Li, Yaqi;
(2023)
Strain and electrostatic engineering in ferroelectric-dielectric superlattices.
Doctoral thesis (Ph.D), UCL (University College London).
Abstract
This thesis focuses on the study of nanoscale domain structures in heterostructures of the prototypical ferroelectric lead titanate (PbTiO3). Epitaxial multilayers and superlattices consisting of ferroelectric lead titanate (PbTiO3) and dielectric strontium titanate (SrTiO3) are exploited to simultaneously manipulate both the mechanical and electrostatic boundary conditions and hence to study their influence on the domain structures and related properties. Off-axis radio-frequency magnetron sputtering was used to fabricate epitaxial thin films and heterostructures, while a combination of laboratory and synchrotron x-ray diffraction, and atomic and piezoresponse force microscopies were used to characterise their structure and domain patterns. The thesis initially focuses on tailoring domain structures through conventional strain engineering, where a thin film or multilayer is strained through coherent epitaxy on a crystalline substrate. Unusual polarisation textures are observed and discussed, including flux closure patterns, polar vortices, and zig-zag domains that are normally forbidden in the bulk. Despite its many possibilities, however, conventional strain engineering is also somewhat restrictive due to rigid substrate clamping and limited available substrates. Therefore, the focus of the thesis then turns to free-standing ferroelectric-dielectric superlattices, where the thin film components exert strain on each other elastically. An unusual in-plane domain asymmetry is reported in the curved free-standing PbTiO3/SrTiO3 superlattices, and the role of domains in accommodating the macroscopic curvature of the free-standing heterostructure is examined.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Strain and electrostatic engineering in ferroelectric-dielectric superlattices |
| Language: | English |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > London Centre for Nanotechnology |
| URI: | https://discovery-pp.ucl.ac.uk/id/eprint/10164061 |
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