Imaging of carbon nanomembranes with helium ion microscopy

Abstract

SummaryCarbon nanomembranes (CNMs) prepared from aromatic self-assembled monolayers constitute a recently developed class of 2D materials. They are made by a combination of self-assembly, radiation-induced cross-linking and the detachment of the cross-linked SAM from its substrate. CNMs can be deposited on arbitrary substrates, including holey and perforated ones, as well as on metallic (transmission electron microscopy) grids. Therewith, freestanding membranes with a thickness of 1 nm and macroscopic lateral dimensions can be prepared. Although free-standing CNMs cannot be imaged by light microscopy, charged particle techniques can visualize them. However, CNMs are electrically insulating, which makes them sensitive to charging. We demonstrate that the helium ion microscope (HIM) is a good candidate for imaging freestanding CNMs due to its efficient charge compensation tool. Scanning with a beam of helium ions while recording the emitted secondary electrons generates the HIM images. The advantages of HIM are high resolution, high surface sensitivity and large depth of field. The effects of sample charging, imaging of multilayer CNMs as well as imaging artefacts are discussed.

Synthesis of Molecular 2D Materials via Low-energy Electron Induced Chemical Reactions

“…These imaging effects are related to the dielectric properties of the CNMs resulting in their electrostatic charging upon imaging with ions and thereby with a lower yield of secondary electrons reaching the detector of the HIM. [29] The presented examples demonstrate that the application of EUV-IL on the nanopatterning of CNMs results in perforated~1 nm thick molecular nanosheets and nanoribbons, which can be prepared as free-standing objects on holey supports. This methodology opens up manifold possibilities of implementing the supported or free-standing nanopatterned CNMs in devices such as nanomechanical, nanophotonic and nanoelectrical systems, as well as their integration into lateral heterostructures with other 2D materials, which will be presented in section 4 of this review.…”

“…a) Large-area CNM with~1 nm thickness spanning a hexagonal metal grid. [29] b) Janus CNM on a metal grid with 16 nm gold nanoparticles immobilized on its S-face. [49] c) A van der Waals heterostructure consisting of four layers: (Janus CNM)/(C60-Janus CNM) 3 -spanning an orifice in a SiN membrane with dimensions of 40×44 µm 2 .…”

“…Furthermore BPT CNMs with extremely large free-standing lateral dimensions over~0.5 mm were demonstrated recently. [29] A typical helium ion microscope (HIM) image of a BPT CNM lying on a hexagonal metal grid is presented in Fig. 3a.…”

Graphene Growth by Conversion of Aromatic Self‐Assembled Monolayers

“…a–c. It has been shown that CNMs with free‐standing areas of up to 0.3 mm 2 can be obtained in this way . Fig.…”

Multi‐Scale Imaging of Polymer Electrolyte Fuel Cells using X‐ray Micro‐ and Nano‐Computed Tomography, Transmission Electron Microscopy and Helium‐Ion Microscopy

“…It has the advantage of causing less charging artefacts and damage induced by the beam for small and delicate surface features than SEM. Furthermore, it does not require the sample to be as conductive or require gold coating , . So far, it has predominately been used to characterize biological samples, nanostructured polymers and for manufacturing nanostructures for nanoelectronics/energy storage , .…”