A comparative Electron Paramagnetic Resonance study of expanded graphites and graphene

Graphene, a novel electronic system with unprecedented characteristics, can be obtained using different methods, each producing materials with specific characteristics from the electronic point of view. Among these procedures, methods based on the expansion of graphite allow to obtain graphene material in rather high quantities. We have, then, conducted a comparative study of graphene materials produced by these methods by using electron paramagnetic resonance (EPR) techniques; single-layer commercial graphene produced using the Hummers method has been used as the reference. EPR techniques enable the study of some magnetic properties of different types of electrons exhibiting paramagnetic nature. We have analysed the EPR spectra to identify the different types of paramagnetic centres contributing to the spectrum. The analysis of the temperature-dependent EPR spectra and the use of pulse techniques allowed us to separate and characterize the contribution of free conduction electrons from the contributions of localized edge states and molecular-type paramagnetic states.