title: The Evidence of Giant Surface Flexoelectric Field in (111) Oriented BiFeO3Thin Film.
abstract: In this work, the surface structure of a single-domain epitaxial BiFeO3film with (111) orientation was investigated by in situ grazing incidence X-ray diffraction and X-ray reflectivity. We found that a large strain gradient exists in the surface region (2-3 nm) of the BiFeO3film. The strain gradient is approximately 107m-1, which is 2 or 3 orders of magnitude larger than the value inside the film. Moreover, we found that a surface layer with a lower electron density compared with the underlying BiFeO3layer exists on the surface of BiFeO3film, and this layer exhibits an irreversible surface structure transition occurs at 500 K, which should be associated with the surface flexoelectric field. We considered that this large strain gradient is originated from the surface depolarization field of ferroelectrics. Our results suggest a coupling between the surface structure and the flexoelectricity and imply that the surface layer and properties would be controlled by the strain gradient in ferroelectric films.
authors.affiliation: Shanghai Institute of Applied Physics, Chinese Academy of Sciences , Shanghai, 201204, China.
authors.forename: Tieying
authors.identifier: http://orcid.org/0000-0002-4728-7438
authors.initials: T
authors.lastname: Yang
authors.affiliation: Shanghai Institute of Applied Physics, Chinese Academy of Sciences , Shanghai, 201204, China.
authors.forename: Xingmin
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences , Ningbo, 315201, China.
authors.forename: Bin
authors.initials: B
authors.lastname: Chen
authors.affiliation: Institute of Physics, Chinese Academy of Sciences , Beijing, 100190, China.
authors.forename: Haizhong
authors.initials: H
authors.lastname: Guo
authors.affiliation: Institute of Physics, Chinese Academy of Sciences , Beijing, 100190, China.
authors.forename: Kuijuan
authors.identifier: http://orcid.org/0000-0002-0047-4375
authors.initials: K
authors.lastname: Jin
authors.affiliation: Department of Physics, Nanjing University , Nanjing, 210093, China.
authors.forename: Xiaoshan
authors.initials: X
authors.lastname: Wu
authors.affiliation: Shanghai Institute of Applied Physics, Chinese Academy of Sciences , Shanghai, 201204, China.
authors.forename: Xingyu
authors.initials: X
authors.lastname: Gao
authors.affiliation: Shanghai Institute of Applied Physics, Chinese Academy of Sciences , Shanghai, 201204, China.
authors.forename: Zhong
authors.initials: Z
authors.lastname: Li
authors.affiliation: Institute of Physics, Chinese Academy of Sciences , Beijing, 100190, China.
authors.forename: Can
authors.initials: C
authors.lastname: Wang
authors.affiliation: Shanghai Institute of Applied Physics, Chinese Academy of Sciences , Shanghai, 201204, China.
authors.forename: Xiaolong
authors.identifier: http://orcid.org/0000-0002-1674-9345
authors.initials: X
authors.lastname: Li
keywords: Surface layer; X-ray diffraction; ferroelectric thin films; flexoelectrics; microstructure