UNIVERSITI TEKNIKAL MALAYSIA MELAKAeprints.utem.edu.my/16348/2/Comparative Study Of...gas. Gas yang telah dipilih ialah karbon dioksida, oksigen dan metanol disebabkan oleh penggunaan

UNIVERSITI TEKNIKAL MALAYSIA MELAKA

COMPARATIVE STUDY OF ELECTRONIC PROPERTIES IN

PRISTINE AND SI-DOPED SINGLE-WALLED CARBON

NANOTUBE AS GAS SENSOR: A FIRST PRINCIPLE STUDY

This report submitted in accordance with requirement of the Universiti Teknikal

Malaysia Melaka (UTeM) for the Bachelor Degree of Manufacturing Engineering

(Engineering Materials) (Hons.)

by

FARIZUL MUIZ BIN ALIAS

B051210136

910718-11-5425

FACULTY OF MANUFACTURING ENGINEERING

2015

UNIVERSITI TEKNIKAL MALAYSIA MELAKA

BORANG PENGESAHAN STATUS LAPORAN PROJEK SARJANA MUDA

TAJUK: Comparative Study of Electronic Properties in Pristine and Si-Doped Single-Walled Carbon Nanotube as Gas Sensor: A First Principle Study

SESI PENGAJIAN: 2014/15 Semester 2 Saya FARIZUL MUIZ BIN ALIAS mengaku membenarkan Laporan PSM ini disimpan di Perpustakaan Universiti Teknikal Malaysia Melaka (UTeM) dengan syarat-syarat kegunaan seperti berikut:

1. Laporan PSM adalah hak milik Universiti Teknikal Malaysia Melaka dan penulis. 2. Perpustakaan Universiti Teknikal Malaysia Melaka dibenarkan membuat salinan

untuk tujuan pengajian sahaja dengan izin penulis. 3. Perpustakaan dibenarkan membuat salinan laporan PSM ini sebagai bahan

pertukaran antara institusi pengajian tinggi.

4. **Sila tandakan ( )

SULIT

TERHAD

TIDAK TERHAD

(Mengandungi maklumat yang berdarjah keselamatan atau kepentingan Malaysia sebagaimana yang termaktub dalam AKTA RAHSIA RASMI 1972)

(Mengandungi maklumat TERHAD yang telah ditentukan oleh organisasi/badan di mana penyelidikan dijalankan)

Alamat Tetap:

NO. 712, Jalan Sekolah Sungai

Kechil, Nibong Tebal, 14300,

Seberang Prai Selatan, Pulau Pinang

Tarikh: 2 July 2015

Disahkan oleh:

Cop Rasmi: Tarikh: 2 July 2015

** Jika Laporan PSM ini SULIT atau TERHAD, sila lampirkan surat daripada pihak berkuasa/organisasi berkenaan dengan menyatakan sekali sebab dan tempoh laporan PSM ini perlu dikelaskan sebagai SULIT atau TERHAD.

DECLARATION

I hereby, declared this report entitled “Comparative study of electronic properties in

pristine and Si-doped single-walled carbon nanotube as gas sensor: A first principle

study” is the results of my own research except as cited in references.

Signature : ………………………………

Author’s Name : Farizul Muiz bin Alias

Date : 2 July 2015

APPROVAL

This report is submitted to the Faculty of Manufacturing Engineering of UTeM as a

partial fulfillment to the requirements for the degree of Bachelor of Manufacturing

Engineering (Engineering Materials) (Hons.). The member of the supervisory is as

follow:

……………………………………..

(Dr. Mohd Asyadi Azam bin Mohd Abid)

i

ABSTRAK

Nanotiub karbon berdinding tunggal dan silikon pendopan nanotiub karbon

berdinding tunggal telah disiasat sebagai salah satu bahan untuk peranti pengesan

gas. Gas yang telah dipilih ialah karbon dioksida, oksigen dan metanol disebabkan

oleh penggunaan yang meluas dan dikawal dalam penggunaan dalam sector industri.

