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e-book Graphene: Synthesis, Properties, and Phenomena

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Figure 8 In terms of how far along we are to understanding the true properties of graphene, this is just the tip of the iceberg. Before graphene is heavily integrated into the areas in which we believe it will excel at, we need to spend a lot more time understanding just what makes it such an amazing material.

Unfortunately, while we have a lot of imagination in coming up with new ideas for potential applications and uses for graphene, it takes time to fully appreciate how and what graphene really is in order to develop these ideas into reality. This is not necessarily a bad thing, however, as it gives us opportunities to stumble over other previously under-researched or overlooked super-materials, such as the family of 2D crystalline structures that graphene has born. In actuality, the structural make-up of graphite and graphene, and the method of how to create one from the other, is slightly different.

In fact, rather than referring to the chemical element and heavy metal, lead, this central core is most commonly made from graphite mixed with clay. Figure 9 Figure 10 Graphite is a mineral that occurs in metamorphic rock in different continents of the world, including Asia, South America and North America. It is formed as a result of the reduction of sedimentary carbon compounds during metamorphism. Contrary to common belief, the chemical bonds in graphite are actually stronger than those that make up diamond. However, what defines the difference in hardness of the two compounds is the lattice structure of the carbon atoms contained within; diamonds containing three dimensional lattice bonds, and graphite containing two dimensional lattice bonds.

While within each layer of graphite the carbon atoms contain very strong bonds, the layers are able to slide across each other, making graphite a softer, more malleable material. Extensive research over hundreds of years has proved that graphite is an impressive mineral showing a number of outstanding and superlative properties including its ability to conduct electricity and heat well, having the highest natural stiffness and strength even in temperatures exceeding degrees Celsius, and it is also highly resistant to chemical attack and self-lubricating.

However, while it was first identified over a thousand years ago and first named in , it has taken a while for industry to realise the full potential of this amazing material. Graphite is one of only three naturally occurring allotropes of carbon the others being amorphous carbon and diamond. The difference between the three naturally occurring allotropes is the structure and bonding of the atoms within the allotropes; diamond enjoying a diamond lattice crystalline structure, graphite having a honeycomb lattice structure, and amorphous carbon such as coal or soot does not have a crystalline structure.

While there are many different forms of carbon, graphite is of an extremely high grade and is the most stable under standard conditions. Therefore, it is commonly used in thermochemistry as the standard state for defining the heat formation of compounds made from carbon. It is found naturally in three different forms: crystalline flake, amorphous and lump or vein graphite, and depending on its form, is used for a number of different applications.

As previously touched upon, graphite has a planar, layered structure; each layer being made up of carbon atoms linked together in a hexagonal lattice. These links, or covalent bonds as they are more technically known, are extremely strong, and the carbon atoms are separated by only 0. The carbon atoms are linked together by very sturdy sp2 hybridised bonds in a single layer of atoms, two dimensionally. Each individual, two dimensional, one atom thick layer of sp2 bonded carbon atoms in graphite is separated by 0.

Essentially, the crystalline flake form of graphite, as mentioned earlier, is simply hundreds of thousands of individual layers of linked carbon atoms stacked together. Graphene- So, graphene is fundamentally one single layer of graphite; a layer of sp2 bonded carbon atoms arranged in a honeycomb hexagonal lattice. Graphite is naturally a very brittle compound and cannot be used as a structural material on its own due to its sheer planes although it is often used to reinforce steel.


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Graphene, on the other hand, is the strongest material ever recorded, more than three hundred times stronger than A36 structural steel, at gigapascals, and more than forty times stronger than diamond. Figure 11 Figure 12 Figure 13 However, for this high level of electronic conductivity to be realised, doping with electrons or holes must occur to overcome the zero density of states which can be observed at the Dirac points of graphene. The high level of electronic conductivity has been explained to be due to the occurrence of quasiparticles; electrons that act as if they have no mass, much like photons, and can travel relatively long distances without scattering these electrons are hence known as massless Dirac fermions.

Creating or Isolating Graphene There are a number of ways in which scientists are able to produce graphene.

