Atomic-Scale Carving of Nanopores into a van der Waals Heterostructure with Slow Highly Charged Ions

Abstract

The growing family of 2D materials led not long ago to combining different 2D layers and building artificial systems in the form of van der Waals heterostructures. Tailoring of heterostructure properties postgrowth would greatly benefit from a modification technique with a monolayer precision. However, appropriate techniques for material modification with this precision are still missing. To achieve such control, slow highly charged ions appear ideal as they carry high amounts of potential energy, which is released rapidly upon ion neutralization at the position of the ion. The resulting potential energy deposition is thus limited to just a few atomic layers (in contrast to the kinetic energy deposition). Here, we irradiated a freestanding van der Waals MoS 2 /graphene heterostructure with 1.3 keV/amu xenon ions in high charge states of 38, which led to nanometer-sized pores that appear only in the MoS 2 facing the ion beam, but not in graphene beneath the hole. Reversing the stacking order leaves both layers undamaged, which we attribute to the high conductivity and carrier mobility in graphene acting as a shield for the MoS 2 underneath. Our main focus is here on monolayer MoS 2 , but we also analyzed areas with few-layer structures and observed that the perforation is limited to the two topmost MoS 2 layers, whereas deeper layers remain intact. Our results demonstrate that in addition to already being a valuable tool for materials processing, the usability of ion irradiation can be extended to mono- (or bi)layer manipulation of van der Waals heterostructures when the localized potential energy deposition of highly charged ions is also added to the toolbox.

Facile Fabrication of Subnanopores in Graphene under Ion Irradiation: Molecular Dynamics Simulations

“…Among numerous fabrication methods, the ion beam irradiation is promising due to lots of adjustable parameters, for example, energy, incident angle, and fluence of the ions. For instance, Schwestka et al 15 recently reported that in van der Waals heterostructures, nanopores with a mean radius of 3.2 ± 1.0 nm could be created under the irradiation of slow highly charged ions, and the smallest pore was about 1.6 nm in diameter. Schlichting and Poulikakos 16 found that gallium ion bombardment followed by oxygen etching could generate sub-5 nm pores in double-layer graphene.…”

Model for Nanopore Formation in Two-Dimensional Materials by Impact of Highly Charged Ions

“…While HCI-induced pores were never seen on SLG , (semimetal with very small t h ), increasing fluorination (increasing t h ) leads to pore formation with increasing probability. Irradiation of MoS 2 with its very small charge mobility (outside the range of t h covered in this work) always results in pore formation even for moderate initial charge states of the HCI. , Below a critical hopping time t c ≈ 2.5 au, surface restructuring was never observed in our simulation irrespective of the initial charge of the HCI. The transition region between stable and unstable regions loosely follows a Q normali normaln ∝ 1 / t h − t normalc ∝ μ dependence.…”

Are two-dimensional materials radiation tolerant?

“…Besides, making heterostructures by combining semiconducting/insulating 2D materials with metallic ones can increase the stability of the former under high-energy ion bombardment by decreasing charge accumulation and also suppressing sputtering, similar to the results of the experiments on the behavior of TMD/graphene heterostructures under electron beam. 45 The results of very recent experiments 46 on the response of such heterostructures to impacts of highly-charged ions seem to confirm this.…”