*2.1.1 Chemical vapor deposition method*

*21st Century Surface Science - a Handbook*

not as individual nano-sized particles [5].

is most suitable as a primary structure for other sp2

three different forms such as sp/sp2

of carbon nanotubes, and thickness of graphene, drops are on the nanometer scale [4]. Carbon blacks in great carbon are made out of nano-sized particles, yet they are not typically named nanocarbons since they have different applications as a mass,

Carbon, a basic chemical substance containing 6 as atomic number with 6 electrons tend to occupy s and p orbitals. It can able to undergo hybridization through

tured carbon materials such as fullerene [6], graphene [7], and carbon nanotubes [8] have envisaged prompt enquiries into this emerging field. Various physical properties of carbon nanotubes were mostly derived from base material (graphene). Such graphene involves the dense packing arrangement of carbon atoms in a regular sp2 pattern bonded to honeycomb based atomic scale structure and especially this pattern

judgment, this CNT is explicitly distinct in the cylinder form fabricated of swirled up graphene thick sheet, which can delineate itself to single or multiple well. The single well nanotubes were known as single walled carbon tubes which were investigated

CNTs have outstanding mechanical, thermal, electrical, and optical properties that are being used exclusively or in mix to deliver keen sensors or on the other hand multifunctional materials [11, 12]. They have high angle proportions that are perfect for long and persistent detecting. Their high surface region, for example, can be misused for storing materials to make half breed useful materials or functionalized to make cathodes for an assortment of uses [13]. CNTs are additionally known to display ballistic conductivity because of insignificant electron dispersing in their 1D

Mechanical strain may cause reproducible changes in the electrical properties of CNT filaments, making it conceivable to misuse them as electromechanical sensors [16, 17]. The partner changes incorporate inductance, capacitance, and obstruction which can be associated to the strain. Of incredible significance is that CNT filaments are receptive to elastic, compressive, flexural, and torsional strain [18].

The working standards of sensors produced using a CNT plainly visible get together incorporate difference in their electrical resistivity or obstruction because of mechanical strain known as piezoresistivity, change of their inductance and capacitance because of mechanical strain, change of their electrical resistivity because of variety in temperature known as thermoresistivity [19], change of their electrical obstruction because of variety in an attractive field known as magnetoresistance [20], and change in their electrical opposition with change of their mechanical thunderous recurrence because of variety of temperature, weight, mass, and strain [11]. The adjustment in conductance or obstruction is substantially more predominant than other variety in electrical properties. This is somewhat in light of the fact that charge transporters are handily isolated under simultaneous deformation prompting an expansion in obstruction. For extremely little strains, the total deformation has demonstrated to be flexible and the conductive system is completely recouped when the strain is evacuated, prompting an abatement in opposition [21]. Thus, the presented chapter highlights the synthesis

means. Recent inventions of compact struc-

materials [9]. Based on theoretical

or sp3

during 1993 whereas multi-walled ones were found during 1991 itself [10].

structure with mean free-ways of the request of several microns [14, 15].

details, associated properties and current applications of carbon nanotubes.

important and commonly used methods. They are as follows.

There are many methods to synthesize CNTs, but these three methods are most

**28**

**2. Discussion**

**2.1 Synthesis of carbon nanotubes**

**Chemical vapor deposition (CVD):** CVD is a technique in which the vaporized reactants react chemically and forms a nanomaterial product that is deposited on the substrate **Figure 1**.

**Sources for carbon:** The precursor for carbon nanotubes are hydrocarbon gases such as acetylene, ethylene, methane, etc. [22].

**Substrate used:** Substrates are materials on which the CNTS are grown. The commonly used substrates in CVD method are zeolite, silica, silicon plate coated with iron particles, etc.

**Catalyst used:** To produce single-walled carbon nanotubes metal catalyst nanoparticles such as iron, cobalt, nickel, molybdenum, iron-molybdenum alloys, etc. are used.

**Sources for CVD used:** Based on the heating source, the CVD can be:


**Conditions maintained:** The following conditions are maintained inside the furnace.

