Focused Helium Ion Beam for Direct Patterning of Monolayer MoS₂ Nanoribbon Field Effect Devices

The helium ion microscope (HIM) focused ion beam (FIB) has emerged as a powerful tool to directly pattern nanostructures below 10 nm due to its high-resolution capabilities and the inert nature of the ion source. These attributes make HIM FIB particularly interesting for patterning 2D materials such as transition metal dichalcogenides (TMDs) to investigate transport phenomena at the nanoscale. Reported here is the fabrication of MoS₂ nanoribbon devices using HIM FIB-induced etching (FIBIE) with XeF₂, allowing for reduced ion dose compared to direct sputtering. While patterning is efficacious, the devices exhibit performance degradation with decreasing nanoribbon width due to damage up to 150 nm beyond the patterned edge. Incorporating an hBN encapsulation improves device performance by one order of magnitude, although the lateral extent of damage remains unchanged. The spatial distribution of damage is shown to be determined by the forward- and backscattered ions and electrons, while the hBN encapsulation layer substantially reduces damage from XeF₂ interactions in unexposed regions. Raman and photoluminescence (PL) measurements corroborate these findings, while ion/solid interaction simulations further elucidate the resolution limits imposed by substrate interactions. This work provides critical insights and a practical pathway for utilizing HIM FIBIE in 2D TMD functional device patterning.