Nonadiabatic Effects on Defect Diffusion in Silicon-Doped Nanographenes.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Computational Chemistry

Background:

• Single atom impurities, specifically substitutional silicon (Si) defects in graphene, exhibit diffusion under electron beam irradiation.
• The precise mechanisms, particularly the roles of elastic and inelastic scattering, driving this mobility are not fully understood.

Purpose of the Study:

• To investigate the influence of inelastic scattering on the diffusion of silicon defects in graphene.
• To explore potential excited-state pathways and their impact on defect mobility under electron irradiation.

Main Methods:

• Utilized excited-state electronic structure calculations to model defect behavior.
• Calculated potential inelastic effects and nonadiabatic transition rates.
• Determined ground-state and excited-state diffusion pathways and associated energy barriers.

Main Results:

• Identified an electronically nonadiabatic excited-state diffusion pathway for silicon defects.
• This pathway, involving softened Si-C bonds, exhibits a diffusion barrier approximately 2 eV lower than the ground-state pathway.
• Calculated transition rates suggest this excited-state pathway is accessible under electron irradiation.
• Even elastic scattering can induce nonadiabatic transitions, potentially increasing the diffusion barrier.

Conclusions:

• Electronic nonadiabaticity plays a significant role in beam-induced atomic transformations in materials.
• Excited-state pathways can facilitate defect diffusion in graphene under irradiation.
• Proposed experimentally verifiable signatures to confirm the existence of these excited-state pathways.