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Song M, Ma BS, Oh SJ, Kim TS. Plane Stress Fracture Toughness Testing of Freestanding Ultra-Thin Nanocrystalline Gold Films on Water Surface. SMALL METHODS 2024; 8:e2301220. [PMID: 38279567 DOI: 10.1002/smtd.202301220] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/11/2023] [Revised: 01/08/2024] [Indexed: 01/28/2024]
Abstract
Fracture toughness, which is the resistance of a material to crack propagation, is a critical material property for ensuring the mechanical reliability of damage-tolerant design. Recently, damage-tolerant design is introduced to flexible electronics by adopting micro-cracked ultra-thin nanocrystalline (NC) gold films as stretchable electrodes in a plane stress state. However, experimental investigation of the plane stress fracture toughness of those films remains challenging due to the intrinsic fragility from their sub-100 nm thicknesses. Here, a quantitative method for systematically evaluating the plane stress fracture toughness of freestanding ultra-thin NC gold film on water surface platform is presented. After effectively fabricating single-edge-notched-tension samples with femtosecond laser, mode I stress intensity factors are measured in the plane stress state on water surface. Moreover, investigation regarding the effect of notch length, notch sharpness, and notch tip plasticity validates this method based on linear elastic fracture mechanics theory. As a demonstration, the thickness-dependent plane stress fracture toughness of ultra-thin NC gold films is qualitatively unveiled. It is revealed that the thickness confinement effect on grain boundary sliding induces a transition in fracture behavior. This method is expected to further clarify the fracture-related properties of various ultra-thin films for next-generation electronics.
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Affiliation(s)
- Myoung Song
- Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
| | - Boo Soo Ma
- Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
| | - Seung Jin Oh
- Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
| | - Taek-Soo Kim
- Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
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Lee TI, Kim JH, Kim DJ, Kim TS. Evaluating Free Thermal Expansion and Glass Transition of Ultrathin Polymer Films on Heated Liquid. ACS APPLIED MATERIALS & INTERFACES 2024; 16:30336-30343. [PMID: 38781291 DOI: 10.1021/acsami.4c02279] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2024]
Abstract
Thermomechanical properties of ultrathin films are crucial for fabrication and use of reliable thin electronic devices. Due to the lack of precise measurement techniques, the thermal deformation behavior of ultrathin films has not yet been clarified. Here, we propose a film on heated liquid (FOHL) method to simultaneously measure the coefficient of thermal expansion (CTE) and glass transition temperature (Tg) of multiple ultrathin polymer films. Free thermal expansion of thin films without substrate interaction can be guaranteed when the thin films are afloat on a liquid surface. To investigate the thermal behavior in a wide temperature range, glycerol is adopted as a thermally stable heating platform owing to its high boiling point of 290 °C. The thin films are transferred onto the glycerol surface from the water surface using the hygroscopic properties of glycerol. Highly accurate and high-throughput thermal strain measurement is achieved using three-dimensional digital image correlation (3D-DIC). The thermomechanical properties of ultrathin polystyrene thin films of various thicknesses (25-400 nm) are precisely characterized utilizing the FOHL and 3D-DIC method.
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Affiliation(s)
- Tae-Ik Lee
- Advanced Packaging and Integration Center, Joining R&D Group, KITECH, 156 Gaetbeol-ro, Yeonsu-gu, Incheon 21999, Republic of Korea
| | - Ji Hun Kim
- Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - Dong Jun Kim
- Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - Taek-Soo Kim
- Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
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Park H, Ma BS, Kim Y, Lee D, Li S, Kim HJ, Kim TS, Kim BJ. Direct Measurement of the Thermomechanical Properties of Poly(3-hexylthiophene) Thin Films on Ionic Liquid Surfaces. Macromolecules 2023. [DOI: 10.1021/acs.macromol.2c02275] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/17/2023]
Affiliation(s)
| | | | | | | | | | - Hyeong Jun Kim
- Department of Chemical and Biomolecular Engineering, Sogang University, Seoul 04107, Republic of Korea
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Lee JW, Seo S, Lee SW, Kim GU, Han S, Phan TNL, Lee S, Li S, Kim TS, Lee JY, Kim BJ. Intrinsically Stretchable, Highly Efficient Organic Solar Cells Enabled by Polymer Donors Featuring Hydrogen-Bonding Spacers. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2022; 34:e2207544. [PMID: 36153847 DOI: 10.1002/adma.202207544] [Citation(s) in RCA: 21] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/18/2022] [Revised: 09/15/2022] [Indexed: 06/16/2023]
Abstract
Intrinsically stretchable organic solar cells (IS-OSCs), consisting of all stretchable layers, are attracting significant attention as a future power source for wearable electronics. However, most of the efficient active layers for OSCs are mechanically brittle due to their rigid molecular structures designed for high electrical and optical properties. Here, a series of new polymer donors (PD s, PhAmX) featuring phenyl amide (N1 ,N3 -bis((5-bromothiophen-2-yl)methyl)isophthalamide, PhAm)-based flexible spacer (FS) inducing hydrogen-bonding (H-bonding) interactions is developed. These PD s enable IS-OSCs with a high power conversion efficiency (PCE) of 12.73% and excellent stretchability (PCE retention of >80% of the initial value at 32% strain), representing the best performances among the reported IS-OSCs to date. The incorporation of PhAm-based FS enhances the molecular ordering of PD s as well as their interactions with a Y7 acceptor, enhancing the mechanical stretchability and electrical properties simultaneously. It is also found that in rigid OSCs, the PhAm5:Y7 blend achieves a much higher PCE of 17.5% compared to that of the reference PM6:Y7 blend. The impact of the PhAm-FS linker on the mechanical and photovoltaic properties of OSCs is thoroughly investigated.
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Affiliation(s)
- Jin-Woo Lee
- Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
| | - Soodeok Seo
- Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
| | - Sun-Woo Lee
- Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
| | - Geon-U Kim
- Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
| | - Seungseok Han
- Department of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
| | - Tan Ngoc-Lan Phan
- Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
| | - Seungjin Lee
- Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
| | - Sheng Li
- Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
| | - Taek-Soo Kim
- Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
| | - Jung-Yong Lee
- Department of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
| | - Bumjoon J Kim
- Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
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