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The first successful way of producing monolayer and few layer graphene was by mechanical exfoliation the adhesive tape technique. However, many research institutions around the world are currently racing to find the best, most efficient and effective way of producing high quality graphene on a large scale, which is also cost efficient and scalable. The most common way for scientists to create monolayer or few layer graphene is by a method known as chemical vapour deposition CVD.

This is a method that extracts carbon atoms from a carbon rich source by reduction.

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The main problem with this method is finding the most suitable substrate to grow graphene layers on, and also developing an effective way of removing the graphene layers from the substrate without damaging or modifying the atomic structure of the graphene. Figure 14 Other methods for creating graphene are: growth from a solid carbon source using thermo- engineering , sonication, cutting open carbon nanotubes, carbon dioxide reduction, and also graphite oxide reduction.

This latter method of using heat either by atomic force microscope or laser to reduce graphite oxide to graphene has received a lot of publicity of late due to the minimal cost of production. However, the quality of graphene produced currently falls short of theoretical potential and will inevitably take some time to perfect. Graphene Applications and Uses Graphene, the well-publicised and now famous two-dimensional carbon allotrope, is as versatile a material as any discovered on Earth.

Its amazing properties as the lightest and strongest material, compared with its ability to conduct heat and electricity better than anything else, mean that it can be integrated into a huge number of applications.

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Initially this will mean that graphene is used to help improve the performance and efficiency of current materials and substances, but in the future it will also be developed in conjunction with other two-dimensional 2D crystals to create some even more amazing compounds to suit an even wider range of applications.

The first time graphene was artificially produced; scientists literally took a piece of graphite and dissected it layer by layer until only 1 single layer remained. This process is known as mechanical exfoliation. This resulting monolayer of graphite known as graphene is only 1 atom thick and is therefore the thinnest material possible to be created without becoming unstable when being open to the elements temperature, air, etc.

Figure 15 Because graphene is only 1 atom thick, it is possible to create other materials by interjecting the graphene layers with other compounds effectively using graphene as atomic scaffolding from which other materials are engineered. These newly created compounds could also be superlative materials, just like graphene, but with potentially even more applications. After the development of graphene and the discovery of its exceptional properties, not surprisingly interest in other two-dimensional crystals increased substantially.

These other 2D crystals can be used in combination with other 2D crystals for an almost limitless number of applications. It improves its efficiency as a superconductor. Or, another example would be in the case of combining the mineral Molybdenite MoS2 , which can be used as a semiconductor, with graphene layers when creating NAND flash memory, to develop flash memory to be much smaller and more flexible than current technology.


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The only problem with graphene is that high-quality graphene is a great conductor that does not have a band gap. Therefore to use graphene in the creation of future nano-electronic devices, a band gap will need to be engineered into it, which will, in turn, reduce its electron mobility to that of levels currently seen in strained silicone films.

This essentially means that future research and development needs to be carried out in order for graphene to replace silicone in electrical systems in the future In any case, these two examples are just the tip of the iceberg in only one field of research, whereas graphene is a material that can be utilized in numerous disciplines including, but not limited to: bioengineering, composite materials, energy technology and nanotechnology. Biological Engineering Bioengineering will certainly be a field in which graphene will become a vital part of in the future; though some obstacles need to be overcome before it can be used.

Current estimations suggest that it will not be until when we will begin to see graphene widely used in biological applications as we still need to understand its biocompatibility. However, the properties that it displays suggest that it could revolutionise this area in a number of ways. With graphene offering a large surface area, high electrical conductivity, thinness and strength, it would make a good candidate for the development of fast and efficient bioelectric sensory devices, with the ability to monitor such things as glucose levels, haemoglobin levels, cholesterol and even DNA sequencing.

It is able to be used as an antibiotic or even anticancer treatment. Optical Electronics One particular area in which we will soon begin to see graphene used on a commercial scale is that in optoelectronics; specifically touchscreens, liquid crystal displays LCD and organic light emitting diodes OLEDs. Graphene is an almost completely transparent material and is able to optically transmit up to It is also highly conductive, as we have previously mentioned and so it would work very well in optoelectronic applications such as LCD touchscreens.

