*2.2.1 Structure of SWCNT and MWCNT*

Based on wrapping mechanism, three different forms of SWCNTs include chiral, armchair, and zigzag pattern. The single walled structure is primarily characterized by a set of indices (n and m) which describes the vector mechanism of chiral and absolutely it impinges an impact on electrical tendency of both nanotubes **Figure 6**.

**Figure 5.** *Graphene to CNT.*

**Figure 6.** *Different forms of SWCNTs.*

As a general predict, when n = m, these nanotubes are known as armchair ones and if m = 0, they are said to be zigzag and for other range as chiral pattern [30].

The vector value of chiral mechanism can be determined using C = na1 + ma2, where a1 and a2 represent the base vectors of graphite cell and also used to evaluate the tube radius and moreover this vector function also estimates the rolling direction of graphene sheet. Hence, the radius of carbon nanotube can be estimated using.

$$\mathbf{r} = \mathbf{a} \frac{m\mathbf{2} + mn + n\mathbf{2}}{2\prod}$$

where a takes the lattice parameter in graphite sheet.

Whenever n − m = 3 times of any value, it indicates the carbon nanotube to be metallic or extremely conducting nature and if it is not so, it can be semi-metallic type or a semi-conductor. At most of the times, armchair type can be referred as metallic one whereas all other forms can be denoted as a semi-conductor. Various involved parameters and vector representations [31] can provide an impinging impact on structure of CNT as follows.

1. chiral vector = na1 + na2> > (n,m)


#### *2.2.2 Formation of multi walled nanotubes*

Such MWCNTs can be developed via two distinct models such as Russian doll and Parchment type model. If the diameter of outer CNT exceeds the inner tube, such a model is prescribed as Russian type model whereas, wrapping of a single graphite sheet to many a fold around itself constitutes the simple Parchment model. Both multi walled and single walled CNTs possess similar properties. Due to multi-layered

**35**

*Carbon Nanotubes: Synthesis, Properties and Applications*

arrangement of multi walled nanotubes, the outer portion not only cover the inner tubes from certain chemical reactions when contaminate with ambient substances but also exhibit greater tensile characteristics, which would be a drawback of single

CNTs possess higher tensile property compared to steel as well as Kevlar. such a bond

An amazing feature of CNTs is its elasticity. Under maximum force and high pressure by exposing it to greater compressive forces along axial direction, it can even bend, kink, twist and ultimately buckle without causing any damage to CNT. Thus nanocarbon tubes can retain its original geometric structure. But sometimes, elasticity tends to cope up with a limit and hence under the influence of stronger physical pressure forces, it can even undergo a temporary deformation to form the nanotube shape. Few defects may weaken its structure which includes the atomic

The elasticity property for both single walled and multi walled CNTs is examined by the term known as modulus of elasticity or elastic modulus. Such property of multi-walled CNTs can be analyzed using transmission electron microscopy (TEM). Using such an apparatus, the researchers examine and investigate the molecular vibrations owing to thermal forces created at both edges of tubes [34]. As the atomic bond strength is high, CNTs not only withstand elevated temperature levels but also act as excellent thermal conductors. Hence under vacuum atmospheric pressure ranges, they are able to withstand 2900°C and nearly 800°C at normal pressure conditions. But the prevailing tube temperature and ambient environment may have an impact on thermal conductivity of carbon nanotubes

Various types of indigenous single walled CNTs obtained using chemical vapor deposition technique onto a supporting chemical agent are mostly of semi-conducting nature (I type). Such nanotube type depicts the impact of field transistor (FET) nature at atmospheric conditions and these have been recently attaining greater interest and also achieved extensive exploration towards their application as nanoelectronic materials indulging logic circuit devices and electronic transistors. Such growing CNTs are seemed to be p-type containing doped holes with absolute hole depletion and reduced conductance values (100 kΩ to 1 MΩ) in specific to positive logic gate voltages. in the present context, it has been demonstrated that adsorption of molecular oxygen onto the CNTs is a contributing factor do drive the hole doping effect of SWCNTs. Oxygen removal can even lead to mere existence of semi-conducting nature. Instead, day by day investigations on CNTs reveals that the electrical properties of such carbon nanotubes are much sensitive to chemical doping impacts and charge transfer mechanism in spite of exhibiting extreme robustness [36]. The II type CNTs developed by CVD technique appears to be quasi metallic consisting smaller band gaps in the order of 10 meV. Such CNTs are not sensitive compared to semi-conducting type due to their electrostatic doping mechanism through gate potentials but exhibit a mere conductance dip occluded with that of smaller band gap. These CNTs origin towards a class of non-armchair single walled

to sp3

occurs prominently by the existence of non-flat hexagonal nature of tube walls. Quasi metallic types exhibit enhanced electrical conductivity at low temperature levels when subjected to temperature dependent experimental studies [37].

