Chapter 1

The History of Graphene

A pencil and a dream can take you anywhere.

Joyce A. Meyers

Prior to excavating the history of graphene, one has to know graphite, which is composed of many layers of graphene stacked together. This stacking makes a three-dimensional structure, the graphite, whereas graphene is a two-dimensional, one-atom-thick material. Evidence of the uses of graphite in Europe has been recorded in pottery decorated with graphite some 6000 years ago. The present concept and clarity about graphite is nearly 500 years old. Graphite ore (Figure 1.1) was found and mined in England in the sixteenth century.

Figure 1.1 Graphite ore. Courtesy: http://en.wikipedia.org/wiki/Graphite.

People used graphite to mark their sheep. However, it was believed that this mineral was lead ore and it was called "plumbago". Scheele, in 1779, demonstrated that plumbago is actually carbon, not lead. Because people used it to write marks on their sheep, a German scientist, Verner (1789) named it graphite (a Greek word for "writing"). With the development of the pencil industry, it has been used as a writing material in a pencil (Figure 1.2) since the eighteenth century.

Figure 1.2 A lead pencil tip made of graphite. Courtesy: http://commons.wikimedia.org/wiki/File:Pencils_hb.jpg.

Because of its layered morphology and weak dispersion forces between adjacent sheets, it was utilized as solid lubricant. Before proceeding further with the history of graphene, it is necessary to define what a graphene is.

The term "graphene" first appeared in 1987 (Mouras et al. 1987) to describe single sheets of graphite as one of the constituents. The term "graphite layers" was replaced with "graphene" by the IUPAC commission. According to the recent definition, "graphene is a two-dimensional monolayer of carbon atoms, which is the basic building block of graphitic materials (i.e., fullerene, carbon nano tubes, graphite)". Graphene is a two-dimensional material. It consists of a single layer of carbon atoms arranged in a honeycomb-like structure (Figure 1.3B).

Figure 1.3 Schematic diagram of (a) Graphite and (b) Four layers of graphene from graphite.

The carbon-carbon bond length in graphene is about 0.142 nanometers (Figure 1.3B). Its layer height was measured to be just 0.33nm (Figure 1.3A). It is the thinnest material known, and yet is also one of the strongest. Graphene is almost completely transparent. Its structure is so dense that even the smallest atom helium cannot pass through it. It conducts electricity as efficiently as copper and outperforms all other materials as a heat conductor.

In 1859 a British chemist, Benjamin Bordie, prepared a highly lamellar structure by thermally reducing graphite oxide by reacting graphite with potassium chlorate and fuming nitric acid, resulting in the formation of a suspension of graphene oxide crystallite. This graphene oxide was later woven into a paper. An early study the properties of this graphene oxide paper was completed by Kohlschutter and Haenni in 1919. Graphene, a molecule arranged in a single atomic plane, is accepted as a two-dimensional crystal. Earlier it was believed it could not be grown, because thermodynamics had been shown to prevent the formation of two-dimensional crystal in free state by Landau (1930).

Wallace (1947), while trying to study the electronic properties of three-dimensional graphite, came up with the band theory of graphite. According to him,

The structure of the electronic energy bands and Brillouin zones for graphite is developed using the 'tight binding' approximation. Graphite is found to be a semi-conductor with zero activation energy, i.e., there are no free electrons at zero temperature, but they are created at higher temperatures by excitation to a band contiguous to the highest one which is normally filled. The electrical conductivity is treated with assumptions about the mean free path. It is found to be about 100 times as great parallel to as across crystal planes. A large and anisotropic diamagnetic susceptibility is predicted for the conduction electrons; this is greatest for fields across the layers. The volume optical absorption is accounted for.

The next milestone work regarding graphene was the publication of the first TEM image of a few layers of graphene by Ruess and Vogt (1948).

Ubbelohde and Lewis (1960) isolated a single-atom plane of graphite and reported surprisingly higher basal-plane conductivity of graphite intercalation compounds as compared to that of the original graphite. They pointed out that graphite consists of layers, which are a network of hexagonal rings of carbon atoms.

