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Kim BJ, Jo MS, Yang JS, Chung MK, Kim SH, Yoon JB. Quintic refractive index profile-based funnel-shaped silicon antireflective structures for enhanced photodetector performance. Sci Rep 2024; 14:10410. [PMID: 38710917 DOI: 10.1038/s41598-024-61156-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2024] [Accepted: 05/02/2024] [Indexed: 05/08/2024] Open
Abstract
Antireflection, vital in optoelectronics devices such as solar cells and photodetectors, reduces light reflection and increases absorption. Antireflective structures (ARS), a primary method by which to realize this effect, control the refractive index (RI) profile based on their shape. The antireflection efficiency depends on the refractive index profile, with the quintic RI profile being recognized as ideal for superior antireflection. However, fabricating nano-sized structures with a desired shape, particularly in silicon with a quintic RI profile, has been a challenge. In this study, we introduce a funnel-shaped silicon (Si) ARS with a quintic RI profile. Its antireflective properties are demonstrated through reflectance measurements and by an application to a photodetector surface. Compared to the film Si and cone-shaped ARS types, which are common structures to achieve antireflection, the funnel-shaped ARS showed reflectance of 4.24% at 760 nm, whereas those of the film Si and cone-shaped ARS were 32.8% and 10.6%, respectively. Photodetectors with the funnel-shaped ARS showed responsivity of 0.077 A/W at 950 nm, which is 19.54 times higher than that with the film Si and 2.45 times higher than that with the cone-shaped ARS.
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Affiliation(s)
- Beom-Jun Kim
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea
| | - Min-Seung Jo
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea
- Center for Bio-Integrated Electronics, Northwestern University, 633 Clark St, Evanston, IL, 60208, USA
| | - Jae-Soon Yang
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea
| | - Myung-Kun Chung
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea
| | - Sung-Ho Kim
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea
| | - Jun-Bo Yoon
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea.
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Jo MS, Kim SH, Park SY, Choi KW, Kim SH, Yoo JY, Kim BJ, Yoon JB. Fast-Response and Low-Power Self-Heating Gas Sensor Using Metal/Metal Oxide/Metal (MMOM) Structured Nanowires. ACS Sens 2024. [PMID: 38626402 DOI: 10.1021/acssensors.3c02613] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/18/2024]
Abstract
With the escalating global awareness of air quality management, the need for continuous and reliable monitoring of toxic gases by using low-power operating systems has become increasingly important. One of which, semiconductor metal oxide gas sensors have received great attention due to their high/fast response and simple working mechanism. More specifically, self-heating metal oxide gas sensors, wherein direct thermal activation in the sensing material, have been sought for their low power-consuming characteristics. However, previous works have neglected to address the temperature distribution within the sensing material, resulting in inefficient gas response and prolonged response/recovery times, particularly due to the low-temperature regions. Here, we present a unique metal/metal oxide/metal (MMOM) nanowire architecture that conductively confines heat to the sensing material, achieving high uniformity in the temperature distribution. The proposed structure enables uniform thermal activation within the sensing material, allowing the sensor to efficiently react with the toxic gas. As a result, the proposed MMOM gas sensor showed significantly enhanced gas response (from 6.7 to 20.1% at 30 ppm), response time (from 195 to 17 s at 30 ppm), and limit of detection (∼1 ppm) when compared to those of conventional single-material structures upon exposure to carbon monoxide. Furthermore, the proposed work demonstrated low power consumption (2.36 mW) and high thermal durability (1500 on/off cycles), demonstrating its potential for practical applications in reliable and low-power operating gas sensor systems. These results propose a new paradigm for power-efficient and robust self-heating metal oxide gas sensors with potential implications for other fields requiring thermal engineering.
