School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14853, United States.
Nano Lett. 2012 Sep 12;12(9):4791-8. doi: 10.1021/nl3026289. Epub 2012 Aug 17.
The self-assembly of colloidal nanocrystals into ordered superstructures depends critically on the shape of the nanocrystal building blocks. We investigated the self-assembly of cubic PbSe nanocrystals from colloidal suspensions in real-time using in situ synchrotron-based X-ray scattering. We combined small-angle and wide-angle scattering to investigate the translational ordering of nanocrystals and their orientational ordering in the lattice sites, respectively. We found that cubic PbSe nanocrystals assembled into a face-up (i.e., [100] normal to the interface) configuration at the liquid/substrate interface whereas nanocubes at the liquid/air interface assume a corner-up (i.e., [111] normal to the interface) configuration. The latter nanocrystal superlattice displays polymorphism as a function inter-NC separation distance. We explain the observed superlattice structure polymorphs in terms of the interactions directing the self-assembly. Insights into the directed self-assembly of superlattices gained from this study have important implication on the future development of nanocrystals as building blocks in artificial solids.
胶体纳米晶体自组装成有序超结构，关键取决于纳米晶体构建块的形状。我们使用基于同步加速器的原位 X 射线散射实时研究了立方 PbSe 纳米晶体从胶体悬浮液中的自组装。我们结合小角和广角散射，分别研究了纳米晶体的平移有序性及其在晶格位置的取向有序性。我们发现立方 PbSe 纳米晶体在液体/基底界面处自组装成面朝上（即[100]垂直于界面）的配置，而在液体/空气界面处的纳米立方则采用角朝上（即[111]垂直于界面）的配置。后者的纳米晶体超晶格作为 NC 分离距离的函数显示出多晶型性。我们根据指导自组装的相互作用解释了观察到的超晶格结构多晶型。本研究中获得的超晶格定向自组装的见解对纳米晶体作为人工固体中构建块的未来发展具有重要意义。
