Université Pierre et Marie Curie Paris 6, UMR 7070, LM2N, BP 52, 4 place Jussieu, 75005 Paris, France.
Nano Lett. 2012 Oct 10;12(10):5292-8. doi: 10.1021/nl3029009. Epub 2012 Sep 21.
Spontaneous separation of single from polycrystalline 5 nm gold nanocrystals (NCs) is observed in colloidal solution. This segregation takes place upon self-assembling of single crystalline NCs at the air-solvent interface and in precipitated superlattices. Polycrystalline NCs are observed to remain in the suspension. Transmission electron microscopy analysis of the size distribution of NCs issued from the different populations indicates that the NC size does not change from each other, excluding therefore any size segregation in this process. Using both low-frequency Raman scattering and X-ray diffraction provides reliable characterization of nanocrystallinity for each population of NCs, thus confirming the crystallinity segregation. The single crystalline NCs are found by electron diffraction to self-assemble into close-packed superlattices with long-range translational and orientational ordering, while polycrystalline NCs behave like spheres with no preferential orientation. The face-to-face orientational ordering, which is only observed for single crystalline NCs, supports the relevance of the specific crystallinity-related morphologies of these NCs in their better ability to self-assemble. Exploiting this spontaneous segregation would open up a simple alternative to other demanding routes for controlling crystallinity of nanocrystals and optimizing their properties for potential applications.
在胶体溶液中观察到单晶 5nm 金纳米晶体（NCs）从多晶 NCs 中自发分离。这种分离发生在单晶 NCs 在空气-溶剂界面处自组装和沉淀超晶格时。多晶 NCs 被观察到仍留在悬浮液中。对来自不同群体的 NCs 的尺寸分布的透射电子显微镜分析表明，NC 尺寸彼此之间没有变化，因此排除了该过程中的任何尺寸分离。使用低频 Raman 散射和 X 射线衍射对 NCs 的每个群体进行可靠的纳米结晶度表征，从而确认了结晶度分离。电子衍射发现单晶 NCs 自组装成具有长程平移和取向有序的密堆积超晶格，而多晶 NCs 则表现为无择优取向的球体。仅观察到单晶 NCs 的面对面取向有序性，支持这些 NCs 特定结晶度相关形态在其更好的自组装能力中的相关性。利用这种自发分离将为控制纳米晶体的结晶度和优化其性能以用于潜在应用提供一种简单的替代其他苛刻途径。
