Substrate-dependent pore formation in molybdenum disulfide monolayers under ion irradiation
Ion irradiation is a versatile tool for nanostructuring surfaces, yet the roles of energy deposition and dissipation at the surface and in ultrathin materials remain poorly understood. In this study, we investigate nanopore formation in monolayer MoS$_2$ on different substrates under irradiation of highly charged ions (HCIs) and swift heavy ions (SHIs): two types of ions that, despite having vastly different kinetic energies, interact primarily with the electronic system of the target. Using scanning transmission electron microscopy, we quantify pore radii and pore formation efficiencies for suspended MoS$_2$, MoS$_2$ on SiO$_2$, bilayer MoS$_2$ and MoS$_2$ on gold. Both pore size and pore formation efficiency exhibit a pronounced dependence on the type of substrate. Pores are largest and most frequent in MoS$_2$ on SiO$_2$, while the gold substrate massively quenches pore formation. The results indicate that the observed pore dimensions under both HCI and SHI irradiation are consistent with a central role of substrate and interface-dependent electronic dissipation pathways.