orbital hybridization which

maximum tensile property which may be nearly 100 times as that of steel [33].

defects or else rearrangement developed on the carbon bonds.

[35]. The prescribed physical properties were outlined in **Table 1**.

CNTs and band origin may be due to shift of sp2

bonds available betwixt indigenous carbon atoms,

bonding of diamond. Hence, SWCNTs possess

*DOI: http://dx.doi.org/10.5772/intechopen.92995*

Owing to the presence of sp2

exhibits more strength rather than sp3

walled CNTs [32].

*2.2.3 Elasticity property*

arrangement of multi walled nanotubes, the outer portion not only cover the inner tubes from certain chemical reactions when contaminate with ambient substances but also exhibit greater tensile characteristics, which would be a drawback of single walled CNTs [32].

Owing to the presence of sp2 bonds available betwixt indigenous carbon atoms, CNTs possess higher tensile property compared to steel as well as Kevlar. such a bond exhibits more strength rather than sp3 bonding of diamond. Hence, SWCNTs possess maximum tensile property which may be nearly 100 times as that of steel [33].

## *2.2.3 Elasticity property*

*21st Century Surface Science - a Handbook*

**Figure 6.**

*Different forms of SWCNTs.*

As a general predict, when n = m, these nanotubes are known as armchair ones and if m = 0, they are said to be zigzag and for other range as chiral pattern [30].

The vector value of chiral mechanism can be determined using C = na1 + ma2, where a1 and a2 represent the base vectors of graphite cell and also used to evaluate the tube radius and moreover this vector function also estimates the rolling direction of graphene sheet. Hence, the radius of carbon nanotube can be estimated using.

> 2 2 2 *m mn n* + + ∏

Whenever n − m = 3 times of any value, it indicates the carbon nanotube to be metallic or extremely conducting nature and if it is not so, it can be semi-metallic type or a semi-conductor. At most of the times, armchair type can be referred as metallic one whereas all other forms can be denoted as a semi-conductor. Various involved parameters and vector representations [31] can provide an impinging

+ n.m + m2

)

Such MWCNTs can be developed via two distinct models such as Russian doll and Parchment type model. If the diameter of outer CNT exceeds the inner tube, such a model is prescribed as Russian type model whereas, wrapping of a single graphite sheet to many a fold around itself constitutes the simple Parchment model. Both multi walled and single walled CNTs possess similar properties. Due to multi-layered

+ n.m + m2

) 1/2

1/2 a is constant of lattice parameter.

r = a

where a takes the lattice parameter in graphite sheet.

impact on structure of CNT as follows.

3.Chiral vector length, L = a(n<sup>2</sup>

6.Rotation angle, ᴪ = 2∏/N

7.vector of symmetry, R = pa1 + qa2

*2.2.2 Formation of multi walled nanotubes*

5. radius = L/2∏

1. chiral vector = na1 + na2> > (n,m)

2.Translational vector, T = t1a1 + t2a2 > > (t1, t2)

4. angle of chiral vector = (2n + m)/2\*(n2

**34**

An amazing feature of CNTs is its elasticity. Under maximum force and high pressure by exposing it to greater compressive forces along axial direction, it can even bend, kink, twist and ultimately buckle without causing any damage to CNT. Thus nanocarbon tubes can retain its original geometric structure. But sometimes, elasticity tends to cope up with a limit and hence under the influence of stronger physical pressure forces, it can even undergo a temporary deformation to form the nanotube shape. Few defects may weaken its structure which includes the atomic defects or else rearrangement developed on the carbon bonds.

