Probing the effects of gold doping on structural, electronic and nonlinear optical properties of caged X20H20 (X=Si, Ge, Sn, Pb) clusters

Using first-principles methods, we explored the doping of gold atom into carbon family clusters (Si₂₀, Ge₂₀, Sn₂₀, Pb₂₀), and the Au atom and charged states can effectively modulate the electronic properties of clusters, while the neutral Au@X₂₀H₂₀ (X=Si, Sn) clusters possess the large nonlinear optical responses, especially for Au@Sn₂₀H₂₀, served as novel optoelectronic materials.

Abstract

Carbon family elements (Si, Ge, Sn, Pb) have attracted a lot of attention because of their unique structural features and potential applications in microelectronics industry. Here, the structure, chemical stability, electronic properties, and nonlinear optical properties of neutral and charged Au@X₂₀H₂₀ (X=Si, Ge, Sn, Pb) clusters have been systematically studied using density-functional theory calculations. Structurally, the neutral/anionic Au@X₂₀H₂₀ (X=Si, Ge, Sn) as well as cationic Au@Pb₂₀H₂₀ possess Au-endohedral (XH)₂₀ unit, forming fullerene-like framework, whereas other species are Au-doped structures with hydrogen-bridged bond. Analysis of binding energy and HOMO-LUMO energy gaps reveals that the charged clusters possess high chemical stabilities due to closed-shell structures. The charge transfers from X₂₀ cage to Au atom, and the Au atom acts as electron acceptor. The Au atom and charged states play an important role in the structural stability, and can effectively modulate the electronic properties of clusters. Interestingly, the neutral Au@X₂₀H₂₀ (X=Si, Sn) clusters possess large first hyperpolarizabilities, especially for Au@Sn₂₀H₂₀, which has remarkably giant value (~5.65×10⁸ a. u.), and the enhanced NLO behaviors can be further explained by the TDDFT calculation. The work may provide a theoretical reference for further applications considered as novel cluster-assembled nanomaterials.

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