Instruct: Given a question, retrieve passages that answer the question.
Query: When was the first graphene production technique developed?
Single-layer graphene was explored theoretically by P. R. Wallace in 1947. It 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.[1][2] Boehm et al. introduced the term graphene in 1986.[3][4]
Epitaxial graphene films can be grown on various crystalline surfaces. The atomic lattice of the substrate facilitate in orientationally registering the carbon atoms of the graphene layer. The chemical interaction of the graphene with the substrate can vary from weak to strong. This also modifies the properties of the graphene layer. The need for epitaxial graphene arises from the challenges of incorporating carbon nanotubes in large-scale integrated electronic architectures. Research on 2D graphene was thus initiated by experiments on epitaxially grown graphene on single crystal silicon carbide. While significant control has been in growing and characterizing epitaxial graphene, challenges remain in being able to fully exploit the potential of these structures. The promise lies in the hope that charge carriers on these graphene structures, like carbon nanotubes, remain ballistic. If so, it could revolutionize the world of electronics.
Epitaxial graphene growth on silicon carbide (SiC) by thermal decomposition is a methods to produce large-scale few-layer graphene (FLG).
Graphene is one of the most promising nanomaterials for the future because of its various characteristics, like strong stiffness and high electric and thermal conductivitiy.
Still, reproducible production of Graphene is difficult, thus lots of different techniques have been developed.
The main advantage of epitaxial graphene growth on silicon carbide over other techniques is to obtain graphene layers directly on a semiconducting or semi-insulating substrate which is commercially available.
A normal silicon wafer coated with a layer of germanium (Ge) dipped in dilute hydrofluoric acid strips the naturally forming germanium oxide groups, creating hydrogen-terminated germanium. Chemical vapor deposition deposits a layer of graphene on top. The graphene can be peeled from the wafer using a dry process and is then ready for use. The wafer can be reused. The graphene is wrinkle-free, high quality and low in defects.
Epitaxy refers to the deposition of a crystalline overlayer on a crystalline substrate, where there is registry between the two. In some cases epitaxial graphene layers are coupled to surfaces weakly enough (by Van der Waals forces) to retain the two dimensional electronic band structure of isolated graphene. An example of this weak coupling is epitaxial graphene on SiC and on Pt(111). On the other hand, the epitaxial graphene layer on some metals can be strongly bonded to the surface with covalent bonds. The properties of the covalently bonded graphene can differ from the ones of free-standing graphene. An example of this strong coupling is epitaxial graphene on Ru(0001). However, the coupling is strong only for the first graphene layer on Ru(0001): the second layer is more weakly coupled to the first layer and has already properties very close to the free standing graphene.
3- Introduction of defects with techniques such as oxygen plasma treatment. A more systemic way of introducing defects in graphene structure is done through O plasma treatment. Ultimately, the graphene sample will contain prescribed-holes spaced and numbered according to the plasma intensity. People were able to improve ZT of graphene from 1 to a value of 2.6 when the defect density is raised from 0.04 to 2.5 (this number is an index of defect density and usually understood when compared to the corresponding value of the un-treated graphene, 0.04 in our case). Nevertheless, this technique would lower the electrical conductivity as well, which can be kept unchanged if the plasma processing parameters are optimized.
High-quality sheets of few-layer graphene exceeding in area have been synthesized via CVD on thin nickel films using multiple techniques. First the film is exposed to argon gas at 900–1000 degrees Celsius. Methane is then mixed into the gas, and the methane's disassociated carbon is absorbed into the film. The solution is then cooled and the carbon diffuses out of the nickel to form graphene films. CVD grown graphene on Ni(111) surface forms (1 x 1) structure, i.e. the lattice constants of Ni and graphene matches and no moiré pattern is formed. There are still different possible adsorption sites for carbon atoms on nickel, at least top, hcp hollow, fcc hollow and bridge sites have been reported [17].
Graphene can be grown on ruthenium(0001) surface with CVD, temperature programmed growth (TPG) or segregation. In CVD, a hot ruthenium surface is exposed for some carbon containing molecule like methane or ethene. This results in graphene formation. It has been observed that the graphene can grow only “downhill” of the ruthenium surface steps, not uphill. 
