Nearly monodisperse and shape-controlled CdSe nanocrystals via alternative routes: Nucleation and growth
Nearly monodisperse and shape-controlled CdSe nanocrystals via alternative routes: Nucleation and growth
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DOI：
10.1021/ja0173167
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发表时间：
2002-04-03
影响因子：
15
通讯作者：
Peng, XG
中科院分区：
文献类型：
--
作者：
Peng, ZA;Peng, XG
详细探讨了具有各种细长形状的胶体 CdSe 纳米晶体的成核和生长。该系统的临界尺寸核是幻数尺寸的非团簇，其在 349 nm 处具有尖锐且占主导地位的吸收峰。在广泛的单体浓度范围内形成独特的神奇大小的核是经典成核理论所没有预料到的。我们认为这是由于极高的化学势环境造成的，即溶液中的单体浓度非常高，这是这些细长纳米晶体生长所需的。所得纳米晶体的形状、尺寸和尺寸/形状分布均由两个相关因素决定，即神奇尺寸的核和初始成核阶段后剩余单体的浓度。在没有任何尺寸分类的情况下，通过使用替代的镉前体——镉-膦酸络合物，可重复地合成具有不同形状的近单分散的 CdSe 量子结构。人们发现，相当大量过量的镉前体（其反应性低于硒前体）有利于系统在成核和生长之间达到所需的平衡。这些细长纳米晶体的形状演变和生长动力学与之前提出的扩散控制模型一致。支化纳米晶体必须在非常高的单体浓度下生长，因为每个分支末端的多个生长中心必须提供非常高的扩散通量以保持所有分支处于一维生长模式。米状纳米晶体是 3D 生长阶段的特殊产物。当纳米晶体的长度达到一定阈值后，一维生长阶段的纳米晶体的生长被证明不是单向的。实验结果表明，配位溶剂和具有不同配位能力的两个配体都不是细长 CdSe 纳米晶体生长的内在要求。
The nucleation and growth of colloidal CdSe nanocrystals with a variety of elongated shapes were explored in detail. The critical size nuclei for the system were magic sized nonoclusters, which possessed a sharp and dominated absorption peak at 349 nm. The formation of the unique magic sized nuclei in a broad monomer concentration range was not expected by the classic nucleation theory. We propose that this was a result of the extremely high chemical potential environment, that is, very high monomer concentrations in the solution, required for the growth of those elongated nanocrystals. The shape, size, and size/shape distributions of the resulting nanocrystals were all determined by two related factors, the magic sized nuclei and the concentration of the remaining monomers after the initial nucleation stage. Without any size sorting, nearly monodisperse CdSe quantum structures with different shapes were reproducibly synthesized by using the alternative cadmium precursors, cadmium-phosphonic acid complexes. A reasonably large excess of the cadmium precursor, which is less reactive than the Se precursor, was found beneficial for the system to reach the desired balance between nucleation and growth. The shape evolution and growth kinetics of these elongated nanocrystals were consistent with the diffusion-controlled model proposed previously. The branched nanocrystals had to grow at very high monomer concentrations because the multiple growth centers at the end of each branch must be fed with a very high diffusion flux to keep all branches in the 1 D-growth mode. The rice-shaped nanocrystals were found as special products of the 3D-growth stage. The growth of the nanocrystals in the 1 D-growth stage was proven to be not unidirectional after the length of the nanocrystals reached a certain threshold. Experimental results indicate that coordinating solvents arid two ligands with distinguishable coordinating abilities are both not intrinsic requirements for the growth of elongated CdSe nanocrystals.