However, recent tests have shown that graphene is potentially able to match the properties of ITO, even in current states. While this does not sound like much of an improvement over ITO, graphene displays additional properties which can enable very clever technology to be developed in optoelectronics by replacing the ITO with graphene. The fact that high quality graphene has a very high tensile strength, and is flexible makes it almost inevitable that it will become utilized in mentioned applications. Figure 16 In terms of potential real-world electronic applications we can eventually expect to see such devices as graphene based e-paper with the ability to display interactive and updatable information and flexible electronic devices including portable computers and televisions.

Ultrafiltration Another standout property of graphene is that while it allows water to pass through it, it is almost completely impervious to liquids and gases even relatively small helium molecules.

A Review on Modeling, Synthesis, and Properties of Graphene

This means that graphene could be used as an ultrafiltration medium to act as a barrier between two substances. The benefit of using graphene is that it is only 1 single atom thick and can also be developed as a barrier that electronically measures strain and pressures between the 2 substances amongst many other variables. A team of researchers at Columbia University have managed to create monolayer graphene filters with pore sizes as small as 5nm currently, advanced nanoporous membranes have pore sizes of nm. Figure 17 Figure 18 While these pore sizes are extremely small, as graphene is so thin, pressure during ultrafiltration is reduced.

Co-currently, graphene is much stronger and less brittle than aluminium oxide currently used in subnm filtration applications. What does this mean? Well, it could mean that graphene is developed to be used in water filtration systems, desalination systems and efficient and economically more viable biofuel creation.

Composite Materials Graphene is strong, stiff and very light. Currently, aerospace engineers are incorporating carbon fibre into the production of aircraft as it is also very strong and light. However, graphene is much stronger whilst being also much lighter. Ultimately it is expected that graphene is utilized to create a material that can replace steel in the structure of aircraft, improving fuel efficiency, range and reducing weight.

Due to its electrical conductivity, it could even be used to coat aircraft surface material to prevent electrical damage resulting from lightning strikes. In this example, the same graphene coating could also be used to measure strain rate, notifying the pilot of any changes in the stress levels that the aircraft wings are under.

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These characteristics can also help in the development of high strength requirement applications such as body armour for military personnel and vehicles. Photovoltaic Cells Offering very low levels of light absorption at around 2. Silicon is currently widely used in the production of photovoltaic cells, but while silicon cells are very expensive to produce, graphene based cells are potentially much less so. When materials such as silicon turn light into electricity it produces a photon for every electron produced, meaning that a lot of potential energy is lost as heat.

Recently published research has proved that when graphene absorbs a photon, it actually generates multiple electrons. Also, while silicon is able to generate electricity from certain wavelength bands of light, graphene is able to work on all wavelengths, meaning that graphene has the potential to be as efficient as, if not more efficient than silicon, ITO or also widely used gallium arsenide. Being flexible and thin means that graphene based photovoltaic cells could be used in clothing; to help recharge your mobile phone, or even used as retro-fitted photovoltaic window screens or curtains to help power your home.

Energy Storage One area of research that is being very highly studied is energy storage. These energy storage solutions have been developing at a much slower rate. The solution is to develop energy storage components such as either a supercapacitors or a battery that is able to provide both of these positive characteristics without compromise. Currently, scientists are working on enhancing the capabilities of lithium ion batteries by incorporating graphene as an anode to offer much higher storage capacities with much better longevity and charge rate. Also, graphene is being studied and developed to be used in the manufacture of supercapacitors which are able to be charged very quickly, yet also be able to store a large amount of electricity.

Figure 19 Figure 20 Graphene based micro-supercapacitors will likely be developed for use in low energy applications such as smart phones and portable computing devices and could potentially be commercially available within the next years. Graphene-enhanced lithium ion batteries could be used in much higher energy usage applications such as electrically powered vehicles, or they can be used as lithium ion batteries are now, in smartphones, laptops and tablet PCs but at significantly lower levels of size and weight. Graphene Supercapacitors - What Are They?

Figure 21 Scientists have been struggling to develop energy storage solutions such as batteries and capacitors that can keep up with the current rate of electronic component evolution for a number of years. Unfortunately, the situation we are in now is that while we are able to store a large amount of energy in certain types of batteries, those batteries are very large, very heavy, and charge and release their energy relatively slowly.

Capacitors, on the other hand, are able to be charged and release energy very quickly, but can hold much less energy than a battery.