Modeling the intrusion of molecules into graphite: Origin and shape of the barriers ^☆

Graphical abstract

Highlights

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  We model the interaction of fusion-relevant molecules with graphite.

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  Coronene serves as a cluster model for the graphite(0 0 0 1) surface.

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  We calculate energy barriers upon permeation of a molecule through coronene.

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  Energy barriers for (closed-shell) molecules are much higher than for atoms.

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  Barrier heights can be diminished by temporary bonding.

Abstract

We performed density functional theory calculations to explore the energetic and geometric aspects of the permeation of H ₂, BeH _x , OH _x ( x = 1, 2) and CH _y ( y = 1–4) through the central hexagon of coronene. Coronene serves as a cluster model for extended graphene which can be regarded as the first layer of a graphite (0 0 0 1) surface. We compare the energy barriers encountered by these molecular projectiles with the ones that are obtained for atomic H, Be, C and O. The barriers are substantially lower if projectiles possess free valences that can bind to the carbon entity. Furthermore, for some of the species fragmentation is observed. Implications with respect to plasma-surface interaction are discussed.