Optical Imaging of the Interlayer Sliding in Two-Dimensional 1T'-ReS₂

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology

Background:

• Van der Waals layered materials offer pathways to novel electronic properties, including two-dimensional ferroelectricity.
• Controlling and measuring relative atomic motion between layers is key to harnessing these properties.
• Directly quantifying interlayer sliding, a mechanism for sliding ferroelectricity, has been a significant experimental challenge.

Purpose of the Study:

• To develop and apply a quantitative optical imaging technique for measuring interlayer sliding in van der Waals materials.
• To investigate the relationship between interlayer sliding configurations and ferroelectric properties in 1T'-ReS₂.
• To provide direct evidence for anisotropy-confined translational interlayer sliding.

Main Methods:

• Wide-field second-harmonic generation (SHG) imaging was employed to quantitatively map interlayer sliding.
• Raman and photoluminescence (PL) spectroscopy were used for corroboration and detailed characterization.
• Analysis focused on few-layer 1T'-ReS₂, chosen for its monolayer centrosymmetry and weak interlayer coupling.

Main Results:

• Multiple discrete stacking configurations were identified in trilayer and four-layer 1T'-ReS₂, indicated by distinct SHG intensity values.
• These configurations correspond to anisotropy-confined translational interlayer sliding along the b-axis.
• The observed sliding subtly modulates the electronic structure by approximately 5 meV.

Conclusions:

• Quantitative optical imaging of discrete interlayer sliding in 1T'-ReS₂ has been achieved.
• The findings provide direct evidence for the role of interlayer sliding in two-dimensional ferroelectricity.
• This work offers a method to understand and potentially manipulate sliding ferroelectric phenomena in layered materials.