Graphene is a 2-dimensional crystalline allotrope of carbon, where the carbon atoms are arranged in a honeycomb lattice. Each carbon atom forms σ σ -bonds to the three neighboring atoms that lie in the graphene plane at angles of 120 ∘ ∘ . These bonds are mediated by three of carbon's four electrons while the fourth electron, which occupies a p z orbital, mediates an out-of-plane π -bond that leads to the electronic bands at the Fermi level. The unique transport properties and the semimetallic state of graphene are the result of the delocalized electrons occupying these p z orbitals.