Caracterização estrutural da interface grafeno/SiC após intercalação de oxigênio

Abstract

The electronic and structural properties of low-dimensional materials, such as graphene, are highly related to the characteristics of the interface between them and the substrate where they are found. In this work we study the structure of the interface formed between epitaxial graphene bilayers and the silicon carbide (SiC) substrate after oxygen intercalation in the graphene/SiC system. This intercalation process converts the buffer-layer into a graphene layer and thereby generates an AB graphene bilayer with high structural quality decoupled from the oxidized substrate. However, already published results indicate that the electronic mobility of the system decreases from values typically around 3000 cm²/Vs to only 700 cm²/Vs after the intercalation process. Theoretical DFT calculations, performed in a previous work, showed that defects at the oxidized interface generate a high density of states near to the Fermi level, which are responsible for the reduction of electronic mobility. We used two structural characterization techniques (x-ray diffraction and photoelectron diffraction) to understand in detail the structure formed at the interface. The results obtained indicate that a high percentage of the interface is amorphous and presents defects such as local substitutions of oxygen atoms by carbon atoms at the oxide region or of carbon atoms by oxygen atoms at the surface of SiC. These substitutions generate silicon oxycarbides (SiOxCy) at the interface, and these are the structures responsible for the high density of states near to the Fermi level and consequently the low electronic mobility of the system.