Atomic mechanism of polarization-controlled surface reconstruction in ferroelectric thin films.

Peng Gao,Bin Feng,Naoya Shibata,Ying-Hao Chu,Ryo Ishikawa,Heng-Jui Liu,Ying Jiang,Yen-Lin Huang,En-Ge Wang,Yuichi Ikuhara

doi:10.1038/ncomms11318

Peng Gao, Bin Feng + Show 8 more

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https://doi.org/10.1038/ncomms11318

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At the ferroelectric surface, the broken translational symmetry induced bound charge should significantly alter the local atomic configurations. Experimentally revealing the atomic structure of ferroelectric surface, however, is very challenging due to the strong spatial variety between nano-sized domains, and strong interactions between the polarization and other structural parameters. Here, we study surface structures of Pb(Zr0.2Ti0.8)O3 thin film by using the annular bright-field imaging. We find that six atomic layers with suppressed polarization and a charged 180° domain wall are at negatively poled surfaces, no reconstruction exists at positively poled surfaces, and seven atomic layers with suppressed polarization and a charged 90° domain wall exist at nominally neutral surfaces in ferroelastic domains. Our results provide critical insights into engineering ferroelectric thin films, fine grain ceramics and surface chemistry devices. The state-of-the-art methodology demonstrated here can greatly advance our understanding of surface science for oxides.

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At the ferroelectric surface, the broken translational symmetry induced bound charge should significantly alter the local atomic configurations
Revealing the surface structure and relation with the subsurface is vital for applications in electronic devices and lies at the heart of the ferroelectric surface chemistry[12,15,16,17]
The commonly used surface probe technique scanning tunnelling microscopy (STM) is usually not suitable to study these insulatorlike ferroelectric oxides and unable to obtain the information underneath the surface

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The broken translational symmetry induced bound charge should significantly alter the local atomic configurations. Despite a lot of simulation efforts have so far been devoted and predicted various properties of ferroelectric surfaces[4,5,6,7,8], only few experimental studies can be found[9,18] By using those bulk-based techniques such as the X-ray characterization[9,18], it is extremely difficult to extract the information of surface structures or determine the relation with subsurface structures because of the strong spatial variety between nano-sized domains and ultrathin thickness of surface reconstruction layers. The ferroelastic domain with the polarization parallel to the surface has a seven-atomic-layer-thick reconstruction layer in which the lattice constant is contracted B2.5% and the in-plane polarization gradually decreases and rotates towards to the free surface, forming an unusual charged 90° domain wall in the (100) plane. The ability to simultaneously determine the structures of surface and subsurface provides a unique and powerful method to explore the surfaces of functional materials in particular for those insulators, which are usually not suitable for STM study

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