Exploring the fundamental effects of miniaturisation on ferroelectrics by focused ion beam processing of single crystal material

Abstract
The focused ion beam microscope has been used to make thin lamellae and nanoscale washers from single crystals of BaTiO₃. The thin lamellae were used as the dielectric layers in `thin film' capacitor heterostructures, and investigated for their functional behaviour. This gave insight into the dielectric properties of thin film ferroelectrics without the usual influences of substrate clamping, grain boundaries, through film microstructural and defect chemistry variation, and inherent asymmetry associated with the electrode-dielectric boundary conditions. In essence the investigation allowed the inherent dielectric response of thin film ferroelectrics to be examined. It was found that, unlike any conventionally grown thin film capacitor heterostructures made to date, the single crystal lamellae demonstrated bulk-like functional behaviour down to a thickness of ~75nm. The fabrication of nanoscale washers, or doughnuts, has allowed an investigation into the kinds of domain configurations that occur in highly constrained and surface-dominated 3 Dimensional architectures using Scanning Transmission Electron Microscopy. Initial work shows the existence of `herringbone' domain structures which look to be shape or field compensating.