Modificación superficial de materiales de carbonografito y grafeno

Resumo

[EN]The present work mainly aims at investigating, both on the nanometer and atomic scales, the effect of different types of oxidation on graphite as well as on graphene sheets prepared by chemical methods. The basic characterization tools have been scanning tunneling and atomic force microscopies (STM/AFM), which in combination with several complementary techniques (e.g., Raman and X-ray photoelectron spectroscopies) have afforded a detailed knowledge of the surface morphology, structure and chemistry of the different oxidized materials. Highly oriented pyrolytic graphite (HOPG) was employed as a model carbon material for studies of oxidation by dielectric barrier discharge (DBD) plasma and ultraviolet-generated ozone. The main differences between the two basic (physical and chemical) mechanisms that drive the oxidative etching of carbon materials could be established. For DBD plasma-oxidized samples, a type of atomic-scale defect hitherto unreported on carbon materials was observed by STM. A combination of experimental and theoretical work indicated that such type of defect could be attributed to two-dimensional interstitial clusters of oxygen trapped beneath the surface graphene of HOPG. The structure of the graphene sheets and their precursor (graphene oxide) was examined in detail by STM and AFM. These sheets exhibited a large degree of structural disorder. Likewise, an in-depth study concerning the accurate measurement of sheet thickness by AFM/STM was carried out. Finally, studies on the oxidation of graphene sheets revealed their high reactivity compared with that of graphitic materials with more perfect structure (HOPG and pristine graphene). Such studies showed evidence of the heterogeneous structure that this type of graphene is believed to exhibit on a scale of just a few nm, so that relatively pristine regions coexist with areas where the large majority of the defects are located.