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 MoS<sub>2</sub> 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.

The authors acknowledge funding from the Office of Naval Research (Naval Research Laboratory Basic Research Program).