  The Helium Ion Microscope (HIM) has the capability to image small features
with a resolution down to 0.35 nm due to its highly focused gas field
ionization source and its small beam-sample interaction volume. In this work,
the focused helium ion beam of a HIM is utilized to create nanopores with
diameters down to 1.3 nm. It will be demonstrated that nanopores can be milled
into silicon nitride, carbon nanomembranes (CNMs) and graphene with
well-defined aspect ratio. To image and characterize the produced nanopores,
helium ion microscopy and high resolution scanning transmission electron
microscopy were used. The analysis of the nanopore's growth behavior, allows
inferring on the profile of the helium ion beam.
