title: Surface reconstructions and related local properties of a BiFeO3thin film.
abstract: Coupling between lattice and order parameters, such as polarization in ferroelectrics and/or polarity in polar structures, has a strong impact on surface relaxation and reconstruction. However, up to now, surface structures that involve the termination of both matrix polarization and polar atomic planes have received little attention, particularly on the atomic scale. Here, we study surface structures on a BiFeO3thin film using atomic-resolution scanning transmission electron microscopy and spectroscopy. Two types of surface structure are found, depending on the polarization of the underlying ferroelectric domain. On domains that have an upward polarization component, a layer with an Aurivillius-Bi2O2-like structural unit is observed. Dramatic changes in local properties are measured directly below the surface layer. On domains that have a downward polarization component, no reconstructions are visible. Calculations based on ab initio density functional theory reproduce the results and are used to interpret the formation of the surface structures.
authors.affiliation: Peter Grünberg Institute (PGI-5), Research Centre Jülich, 52425 Jülich, Germany.|Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons (ER-C), Research Centre Jülich, 52425 Jülich, Germany.
authors.forename: L
authors.initials: L
authors.lastname: Jin
authors.affiliation: Institute for Theoretical Physics, ETH Zurich, 8093 Zurich, Switzerland.
authors.forename: P X
authors.initials: PX
authors.lastname: Xu
authors.affiliation: Peter Grünberg Institute (PGI-5), Research Centre Jülich, 52425 Jülich, Germany.|The School of Electronic and Information Engineering, Xi'an Jiaotong University (XJTU), Xi'an 710049, China.|State Key Lab of New Ceramics and Fine Processing and School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China.
authors.forename: Y
authors.initials: Y
authors.lastname: Zeng
authors.affiliation: The School of Electronic and Information Engineering, Xi'an Jiaotong University (XJTU), Xi'an 710049, China.
authors.forename: L
authors.initials: L
authors.lastname: Lu
authors.affiliation: Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons (ER-C), Research Centre Jülich, 52425 Jülich, Germany.|Central Facility for Electron Microscopy, RWTH Aachen University, 52074 Aachen, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Barthel
authors.affiliation: Institute for Theoretical Physics, ETH Zurich, 8093 Zurich, Switzerland.
authors.forename: T
authors.initials: T
authors.lastname: Schulthess
authors.affiliation: Peter Grünberg Institute (PGI-5), Research Centre Jülich, 52425 Jülich, Germany.|Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons (ER-C), Research Centre Jülich, 52425 Jülich, Germany.
authors.forename: R E
authors.initials: RE
authors.lastname: Dunin-Borkowski
authors.affiliation: The School of Electronic and Information Engineering, Xi'an Jiaotong University (XJTU), Xi'an 710049, China.|State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University (XJTU), Xi'an 710049, China.
authors.forename: H
authors.initials: H
authors.lastname: Wang
authors.affiliation: Peter Grünberg Institute (PGI-5), Research Centre Jülich, 52425 Jülich, Germany.|Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons (ER-C), Research Centre Jülich, 52425 Jülich, Germany.|The School of Electronic and Information Engineering, Xi'an Jiaotong University (XJTU), Xi'an 710049, China.|State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University (XJTU), Xi'an 710049, China.
authors.forename: C L
authors.initials: CL
authors.lastname: Jia