Title Page
ABSTRACT
국문 초록
Contents
CHAPTER 1. INTRODUCTION 20
1.1. Next-Generation Wearable Devices 20
1.1.1. Colloidal Nanocrystalline Materials 20
1.2. Stretchable Devices for Wearable Applications 21
1.2.1. Highly Sensitive Temperature Sensor 21
1.2.2. Stretchable Electrodes 23
1.2.3. Stretchable Optoelectronic Sensor 24
CHAPTER 2. EXPERIMENTAL SECTION 26
2.1. Materials 26
2.2. Synthesis Methods 27
2.3. Preparation and Characterization for Temperature Sensors 29
2.4. Preparation and Characterization for Stretchable Electrodes 31
2.5. Preparation and Characterization for Stretchable Optoelectronic Sensors 33
CHAPTER 3. RESULTS AND DISCUSSION 34
3.1. Highly Sensitive Temperature Sensor: Ligand-Treated Ag Nanocrystal Thin Films on PDMS with Thermal Expansion Strategy 34
3.2. Stretchable and Directly Patternable Double-Layer Structure Electrodes with Complete Coverage 58
3.3. Wavelength-selective and Stretchable Infrared and Visible Photodetectors with Coupled Quantum Dots/Nanowires 92
CHAPTER 4. CONCLUSION 104
REFERENCES 106
Table 1. The summary table for temperature sensor performance comparison 56
Table 2. The summary table for stretchable electrode performance comparison 77
Table 3. The summary table for stretchable photodetector performance comparison 103
Figure 1. A) UV-vis, B) FTIR, and C) XRD spectra of Ag NC thin films before (black) and after ligand treatment with TBAB (red), and EDT (blue). D) Resistivity data of as-... 35
Figure 2. A) Fabrication process of EDT ligand-treated Ag NCs films on a PDMS substrate temperature sensor. B) I-V characteristics of Ag NC films treated with EDT... 38
Figure 3. Response time of Ag NC thin films on SiO₂ wafer (303–308 K temperature range) 41
Figure 4. A) Schematics indicating the effect of thermal expansion of EDT-treated Ag NC thin films on PDMS without cracks. B) Relative resistance changes from 303 to 313 K of... 42
Figure 5. A) optical microscope and B) SEM images of EDT-treated Ag NC thin films on PDMS. 45
Figure 6. Orthogonal cracks filled with A) Ag NCs, the strain(stress) concentration was monitored for temperature increases from 298K to 299K, and filled with PDMS when the... 47
Figure 7. 3D structure of nanocracks on EDT-treated Ag NC thin films 47
Figure 8. A) Relative resistance change of Ag NC thin films with cracks on PDMS versus temperature (1st and 2nd terms of Equation (1) and their combined effect), B) Effect of crack... 51
Figure 9. I-V characteristics of Ag NC films treated with TBAB at 303 K (black) and 323 K (red) on A) glass substrate and B) PDMS substrate. C) Resistance of Ag NC films treated... 52
Figure 10. Relative resistance changes from 303 to 323 K of 1st term of Equation (1) in the main article, 2nd term, and the combined effect of the two terms. 52
Figure 11. A) Fabrication process of all-NC based and all-solution processed temperature sensor. B) I-V characteristics in the 0–2 V range of EDT-treated Ag NCs films and TBAB-... 55
Figure 12. Relative TCR changes during the attaching and detaching cycles when the temperature changes from 303K to 323K. 56
Figure 13. A) Proposed design of Ag NW and Au hybrid thin-film-based stretchable electrodes. B) Fabrication process of Ag NW & Au hybrid thin film stretchable electrodes. 58
Figure 14. XPS spectra of A) C1s binding energy of PDMS and PDMS/PVP and B) O1s binding energy of PVP and Ag/PVP. 60
Figure 15. Contact angle of A) PDMS, B) PDMS+UVO 30 min, and C) PDMS+UVO 30 min +Ag NW. 62
Figure 16. Cross-sectional SEM images of A) Ag NW+Au, B) Au only, and C) Ag NW only. 62
Figure 17. A) Adhesion test data of i) Au only, ii) Ag NW+Au, iii) PVP+Au, and iv) PVP+Ag NW+Au electrode surfaces scratched using a cotton swab. B) Areal fill factor data... 63
