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

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20 (a) (b) Fig. 2.17. The dissociation of (a) an edge dislocation in an fcc lattice into (b) two partial dislocations bounding between them a ribbon of stacking fault (from Hull et al. (1984)) A stacking fault is generated by the dissociation of an edge dislocation into two partial dislocations by a reaction of the type, _ _ _ b edge b p b 1 p2 (2.7) An edge dislocation present in the crystal with Burgers vector of the type 1/2 (Fig. 2.17(a)) dissociates into two partials with Burgers vector of the type 1/6 type through a reaction shown in equation 2.7 (Fig. 2.17(b)). With the dissociation the two partial dislocations leave between them a stacking fault and are in turn referred to as the bonding partials. The associated energy per unit area γ of a stacking fault is known as the stacking-fault energy and is given by the relation, [ E ( faulted) E( perfect)] / A (2.8) with E being the energy and A the area. Values typically lie in the range 1-1000 mJ/m 2 .
2.8 Twinning 21 Twinning is a process in which a region of the crystal is deformed through a homogenous shear process. This produces the original crystal structure but in a different orientation. The simplest case is the result in which the twinned area is a mirror image of the original crystal. This is depicted in Fig. 2.18. Fig. 2.18. A geometrical description of twinning in a crystal lattice (from Hull et al. (1984)) The open circles represent the position of the atoms before twinning and the filled circles after. The line x-y is termed the twin boundary with atoms above and below it mirror images of one another. Twinning may occur due to plastic deformation or introduced into the material during the CVD growth process. It differs from the process of slip since no rotation of the lattice is taking place. In the fcc and zinc- blende structures twinning takes place on the {111} system. It is as a result of a shear causing a displacement of 1/6 on each consecutive plane and can be seen as the motion of partial dislocations with b = 1/6 on consecutive {111} planes lying parallel to x-y. Furthermore a modification to the electron diffraction pattern obtained from a twinned area in a crystal also occurs. The twinned sections generate a different set of diffractions spots according to its crystallographic orientation which are superimposed onto the diffraction pattern from the perfect crystal. Such a situation is depicted in Fig. 2.19.
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 and 16: 1 CHAPTER ONE INTRODUCTION Silicon
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: 19 extrinsic stacking faults are th
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
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 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 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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