Supported Two-Dimensional Materials under Ion Irradiation: The Substrate Governs Defect Production

Abstract

Focused ion beams perfectly suit for patterning two-dimensional (2D) materials, but the optimization of irradiation parameters requires full microscopic understanding of defect production mechanisms. In contrast to freestanding 2D systems, the details of damage creation in supported 2D materials are not fully understood, whereas the majority of experiments have been carried out for 2D targets deposited on substrates. Here, we suggest a universal and computationally efficient scheme to model the irradiation of supported 2D materials, which combines analytical potential molecular dynamics with Monte Carlo simulations and makes it possible to independently assess the contributions to the damage from backscattered ions and atoms sputtered from the substrate. Using the scheme, we study the defect production in graphene and MoS sheets, which are the two most important and wide-spread 2D materials, deposited on a SiO substrate. For helium and neon ions with a wide range of initial ion energies including those used in a commercial helium ion microscope (HIM), we demonstrate that depending on the ion energy and mass, the defect production in 2D systems can be dominated by backscattered ions and sputtered substrate atoms rather than by the direct ion impacts and that the amount of damage in 2D materials heavily depends on whether a substrate is present or not. We also study the factors which limit the spatial resolution of the patterning process. Our results, which agree well with the available experimental data, provide not only insights into defect production but also quantitative information, which can be used for the minimization of damage during imaging in HIM or optimization of the patterning process.

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

“…In addition, the formation thresholds for Mo-vacancy and DIV are not very high (18-29 eV). Kretschmer et al [168] combined analytical potential molecular dynamics with Monte Carlo simulations to simulate helium and neon ion irradiation of MoS 2 nanosheets deposited on SiO 2 substrates. Their simulation indicated that substrates governed the defect production of irradiated MoS 2 layers.…”

Irradiation of Transition Metal Dichalcogenides Using a Focused Ion Beam: Controlled Single‐Atom Defect Creation

“…[15,16] More recently, FIB irradiation has been extended as a means of structural modification and nanopatterning in 2D materials such as graphene. [17] Theoretical studies [18][19][20][21] on the role of ion incidence angle and substrate effects in the defect creation process in 2D materials like TMDs and graphene, and similar experimental studies, [8,22,23] are starting to emerge. A wide range of techniques for defect creation have been reported in literature including plasma etching, [24] thermal decomposition, [25] acid etching, [26,27] electron irradiation, [28] and ion irradiation.…”

“…[8] As of now, there is a relatively poor correspondence between ion irradiation experiments and theory in 2D materials. [8,9,18,19,31] One likely reason for these discrepancies is the inadequate understanding of experimental parameters. For example, material contamination has been ubiquitously reported after ion irradiation and while it plays a significant role in analytical and structural characterization, such "substrates" are rarely accounted for in theoretical simulations.…”

Effect of localized helium ion irradiation on the performance of synthetic monolayer MoS2 field-effect transistors

“…For a given delivered dose, the ion beam provides a high concentration of effective adsorption sites for atmospheric p-dopants (or adventitious hydrocarbons) within the area defined by the spread of the Gaussian probe extension. The probe has spatially trailing lower-dose tails, the damage of which extends to more than 10 nm and may induce additional n-doping with no complementary adsorbant saturation, i.e., by creating unsaturated SVs in the bottom sulfuric layer [34,39]. A larger irradiation area will thus provide more effective p-doping sites while stifling the n-doping response as the probe tails begin to extend past the FET channel.…”