Probing the origin of lateral heterogeneities in synthetic monolayer molybdenum disulfide
Probing the origin of lateral heterogeneities in synthetic monolayer molybdenum disulfide
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DOI：
10.1088/2053-1583/aafd9a
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发表时间：
2019-02
期刊：
影响因子：
5.5
通讯作者：
Kehao Zhang;Yuanxi Wang;Jaydeep Joshi;Fu Zhang;S. Subramanian;M. Terrones;P. Vora;V. Crespi;J. Robinson
中科院分区：
文献类型：
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作者：
Kehao Zhang;Yuanxi Wang;Jaydeep Joshi;Fu Zhang;S. Subramanian;M. Terrones;P. Vora;V. Crespi;J. Robinson
合成二维（2D）材料提供了在下一代电子和光电器件中实现大规模应用的机会。合成2D材料的最大挑战之一是横向不均匀性，例如不均匀的应变，成分和缺陷密度。在许多情况下，电子和光学性质并不均匀，即使在单晶域内也是如此，这可能会限制先进设备中的合成2D材料。在这项工作中，我们探测的起源广泛观察到的横向异质性在合成单层二硫化钼。外延单晶畴（~10 µm）在0.3%-0.4%的拉伸应变下是光学均匀的，而取向错误的畴（>20 µm）从中心到边缘呈现出不同的光致发光（PL）发射，沿着中心释放应变。温度依赖的拉曼和PL映射显示，非外延域的中心表现出增强的PL由于增加的缺陷密度。密度泛函理论（DFT）的计算表明，氧缺陷可以很容易地导致外延的损失，与我们观察到的MoOx核壳结构，只存在于取向错误的域相一致。结合实验和密度泛函理论，我们假设两种生长机制，固-固和气-固生长，可能是负责横向不均匀性。
Synthetic two-dimensional (2D) materials provide an opportunity to realize large-scale applications in next generation electronic and optoelectronic devices. One of the biggest challenges of synthetic 2D materials is the lateral heterogeneity such as non-uniform strain, composition and defect density. The electronic and optical properties are found to be not uniform in many cases, even within a single crystalline domain, potentially limiting synthetic 2D materials in advanced devices. In this work, we probe the origin of the widely observed lateral heterogeneities in synthetic monolayer MoS2. Epitaxial single crystalline domains (~10 µm) are optically homogeneous and uniform with 0.3%–0.4% tensile strain, while misoriented domains (>20 µm) exhibit distinct photoluminescence (PL) emissions from the center to the edge, along with released strain at the center. Temperature-dependent Raman and PL mapping reveals that the center of non-epitaxial domains exhibits an enhanced PL due to increased defect density. Density function theory (DFT) calculations suggest that oxygen defects can readily lead the loss of epitaxy, consistent with our observation of a MoOx core–shell structure that only exists in misoriented domains. Combining experiment and DFT, we hypothesize that two growth mechanisms, solid–solid and vapor–solid growth, may be responsible for the lateral heterogeneities.