4.7 Article

Direct observation of trapped charges at ReSe2 and graphene heterojunctions

Journal

APPLIED SURFACE SCIENCE
Volume 579, Issue -, Pages -

Publisher

ELSEVIER
DOI: 10.1016/j.apsusc.2021.152187

Keywords

van der Waals heterojunction; Charge redistribution; Trapped charge; ReSe2; Scanning tunneling microscopy; Density functional theory

Funding

  1. National Research Foundation (NRF) - Korean government [NRF-2018R1D1A1B07050144, NRF-2019R1A6A1A11053838, NRF-2021R1A6A3A14040322, NRF-2020R1A2C200373211]
  2. Technology Innovation Programme - Ministry of Trade, Industry & Energy (MOTIE, Korea) [20012430]
  3. KISTI Super-computing Center [KSC-2021-CRE-0044]
  4. Janos Bolyai Research Scholarship of the Hungarian Academy of Sciences
  5. National Research Development and Innovation Office of Hungary [FK124100]
  6. Korea Evaluation Institute of Industrial Technology (KEIT) [20012430] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)

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Researchers investigate an emergent interface phenomenon between monolayer ReSe2 and graphene through combined STM and DFT studies, revealing a confined layer of electron density with trapped charges that is asymmetrically polarized and enhanced at the edge of ReSe2.
The van der Waals (vdW) heterojunction often reveals unexpected characteristics distinct from conventional junctions. We investigate an emergent interface phenomenon between monolayer ReSe2 and graphene via combined studies of scanning tunneling microscopy (STM) and density functional theory (DFT). When probing monolayer ReSe2 on graphene at bias voltages within the ReSe2 band gap (in-gap bias; -1.2 V to 0.5 V), strikingly, observed topograph appears just like ReSe2 as it shows precisely the same hexagonal periodicity of ReSe2 lattice instead of the underlying graphene lattice. To answer this puzzle, we examine the nature of charge redistribution at the confined vdW gap between ReSe2 and graphene. DFT calculations indicate that the electron accumulation arises right below the ReSe2 layer, while the electron depletion occurs from the graphene layer. This leads to an asymmetrically polarized two-dimensional layer of confined electron density (termed as trapped charges) in the vdW gap, which agrees well with the in-gap STM topograph. We also find that the accumulation of the trapped charge is enhanced strongly at the edge of ReSe2.

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