The crystal configuration of sandwiched S–Mo–Se structure (Janus SMoSe) at the monolayer limit has been synthesized and carefully characterized in this work. By controlled sulfurization of monolayer MoSe₂, the top layer of selenium atoms is substituted by sulfur atoms, while the bottom selenium layer remains intact. The structure of this material is systematically investigated by Raman, photoluminescence, transmission electron microscopy, and X-ray photoelectron spectroscopy and confirmed by time-of-flight secondary ion mass spectrometry. Density functional theory (DFT) calculations are performed to better understand the Raman vibration modes and electronic structures of the Janus SMoSe monolayer, which are found to correlate well with corresponding experimental results. Finally, high basal plane hydrogen evolution reaction activity is discovered for the Janus monolayer, and DFT calculation implies that the activity originates from the synergistic effect of the intrinsic defects and structural strain inherent in the Janus structure.

中文翻译：

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Janus单层过渡金属硫属元素化物

在这项工作中，已经合成并仔细表征了夹层S–Mo–Se结构（Janus SMoSe）在单层极限的晶体构型。通过单层MoSe _2的受控硫化，硒原子的顶层被硫原子取代，而硒底层则保持完整。该材料的结构通过拉曼光谱，光致发光，透射电子显微镜和X射线光电子能谱进行了系统研究，并通过飞行时间二次离子质谱法进行了确认。进行密度泛函理论（DFT）计算以更好地了解Janus SMoSe单层的拉曼振动模式和电子结构，并发现它们与相应的实验结果紧密相关。最后，对Janus单层发现了高的基面氢析出反应活性，DFT计算表明该活性源自Janus结构固有的固有缺陷和结构应变的协同效应。