Nanopore Fabrication of Two-Dimensional Materials on SiO2 Membranes Using He Ion Microscopy

Structures with pores having diameters of several nanometers can be used for distinguishing nucleotides in DNA. A 2-D material such as a thin membrane is expected to enhance precise molecule recognition. Here, we present the nanopore fabrication to thin 2-D membranes using He ion microscopy (HIM). We transferred three 2-D materials, chemical vapor deposition (CVD) graphene, CVD boron nitride, and peel-off MoS2, to the submicrometer pore of freestanding SiO2 membranes on a silicon substrate. The number of atomic layers of the 2-D materials was confirmed via Raman spectroscopy and X-ray photoelectron spectroscopy. We examined the reproducibility and accuracy of nanopore fabrication as a function of the focal position and beam irradiation intensity of the HIM system. Reproducible nanopores having diameters of less than 10 nm were realized by optimizing the intensity and focal position. We achieved 1.5-nm-diameter nanopores in a single layer of graphene using this HIM technique.