Atomscopic of ripple origins for two-dimensional monolayer transition metal dichalcogenides

During the development of ultrathin two-dimensional (2D) materials, the appearance of ripples has been widely observed. However, the formation mechanisms and their influences are still rarely investigated, especially their contributions to the electronic structures and optical properties. To compensate for the knowledge gap, we have carried out comprehensive theoretical studies on the monolayer WSe₂ with a series of ripple structures from 0 to 12 Å in different lattice sizes. The sensitivity of the formation energy, band structures, electronic structures, and optical properties to the ripple structures have been performed systematically for the first time. The formation of ripples in Armchair and Zigzag simultaneously are more energetically favorable, leading to more flexible optimizations of the optoelectronic properties. The improved charge-locking effect and extension of absorption ranges indicate the significant role of ripple structures. The spontaneous formation of ripples is associated with orbital rearrangements and structural distortions. This leads to the unique charge carrier correlate inversion between W-5d and Se-4p orbitals, resulting in the pinning of the Fermi level. This work has supplied significant references to understand ultrathin 2D structures and benefit their future developments and applications in high-performance optoelectronic devices. © Tsinghua University Press 2023.