Title Page

Contents

Abstract 11

Chapter 1. Introduction 13

1.1. Background and rationale 13

1.2. Structure of thesis 15

References 18

Chapter 2. Theoretical background 20

2.1. Introduction 20

1) Polymers 20

2) Inorganic-based materials 23

2.2. Thin film instability 24

2.2.1. Hydrodynamic 25

2.2.2. Interfacial pressure 29

2.2.3. Linear stability analysis and dispersion relation 33

2.3. Electrohydrodynamic instability 34

2.4. Surface wettability 38

1) Surface chemistry 40

2) Surface roughness 41

2.5. Conclusion 44

References 45

Chapter 3. Experimental preparations and analytical techniques 49

3.1. Sample preparation 49

3.1.1. Preparation of precursor solutions 49

3.1.2. Substrate cleaning 51

3.1.3. Spin coating 52

3.2. High voltage EHD process 53

3.3. Characterizations 54

3.3.1. AFM analysis 54

3.3.2. SEM Analysis 55

3.3.3. Contact angle measurement 56

3.4. Conclusion 57

References 58

Chapter 4. Pillar structure Formation 60

4.1. Introduction 60

4.2. EHD-induced pillar structure formation 61

1) Basic concept of pillar structure formation 61

2) Influence by air gap 62

3) Low voltage vs. high voltage 63

4.3. Aspect ratio controlled by film filling ratio 66

1) Theory 66

2) Results and discussions 67

4.4. Tuning the surface wettability 69

1) Surface wettability by resulting pillars 69

2) Application: Pattern transfer on non - traditional substrates 71

4.4. Templated-assisted EHD-induced patterns 74

1) Secondary instability 75

2) Results and discussion 78

4.6. Conclusion 78

References 80

Chapter 5. Conclusions 82

5.1. Conclusions 82

5.2. Future research 83

References 85

Table 2.1. Properties of organic materials 50

Table 2.2. Properties of inorganic materials 50

Figure 2.1. Schematic illustration of thin film instability on substrate. Surface fluctuations with wavelength λ＝2π/q. The velocity profile υ for... 26

Figure 2.2. Schematic illustration of the polarized dielectric in the electric field. The electrostatic pressure resulting due to opposing charges by the applied... 36

Figure 2.3. Schematic diagram of relationship between the contact angle and the interfacial surface energies 39

Figure 2.4. Wetting states explained by (a) Wenzel model and (b) Cassie-Baxter model. 42

Figure 4.1. Schematic illustrations for overview process (a) Pillar growth induced by the external electric field over time (b) Pattern film transferred assisted by... 61

Figure 4.2. Optical images for pillar pattern evolution influenced by air gap (a) Spatiotemporal evolution of pillar formation over time with the air gap... 64

Figure 4.3. Surface wettability corresponding to their surface roughness (a) Interplay of filling ratio applied by the uniform electric field determines the... 70

Figure 4.4. Peeling and transferring process (a) Schematic representation for the peeling process (b) Sacrificial layer between pillar and substrate all dissolves... 72

Figure 4.5. Pillar film transferred on non-conventional substrates (a) PDMS, PET, Lens (b) Transferred thin film still have hydrophobic property by the water... 74

Figure 4.6. Formation of secondary instability (a) Photographic image of line patterned master stamp (b) Line pattern s are replicated with the low voltage... 75

Figure 4.7. Surface wettability corresponding to their surface roughness (a) Interplay of filling ratio applied by electric field determines the final geometry... 76

Figure 4.8. Peeling and transferring process (a) Schematic representation for the peeling process (b) Sacrificial layer between pattern and substrate all dissolves... 77