Graphene bonds strongly with covalent bonds to the surface and has only 1.45 Å separation to the surface. This affects the electronic structure of the graphene layer, and the layer behaves differently than a free-standing graphene layer. However, the CVD graphene growth on ruthenium is not totally self-terminating and multilayer graphene formation is possible. The second and higher layers cannot bond to the existing graphene layers as strongly as the first layer bonds to the metal surface, which results in higher 3 Å separation between the graphene layers. The second layer thus has much weaker interaction with the substrate and has very similar electronic properties as free-standing graphene.
Due to the strong bonding of graphene on the ruthenium surface, only R0 orientation is observed for graphene layer. Although, different studies have shown different lengths for the moiré repeat distance, varying around Graphene(11 x 11) and Ru(10 x 10). The moiré pattern also causes strong corrugation for the graphene layer, peak height being as much as 1.5 Å.
In 2014, carbon nanotube-reinforced graphene was made via spin coating and annealing functionalized carbon nanotubes. The resulting material was stronger, flexible and more conductive than conventional graphene.
Adding a surfactant to a solvent prior to sonication prevents restacking by adsorbing to the graphene's surface. This produces a higher graphene concentration, but removing the surfactant requires chemical treatments.
Heating silicon carbide (SiC) to high temperatures (>) under low pressures (~10 torr) reduces it to graphene. This process produces epitaxial graphene with dimensions dependent upon the size of the wafer. The face of the SiC used for graphene formation, silicon- or carbon-terminated, highly influences the thickness, mobility and carrier density.
In 2014 a laser-based single-step, scalable approach to graphene production was announced. The technique produced and patterned porous three-dimensional graphene film networks from commercial polymer films. The system used a CO2 infrared laser. The sp-carbon atoms were photothermally converted to sp-carbon atoms by pulsed laser irradiation. The result exhibits high electrical conductivity. The material can produce interdigitated electrodes for in-plane microsupercapacitors with specific capacitances of >4 mF cm and power densities of ~9 mW cm. Laser-induced production appeared to allow roll-to-roll manufacturing processes and provides a route to electronic and energy storage devices.
Growing graphene in an industrial resistive-heating cold wall CVD system was claimed to produce graphene 100 times faster than conventional CVD systems, cuts costs by 99 percent and produce material with enhanced electronic qualities.
Graphene's electronic band-structure (so-called Dirac cone structure) was first visualized in this material. Weak anti-localization is observed in this material, but not in exfoliated graphene produced by the drawing method. Large, temperature-independent mobilities approach those in exfoliated graphene placed on silicon oxide, but lower than mobilities in suspended graphene produced by the drawing method. Even without transfer, graphene on SiC exhibits massless Dirac fermions. The graphene–substrate interaction can be further passivated.
One of the first patents pertaining to the production of graphene was filed in October 2002 and granted in 2006. Two years later, in 2004 Geim and Novoselov extracted single-atom-thick crystallites from bulk graphite and transferred them onto thin silicon dioxide () on a silicon wafer, which electrically isolated the graphene. The cleavage technique led directly to the first observation of the anomalous quantum Hall effect in graphene, which provided direct evidence of graphene's theoretically predicted Berry's phase of massless Dirac fermions. The effect was reported by Geim's group and by Kim and Zhang, whose papers appeared in "Nature" in 2005. Geim and Novoselov received awards for their pioneering research on graphene, notably the 2010 Nobel Prize in Physics.
Graphene oxide can be converted to graphene using the bacteria Shewanella oneidensis
Tin has been recently used for synthesis of graphene at 250°C. Low-temperature as well as the transfer free graphene growth on substrates is the major concern of graphene research for its practical applications. The transfer free graphene growth on SiO2 covered Si (SiO2/Si) substrate at 250 °C based on a solid-liquid-solid reaction has been achieved by tin.
Multiple production techniques have been developed. Isolated 2D crystals cannot be grown via chemical synthesis beyond small sizes even in principle, because the rapid growth of phonon density with increasing lateral size forces 2D crystallites to bend into the third dimension. In all cases, graphene must bond to a substrate to retain its two-dimensional shape.