Penjerapan dan ciri-ciri elektronik telah disiasat keatas nanotube karbon berdinding

tunggal yang tulen dan yang telah didopan keatas reaksi gas kepada dinding nanotiub

karbon berdinding tunggal. Semua pengiraan dijalankan menggunakan kajian prinsip

pertama berteraskan teori fungsian ketumpatan (DFT) dimana telah dilaksanakan

dalam kod komputer CASTEP and DMol3. Untuk pengoptimuman geometri, telah

mengunakan korelasi pertukaran anggaran-anggaran fungsian seperti Local Density

Approximation (LDA) and Generalized Gradient Approximation (GGA) supaya

struktur menjadi tepat. Dengan menggunakan GGA, didapati bahawa ketepatan

pengiraan sebanyak 80% ke 90% pada keseluruhan hasil. Dari segi tenaga serapan

menunjukkan O2 dan CO2 mempunyai serapan yang lemah terhadap nanotube

berdinding tunggal namun CH3OH dengan kadar -0.61 eV dan gas yang terletak pada

silikon pendopan nanotiub karbon berdinding tunggal menunjukkan tenaga serapan

yang tinggi menghasilkan reaksi dengan kadar diantara -1.6 eV ke -3.99 eV. Untuk

pengiraan ciri-ciri elektronik, hasil menunjukkan penambahan state berdekatan

valance band dan mengurangkan jurang band sebanyak 0.5 eV daripada strakture

original nanotube berdinding tunggal sebanyak 0.6 eV sementara DOS menunjukkan

jenis-P semikonduktur menghasilkan lebih sensatif gas sensor ketika diekposkan

dengan gas. Oleh itu, dengan pencarian ini mampu menaikan usaha untuk

mengoptimumkan pengunaan gas sensor dan akan menyumbang kepada lebih

sensatif gas sensor.

ii

ABSTRACT

A pristine single-walled carbon nanotube (SWCNT) and silicon-doped SWCNT have

been investigated as materials for gas sensor. The gases that had been chosen were

carbon dioxide, oxygen, and methanol due to their widely use and controlled in

industrial sector. Adsorption and electronic properties were investigated on the

pristine and doped SWCNT upon the gas reacted to SWCNT wall. All the calculation

were performed using a first principle study base on density functional theory that

has been implemented in CASTEP and DMol3 computer code. For geometry

optimization, exchange correlation functional approximations such as Local Density

Approximation (LDA) and Generalized Gradient Approximation (GGA) have been

utilized in order to get accurate structural information. Using GGA showing

improvement in accuracy of data by 80% to 90% in overall calculation. In term of

adsorption energy indicates that the O2 and CO2 are weakly adsorbed on the pristine

SWCNT but CH3OH with value of -0.61 eV and all other gases attached on Si doped

SWCNT showing higher amount of adsorption energy that promote to chemisorption

reaction with value range of -1.6 eV to -3.99 eV. As the electronic properties been

calculate, the result indicate there is additional state produce at valance band and

reducing the band gap structure in silicon-doped SWCNT of 0.5 eV from the original

pristine structure of 0.6 eV while DOS showing a p-type semiconductor properties

producing a more sensitive electronic properties upon doping and exposure of gases.

Thus, these finding will be able to gear up efforts in optimizing the usage of gas

sensor and hence will substantially contribute to the more sensitive gas sensor.

iii

DEDICATION

To everyone that contributes to this research, my family and my friend that has been

helping me all along.

iv

ACKNOWLEDGEMENT

First of all I would like to express my gratitude to Allah S.W.T. for blessing on me

throughout this while in completing this final year report. Therefore, I would like to

take this opportunity to express our gratitude to all those who helped me either

directly or indirectly in carrying out this research.

