Structure, Stability, Edge States and Aromaticity of Graphene Ribbons

TL;DR

This study uses density functional theory to analyze the stability, structure, and electronic properties of hydrogen-terminated graphene nanoribbons under various hydrogen environments, revealing conditions for stability and edge state phenomena.

Contribution

It provides a comprehensive theoretical analysis of how hydrogen content influences the stability and electronic structure of graphene nanoribbons, connecting organic chemistry concepts to edge state behavior.

Findings

Antiferromagnetic zigzag ribbons are stable only at very low vacuum pressures.

Most stable structures at typical conditions are mono- and di-hydrogenated armchair edges.

High hydrogen concentration causes graphene to spontaneously break into nanoribbons.

Abstract

We determine the stability, the geometry, the electronic and magnetic structure of hydrogen-terminated graphene-nanoribbons edges as a function of the hydrogen content of the environment by means of density functional theory. Antiferromagnetic zigzag ribbons are stable only at extremely-low ultra-vacuum pressures. Under more standard conditions, the most stable structures are the mono- and di-hydrogenated armchair edges and a zigzag edge reconstruction with one di- and two mono-hydrogenated sites. At high hydrogen-concentration ``bulk'' graphene is not stable and spontaneously breaks to form ribbons, in analogy to the spontaneous breaking of graphene into small-width nanoribbons observed experimentally in solution. The stability and the existence of exotic edge electronic-states and/or magnetism is rationalized in terms of simple concepts from organic chemistry (Clar's rule)