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Bi-directional LEEM and eV-TEM spectroscopy on a graphene-hBN heterostack.

Peter S Neu1, Eugene E Krasovskii2, Rudolf M Tromp3

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Summary

We studied graphene-hBN heterostacks, observing emergent properties from layer coupling. Electron spectroscopy revealed insights into unoccupied states and inelastic losses, crucial for understanding these advanced materials.

Keywords:
InterferenceLEEMProbing depthUnoccupied statesVan der WaalseV-TEM

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Area of Science:

  • Condensed Matter Physics
  • Materials Science
  • Surface Science

Background:

  • Van der Waals heterostructures exhibit unique properties due to interlayer coupling.
  • Graphene and hexagonal boron nitride (hBN) are key materials for creating such heterostructures.
  • Emergent phenomena arise from the interaction between stacked 2D materials.

Purpose of the Study:

  • Investigate coherent electron resonances (unoccupied states) and inelastic losses in graphene-hBN heterostructures.
  • Analyze the symmetry of electron reflection and transmission spectra with respect to heterostack orientation.
  • Correlate experimental measurements with theoretical models of electron interactions.

Main Methods:

  • Electron spectroscopy techniques, specifically Low-Energy Electron Microscopy (LEEM) for reflection and Electron-Energy Loss Spectroscopy in Transmission Electron Microscopy (eV-TEM) for transmission.
  • Measurement of electron reflection and transmission spectra as a function of electron energy.
  • Theoretical modeling, including a wave interference model and calculations of unoccupied state densities.

Main Results:

  • Observed distinct electron reflection and transmission spectra for graphene-hBN heterostructures.
  • Demonstrated that electron transmission is orientation-independent, while reflection shows sensitivity to sample surface.
  • Successfully modeled resonances and inelastic losses using wave interference and density of states calculations.

Conclusions:

  • The study provides a comprehensive understanding of electron dynamics in graphene-hBN heterostructures.
  • Experimental and theoretical results highlight the role of interlayer coupling in emergent properties.
  • The findings are crucial for the design and application of van der Waals heterostructures in electronic devices.