Quantifying the sp/sp ratio in functionalized graphene

A major challenge in graphene nanoscience is quantifying the concentration of molecules or atoms grafted onto the graphene surface. Raman spectroscopy, a non-contact optical technique, is well suited to achieve this purpose. However, calibration becomes challenging at low coverage due to the weak signal, and at high coverage due to local fluctuations and large regions that yield no Raman response with visible light excitation. In this work, we propose a tailored continuous model that enables accurate quantification of the concentration of covalently bonded molecules or atoms and incorporates input parameters from quantum chemistry calculations that account for surface modifications. We analyze the intensity ratio of the defect-induced D band over the primary G band, along with their broadenings. This approach is validated through the comparison with both our experimental observations and previously published results on various adatom coverage rates. Good agreement is found for both low coverage rates, where the sizes of distorted and activated regions are derived from calculations, and high coverage rates, where sp 3 -hybridized, Raman-inactive regions are included. A detailed analysis of the electronic modifications induced by chemisorbed atomic hydrogen on the graphene surface enables a non-empirical approach to quantify the coverage rate.