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Affiliation(s)
- Min-Seung Jo
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - Sung-Ho Kim
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - So-Yoon Park
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - Kwang-Wook Choi
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
- SAMSUNG ELECTRONICS Co., Ltd., 130 Samsungjeonja-ro, Yeongtong-gu, Suwon-si, Gyenggi-do 16678, Republic of Korea
| | - Sang-Hee Kim
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
- SAMSUNG ELECTRONICS Co., Ltd., 1, Samsungjeonja-ro, Hwaseong-si, Gyeonggi-do 18448, Republic of Korea
| | - Jae-Young Yoo
- Center for Bio-Integrated Electronics, Northwestern University, Evanston, Illinois 60208, United States
| | - Beom-Jun Kim
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - Jun-Bo Yoon
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
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Kim SH, Choi PK, Lee YB, Kim TS, Jo MS, Lee SY, Min HW, Yoon JB. An experimental and numerical study on adhesion force at the nanoscale. Nanoscale Adv 2024; 6:2013-2025. [PMID: 38633052 PMCID: PMC11019507 DOI: 10.1039/d3na01044a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/24/2023] [Accepted: 02/14/2024] [Indexed: 04/19/2024]
Abstract
Adhesion has attracted great interest in science and engineering especially in the field pertaining to nano-science because every form of physical contact is fundamentally a macroscopic observation of interactions between nano-asperities under the adhesion phenomenon. Despite its importance, no practical adhesion prediction model has been developed due to the complexity of examining contact between nano-asperities. Here, we scrutinized the contact phenomenon and developed a contact model, reflecting the physical sequence in which adhesion develops. For the first time ever, our model analyzes the adhesion force and contact properties, such as separation distance, contact location, actual contact area, and the physical deformation of the asperities, between rough surfaces. Through experiments using atomic force microscopy, we demonstrated a low absolute percentage error of 2.8% and 6.55% between the experimental and derived data for Si-Si and Mo-Mo contacts, respectively, and proved the accuracy and practicality of our model in the analysis of the adhesion phenomenon.
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Affiliation(s)
- Su-Hyun Kim
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST) 291 Daehak-ro, Yuseong-gu Daejeon 34141 Republic of Korea
- Samsung Electronics Co., Ltd. 1, Samsungjeonja-ro Hwaseong-si Gyeonggi-do 18448 Republic of Korea
| | - Pan-Kyu Choi
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST) 291 Daehak-ro, Yuseong-gu Daejeon 34141 Republic of Korea
- Samsung Electronics Co., Ltd. 1, Samsungjeonja-ro Hwaseong-si Gyeonggi-do 18448 Republic of Korea
| | - Yong-Bok Lee
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST) 291 Daehak-ro, Yuseong-gu Daejeon 34141 Republic of Korea
| | - Tae-Soo Kim
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST) 291 Daehak-ro, Yuseong-gu Daejeon 34141 Republic of Korea
| | - Min-Seung Jo
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST) 291 Daehak-ro, Yuseong-gu Daejeon 34141 Republic of Korea
| | - So-Young Lee
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST) 291 Daehak-ro, Yuseong-gu Daejeon 34141 Republic of Korea
| | - Hyun-Woo Min
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST) 291 Daehak-ro, Yuseong-gu Daejeon 34141 Republic of Korea
- Samsung Electronics Co., Ltd. 1, Samsungjeonja-ro Hwaseong-si Gyeonggi-do 18448 Republic of Korea
| | - Jun-Bo Yoon
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST) 291 Daehak-ro, Yuseong-gu Daejeon 34141 Republic of Korea
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Kim SH, Jo MS, Choi KW, Yoo JY, Kim BJ, Yang JS, Chung MK, Kim TS, Yoon JB. Ultrathin Serpentine Insulation Layer Architecture for Ultralow Power Gas Sensor. Small 2024; 20:e2304555. [PMID: 37649204 DOI: 10.1002/smll.202304555] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2023] [Revised: 08/01/2023] [Indexed: 09/01/2023]
Abstract
Toxic gases have surreptitiously influenced the health and environment of contemporary society with their odorless/colorless characteristics. As a result, a pressing need for reliable and portable gas-sensing devices has continuously increased. However, with their negligence to efficiently microstructure their bulky supportive layer on which the sensing and heating materials are located, previous semiconductor metal-oxide gas sensors have been unable to fully enhance their power efficiency, a critical factor in power-stringent portable devices. Herein, an ultrathin insulation layer with a unique serpentine architecture is proposed for the development of a power-efficient gas sensor, consuming only 2.3 mW with an operating temperature of 300 °C (≈6% of the leading commercial product). Utilizing a mechanically robust serpentine design, this work presents a fully suspended standalone device with a supportive layer thickness of only ≈50 nm. The developed gas sensor shows excellent mechanical durability, operating over 10 000 on/off cycles and ≈2 years of life expectancy under continuous operation. The gas sensor detected carbon monoxide concentrations from 30 to 1 ppm with an average response time of ≈15 s and distinguishable sensitivity to 1 ppm (ΔR/R0 = 5%). The mass-producible fabrication and heating efficiency presented here provide an exemplary platform for diverse power-efficient-related devices.