The elasticity property for both single walled and multi walled CNTs is examined by the term known as modulus of elasticity or elastic modulus. Such property of multi-walled CNTs can be analyzed using transmission electron microscopy (TEM). Using such an apparatus, the researchers examine and investigate the molecular vibrations owing to thermal forces created at both edges of tubes [34].

As the atomic bond strength is high, CNTs not only withstand elevated temperature levels but also act as excellent thermal conductors. Hence under vacuum atmospheric pressure ranges, they are able to withstand 2900°C and nearly 800°C at normal pressure conditions. But the prevailing tube temperature and ambient environment may have an impact on thermal conductivity of carbon nanotubes [35]. The prescribed physical properties were outlined in **Table 1**.

Various types of indigenous single walled CNTs obtained using chemical vapor deposition technique onto a supporting chemical agent are mostly of semi-conducting nature (I type). Such nanotube type depicts the impact of field transistor (FET) nature at atmospheric conditions and these have been recently attaining greater interest and also achieved extensive exploration towards their application as nanoelectronic materials indulging logic circuit devices and electronic transistors. Such growing CNTs are seemed to be p-type containing doped holes with absolute hole depletion and reduced conductance values (100 kΩ to 1 MΩ) in specific to positive logic gate voltages. in the present context, it has been demonstrated that adsorption of molecular oxygen onto the CNTs is a contributing factor do drive the hole doping effect of SWCNTs. Oxygen removal can even lead to mere existence of semi-conducting nature. Instead, day by day investigations on CNTs reveals that the electrical properties of such carbon nanotubes are much sensitive to chemical doping impacts and charge transfer mechanism in spite of exhibiting extreme robustness [36].

The II type CNTs developed by CVD technique appears to be quasi metallic consisting smaller band gaps in the order of 10 meV. Such CNTs are not sensitive compared to semi-conducting type due to their electrostatic doping mechanism through gate potentials but exhibit a mere conductance dip occluded with that of smaller band gap. These CNTs origin towards a class of non-armchair single walled CNTs and band origin may be due to shift of sp2 to sp3 orbital hybridization which occurs prominently by the existence of non-flat hexagonal nature of tube walls. Quasi metallic types exhibit enhanced electrical conductivity at low temperature levels when subjected to temperature dependent experimental studies [37].


#### **Table 1.**

*Physical properties of CNTs.*

Even quantum interfering impacts were also being observed: (1) phonon acts as the basic scattering mechanism existing in single walled CNTs at ambient conditions and (2) excellent levels of ohmic frequency contacts can be proliferated in the nanotubes with a probability of adequate transmission T = 1 and 3 electron transfer is explicitly phase coherent along with ballistic ability in CNTs at even low temperature levels. This also suggest a lengthy mean distance for ballistic electron transfer in super quality CVD developed SWCNTs [39].

#### *2.2.4 Electromechanical properties*

Schematic pattern of growth has been extensively used to obtain suspended CNTs in single wall across certain trenches along with normal nanotubes which may be electrically wired up with relative easiness. By manipulating a suspended CNT using an AFM probe while measuring its electrical conductivity, the impact of mechanical deformation on electrical characteristics of CNT can be judged. The wide scope of CNTs based on nanoelectro-mechanic (NEM) devices are invented to explore twisting pattern of single nanowires, pure stretching levels and also due to their high frequency characteristics of resonance measurements. Operated NEMs switches and accessible memory devices have also been envisioned in nearby future. Powerful control and deterministic mode of synthesis of CNT will further explore exciting opportunities and greater possibilities of finding novel nanomaterials and other devices [38].

#### *2.2.5 Chemical properties and species interaction*

SWCNTs are mostly inert in nature. The covalent attachment agglomerated the molecular species with fully bonded sp2 hybridization onto sidewalls of CNT proves

**37**

*Carbon Nanotubes: Synthesis, Properties and Applications*

heating the nanotubes to higher temperature levels [40].

to be complex. The adsorbed molecules onto CNTs through the development of non-covalent forces has evidently turned to be facile and consequently lead to possible effects on their physical properties and also with their potential applications. Desorption of orientation molecules from single walled tubes can be achieved by

