Methods of making graphene

                              How to make graphene?

1. Mechanical Exfoliation (a.k.a. Scotch-tape method) 
     a) repeated peeling of graphite to get an atom-thick layer of graphite, which is called graphene

2. Hummer's method (top-down) = to make graphene layers from a bulk of graphite
     a) Oxidize graphite using KMnO4 and NaNO3 in concentrated      H2SO4.
     b) put it in water to open up the layers of graphite. *Now it is in the form of graphene oxide (GO)
     c) Anneal it to remove oxygen groups on the graphene oxide by reduction. *Now it is called reduced graphene oxide. The purpose of this is to change the phase of graphene oxide to that of graphene. 100% of graphene's properties will not be able to be obtained. 

3. Chmical Vapor Deposition (bottom-up) a.k.a. the best method => to make thin films

(Copper as a substrate)

     a) Anneal copper foil in hydrogen atmostphere at 1000 degrees Celsius
     b) Inject the mixture of H2 and CH4 gases.
     c) Cool it down to room temperature after a continuous layer of graphene is formed on Cu foil. 
    
*the metal substrate works as a catalyst to lower the activation energy and determines graphene deposition mechanism.

Note: Physical Vapor Deposition (PVD) cannot be used to make graphene. => PVD is to deposit thin films by changing its phase to gas from solid or liquid and then condensing it to solid, which will result in change in physical morphology. 

4. Using SiC => Colet carbon atoms from SiC and make graphene sheets out of it. Then get rid of Si atoms by sublimation which is to convert the phase from solid to gas. It is to change the phase of Si to gas so that it does not exist in the sheets anymore.