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Affiliation(s)
- Sung-Ho Kim
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea
| | - Min-Seung Jo
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea
| | - Kwang-Wook Choi
- Samsung Electronics Co., Ltd., 1, Samsungjeonja-ro, Hwaseong-si, Gyeonggi-do, 18448, Republic of Korea
| | - Jae-Young Yoo
- Center for Bio-Integrated Electronics, Northwestern University, Evanston, IL, 60208, USA
| | - Beom-Jun Kim
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea
| | - Jae-Soon Yang
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea
| | - Myung-Kun Chung
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea
| | - Tae-Soo Kim
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea
| | - Jun-Bo Yoon
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea
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Jo MS, Kim KH, Lee JS, Kim SH, Yoo JY, Choi KW, Kim BJ, Kwon DS, Yoo I, Yang JS, Chung MK, Park SY, Seo MH, Yoon JB. Ultrafast (∼0.6 s), Robust, and Highly Linear Hydrogen Detection up to 10% Using Fully Suspended Pure Pd Nanowire. ACS Nano 2023. [PMID: 38039345 DOI: 10.1021/acsnano.3c06806] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/03/2023]
Abstract
The high explosiveness of hydrogen gas in the air necessitates prompt detection in settings where hydrogen is used. For this reason, hydrogen sensors are required to offer rapid detection and possess superior sensing characteristics in terms of measurement range, linearity, selectivity, lifetime, and environment insensitivity according to the publicized protocol. However, previous approaches have only partially achieved the standardized requirements and have been limited in their capability to develop reliable materials for spatially accessible systems. Here, an electrical hydrogen sensor with an ultrafast response (∼0.6 s) satisfying all demands for hydrogen detection is demonstrated. Tailoring structural engineering based on the reaction kinetics of hydrogen and palladium, an optimized heating architecture that thermally activates fully suspended palladium (Pd) nanowires at a uniform temperature is designed. The developed Pd nanostructure, at a designated temperature distribution, rapidly reacts with hydrogen, enabling a hysteresis-free response from 0.1% to 10% and durable characteristics in mechanical shock and repetitive operation (>10,000 cycles). Moreover, the device selectively detects hydrogen without performance degradation in humid or carbon-based interfering gas circumstances. Finally, to verify spatial accessibility, the wireless hydrogen detection system has been demonstrated, detecting and reporting hydrogen leakage in real-time within just 1 s.
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Affiliation(s)
- Min-Seung Jo
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - Ki-Hoon Kim
- Department of Information Convergence Engineering, Pusan National University, 2, Busandaehak-ro 63beon-gil, Geumjeong-gu, Busan 46241, Republic of Korea
| | - Jae-Shin Lee
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - Sung-Ho Kim
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - Jae-Young Yoo
- Center for Bio-Integrated Electronics, Northwestern University, Evanston, Illinois 60208, United States
| | - Kwang-Wook Choi
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - Beom-Jun Kim
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - Dae-Sung Kwon
- Electronic Devices Research Team, Hyundai Motor Group, 37, Cheoldobangmulgwan-ro, Uiwang-si, Gyeonggi-do 16082, Republic of Korea
| | - Ilseon Yoo
- Electronic Devices Research Team, Hyundai Motor Group, 37, Cheoldobangmulgwan-ro, Uiwang-si, Gyeonggi-do 16082, Republic of Korea
| | - Jae-Soon Yang
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - Myung-Kun Chung
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - So-Yoon Park
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - Min-Ho Seo
- Department of Information Convergence Engineering, Pusan National University, 2, Busandaehak-ro 63beon-gil, Geumjeong-gu, Busan 46241, Republic of Korea
- School of Biomedical Convergence Engineering, College of Information & Biomedical Engineering, Pusan National University, 49, Busandaehak-ro, Yangsan-si, Gyeongsangnam-do 43241, Republic of Korea
| | - Jun-Bo Yoon
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
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Lee YB, Kang MH, Choi PK, Kim SH, Kim TS, Lee SY, Yoon JB. Sub-10 fJ/bit radiation-hard nanoelectromechanical non-volatile memory. Nat Commun 2023; 14:460. [PMID: 36709346 PMCID: PMC9884203 DOI: 10.1038/s41467-023-36076-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2022] [Accepted: 01/12/2023] [Indexed: 01/30/2023] Open
