Persistence of ferroelectricity close to unit-cell thickness in structurally disordered Aurivillius phases

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Keeney, Lynette
Saghi, Zineb
O'Sullivan, Marita
Alaria, Jonathan
Schmidt, Michael
Colfer, Louise
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Multiferroics intertwine ferroelectric and ferromagnetic properties, allowing for novel ways of manipulating data and storing information. To optimize the unique Bi6TixFeyMnzO18 (B6TFMO), multiferroic, ultrathin (<7 nm) epitaxial films were synthesized by direct liquid injection chemical vapor deposition (DLI-CVD). Epitaxial growth is, however, confounded by the volatility of bismuth, particularly when utilizing a postgrowth anneal at 850 °C. This results in microstructural defects, intergrowths of differing Aurivillius phases, and formation of impurities. Improved single-step DLI-CVD processes were subsequently developed at 710 and 700 °C, enabling lowering of crystallization temperature by 150 °C and significantly enhancing film quality and sample purity. Ferroelectricity is confirmed in 5 nm (1 unit-cell thick) B6TFMO films, with tensile epitaxial strain enhancing the piezoresponse. In-plane ferroelectric switching is demonstrated at 1.5 unit-cell thickness. The persistence of stable ferroelectricity near unit-cell thickness in B6TFMO, both in-plane and out-of-plane, is significant and initiates possibilities for miniaturizing novel multiferroic-based devices.
Bismuth titanate , Thin films , Polarization , Technology , Behavior , Epitaxy
Keeney, L., Saghi, Z., O'Sullivan, M., Alaria, J., Schmidt, M. and Colfer, L. (2020) 'Persistence of ferroelectricity close to unit-cell thickness in structurally disordered Aurivillius phases', Chemistry of Materials, 32(24), pp. 10511-10523. doi: 10.1021/acs.chemmater.0c03454
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© 2020, American Chemical Society. This document is the Accepted Manuscript version of a Published Work that appeared in final form in Chemistry of Materials, after technical editing by the publisher. To access the final edited and published work see