Layered transition metal dichalcogenides (TMDCs) such as MoS₂, MoSe_2, and WSe₂ are under intense investigation because they are atomically thin semiconductors with photophysical properties that can be tuned by changing their composition or morphology. Mechanochemical processing has been proposed as a method to obtain alloyed TMDCs in the series Mo_1–xW_xS_ySe_2–y (x = 0–1; y = 0–2). However, elucidating the chemical transformations occurring at the atomic scale following mechanochemical processing can be challenging because the products are often amorphous or microcrystalline. To address this challenge, we probe TMDC mixing and alloying by using a combination of powder X-ray diffraction, Raman spectroscopy, diffuse reflectance spectroscopy, ⁷⁷Se solid-state nuclear magnetic resonance (SSNMR) spectroscopy, and planewave density functional theory (DFT) calculations. The nature of the milling material and reaction atmosphere are shown to be essential factors in limiting the formation of undesired oxide byproducts. We demonstrate acquisition of ⁷⁷Se SSNMR spectra using different combinations of Carr-Purcell Meiboom-Gill acquisition (CPMG) pulse sequences, magic angle spinning (MAS), and MAS dynamic nuclear polarization. The combination of SSNMR with the other characterization methods clearly demonstrates that high energy impact ball milling induces molecular level alloying of Mo, W and chalcogen atoms in the family Mo_1–xW_xS_ySe_2–y. Gauge including projector augmented wave DFT calculations yield accurate ⁷⁷Se chemical shift (CS) tensor components. ⁷⁷Se SSNMR spectroscopy was also applied to study the structure of WSe₂ nanocrystals intercalated with ethylenediamine. The intercalated WSe₂ nanocrystals exhibit a more positive isotropic ⁷⁷Se CS as compared to bulk WSe₂, however, the ⁷⁷Se CS anisotropy is the same, confirming the WSe₂ layers have a similar structure as in their bulk counterparts.

中文翻译：

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硒-77 固态核磁共振波谱对合金和纳米颗粒过渡金属二硫化物的结构研究


层状过渡金属硫化物 （TMDC），如 MoS₂、MoSe₂ 和 WSe₂ 正在接受深入研究，因为它们是原子薄的半导体，具有光物理特性，可以通过改变其成分或形态来调整。机械化学加工已被提议作为获得 Mo _1-xW_xS_ySe _2-y 系列中的合金 TMDC 的方法 （x = 0-1;y = 0-2）。然而，阐明机械化学加工后在原子尺度上发生的化学转变可能具有挑战性，因为这些产物通常是无定形或微晶的。为了应对这一挑战，我们结合使用粉末 X 射线衍射、拉曼光谱、漫反射光谱、⁷⁷Se 固态核磁共振 （SSNMR） 光谱和平面波密度泛函理论 （DFT） 计算来探测 TMDC 混合和合金化。研磨材料的性质和反应气氛被证明是限制不需要的氧化物副产物形成的重要因素。我们展示了使用 Carr-Purcell Meiboom-Gill 采集 （CPMG） 脉冲序列、魔角旋转 （MAS） 和 MAS 动态核极化的不同组合采集 ⁷⁷Se SSNMR 光谱。SSNMR 与其他表征方法的结合清楚地表明，高能冲击球磨会诱导 Mo _1-xW_xS_ySe _2-y 家族中 Mo、W 和硫族原子的分子水平合金化。 包括投影仪增强波 DFT 计算的仪表可产生准确的 ⁷⁷Se 化学位移 （CS） 张量分量。⁷⁷Se SSNMR 光谱还用于研究 WSe₂ 纳米与乙二胺插层的结构。与本体 WSe₂ 相比，插层 WSe₂ 纳米晶体表现出更正的各向同性 ⁷⁷Se CS，但是，⁷⁷Se CS 各向异性相同，证实了 WSe₂ 层具有与本体对应物相似的结构。