Similarly, illumination of UV light at low photon intensity forces a drastic molecular desorption rate from SWCNTs at even ambient conditions whereas, wavelength governing measurements predict that photo-desorption process may occur due to sudden excitation of electrons occluded in the nanotubes and perhaps it is a non-thermal process. The excitation of electrons in specific by ∏ plasmons included in SWCNTs due to UV light results in electron/hole pair formation which occur through Landau damping. The studies portray that surface and photochemistry problems are much predominant to exhibit properties and to create molecular nano surface wires that possess ultrahigh surface distribution with each and every atom accommodating onto the surface. Therefore, surface science study can be evaluated at single wire level itself by incorporating both chemical and electrical

Carbon nanotubes have helpful assimilation, photoluminescence (fluorescence), and Raman spectroscopy properties. Spectroscopic strategies offer the chance of speedy and non-dangerous portrayal of moderately a lot of carbon nanotubes. There is a solid interest for such portrayal from the mechanical perspective: various parameters of nanotube union can be changed, purposefully or accidentally, to modify the nanotube quality. As demonstrated as follows, optical assimilation, photoluminescence, and Raman spectroscopies permit brisk and solid portrayal of this "nanotube quality" as far as non-rounded carbon content, structure (chirality) of the delivered nanotubes, and auxiliary imperfections. These highlights decide about some other properties, for example, optical, mechanical, and electrical

Carbon nanotubes are novel "one-dimensional frameworks" which can be imagined as moved single sheets of graphite (or all the more accurately graphene). This rolling should be possible at various points and ebbs and flows bringing about various nanotube properties. The width normally fluctuates in the range 0.4–40 nm (i.e., "just" ~100 times), yet the length can shift ~100,000,000,000 times, from 0.14 nm to 55.5 cm [43]. The nanotube perspective proportion, or the length-tobreadth proportion, can be as high as 132,000,000:1 [44] which is unmatched by some other material. Thusly, all the properties of the carbon nanotubes comparative with those of common semiconductors are incredibly anisotropic (directionally

While mechanical, electrical, and electrochemical (supercapacitor) properties of the carbon nanotubes are entrenched and have quick applications, the down to earth utilization of optical properties is yet muddled. The previously mentioned tunability of properties is conceivably helpful in optics and photonics. Specifically, light-discharging diodes (LEDs) and photograph detectors dependent on a solitary nanotube have been created in the lab. Their exceptional element is not the effectiveness, which is yet moderately low, however the limited selectivity in the frequency of discharge and recognition of light and the chance

*DOI: http://dx.doi.org/10.5772/intechopen.92995*

properties of CNTs as thin probes [41].

*2.2.6 Optical properties*

properties [42].

reliant) and tunable.

*2.2.7 Outline information*

#### *Carbon Nanotubes: Synthesis, Properties and Applications DOI: http://dx.doi.org/10.5772/intechopen.92995*

to be complex. The adsorbed molecules onto CNTs through the development of non-covalent forces has evidently turned to be facile and consequently lead to possible effects on their physical properties and also with their potential applications. Desorption of orientation molecules from single walled tubes can be achieved by heating the nanotubes to higher temperature levels [40].

Similarly, illumination of UV light at low photon intensity forces a drastic molecular desorption rate from SWCNTs at even ambient conditions whereas, wavelength governing measurements predict that photo-desorption process may occur due to sudden excitation of electrons occluded in the nanotubes and perhaps it is a non-thermal process. The excitation of electrons in specific by ∏ plasmons included in SWCNTs due to UV light results in electron/hole pair formation which occur through Landau damping. The studies portray that surface and photochemistry problems are much predominant to exhibit properties and to create molecular nano surface wires that possess ultrahigh surface distribution with each and every atom accommodating onto the surface. Therefore, surface science study can be evaluated at single wire level itself by incorporating both chemical and electrical properties of CNTs as thin probes [41].

#### *2.2.6 Optical properties*

*21st Century Surface Science - a Handbook*

Even quantum interfering impacts were also being observed: (1) phonon acts as the basic scattering mechanism existing in single walled CNTs at ambient conditions and (2) excellent levels of ohmic frequency contacts can be proliferated in the nanotubes with a probability of adequate transmission T = 1 and 3 electron transfer is explicitly phase coherent along with ballistic ability in CNTs at even low temperature levels. This also suggest a lengthy mean distance for ballistic electron transfer

**Physical properties Parameter Range References** Structure during equilibrium Mean diameter 1.3–1.5 nm [31] Density Zig zag (16,0) 1.33 g/cm3 [30]