Abstract
With the exponential growth of the semiconductor industry, radiation-hardness has become an indispensable property of memory devices. However, implementation of radiation-hardened semiconductor memory devices inevitably requires various radiation-hardening technologies from the layout level to the system level, and such technologies incur a significant energy overhead. Thus, there is a growing demand for emerging memory devices that are energy-efficient and intrinsically radiation-hard. Here, we report a nanoelectromechanical non-volatile memory (NEM-NVM) with an ultra-low energy consumption and radiation-hardness. To achieve an ultra-low operating energy of less than 10 [Formula: see text], we introduce an out-of-plane electrode configuration and electrothermal erase operation. These approaches enable the NEM-NVM to be programmed with an ultra-low energy of 2.83 [Formula: see text]. Furthermore, due to its mechanically operating mechanisms and radiation-robust structural material, the NEM-NVM retains its superb characteristics without radiation-induced degradation such as increased leakage current, threshold voltage shift, and unintended bit-flip even after 1 Mrad irradiation.
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Affiliation(s)
- Yong-Bok Lee
- grid.37172.300000 0001 2292 0500School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu Daejeon, 34141 Republic of Korea
| | - Min-Ho Kang
- grid.496766.c0000 0004 0546 0225National NanoFab Center (NNFC), 291 Daehak-ro, Yuseong-gu Daejeon, 34141 Republic of Korea
| | - Pan-Kyu Choi
- grid.37172.300000 0001 2292 0500School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu Daejeon, 34141 Republic of Korea ,Taiwan Semiconductor Manufacturing Company (TSMC) Ltd, Fab 21 Phoenix, AZ USA
| | - Su-Hyun Kim
- grid.37172.300000 0001 2292 0500School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu Daejeon, 34141 Republic of Korea ,grid.419666.a0000 0001 1945 5898SAMSUNG ELECTRONICS Co., Ltd, 1, Samsungjeonja-ro, Hwaseong-si, Gyeonggi-do 18448 Republic of Korea
| | - Tae-Soo Kim
- grid.37172.300000 0001 2292 0500School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu Daejeon, 34141 Republic of Korea
| | - So-Young Lee
- grid.37172.300000 0001 2292 0500School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu Daejeon, 34141 Republic of Korea
| | - Jun-Bo Yoon
- grid.37172.300000 0001 2292 0500School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu Daejeon, 34141 Republic of Korea
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Jo MS, Kim KH, Choi KW, Lee JS, Yoo JY, Kim SH, Jin H, Seo MH, Yoon JB. Wireless and Linear Hydrogen Detection up to 4% with High Sensitivity through Phase-Transition-Inhibited Pd Nanowires. ACS Nano 2022; 16:11957-11967. [PMID: 35621510 DOI: 10.1021/acsnano.2c01783] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Palladium (Pd) has been drawing increasing attention as a hydrogen (H2) detecting material due to its highly selective sensitivity to H2. However, at H2 concentrations above 2%, Pd undergoes an inevitable phase transition, causing undesirable electrical and mechanical alterations. In particular, nonlinear gas response (ΔR/R0) that accompanies phase transition has been a great bottleneck for detecting H2 in high concentrations, which is especially important as there is a risk of explosion over 4% H2. Here, we propose a phase-transition-inhibited Pd nanowire H2 sensor that can detect up to 4% H2 with high linearity and high sensitivity. Based on the calculation of the change in free energy, we designed Pd nanowires that are highly adhered to the substrate to withstand the stress that leads to phase transition. We theoretically optimized the Pd nanowire dimensions using a finite element method simulation and then experimentally fabricated the proposed sensor by exploiting a developed nanofabrication method. The proposed sensor exhibits a high sensing linearity (98.9%) with high and stable sensitivity (ΔR/R0/[H2] = 875%·bar-1) over a full range of H2 concentrations (0.1-4%). Using the fabricated Pd sensors, we have successfully demonstrated a wireless sensor module that can detect H2 with high linearity, notifying real-time H2 leakage through remote communication. Overall, our work suggests a nanostructuring strategy for detecting H2 with a phase-transition-inhibited pure Pd H2 sensor with rigorous scientific exploration.
