Real-Time Monitoring of Nanoscale Polarization Switching
School of Engineering researchers have visualized nanoscale jumps in a ferroelectric’s polarization that are thought to play a key role in how well some ferroelectric devices function.
Electrically polarize a ferroelectric material and tiny discontinuous jumps can appear in the strength of its polarization. These jumps, known as Barkhausen pulses, create noise that can inhibit the functionality of nanoscale optical and electronic devices that rely on polarization switching. As such, researchers want to understand the pulses’ origin. Until now, however, the pulses had only been measured in terms of noise and a material’s average properties. Now, using a technique that they developed for imaging the real-time motion of ferroelectric domains, Vasiliki Tileli and her colleagues at EPFL in Lausanne have observed the motion and origin of Barkhausen pulses at the nanoscale. The researchers hope that their demonstration will lead to a better understanding of the kinetics of polarization switching, enabling its use in novel devices for electro-optical, computing, and data storage applications.
For their experiments, the researchers placed a thin layer of a BaTiO3, a single-crystal ferroelectric, on a microdevice. BaTiO3 consists of groups of 33 nm-wide needle-shaped domains. Using a transmission electron microscope, the researchers tracked the motion of the needles when they applied an electric field to the BaTiO3.
The needle domains formed a herringbone pattern and could move forward and backward upon application of an electric field. Observations of the domain evolution showed that an individual domain jumped forward to its new position when the one perpendicular to it retracted. Tileli and her colleagues conclude that these discreet jumps—the Barkhausen pulses--arise from extended electromechanical fields around perpendicular domain walls and the needle tips, that pinned their movement.