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

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4.2.5. Two-Beam Scattering Matrix 44 4.2.6. Crystal Defects and Displacement Fields 45 4.3. Image Contrast for Selected Defects 47 4.3.1. Line Defects 47 4.3.2. Stacking Faults 47 4.3.3. Fringe Contrast Observed from Twinning 51 Chapter 5: LITERATURE REVIEW OF SiC 53 5.1. Introduction 53 5.2. CVD Growth of β-SiC on Si 53 5.3. Crystal Defects in β-SiC 56 5.3.1. Introduction 56 5.3.2. Accommodation of Misfit and Interfacial Twinning 57 5.3.3. Mechanisms for the Formation of Stacking Faults 58 5.3.4. Stacking Fault Energy in β-SiC 61 5.4. Ion Implantation and Radiation Damage in β-SiC 61 Chapter 6: EXPERIMENTAL DETAILS 64 6.1. Introduction 64 6.2. CVD Growth of β-SiC 64 6.3. Proton Implantation in β-SiC 64 6.3.1. Ion Ranges and Defect Production 65 6.4. Annealing Procedure 67 6.5. Sample Preparation 68 Chapter 7: RESULTS AND DISCUSSION 69 7.1. Introduction 69 7.2. Extended Defects in β-SiC Grown by CVD on (001) Si 69 7.2.1. Crystal Structure and the SiC/Si Interface 70 7.2.2. Stacking Faults and Partial Dislocations 74 7.2.3. Twinning 82 7.3. Hydrogen Implanted β-SiC 83 7.3.1. Unannealed 83 7.3.2. Annealed at 1300°C 84 7.3.3. Annealed at 1600°C 85 7.4. Reassessment of Unimplanted Sample 94 7.4.1. Overview of Investigation 94 7.4.2. Results 95 Chapter 8: CONCLUSION 96 8.1. Introduction 96 8.2. TEM Analysis of β-SiC Grown on (001) Si by CVD 96 8.3. TEM Analysis of β-SiC Proton Bombarded and Annealed 97 β-SiC References 99
1 CHAPTER ONE INTRODUCTION Silicon carbide (SiC) is a wide band gap semiconducting ceramic with excellent thermal, mechanical and electrical properties. It has a wide range of applications, which include its use as structural material for high temperature applications in aggressive environments (Eveno et al. (1992)). It is proposed as an encapsulating material for nuclear fuel in light water and gas-cooled fission reactors due to its good resistance to neutron radiation damage and also as material to be used in fusion environments due to its excellent thermal stability. Hence the study of this material and its structural integrity under different conditions similar to that experienced in the reactor environment is important. A detailed knowledge of the extended defects present in the SiC after the growth process is required together with the study of the evolution of the micro and nano-structure of SiC at high temperatures and irradiation conditions. This dissertation focuses on a transmission electron microscopy (TEM) study of the extended defects in 3C-SiC prepared by chemical vapour deposition on silicon (Si) substrates, as well as the investigation of the defects produced in this material by 400 keV hydrogen implanted to a dose of 2.8 × 10 16 protons/cm 2 . The effects of post irradiation annealing on the implanted material was also investigated for samples annealed at temperatures of 1300°C and 1600°C for one hour. Silicon is the preferred substrate for the CVD growth of single crystalline 3C-SiC and due to the lattice mismatch between SiC and Si, the twins, stacking faults, partial dislocations and misfit dislocations present in the SiC will be similar to the lattice defects present in SiC grown on other substrates. In a nuclear reactor such as the pebble bed modular reactor, the SiC layers in the nuclear fuel particles are irradiated with high energy neutrons. The point defects produced by the neutrons will be the same type as those produced by high energy protons. In this investigation SiC were bombarded with protons and then annealed to determine the critical proton dose needed to produce extended defect clusters during post-implantation annealing. The annealing at elevated temperatures also allowed the investigation of possible phase transformations in the 3C-SiC.
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: CONTENTS Chapter 1: INTRODUCTION 1
Page 17 and 18: 2.1. Introduction 3 CHAPTER TWO OVE
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
Page 99 and 100:
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
Page 105 and 106:
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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Analysis of the extended defects in 3C-SiC.pdf - Nelson Mandela ...

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