Possible absence of critical thickness and size effect in ultrathin perovskite ferroelectric films

作者：Gao, Peng^*; Zhang, Zhangyuan; Li, Mingqiang; Ishikawa, Ryo; Feng, Bin; Liu, Heng-Jui; Huang, Yen-Lin; Shibata, Naoya; Ma, Xiumei; Chen, Shulin; Zhang, Jingmin; Liu, Kaihui; Wang, En-Ge; Yu, Dapeng; Liao, Lei^*; Chu, Ying-Hao; Ikuhara, Yuichi^*

来源：Nature Communications, 2017, 8(1): 15549.

DOI：10.1038/ncomms15549

• SURFACE

Although the size effect in ferroelectric thin films has been known for long time, the underlying mechanism is not yet fully understood and whether or not there is a critical thickness below which the ferroelectricity vanishes is still under debate. Here, we directly measure the thickness-dependent polarization in ultrathin PbZr0.2Ti0.8O3 films via quantitative annular bright field imaging. We find that the polarization is significantly suppressed for films <10-unit cells thick (similar to 4 nm). However, approximately the polarization never vanishes. The residual polarization is similar to 16 mu Ccm(-2) (similar to 17%) at 1.5-unit cells (similar to 0.6 nm) thick film on bare SrTiO3 and similar to 22 mu Ccm(-2) at 2-unit cells thick film on SrTiO3 with SrRuO3 electrode. The residual polarization in these ultrathin films is mainly attributed to the robust covalent Pb-O bond. Our atomic study provides new insights into mechanistic understanding of nanoscale ferroelectricity and the size effects.

• 出版日期2017-6-6
• 单位中国科学院; 南方科技大学; 北京大学; 武汉大学