Effect of topological non-hexagonal rings and Stone Wale defects on the vibrational response of single and multi-layer ion irradiated graphene

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 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. [Display omitted] •Observing Stone Wale/Non-hexagonal ring (SW/NHR) defects in graphene by Raman.•Predicted by theory, SW/NHR observed here first time by Raman experiments.•Irradiation ion energy (100–300 eV) affects disorder modes in Raman.•Transition stage, in energy 100–150 eV, in single and multilayers (SLG, MLG).•SW/NHR Raman mode is significant for studying topological aspects of Graphene.