The focus of this chapter is set on the application of EPR methods to
carbon-based materials, from nanographites to graphene-based materials, for the
resolution and characterization of the different signals, related to the presence of
specific species, or structures. Because of the intrinsic heterogeneity of the samples,
this goal is not simple: most of the signals coming from different types of structures
have similar spectroscopic features and are overlapping in the cw-EPR spectra with
very different relative intensities. It is then necessary to use all possibilities that EPR
offers, from the cw-EPR techniques to pulse EPR methods, to disentangle ideally all
contributions. Our analysis of the EPR spectra considers the presence of three types of
paramagnetic contributions: conduction electrons, edge states and molecular states.
This interpretation framework has been shown to be effective for the considered
materials, characterized by the presence of finite-dimension graphene layers, eventually
stacked one above the other. In our analysis, we investigated different experimental
parameters, like the variation in the temperature of the EPR intensity, the values of the
g-tensors and the homogeneous lineshapes of the spectra to obtain further structural
information. Pulse EPR methods were used to study and characterize species with long
relaxation times (molecular states). Echo-detected EPR enabled to obtain their spectral
lineshapes. Hyperfine spectroscopies, ESEEM, ENDOR and HYSCORE, determined
the electron hyperfine couplings of unpaired electrons with magnetic nuclei, thus
allowing the evaluation of the extent of the π-system and the presence of different types
of nuclei.
Keywords: Conduction electrons, Dysonian lineshape, Edge states, Echodetected
EPR (ED-EPR), ENDOR, EPR, ESEEM, Expanded graphite, FT EPR,
Graphene defects, Graphite, Hyperfine interaction, HYSCORE, Lorentzian
lineshape, Molecular states, Nanographite, Natural graphite, π-systems, Reduced
graphene oxide (RGO), Synthetic graphite.
