X射线吸收光谱法研究CdS团簇的原子结构
Atomic structure of CdS magic-size clusters by X-ray absorption spectroscopy
摘要：
魔术大小团簇是超小的胶体半导体系统，由于其单分散性和尖锐的紫外-可见吸收峰相比，规则的量子点，是深入研究。然而，这种簇的小尺寸（<2nm）和大的表面与体积比显著限制了可以利用的表征技术。在这里，我们演示了如何结合EXAFS和XANES可以用来获得有关样品的化学计量和集群对称性的信息。研究两种类型的簇，在311 nm和322 nm处显示尖锐的紫外-可见吸收峰，我们发现，这两种样品具有约2：1的Cd：S比，并具有相似的最近邻结构排列。然而，两个样品都表现出与四面体结构排列的显著偏离，平均键角确定为约106.1度，显示出双折叠键角分布。我们的研究结果表明，这两个样品是准异构体。它们的核心结构具有相同的化学组成，但原子排列不同，键角分布不同。
英文摘要：
Magic-size clusters are ultra-small colloidal semiconductor systems that are intensively studied due to their monodisperse nature and sharp UV-vis absorption peak compared with regular quantum dots. However, the small size of such clusters (<2 nm), and the large surface-to-bulk ratio significantly limit characterisation techniques that can be utilised. Here we demonstrate how a combination of EXAFS and XANES can be used to obtain information about sample stoichiometry and cluster symmetry. Investigating two types of clusters that show sharp UV-vis absorption peaks at 311 nm and 322 nm, we found that both samples possess approximately 2:1 Cd:S ratio and have similar nearest-neighbour structural arrangements. However, both samples demonstrate a significant departure from the tetrahedral structural arrangement, with an average bond angle determined to be around 106.1 degree showing a bi-fold bond angle distribution. Our results suggest that both samples are quazi-isomers. Their core structure has identical chemical composition but a different atomic arrangement with distinct bond angle distributions.
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