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Abstract
This dissertation is focused on the study of polarization-related electronic properties of ferroelectric thin films and complex-oxide heterostructures by Scanning Probe Microscopy (SPM) techniques.
Switching characteristics of polyvinylidene fluoride trifluoroethylene (PVDF-TrFE) nanostructures fabricated by Langmuir-Blodgett (L-B) technique has been investigated by visualizing the field-time dependence of the evolving domain configurations using Piezoresponse Force Microscopy (PFM). The nanoscale features of the switching process associated with defects in conformation and molecular packing in the L-B processed films include remote domain nucleation and spatially nonuniform wall velocity. A distinct feature of domain dynamics in spin-coated PVDF-TrFE films is roughening of the domain walls during switching to the preferred polarization state as opposed to smooth domain boundaries during switching to the opposite direction. The observed switching behavior in spin-cast films is explained by a combined effect of the spatially uniform built-in electric field and local disorder potential.
Single-crystalline BaTiO3 lamellae have been used as a model system to investigate the effect of scaling on domain topologies and dynamics of complex domain boundaries (superdomain boundaries). The distinct consequences of the scaling is observation of the meso-scale in-plane flux closure domain topology, and boundary dynamics determined by the interplay of rate of screening charge accumulation and depolarizing fields of the newly switched domains.
In LaAlO3/SrTiO3 (LAO/STO) heterostructures, a switchable electromechanical response has been observed, which is attributed to the motion of oxygen vacancies through the LAO layer thickness. These electrically induced reversible changes in bulk stoichiometry of the LAO layer are a signature of a possible mechanism for nanoscale 2-dimensional electron gas control on LAO/STO interfaces.
