Chapter 1 8 Bottom-up growth methods 8 Abstract 8 1.1. Introduction 9 1.2. Bottom-up growth mechanisms 10 1.2.1. Vapor-liquid-solid growth mechanism 10 1.

2.2. Vapor-solid-solid growth mechanism 16 1.2.3. Vapor-solid growth mechanism 22 1.2.4.

Solution-liquid-solid growth mechanism 26 1.3. Bottom-up growth techniques 29 1.3.1. Chemical Vapor Deposition 29 1.3.2.

Metal-organic chemical vapor deposition 33 1.3.3. Plasma-enhanced chemical vapor deposition 36 1.3.4. Hydride vapor phase epitaxy 38 1.3.

5. Molecular Beam Epitaxy 41 1.3.6. Laser ablation 44 1.3.7. Thermal evaporation 46 1.

3.8. Carbothermal reduction 48 References 51 Chapter 2 65 Top-down fabrication processes 65 Abstract 65 2.1. Introduction 66 2.2. Top-down fabrication techniques 68 2.2.

1. Focused ion beam 68 2.2.2. Electron beam lithography 69 2.2.3. Reactive ion etching 72 2.

2.4. Combined lithography techniques 74 References 76 Chapter 3 81 Hybrid fabrication techniques and nanowire heterostructures 81 Abstract 81 3.1. Introduction 82 3.2. Bottom-up meets top-down approaches 84 3.3.

Integration of nanowires onto unconventional substrates 86 3.3.1. Transferring nanowires onto flexible substrates 86 3.3.2. Growing nanowires on graphene and layered material substrates 92 3.4.

Synthesis of nanowire heterostructures 95 3.4.1. Synthesis of one-dimensional heterostructures 95 3.4.2. Synthesis of mixed dimensional heterostructures 98 References 101 Chapter 4 108 Electrical properties of wide bandgap nanowires 108 Abstract 108 4.1.

Electrical properties 109 4.2. Measurement of electrical conductivity 109 4.3. Fundamental electrical properties of nanowires 112 4.3.1 Effect of doping on electrical properties 113 4.3.

2 Mobility 115 4.3.3 Activation/ionization energy 116 4.3.4 Dependence of activation/ionization energy on NW dimensions 118 4.4 Electrical properties of wide bandgap nanowire based devices 118 4.4.1 Single NW electrical sensing devices 118 4.

4.2 Field-effect transistors (FETs) 120 References 129 Chapter 5 132 Mechanical properties of wide bandgap nanowires 132 Abstract 132 5.1. Characterization techniques 133 5.1.1 Bending and buckling methods 133 5.1.2 Nano indenting method 138 5.

1.3 Resonance testing method 139 5.2. Impact of defects and microstructures on mechanical properties of NWs 140 5.2.1. Defects 140 5.2.

2 Effect of structures, dimensions and temperatures 143 5.3. Anelasticity and plasticity properties 148 5.3.1 Anelasticity 148 5.3.2 Plasticity 148 5.3.

3 Brittle to ductile transition 150 References 152 Chapter 6 155 Optical properties of wide bandgap nanowires 155 Abstract 155 6.1 Optical properties of WBG NWs 156 6.1.1 Photoluminescence characterization of NWs 156 6.1.2 Size-dependent optical properties 157 6.1.3 Shape/morphology-dependent optical properties 158 6.

1.4 Effect of crystal orientation 159 6.1.5 Tuning optical properties of NWs 160 6.2 Wide bangap nanowire light-emitting diodes (LEDs) 164 6.2.1 GaN nanowire based LEDs 164 6.2.

2 GaN nanowire UV LEDs 169 6.2.3 ZnO nanowire based LEDs 172 References 175 Chapter 7 180 Thermal properties of wide bandgap nanowires 180 Abstract 180 7.1. Thermal conductivity 181 7.1.1 Fundamental of thermal transport and thermal conductivity 181 7.1.

2 Measurement of thermal conductivity 182 7.1.3 Effect of diameters on thermal properties 183 7.1.4 Effect of orientation on thermal properties 186 7.1.5 Tenability of thermal properties 187 7.2 Thermoelectric properties 190 7.

2.1 Fundamental thermoelectric properties 190 7.2.2 Thermoelectric properties of ZnO and GaN NWs 191 7.2.3 Thermoelectric properties of SiC NWs 193 7.2.4 Optimisation of the thermoelectric properties 194 References 196 Chapter 8 200 Ultraviolet sensors 200 Abstract 200 8.

1. Introduction 201 8.2. Sensing mechanism 201 8.2.1. Photoconductor architectures 202 8.2.

2. Schottky diode photo sensors 204 8.2.3. Semiconductor p-n junction 206 8.2.4. Field effect transistor-based UV sensors 208 8.

3. Device development technologies 210 8.3.1. The choice of wide band gap materials for UV sensing 210 8.3.2 Top down fabrication of wide band gap nanowire UV sensors 216 8.3.

4. Transfer process for nanowires 219 8.4. Applications of nanowire UV sensors 222 8.4.1 Flame sensors 222 8.4.2.

Environmental monitoring 224 8.4.4 Biological sensors and health care applications 225 References 227 Chapter 9 233 Mechanical Sensors 233 Abstract 233 9.1. Introduction 234 9.2. Sensing mechanisms and corresponding materials 234 9.2.

1. The piezoresistive effect 234 9.2.2. Piezotronics effect in nanowires 239 9.2.3 Capacitive sensing 243 9.3.

Transducer configurations and fabrication technologies 244 9.3.1. Strain sensors 244 9.3.2. Pressure sensors 248 9.3.

3 Tactile sensors 253 9.3.4. Acceleration and vibration sensors 256 9.3.5. Energy harvesting devices 257 9.4.

Applications of mechanical sensors using wide band gap materials 261 9.4.1. Structural heath monitoring 261 9.4.2. Advanced health care 262 9.4.

3 Robotics 265 References 267 Chapter 10 273 Gas sensors 273 Abstract 273 10.1. Introduction 274 10.2. Principle of gas sensing 274 10.2.1. Transconductance sensing mechanism 274 10.

2.2. Field effect transistor-based gas sensors 276 10.2.3. Metal-semiconductor Schottky contact based gas sensors 277 10.2.4.

Integration of nanowires with micro heaters 278 10.3. Standard physical parameters for gas sensors 280 10.3.1. Sensitivity 280 10.3.2.

Selectivity 281 10.3.3. Response time 282 10.4. Materials for different types of gases 284 10.4.1 Oxygen sensors 284 10.

4.2 Carbon dioxide 285 10.4.3 Organic gases 287 10.4.4 Hydrogen gas 290 References 301 Chapter 11 308 Wide band gap nanoresonators 308 Abstract 308 11.1. Introduction 309 11.

2. Principle of nanoresonators 310 11.3. Actuation and measurement techniques 316 11.3.1 Electrostatic actuation 316 11.3.2 Piezoelectric actuation 318 11.

3.3 Magnetomotive actuation 320 11.3.4. Thermal actuator 323 11.4. Engineering the performance of nanoresonators using wide band gap materials 325 11.4.

1. Residual stress 325 11.4.2 Mechanical clamping enhancement 329 11.4.3 Tunning resonant frequency using electrically driven forces 331 11.5. Applications of nanoresonators 334 11.

5.1 Logic Circuit at high temperatures 334 11.5.2 Mass sensing applications 337 11.5.3 Biosensors 338 11.5.4 Mechanical sensing 339 11.

5.5 Optical devices 341 References 343.