Helium ion microscopy of carbon nanomembranes

Abstract

Carbon Nanomembranes (CNMs) are extremely thin (0.5–3.0 nm), synthetic two-dimensional (2D) layers or sheets with tailored physical, chemical or biological function. With two opposing surfaces they interface and link different environments by their distinct physical and chemical properties, which depend on their thickness, molecular composition, structure and the environment on either side. Due to their nanometer thickness and 2D architecture, they can be regarded as “surfaces without bulk” separating regions with different gaseous, liquid or solid components and controlling any materials exchange between them. Helium Ion Microscopy is very well suited to investigate CNMs. Its main advantage is its high surface sensitivity that generates high contrast images, even in samples where there is very little material available. It is shown that HIM imaging is an effective tool for the characterization of “free-standing” as well as “supported” CNMs. Effects of sample charging, the imaging of multilayer-CNMs and the identification of image artefacts are discussed. It will be shown that at even low magnification, single sheets of CNM can be clearly detected and HIM images show a lot of detail. Folds, wrinkles and pores in the membrane are clearly seen and can be used to characterize the quality of CNMs. In addition, the high depth of focus eases the HIM operation. CNMs can also be milled with the HIM, and nanopores of very small diameter (down to 1.3 nm) have been fabricated.