Qi Zhang1, Sergei Prokhorenko2, Yousra Nahas2, Lin Xie3, Laurent Bellaiche2, Alexei Gruverman4 and Nagarajan Valanoor1
1School of Materials Science and Engineering, The University of New South Wales, Sydney, New South Wales 2052, Australia; 2 Physics Department and Institute for Nanoscience and Engineering, University of Arkansas, Fayetteville, AR 72701, USA; 3Department of Physics, Southern University of Science and Technology, Shenzhen, 518055 China; 4 Department of Physics and Astronomy, University of Nebraska, Lincoln, NE 68588, USA
A new type of nanoscale ferroelectric domains, termed as “bubble domains”, has been observed in ultrathin epitaxial PbZr0.2Ti0.8O3/SrTiO3/PbZr0.2Ti0.8O3 ferroelectric sandwich structures. It is confirmed that these bubble domains are laterally confined spheroids of sub-10 nm size with local dipoles opposite to the macroscopic polarization of their surrounding ferroelectric matrix via high-resolution piezoresponse force microscopy (PFM), and aberration-corrected atomic-resolution scanning transmission electron microscopy.
Here we demonstrate the deterministic and reversible transformation of nanoscale ferroelectric bubbles into cylindrical domains using a scanning probe microscopy (SPM) approach. The bubble domains can be erased by applying a mechanical force via the SPM tip, and on the other hand, application of an electrical pulse with a specific combination of amplitude and duration can recreate the bubble domain state. This combination of mechanical and electrical passes is essential for realization of reversible transformation as application of only electrical pulses results in complete erasure of the bubble domain state. Effective Hamiltonian‐based simulations reproduce phase sequences for both the mechanical and electric passes and confirm the intrinsic nature of these transitions. This simple and effective pathway for switching between various topological defect states may be exploited for emergent devices.
About the speaker
One of the three inaugural Women in FLEET fellows, Dr Peggy (Qi) Zhang studies topological domains in ultrathin, ferroelectric materials, investigating nanoscale bubble domains and topological transitions as part of FLEET’s research theme 1, working with Nagarajan Valanoor at UNSW.
Peggy characterises topological domains using piezoresponse force microscopy. The nanoscale ferroelectric domains she studies have topological domain structures of the smallest size so-far achieved. The rotated polarisation and enhanced electromechanical response of these domains, makes them a promising candidate for novel, low-energy memory devices. She also studies design and fabrication of nanoscale memory devices using e-beam lithography and e-beam evaporation.