Analysis of the extended defects in 3C-SiC.pdf - Nelson Mandela ...

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2 The characteristics of two-beam diffraction contrast TEM images of stacking faults (SFs) and thin twin platelets in SiC were investigated by using image simulation. Since it is expected that the anomalous absorption ratio of SiC should lie between that of diamond and Si, it is important to investigate how the value of this ratio would affect the symmetry of bright and dark-field TEM images of SFs in SiC. Image simulation was carried out using the software developed by Head et al. (1973) published by Marc De Graef (2003). The outline of the dissertation is as follows. In Chapter 2 a brief discussion of the crystal defects found in face-centred cubic (fcc) and zinc-blende crystal structures is given. Emphasis is placed on the extended defects found in 3C-SiC. Defects created during ion bombardment and their migration during heat treatment is also discussed in general. Chapter 3 discusses the theory of ion implantation and radiation damage in materials. Fundamental theories used in calculating the ion ranges and displacement damage are given and the coalescence of point defects leading to the formation of defect clusters during heat treatment is discussed. Chapter 4 deals with the theory relating to the method of image simulation. This is done by briefly discussing the dynamical theory of electron diffraction and the derivation of the Darwin-Howie- Whelan (DHW) equations. A simple method for calculating a line profile across the fringes of a stacking fault is also given. Chapter 5 is a literature review of previous research done on 3C-SiC focusing on crystal growth, crystal defects and behaviour under irradiation conditions. Chapter 6 gives the experimental details of the current investigation on 3C-SiC. Chapter 7 contains the results of a transmission electron microscopy (TEM) study of the as-grown and implanted 3C-SiC along with the discussion of the results. Chapter 8 lists the conclusions derived from the results of this dissertation.
2.1. Introduction 3 CHAPTER TWO OVERVIEW OF CRYSTAL DEFECTS IN 3C-SiC In this chapter a short overview of the types of crystal defects found in 3C-SiC is presented. The content presented is by no means complete but focuses on the important aspects needed to understand the analysis of the experimental results later on. The reader is advised to consult other references written specifically for this purpose if a deeper understanding is required (Hull et al. (1984)). This chapter focuses mainly on the defects found in the zinc-blende structure since this is the crystal structure of 3C-SiC. The structure itself is explained firstly by referring to a more simple structure i.e. the fcc structure with special attention given to the atomic stacking sequences in the principal crystallographic directions. Furthermore the types of point defects found in SiC are discussed and their diffusion characteristics are reviewed. Finally the nature of the extended defects present in 3C-SiC is discussed. 2.2. Cubic and Zinc-Blende Crystal Structures 2.2.1 The Face-Centred Cubic Structure The unit cell of the face-centred cubic (fcc) structure is a cube with atoms situated at the corners and centres of the cube faces as illustrated in Fig. 2.1. It contains four 1 atoms in positions 000 ; 0 1 1 2 2 ; 2 2 1 1 1 0 and 0 2 2 , with the smallest translation vectors being of the type (1/2). This corresponds to half a surface diagonal of the unit cell.
Page 1 and 2: Analysis of the Extended Defects in
Page 3 and 4: My sincere thanks to the following
Page 5 and 6: OPSOMMING Hierdie dissertasie hande
Page 7 and 8: 4.2.5. Two-Beam Scattering Matrix 4
Page 9 and 10: Dedicated to my wife and parents
Page 11 and 12: SUMMARY The dissertation focuses on
Page 13 and 14: CONTENTS Chapter 1: INTRODUCTION 1
Page 15: 1 CHAPTER ONE INTRODUCTION Silicon
Page 19 and 20: 2.2.2 The Zinc-Blende Structure 5 T
Page 21 and 22: 2.3 Point Defects, Defect Migration
Page 23 and 24: v m Em vm0 exp( ) (2.2) kT 9 wher
Page 25 and 26: 11 explained and the concept of par
Page 27 and 28: 13 Straight dislocations furthermor
Page 29 and 30: 2.5 Partial Dislocations and Slip 1
Page 31 and 32: 17 Fig. 2.13. The geometrical setup
Page 33 and 34: 19 extrinsic stacking faults are th
Page 35 and 36: 2.8 Twinning 21 Twinning is a proce
Page 37 and 38: 23 Fig. 2.20. The process of vacanc
Page 39 and 40: S n Td (3.2) 25 and is also referr
Page 41 and 42: 27 where a = a0(Z1 2/3 + Z2 2/3 ) -
Page 43 and 44: 29 Using this expression, curves of
Page 45 and 46: 31 As stated previously hard-sphere
Page 47 and 48: 33 where A is the atomic weight. Th
Page 49 and 50: 35 a vacancy dislocation loop if th
Page 51 and 52: 37 Fig. 4.1. (a) A wave incident on
Page 53 and 54: 39 Consider Fig. 4.2 which illustra
Page 55 and 56: 41 V0 is the mean inner potential o
Page 57 and 58: 43 beam left-hand side g' = 0 g' =
Page 59 and 60: 45 In addition another set of indep
Page 61 and 62: 47 When this is incorporated into t
Page 63 and 64: S ( s , z ) e T i Se ( / 0 )
Page 65 and 66: z0 z2 . xn cos and (4.47) D 1 proj
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5.1 Introduction 53 CHAPTER FIVE LI
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55 different orientations. The inte
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57 Furthermore Pirouz et al. (1987)
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59 intersection of the fault, the f
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61 each nuclei because of the low s
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63 (2000) found that subsequent ann
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6.3.1 Ion Range and Defect Producti
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67 Fig. 6.3. Total number of displa
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7.1 Introduction 69 CHAPTER SEVEN R
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Fig. 7.2. Simulated diffraction pat
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73 Fig. 7.3. A HRTEM image of the S
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75 Fig. 7.5. The stacking fault sel
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(Si/ni) 2 0.000018 0.000016 0.00001
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79 may be concluded that the initia
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81 Fig. 7.11. Bright field TEM micr
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83 Fig. 7.12 which was obtained by
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85 Fig. 7.13. Bright-field TEM micr
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87 (a) (b) Fig. 7.15. The (a) exper
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89 In the following paragraphs the
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Fig. 7.18. CBED pattern taken of th
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93 Table 7.5. The measured paramete
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7.4.2 Results 95 Fig. 7.22. Bright-
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97 Twin platelets on {111} planes
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99 REFERENCES Blumenau, A.T., Jones
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101 Hull, D., Bacon, D.J. : (1984)
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103 Smith, D.J., Jepps, N.W. and Pa
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