Molybdenum Disulfide Nanoribbons with Enhanced Edge Nonlinear Response and Photoresponsivity

MoS₂ nanoribbons have attracted an increased interest due to their properties, which can be tailored by tuning their dimensions. Herein, we demonstrate the growth of MoS₂ nanoribbons and 3D triangular crystals formed by the reaction between ultra-thin films of MoO₃ grown by Pulsed Laser Deposition and NaF in a sulfur-rich environment. The multilayer nanoribbons can reach up to 10 µm in length, and feature single-layer edges, forming a monolayer-multilayer MoS₂ junction enabled by the lateral modulation in thickness. The single-layer edges of the nanoribbons show a pronounced second harmonic generation due to the symmetry breaking, in contrast to the centrosymmetric multilayer structure, which is unsusceptible to the second-order nonlinear process. A pronounced splitting of the Raman spectra was observed in MoS₂ nanoribbons arising from distinct contributions from the monolayer edges and multilayer core. Nanoscale imaging reveals a blue-shifted exciton emission of the monolayer edge compared to the triangular MoS₂ monolayers due to built-in local strain and disorder. We further report on an ultrasensitive photodetector made of a single MoS₂ nanoribbon with a responsivity of 8.72×10² A/W at 532 nm, which is among the highest reported up-todate for single-nanoribbon photodetectors. Our findings can inspire the design of MoS₂ semiconductors with tunable geometries for efficient optoelectronic devices.