Dynamics and Removal Pathway of Edge Dislocations in Imperfectly Attached PbTe Nanocrystal Pairs: Toward Design Rules for Oriented Attachment

Using in situ high-resolution TEM, we study the structure and dynamics of well-defined edge dislocations in imperfectly attached PbTe nanocrystals. We identify that attachment of PbTe nanocrystals on both {100} and {110} facets gives rise to b = a/2⟨110⟩ edge dislocations. Based on the Burgers vector of individual dislocations, we can identify the glide plane of the dislocations. We observe that defects in particles attached on {100} facets have glide planes that quickly intersect the surface, and HRTEM movies show that the defects follow the glide plane to the surface. For {110} attached particles, the glide plane is collinear with the attachment direction, which does not provide an easy path for the dislocation to reach the surface. Indeed, HRTEM movies of dislocations for {110} attached particles show that defect removal is much slower. Further, we observe conversion from pure edge dislocations in imperfectly attached particles to dislocations with mixed edge and screw character, which has important implications for crystal growth. Finally, we observe that dislocations initially closer to the surface have a higher speed of removal, consistent with the strong dislocation free surface attractive force. Our results provide important design rules for defect-free attachment of preformed nanocrystals into epitaxial assemblies

本研究借助原位高分辨透射电子显微镜（in situ high-resolution TEM），对结合不完全的碲化铅（PbTe）纳米晶中规整刃型位错的结构与动力学行为展开探究。我们发现，在{100}与{110}晶面均发生结合的碲化铅纳米晶，会产生b = a/2⟨110⟩型刃型位错。基于单个位错的柏格斯矢量（Burgers vector），可确定位错的滑移面。实验观察到，结合于{100}晶面的纳米晶内部缺陷，其滑移面会快速与晶体表面相交，高分辨透射电子显微镜（HRTEM）序列影像显示，此类缺陷会沿滑移面运动至晶体表面。而结合于{110}晶面的纳米晶，其滑移面与结合方向共线，无法为位错抵达晶体表面提供便捷路径。相应地，针对{110}晶面结合纳米晶的位错观测序列影像显示，缺陷的移除速率要慢得多。此外，我们还观察到，结合不完全的纳米晶内的纯刃型位错，会转变为刃螺混合型位错，这一现象对晶体生长具有重要意义。最终我们发现，初始位置更接近晶体表面的位错，其移除速率更高，这与位错受自由表面的强吸引力作用的结论相符。本研究结果为将预制纳米晶无缺陷组装为外延组装体提供了重要的设计准则。