A million awards to my supervisor, Dr. Mohd Asyadi Azam bin Mohd Abid for his

unfailing patience, concerned, advice and encouragement throughout this research.

Besides that, not to forget Dr. Mohamad Fariz bin Mohamad Taib from UiTM Shah

Alam and Mrs. Husna A. Hamid for given guidance and support to me that enabled

me to complete my PSM log book and report as well as my research.

Last but not least, thanks also to all the parties involved in providing encouragement

to me while completing this research, including both my parents and all staffs of FKP

for giving me guidance to accomplish my research. Not forgotten, I would like to

thank to all my friends that have helped me a lot by giving some ideas and

suggestions to accomplish this research.

v

TABLE OF CONTENT

Abstract i

Abstrak ii

Dedication iii

Acknowledgement iv

Table of Content v

List of Tables viii

List of Figures ix

List of Abbreviations, Symbols and Nomenclatures xi

CHAPTER 1: INTRODUCTION

1.1 Background 1

1.2 Problem statement 3

1.3 Objectives 5

1.4 Scope 5

CHAPTER 2: LITERATURE REVIEW

2.1 Introduction 7

2.2 The nature of Carbon 7

2.3 Carbon nanotube 9

2.3.1 Single-walled carbon nanotube (SWCNTs) 10

2.3.2 Chirality of SWCNT 10

2.3.3 Multi-walled carbon nanotube (MWCNTs) 12

2.4 Doping system of CNT 13

2.4.1 Si atom doping system 14

2.5 CNTs based gas sensor 15

2.6 The nature of gas molecules 18

2.6.1 Carbon dioxide 18

2.6.2 Oxygen 19

2.6.3 Methanol 19

vi

2.7 Theoretical studies of nanotube on gas adsorption 19

2.8 Computational molecular modelling 21

2.8.1 First principles of quantum theory 21

2.8.2 Density functional theory 23

2.8.2.1 The Hohenberg-Kohn Theorems 24

2.8.2.2 Kohn-Sham Method 24

2.8.2.3 Exchange-Corellation Functional 25

2.8.3 Local density approximation 26

2.8.4 Generalized gradient approximation 26

2.8.5 K-Point Sampling 27

2.8.6 Materials studio software 28

2.8.6.1 CASTEP (Cambridge serial total energy package) 30

2.8.6.2 Dmol3 (density functional calculation on

molecules)

