Single-layer graphene was first unambiguously produced and identified in 2004, by the group of Andre Geim and Konstantin Novoselov, though they credit Hanns-Peter Boehm and his co-workers for the experimental discovery of graphene in 1962; while it had been explored theoretically by P. R. Wallace in 1947. Boehm et al. introduced the term graphene in 1986
In 1859 Benjamin Collins Brodie became aware of the highly lamellar structure of thermally reduced graphite oxide.
The structure of graphite was identified in 1916[7] by the related method of powder diffraction.It was studied in detail by Kohlschütter and Haenni in 1918, who described the properties of graphite oxide paper]Its structure was determined from single-crystal diffraction in 1924.[10]
The theory of graphene was first explored by P. R. Wallace in 1947 as a starting point for understanding the electronic properties of 3D graphite.[3][11] The emergent massless Dirac equation was first pointed out by Gordon W. Semenoff, David DiVincenzo and Eugene J. Mele.[12] Semenoff emphasized the occurrence in a magnetic field of an electronic Landau level precisely at the Dirac point. This level is responsible for the anomalous integer quantum Hall effect.[13][14][15]
The earliest TEM images of few-layer graphite were published by G. Ruess and F. Vogt in 1948.[16] Later, single graphene layers were observed directly by electron microscopy.[17] Before 2004 intercalated graphite compounds were studied under a transmission electron microscope (TEM). Researchers occasionally observed thin graphitic flakes ("few-layer graphene") and possibly even individual layers. An early, detailed study on few-layer graphite dates to 1962 when Boehm reported producing monolayer flakes of reduced graphene oxide.[18][19][20][21]
Starting in the 1970s single layers of graphite were grown epitaxially on top of other materials.[22] This "epitaxial graphene" consists of a single-atom-thick hexagonal lattice of sp2-bonded carbon atoms, as in free-standing graphene. However, significant charge transfers from the substrate to the epitaxial graphene, and in some cases, the d-orbitals of the substrate atoms hybridize with the π orbitals of graphene, which significantly alters the electronic structure of epitaxial graphene.
Single layers of graphite were observed by TEM within bulk materials, in particular inside soot obtained by chemical exfoliation. Efforts to make thin films of graphite by mechanical exfoliation started in 1990,[23] but nothing thinner than 50 to 100 layers was produced before 2004.
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