Strain mapping of three-dimensionally structured two-dimensional materials

Area of Science:

• Materials Science
• Nanotechnology
• Condensed Matter Physics

Background:

• Strain engineering is vital for tuning the properties of two-dimensional (2D) materials.
• Out-of-plane deformation in 2D materials creates complex 3D topography, challenging conventional strain mapping.
• Accurate characterization of strain in 3D-structured 2D materials is crucial for advanced applications.

Purpose of the Study:

• To introduce a new integrated method, BRIGHT (Bragg-Rod Informed, Gradient-based Height-mapping Technique), for simultaneous reconstruction of topography and planar strain.
• To demonstrate the capability of BRIGHT for analyzing 3D-structured 2D materials with complex morphologies.
• To provide a foundation for enhanced strain engineering in 2D materials by considering out-of-plane features.

Main Methods:

• Utilized nanobeam four-dimensional scanning transmission electron microscopy (4D-STEM).
• Developed the BRIGHT technique integrating Bragg-Rod information and gradient-based height mapping.
• Applied the method to MoS₂-MoSe₂ transition metal dichalcogenide (TMD) lateral heterojunctions.

Main Results:

• Successfully reconstructed both the 3D topography and planar strain profile of the 2D material heterojunctions.
• Observed distinct surface morphologies and corresponding planar strain distributions influenced by heterojunction width.
• Quantified the impact of out-of-plane ripples on the strain landscape.

Conclusions:

• BRIGHT is an effective technique for characterizing strain in 3D-structured 2D materials.
• Understanding the interplay between topography and strain is essential for precise control of material properties.
• This work enables more sophisticated strain engineering strategies for 2D materials.