Sonicating graphite at the interface of two immiscible liquids, most notably heptane and water, produced macro-scale graphene films. The graphene sheets are adsorbed to the high energy interface between the heptane and the water, where they are kept from restacking. The graphene remained at the interface even when exposed to force in excess of 300,000 g. The solvents may then be evaporated. The sheets are up to ~95% transparent and conductive.
A graphene spray gun is a kinetic spray system that deposits, through supersonic acceleration, a one atom thick sheet of pure carbon named graphene by means of a de Laval nozzle, a pinched tube with an hourglass type shape. The system deposits graphene flakes and a hexagonal graphene lattice is created upon impact of the desired surface. The graphene spray gun would be utilized onto large-scale applications such as circuits, radio transmitters, and optical electronics due to the grapehene’s transparency and its remarkable conductivity of electricity. The supersonic spray system was first developed in May 2014 by University of Illinois professor Alexander Yarin, and Korea University professor Sam Yoon. Yarin went to Yoon when he learned about his work regarding kinetic spray deposition systems. Yarin believed that graphene could be applied to the system in order to create a layer of the material. After conducting experiments with the newly created system, they concluded that the graphene spray system was a success. The spray gun is still in its early stages of development, but is considered by many scientists and researchers to be the solution of various predicaments that occur when applying graphene onto large-scale products. The most common problem that would transpire within the other methods is that the layer would be uneven and coated by aggregations. The energy delivered by the supersonic spraying stretches the graphene evenly upon impact, and is the main reason for the spray system’s lack of defects that are common within other graphene deposition methods.
Producing graphene via intercalation splits graphite into single layer graphene by inserting guest molecules/ions between the graphite layers. Graphite was first intercalated in 1841 using a strong oxidizing or reducing agent that damaged the material's desirable properties. Kovtyukhova developed a widely used oxidative intercalation method in 1999. In 2014, she was able to achieve intercalation using non-oxidizing Brønsted acids (phosphoric, sulfuric, dichloroacetic and alkylsulfonic acids), but without oxidizing agents. The new method has yet to achieve output sufficient for commercialization.
Large scale roll-to-roll production of graphene based on chemical vapor deposition, was first demonstrated in 2010. In 2014 a two-step roll-to-roll manufacturing process was announced. The first roll-to-roll step produces the graphene via chemical vapor deposition, and the second step binds the graphene to a substrate. In 2018, researchers at MIT refined the roll-to-roll process, creating a promising way to produce large amounts of graphene.
Supersonic acceleration of droplets through a Laval nozzle was used to deposit small droplets of reduced graphene-oxide in suspension on a substrate. The droplets disperse evenly, evaporate rapidly and display reduced flake aggregations. In addition, the topological defects (Stone-Wales defect and vacancies) originally in the flakes disappeared. The result was a higher quality graphene layer. The energy of the impact stretches the graphene and rearranges its carbon atoms into flawless hexagonal graphene with no need for post-treatment. The high amount of energy also allows the graphene droplets to heal any defects in the graphene layer that occur during this process.
Graphene on cobalt(0001) is grown similarly as on a Ni substrate. A Co(0001) film is first grown on a wolfram(110) substrate, following which chemical vapor deposition of propylene at 450 °C enables graphene growth on Co(0001). This results in a p(1x1) structure along with structures that indicated domains of graphene slightly rotated with respect to the Co lattice. Graphene structures grown on Co(0001) are found to be identical to those grown on Ni(111) upon structural and electronic characterization. Co(0001) is ferromagnetic but the graphene monolayer grown over was found to not diminish the spin polarization. Unlike its Ni(111) counterpart, graphene grown on Co(0001) does not show the Rashba effect.
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 thin silicon dioxide (SiO 2) on a silicon wafer in a process called either micromechanical cleavage or the Scotch tape technique.[26] The SiO 2 electrically isolated the graphene and weakly interacted with it, providing nearly charge-neutral graphene layers. The silicon beneath the SiO 2 could be used as a "back gate" electrode to vary the charge density in the graphene over a wide range. 6667100, filed in 2002, describes how to process expanded graphite to achieve a graphite thickness of one hundred-thousandth of an inch (0.25nm). The key to success was high-throughput visual recognition of graphene on a properly chosen substrate that provides a small but noticeable optical contrast.