**6. Detailed overview of graphene**

"Graphene" [20] is just a single thin layer of carbon atoms separated from the overall graphite structure. In the ideal scenario, graphene is an perfect (2D) material because it is an atomically thick and thermodynamically stable monatomic sheet of carbon atoms organized in a honeycomb structure [33]. "Hanns-Peter Boehm" was the first to create the name "graphene" in 1962. The idea of graphite layers had been investigated before to this date [32]. In 1947, Wallace exploring the graphite layers which proves as a beginning point for better understanding the physical properties of the three-dimensional graphite. Several papers were published during the next few decades in an attempt to isolate or grow graphene. In 2004, "Andre Geim and Kostya Novoselov" have been succeeded in isolating a single sheet of 2-D graphene from the raw graphite [19, 20, 34]. Single layers can be separated from graphite and produced using traditional CVD or micromechanical cleavage techniques [17, 19]. Recently, Single graphene layers have been successfully generated utilizing a basic mechanical exfoliation of graphite using Scotch tape [20].

In Graphene, only the layer extensions and characteristics of edges might be different, making it the most fundamentally uniform material [20]. In other words, graphene is a fundamental basis [35] for all fullerene allotropic dimensionalities, and it tends to evolve into different sorts of structures with greater structural stability. It can be rolled into (0-D)fullerenes [36], wrapped into (1-D) carbon nanotubes (CNTS), and layered into (3-D) graphite (with 3.37Ao separation distance) [37] and derivatives between layers [17, 34, 35]. Single-layer graphene (SLG) [38], Graphene Nano-platelets (GNPs) 100 nm to 100 μm [37], Graphene oxide (GO) (single-layer material with a high oxygen concentration), Reduced graphene oxide (RGO) (monolayer form), and functionalized/chemically modified graphene are all examples of graphene. All of them are graphene-related compounds and can be classified as graphene family materials (GFMs) [39].

#### **6.1 Brief lattice structure of 2-D graphene**

Graphene is consist of two interpenetrating Bravais sub-lattices, which allows us to define a primitive unit cell, which is the simplest building block from which the graphene lattice may be constructed. Due to the hexagonal shape, the primordial cell encompassed by the two lattice vectors below includes two atoms as shown in **Figure 2**, one of type A and the other of type B, which represent the two triangular lattices. The size of the graphite primitive unit cell is determined by how individual graphene layers stack together to form the graphite crystal [40]. The lattice positions ( *R*) are filled

*Introductory Chapter: Brief Scientific Description to Carbon Allotropes – Technological Perspective DOI: http://dx.doi.org/10.5772/intechopen.107940*

#### **Figure 2.**

*Single layer graphene lattice with two lattice vectors.*

with Type (A) atoms and the type (B) atoms are shifted with respect to the A atoms in each primitive cell by τ = + ( ) 1 2 *a a* / 3 [17].

$$\vec{a}\_1 = \left(\frac{3}{2}a\_o, -\frac{\sqrt{3}}{2}a\_o\right), \,\vec{a}\_2 = \left(\frac{3}{2}a\_o, \frac{\sqrt{3}}{2}a\_o\right), \,\vec{R} = m\vec{a}\_1 + n\vec{a}\_2 \dots$$

Here, *a nm <sup>o</sup>* = 0.142 is the bond length of carbon. Where *m* and *n* are integers.

#### **6.2 Morphology of graphene**

AFM, TEM, and FESEM can be used to study the morphology of graphene. AFM has measured the accurate thickness of single sheet of graphene to be (0.34–1.2 nm), and determining these thicknesses is crucial. Graphene has a higher thickness (2 nm) and the mean thickness of hydrazine-reduced GO, on the other hand, is only 0.8 nm, indicating the creation of single-layer graphene. The 'TEM and high-resolution TEM (HR-TEM)' are highly useful for detecting the number of layers in transparent graphene layers with crumples. The researchers looked into the microstructure variations between graphite and graphene and they found that Graphite layers are darker, thicker, and longer than graphene layers [41].

#### **6.3 Physical properties of graphene**

Graphene has attracted a lot of attention as a rising star in material science, solidstate physics, chemistry, and technology research because of its unique features, such as the quantum Hall effect, extraordinarily high (elasticity and tension), and optical transparency [17]. The 2p orbitals are responsible for graphene's amazing properties, as they cause the p bands to travel over the carbon sheets that make up the graphene. Graphene has a spectrum of remarkable features that other metals and semiconductors lack due to its unique lattice structure, shape, and surface morphology [17]. The material graphene is semimetal. Its zero bandgaps [37, 42], linear energy spectrum, excellent carrier mobility, frequency-independent absorption, and long spin diffusion length make it a popular material for electrical, photonic, and spintronic devices. Researchers discovered that graphene is highly rigid and extraordinarily

good conductors of electricity and heat in the free-state, but are unstable at finite temperatures in the free-state [40], and is impermeable to gases especially [43]. Graphene is a semimetal with zero bandgap due to its Fermi level, which is located at the exact intersection of "conduction and valence bands" in pure substance and may be changed to make it (either N-Type or P-Type) by chemical modifications or more readily, by an electric field [44]. The inability to analyze the mechanical properties of single layer graphene is hampered by the fact that (SLG) is thermodynamically unstable and that an X-ray diffraction experiment on an (SLG) is not conceivable, owing to graphene's smallest size and outstanding surface-area-to-volume ratio. The tensile and compressive forces applied to the graphene lattice are tiny—around 1%. It's impossible to apply a substantially higher compressive strain without the sample slipping off the substrate (in the case of graphene). This can be accomplished by creating a monolayer graphene sample on a substrate having an aperture and pressing down on the graphene sample [40] with an (AFM) tip over the aperture. Graphene has been shown to endure a tensile strain of up to 20% using this method which will be beneficial from technological perspective.