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Affiliation(s)
- Min-Seung Jo
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - Ki-Hoon Kim
- Department of Information Convergence Engineering, College of Information and Biomedical Engineering, Pusan National University, Yangsan-si, Gyeongsangnam-do 43241, Republic of Korea
| | - Kwang-Wook Choi
- Samsung Electronics Co., Ltd., Suwon 18448, Republic of Korea
| | - Jae-Shin Lee
- Samsung Electronics Co., Ltd., Suwon 18448, Republic of Korea
| | - Jae-Young Yoo
- Center for Bio-Integrated Electronics, Northwestern University, Evanston, Illinois 60208, United States
| | - Sung-Ho Kim
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - Heejeong Jin
- School of Biomedical Convergence Engineering, College of Information and Biomedical Engineering, Pusan National University, Yangsan-si, Gyeongsangnam-do 43241, Republic of Korea
| | - Min-Ho Seo
- Department of Information Convergence Engineering, College of Information and Biomedical Engineering, Pusan National University, Yangsan-si, Gyeongsangnam-do 43241, Republic of Korea
- School of Biomedical Convergence Engineering, College of Information and Biomedical Engineering, Pusan National University, Yangsan-si, Gyeongsangnam-do 43241, Republic of Korea
| | - Jun-Bo Yoon
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
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Jo E, Lee YB, Jung Y, Kim SB, Kang Y, Seo MH, Yoon JB, Kim J. Integration of Gold Nanoparticle-Carbon Nanotube Composite for Enhanced Contact Lifetime of Microelectromechanical Switches with Very Low Contact Resistance. ACS Appl Mater Interfaces 2021; 13:16959-16967. [PMID: 33797217 DOI: 10.1021/acsami.0c22084] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Electrical circuits require ideal switches with low power consumption for future electronic applications. However, transistors, the most developed electrical switches available currently, have certain fundamental limitations such as increased leakage current and limited subthreshold swing. To overcome these limitations, micromechanical switches have been extensively studied; however, it is challenging to develop micromechanical switches with high endurance and low contact resistance. This study demonstrates highly reliable microelectromechanical switches using nanocomposites. Nanocomposites consisting of gold nanoparticles (Au NPs) and carbon nanotubes (CNTs) are coated on contact electrodes as contact surfaces through a scalable and solution-based fabrication process. While deformable CNTs in the nanocomposite increase the effective contact area under mechanical loads, highly conductive Au NPs provide current paths with low contact resistance between CNTs. Given these advantages, the switches exhibit robust switching operations over 5 × 106 cycles under hot-switching conditions in air. The switches also show low contact resistance without subthreshold region, an extremely small leakage current, and a high on/off ratio.
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Affiliation(s)
- Eunhwan Jo
- School of Mechanical Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Republic of Korea
| | - Yong-Bok Lee
- School of Electrical Engineering, Korea Advanced Institute of Science Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - Yohan Jung
- School of Mechanical Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Republic of Korea
| | - Su-Bon Kim
- School of Electrical Engineering, Korea Advanced Institute of Science Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - Yunsung Kang
- School of Mechanical Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Republic of Korea
| | - Min-Ho Seo
- School of Biomedical Convergence Engineering, College of Information & Biomedical Engineering, Pusan National University, 49 Busandaehak-ro, Yangsan-si, Gyeongsangnam-do 50612, Republic of Korea
| | - Jun-Bo Yoon
- School of Electrical Engineering, Korea Advanced Institute of Science Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - Jongbaeg Kim
- School of Mechanical Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Republic of Korea
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Seo MH, Kang K, Yoo JY, Park J, Lee JS, Cho I, Kim BJ, Jeong Y, Lee JY, Kim B, Rho J, Yoon JB, Park I. Chemo-Mechanically Operating Palladium-Polymer Nanograting Film for a Self-Powered H 2 Gas Sensor. ACS Nano 2020; 14:16813-16822. [PMID: 33263256 DOI: 10.1021/acsnano.0c05476] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
This study proposes a reliable and self-powered hydrogen (H2) gas sensor composed of a chemo-mechanically operating nanostructured film and photovoltaic cell. Specifically, the nanostructured film has a configuration in which an asymmetrically coated palladium (Pd) film is coated on a periodic polyurethane acrylate (PUA) nanograting. The asymmetric Pd nanostructures, optimized by a finite element method simulation, swell upon reacting with H2 and thereby bend the PUA nanograting, changing the amount of transmitted light and the current output of the photovoltaic cell. Since the degree of warping is determined by the concentration of H2 gas, a wide concentration range of H2 (0.1-4.0%) can be detected by measuring the self-generated electrical current of the photovoltaic cell without external power. The normalized output current changes are ∼1.5%, ∼2.8%, ∼3.5%, ∼5.0%, ∼21.5%, and 25.3% when the concentrations of H2 gas are 0.1%, 0.5%, 1.0%, 1.6%, 2%, and 4%, respectively. Moreover, because Pd is highly chemically reactive to H2 and also because there is no electrical current applied through Pd, the proposed sensor can avoid device failure due to the breakage of the Pd sensing material, resulting in high reliability, and can show high selectivity against various gases such as carbon monoxide, hydrogen sulfide, nitrogen dioxide, and water vapor. Finally, using only ambient visible light, the sensor was modularized to produce an alarm in the presence of H2 gas, verifying a potential always-on H2 gas monitoring application.
