Electron Microscopy and Optical Spectroscopy of MoS₂ Nanoribbons from Catalyst-Free Vapor Phase Synthesis

We characterize MoS₂ nanoribbons grown using a catalyst-free vapor phase synthesis that relies on pre-treatment of a bare Si surface. This growth method leads to the spontaneous formation of long ‘nanoribbons,’ with typical diameters of 100 nm and lengths greater than 10 µm. Despite their high aspect ratio and inherent flexibility, the nanoribbons are robust upon handling and are self-supporting, rendering them stable during transfer to support structures to allow electron microscopy. We use scanning electron microscopy to characterize the ribbon morphology and aberration-corrected scanning transmission electron microscopy to identify the phase, composition, and atomic structure of the samples. We identify that the MoS₂ nanoribbons (1) are predominantly 2H-phase, (2) display a ‘sawtooth’ edge structure with corrugations on the order of 2–5 nm, (3) fold to give very low radii of curvature, and (4) contain occasional nanometer-scale triangular inclusions. Intriguingly, these high aspect ratio nanoribbons exhibit a PL peak that is blue-shifted significantly relative to that of as-synthesized and transferred 2-dimensional MoS₂ sheets.