Pt heterostructure grown on sapphire substrate—Influence of annealing processes (original) (raw)

Simple gas sensors based on resistivity change of TiO 2 thin films using combined top and bottom metallic contacts are very promising. In this work influence of ex situ annealing in ambient air on structure of TiO 2 thin film stacked between two platinum contact layers has been studied. The layers were deposited using DC magnetron sputtering on unheated c-cut sapphire substrates. For lowering of the Schottky barrier at the Pt-TiO 2 interfaces and for improved crystalline stability, ex situ annealing at 600 • C in air was carried out. In order to study separately influence of top and bottom platinum layers on crystal structure, also reference samples Pthave been prepared. Non-ambient X-ray diffraction measurement during annealing process and X-ray pole figures after annealing has been measured. Near epitaxial relationship was observed for bottom Pt layer grown on c-cut sapphire substrate: [110]||Al 2 O 3 (0 0 0 1) [1100]. Inner titania layer shows randomly oriented both TiO 2 -rutile (R) and anatase (A) phases with the volumetric ratio of R/A ∼ 2.7. If prepared without top Pt contact layer, the TiO 2 transforms during annealing to random single anatase phase. The TiO 2 layer overgrown with only single Pt top contact layer shows randomly oriented both rutile and anatase phases with volumetric ratio R/A ∼ 2.3. The top Pt layer on TiO 2 shows filamentary uniaxial orientation Pt(1 1 1)||Al 2 O 3 (0 0 0 1). The interdiffusion at the Pt-TiO 2 interfaces extends to several nm.