van der Sluijs Maaike M, Vliem Jara F, de Wit Jur W, Rietveld Jeppe J, Meeldijk Johannes D, Vanmaekelbergh Daniel A M
Condensed Matter & Interfaces, Debye Institute for Nanomaterials Science, Utrecht University, 3584 CC Utrecht, The Netherlands.
Electron Microscopy Centre, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht, Netherlands.
Chem Mater. 2023 Sep 28;35(19):8301-8308. doi: 10.1021/acs.chemmater.3c01900. eCollection 2023 Oct 10.
Cation exchange has become a major postsynthetic tool to obtain nanocrystals with a combination of stoichiometry, size, and shape that is challenging to achieve by direct wet-chemical synthesis. Here, we report on the transformation of highly anisotropic, ultrathin, and planar PbS nanosheets into CdS nanosheets of the same dimensions. We monitor the evolution of the Cd-for-Pb exchange by TEM, HAADF-STEM, and EDX. We observe that in the early stages of the exchange the sheets show large in-sheet voids that repair spontaneously upon further exchange and annealing, resulting in ultrathin, planar, and crystalline CdS nanosheets. After cation exchange, the nanosheets show broad sub-band gap luminescence, as often observed in CdS nanocrystals. The photoluminescence excitation spectrum reveals the heavy- and light-hole exciton features, with very strong quantum confinement and large electron-hole Coulomb energy, typical for 2D ultrathin Cd-chalcogenide nanosheets.
阳离子交换已成为一种主要的合成后工具，用于获得具有特定化学计量比、尺寸和形状组合的纳米晶体，而这些通过直接湿化学合成很难实现。在此，我们报道了将高度各向异性、超薄且平面的硫化铅纳米片转化为相同尺寸的硫化镉纳米片。我们通过透射电子显微镜（TEM）、高角度环形暗场扫描透射电子显微镜（HAADF-STEM）和能谱仪（EDX）监测镉置换铅的交换过程。我们观察到，在交换的早期阶段，纳米片内会出现较大的片内空隙，在进一步交换和退火后这些空隙会自发修复，从而形成超薄、平面且结晶的硫化镉纳米片。阳离子交换后，纳米片呈现出宽的子带隙发光，这在硫化镉纳米晶体中经常观察到。光致发光激发光谱揭示了重空穴和轻空穴激子特征，具有很强的量子限制和大的电子 - 空穴库仑能，这是二维超薄镉硫族化物纳米片的典型特征。
