过渡金属双硫族化合物单层结构中多产点缺陷氧的实验和理论研究
Identifying substitutional oxygen as a prolific point defect in monolayer transition metal dichalcogenides with experiment and theory
摘要：
硫族元素空位被认为是二维过渡金属二硫族化物（TMD）半导体中最丰富的点缺陷，并被预测会导致深能隙态（IGS）。因此，2D-TMD的光学响应中的重要特征通常归因于硫族元素空位，并得到透射电子显微镜（TEM）和扫描隧道显微镜（STM）图像的间接支持。然而，TEM成像测量不提供对单个缺陷的电子结构的直接访问;并且虽然扫描隧道能谱（STS）是局部电子结构的直接探针，但对2D-TMD中点缺陷的原子分辨STM图像的化学性质的解释可能是模糊的。因此，在2D-TMD中，点缺陷作为空位或不同种类的替代原子的分配，以及它们对它们的电子性质的影响，一直不一致，缺乏共识。在这里，我们结合低温非接触式原子力显微镜（nc-AFM），STS，和国家的最先进的从头计算密度泛函理论（DFT）和GW计算，以确定最丰富的个人硫属元素常见的2D-TMD网站缺陷的结构和电子特性。令人惊讶的是，我们没有观察到任何探测的硫族元素缺陷的IGS。我们的研究结果和分析强烈表明，在我们的2D-TMD，在标准环境中制备和测量，常见的硫族元素缺陷是替位氧，而不是空位。
英文摘要：
Chalcogen vacancies are considered to be the most abundant point defects in two-dimensional (2D) transition-metal dichalcogenide (TMD) semiconductors, and predicted to result in deep in-gap states (IGS). As a result, important features in the optical response of 2D-TMDs have typically been attributed to chalcogen vacancies, with indirect support from Transmission Electron Microscopy (TEM) and Scanning Tunneling Microscopy (STM) images. However, TEM imaging measurements do not provide direct access to the electronic structure of individual defects; and while Scanning Tunneling Spectroscopy (STS) is a direct probe of local electronic structure, the interpretation of the chemical nature of atomically-resolved STM images of point defects in 2D-TMDs can be ambiguous. As a result, the assignment of point defects as vacancies or substitutional atoms of different kinds in 2D-TMDs, and their influence on their electronic properties, has been inconsistent and lacks consensus. Here, we combine low-temperature non-contact atomic force microscopy (nc-AFM), STS, and state-of-the-art ab initio density functional theory (DFT) and GW calculations to determine both the structure and electronic properties of the most abundant individual chalcogen-site defects common to 2D-TMDs. Surprisingly, we observe no IGS for any of the chalcogen defects probed. Our results and analysis strongly suggest that the common chalcogen defects in our 2D-TMDs, prepared and measured in standard environments, are substitutional oxygen rather than vacancies.
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