Adsorption of Group-IV Elements on Graphene, Silicene, Germanene, Stanene: Dumbbell Formation

TL;DR

This study uses first-principles calculations to explore how Group IV atoms form dumbbell structures on graphene, silicene, germanene, and stanene, revealing their stability, mobility, and impact on electronic properties.

Contribution

It provides new insights into the formation mechanisms, stability, and properties of dumbbell structures of Group IV elements on 2D honeycomb materials, including compounds.

Findings

Dumbbell structures form on silicene and germanene with stable binding.

Stanene is structurally unstable upon adatom adsorption.

Dumbbells are mobile due to low migration energy barriers.

Abstract

Silicene and germanene derivatives constructed from periodic dumbbell units play a crucial role in multilayers of these honeycomb structures. Using first-principles calculations based on density functional theory, here we investigate the dumbbell formation mechanisms and energetics of Group IV atoms adsorbed on graphene, silicene, germanene and stanene monolayer honeycomb structures. The stabilities of the binding structures are further confirmed by performing ab-initio molecular dynamics calculations at elevated temperatures, except for stanene which is subject to structural instability upon the adsorption of adatoms. Depending on the row number of the adatoms and substrates we find three types of binding structures, which lead to significant changes in the electronic, magnetic, and optical properties of substrates. In particular, Si, Ge and Sn adatoms adsorbed on silicene and germanene form dumbbell structures. Furthermore, dumbbell structures occur not only on single layer, monatomic honeycomb structures, but also on their compounds like SiC and SiGe. We show that the energy barrier to the migration of a dumbbell structure is low due to the concerted action of atoms. This renders dumbbells rather mobile on substrates to construct new single and multilayer Si and Ge phases.