Ultralow-Frequency Raman Spectroscopy for Quantifying Interlayer Interactions in Two-Dimensional Materials

Shu-Chen Liu¹, Jian-Syun Lin², Min-Jia Zhang², Yi-Yao Lo³, Shao-Yu Chen^3,4,5*

¹Department of Physics, National Taiwan Normal University, Taipei, Taiwan
²Department of Physics, National Taiwan University, Taipei, Taiwan
³Center for Condensed Matter Sciences, National Taiwan University, Taipei, Taiwan
⁴Center of Atomic Initiative for New Materials, National Taiwan University, Taipei, Taiwan
⁵Institute of Physics, National Yang Ming Chiao Tung University, Hsinchu, Taiwan

* Presenter:Shao-Yu Chen, email:shaoyuchen@ntu.edu.tw

Recent advances in optical spectroscopy have enabled precise probing of interlayer interactions in two-dimensional (2D) materials. Ultralow-frequency Raman spectroscopy, in particular, extends the measurable phonon range down to ~5 cm⁻¹, providing direct access to the low-energy vibrational modes that reflect weak van der Waals coupling and stacking configurations.
We have established a high-resolution optical spectroscopy platform optimized for detecting interlayer shear and breathing phonons in a wide variety of 2D materials. Through systematic measurements, we demonstrate that this technique allows quantitative evaluation of interlayer coupling strength and its modulation by substrate interaction. The results reveal that substrate bonding can significantly modify the interlayer vibrational response, leading to deviations from predictions of the conventional linear-chain model.
This optical spectroscopy approach offers a powerful pathway for investigating interface coupling, stacking order, and strain effects in emerging 2D heterostructures, with potential applications in nanoscale mechanical engineering, optoelectronic device design, and quantum material characterization.

Keywords: Ultra low-Frequency Raman Spectroscopy, Interlayer Phonons, Two-Dimensional Materials, Substrate Interaction