Université Grenoble Alpes, CEA, INAC, MEM , Grenoble 38000, France.
Université Grenoble Alpes, CEA, CNRS, INAC, UMR5819 SyMMES , Grenoble 38000, France.
J Am Chem Soc. 2017 Nov 8;139(44):15748-15759. doi: 10.1021/jacs.7b07401. Epub 2017 Oct 19.
Ternary metal chalcogenide nanocrystals (NCs) offer exciting opportunities as novel materials to be explored on the nanoscale showing optoelectronic properties tunable with size and composition. CuInS (CIS) NCs are the most widely studied representatives of this family as they can be easily prepared with good size control and in high yield by reacting the metal precursors (copper iodide and indium acetate) in dodecanethiol (DDT). Despite the widespread use of this synthesis method, both the reaction mechanism and the surface state of the obtained NCs remain elusive. Here, we perform in situ X-ray diffraction using synchrotron radiation to monitor the pre- and postnucleation stages of the formation of CIS NCs. SAXS measurements show that the reaction intermediate formed at 100 °C presents a periodic lamellar structure with a characteristic spacing of 34.9 Å. WAXS measurements performed after nucleation of the CIS NCs at 230 °C demonstrate that their growth kinetics depend on the degree of precursor conversion achieved in the initial stage at 100 °C. NC formation requires the cleavage of S-C bonds. We reveal by means of combined 1D and 2D proton and carbon NMR analyses that the generated dodecyl radicals lead to the formation of a new thioether species R-S-R. The latter is part of a ligand double layer, which consists of dynamically bound dodecanethiolate ligands as well as of head-to-tail bound R-S-R molecules. This ligand double layer and a high ligand density (3.6 DDT molecules per nm) are at the origin of the apparent difficulty to functionalize the surface of CIS NCs obtained with the DDT method.
三元金属硫属化物纳米晶体 (NCs) 作为新型材料在纳米尺度上具有令人兴奋的应用前景，其光电性质可以通过尺寸和组成进行调节。CuInS (CIS) NCs 是该家族中研究最广泛的代表，因为它们可以通过在十二硫醇 (DDT) 中反应金属前体 (碘化铜和乙酸铟) 来轻松制备，并且具有良好的尺寸控制和高产率。尽管这种合成方法得到了广泛的应用，但反应机制和获得的 NCs 的表面状态仍然难以捉摸。在这里，我们使用同步辐射进行原位 X 射线衍射，以监测 CIS NCs 形成的成核前和成核后阶段。SAXS 测量表明，在 100°C 下形成的反应中间体具有周期性的层状结构，特征间距为 34.9 Å。在 230°C 下进行 CIS NCs 成核后进行的 WAXS 测量表明，它们的生长动力学取决于在 100°C 的初始阶段实现的前体转化率。NC 的形成需要 S-C 键的断裂。我们通过结合 1D 和 2D 质子和碳 NMR 分析揭示，生成的十二烷基自由基导致新的硫醚物种 R-S-R 的形成。后者是配体双层的一部分，该双层由动态结合的十二硫醇配体以及头到尾结合的 R-S-R 分子组成。这种配体双层和高配体密度（每个 nm 有 3.6 个 DDT 分子）是使用 DDT 方法获得的 CIS NCs 表面难以功能化的原因。
