Processing, Properties, and Design of Advanced Ceramics and Composites E-Book

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Serie: Ceramic Transaction Series
• Sprache: Englisch

Seitenzahl: 695

Veröffentlichungsjahr: 2016

Beschreibung

This proceedings volume contains a collection of 34 papers from the following symposia held during the 2015 Materials Science and Technology (MS&T '15) meeting: * Innovative Processing and Synthesis of Ceramics, Glasses and Composites * Advances in Ceramic Matrix Composites * Advanced Materials for Harsh Environments * Advances in Dielectric Materials and Electronic Devices * Controlled Synthesis, Processing, and Applications of Structure and Functional Nanomaterials * Processing and Performance of Materials Using Microwaves, Electric and Magnetic Fields, Ultrasound, Lasers, and Mechanical Work, Rustum Roy Memorial Symposium * Sintering and Related Powder Processing Science and Technologies * Surface Protection for Enhanced Materials Performance: Science, Technology, and Application * Thermal Protection Materials and Systems * Ceramic Optical Materials * Alumina at the Forefront of Technology

Leseprobe

Processing, Properties, and Design of Advanced Ceramics and Composites

Ceramic Transactions, Volume 259

Edited byGurpreet SinghAmar BhallaMorsi M. MahmoudRicardo H. R. CastroNarottam P. BansalDongming ZhuJ. P. SinghYiquan Wu

Copyright © 2016 by The American Ceramic Society. All rights reserved.

Published by John Wiley & Sons, Inc., Hoboken, New Jersey.Published simultaneously in Canada.

No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning, or otherwise, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, [phone], fax [phone], or on the web at www.copyright.com. Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, [phone], fax [phone], or online at http://www.wiley.com/go/permission.

Limit of Liability/Disclaimer of Warranty: While the publisher and author have used their best efforts in preparing this book, they make no representations or warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives or written sales materials. The advice and strategies contained herein may not be suitable for your situation. You should consult with a professional where appropriate. Neither the publisher nor author shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages.

For general information on our other products and services or for technical support, please contact our Customer Care Department within the United States at [phone], outside the United States at [phone] or fax [phone].

Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic formats. For more information about Wiley products, visit our web site at www.wiley.com.

Library of Congress Cataloging-in-Publication Data is available.

ISBN: 978-1-119-32364-8ISSN: 1042-1122

List of Tables

Chapter 2

Table I

Table II

Table III

Chapter 5

Table I

Table II

Chapter 6

Table I

Chapter 7

Table I

Chapter 9

Table 1

Table 2

Chapter 10

Table 1

Table 2

Chapter 12

Table I

Table II

Chapter 13

Table I

Table II

Chapter 14

Table 1

Table 2

Chapter 15

Table 1

Table 2

Chapter 16

Table 1

Table 2

Chapter 17

Table 1

Chapter 18

Table I

Table II

Chapter 22

Table 1

Table 2

Table 3

Table 4

Chapter 23

Table 1

Chapter 24

Table I

Chapter 26

Table I

Chapter 27

Table I

Table II

Chapter 28

Table 1

Table 2

Chapter 32

Table I

Table II

Table I

Chapter 33

Table 2

Guide

Cover

Contents

Preface

Pages

iv

ix

1

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

45

46

47

48

49

50

51

52

53

54

57

58

59

60

61

62

63

64

65

66

67

68

69

71

72

73

74

75

76

77

78

79

81

82

83

84

85

86

87

88

89

90

91

92

93

94

95

96

97

99

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

132

133

134

135

136

137

138

139

140

141

143

144

145

146

147

148

149

150

151

153

154

155

156

157

158

159

160

161

162

163

164

165

166

167

168

169

170

171

172

173

174

175

176

177

178

179

180

181

182

183

185

187

188

189

190

191

192

193

194

195

196

197

199

200

201

202

203

204

205

206

207

208

209

210

211

212

213

214

215

216

217

218

219

220

221

223

224

225

226

227

228

229

230

231

233

234

235

236

237

238

239

240

241

242

243

243

244

245

246

247

248

249

250

251

252

253

254

255

256

257

258

259

261

262

263

264

265

266

267

268

269

271

273

274

275

276

277

278

279

280

281

282

283

284

285

286

287

288

289

290

291

293

295

296

297

298

299

300

301

302

303

304

305

306

307

308

309

310

311

312

313

314

315

316

317

318

319

320

321

322

323

324

325

327

328

329

330

331

332

333

334

335

337

338

339

340

341

343

344

345

346

347

348

349

350

351

352

353

354

355

356

357

358

359

361

362

363

364

365

366

367

368

369

370

371

373

374

375

376

377

378

379

380

381

382

383

384

385

386

387

388

Preface

This volume contains 33 papers presented during the Materials Science & Technology 2015 Conference (MS&T'15), held October 4–8, 2015 at The Columbus Convention Center, Columbus, Ohio. Papers from the following symposia are included in this volume: Controlled Synthesis, Processing, and Applications of Structural and Functional Nanomaterials.

Advances in Dielectric Materials and Electronic Devices

Innovative Processing and Synthesis of Ceramics, Glasses and Composites

Advances in Ceramic Matrix Composites

Rustum Roy Memorial Symposium on Processing and Performance of Materials Using Microwaves, Electric, and Magnetic Fields

Sintering and Related Powder Processing Science and Technology

Thermal Protection Materials and Systems

Surface Protection for Enhanced Performance

Ceramic Optical Materials, and

Alumina at the Forefront of Technology

These conference symposia provided a forum for scientists, engineers, and technologists to discuss and exchange state-of-the-art ideas, information, and technology on advanced methods and approaches for processing, synthesis, characterization, and applications of ceramics, glasses, and composites.

