Formation of high-quality CdTe, CdSe, and CdS nanocrystals using CdO as precursor
Formation of high-quality CdTe, CdSe, and CdS nanocrystals using CdO as precursor
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DOI：
10.1021/ja003633m
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发表时间：
2001-01-10
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
高质量的胶体半导体纳米晶体是相应块状晶体的纳米尺寸的单晶片段，其具有良好控制的尺寸和尺寸分布，并且可分散在所需的溶剂/介质中。近来，半导体纳米晶体由于其强的尺寸依赖性和优异的化学可加工性而在基础研究和技术应用中引起极大的兴趣。高质量半导体纳米晶的合成在这一非常活跃的领域中一直扮演着关键的角色。1，9-15作为合成方面最发达的系统，1，9，10，15具有接近单分散尺寸和形状的高质量CdSe纳米晶体正处于生物标记试剂的积极工业开发中。5，6自从Murray等人15报道了使用二甲基镉（Cd（CH 3）2）作为镉前体来合成高质量的镉硫属化物纳米晶体以来，使用该前体来合成CdSe纳米晶体已经得到了很好的发展。1，9，10相比之下，CdTe和CdS的合成并不先进15，16。例如，没有方法可控制地改变CdTe和CdS纳米晶体的形状。Cd（CH 3）2具有极高的毒性、自燃性、昂贵、在室温下不稳定，并且在高温下通过释放大量气体而爆炸。由于这些原因，Cd（CH 3）2相关的方案需要非常有限的设备和条件，并且不适合于大规模合成。在本文中，我们将证明Cd（CH 3）2可以被CdO取代。令人惊讶的是，这种新的合成方案比Cd-（CH 3）2相关的方案效果明显更好。在没有任何尺寸分选的情况下，通过新方法形成的所有镉硫族化物的量子限制点和棒（量子点和量子棒）的质量与文献中报道的最好的CdSe纳米晶体的质量相当。新的方案是可重复的和简单的，因此可以很容易地放大用于工业生产。最近，我们发现Cd（CH 3）2在热的三辛基氧化膦（TOPO）中分解，生成不溶性的金属沉淀。如果镉与HPA/TDPA的比例低于1，那么在强配体（己基膦酸（HPA）或十四烷基膦酸（TDPA））的作用下，Cd（CH 3）2会立即转化为镉HPA/TDPA络合物（Cd-HPA/Cd-TDPA）。络合物形成后，注入溶解在三丁基膦（TBP）中的Se生成高质量的CdSe纳米晶体。这一结果意味着，如果我们可以通过其他方法生成配合物，Cd（CH 3）2可能不是必需的。我们首先从CdCl_2或Cd（CH_3）_2合成并纯化了Cd-HPA。高质量的CdSe纳米晶体确实产生了从这个复杂的。这一成功鼓励我们开发一种不需要单独制备镉络合物的一锅合成法。我们未能通过一锅法使用CdCl 2制备高质量的CdSe纳米晶体，尽管CdCl 2可以在升高的温度下溶解在反应混合物中。相比之下，CdO对于一锅法非常有效。我们认为这是由于与CdCl 2相比，CdO相对于膦酸的稳定性较低。
High-quality colloidal semiconductor nanocrystals are nanometer-sized, single crystalline fragments of the corresponding bulk crystals, which have well-controlled size and size distribution and are dispersible in desired solvents/media. Recently, semiconductor nanocrystals are of great interest for both fundamental research and technical applications, 1-8 due to their strong size dependent properties and excellent chemical processibility. Synthesis of highquality semiconductor nanocrystals has been playing a critical role in this very active field. 1, 9-15 As the most developed system in terms of synthesis, 1, 9, 10, 15 high-quality CdSe nanocrystals with nearly monodisperse size and shape are in active industrial development for biological labeling reagents. 5, 6 Since Murray et al. 15 reported the synthesis of high quality cadmium chalcogenides nanocrystals using dimethyl cadmium (Cd (CH3) 2) as the cadmium precursor, the synthesis of CdSe nanocrystals using this precursor has been well developed. 1, 9, 10 In comparison, the synthesis of CdTe and CdS15, 16 are not as advanced. For instance, there is no method to controllably vary the shape of CdTe and CdS nanocrystals. Cd (CH3) 2 is extremely toxic, pyrophoric, expensive, unstable at room temperature, and explosive at elevated temperatures by releasing large amount of gas. Due to these reasons, the Cd (CH3) 2-related schemes require very restricted equipments and conditions and are not suited for large-scale synthesis. In this paper, we will prove that Cd (CH3) 2 can be replaced by CdO. Surprisingly, this new synthetic scheme works significantly better than the Cd-(CH3) 2-related ones. Without any size-sorting, the quality of quantum-confined dots and rods (quantum dots and quantum rods) of all cadmium chalcognides formed by the new method is comparable to that of the best CdSe nanocrystals reported in the literature. The new scheme is reproducible and simple and thus can be readily scaled up for industrial production. Recently, we identified that Cd (CH3) 2 decomposes in hot trioctylphosphine oxide (TOPO) and generates insoluble metallic precipitate. 9 With a strong ligand, either hexylphosphonic acid (HPA) or tetradecylphosphonic acid (TDPA), Cd (CH3) 2 is immediately converted into cadmium HPA/TDPA complex (Cd-HPA/Cd-TDPA) if the cadmium to HPA/TDPA ratio is lower than 1. After the formation of the complex, an injection of Se dissolved in tributylphosphine (TBP) generates high-quality CdSe nanocrystals. This result implies that Cd (CH3) 2 may not be necessary, if we can generate the complex by other means. We first synthesized and purified Cd-HPA from CdCl2 or Cd (CH3) 2. High-quality CdSe nanocrystals were indeed yielded from this complex. This success encouraged us to develop a one-pot synthesis which does not require separated preparation of cadmium complex. We failed to make high-quality CdSe nanocrystals using CdCl2 by the one-pot approach although CdCl2 can be dissolved in the reaction mixture at elevated temperatures. In contrast, CdO works very well for the one-pot approach. We think this is due to the low stability of CdO relative to phosphonic acids, compared to that of CdCl2.