title: Evolution of structural distortion in BiFeO3thin films probed by second-harmonic generation.
abstract: BiFeO3thin films have drawn much attention due to its potential applications for novel magnetoelectric devices and fundamental physics in magnetoelectric coupling. However, the structural evolution of BiFeO3films with thickness remains controversial. Here we use an optical second-harmonic generation technique to explore the phase-related symmetry evolution of BiFeO3thin films with the variation of thickness. The crystalline structures for 60 and 180-nm-thick BiFeO3thin films were characterized by high-resolution X-ray diffractometry reciprocal space mapping and the local piezoelectric response for 60-nm-thick BiFeO3thin films was characterized by piezoresponse force microscopy. The present results show that the symmetry of BiFeO3thin films with a thickness below 60 nm belongs to the point group 4 mm. We conclude that the disappearance of fourfold rotational symmetry in SHG s-out pattern implies for the appearance of R-phase. The fact that the thinner the film is, the closer to 1 the tensor element ratio χ31/χ15tends, indicates an increase of symmetry with the decrease of thickness for BiFeO3thin films.
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.|University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Jie-Su
authors.initials: JS
authors.lastname: Wang
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.|University of Chinese Academy of Sciences, Beijing 100049, China.|Collaborative Innovation Center of Quantum Matter, Beijing 100190, China.
authors.forename: Kui-Juan
authors.initials: KJ
authors.lastname: Jin
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Hai-Zhong
authors.initials: HZ
authors.lastname: Guo
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Jun-Xing
authors.initials: JX
authors.lastname: Gu
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Qian
authors.initials: Q
authors.lastname: Wan
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Xu
authors.initials: X
authors.lastname: He
authors.affiliation: Shanghai Synchrotron Radiation Facility (SSRF), Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201204, China.
authors.forename: Xiao-Long
authors.initials: XL
authors.lastname: Li
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Xiu-Lai
authors.initials: XL
authors.lastname: Xu
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.|Collaborative Innovation Center of Quantum Matter, Beijing 100190, China.
authors.forename: Guo-Zhen
authors.initials: GZ
authors.lastname: Yang