In the article "Probing the nature of defects in graphene by Raman spectroscopy" [Nano Lett., 2012, 12 (8), pp 3925–3930], the author mentioned that ID/ID' is the measure of nature of defects. If this ratio is 7, defect corresponds to vacancy-like defects, whereas ID/ID' = 10.5 attributed as hopping defect. In addition, the author mentioned "hopping defect should describe defective graphene containing vacancies."
Similar for on-site defect and defect associated with sp3 hybridization.
Can someone tell me the difference between these types of defects?
Thanks in advance.
By hopping defects, the authors seem to mean any defect that distorts the bonds between the carbon atoms, retaining the general sp2 configuration. A simple example of such a defect is te Stone-Wales defect, where you take one C-C pair and rotate it by 90 degrees, resulting in two pentagons and two heptagons (can be referred to as 5577 also). Typically this makes the carbon atoms move out of the plane somewhat. With this definition, vacancies also belong to hopping defects (as the bonds are distorted, but sp2-like bonding remains), but have the additional property of a removed atom. I guess what the authors want to say is that graphene that produces hopping defect -like signals is likely to contain vacancies.
With a bit similar reasoning, an on-site defect appears to be thought to only have the property of an added bond on top of the graphene sheet, but when thinking of a sp3 defect the distortion of the graphene lattice (buckling out of plane) is taken into account as well.
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