Low-Energy Electron Microscopy in Two-Dimensional Materials

Low-Energy Electron Microscopy (LEEM) has emerged as a versatile tool for probing the structural, electronic and morphological properties of atomically thin materials. By employing electrons with energies typically below 100 eV, LEEM combines high spatial resolution imaging with energy-dependent spectroscopic contrast. This enables real-time observation of growth dynamics, layer thickness variations and domain boundaries in graphene, transition-metal dichalcogenides and other two-dimensional systems. Spectroscopic modes of LEEM measure the reflectivity as a function of incident energy, revealing quantized oscillations that correspond to layer number and electronic band features. Variants such as micro-LEED and divergent-beam electron diffraction extend the technique to diffraction-based surface topography mapping and local crystallographic analysis. Together, these capabilities provide critical insights into interlayer coupling, strain distributions and defect landscapes, underpinning applications in nanoelectronics, quantum devices and catalytic surfaces. Continuous improvements in electron optics and data analysis now permit sub-10 nm resolution and sub-ångström sensitivity to atomic displacements, paving the way for routine characterisation of complex van der Waals heterostructures and in situ studies of functional device operation.

Research from Nature Portfolio

Recent studies have employed LEEM-based reflectivity to directly map the unoccupied band dispersion in graphene layers. By analysing the dependence of electron reflectivity on incidence angle and energy, researchers achieved nanometre-scale resolution of monolayer to trilayer band structures and quantified electron confinement effects in few-layer graphene.

Advances in divergent-beam electron diffraction have demonstrated three-dimensional surface topography imaging of free-standing two-dimensional crystals. Low-energy electrons (50–250 eV) were used to convert atomic displacement inhomogeneities into intensity contrast within first-order diffraction spots, enabling detection of sub-ångström vertical displacements and strain with single-shot experiments.

Angle-resolved reflected-electron spectroscopy has been applied to van der Waals heterostructures to quantify band interactions between graphene and hexagonal boron nitride. Surprisingly minimal hybridisation was observed over a wide energy range, providing a quantitative framework for electronic coupling in artificial layered assemblies.

Low-Energy Electron Microscopy in Two-Dimensional Materials publication trend

The graph below shows the total number of articles in low-energy electron microscopy in two-dimensional materials across all publications each year (not limited to Nature Index journals).

Technical terms

Low-Energy Electron Microscopy (LEEM): A surface-sensitive imaging technique using electrons below 100 eV to provide real-space images and energy-dependent reflectivity spectra of materials.

Electron band structure: The relationship between electron energy and momentum in a solid, determining its electronic and optical properties.

Reflectivity: The fraction of incident electrons that are elastically scattered or reflected by a surface as a function of energy and angle.

Divergent Beam Electron Diffraction (DBED): A diffraction method in which a divergent electron beam generates diffraction patterns sensitive to three-dimensional surface topography and strain.

Moiré pattern: An interference pattern formed when two periodic lattices are overlaid with a relative rotation or lattice mismatch, often used to probe stacking and twist angles in heterostructures.

References

1. Nanoscale measurements of unoccupied band dispersion in few-layer graphene. Nature Communications (2015).
2. Three-dimensional surface topography of graphene by divergent beam electron diffraction. Nature Communications (2017).
3. Quantifying electronic band interactions in van der Waals materials using angle-resolved reflected-electron spectroscopy. Nature Communications (2016).
4. Transmission through graphene of electrons in the 30 – 900 eV range. Carbon (2024).
5. Integration of CVD graphene in gaseous electron multipliers for high energy physics experiments. Journal of Instrumentation (2023).