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

Abstract

TiO 2 thin films were synthesized using Low Pressure Chemical Vapour Deposition (LPCVD) onto glass substrates. Titanium isopropoxide (TTIP) and N 2 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 TiO 2 (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 preferr ed orientation of TiO 2 (B) needles in the [001] direction of average crystallite size 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 ph ase of TiO 2 was 550 o C (actual temperature) with a 1 mL/s N 2 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 selfcleaning structures.

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