Distinguishing disorder-induced bands from allowed Raman bands in graphite

The nature of the D band in the Raman spectrum of graphite has been the subject of considerable discussion. We examine the relationship between the depolarization characteristics of the D, ${D}^{\ensuremath{'}},$ and G fundamentals and their corresponding overtones and combinations on the basal and damaged edge planes of highly oriented pyrolytic graphite in the range 800\char21{}4800 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. A clear distinction is found between the depolarization ratios of bands that are Raman allowed $(2D,$ ${2D}^{\ensuremath{'}},$ $2D+G)$ and those that are disorder induced $(D,$ ${D}^{\ensuremath{'}},$ $D+G),$ implying that they are dictated by whether a Raman band is allowed in the infinite crystal, rather than by the bands' symmetry, as derived from previously proposed assignments of the D and G bands. Furthermore, although the ${D}_{a/b}$ vs ${2D}_{a/b}$ intensity ratios could differ considerably (where $a/b=HH/VV,$ $HV/VV),$ the participation of a G phonon in the scattering process changes their value in the same amount, i.e., ${D}_{a/b}{/D+G}_{a/b}\ensuremath{\approx}{2D}_{a/b}{/2D+G}_{a/b}.$ Such a simple result is surprising in view of the complexity of multiphonon scattering that involves several coupled scattering events.