Figure 18. A) Pixel-converted image of Figure 1a to calculate the degree of delamination; B) transmittance data under 550 nm visible light of each electrode condition after scratching. 64
Figure 19. Solvent test results of A) Au only, B) Ag NW+Au, C) PVP+Au, and D) PVP+Ag NW+Au washed by acetone, ethanol, and toluene, respectively. 66
Figure 20. Current change of Au only (black), Ag NW only (red), and Ag NW+Au (blue) thin films on PDMS substrate at 0%, 10%, 20%, and 30% strain. 68
Figure 21. Images of light-emitting diodes fabricated using A) Ag NW only thin film electrodes and B) Ag NW+Au thin film electrodes. C) Luminance-areal fill factor plot of Ag... 68
Figure 22. Three-dimensional view of the FEM-simulated samples of the Au only thin films (left) and Ag NW+Au thin films (right) with dimensions of 2 μm x 2 μm x 1000.60 μm. 70
Figure 23. A) Patterning/etching of a double-layer electrode. B–D) Optical microscope images of Au only B), Ag NW only C), and Ag NW+Au D) in step (iv) (left) and (vi) (right)... 72
Figure 24. Patterned and etched Ag NW only thin films with a chemically ruptured region through etchant penetration. 74
Figure 25. SEM images of dog-bone patterns; A) interval 20 µm, width 300 µm; B) interval 15 µm, width 150 µm; and C) interval 10 µm, width 75 µm; square array pattern. D) 100 µm... 75
Figure 26. A) Pristine, B) stretched, C) tilted, and D) bended images of fabricated double- layer thin film stretchable electrode. 76
Figure 27. A) Surface electrocardiogram (ECG) performed by a placing stretchable electrode on the forelimb (left and right) and hindlimb (left). B) Representative data of the... 79
Figure 28. Image of the 2 × 2 electrode arrays attached directly to the surface of the heart and two needle-shaped electrodes inserted under the armpit. 81
Figure 29. A) Photographs of the antenna under stretching. B) Return loss (S₁₁) spectra of the antenna under stretching up to 30%. C) Return loss (S₁₁) spectra of the antenna under up... 83
Figure 30. A) Capacitance of a stretchable strain sensor when strain was applied. B) Relative capacitance change of a stretchable strain sensor when bending was applied. C) Relative... 85
Figure 31. Cycle test data of double-layer thin film stretchable electrode under 0% to 10% strain. 87
Figure 32. A) Relative capacitance change of stretchable a pressure sensor. B) Relative capacitance change of a 4 × 4 array stretchable pressure sensor. C) Images of a 4 × 4 array... 89
Figure 33. A) I–V characteristics, B) cycle test data of double-layer thin film stretchable- electrode-based temperature sensors at 303–323 K. 91
Figure 34. A) I–V characteristics, B) cycle test data of double-layer thin film stretchable- electrode-based on temperature sensors after stretching at 303–323 K. 91
Figure 35. A) Schematic representations of the stretchable PD under strain and B) of simultaneous ligand exchange with band structures of the CdSe NWs, the PbS QDs, and... 95
Figure 36. A) Onset and B) cut-off of the ultraviolet photoelectron spectra (UPS) recorded for the CdSe NWs and the PbS QDs. C) Tau plot of CdSe NWs and PbS QDs. 96
Figure 37. A) Schematic outline of the fabrication process employed to prepare the CdSe NW + PbS QD hybrid PD. TEM images are also shown for the various fabrications steps. I–... 99
Figure 38. Rise and falling time data of the CdSe NWs + PbS QDs under visible light conditions with applied strains of: A) 0%, B) 10%, C) 20%, D) 30%, E) 40%, and F) 50%. 100
Figure 39. Rise and falling time data of the CdSe NWs + PbS QDs under IR light conditions with applied strains of: A) 0%, B) 10%, C) 20%, D) 30%, E) 40%, and F) 50%. 100
Figure 40. A) Schematic representation of the vertically stacked two-channel hybrid PD system. B) Comparison of the current between device 1 (black solid line) and device 2 (red... 102