Biexciton Emission from Edges and Grain Boundaries of Triangular WS2 Monolayers

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• 作者：Min Su Kim ; Seok Joon Yun ; Yongjun Lee ; Changwon Seo ; Gang Hee Han ; Ki Kang Kim ; Young Hee Lee ; Jeongyong Kim
• 刊名：ACS Nano
• 出版年：2016
• 出版时间：February 23, 2016
• 年：2016
• 卷：10
• 期：2
• 页码：2399-2405
• 全文大小：421K
• ISSN：1936-086X

文摘

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 WS₂, suggesting a rich variety of ways to engineer new nanophotonic functions using 2D transition metal dichalcogenide monolayers.