The XRD and AFM analysis indicated that the BFO thin film sample is grown well with epitaxial structure and smooth surface. Then SE measurements were taken to get the ellipsometric

spectra of the STO substrate, signaling pathway the SRO buffer layer and the BFO thin film, respectively, in the photon energy range 1.55 to 5.40 eV. The dielectric functions of STO, SRO, and BFO are obtained by fitting their spectra data to different models in which BFO corresponds to a five-medium optical model consisting of a semi-infinite STO substrate/SRO film/BFO film/surface roughness/air ambient structure. The BFO film and surface roughness thickness are identified as 99.19 and 0.71 nm, respectively. The optical constants of the BFO film are determined through the Lorentz model describing the optical response, and a direct bandgap at 2.68 eV is obtained which near-bandgap transitions could contribute to. Moreover, the gap value is compared to the BFO thin film with similar thickness deposited on various substrate prepared by PLD, indicating the dependence of the bandgap for the epitaxial BFO thin film on the in-plane compressive strain. In addition, the transition at 3.08 eV disclosed by the Lorentz model in our work suggests that the bandgap of BFO single crystals

is less than 3 eV as previously reported. The results given in this work are helpful in understanding the optical properties of the BFO thin film and developing its application GW2580 in optical field. Acknowledgements This work has been financially supported by the Miconazole National Natural Science Foundation of China (Nos. 11174058, 61275160, and 61222407), the No. 2 National Science and Technology Major Project of China (No. 2011ZX02109-004), and the STCSM project of China with Grant Nos. 12XD1420600 and 11DZ1121900. References 1. Catalan G, Scott JF: Physics and applications of Bismuth Ferrite.

Adv Mater 2009, 21:2463–2485.CrossRef 2. MGCD0103 molecular weight Neaton JB, Ederer C, Waghmare UV, Spaldin NA, Rabe KM: First-principles study of spontaneous polarization in multiferroic BiFeO 3 . Phys Rev B 2005, 71:014113.CrossRef 3. Wang J, Neaton JB, Zheng H, Nagarajan V, Ogale SB, Liu B, Viehland D, Vaithyanathan V, Schlom DG, Waghmare UV, Spaldin NA, Rabe KM, Wutting M, Ramesh R: Epitaxial BiFeO 3 multiferroic thin film heterostructures. Science 2003, 299:1719–1722.CrossRef 4. Martin LW, Crane SP, Chu YH, Holcomb MB, Gajek M, Huijben M, Yang CH, Balke N, Ramesh R: Multiferroics and magnetoelectrics: thin films and nanostructures. J Phys Condens Matter 2008, 20:434220.CrossRef 5. Ihlefeld JF, Podraza NJ, Liu ZK, Rai RC, Xu X, Heeg T, Chen YB, Li J, Collins RW, Musfeldt JL, Pan XQ, Schubert J, Ramesh R, Schlom DG: Optical band gap of BiFeO 3 grown by molecular-beam epitaxy. Appl Phys Lett 2008, 92:142908.CrossRef 6.