On-surface synthesis of graphene nanoribbons with zigzag edge topology

TL;DR

This paper reports the successful bottom-up synthesis of atomically precise zigzag graphene nanoribbons with controlled edges, enabling the study of their predicted spin-polarized edge states for potential spintronic applications.

Contribution

It introduces a novel bottom-up fabrication method for zigzag graphene nanoribbons with precise edge control, previously unachieved with top-down approaches.

Findings

Edge-localized states with large energy splittings confirmed by spectroscopy

Atomically precise zigzag edges achieved through surface-assisted synthesis

Potential for exploring spin-related properties in graphene nanostructures

Abstract

Graphene-based nanostructures exhibit a vast range of exciting electronic properties that are absent in extended graphene. For example, quantum confinement in carbon nanotubes and armchair graphene nanoribbons (AGNRs) leads to the opening of substantial electronic band gaps that are directly linked to their structural boundary conditions. Even more intriguing are nanostructures with zigzag edges, which are expected to host spin-polarized electronic edge states and can thus serve as key elements for graphene-based spintronics. The most prominent example is zigzag graphene nanoribbons (ZGNRs) for which the edge states are predicted to couple ferromagnetically along the edge and antiferromagnetically between them. So far, a direct observation of the spin-polarized edge states for specifically designed and controlled zigzag edge topologies has not been achieved. This is mainly due to the limited precision of current top-down approaches, which results in poorly defined edge structures. Bottom-up fabrication approaches, on the other hand, were so far only successfully applied to the growth of AGNRs and related structures. Here, we describe the successful bottom-up synthesis of ZGNRs, which are fabricated by the surface-assisted colligation and cyclodehydrogenation of specifically designed precursor monomers including carbon groups that yield atomically precise zigzag edges. Using scanning tunnelling spectroscopy we prove the existence of edge-localized states with large energy splittings. We expect that the availability of ZGNRs will finally allow the characterization of their predicted spin-related properties such as spin confinement and filtering, and ultimately add the spin degree of freedom to graphene-based circuitry.