Brookite TiO2 Thin Film Epitaxially Grown on (110) YSZ Substrate by Atomic Layer Deposition

Epitaxial brookite TiO2 (B-TiO2) film was deposited on (110) yttria-stabilized zirconia (YSZ) substrate using plasma-enhanced atomic layer deposition, and its structural, optical, and gas sensing properties were investigated. As-deposited TiO2 film was a pure brookite and (120) oriented. The determined in-plane orientation relationships were [2 (1) over bar0](B-TiO2)//[(1) over bar 10](YSZ) and [001](B-TiO2) //[001](YSZ). The B-TiO2 film showed similar to 70% transmittance and the optical band gap energy was 3.29 eV. The B-TiO2 film-based gas sensor responded to H-2 gas even at room temperature and the highest magnitude of the gas response was determined to be similar to 150 toward 1000 ppm of H-2/air at 150 degrees C. In addition, B-TiO2 sensor showed a high selectivity for H-2 against CO, EtOH, and NH3.