Debye Institute for Nanomaterials Science, Utrecht University, CS Utrecht 3584, The Netherlands.
Laboratory of Physical Chemistry, Eindhoven University of Technology, AZ Eindhoven 5612, The Netherlands.
J Am Chem Soc. 2022 May 11;144(18):8096-8105. doi: 10.1021/jacs.2c00423. Epub 2022 Apr 28.
The growth of two-dimensional platelets of the CdX family (X = S, Se, or Te) in an organic solvent requires the presence of both long- and short-chain ligands. This results in nanoplatelets of atomically precise thickness and long-chain ligand-stabilized Cd top and bottom surfaces. The platelets show a bright and spectrally pure luminescence. Despite the enormous interest in CdX platelets for optoelectronics, the growth mechanism is not fully understood. Riedinger studied the reaction without a solvent and showed the favorable role for short-chain carboxylates for growth in two dimensions. Their model, based on the total energy of island nucleation, shows favored side facet growth growth on the top and bottom surfaces. However, several aspects of the synthesis under realistic conditions are not yet understood: Why are both short- and long-chain ligands required to obtain platelets? Why does the synthesis result in both isotropic nanocrystals and platelets? At which stage of the reaction is there bifurcation between isotropic and 2D growth? Here, we report an study of the CdSe nanoplatelet reaction under practical synthesis conditions. We show that without short-chain ligands, both isotropic and mini-nanoplatelets form in the early stage of the process. However, most remaining precursors are consumed in isotropic growth. Addition of acetate induces a dramatic shift toward nearly exclusive 2D growth of already existing mini-nanoplatelets. Hence, although myristate stabilizes mini-nanoplatelets, mature nanoplatelets only grow by a subtle interplay between myristate and acetate, the latter catalyzes fast lateral growth of the side facets of the mini-nanoplatelets.
二维 CdX 家族（X=S、Se 或 Te）纳米片在有机溶剂中的生长需要长链和短链配体的同时存在。这导致了原子精确厚度的纳米片和长链配体稳定的 Cd 顶底表面。这些纳米片表现出明亮且光谱纯的发光。尽管人们对 CdX 纳米片在光电子学方面非常感兴趣，但生长机制尚未完全理解。Riedinger 研究了无溶剂反应，并表明短链羧酸对二维生长有利。他们的模型基于岛核形成的总能量，表明有利于侧面对生长和顶底表面的生长。然而，在实际条件下进行合成的几个方面尚未得到理解：为什么获得纳米片需要长链和短链配体？为什么合成会产生各向同性纳米晶体和纳米片？在反应的哪个阶段会发生各向同性和 2D 生长之间的分叉？在这里，我们报告了在实际合成条件下对 CdSe 纳米片反应的深入研究。我们表明，没有短链配体，各向同性和迷你纳米片在反应的早期阶段形成。然而，大多数剩余的前体都消耗在各向同性生长中。添加醋酸盐会导致几乎只进行已存在的迷你纳米片的二维生长的急剧转变。因此，虽然肉豆蔻酸盐稳定了迷你纳米片，但成熟的纳米片仅通过肉豆蔻酸盐和醋酸盐之间的微妙相互作用生长，后者催化迷你纳米片的侧面对的快速横向生长。
