Probing Exfoliated Graphene Layers and Their Lithiation with Microfocused X-rays

Area of Science:

• Materials Science
• Solid-State Physics
• Nanotechnology

Background:

• Graphene, a 2D material, exhibits unique electronic and mechanical properties.
• Understanding the structural changes in few-layer graphene during ion intercalation is crucial for device applications.
• Current methods often lack the resolution to probe individual, micron-sized graphene crystallites.

Purpose of the Study:

• To develop and demonstrate an in situ X-ray diffraction technique for analyzing individual few- and bilayer graphene single crystals.
• To investigate the structural response of graphene to electrochemical lithium intercalation at the single-crystal level.
• To extract key crystallographic parameters, including the c-axis lattice parameter, of individual graphene flakes.

Main Methods:

• Utilized grazing incidence X-ray diffraction to observe in-plane Bragg peaks.
• Employed specular X-ray reflectivity with a focused beam (10 μm × 10 μm) to probe individual graphene flakes.
• Applied a recursive Parratt algorithm to model experimental data and extract crystallographic parameters.

Main Results:

• Successfully measured X-ray diffraction on individual bilayer and multilayer graphene single crystals.
• Observed an increase in the graphene c-axis lattice parameter upon electrochemical lithium intercalation.
• Demonstrated the ability to control lithiation using an on-chip peripheral electrochemical cell.

Conclusions:

• The developed in situ X-ray diffraction method is feasible for studying individual, micron-sized 2D material single crystals.
• Lithiation induces measurable changes in the crystallographic structure of few- and bilayer graphene.
• This technique provides direct access to structural parameters, enabling a deeper understanding of intercalation phenomena in 2D materials.