Experimental Micro/Nanoscale Thermal Transport

A unique focus on experimental techniques for the characterization of thermal transport in micro/nanoscale materials

In the rapidly evolving field of nanotechnology, it ultimately comes down to experiments and measurement techniques to obtain and validate data on the thermophysical properties of nanoscale and nanostructured materials for various engineering applications. Experimental Micro/Nanoscale Thermal Transport details techniques developed in the author′s own laboratory that boast significantly reduced experimental time, superior signal–to–noise ratio, and high–accuracy measurement results.

The book walks readers through the entire process of setting up and implementing advanced new technologies, including physical principles and data analysis for measuring the thermal conductivity/diffusivity of micro/nanoscale films and wires, while giving clear instructions on how to conduct experiments, assess uncertainties, and interpret physical results.

Highlights of Experimental Micro/Nanoscale Thermal Transport include: The introduction of the superior optical heating and electrical thermal sensing (OHETS) technique, along with other techniques in the frequency domain Highly efficient methods for accurate transient measurement in the time domain, such as transient electro–thermal (TET), transient photo–electro–thermal (TPET), and pulsed laser–assisted–thermal relaxation (PLTR) techniques Measurement of full–spectrum thermophysical properties using the generalized electro–thermal (GET) technique, one of the most advanced technologies available Novel temperature differential measurement using Raman spectroscopy to achieve direct evaluation of the local thermal resistance at material interface

The first of its kind to focus on thermal characterization of the thermophysical properties of micro/nanoscale materials, this book will help researchers in material design and characterization tackle challenging thermal transport problems, quickly establish their own measurement techniques, and gain invaluable insight into experimental design.

