Nanocrystalline Cr2O3-TiO2 thin films by pulsed laser deposition

In the present work, pulsed laser deposition (PLD) technique was applied to Cr2O3-TiO2 mixed oxide (5-20 at.% TiO2) gas sensing materials with the aim to find the feasibility and optimal conditions for the growth of nanostructured thin films. The films were deposited by KrF laser (λ = 248 nm) on Si(1 0 0) substrates in low-pressure oxygen environment, and characterised by X-ray diffraction, X-ray reflection, reflection high-energy electron diffraction and atomic force microscopy. The substrate temperature (450-700 °C), oxygen pressure (10−3 to 5 × 10−2 mbar), and laser energy density (1.5-4.5 J/cm2) were varied for optimising the growth conditions. Structural and morphological analysis showed that the films started to crystallize at oxygen pressures above 10−2 mbar. At the highest oxygen pressure the first traces of crystallization appeared at raising the temperature over 400 °C (20 at.% of Ti) or 450 °C (at 5 at.% Ti). Smallest particle sizes (10-20 nm) were obtained at 500-550 °C, whereas the best degree of crystallinity of nanostructured films was observed at higher temperature but at lower laser energy densities. When the films were grown or annealed at temperatures over 600 °C the crystallinity further improved but the particle size grew over 100 nm.