31

2.8 Summary of computational theory 32

CHAPTER 3: METHODOLOGY

3.1 Introduction 33

3.2 The computational materials studio software 34

3.3 Computer system specification 38

3.4 Building structure of single-wall carbon nanotube - STEP 1 39

3.5 Structure refinement – STEP 2 44

3.6 Calculation of material properties using quantum based software

(CASTEP and DMol3) – STEP 3

45

3.7 Analysis structure – STEP 4 48

3.7.1 Adsorption Energy 48

3.7.2 Electronic band structure 49

3.7.1.1 Band structure 49

3.6.1.2 High symmetry of Brillouin zone 50

3.7.3 Density of state 52

CHAPTER 4: RESULTS AND DISCUSSION

vii

4.1 Geometry properties 54

4.1.1 Pristine SWCNT and Si-doped SWCNT 56

4.1.2 O2 on pristine SWCNT and Si-doped SWCNT 58

4.1.3 CO2 on pristine SWCNT and Si-doped SWCNT 60

4.1.4 CH3OH on pristine SWCNT and Si-doped SWCNT 62

4.2 Adsorption energy analysis 65

4.3 Electronic properties 68

4.3.1 Pristine and Si doped SWCNT electronic properties analysis 68

4.3.2 O2 adsorption 71

4.3.3 CO2 adsorption 74

4.3.4 CH3OH adsorption 77

CHAPTER 5: CONCLUSIONS AND RECOMMENDATIONS

5.1 Conclusion 80

5.2 Recommendations 81

REFERENCES 82

APPENDICES

Appendix A: Adsorption energy calculations 94

Appendix C: PSM gantt chart 95

viii

LIST OF TABLES

2.1 Cross section view of CNT 12

3.1 Overview of materials studio system requirement 37

3.2 Convergence thresholds in DMol3 44

3.3 Brillouin Zone symmetry points 50

3.4 Brillouin Zone SWCNT structure path 51

4.1 Adsorption energy of gases 64

ix

LIST OF FIGURES

2.1 Summary of different carbon form 8

2.2 Graphite rolled up to form CNT 9

2.3 Single-walled carbon nanotube 10

2.4 The chiral vector of CNT 11

2.5 Multi-walled carbon nanotube 13

2.6 Si doping on SWCNT 15

2.7 Typical CNTs gas sensor 17

2.8 Homogeneous gas concepts 26

2.9 The time and size in materials multi-scale characterization 31

3.1 General step for quantum modelling 35

3.2 Molecular modelling using first principle 36

3.3 Four main step in quantum modelling 36

3.4 PSM work flow chart 37

3.5 Creating structural in visualizer 40

3.6 Structure of (8, 0) zigzag single-walled pristine carbone nanotube 41

3.7 A (8, 0) zigzag single-walled Silicon doped single-walled 42

carbon nanotube

3.8 Gas molecules (a) O2 (b) CO2 (c) CH3OH 42

3.9 The side view upon gasses location above SWCNT where 43

(a) O2 (b) CO2 (c) CH3OH

3.10 DFT exchange-correlation energy 44

3.11 Parameter setup in DMol3 and CASTEP 47

3.12 Band structure of metal, semiconductor and insulator 49

3.13 Brillouin Zone band structure 50

3.14 SWCNT structure Brillouin Zone 52

3.15 Example of DOS of various CNTs structure 53

4.1 Possible adsorption location for gases (a) Pristine SWCNT 55

(b) Si doped SWCNT

x

4.2 Geometry structure of (a) Pristine SWCNT; (b) Si doped SWCNT 56

4.3 Representing the side view of (a) Pristine SWCNT; 57

(b) Si doped SWCNT

4.4 The binding energy of pristine SWCNT with O2 58

4.5 The binding energy of Si doped SWCNT with O2 58

4.6 Geometry structure of O2 adsorbed on a) Pristine SWCNT; 60

b) Si doped SWCNT 60

4.7 The binding energy of pristine SWCNT with CO2 61

4.8 The binding energy of Si doped SWCNT with CO2 61

4.9 Geometry structure of CO2 adsorbed on a) Pristine SWCNT; 62

b) Si doped SWCNT

4.10 The binding energy of pristine SWCNT with CH3OH 62

4.11 The binding energy of Si doped SWCNT with CH3OH 63

4.12 Geometry structure of CH3OH adsorbed on a) Pristine SWCNT; 64

b) Si doped SWCNT

4.13 Pristine SWCNT (a) Band structure (b) DOS 69

4.14 Si doped SWCNT (a) Band structure; (b) DOS 70

4.15 Electronic properties of O2 on Pristine SWCNT 72

(a) Band structure; (b) DOS

4.16 Electronic properties of O2 on Si doped SWCNT 73

(a) Band structure; (b) DOS

4.17 Electronic properties of CO2 on Pristine SWCNT 75

(a) Band structure; (b) DOS

4.18 Electronic properties of CO2 on Pristine SWCNT 76

(a) Band structure; (b) DOS

4.19 Electronic properties of CH3OH on Pristine SWCNT 78

(a) Band structure; (b) DOS

4.20 Electronic properties of CH3OH on Pristine SWCNT 79

(a) Band structure; (b) DOS

xi

LIST OF ABBREVIATIONS, SYMBOLS AND

NOMENCLATURES

1D - One dimensional

2D - Two dimensional

3D - Three dimensional

µm - Micrometer

H - Hamiltonian operator

Ψ - Wavefunction

Å - Angstrom

a - lattice vectors

B - Boron

BZ - Brillouin-zone

