Optical constants of MOCVD-grown Aurivillius phases in the Bi4Ti3O12–Na0.5Bi0.5TiO3 system measured by spectroscopic ellipsometry

• Published in: Applied physics. A, Materials science & processing Materials science & processing, 2011-10, Vol.105 (1), p.81-88
• Main Authors: Bin Anooz, S., Schwarzkopf, J., Petrik, P., Schmidbauer, M., Duk, A., Agocs, E., Fornari, R.
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Condensed Matter Physics; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Dielectric thin films; Dielectrics, piezoelectrics, and ferroelectrics and their properties; Exact sciences and technology; Insulators; Machines; Manufacturing; Nanotechnology; Optical and Electronic Materials; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of specific thin films; Physics; Physics and Astronomy; Processes; Surfaces and Interfaces; Thin Films
• ISSN: 0947-8396; 1432-0630
• DOI: 10.1007/s00339-011-6581-z

Thin films of bismuth titanate Bi 4 Ti 3 O 12 and different sodium–bismuth–titanate phases Na 0.5 Bi 8.5 Ti 7 O 27 , Na 0.5 Bi 4.5 Ti 4 O 15 , and Na 0.5 Bi 0.5 TiO 3 with different numbers of perovskite units ( m ) between two Bi 2 O 2 intermediate layers were epitaxially grown on (001) SrTiO 3 substrates by metal-organic chemical vapor deposition. The optical properties of these ferroelectric thin films were investigated by spectroscopic ellipsometry (SE) at room temperature in the 0.73–6.48 eV spectral range. In the analysis of the SE measured spectra Cauchy transparent, Tauc–Lorentz and Gaussian dispersion relations were used to characterize the optical properties of the films. Our analysis clearly shows that the refractive index of the Aurivillius phases decreases with increasing m , while the optical band gap increases with increasing m . The obtained dielectric function spectra revealed a shoulder and a broad absorption band at about 3.7 and 4.5 eV, respectively, for Bi 4 Ti 3 O 12 and a broad absorption band around 4.5 eV for the perovskite phase Na 0.5 Bi 0.5 TiO 3 . A shift in the resonance energies to lower energy with increasing m is observed.