EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Since the discovery of 2D materials almost two decades ago, the family of atomically thin materials has grown immensely and includes now not only semi-metallic graphene but also semi-conducting and insulating representatives. The ability to draw from a set of materials with such diverse properties is highly beneficial in the development of new applications. Combining two or more 2D materials in the form of van-der-Waals (vdW) heterostructures and thus utilising the outstanding properties of, e.g., semi-conducting monolayer MoS$_2$ and semi-metallic graphene, even enhances the application potential in these artificial solids. However, post-growth modification techniques on the nanoscale for vdW heterostructures that can be applied with monolayer precision are still missing.
Here we present slow highly charged ions (HCIs) as a tool to carve nano-pores into the topmost monolayer of a vdW heterostructures only. HCIs carry high amounts of potential energy, which is - in contrast to their kinetic energy - released within a few atomic layers only upon impact on the surface. We show that irradiation of a MoS$_2$/graphene heterostructure with slow highly charged xenon ions thus allows to perforate the MoS$_2$ layer whereas the graphene layer stays intact. By irradiation of a heterostructure with reversed stacking order, i.e., graphene on top of MoS$_2$, we find that, owing to its high carrier mobility, graphene acts as a shield and prevents the MoS$_2$ from being damaged. But even for MoS$_2$ which is more susceptible to HCI induced potential sputtering, the perforation of up to three MoS2 layers on top of graphene is limited to the topmost 1-2 layers [1].

[1] J. Schwestka, H. Inani, M. Tripathi, A. Niggas, N. McEvoy, F. Libisch, F. Aumayr, J. Kotakoski, and R.A. Wilhelm ACS Nano 2020 14 10536