Biexciton Emission from Edges and Grain Boundaries of Triangular WS2 Monolayers
Biexciton Emission from Edges and Grain Boundaries of Triangular WS2 Monolayers
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DOI：
10.1021/acsnano.5b07214
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发表时间：
2016-02-01
期刊：
影响因子：
17.1
通讯作者：
Kim, Jeongyong
中科院分区：
文献类型：
--
作者：
Kim, Min Su;Yun, Seok Joon;Kim, Jeongyong
单层二硫化钨（WS2）是一种高量子产率的二维（2D）体系，可以用化学气相沉积（CVD）法大面积合成，具有良好的纳米光子学应用前景。然而，在单个WS2晶粒中观察到的空间不均匀的光致发光（PL）强度和峰值波长一直困扰着研究人员，激子，trions和双激子对PL发射的相对贡献的变化的起源还不清楚。在这里，我们提出了纳米级PL和拉曼光谱图像的三角形CVD生长的WS2单层的不同大小，这些图像下获得不同的温度和值的激发功率。观察到强烈的PL发射周围的个别WS2晶粒的边缘和部分合并的WS2晶粒之间的晶界。随着激光激发功率的增加，这些区域的主要PL发射的主要来源从中性激子变为trions和双激子，双激子完全主导高功率条件下的PL发射。强烈的PL发射和双激子在单层WS2的边缘和晶界的优先形成归因于较大的人口的电荷载流子所造成的过度纳入生长促进剂在CVD过程中，这表明积极的作用，过量的载流子在TMD单分子膜的PL效率。我们全面的纳米级光谱研究揭示了单层WS中激子复合物之间的动态竞争，提出了丰富的各种方法来设计新的纳米光子功能，使用2D过渡金属二硫属化物单层。
Monolayer tungsten disulfides (WS2) constitute a high quantum yield two-dimensional (2D) system, and can be synthesized on a large area using chemical vapor deposition (CVD), suggesting promising nanophotonics applications. However, spatially nonuniform photoluminescence (PL) intensities and peak wavelengths observed in single WS2 grains have puzzled researchers, with the origins of variation in relative contributions of excitons, trions, and biexcitons to the PL emission not well understood. Here, we present nanoscale PL and Raman spectroscopy images of triangular CVD-grown WS2 monolayers of different sizes, with these images obtained under different temperatures and values of excitation power. Intense PL emissions were observed around the edges of individual WS2 grains and the grain boundaries between partly merged WS2 grains. The predominant origin of the main PL emission from these regions changed from neutral excitons to trions and biexcitons with increasing laser excitation power, with biexcitons completely dominating the PL emission for the high-power condition. The intense PL emission and the preferential formation of biexcitons in the edges and grain boundaries of monolayer WS2 were attributed to larger population of charge carriers caused by the excessive incorporation of growth promoters during the CVD, suggesting positive roles of excessive carriers in the PL efficiency of TMD monolayers. Our comprehensive nanoscale spectroscopic investigation sheds light on the dynamic competition between exciton complexes occurring in monolayer WS,, suggesting a rich variety of ways to engineer new nanophotonic functions using 2D transition metal dichalcogenide monolayers.