**4. Overview of graphite and diamond**

At the mesoscopic scale, a material's properties are dictated not only by its chemical bonding but also by its dimensions and structure. This is especially true in the case of carbon-based substances. Carbon is abundant in nature, with most of it in the form of composite. Most of them are natural chemicals that are needed to make artificial carbon and carbon-based products. Natural graphite and diamond are the only two allotropes of carbon found as minerals on Earth [2]. Despite the fact that both materials are relatively inert at normal temperatures and pressures, they can transition into one another when subjected to certain conditions [19, 21]. In the lowest energy state, carbon possesses four electrons in its valence shell, two in the 2 s sub-shell and two in the 2p sub-shell. The development of three types of sp. composite orbitals (sp, sp2 , and sp3 ) depends on the amount of p orbitals (1 to 3) mingling with the s orbital. The bases of graphite and diamond are formed by carbon atoms with (sp2 and sp)3 composite orbitals, which may make 3 and 4 bonds with nearby carbon atoms, sequentially [17].

## **4.1 Graphite overview**

Graphite was proposed by "Werner and D.L.G. Harsten", who derived it from the specific Greek 'γράφειν' (Graphein), which means "to write," and it was first used in pencils in 1594. "Abraham Gottlob Werner "was the first to name it in 1789 and is made up of large flat networks of carbon atoms layered on top of one another [17]. This carbon allotrope has a honeycomb layered structure and is made of flat twodimensional layers of carbon atoms (sp2 hybridized). Each layer is specifically consist of the carbon atoms arranged in planar hexagonal rings with a carbon–carbon bond length of 141.5 pico-meters. A C∙C covalent bond connects each C atom in each layer to three other C atoms [22].
