Grephene.docx

GREPHENE: By contrast, current techniques for making graphene yield small quantities of the material, fit only for experimental use. One common technique is called the “Scotch tape method,” in which a piece of tapeis used to peel graphene flakes off of a chunk of graphite, which is essentially a stack of graphene sheets

(1) Scotch tape method: One common technique is called the “Scotch tapemethod,” in which a piece of tape is used to peelgraphene flakes off of a chunk of graphite, which is essentially a stack of graphene sheets. This results in micrometer-sized graphene fragments, which are placed between electrodes to make a transistor. Graphene is the ultrathin form of carbon that was first discovered at the University of Manchester in 2004. It is often dubbed “the wonder material” on account of its incredible properties, which promise many applications – from ultrafast transistors to DNA sequencing. For discovering graphene and for their pioneering studies of the material, Andre Geim and Konstantin Novoselov shared the 2010 the Nobel Prize for Physics. To begin, Dacey meets researcher Branson Belle who demonstrates the famous “Scotch tape method” a sample of graphite onto sticky tape and then folding and peeling the tape several times to create progressively thinner layers of graphite – eventually leading to a single layer of carbon.

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Advantages of scotch tape:           

Provides structural strength that can replace bolts, rivets, welds and other mechanical fasteners. Can use lighter thinner materials. Bond dissimilar materials without incompatibility concerns. Acts as a moisture seal/environmental barrier. Provides vibration deadening and noise reduction. Shortens assembly time. Eliminates the need for surface refinishing to remove weld distortions. Eliminates visible mechanical fasteners for cosmetic superiority. Provides adhesion to difficult surfaces such as glass. Provides uniform thickness and gap filling properties. Eliminates the need for bonding “both” substrates together at the same time and location providing optimum manufacturing flexibility. (2)

Disadvantages of scotch tape : 

Time to cure - The final strength of the adhesive bond is not obtained immediately, unlike the case with a rivet or a screw, you must wait a time to solidify or cure the adhesive, this time depends on the choice of adhesive to be used, and also

sometimes it depends on the environmental conditions that make the bonding process. If you want to reduce this waiting time you can use a chemical booster compatible with the adhesive. 

Resistance to temperature - Adhesives are polymer-based materials, for this reason the adhesives and glues have an average resistance to temperature, adhesives silicone-based are more resistant to temperature adhesives, that kind of glues can withstand temperatures reaching point of 800 °C.

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Ageing - The long-term strength of adhesive bonding is affected by various physical and chemical actions which are in the environment, actions such as ultraviolet light, chemical attacks on the environment, the presence of moisture . There are adhesives that are not altered against ultraviolet light while others break down in front of this radiation. The solution to this problem is to select an adhesive according to the environmental conditions in later work; this will allow us to perform a series of accelerated aging tests in order to observe the goodness of the adhesive bond.

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Surface Preparation - As in the process of painting, surface preparation required prior to adhesive application process in order to achieve good adhesion between the adhesive and the substrate. Surface preparation that will vary depending on the materials to be bonded, the adhesive selected and technical requirements needed to fulfill the adhesive bond.

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Removal or disassembly - As in the welding or rivet process, the process of disassembly adhesive bonds can destroy or distort the substrates joint together, being an expensive process to do, this does not happen when using techniques such as bolting, is so that those unions that require disassembly during maintenance work during the life of the product, must perform techniques that allow easy disassembly and assembly, such as using screws, velcro, etc...

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Safety and Environment - Due the basis of the adhesives are chemical compounds, it is necessary to define the necessary actions to prevent human exposure to these products during the time of application, these measures will depend on the application amount and the type of the adhesive, glue or sealant used. Also you must properly manage the waste generated during the application process for further treatment and recycling. (3)

(2) FUNDAMENTAL PROCESSES IN THE CREATION OF CVD

GRAPHENE 

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CVD graphene is created in two steps, the precursor pyrolysis of a material to form carbon, and the formation of the carbon structure of graphene using the disassociated carbon atoms. The first stage, the pyrolysis to disassociated carbon atoms, must be carried out on the surface of the substrate to prevent the precipitation of carbon clusters (soot) during the gas phase. The problem with this is that the pyrolytic decomposition of precursors requires extreme levels of heat, and therefore metal catalysts must be used to reduce the reaction temperature. The second phase of creating the carbon structure out of the disassociated carbon atoms, also requires a very high level of heat (over 2500 degrees Celsius without a catalyst), so a catalyst is imperative at this stage to reduce the temperature needed for a reaction to occur to around 1000 degrees Celsius. The problem with using catalysts is that you are effectively introducing more compounds into the reaction chamber, which will have an

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effect on the reactions inside the chamber. One example of these effects is the way the carbon atoms dissolve into certain substrates such as Nickel during the cooling phase. What all this means is that it is vitally important that the CVD process is very stringently co-ordinated, and that controls are put in place at every stage of the process to ensure that the reactions occur effectively, and that the quality of graphene produced is of the highest attainable.