Characterization of 2D Transition Metal Dichalcogenides Through Anisotropic Exciton Behaviors

This study reports the first attempt to characterize the quality, defects, and strain of as-grown monolayer transition metal dichalcogenide (IMDC)-based 2D materials through exciton anisotropy. A standard ellipsometric parameter (Ψ) to observe anisotropic exciton behavior in monolayer 2D materials is used. According to the strong exciton effect from phonon-electron coupling processes, the change in the exciton in the Van Hove singularity is sensitive to lattice distortions such as defects and strain. In comparison with Raman spectroscopy, the variations in exciton anisotropy in Ψ are more sensitive for detecting slight changes in the quality and strain of monolayer MDC films. Moreover, the optical power requirement for TMDC characterization through exciton anisotropy in Ψ is ~10-5 mW·cm-2, which is significantly less than that of Raman spectroscopy (~106 mW·cm-2). The standard deviation of the signals varies with strain (defects) in Raman spectra and exciton anisotropies in Ψ are 0.700 (0.795) and 0.033 (0.073), indicating that exciton anisotropy is more sensitive to slight changes in the quality of monolayer TMDC films.

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Showcasing research from Professor Hsuen-Li Chen’s laboratory, Department of Materials Science and Engineering, National Taiwan University, Taipei, Taiwan.

National Taiwan University

This study reports the first attempt to characterize the as-grown quality, defects, and strain of transition metal dichalcogenide (TMDC)-based two-dimensional (2D) materials through exciton anisotropy. We demonstrate a simple ellipsometric parameter-based method for observing the anisotropic excitonic behavior in 2D monolayer materials. The change in the exciton of TMDCs in the Van Hove singularity is superior as the detection indicator. This study has been published and highlighted on the Back Cover of Small Methods.

The team would like to acknowledge and appreciate the financial support from the National Science and Technology Council (NSTC), the Higher Education Sprout Program at the Department of Materials Science and Engineering, and the Center of Atomic Initiative for New Materials National Taiwan University, Taiwan.

Contact: Prof. Hsuen-Li Chen

[email protected]

More information:

S. H. Chen, S. W. Chang, and H. L Chen*, “Characterization of 2D Transition Metal Dichalcogenides Through Anisotropic Exciton Behaviors,” Small Methods, 2024, 8, 2301061 (highlighted on the Journal Back Cover).