Two-dimensional MoS₂ under ion irradiation: from controlled defect production to electronic structure engineering

Abstract

Two-dimensional (2D) transition metal dichalcogenides (TMDs), like MoS2, have unique electronic and optical properties, which can further be tuned using ion bombardment and post-synthesis ion-beam mediated methods combined with exposure of the irradiated sample to precursor gases. The optimization of these techniques requires a complete understanding of the response of 2D TMDs to ion irradiation, which is affected by the reduced dimensionality of the system. By combining analytical potential molecular dynamics with first-principles calculations, we study the production of defects in free-standing MoS2 sheets under noble gas ion irradiation for a wide range of ion energies when nuclear stopping dominates, and assess the probabilities for different defects to appear. We show that depending on the incident angle, ion type and energy, sulfur atoms can be sputtered away predominantly from the top or bottom layers, creating unique opportunities for engineering mixed MoSX compounds where X are chemical elements from group V or VII. We study the electronic structure of such systems, demonstrate that they can be metals, and finally discuss how metal/semiconductor/metal junctions, which exhibit negative differential resistance, can be designed using focused ion beams combined with the exposure of the system to fluorine.

Controllable, Wide‐Ranging n‐Doping and p‐Doping of Monolayer Group 6 Transition‐Metal Disulfides and Diselenides

“…Many studies have focused on modulating the carrier type and density in a controllable manner . Adapting ideas from Si‐based semiconductor technology, several approaches have been reported, including synthesis of mixed‐chalcogen TMD alloys, substitutional doping with other elements that contribute a different number of valence electrons (e.g., replacing Mo by Re, Nb, or Zr), thermal diffusion or implantation of foreign atoms, and plasma etching . However, unwanted side‐effects may generate defects in the crystalline lattice of the sub‐nanometer thick films .…”

Recent Progress on Irradiation-Induced Defect Engineering of Two-Dimensional 2H-MoS2 Few Layers

“…Molecular dynamics simulations were also employed to study the production of defects in MoS 2 mono-layers under noble gas ion irradiation, such as He, Ne, Ar, Kr and Xe [169]. Sulfur atoms were sputtered away predominantly from the top or bottom layers by the ion irradiation, depending on the incident angle, ion type, and ion energy.…”

High Conduction Hopping Behavior Induced in Transition Metal Dichalcogenides by Percolating Defect Networks: Toward Atomically Thin Circuits

“…It is worth noting that the defect concentration in the free-standing WSe2 induced by a particular He + dose is slightly lower than the defect concentration that can be expected for material exposed on a bulk substrate. This is because the primary He + beam energy has a small interaction cross-section with the freestanding WSe2 [28] and back-scattered He + and recoil atoms contribute significantly toward defect introduction. For atomically thin free-standing material, the vast majority of He + transmit or forward-scatter through the material, thus minimizing defects generated from backscattered He + .…”