Department of Physics and Astronomy , Iowa State University, and Ames Laboratory , Ames , Iowa 50011 , United States.
Department of Materials Science and Engineering , Iowa State University, and Ames Laboratory , Ames , Iowa 50011 , United States.
J Am Chem Soc. 2018 Jul 5;140(26):8236-8245. doi: 10.1021/jacs.8b03895. Epub 2018 Jun 26.
We elucidate how nanocrystals "bond" to form ordered structures. For that purpose we consider nanocrystal configurations consisting of regular polygons and polyhedra, which are the motifs that constitute single component and binary nanocrystal superlattices, and simulate them using united atom models. We compute the free energy and quantify many body effects, i.e., those that cannot be accounted for by pair potential (two-body) interactions, further showing that they arise from coalescing vortices of capping ligands. We find that such vortex textures exist for configurations with local coordination number ≤6. For higher coordination numbers, vortices are expelled and nanocrystals arrange in configurations with tetrahedral or icosahedral order. We provide explicit formulas for the optimal separations between nanocrystals, which correspond to the minima of the free energies. Our results quantitatively explain the structure of superlattice nanocrystals as reported in experiments and reveal how packing arguments, extended to include soft components, predict ordered nanocrystal aggregation.
我们阐明了纳米晶体如何“键合”形成有序结构。为此，我们考虑了由正多边形和多面体组成的纳米晶体构型，这些是构成单组分和双组分纳米晶体超晶格的图案，并使用统一原子模型对其进行了模拟。我们计算了自由能并量化了多体效应，即那些不能用对势能（二体相互作用）来解释的效应，进一步表明它们是由帽状配体的合并涡旋引起的。我们发现，对于局部配位数≤6 的构型，存在这种涡旋结构。对于更高的配位数，涡旋被排出，纳米晶体以四面体或二十面体有序排列。我们提供了纳米晶体之间最佳分离的显式公式，这些公式对应于自由能的最小值。我们的结果定量解释了实验中报道的超晶格纳米晶体的结构，并揭示了如何将扩展到包括软组件的包装论点，预测有序的纳米晶体聚集。
