Directed Growth of Hydrogen Lines on Graphene: High Throughput Simulations Powered by Evolutionary Algorithm

TL;DR

This study uses an evolutionary algorithm combined with DFTB calculations to simulate hydrogen line growth on graphene, revealing a mechanism for line formation along the minimum curvature line that could enable edge or nanoribbon creation without cutting.

Contribution

The paper introduces a high-throughput simulation method that uncovers a new hydrogenation growth mechanism along the minimum curvature line on graphene.

Findings

Hydrogen lines preferentially grow along the minimum radius of curvature line.

The growth mechanism reduces reaction barriers, enabling chain-like hydrogenation.

Potential to form graphene edges or nanoribbons without physical cutting.

Abstract

We set up an evolutionary algorithm combined with density functional tight-binding (DFTB) calculations to investigate hydrogen adsorption on flat graphene and graphene monolayers curved over substrate steps. During the evolution, candidates for the new generations are created by adsorption of an additional hydrogen atom to the stable configurations of the previous generation, where a mutation mechanism is also incorporated. Afterwards a two-stage selection procedure is employed. Selected candidates act as the parents of the next generation. In curved graphene, the evolution follows a similar path except for a new mechanism, which aligns hydrogen atoms on the line of minimum curvature. The mechanism is due to the increased chemical reactivity of graphene along the minimum radius of curvature line (MRCL) and to sp$^3$ bond angles being commensurate with the kinked geometry of hydrogenated graphene at the substrate edge. As a result, the reaction barrier is reduced considerably along the MRCL, and hydrogenation continues like a mechanical chain reaction. This growth mechanism enables lines of hydrogen atoms along the MRCL, which has the potential to overcome substrate or rippling effects and could make it possible to define edges or nanoribbons without actually cutting the material.