Tunability of band-gap in barium strontium titanate films on anodic aluminum oxide templates

Evolution of the band-gap and surface topography in Ba_0.6Sr_0.4TiO₃ films fabricated on the anodic aluminum oxide templates with different pore diameters has been investigated by forming the nanostructure. Scanning electron microscope images show that the films tend to grow along the edge of the pores of templates. The optical band-gap of films is broadened from 3.25 to 4.20 eV with the pore diameters decreasing from 400 to 30 nm. Meanwhile, the optical band-gap of films on templates with the 30 nm pore diameter is nearly independent on the deposition time. These results are attributed to the quantum size effect and the specific structure of films. Our experimental work provides a further understanding of the modulated optical properties of oxides by controlling the diameter of templates.