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Ultrafast Electron Cooling and Decay in Monolayer WS2 Revealed by Time- and Energy-Resolved Photoemission Electron Microscopy.

Yaolong LiWei LiuYunkun WangZhaohang XueYu-Chen LengAiqin HuHong YangPing-Heng TanYunquan LiuHiroaki MisawaQuan SunYunan GaoXiaoyong HuQihuang Gong
Published in: Nano letters (2020)
A comprehensive understanding of the ultrafast electron dynamics in two-dimensional transition metal dichalcogenides (TMDs) is necessary for their applications in optoelectronic devices. In this work, we contribute a study of ultrafast electron cooling and decay dynamics in the supported and suspended monolayer WS2 by time- and energy-resolved photoemission electron microscopy (PEEM). Electron cooling in the Q valley of the conduction band is clearly resolved in energy and time, on a time scale of 0.3 ps. Electron decay is mainly via a defect trapping process on a time scale of several picoseconds. We observed that the trap states can be produced and increased by laser illumination under an ultrahigh vacuum, and the higher local optical-field intensity led to the faster increase of trap states. The enhanced defect trapping could significantly modify the carrier dynamics and should be paid attention to in photoemission experiments for two-dimensional materials.
Keyphrases
  • electron microscopy
  • electron transfer
  • transition metal
  • energy transfer
  • high resolution
  • high speed
  • working memory
  • mass spectrometry
  • high intensity
  • solar cells
  • quantum dots