Nano-patterning of a monolayer molybdenum disulfide with sub-nanometer helium ion beam: considering its shape, size and damage

Abstract

We have studied nano-patterning of a two-dimensional (2D) material with an ultrafine helium ion beam considering shape-, size- and damage-control. The study reveals that the crystalline structure plays an important role in shape-control. Instead of commonly circular-shaped nanopores, spot irradiation onto a single layer of molybdenum disulfide (MoS2) gives rise to a rhombus-shaped nanopore, which is well explained by the sub-rhombus crystalline structure of MoS2. Helium ion beams also show promising capability to precisely control size using a delivered dose. However, the size of the nanopores is not linear with the delivered dose, due to the Gaussian distributed intensity profile of the helium ion beam. The intensity profiles are further estimated by considering aperture size, those results could be taken as a significant reference for size-control. In addition, we clarify that most of the damage is a result of re-deposition, thus controlling re-deposition might be a useful way to alleviate the damage.

Resists for Helium Ion Beam Lithography: Recent Advances

“…69 Recently, rhombus-shaped nanopores were created in MoS 2 monolayers using He + beam. 70 In this work, the effect of He + dose on the shape and size of the nanopore has been investigated. At lower, medium, and high doses corresponding elliptical-, rhombus-, and polygon-shaped nanopores were observed, respectively (Figure 14).…”

A review of defect engineering, ion implantation, and nanofabrication using the helium ion microscope

“…(f) Rhombus-shaped nanopores in free-standing MoS 2 fabricated using helium FIB milling implementing an elliptical beam shape. Adapted from [ 137 ], Deng et al, Nano-patterning of a monolayer molybdenum disulfide with sub-nanometer helium ion beam: considering its shape, size and damage, Nanotechnology, Vol. 31(34), 345302, first published 12 June 2020, Copyright © 2020 IOP Publishing Ltd. Reproduced with permission.…”

“…In recent work on free-standing MoS 2 , another interesting phenomenon was observed, namely that by milling with a slightly stigmated beam (again, in spot mode), rhombus-shaped nanopores could be obtained with a geometry following that of the hexagonal MoS 2 lattice [ 137 ] ( Figure 6f ). By helium FIB milling sub-10 nm pores into hBN and growing graphene into the voids, stable graphene quantum dot arrays have also been produced [ 166 ].…”

“…For the fully cleaned membranes, the scan strategy had no effect on the final pore size, since the hydrocarbon effect was no longer at play. Apart from silicon nitride, helium FIB milling has also been used to create nanopores in other free-standing membranes, with minimum pore diameter records as follows: 1.3 nm diameter in a 1 nm thick carbon nanomembrane [164], 2.6 nm diameter in single-layer graphene [145], 4 nm diameter in few-layer and monolayer hBN [152,166], and 1.3 nm diameter in monolayer MoS 2 [137]. Ion conductance and DNA translocation through helium FIB-milled graphene nanopores has been reported [167], as has the fabrication of suspended graphene nanomesh structures (3-4 nm pores on a pitch of ≤10 nm, Figure 6e) that demonstrated bandgap opening by quantum confinement [136].…”

Organoiodine Functionality Bearing Resists for Electron-Beam and Helium Ion Beam Lithography: Complex and Sub-16 nm Patterning

“…While the potential of EBL is well documented in the literature, helium ion beam lithography (HIBL) is becoming an emerging technique for patterning very low-node features with a good pattern profile. − Although substantial technological development has been made in terms of tool specification and features, in particular, subnanometer spot size, high-intensity lighter ions, reduced backscattering leading to minimized proximity effects, etc., the tested resist platforms for HIBL are quite limited. − Hence, there is a need for new efficient resist compositions for HIBL applications.…”