Layer-dependent signatures for exciton dynamics in monolayer and multilayer WSe2 revealed by fluorescence lifetime imaging measurement

• Published in: Nano research 2020-03, Vol.13 (3), p.661-666
• Main Authors: Liu, Yuanshuang, Li, Huanglong, Qiu, Cuicui, Hu, Xiangmin, Liu, Dameng
• Format: Article
• Language: English
• Subjects: Atomic/Molecular Structure and Spectra; Biomedicine; Biotechnology; Charge transport; Chemical vapor deposition; Chemistry and Materials Science; Condensed Matter Physics; Control methods; Dynamics; Excitons; Fluorescence; Lasers; Lifetime; Materials Science; Microscopy; Monolayers; Multilayers; Nanotechnology; Optical properties; Optoelectronic devices; Research Article; Room temperature; Spectrum analysis; Temperature dependence; Transition metal compounds; Trions
• ISSN: 1998-0124; 1998-0000
• DOI: 10.1007/s12274-020-2670-7

Two-dimensional (2D) transition-metal dichalcogenide (TMD) materials have aroused noticeable interest due to their distinguished electronic and optical properties. However, little is known about their complex exciton properties together with the exciton dynamics process which have been expected to influence the performance of optoelectronic devices. The process of fluorescence can well reveal the process of exciton transition after excitation. In this work, the room-temperature layer-dependent exciton dynamics properties in layered WSe 2 are investigated by the fluorescence lifetime imaging microscopy (FLIM) for the first time. This paper focuses on two mainly kinds of excitons including the direct transition neutral excitons and trions. Compared with the lifetime of neutral excitons (< 0.3 ns within four-layer), trions possess a longer lifetime (~ 6.6 ns within four-layer) which increases with the number of layers. We attribute the longer-lived lifetime to the increasing number of trions as well as the varieties of trion configurations in thicker WSe 2 . Besides, the whole average lifetime increases over 10% when WSe 2 flakes added up from monolayer to four-layer. This paper provides a novel tuneable layer-dependent method to control the exciton dynamics process and finds a relatively longer transition lifetime of trions at room temperature, enabling to investigate in the charge transport in TMD-based optoelectronics devices in the future.