Ferroelectric materials are a promising platform for energy-efficient electronic and optical devices. However, determining the polarization direction, magnitude, and domain configuration, as key properties in applications, remains a challenge in ultrathin layers and multilayers. In common ferroelectric materials, thickness reduction leads to a degradation of ferroelectric properties. On the other hand, recent discoveries have identified materials which are non-polar in bulk but become ferroelectric at the nanoscale. Many open questions thus remain in nanoscale ferroelectricity, such as the detriments and benefits of size effects, the role of ionic migration and electronic polarization, and the potential of ferroelectrics in devices.

I will present my previous work and future goals in exploring these questions along the following lines. I will highlight the findings on the emergence and evolution of ferroelectricity in oxide heterostructures. Using in situ second harmonic generation, a tool for monitoring polarization during deposition, I discovered overlooked transient effects with lasting consequences on the final ferroelectric response. Based on these findings, I will emphasize pathways to achieve robust polarization in nanoscale films, such as tuning the depolarizing field and achieving synergy in the polarization direction set at interfaces. I will then present means of elucidating the polarization state and complex domain configurations in buried layers and superlattices. Finally, I will demonstrate how ferroelectric polarization can be used to control properties of heterostructures, such as electroresistance.