C - Carbon

CASTEP - Cambridge serial total energy package

Ch - Chiral vector

CB - Conduction band

CH3OH - Methanol

CNT - Carbon nanotube

CO - Carbon monoxide

CVD - Chemical vapor disposition

DFT - Density functional theory

DFPT - Density functional perturbation theory

DMol3 - Density functional calculation on molecules

DOS - Density of state

E - Energy

e - Electron charge

Ead - Adsorption energy

eV - Electron volt

FFT - Fast Fourier transform

GGA - Generalized gradient approximation

xii

HCP - High performance computer

IR - Infrared

LDA - Local density approximation

NH3 - Ammonia

NO2 - Nitrogen dioxide

nm - Nanometer

M - Electron mass

MS - Materials studio

MWCNT - Multi-walled carbon nanotube

O2 - Oxygen

P - Momenta of ions

PC - Personal computer

PW91 - Perdew and Wang

r - Radius

rc - Cut-off radius

SCF - Self consistence field

Si - Silicon

SWCNT - Single-walled carbon nanotube

USP - Ultra-soft pseudopotential

VB - Valance band

Viz. - Visualizer

WDA - Weight density approximation

XC - Exchange-correlation

Z - Charge of ion

1

1.1 Background Study

Nowadays, gas sensors are becoming more essential measurement for the used in

industries and factories as well as in the daily life. Many gases can be a perfect example

of a gas that can be harmful such as carbon monoxide, carbon dioxide and many others.

Due to this causes, detectors for this gas can be found in many mass market retailers and

industries across the country. As a results, gas sensors are being extensively studied to

develop a sensitive, low cost and reliable gas sensor.

Basically, chemical gas sensor is well defines as a device that is able to change

the physical properties upon exposure to gas molecules through electrical conductance.

An electrical signal is measured upon the change in these properties and the results are

then used to detect the gas molecules. Fast response time and high accuracy are the two

basic requirements for gas sensors. According to Kerotocenkov (2013), the size, cost and

weight are the main constraints along producing sensor with capability to measure the

physical properties over a certain lifetime. In contrast, commercially market available

for gas sensors have advantages in lower cost, smaller size and easy to operate. Typical

gas sensors can be from in a variety of size micrometers to centimeters while the size

can be reduced due to rapid large scale ups of such productions (Yamazoe, 2005). These

all make these gas sensors viable for real time in situ environments. Meanwhile, the

INTRODUCTION

CHAPTER 1

2

major drawbacks for gas sensors include stability, sensitivity, selectivity, and

reproducibility which could render these gas sensors unsuitable for long term usage.

Nanotechnology is known as any process or product that has sub micrometer

dimensions. Since 1990s, there is a rapid growth in research interest of nanotechnology

including increasing in high performance of nanomaterials and nanoscale electronic

devices. (Pandyan, 2012). The discovery of carbon nanotubes (CNTs) has been attracted

considerable attention since they have a wide range of applications in nanometer-scale

electronic devices. Furthermore, carbon material in sensor technology becoming an ideal

component, since they have a very good sensitivity on sensing with interesting electronic

properties of the materials (Roberts et al, 2009). As a result, recent advancements in

nanotechnology have provided opportunities to improve sensor performances in

detecting gases dramatically. Considerable interests have been on new room temperature

operated gas sensing materials. Due to their ability to change the electrical properties

upon exposure to the gas molecule and high surface, CNTs have been a promising as

new gas sensing material combining with outstanding properties which include high

performance, fast respond upon exposure of gas and wide selectivity of gases that able to

be detected (Jung et al, 2014). Therefore, a huge effort in research has been carried out

in new gas sensors as the demand of gas detection technologies is increased. It is indeed

not surprising to see the sensor research community as a beneficiary due to advanced

nanomaterial developments as carbon nanotubes have been one of the mostly studied

nanomaterial.

