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Title: Unraveling spatially heterogeneous ultrafast carrier dynamics of single-layer WSe2 by femtosecond time-resolved photoemission electron microscopy
Authors: Wang, Lin
Xu, Ce
Li, Ming-Yang
Li, Lain-Jong
Loh, Zhi-Heng
Keywords: Science::Physics
Issue Date: 2018
Source: Wang, L., Xu, C., Li, M.-Y., Li, L.-J., & Loh, Z.-H. (2018). Unraveling spatially heterogeneous ultrafast carrier dynamics of single-layer WSe2 by femtosecond time-resolved photoemission electron microscopy. Nano Letters, 18(8), 5172-5178. doi:10.1021/acs.nanolett.8b02103
Journal: Nano Letters 
Abstract: Studies of the ultrafast carrier dynamics of transition metal dichalcogenides have employed spatially averaged measurements, which obfuscate the rich variety of dynamics that originate from the structural heterogeneity of these materials. Here, we employ femtosecond time-resolved photoemission electron microscopy (TR-PEEM) with sub-80 nm spatial resolution to image the ultrafast subpicosecond to picosecond carrier dynamics of monolayer tungsten diselenide (WSe2). The dynamics observed following 2.41 eV pump and 3.61 eV probe occurs on two distinct time scales. The 0.1 ps process is assigned to electron cooling via intervalley scattering, whereas the picosecond dynamics is attributed to exciton-exciton annihilation. The 70 fs decay dynamics observed at negative time delay reflects electronic relaxation from the Γ point. Analysis of the TR-PEEM data furnishes the spatial distributions of the various time constants within a single WSe2 flake. The spatial heterogeneity of the lifetime maps is consistent with increased disorder along the edges of the flake and the presence of nanoscale charge puddles in the interior. Our results indicate the need to go beyond spatially averaged time-resolved measurements to understand the influence of structural heterogeneities on the elementary carrier dynamics of two-dimensional materials.
ISSN: 1530-6984
DOI: 10.1021/acs.nanolett.8b02103
Rights: This document is the Accepted Manuscript version of a Published Work that appeared in final form in Nano Letters, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see
Fulltext Permission: open
Fulltext Availability: With Fulltext
Appears in Collections:SPMS Journal Articles

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