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

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86 (a) (b) Fig. 7.14. (a) Bright-field TEM micrograph of the bulk of the 3C- SiC sample annealed at 1600°C for 1 hr. (b) Bright field micrograph showing dislocation complexes in 3C-SiC sample annealed at 1600°C for 1 hr. B = [111], g = 220, s ≥0. The dislocation complexes seen in Fig. 7.14 (b) were initially not observed in the unimplanted sample and it was initially thought that they might have formed due to either the irradiation or annealing process. This was found not to be the case since a reassessment (Section 7.3) of the unimplanted sample in the {111} beam direction showed similar defect complexes. Furthermore an electron diffraction investigation was done to confirm that no phase change occurred during the annealing of the sample at 1600°C. A diffraction pattern of the zone axis was taken and matched with simulated patterns. This was done for the since this direction allows an unambiguous differentiation between cubic and hexagonal SiC phases. Excellent agreement was found and it was concluded that the crystal structure remained that of the cubic 3C phase. The results are shown in Fig. 7.15.
87 (a) (b) Fig. 7.15. The (a) experimental (b) simulated SAD pattern of the [110] zone axis in the 3C-SiC sample annealed at 1600°C for 1 hr To explain the results obtained for the implanted SiC the following is proposed. During proton implantation point defects (interstitial atoms, vacancies and hydrogen atoms) are generated simultaneously in the specimen. In the case of SiC the interstitial atoms and vacancies are from both sublattices, i.e. silicon and carbon. Since interstitials and vacancies can have a charge, they can trap electrons or holes. Point defects produced by irradiation can be trapped by a number of sinks of which the following are the most important: 1. Interstitial and vacancy recombination will result in mutual annihilation. 2. Some vacancies may trap hydrogen atoms leading to the formation of gas filled bubbles or two dimensional platelets. 3. Interstitials and vacancies can be trapped by dislocations, dislocation loops and voids. In order for the displaced atoms and hydrogen to interact during post irradiation annealing, they must be mobile enough to migrate to the various sinks. Since dislocation loops on {111} and {110} planes consist of double layers of silicon and carbon atoms charge neutrality is maintained. This is a result of the Coulomb repulsion in dielectric ionic materials which ensures that interstitial coalescence into a dislocation loop remains stoichiometric (Ryazanov et al. 2002). The same argument would apply to vacancy loops.
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Analysis of the Extended Defects in
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My sincere thanks to the following
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OPSOMMING Hierdie dissertasie hande
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4.2.5. Two-Beam Scattering Matrix 4
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Dedicated to my wife and parents
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SUMMARY The dissertation focuses on
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CONTENTS Chapter 1: INTRODUCTION 1
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1 CHAPTER ONE INTRODUCTION Silicon
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2.1. Introduction 3 CHAPTER TWO OVE
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2.2.2 The Zinc-Blende Structure 5 T
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2.3 Point Defects, Defect Migration
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v m Em vm0 exp( ) (2.2) kT 9 wher
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11 explained and the concept of par
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13 Straight dislocations furthermor
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2.5 Partial Dislocations and Slip 1
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17 Fig. 2.13. The geometrical setup
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19 extrinsic stacking faults are th
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2.8 Twinning 21 Twinning is a proce
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23 Fig. 2.20. The process of vacanc
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S n Td (3.2) 25 and is also referr
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27 where a = a0(Z1 2/3 + Z2 2/3 ) -
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29 Using this expression, curves of
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31 As stated previously hard-sphere
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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
Page 67 and 68: 5.1 Introduction 53 CHAPTER FIVE LI
Page 69 and 70: 55 different orientations. The inte
Page 71 and 72: 57 Furthermore Pirouz et al. (1987)
Page 73 and 74: 59 intersection of the fault, the f
Page 75 and 76: 61 each nuclei because of the low s
Page 77 and 78: 63 (2000) found that subsequent ann
Page 79 and 80: 6.3.1 Ion Range and Defect Producti
Page 81 and 82: 67 Fig. 6.3. Total number of displa
Page 83 and 84: 7.1 Introduction 69 CHAPTER SEVEN R
Page 85 and 86: Fig. 7.2. Simulated diffraction pat
Page 87 and 88: 73 Fig. 7.3. A HRTEM image of the S
Page 89 and 90: 75 Fig. 7.5. The stacking fault sel
Page 91 and 92: (Si/ni) 2 0.000018 0.000016 0.00001
Page 93 and 94: 79 may be concluded that the initia
Page 95 and 96: 81 Fig. 7.11. Bright field TEM micr
Page 97 and 98: 83 Fig. 7.12 which was obtained by
Page 99: 85 Fig. 7.13. Bright-field TEM micr
Page 103 and 104: 89 In the following paragraphs the
Page 105 and 106: Fig. 7.18. CBED pattern taken of th
Page 107 and 108: 93 Table 7.5. The measured paramete
Page 109 and 110: 7.4.2 Results 95 Fig. 7.22. Bright-
Page 111 and 112: 97 Twin platelets on {111} planes
Page 113 and 114: 99 REFERENCES Blumenau, A.T., Jones
Page 115 and 116: 101 Hull, D., Bacon, D.J. : (1984)
Page 117: 103 Smith, D.J., Jepps, N.W. and Pa
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