Distinguishing disorder-induced bands from allowed Raman bands in graphite

Abstract

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, $D^{\prime },$ and G fundamentals and their corresponding overtones and combinations on the basal and damaged edge planes of highly oriented pyrolytic graphite in the range 800–4800 ${\mathrm{cm}}^{\mathrm{-}1}$. A clear distinction is found between the depolarization ratios of bands that are Raman allowed $(2D,$ ${2D}^{\prime },$ $2D+G)$ and those that are disorder induced $(D,$ $D^{\prime },$ $D+G),$ 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., $D_{a/b}{/D+G}_{a/b}\approx {2D}_{a/b}{/2D+G}_{a/b}.$ Such a simple result is surprising in view of the complexity of multiphonon scattering that involves several coupled scattering events.