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Effect of Dielectric Environment on Excitonic Dynamics in Monolayer WS 2
Author(s) -
Fu Yang,
He Dawei,
He Jiaqi,
Bian Ang,
Zhang Lu,
Liu Shuangyan,
Wang Yongsheng,
Zhao Hui
Publication year - 2019
Publication title -
advanced materials interfaces
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.671
H-Index - 65
ISSN - 2196-7350
DOI - 10.1002/admi.201901307
Subject(s) - exciton , materials science , monolayer , photoluminescence , hexagonal boron nitride , diffusion , semiconductor , scattering , absorption (acoustics) , condensed matter physics , molecular physics , nanotechnology , optoelectronics , graphene , optics , chemistry , physics , composite material , thermodynamics
An experimental study on the effect of hexagonal boron nitride ( h ‐BN) underlay and cap layers on excitonic dynamics in monolayer WS 2 is reported. A monolayer WS 2 flake is fabricated by mechanical exfoliation. By using a dry transfer technique, three regions of the sample are obtained: WS 2 directly on SiO 2 , WS 2 on h ‐BN, and WS 2 sandwiched by two h ‐BN flakes. Photoluminescence measurements show higher yield and narrower linewidth of the h ‐BN/WS 2 / h ‐BN region. Transient absorption measurements reveal that the top h ‐BN layer enhances the exciton formation, prolongs the exciton lifetime, and slightly affects the exciton–exciton annihilation. By performing spatially resolved transient absorption measurements, exciton diffusion coefficients of about 100, 40, and 26 cm 2 s − 1 for the regions of WS 2 , h ‐BN/WS 2 , and h ‐BN/WS 2 / h ‐BN, respectively, are obtained. The suppression of exciton diffusion by h ‐BN is attributed to the additional phonon scattering mechanisms introduced by h ‐BN, which decreases the exciton mean free path and thus the diffusion coefficient. The findings provide useful information for designing and understanding the effect of h ‐BN layers interfacing with 2D semiconductors.