The structure of graphite was identified in 1916[7] by the related method ofpowder diffraction.[8] It was studied in detail by Kohlschütter and Haenni in 1918, who described the properties ofgraphite oxide paper.[9] Its structure was determined from single-crystal diffraction in 1924.[10]
The theory of graphene was first explored byP. 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 byGordon W. Semenoff,David DiVincenzo andEugene J. Mele.[12] Semenoff emphasized the occurrence in a magnetic field of an electronicLandau level precisely at the Dirac point. This level is responsible for the anomalous integerquantum 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 atransmission 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 ofsp2-bonded carbon atoms, as in free-standing graphene. However, significant charge transfers from the substrate to the epitaxial graphene, and in some cases, thed-orbitals of the substrate atoms hybridize with theπ 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.
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. Earlier researchers tried to isolate graphene starting with intercalated compounds, producing very thin graphitic fragments (possibly monolayers).[20] Neither of the earlier observations was sufficient to launch the "graphene gold rush" that awaited macroscopic samples of extracted atomic planes.
One of the first patents pertaining to the production of graphene was filed in October 2002 and granted in 2006.[24] It detailed one of the first large scale graphene production processes. Two years later, in 2004 Geim and Novoselov extracted single-atom-thick crystallites from bulk graphite.[25] They pulled graphene layers from graphite and transferred them onto thinsilicon dioxide (SiO 2) on a silicon wafer in a process called either micromechanical cleavage or theScotch tape technique.[26] TheSiO 2 electrically isolated the graphene and weakly interacted with it, providing nearly charge-neutral graphene layers. The silicon beneath theSiO 2 could be used as a "back gate" electrode to vary the charge density in the graphene over a wide range.US patent 6667100, filed in 2002, describes how to process expanded graphite to achieve a graphite thickness of one hundred-thousandth of an inch (0.25 nm). The key to success was high-throughput visual recognition of graphene on a properly chosen substrate that provides a small but noticeable optical contrast.
The cleavage technique led directly to the first observation of the anomalousquantum Hall effect in graphene,[13][15] which provided direct evidence of graphene's theoretically predictedBerry's phase of masslessDirac fermions. The effect was reported by Geim's group and byPhilip Kim andYuanbo Zhang, whose papers[13][15] appeared inNature in 2005. Before these experiments other researchers had looked for the quantum Hall effect[27] and Dirac fermions[28] in bulk graphite.
Geim and Novoselov received awards for their pioneering research on graphene, notably the 2010Nobel Prize in Physics.[29]
In 2014, theNational Graphene Institute was announced to support applied research and development in partnership with other research organizations and industry.[30]
Commercialization of graphene proceeded rapidly once commercial scale production was demonstrated. In 2014 twoNorth East England commercial manufacturers, Applied Graphene Materials[31] and Thomas Swan Limited[32] (with Trinity College, Dublin researchers),[33] began manufacturing. InEast AngliaCambridge Nanosystems[34][35][36] operates a graphene powder production facility. By 2017, 13 years after creation of the first laboratory graphene electronic device, an integrated graphene electronics chip was produced commercially and marketed to pharmaceutical researchers by Nanomedical Diagnostics in San Diego.[37]
^Boehm, H. P.; Clauss, A.; Fischer, G. O.; Hofmann, U. (1 July 1962). "Das Adsorptionsverhalten sehr dünner Kohlenstoff-Folien".Zeitschrift für Anorganische und Allgemeine Chemie.316 (3–4):119–127.doi:10.1002/zaac.19623160303.ISSN1521-3749.
^DiVincenzo, D. P.; Mele, E. J. (1984). "Self-Consistent Effective Mass Theory for Intralayer Screening in Graphite Intercalation Compounds".Physical Review B.295 (4):1685–1694.Bibcode:1984PhRvB..29.1685D.doi:10.1103/PhysRevB.29.1685.
^This paper reports graphitic flakes that give an additional contrast equivalent of down to ≈0.4 nm or 3 atomic layers of amorphous carbon. This was the best possible resolution for 1960 TEMs. However, neither then nor today it is possible to argue how many layers were in those flakes. Now we know that the TEM contrast of graphene most strongly depends on focusing conditions.[17] For example, it is impossible to distinguish between suspended monolayer and multilayer graphene by their TEM contrasts, and the only known way is to analyse relative intensities of various diffraction spots.[1]
^"The Story of Graphene". October 2014.Following discussions with colleagues, Andre and Kostya adopted a method that researchers in surface science were using –using simple Sellotape to peel away layers of graphite to expose a clean surface for study under the microscope.
