  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.