Each manuscript was peer-reviewed using The American Ceramic Society's review process. The editors wish to extend their gratitude and appreciation to all the authors for their submissions and revisions of manuscripts, to all the participants and session chairs for their time and effort, and to all the reviewers for their valuable comments and suggestions.

We hope that this volume will serve as a useful reference for the professionals working in the field of synthesis and processing of ceramics and composites as well as their properties.

GURPREET SINGHAMAR BHALLAMORSIM. MAHMOUDRICARDO H. R. CASTRONAROTTAMP. BANSALDONGMING ZHUJ. P. SINGHYIQUANWU

Controlled Synthesis, Processing, and Applications of Structural and Functional Nanomaterials

ASSESSING THE LIMITS OF ACCURACY FOR THE TAUC METHOD FOR OPTICAL BAND GAP DETERMINATION

Dunbar P. Birnie, III

Rutgers University, Department of Materials Science and Engineering New Brunswick, New Jersey, 08854-8065

ABSTRACT

Scientists and engineers working with nanotechnology and thin film optical devices often make use of “Tauc plots” to determine band gaps and evaluate the effect of processing conditions on the quality of coatings made for these applications. Broad-band optical data are easy to acquire and usually exhibit a region of reasonable transparency and then a sharp rise in absorption with increasing photon energy as the band-gap energy is exceeded. The shape of the onset of absorption is diagnostic of whether the band-gap is direct or indirect. Then, an appropriate linear regression can be used to extrapolate to the band gap value, though sometimes the extrapolation is quite far in absolute energy terms from the data used to make the extrapolation. This paper covers some of our recent work where we use known materials to standardize the fitting protocols and assess the accuracy of this simple method.

INTRODUCTION

In our earlier work with thin films (and for many studies in the literature that use the Tauc method) we’ve noticed that the distance of extrapolation in the fitting process may be relatively large, and the tail of sub-band-gap absorption can also be quite large. This raised the basic question about how accurate the Tauc method would be, and how to establish procedures that improve the accuracy of the fitting results[1]. We delved deeply into this problem by looking at ZnO thin films because they are an extremely well-studied material and ZnO is known to have a direct band gap. By looking closely at a population of over 120 thin film Tauc fits we found the band-gap results overall were consistent with a value of 3.27 +/- 0.05 eV, with evidence for two small outlier populations [1]. A subpopulation of higher gap values appeared to be caused by nanoparticle quantum confinement effects (not surprisingly), while a subpopulation of lower gap values appeared to be correlated with more defective samples. These were essentially cases that had stronger sub-band-gap absorption, which has the mathematical effect of shifting the intercept point somewhat to the left and making the confidence interval of the band-gap determination wider (less accurate). To quantify this effect and provide a figure of merit for identifying the more accurate samples, we introduced the “near-edge absorptivity ratio (NEAR)”. And, when using the NEAR to focus on the more accurate data sets, we found that the Tauc method generally gave an experimental distribution of results with a standard deviation of only 0.033 eV, thus emphasizing the relatively high accuracy of the method in general.

We extend that work to the case of indirect band-gap materials and examine accuracy limits based on absorption coefficient values and coating thickness effects that can influence the signal-to-noise ratio of real optical absorption data. Indirect band-gaps are more difficult to characterize because their absorption intensities are characteristically weaker, which provides an added difficulty when most optical data are determined from thin film samples. We address this problem by working with single crystal data from silicon, probably the most well-characterized indirect band-gap material available.

BACKGROUND

The seminal work of Tauc, Grigorovici, and Vancu [2] presented a simple method that uses broad band absorption spectra and interpreted the shape of the absorption edge to arrive at a determination of the band gap, and its character. Their method was further developed in Davis and Mott’s more general work on amorphous semiconductors [3, 4]. Together they’ve shown that the optical absorption strength depends on the difference between the photon energy and the band gap as shown in (Eq. 1):

(1)

where h is Planck's constant, v is the photon's frequency, a is the absorption coefficient, Eg is the band gap and A is a proportionality constant. The value of the exponent denotes the nature of the electronic transition, whether allowed or forbidden and whether direct or indirect:

Typically, the allowed transitions dominate the basic absorption processes, giving either n=1/2 or n=2, for direct and indirect transitions, respectively.

Thus, the basic procedure for a Tauc analysis is to acquire optical absorbance data for the sample in question that spans a range of energies from below the band gap transition to above it. Then, plotting the (α h v) with various test exponents versus photon energy allows the researcher to decide which of the exponents gives the most linear plot. Finally, with this exponent, the line is extrapolated down to intersect the X-axis, which will be the band-gap value (as can be interpreted from Equation 1). Of the four exponent choices listed, it is usually found that either the ½ and 2 exponents are most frequently used (being associated with the allowed transitions).

ANALYSIS OF DIRECT-GAP MATERIALS

Zinc oxide was a good candidate for evaluating the Tauc method because it has been widely studied for a number of useful applications [5-13]. Among these applications the band-gap plays a central and fundamental role as it controls many absorption and conductivity phenomena. Single crystal optical studies have found a direct band gap of 3.3 eV[14-16], though many of the papers surveyed in our thin film analysis were collected from very well crystallized films or even epitaxially grown layers[1]. ZnO was also attractive as a reference material because of its high level of stoichiometry. While every stoichiometric compound must thermodynamically have point defects at some level (and therefore by definition be non-stoichiometric), the phase of ZnO has been experimentally studied and found to have very little deviation from the ideal 1:1 ratio. For example, the early work of Allsopp and Roberts found a slight zinc excess, but less than 50 ppm [17]. This is much more stoichiometric than many phases and thus provided a good calibration test-case for the Tauc method.

Figure 1