Graphene-The Wonder Material

                                                  Source: Google

In the previous post, we discussed an allotrope of carbon Buckminster fullerenes. However, carbon is such a wonderful element that it can exist in not just one but a myriad of other forms or allotropes. Now, let's delve deeper into another allotrope of carbon called graphite and its derivative graphene. 

Graphite consists of hexagonal sheets of carbon atoms. Every individual carbon atom is covalently bonded to three other carbon atoms (sp2 hybridized). The atomic orbitals of the extra electrons overlap to form molecular orbitals, which facilitate the movement of delocalized electrons throughout the entire graphite sheet. Moreover, the graphite sheets in graphite are held together by weak van der Waal's forces, which accounts for their lubricating nature.

However, a single sheet of graphite is robust enough because of the interlocking of the carbon-to-carbon covalent bonds. This single sheet of hexagonally arranged carbon atoms is called Graphene.

Properties

Graphene is known as the 'wonder material' due to its intriguing properties. It is the lightest material known to date, which is just one atom thick. Unlike graphite which is actually soft, Graphene is one of the strongest materials known due to the regular arrangement of carbon atoms bonded together by strong covalent bonds. Though it is strong, it has been found that it's not tough. Though these terms (strength and toughness) are often synonymously used, they are actually different. We will discuss this further in the mechanical properties of graphene. It is also a good conductor like graphite due to the presence of delocalized electrons. Graphene is also transparent and has many optical properties that will be discussed later. A single layer of graphene allows 97.7% of light to pass through it and absorbs only 2.3% of light.

Synthesis

Some of the commercially viable methods to synthesize graphene are as follows:

• Chemical Vapour Deposition
• Chemical or Plasma exfoliation of graphite
• Mechanical Cleavage from graphite

Chemical Vapour Deposition

 Source: Google

Chemical Vapour Deposition is the most widely used process to synthesize nanomaterials. It means depositing vapors on a substrate. CVD works by combining gaseous molecules in a reaction chamber divided into different temperature zones. The substrate is kept at a different temperature than the other chemicals. As the gases are passed into the reaction chamber, they react and form a thin film on the substrate. The temperature of the substrate is a primary condition in determining the type of reaction and is, therefore it's vital that the temperature is correct.

The CVD process has many advantages because it yields very high purity, fine-grained and impervious products. The only disadvantage is that the gases used in this process are toxic in nature.

I believe these processes are better understood practically. You can refer to this youtube video here which explains the CVD synthesis of  Boron Nitride nanomaterial on a silicon substrate.

Chemical Exfoliation from graphite

 Source: Google

Chemical exfoliation leads to a solution of charged graphite flakes, barely stable under inert conditions. The resulting aqueous dispersion of graphene is extremely stable without the need for surfactants or organic solvents. Furthermore, chemical exfoliation is highly efficient.

This aqueous graphene dispersion results in high-quality graphene with the versatility of a dispersion.

Mechanical cleavage from graphite

Mechanical cleavage is used to remove layers from bulk highly ordered pyrolytic graphite surfaces. Scotch tape is put on the surface and taken off carefully to execute the process. After many repetitions, the graphite layer thins out with each draw until there is only a single layer of graphene left. This approach yields high-quality graphene flakes too, but it is mainly used for laboratory purposes.

 We will explore more about other properties of graphene in subsequent posts.