6月29日冶金大讲堂：Topological defect engineering in ferroelectrics: from domain wall memory to emergent functionalities（铁电体中的拓扑缺陷工程：从畴壁存储到应急功能）
Ferroelectric domain wall memory device - The discovery of electrical conductivity in specific types of ferroelectric domain walls gave rise to “domain wall nanoelectronics”, a technology in which the wall (rather than the domain) stores information. We have recently demonstrated a prototype non-volatile ferroelectric domain wall memory, scalable to below 100 nm, whose binary state is defined by the existence or absence of conductive walls. The device can be read-out nondestructively at moderate voltages (<3V), exhibits relatively high OFF-ON ratios (~103) with excellent endurance and retention characteristics, and possesses multilevel data storage capacity.
Nanoscale bubble domains - This new type of nanoscale ferroelectric domains has been observed in ultrathin epitaxial PbZr0.2Ti0.8O3/SrTiO3/PbZr0.2Ti0.8O3sandwich structures. Using PFM and aberration-corrected atomic-resolution STEM mapping techniques, it is confirmed that the bubble domains are laterally confined spheroids of sub-10 nm size with local dipoles opposite to the macroscopic polarization of their surrounding ferroelectric matrix. An incommensurate phase and symmetry breaking is found within these domains, which result in local polarization rotation and hence a mixed Néel-Bloch-like character to the bubble domain walls.
These findings highlight the richness of polar topologies that may develop in ultrathin ferroelectric structures and bring forward the prospect of emergent electronic functionalities due to topological transitions.
Nagarajan Valanoor，澳大利亚新南威尔士大学终身教授，主要研究方向为纳米氧化物薄膜材料的界面性能，在澳大利亚、美国、日本等国家获各类学术成就奖10余次，是该领域享有国际声誉的著名学者。在Science, Nature Materials, Nature Communications, Nano Letters, Advanced Materials, Phys. Rev. Lett等国际顶级杂志上发表论文150多篇，被引用7000多次，H因子36；出版专著6部；长期担任Materials Research Society Communications, IEEE等著名杂志主编（副主编），MRS, ISAF, ISIF等国际会议（分会）主席等职务。