'For n-LG , we have n2 (square of n) DR processes' according to Annu.Rev.Condens.Matter Phys.2010.1:89-108. But Physics Report 473 (2009) 51-87 : for 3-LG , ''one should model the DR Raman process, by considering 15 different transitions, but the energy separation of many of these fifteen different processes turn out to be very close to each other from an experimental standpoint'. Whereas from same paper in Fig. 7 , we are getting 6 Lorentzian peaks for 3-LG. But according to previous paper for 3-LG , the corresponding number of DR should be 9.
Are your testing conditions & substrate same as that of Annu Rev Condens and Phys Report papers? Raman spectra is highly dependent on the substrate and sample preparation technique.
But experiment should be matched with theory. I'm comparing the result between two papers.I'm asking that why discrepancy between three different answers?
one is giving 9 DR (n2 formulae ) , 6 DR (from experimental curve from 2nd paper) , 15 DR (from group theory analysis from 2nd paper).
The 9=6 is because "four of these processes are degenerate," (Park et al, Carbon 47, p.1303), so 9 processes result in 5+1=6 peaks. The next problem is how 15 "allowed" DR processes (clearly stated in both Malard's review paper sec 2.3 and their PRB 79, 125426 sec 5) became the "nine optical processes which contribute to the G' band line shape of 3L graphene," in the Park paper. Perhaps some of those processes are not optically active? I share your confusion there.
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