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.
Potential applications of graphene
In 2010, researchers first reported creating a graphene-silicon heterojunction solar cell, where graphene served as a transparent electrode and introduced a built-in electric field near the interface between the graphene and n-type silicon to help collect charge carriers. In 2012 researchers reported efficiency of 8.6% for a prototype consisting of a silicon wafer coated with trifluoromethanesulfonyl-amide (TFSA) doped graphene. Doping increased efficiency to 9.6% in 2013. In 2015 researchers reported efficiency of 15.6% by choosing the optimal oxide thickness on the silicon. This combination of carbon materials with traditional silicon semiconductors to fabricate solar cells has been a promising field of carbon science.