Wang Zhipeng, Byun Jinho, Wang Zhen, Xing Yaolong, Seo Jinsol, Lee Jaekwang, Oh Sang Ho
Department of Energy Science, Sungkyunkwan University, Suwon, 16419, Republic of Korea.
Department of Physics, Pusan National University, Busan, 46241, Republic of Korea.
Adv Mater. 2023 Oct;35(40):e2303051. doi: 10.1002/adma.202303051. Epub 2023 Aug 7.
Polar surfaces are intrinsically unstable and thus highly reactive due to the uncompensated surface charges. The charge compensation is accompanied by various surface reconstructions, establishing novel functionality for their applications. The present in situ atomic-scale electron microscopy study directly shows that the atomic step and step-assisted reconstruction play central roles in the charge compensation of polar oxide surfaces. The flat (LaO) -terminated LaAlO (001) polar surface, when annealed at high temperature in vacuum, transits to the (015) vicinal surface via the dynamic motion and interaction of atomic steps. While the (015) vicinal surface possesses zero polarization along the surface normal, a thermodynamic ground state is achieved when the in-plane polarization is fully compensated via the reconstruction of step-edge atoms; the step-edge La atoms are displaced from their ordinary atomic sites toward the adjacent Al step-edge sites, resulting in the formation of negatively charged La vacancies at the corresponding step edges. As confirmed by first-principles calculations, the observed step reconstruction of (015) vicinal surface can completely cancel both out-of-plane and in-plane electric fields. This hitherto unknown mechanism reveals the central role of step reconstruction in stabilizing a polar surface, providing valuable insights for understanding the novel charge compensation mechanism accompanied by the step reconstruction.
极性表面本质上是不稳定的，因此由于未补偿的表面电荷而具有高反应性。电荷补偿伴随着各种表面重构，为其应用建立了新的功能。目前的原位原子尺度电子显微镜研究直接表明，原子台阶和台阶辅助重构在极性氧化物表面的电荷补偿中起着核心作用。平整的（LaO）端接的LaAlO（001）极性表面在真空中高温退火时，通过原子台阶的动态运动和相互作用转变为（015）近邻表面。虽然（015）近邻表面沿表面法线方向的极化强度为零，但当通过台阶边缘原子的重构使面内极化完全补偿时，就达到了热力学基态；台阶边缘的La原子从其正常原子位置向相邻的Al台阶边缘位置位移，导致在相应的台阶边缘形成带负电的La空位。第一性原理计算证实，观察到的（015）近邻表面的台阶重构可以完全抵消面外和面内电场。这种迄今未知的机制揭示了台阶重构在稳定极性表面中的核心作用，为理解伴随台阶重构的新型电荷补偿机制提供了有价值的见解。
