Vibrational Signatures of Carboxylated Graphene: A First-Principles Study

Raman and infrared (IR) spectroscopies are fast, efficient, and nondestructive techniques commonly used for structural characterization of nanoscale materials. The complimentary characters of the Raman and IR spectroscopies make them ideally suited for experimental studies of carbon nanostructures. Using first-principles computational methods based on density functional perturbation theory, we computed nonresonant Raman and IR absorption spectra of carboxylated graphene containing no surface defects, containing Stone-Wales defects, and containing divacancies. Our calculations demonstrated that the presence of point defects near the functionalization sites significantly altered the Raman and IR spectra of carboxylated graphene. In all cases, we observed the emergence of new Raman and IR absorption bands in the range of low and high vibration frequencies. The calculated Raman and IR spectra showed clearly distinguishable spectroscopic signatures associated to different types of structural defects present in carboxylated graphene. The results of our study provide guidelines for the interpretation of Raman and IR spectra of chemically functionalized graphene.