Lattice parameter Zig zag (16,0) 16.53 nm [32]

Interlayer distance Zig zag 3.40 Å [33]

Elastic nature Young's modulus 1.0–1.27 TPa [35]

Thermal property Mean free path Around 100 nm [36]

Electrical behavior Current density 1015 A/m2 [38]

Armchair (10,9) 1.32 g/cm3 [30] Chiral (12,5) 1.41 g/cm3 [32]

Chiral (12,5) 16.53 nm [33] Arm chair (10,9) 16.55 nm [32]

Chiral 3.38 Å [33] Arm chair 3.37 Å [34]

Tensile strength About 100 GPa [35]

Thermal conductivity Around 2000 W/m-K [37]

Conductance 13.0 (K.Ohms)<sup>−</sup><sup>1</sup> [38]

Schematic pattern of growth has been extensively used to obtain suspended CNTs in single wall across certain trenches along with normal nanotubes which may be electrically wired up with relative easiness. By manipulating a suspended CNT using an AFM probe while measuring its electrical conductivity, the impact of mechanical deformation on electrical characteristics of CNT can be judged. The wide scope of CNTs based on nanoelectro-mechanic (NEM) devices are invented to explore twisting pattern of single nanowires, pure stretching levels and also due to their high frequency characteristics of resonance measurements. Operated NEMs switches and accessible memory devices have also been envisioned in nearby future. Powerful control and deterministic mode of synthesis of CNT will further explore exciting opportunities and greater possibilities of finding novel nanomaterials and

SWCNTs are mostly inert in nature. The covalent attachment agglomerated the

hybridization onto sidewalls of CNT proves

in super quality CVD developed SWCNTs [39].

*2.2.5 Chemical properties and species interaction*

molecular species with fully bonded sp2

*2.2.4 Electromechanical properties*

**Table 1.**

*Physical properties of CNTs.*

**36**

other devices [38].

Carbon nanotubes have helpful assimilation, photoluminescence (fluorescence), and Raman spectroscopy properties. Spectroscopic strategies offer the chance of speedy and non-dangerous portrayal of moderately a lot of carbon nanotubes. There is a solid interest for such portrayal from the mechanical perspective: various parameters of nanotube union can be changed, purposefully or accidentally, to modify the nanotube quality. As demonstrated as follows, optical assimilation, photoluminescence, and Raman spectroscopies permit brisk and solid portrayal of this "nanotube quality" as far as non-rounded carbon content, structure (chirality) of the delivered nanotubes, and auxiliary imperfections. These highlights decide about some other properties, for example, optical, mechanical, and electrical properties [42].

Carbon nanotubes are novel "one-dimensional frameworks" which can be imagined as moved single sheets of graphite (or all the more accurately graphene). This rolling should be possible at various points and ebbs and flows bringing about various nanotube properties. The width normally fluctuates in the range 0.4–40 nm (i.e., "just" ~100 times), yet the length can shift ~100,000,000,000 times, from 0.14 nm to 55.5 cm [43]. The nanotube perspective proportion, or the length-tobreadth proportion, can be as high as 132,000,000:1 [44] which is unmatched by some other material. Thusly, all the properties of the carbon nanotubes comparative with those of common semiconductors are incredibly anisotropic (directionally reliant) and tunable.

### *2.2.7 Outline information*

While mechanical, electrical, and electrochemical (supercapacitor) properties of the carbon nanotubes are entrenched and have quick applications, the down to earth utilization of optical properties is yet muddled. The previously mentioned tunability of properties is conceivably helpful in optics and photonics. Specifically, light-discharging diodes (LEDs) and photograph detectors dependent on a solitary nanotube have been created in the lab. Their exceptional element is not the effectiveness, which is yet moderately low, however the limited selectivity in the frequency of discharge and recognition of light and the chance

of its adjusting through the nanotube structure. What's more, bolometer and optoelectronic memory gadgets have been acknowledged on groups of singlewalled carbon nanotubes [45].

Crystallographic absconds additionally influence the cylinder's electrical properties. A typical outcome is brought down conductivity through the flawed space of the cylinder. An imperfection in easy chair type tubes (which can lead power) can make the encompassing area become semiconducting, and single monatomic opening incite attractive properties.
