Low Energy Electron Point Projection Microscopy of Suspended Graphene, the Ultimate "Microscope Slide"

TL;DR

This paper demonstrates the use of low-energy electron point projection microscopy to image suspended graphene, revealing its transparency, rippling, and diffraction properties, and proposes graphene as an ideal substrate and anode for high-resolution electron imaging.

Contribution

It introduces a novel application of PPM with graphene as both substrate and anode, enabling damage-free imaging and potential electron holography of nanoscale objects.

Findings

Graphene shows 74% transparency at 100-200 eV.

Rippling in suspended graphene has a wavelength of ~26 nm.

Electron source size is estimated at 4.7 Å.

Abstract

Point Projection Microscopy (PPM) is used to image suspended graphene using low-energy electrons (100-200eV). Because of the low energies used, the graphene is neither damaged or contaminated by the electron beam. The transparency of graphene is measured to be 74%, equivalent to electron transmission through a sheet as thick as twice the covalent radius of sp^2-bonded carbon. Also observed is rippling in the structure of the suspended graphene, with a wavelength of approximately 26 nm. The interference of the electron beam due to the diffraction off the edge of a graphene knife edge is observed and used to calculate a virtual source size of 4.7 +/- 0.6 Angstroms for the electron emitter. It is demonstrated that graphene can be used as both anode and substrate in PPM in order to avoid distortions due to strong field gradients around nano-scale objects. Graphene can be used to image objects suspended on the sheet using PPM, and in the future, electron holography.