Effect of Topological Non-hexagonal Rings and Stone Wale Defects on the Vibrational Response of Single and Multi-Layer Ion Irradiated Graphene

TL;DR

This study experimentally demonstrates the Raman signatures of topological non-hexagonal rings and Stone Wale defects in irradiated graphene, revealing defect evolution and the transition to sp3 hybridization with ion energy.

Contribution

First experimental observation of Raman signatures of SW/NHR defects in graphene, linking topological defects to vibrational response and defect evolution under ion irradiation.

Findings

Raman signatures of SW/NHR defects are identified in irradiated graphene.

Defect-related Raman modes diminish at higher ion energies.

Transition to sp3 hybridization occurs beyond certain irradiation energies.

Abstract

Present study explores the observation of topological non-hexagonal rings (NHR) and Stone Wale (SW) defects by Raman experiments in both single (SLG) and multi-layer graphene (MLG) after they are irradiated with 100- 300 eV Ar ions. Although predicted by theoretical studies, here it is experimentally shown for the first time that graphene SW/NHR defects have a signature in Raman. Broad bandwidth of the pertinent Raman features suggests the presence of more than one SW/NHR defect mode, in agreement with the DFT studies. Variations in the SW/NHR related Raman mode intensities demonstrate the annihilation of these topological defects at higher energies. Behavior of Raman allowed G and 2D excitations, as well as the disorder-activated D, D' and G* lines, has also been investigated in SLG and MLG. These indicate an evolution of defects in graphene with ion irradiation, as well as presence of a transition state beyond which the Raman modes are dominated by a rise in sp3 content. Correlation of these aspects with the SW/NHR Raman provide significant insight into ion induced evolution of graphene. The direct observation of SW/NHR defects by Raman spectroscopy could be important in promoting exploration of rich topological aspects of Graphene in various fields.