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

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8.1 Introduction 96 CHAPTER EIGHT CONCLUSION In this chapter the conclusions that are reached from the study are dealt with in two sections. Section 8.2 lists the main results and conclusions for the unirradiated and unannealed samples and Section 8.3 the main results and conclusions for the proton bombarded 3C-SiC. All the results listed and conclusions are from a TEM study of the samples. 8.2 TEM Analysis of ß-SiC Grown in (001) Si by CVD The phase of the SiC was confirmed by electron diffraction and HRTEM to be the cubic ß phase with a lattice parameter of 4.35 0.01 Å. The SiC layer was single crystalline with the same orientation as the Si substrate. HRTEM indicated that planar defects on inclined {111} planes were generated at the Si/SiC interface and propagate through the SiC layer. The SiC layer contained a high density of SFs which were uniformly distributed through the foil. By simulating SFs and matching it with observed SFs, it was found that the SFs have a fault vector of the type 1/3 with bonding partial dislocations of the type 1/6 . Inclined SFs exhibited symmetrical and complementary fringe contrast images in both bright and dark field two-beam imaging conditions. SFs viewed edge-on generated streaks in the diffraction pattern similar to that generated by a thin precipitate viewed edge-on. HRTEM imaging of SFs viewed edge-on indicated that the SF were extrinsic in nature. FFTs obtained of the HRTEM image of these SFs produced streaks similar to those observed in the selected area electron diffraction patterns of edge-on SFs.
97 Twin platelets on {111} planes were observed in the SiC layer. These narrow twins nucleate at the interface and extend only a short distance into the SiC layer. The extended defects observed in the SiC layers were most probably introduced during the CVD growth process as a result of the lattice mismatch between the SiC epitaxial layer and the Si substrate. This inference is strengthened by the fact that hexagonal 6H-SiC, which are grown by a different technique, can be prepared with an extremely low extended defect concentration. Furthermore, it is known that stacking faults form readily in ß-SiC due to the very low (negative) stacking fault energy of this compound. Twins on the other hand can also relieve misfit stress and it is therefore expected that twins would be generated at the Si/SiC interface as was observed in this investigation. High resolution transmission electron microscopy analyses of stacking faults viewed edge-on indicate that the SFs are extrinsic in nature, i.e. it consists of two displaced layers yielding a stacking sequence in the direction of …ABCA/C/BCAB… The symmetrical and complementary nature of two-beam bright and dark-field diffraction contrast images of inclined SFs indicate that SiC has an anomalous absorption ratio between that of Si and diamond. This conclusion was confirmed by matching simulated SF images with experimental SF images, where the best match was obtained for an anomalous absorption ratio of 0.016 for SiC. The values for Si and diamond are 0.1 and 0.01 respectively. 8.3 TEM Analysis of Proton Bombarded and Annealed ß-SiC ß-SiC samples were implanted with 400 keV protons to a total dose of 2.8 × 10 16 protons.cm -2 . Post-implantation annealing was carried for 1 hour at 1300 and 1600 ºC. In all the implanted samples, annealed an unannealed, no evidence of radiation damage was observed. The radiation damage that one would expect to find in proton
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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
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35 a vacancy dislocation loop if th
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37 Fig. 4.1. (a) A wave incident on
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39 Consider Fig. 4.2 which illustra
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41 V0 is the mean inner potential o
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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)
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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
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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 and 100: 85 Fig. 7.13. Bright-field TEM micr
Page 101 and 102: 87 (a) (b) Fig. 7.15. The (a) exper
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: 7.4.2 Results 95 Fig. 7.22. Bright-
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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