Hanns-Peter Boehm and his coworkers isolated and identified single graphene sheets by TEM and XRD in 1961. Their work was published in 1962. Boehm also authored the IUPAC (International Union of Pure and Applied Chemistry) report, formally defining the term graphene in 1994. It is surprising that many reviews and papers have mentioned that graphene was discovered in 2004. The TEM taken by Boehm et al. remained the best observation for over forty years.

These forty years (between 1960 and 2000) exhibited that the research of graphene has grown slowly in multifarious directions, including synthesis. The hope of observing superior electrical properties from thin graphite or graphene layers while obtaining graphene was considered to be a formidable task in both theoretical and experimental aspects. In the graphite intercalation systems, large molecules were inserted between atomic planes, generating isolated graphene layers in a three-dimensional matrix. The subsequent removal of the larger molecules produced a mixture of stacked or scrolled graphene layers without affecting the structure. During this period of research, the cause of the high conductivity of graphite intercalation compounds and the future applications were the main concerns.

There have been attempts to grow graphene using the same approach as the approach generally used for growth of carbon nanotubes, but it allowed the formation of thicker than ~ 100 layers graphite films (Krishnan et al. 1997).

Hess and Ban (1966) were the first to use a chemical-vapor-deposition (CVD) technique, in which carbon atoms were supplied from a gas phase, to achieve the formation of monolayer graphite or graphene.

However, efforts to epitaxially grow few-layer graphene through the chemical vapor deposition of hydrocarbons on metal substrates (Land et al. 1992 and Nagashima et al. 1993) and on top of other materials (Oshima and Nagashima 1997) as well as by thermal decomposition of SiC have also been successful.

Epitaxial growth of graphene offers probably the only viable route towards electronic applications and, with so much at stake, rapid progress in this direction is expected. The approach that seems promising but has not been attempted yet is the use of the previously demonstrated epitaxy on catalytic surfaces (Land et al. 1992 and Nagashim et al. 1993), such as Ni or Pt, followed by the deposition of an insulating support on top of graphene and chemical removal of the primary metallic substrate.

This "epitaxial graphene" consists of a single-atom-thick hexagonal lattice of sp2 bonded carbon atoms, as in free-standing graphene. However, there is significant charge transfer from the substrate to the epitaxial graphene, and, in some cases, hybridization between the d orbitals of the substrate atoms and p orbitals of graphene, which significantly alters the electronic structure of the epitaxial graphene. The fact that electric current would be carried by effectively massless charge carriers in graphene was pointed out theoretically by Semenoff et al. in 1984.

Properties such as the layered morphology and weak dispersion forces between adjacent sheets have made graphite an ideal material for use as a dry lubricant, along with the similarly structured but more expensive compounds hexagonal boronnitride and molybdenum disulfide. High, in-plane electrical (104 O-1 cm-1) and thermal conductivity (3000 W/mK) enable graphite to be used in electrodes and as heating elements for industrial blast furnaces (Bouchard et al. 2001).

The beginning of the twenty-first century saw many important discoveries related to graphene. Enoki et al. in 2003 explained the anisotropy of graphite's material properties. Bulk graphite was first intercalated by Dresselhaus and Dresselhaus (2002) so that graphene planes became separated by layers of intervening atoms or molecules. This usually resulted in new three-dimensional materials. However, in certain cases, large molecules could be inserted between atomic planes, providing greater separation, such that the resulting compounds could be considered as isolated graphene layers embedded in a three-dimensional matrix.

Shioyama et al. (2001) and Hirata et al. (2004) demonstrated that one can often get rid of intercalating molecules in a chemical reaction to obtain a sludge consisting of restacked and scrolled graphene sheets.

Graphene was patented two years before the Nobel Prize Prize-winning work of Andre Geim and Kostya Novoselov (2004) by a company called Nanotek Instruments (US patent number 7071258, entitled "Nano-scaled graphene plates" of 2002, owners, Bor Jang and Wen Huang). This patent includes a sketch of carbon nanotubes unrolling to form graphene...