Graphene and Graphite

Carbon is a unique and very versatile element which is capable of forming different architectures at the nanoscale. Over the last 20 years, new members of the carbon nanostructure family arose, and more are coming. This review provides a brief overview on carbon nanostructures ranging from C60 to graphene, passing through carbon nanotubes. It provides the reader with important definitions in carbon nanoscience and concentrates on novel one- and two-dimensional layered carbon (sp2 hybridized), including graphene and nanoribbons. This account presents the latest advances in their synthesis and characterization, and discusses new perspectives of tailoring their electronic, chemical, mechanical and magnetic properties based on defect control engineering. It is foreseen that some of the structures discussed in the review will have important applications in areas related to electronics, spintronics, composites, medicine and many others.

the following definitions regarding graphene-like structures:

Graphite: A 3D system

We can define graphite as an infinite three-dimensional crystal made of stacked layers consisting of sp2 hybridized carbon atoms (Fig. 1g); each carbon atom is connected to other three making an angle of 120◦ with a bond length of 1.42 Å. Depending on the layers stacking, these crystals could be hexagonal (ABABAB. . .) or rhombohedral (ABCABC. . .). The hexagonal and rhombohedal structures belong to the P63/mmc (194) and R-3m (166) space groups, respectively. In both 3D crystals, the layers interact weakly through van der Waals forces. Graphite crystals can be found naturally, and can also be artificially synthesized by thermolytic processes; such as the production of highly oriented pyrolytic graphite (HOPG).

Graphene: A 2D system

A graphene crystal is an infinite two-dimensional layer consisting of sp2 hybridized carbon atoms , which belongs to one of the five 2D Bravais lattices called the hexagonal (triangular) lattice. It is noteworthy that by piling up graphene layers, in an ordered way, one can form 3D graphite. Graphene was initially considered as a theoretical building block used to describe the graphite crystal, and to study the formation of carbon nanotubes (rolled graphene sheets), and predict their fascinating electronic properties. This 2D atomic (one atom thick) crystal of carbon has as fingerprint a unique electronic structure with linear dispersion close to the Fermi level. Charge carriers in graphene are better described as massless Dirac fermions, which result in new phenomena.