The Raman spectroscopic study of three GO samples was conducted using the 514 nm laser. The Raman spectra (Fig. 4) of all the three GO samples exhibited two strong peaks: the G mode, a doubly degenerate phonon mode at the Brillouin zone observed at 1590 cm1, originating from in-plane vibration of the sp2 domain; the D mode arising from the doubly resonant disorder-induced mode at 1341 cm1. Moreover, for all the GOs synthesized by the modied Hummer’s method, stronger D bands appear in the Raman spectra. Moreover, a very small decrease in the IG/ID intensity ratio (from 0.74 for GO-1 to 0.67 for GO-3) indicates a slight decrease in the in-plane domain size with a minute increase in the sp3 domain (defect density) with oxygenated functional groups on the GO basal plane of GO. Therefore, the Raman analysis result clearly supports previous microscopic analysis.