| Summary: | Observations of enhanced conductivity in ferroelectric domain walls have led to many new electronic applications being envisioned, such as domain wall memistors. A crucial prerequisite to realising such devices is the control over the nucleation and position of the domain walls. This thesis presents different methods of exerting this control in mesoscale ferroelectric capacitors. Investigations 'Were carried out using thin single-crystal slices of the uniaxial ferroelectric KTiOP04 (KTP), embedded into a co-planar capacitor structure. Piezoresponse Force Microscopy (PFM) showed the domain nucleation positions in these capacitors were unpredictable. As ferroelectric domains switch polarisation with an applied electric field, inhomogeneous electric field distributions were created by design in KTP lamellae using Focused Ion Beam (FIB) milled holes and patterned electrode geometries. This inhomogeneity produced localised regions of enhanced field (hot-spots) and diminished field (cold-spots). Investigations showed that when a switching field was applied to these samples, nucleation initialised at the hot-spot locations, injecting domain wall pairs. This meant that the ferroelectric could be engineered to allow site-specific injection of domain walls. These results were extended by creating different magnitudes of hot-spots, allowing the sequential injection of domain walls, to provide multiple domain states required for a domain wall memristor. Further investigation showed that hot-spots Increased domain wall mobility whereas cold-spots could pin domain walls. This effect was utilised to create asymmetric domain wall mobilities and periodic pinning sites, prerequisites for domain wall ratchet devices. Finally, investigations using variations in the ferroelectric thickness were carried out. Switching occurred in smaller thicknesses first, with positive thickness gradients yielding decreased domain wall mobility. A ferroelectric with a ramped topography, then allowed the makings of the first ferroelectric domain wall diode.
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