Introduction

Graphite, which is one of the most prevalent carbon allotropes,

is a layered material in which infinite sheets of hexagonal carbon

networks are stacked in the AB fashion (Bernal stacking) with the

aid of weak intersheet interaction [1], as shown in Fig. 1.1. Each

two-dimensional (2D) sheet is called graphene. The unit cell of

graphene, with a lattice constant of a = 0.246 nm, is formed of two independent carbon sites, where the strong σ -bonds and weak π -

bonds of the carbon atoms give a bond length of 0.142 nm. The σ -

bonds consist of threefold symmetric sp3 hybrid orbitals of 2s , 2px , and 2py orbitals, while the π -bonds consist of 2pz orbitals. Graphite has two independent graphene sheets, where some carbon atoms in

a graphene sheet are on top of carbon atoms in the sheet underneath

and others are over the centers of hexagons in the sheet underneath.