Direct Experimental Evidence of Metal-Mediated Etching of Suspended Graphene

TL;DR

This study provides direct experimental evidence that certain metal atoms can induce the formation of nano-scale holes in suspended graphene, with implications for understanding defect formation and material modification.

Contribution

It demonstrates metal-mediated etching of graphene at atomic resolution and highlights the role of specific metal atoms and oxygen in the process, supported by both experimental imaging and theoretical calculations.

Findings

Metal atoms (except gold) initiate hole formation in graphene.

Electron beam promotes metal atom migration to graphene surface.

Oxygen presence significantly lowers vacancy formation energy.

Abstract

Atomic resolution high angle annular dark field imaging of suspended, single-layer graphene, onto which the metals Cr, Ti, Pd, Ni, Al and Au atoms had been deposited was carried out in an aberration corrected scanning transmission electron microscope. In combination with electron energy loss spectroscopy, employed to identify individual impurity atoms, it was shown that nano-scale holes were etched into graphene, initiated at sites where single atoms of all the metal species except for gold come into close contact with the graphene. The e-beam scanning process is instrumental in promoting metal atoms from clusters formed during the original metal deposition process onto the clean graphene surface, where they initiate the hole-forming process. Our observations are discussed in the light of calculations in the literature, predicting a much lowered vacancy formation in graphene when metal ad-atoms are present. The requirement and importance of oxygen atoms in this process, although not predicted by such previous calculations, is also discussed, following our observations of hole formation in pristine graphene in the presence of Si-impurity atoms, supported by new calculations which predict a dramatic decrease of the vacancy formation energy, when SiOx molecules are present.