Chen Jun, Ryu Gyeong Hee, Sinha Sapna, Warner Jamie H
Department of Materials , University of Oxford , Parks Road , Oxford OX1 3PH , United Kingdom.
ACS Nano. 2019 Jul 23;13(7):8256-8264. doi: 10.1021/acsnano.9b03645. Epub 2019 Jun 26.
We study the atomic structure and dynamics of defects and grain boundaries in monolayer PdSe using annular dark field scanning transmission electron microscopy. The PdSe monolayers are reproducibly created by thermally induced phase transformation of few-layered PdSe films in an heating holder in the TEM to promote Se loss. A variety of point vacancies, one-dimensional defects, grain boundaries (GBs), and defect ring complexes are directly observed in monolayer PdSe, which show a series of dynamics triggered by electron beam irradiation. High mobility of vacancies leads to self-healing of point vacancies by migration to the edge and subsequent edge etching under beam irradiation. Specific defects for PdSe are stabilized by the formation of Se-Se bonds, which can shift in a staggered way to buffer strain, forming a wave-like one-dimensional defect. Bond rotations are also observed and play an important role in defect and grain boundary dynamics in PdSe during vacancy production. The GBs form in a meandering pathway and migrate by a sequence of Se-Se bond rotations without large-scale vacancy formation. In the GB corners and tilted GBs, other highly symmetric vacancy defects also occur to adapt to the orientation change. These results give atomic level insights into the defects and grain boundaries in PdSe 2D monolayers.
我们使用环形暗场扫描透射电子显微镜研究了单层 PdSe 中缺陷和晶界的原子结构与动力学。通过在透射电子显微镜的加热支架中对少层 PdSe 薄膜进行热诱导相变以促进硒损失，可重复性地制备出 PdSe 单层。在单层 PdSe 中直接观察到了各种点空位、一维缺陷、晶界（GBs）和缺陷环复合体，它们展示了由电子束辐照引发的一系列动力学过程。空位的高迁移率导致点空位通过迁移到边缘并在束辐照下随后进行边缘蚀刻而实现自我修复。PdSe 的特定缺陷通过形成 Se-Se 键得以稳定，这些键可以交错方式移动以缓冲应变，形成波浪状的一维缺陷。还观察到键的旋转，并且在空位产生过程中，键的旋转在 PdSe 的缺陷和晶界动力学中起着重要作用。晶界以蜿蜒路径形成，并通过一系列 Se-Se 键的旋转进行迁移，而不会形成大规模的空位。在晶界角和倾斜的晶界中，也会出现其他高度对称的空位缺陷以适应取向变化。这些结果为 PdSe 二维单层中的缺陷和晶界提供了原子层面的见解。
