小角超快电子衍射研究十二硫醇修饰的金纳米粒子超晶体的有序/无序动力学
Order/disorder dynamics in a dodecanethiol-capped gold nanoparticles supracrystal by small-angle ultrafast electron diffraction
摘要：
在金属纳米颗粒（NP）超晶体中，金属核提供一些关键特性，例如磁化、等离子体响应或导电性，配体分子产生其他特性，例如溶解性、组装或与生物分子的相互作用。这些超晶体的形成取决于许多力之间复杂的相互作用，一些来自核心，一些来自配体。目前，还没有已知的方法来表征局部秩序的配体分子或其动力学与原子空间分辨率。在这里，我们开发了一种基于小角度超快电子衍射结合角度互相关分析的方法来表征二维超晶体的十二硫醇涂层金纳米颗粒。我们检索的配位体的静态排列，表明在平衡时，他们为了在一个优先取向的NP表面上，并在整个二维超晶体。在光激发时，位置的无序诱导的超晶体，而其整体均匀性是令人惊讶地发现，瞬时增加。这表明，瞬态退火的超晶体发生在几皮秒（ps）。这种方法将使纳米组装材料的动态结构特性的系统研究，含有轻元素，相关的生物应用。
英文摘要：
In metal nanoparticles (NPs) supracrystals, the metallic core provides some key properties, e.g. magnetization, plasmonic response or conductivity, with the ligand molecules giving rise to others like solubility, assembly or interaction with biomolecules. The formation of these supracrystals depends on a complex interplay between many forces, some stemming from the core, some from the ligands. At present, there is no known approach to characterize the local order of ligand molecules or their dynamics with atomic spatial resolution. Here, we develop a methodology based on small-angle ultrafast electron diffraction combined with angular cross-correlation analysis to characterize a two-dimensional supracrystal of dodecanethiol-coated gold NPs. We retrieve the static arrangement of the ligands, showing that at equilibrium they order in a preferential orientation on the NPs surface and throughout the two-dimensional supracrystal. Upon light excitation, positional disorder is induced in the supracrystal, while its overall homogeneity is surprisingly found to transiently increase. This suggests that transient annealing of the supracrystal takes place within few picoseconds (ps). This methodology will enable the systematic investigation of the dynamical structural properties of nano-assembled materials containing light elements, relevant for biological applications.
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