Department of Chemistry, University of Pennsylvania, 231 S. 34th Street, Philadelphia, Pennslvania 19104 United States.
Dipartimento di Fisica e Chimica, Università degli Studi di Palermo, Via Archirafi 36, 90123 Palermo, Italy.
Nano Lett. 2023 May 24;23(10):4250-4257. doi: 10.1021/acs.nanolett.3c00299. Epub 2023 May 15.
For decades, the spontaneous organization of nanocrystals into superlattices has captivated the scientific community. However, achieving direct control over the formation of the superlattice and its phase transformations has proven to be a grand challenge, often resulting in the generation of multiple symmetries under the same experimental conditions. Here, we achieve direct control over the formation of the superlattice and its phase transformations by modulating the thermal energy of a nanocrystal dispersion without relying on solvent evaporation. We follow the temperature-dependent dynamics of the self-assembly process using synchrotron-based small-angle X-ray scattering. When cooled below -24.5 °C, lead sulfide nanocrystals form micrometer-sized three-dimensional phase-pure body-centered cubic superlattices. When cooled below -35.1 °C, these superlattices undergo a collective diffusionless phase transformation that yields denser body-centered tetragonal phases. These structural changes can be reversed by increasing the temperature of the dispersion and may lead to the direct modulation of the optical properties of these artificial solids.
几十年来，纳米晶体自发形成超晶格一直吸引着科学界。然而，要实现对超晶格形成及其相转变的直接控制，这被证明是一个巨大的挑战，通常会导致在相同的实验条件下产生多种对称性。在这里，我们通过调节纳米晶体分散体的热能，而不依赖于溶剂蒸发，实现了对超晶格形成及其相转变的直接控制。我们使用基于同步加速器的小角 X 射线散射来跟踪自组装过程的温度依赖性动力学。当冷却到-24.5°C以下时，硫化铅纳米晶体形成了微米级的体心立方三维相纯超晶格。当冷却到-35.1°C以下时，这些超晶格经历了一个集体无扩散的相转变，生成了更密集的体心四方相。通过增加分散体的温度，可以使这些结构变化得到逆转，并且可能导致对这些人工固体光学性质的直接调制。
