Mechanical cleaning of graphene using in situ electron microscopy

Abstract

Avoiding and removing surface contamination is a crucial task when handling specimens in any scientific experiment. This is especially true for two-dimensional materials such as graphene, which are extraordinarily affected by contamination due to their large surface area. While many efforts have been made to reduce and remove contamination from such surfaces, the issue is far from resolved. Here we report on an in situ mechanical cleaning method that enables the site-specific removal of contamination from both sides of two dimensional membranes down to atomic-scale cleanliness. Further, mechanisms of re-contamination are discussed, finding surface-diffusion to be the major factor for contamination in electron microscopy. Finally the targeted, electron-beam assisted synthesis of a nanocrystalline graphene layer by supplying a precursor molecule to cleaned areas is demonstrated.

Continuous‐Flow Synthesis of High‐Quality Few‐Layer Antimonene Hexagons

“…[ 15,27,28 ] Additionally, a significant C signal was detected on the edges of the nanosheet, most probably as a result of the presence of capping agents as well as contamination from residual solvents. [ 29 ] The presence of S was not detected on the surface, in good agreement with XPS and thermogravimetric analysis coupled to gas chromatography and mass spectrometry (TG‐GC‐MS), in which ODE, OA, and 9‐octadecenenitrile (an impurity from the OA) were the predominant species detected (Figure S17, Supporting Information).…”

“…After the continuous process, the obtained FLA hexagons are covered with capping agents as well as contamination from residual solvents. [ 29 ] In order to isolate FLA hexagons, we thoroughly washed them to remove any contamination from reaction solvents and surfactants. Thus, we have observed interesting differences between the use of chloroform or isopropanol as washing and redispersing solvents to prepare FLA dispersions.…”

Mechanical removal of surface residues on graphene for TEM characterizations

“…In this study, we explored the potential of using atomic force microscopy (AFM) to remove surface residues from 2D crystals (Goossens et al 2012 ; Jain et al 2018 ; Lindvall et al 2012 ; Rosenberger et al 2018 ; Schweizer et al 2020 ). Using various TEM investigations, we confirmed that polydimethylsiloxane (PDMS) residues on graphene samples are effectively removed by contact-mode AFM sweeping.…”

Imaging Secondary Electron Emission from a Single Atomic Layer

“…[ 36,37 ] STEM‐based studies of graphene have noted the presence of a high degree of inherent contamination and strategies have been developed to mitigate this problem. [ 40–44 ] In the field of accelerator physics, exposure of surfaces to air can lead to an increase in SE yield, [ 38,39 ] which is thought to be a result of adsorbed carbonaceous material and has led to strategies for proper surface conditioning by electron bombardment. [ 45,46 ] Therefore, it is worth comparing the SE yield between pristine (clean) and contaminated regions of suspended graphene (i.e., no substrate).…”