Quantum calculations using first principle study base on the density functional

theory (DFT) provide a great opportunity to prescribe the initial and the fundamentals

properties in materials. Furthermore, the atomic view can be accurately visualized in

detail. Besides that, the first principle calculations require less empirical data with cost

efficient comparing to the experiment laboratory work which will help in term of

reasonable and affordable in large scale material design.

3

The main focus of this study is to investigate and understand the pristine and

doped zigzag (8, 0) single-walled carbon nanotube (SWCNT) reacted toward gas

adsorption. The zigzag (8, 0) SWCNT was choosen because, according to Iijima and

Ichihashi (1993), the (8, 0) CNTs were dominant during synthesized and having a

semiconductor nature. In addition, the gasses consists of O2, CO2, and CH3OH that will

react with pristine SWCNT, but the doping system in SWCNT anticipated to enhance

the adsorption energy as well as the electronic properties upon adsorption of gases which

will promote an impact in sensitivity of the gas sensor technology. Furthermore, the

gases were chosen due to the wide range of industrial application and some of them

having human and environmental issues.

1.2 Problem statement

There have been a high interest studies toward gas sensing application using

CNT. However, there are less fundamental understanding in the interaction behavior

classes of gas molecules (O2, CO2, and CH3OH) with pristine CNT and doped CNT

system (Zanolli et al., 2011). Ironically, there are only investigation on the amount of

gas that can be adsorbed by the CNTs but no identification on binding distance and

stable position of the gas reacted toward the CNTs. Therefore, upon understanding the

sensitivity of the gas molecule adsorption, the geometry and adsorption behavior

(adsorption energy) becoming essential. According to G. Guo et al. (2007), pure CNTs

are sensitive only toward gas molecules such as NO2, SO2, and O2 which have strongly

chemical interaction with CNTs. Thus, it is highly recommended to find the effective

ways to improve the sensitivity of CNTs upon other molecules, in particular industrial

application as well as the human and environmental effects gases. Furthermore, pristine

SWCNT having a weak Vander wall forces and it cannot detect some of gas molecules

such as carbon monoxide and ammonia (Pandyan et al., 2012).

4

It has been widely studied that the electronic properties of CNTs having a

semiconducting nature and very sensitive to only certain gases. Moreover, the range of

gases CNTs sensors can be detected are limited to gas molecules that possess large

binding energies and charge transfers toward nanotube (Wang and Yeow, 2009).

According to Adjizian et al. (2014), the special characteristics of CNT due to they

possess high surface area to interact with gases and the electrical conductivity change

upon the gas adsorption at room temperature. A promising approach to enable single-

walled carbon nanotubes (SWCNTs) to detect gas molecules is by doping (heteroatom

substitution), when heteroatom impurities are being introduced (such as Silicon) or

forming active sites in tube walls, the sensitivity of adsorption on SWCNTs can be

improved (Bai et al., 2007).

Moreover, the use of different doping atom (Si) will produce different electrical

properties for semiconductor SWCNT that also help in producing a sensitive gas sensor,

but there are limited understanding on the changing in electronic properties of doped

CNT (Llobet, 2013). Furthermore, the electronic properties of gas adsorbates upon

molecule adsorption producing different electronic properties with different type of gas

interaction. The effect of the electronic properties through doping and gas adsorption can

be observed in the change in the electrical resistance. Indeed, electronic charge transfer

between the gas molecule and the doped CNT will affect the position of the Fermi

energy and effect the conductivity of gas detection (Zanolli et al., 2011). The need to

understand the adsorption behavior and the electrical properties of doped SWCNT upon

gas adsorption is worth it to study in suggesting the good sensitivity of gas sensor as it

will show the electron charge transfer concepts upon adsorption of gases molecule.

