The screw dislocations are intriguing defects that are often observed in natural and artificial materials. The dislocation spirals break the reflection and inversion symmetries of the lattices and modify the interlayer coupling in layer-structured materials, inducing additional complexity in layer stacking and thus novel properties in materials. Here, we report on the interlayer coupling of two-dimensional (2D) MoSe₂ flakes with screw dislocations by atomic force microscopy (AFM), Raman spectra and photoluminescence (PL) spectra. By controlling the supersaturation conditions, 2D MoSe₂ flakes with screw dislocations are grown on amorphous SiO₂ substrates by chemical vapor deposition (CVD). AFM measurements reveal that the interlayer spacing in such 2D MoSe₂ flakes with screw dislocation is slightly widened with respect to the normal AA- or AB-stacked ones due to the presence of the screw dislocations. Raman and PL spectra show that the interlayer coupling is weaker and thus the band gap is wider than that in the normal AA-or AB-stacked ones. Our work demonstrates that the interlayer coupling of 2D transition metal dichalcogenides (TMDCs) flakes can be tuned by the induction of screw dislocations, which is very helpful for developing novel catalysts and electronic devices.

Two-dimensional semiconducting transition-metal dichalcogenides have attracted considerable interest owing to their unique physical properties and future device applications. In particular, grain boundaries (GBs) have been often observed in single-layer MoS2 grown via chemical vapor deposition, which can significantly influence the material properties. In this study, we examined the electronic structures of various GBs in single-layer MoS₂ grown on highly oriented pyrolytic graphite using low-temperature scanning tunneling microscopy/spectroscopy. By measuring the local density of states of a series of GBs with tilt angles ranging from 0° to 25°, we found that the bandgaps at the GBs can be either broadened or narrowed with respect to the intrinsic single-layer MoS₂. The bandgap broadening shows that the GBs can become more insulating, which may directly influence the transport properties of nanodevices based on polycrystalline single-layer MoS₂ and be useful for optoelectronics.