the [001] direction with an average crystallite size of 50–80 nm in length and 5–10 nm in width, whilst the crystallite size of anatase polygonal-plates was around 200 nm. The optimal LPCVD condition for preparing this mixed phase of TiO₂ was 550 °C (actual temperature) with a 1 mL s⁻¹ N₂ flow rate. A possible mechanism for the mixed-phase formation by LPCVD on the glass substrates is described as well as the implications for the production of self-cleaning structures.