Size dependent polarization reversal at nanoscale metal-ferroelectric interfaces

Ferroelectric oxides possess a unique set of physical properties that have not been maximally exploited due to a lack of understanding of the origins of the switching behavior. Currently, controversy exists over whether switching in ferroelectric oxides is due to polarization or defect mediated switching. Here, we use ultra-high vacuum scanning tunneling microscopy and atomic force microscopy to investigate the process of polarization reversal and to assess the effect of the electronic structure and conductance on the switching behavior of single crystal BaTiO₃ (001). Measurements of the local density of states revealed the surface switching behavior was initially due to polarization and that a transition occurred to defected mediated switching after repeated switching cycles. Atomic force microscopy investigations of the size effects at nanoscale Au-BaTiO₃ (001) interfaces revealed asymmetric polarization reversal at large interfaces with a convergence to symmetric behavior as the size scale decreased, in agreement with the tunneling-based scanning tunneling microscopy technique.