▎ 摘　　要

A helium ion beam (HIB) is ideal for milling monolayer graphene in nanopore applications, but the optimizing irradiation parameter requires a comprehensive microscopic understanding of the interaction between helium ions and the suspended graphene. In this work, we investigate the influence of the substrate hole shape on the interaction between helium ions and suspended monolayer graphene on a substrate with periodic structures of different shapes. Raman spectroscopy is used to correlate the dose of HIB irradiation with engineered defects on freestanding monolayer graphene. Raman characteristics of the suspended monolayer graphene are related to the pore size and shape of the supporting substrate upon helium ion irradiation. These provide insights into the influence of the substrate hole shape on the interaction between helium ions and a freestanding graphene membrane. Our results can be used to analyze ion-membrane interactions in the other suspended monolayer two-dimensional materials for sub-nanometer precision nanopore fabrication.