Decoding ripple formation in single-layer transition metal chalcogenide lateral heterojunctions towards novel optoelectronic properties

For the ultrathin two-dimensional (2D) materials and lateral heterojunction, the formation of unstable but elastic ripples is commonly observed but is rarely studied, especially their correlations with different material properties. To fill the knowledge gap in this field, this work systematically explores transition metal dichalcogenides (TMDCs) in a single component and lateral heterojunction with a series of ripple structures. The ripple formation energy is quantitatively classified into the initial elastic strain stage and fracture threshold stage based on Fermi-like distribution. Electronic structures reveal that the formation of ripples is accompanied by electron accumulations from flat surfaces to ripples. By comparing the unilateral, decaying, and bilateral ripples in 2D lateral heterojunction, we confirm that Fermi-like distribution is still valid regardless of the shape of the ripples, where the thermodynamic and electronic properties are modulated by ripples-induced uneven strain. The main features of optical properties are not affected while the sensitivity to ripple-induced strains is distinguished. More importantly, the phonon properties further demonstrate the potential of ripples in promoting thermal conductivity, which are strongly correlated with the optical branch of anion vibrations. This work provides important theoretical guidance for the design and optimization of high-performance optoelectronic devices based on TMDC heterojunctions.