Abstract
We present an atomic-resolution observation and analysis of graphene constrictions and ribbons with sub-nanometer width. Graphene membranes are studied by imaging side spherical aberration-corrected transmission electron microscopy at 80 kV. Holes are formed in the honeycomb-like structure due to radiation damage. As the holes grow and two holes approach each other, the hexagonal structure that lies between them narrows down. Transitions and deviations from the hexagonal structure in this graphene ribbon occur as its width shrinks below one nanometer. Some reconstructions, involving more pentagons and heptagons than hexagons, turn out to be surprisingly stable. Finally, single carbon atom chain bridges between graphene contacts are observed. The dynamics are observed in real time at atomic resolution with enough sensitivity to detect every carbon atom that remains stable for a sufficient amount of time. The carbon chains appear reproducibly and in various configurations from graphene bridges, between adsorbates, or at open edges and seem to represent one of the most stable configurations that a few atomic carbon system accommodates in the presence of continuous energy input from the electron beam.
Highlights
Carbon is one of the most important elements that occurs in numerous allotropes, displays an exceedingly rich chemistry, and is contained in a staggering number of compounds
We find that graphene constrictions deviate from the hexagonal structure as their width is reduced below one nanometer, and intermediate structures between a graphene constriction and a carbon chain are dominated by pentagons and heptagons
Instead of a synthesis from smaller units, the carbon chains form by self-organization from a continuously diluted set of carbon atoms in the presence of ionizing irradiation
Summary
Carbon is one of the most important elements that occurs in numerous allotropes, displays an exceedingly rich chemistry, and is contained in a staggering number of compounds. We form monoatomic carbon chains by shrinking a graphene constriction under electron irradiation. The amorphous, carbonaceous adsorbates on the graphene membranes form carbon chains while shrinking under electron irradiation, and bended chains appear at the free edges of graphene.
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