Atomically Thin Graphene Windows That Enable High Contrast Electron Microscopy without a Specimen Vacuum Chamber.

Area of Science:

• Materials Science
• Physics
• Electron Microscopy

Background:

• Scanning electron microscopes (SEMs) traditionally require high vacuum, limiting specimen types.
• Electron scattering in air at SEM voltages has a mean free path (MFP) of 50-100 μm.
• Existing airSEM designs are limited by scattering from silicon nitride windows.

Purpose of the Study:

• To develop an improved airSEM by replacing silicon nitride windows with graphene.
• To assess the impact of graphene windows on imaging contrast and resolution in an airSEM.
• To enhance the signal-to-noise ratio for various SEM imaging modes.

Main Methods:

• Demonstrated the use of a robust bilayer graphene window to seal electron optics from the environment.
• Compared imaging performance of the airSEM with graphene windows to traditional vacuum SEM and SEM with silicon nitride windows.
• Evaluated contrast, resolution, and signal-to-noise ratio in backscattered, transmission, and surface imaging modes.

Main Results:

• Bilayer graphene windows provided an electron-transparent barrier with only a 2% drop in contrast.
• Achieved a 5-fold increase in signal/noise ratio compared to multi-MFP-thick silicon nitride windows.
• Comparable imaging quality to all-vacuum SEM was maintained.

Conclusions:

• Bilayer graphene windows are a viable solution for enabling high-quality SEM imaging in ambient air.
• The airSEM with graphene windows overcomes limitations of previous designs, expanding possibilities for in-situ and ambient SEM analysis.
• This advancement facilitates high-contrast imaging across multiple SEM modes without a full vacuum environment.