Graphene
The theory of graphene was first explored by Wallace in 1947 as a starting point for understanding the electronic properties of 3D graphite. The emergent massless Dirac equation was first pointed out by Semenoff, DiVincenzo and Mele. The earliest TEM images of few-layer graphite were published by Ruess and Vogt in 1948. An early, detailed study on few-layer graphite dates to 1962 when Boehm and colleagues reported producing monolayer flakes of reduced graphene oxide. Efforts to make thin films of graphite by mechanical exfoliation started in 1990, but nothing thinner than 50 to 100 layers was produced before 2004. Initial attempts to make atomically thin graphitic films employed exfoliation techniques similar to the drawing method. Multilayer samples down to 10 nm in thickness were obtained.
Graphene production techniques
Graphene is commonly deposited on iridium(111) by CVD but also with temperature programmed growth (TPG) is possible. In CVD, a hot iridium surface is exposed to ethylene. Ethylene decomposes on the surface due to pyrolysis, and the formed carbon adsorbs to the surface forming a graphene monolayer. Thus, only a monolayer growth is possible. The formed graphene layer is weakly bounded to the iridium substrate and is located about 3.3 Å above the surface. The graphene layer and the Ir(111) substrate also forms a moiré pattern with period around 25 Å, depending on the orientation of the graphene on Ir(111). There are many different possibilities for the graphene layer orientation, the most common ones being R0 and R30. The graphene layer has also corrugation due to the moiré pattern, with height varying from 0.04 Å to 0.3 Å. Due to the long-range order of these ripples, minigaps in the electronic band-structure (Dirac cone) become visible.