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Structural and optical properties of BaTiO3 thin films prepared by radio-frequency magnetron sputtering at various substrate temperatures

Thin films of BaTiO3 were prepared by radio-frequency magnetron sputtering at substrate temperatures from 450 to 750 °C and analysed by x-ray diffraction, optical transmittance and Raman spectroscopy. The packing density of the films relative to the crystalline density increases from 0.75 at 450 °C to about 1 at 750 °C. At a substrate temperature of 450 °C, the film is nano-crystalline (5 to 20 nm) with big lattice expansion, large band gap and pronounced hexagonal Raman lines. This film is homogeneous in the thickness direction. Films prepared at higher temperatures exhibit perovskite peaks in the Raman spectrum and an optical band gap of 3.38 eV. At 600 °C, the film exhibits a pronounced two-phase growth with a porous nucleation layer of initial packing density of 0.78, a preferred (100)-orientation of the grains and minimum micro-strain. At 750 °C, the films are again homogeneous in the thickness direction, have nearly crystalline packing density and preferably (110)-oriented grains.