PREFACE xi

1 INTRODUCTION 1

1.1 Unique Feature of Thermal Transport in Nanoscale andNanostructured Materials 1

1.1.1 Thermal Transport Constrained by Material Size 2

1.1.2 Thermal Transport Constrained by Time 6

1.1.3 Thermal Transport Constrained by the Size of PhysicalProcess 8

1.2 Molecular Dynamics Simulation of Thermal Transport atMicro/Nanoscales 10

1.2.1 Equilibrium MD Prediction of Thermal Conductivity 11

1.2.2 Nonequilibrium MD Study of Thermal Transport 15

1.2.3 MD Study of Thermal Transport Constrained by Time 18

1.3 Boltzmann Transportation Equation for Thermal TransportStudy 21

1.4 Direct Energy Carrier Relaxation Tracking (DECRT) 32

1.5 Challenges in Characterizing Thermal Transport atMicro/Nanoscales 44

References 45

2 THERMAL CHARACTERIZATION IN FREQUENCY DOMAIN 47

2.1 Frequency Domain Photoacoustic (PA) Technique 47

2.1.1 Physical Model 48

2.1.2 Experimental Details 50

2.1.3 PA Measurement of Films and Bulk Materials 52

2.1.4 Uncertainty of the PA Measurement 55

2.2 Frequency Domain Photothermal Radiation (PTR) Technique57

2.2.1 Experimental Details of the PTR Technique 57

2.2.2 PTR Measurement of Micrometer–Thick Films 58

2.2.3 PTR with Internal Heating of Desired Locations 60

2.3 Three–Omega Technique 62

2.3.1 Physical Model of the 3 Technique forOne–Dimensional Structures 62

2.3.2 Experimental Details 65

2.3.3 Calibration of the Experiment 67

2.3.4 Measurement of Micrometer–Thick Wires 69

2.3.5 Effect of Radiation on Measurement Result 70

2.4 Optical Heating Electrical Thermal Sensing (OHETS) Technique73

2.4.1 Experimental Principle and Physical Model 73

2.4.2 Effect of Nonuniform Distribution of Laser Beam 74

2.4.3 Experimental Details and Calibration 77

2.4.4 Measurement of Electrically Conductive Wires 79

2.4.5 Measurement of Nonconductive Wires 81

2.4.6 Effect of Au Coating on Measurement 83

2.4.7 Temperature Rise in the OHETS Experiment 84

2.5 Comparison Among the Techniques 85

References 86

3 TRANSIENT TECHNOLOGIES IN THE TIME DOMAIN 87

3.1 Transient Photo–Electro–Thermal (TPET) Technique 87

3.1.1 Experimental Principles 88

3.1.2 Physical Model Development 88

3.1.3 Effect of Nonuniform Distribution and Finite Rising Timeof the Laser Beam 90

3.1.4 Experimental Setup 92

3.1.5 Technique Validation 93

3.1.6 Thermal Characterization of SWCNT Bundles and Cloth Fibers95

3.2 Transient Electrothermal (TET) Technique 98

3.2.1 Physical Principles of the TET Technique 98

3.2.2 Methods for Data Analysis to Determine the ThermalDiffusivity 100

3.2.3 Effect of Nonconstant Electrical Heating 101

3.2.4 Experimental Details 102

3.2.5 Technique Validation 104

3.2.6 Measurement of SWCNT Bundles 105

3.2.7 Measurement of Polyester Fibers 107

3.2.8 Measurement of Micro/Submicroscale Polyacrylonitrile Wires109

3.3 Pulsed Laser–Assisted Thermal Relaxation Technique 113

3.3.1 Experimental Principles 113

3.3.2 Physical Model for the PLTR Technique 114

3.3.3 Methods to Determine the Thermal Diffusivity 116

3.3.4 Experimental Setup and Technique Validation 117

3.3.5 Measurement of Multiwalled Carbon Nanotube (MWCNT) Bundles118

3.3.6 Measurement of Individual Microscale Carbon Fibers 122

3.4 Super Channeling Effect for Thermal Transport inMicro/Nanoscale Wires 123

3.5 Multidimensional Thermal Characterization 128

3.5.1 Sample Preparation 129

3.5.2 Thermal Characterization Design 130

3.5.3 Thermal Transport Along the Axial Direction of AmorphousTiO2 Nanotubes 131

3.5.4 Thermal Transport in the Cross–Tube Direction of AmorphousTiO2 Nanotubes 133

3.5.5 Evaluation of Thermal Contact Resistance Between AmorphousTiO2 Nanotubes 136

3.5.6 Anisotropic Thermal Transport in Anatase TiO2 Nanotubes137

3.6 Remarks on the Transient Technologies 139

References 139

4 STEADY–STATE THERMAL CHARACTERIZATION 141

4.1 Generalized Electrothermal Characterization 142

4.1.1 Generalized Electrothermal (GET) Technique: CombinedTransient and Steady States 142

4.1.2 Experimental Setup 144

4.1.3 Experimental Details 145

4.1.4 Measurement of MWCNT Bundle with L = 3.33 mm and D = 94.5 m 147

4.1.5 Measurement of MWCNT Bundle with L = 2.90 mm and D = 233 m 153

4.1.6 Analysis of the Tube–to–Tube Thermal Contact Resistance157

4.1.7 Effect of Radiation Heat Loss 158

4.2 Get Measurement of Porous Freestanding Thin Films Composedof Anatase TiO2 Nanofibers 159

4.2.1 Sample Preparation 160

4.2.2 R T Calibration 162

4.2.3 TET Measurement of Thermal Conductivity and ThermalDiffusivity 163

4.2.4 Thermophysical Properties of Samples with DifferentDimensions 167

4.2.5 The Intrinsic Thermal Conductivity of TiO2 Nanofibers170

4.2.6 Uncertainty Analysis 172

4.3 Measurement of Micrometer–Thick Polymer Films 173

4.3.1 Sample Preparation 173

4.3.2 Electrical Resistance (R)–Temperature CoefficientCalibration 175

4.3.3 Measurement of Thermal Conductivity and ThermalDiffusivity 175

4.3.4 Thermophysical Properties of P3HT Thin Films withDifferent Dimensions 178

4.4 Steady–State Electro–Raman Thermal (SERT) Technique 182

4.4.1 Experimental Principle and Physical Model Development183

4.4.2 Experimental Setup for Measuring CNT Buckypaper 187

4.4.3 Calibration Experiment 188

4.4.4 Thermal Characterization of MWCNT Buckypapers 190

4.4.5 Thermal Conductivity Analysis 192

4.4.6 Uncertainty Induced by Location of Laser Focal Point195

4.4.7 Effect of Thermal and Electrical Contact Resistances andThermal Transport in Electrodes 196

4.5 SERT Measurement of MWCNT Bundles 197

4.6 Extension of the Steady–State Techniques 202

References 202

5 STEADY–STATE OPTICAL–BASED THERMAL PROBING ANDCHARACTERIZATION 205

5.1 Sub–10–nm Temperature Measurement 205

5.1.1 Introduction to Sub–10–nm Near–Field Focusing 206

5.1.2 Experimental Design and Conduction 208

5.1.3 Measurement Results 210

5.1.4 Physics Behind Near–Field Focusing and Thermal Transport213

5.2 Thermal Probing at nm/SUB–nm Resolution for StudyingInterface Thermal Transport 219

5.2.1 Introduction 219

5.2.2 Experimental Method 220

5.2.3 Experimental Results 221

5.2.4 Comparison with Molecular Dynamics Simulation 225

5.2.5 Discussion 226

5.3 Optical Heating and Thermal Sensing using Raman Spectrometer234

5.3.1 Thermal Conductivity Measurement of Suspended FilmlikeMaterials 234

5.3.2 Thermal Conductivity Measurement of Suspended Nanowires236

5.4 Bilayer Sensor–Based Technique 237

5.5 Further Consideration for Micro/Nanoscale Thermal Sensingand Characterization 238

5.5.1 Electrothermal Sensing in Thermal Characterization ofCoatings/Films 239

5.5.2 Transient Photo–Heating and Thermal Sensing of WirelikeSamples 240

References 242

INDEX 247

XINWEI WANG, PhD, is a Full Professor in the Departmentof Mechanical Engineering at Iowa State University, where he isalso the Director of the Micro/Nanoscale Thermal ScienceLaboratory. His current research focuses on SPM–based thermalprobing and thermal transport in biomaterials.

Experimentalists measuring thermal transport propertiesof micro–or nanoscale materials will definitely find this book wellworth their time.   (IEEE Electrical InsulationMagazine, 1 September 2013