5

1.3 Objectives

The main objectives of this project are:

i. To understand the fundamental insight into the molecular interactions between

common gaseous adsorbates pristine SWCNT and Si-SWCNT models.

ii. To investigate electronic properties of pristine and silicon doped (8, 0) zigzag

SWCNT upon gas molecular adsorption.

1.4 Scope

This project will mainly focus on understanding the right adsorption in term of

high adsorption energy of these molecules base on the geometrical configuration and

structural stability of doped SWCNT. After completing the adsorption energy and

geometrical analysis, there are also several measurements need to be account in order to

achieve high sensitivity which is electronic properties. Furthermore, from electrical

properties involved the study of changing in band structure and density of states using

density functional theory based on computational numerical base to achieve the best

type of doped SWCNT related to gas sensor application. In order to optimize the

structure of pristine and doped SWCNT upon gas adsorption and understanding their

electronic properties, DFT theory were executed. Chapter 1 offers an overview to the

project by describing the important of SWCNT as gases sensor and explain the basic of

using computational as to design a new material base on the quantum theory.

Furthermore, the project problem were identified and proposed solutions that need to be

gain are established in problem statement. Chapter 2 provides review on SWCNT

material as well as Silicon doped SWCNT upon gases molecules. Also, this chapter brief

the first principle study of adsorption behavior between pristine and doped SWCNT on

exposure to gases molecule will be explained in this chapter. More, DFT also been

reviewed in detail starting from Schrodinger equation until energy cut-off for using basis

set of plane wave with Local Density Approximate (LDA) and Generalized Gradient

6

Approximate (GGA) exchange correlation. Chapter 3 describe the methodology on

computational and understanding the usage of first principle calculation that been

applied in this project. The computational methods setting parameters are shown and

well explained to ensure the calculation technique are the most accurate with cut-off

energy and convergence the k-point. The structures of pristine SWCNT and doped

SWCNT are respectively built by using Material Studio Visualizer. The adsorption

energy and electronic properties are perform by using DMol3 and CASTEP computer

modules.

7

2.1 Introduction

This chapter provides an overview on the basic understanding of carbon

nanotube (CNT) and will be discuss in order to understand the molecular structure of the

materials. The literature of doping system in CNT and an understanding the nature of

gas molecules and adsorption for CNT are also stated with regard to cover the scope of

our research. In addition, the density functional theory (DFT) with first principle study

and as one of the mathematical and physic tools to investigate the electronic properties

of pristine and doped CNT upon gas adsorption are also reported in this chapter.

2.2 The nature of carbon

Carbon is an element having 6 as an atomic number with a symbol C. From the

periodic table, the element of carbon belong to the group 14 which is respected having a

non-metallic group with a six elections with two of the electron filling the 1s orbital

another remaining electron fill the sp2 for double bonding or sp3 for single bonding as

well as the sp hybrid orbital for triple bonding. According to Zhang (2012), in

comparison with different bonding state will introduce into certain structural

arrangement in which sp bonding will give rise to one dimensional chain structure, sp2

bonding will produce planar structure and sp3 bonding to tetrahedral structure.

LITERATURE REVIEW

CHAPTER 2

8

The short lived nature of atomic carbon is effect the stability, because of that

carbon is stabilized in different molecular configurations with different structures called

allotropes. Moreover, the several best allotropes are graphite, nanoform, and amorphous

carbon with recent addition of fullerenes and carbon nanotube (D'Souza and Kadish,

2012). The carbon tree family which is shown Figure 2.1 shows that the range in carbon

nanoform family of is significantly larger than mention because of unique bonding

versatility of carbon.

Figure 2.1: Summary of different carbon form

Carbon

Diamond (sp3)

Graphite (sp2)

Turbostratic

Rhombohedral

Hexagonal

Carbynes (sp)

Amorphous (sp3/sp2)

Nanoform (quasi sp2)

Fullerenes

Nanotubes