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Affiliation(s)
- Min-Ho Seo
- School of Biomedical Convergence Engineering, College of Information and Biomedical Engineering, Pusan National University, 49, Busandaehak-ro, Yangsan-si 43241, Gyeongsangnam-do, Republic of Korea
| | - Kyungnam Kang
- Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
| | - Jae-Young Yoo
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
| | - Jaeho Park
- Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
| | - Jae-Shin Lee
- Samsung Electronics Co., Ltd., Suwon 18448, Republic of Korea
| | - Incheol Cho
- Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
| | - Beom-Jun Kim
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
| | - Yongrok Jeong
- Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
| | - Jung-Yong Lee
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
| | - Byeongsu Kim
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
| | - Junsuk Rho
- Department of Mechanical Engineering, Pohang University of Science and Technology (POSTECH), Pohang 37673, Republic of Korea
- Department of Chemical Engineering, Pohang University of Science and Technology (POSTECH), Pohang 37673, Republic of Korea
| | - Jun-Bo Yoon
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
| | - Inkyu Park
- Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
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Seo MH, Yoo JY, Jo MS, Yoon JB. Geometrically Structured Nanomaterials for Nanosensors, NEMS, and Nanosieves. Adv Mater 2020; 32:e1907082. [PMID: 32253800 DOI: 10.1002/adma.201907082] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/29/2019] [Revised: 12/18/2019] [Indexed: 06/11/2023]
Abstract
Recently, geometrically structured nanomaterials have received great attention due to their unique physical and chemical properties, which originate from the geometric variation in such materials. Indeed, the use of various geometrically structured nanomaterials has been actively reported in enhanced-performance devices in a wide range of applications. Recent significant progress in the development of geometrically structured nanomaterials and associated devices is summarized. First, a brief introduction of advanced nanofabrication methods that enable the fabrication of various geometrically structured nanomaterials is given, and then the performance enhancements achieved in devices utilizing these nanomaterials, namely, i) physical and gas nanosensors, ii) nanoelectromechanical devices, and iii) nanosieves are described. For the device applications, a systematic summary of their structures, working mechanisms, fabrication methods, and output performance is provided. Particular focus is given to how device performance can be enhanced through the geometric structures of the nanomaterials. Finally, perspectives on the development of novel nanomaterial structures and associated devices are presented.
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Affiliation(s)
- Min-Ho Seo
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea
- Center for Bio-Integrated Electronics, Northwestern University, Evanston, IL, 60208, USA
| | - Jae-Young Yoo
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea
| | - Min-Seung Jo
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea
| | - Jun-Bo Yoon
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea
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11
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Lee JS, Choi KW, Yoo JY, Jo MS, Yoon JB. Realization of Nanolene: A Planar Array of Perfectly Aligned, Air-Suspended Nanowires. Small 2020; 16:e1906845. [PMID: 32072747 DOI: 10.1002/smll.201906845] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/24/2019] [Revised: 01/23/2020] [Indexed: 06/10/2023]
Abstract
Air suspension and alignment are fundamental requirements to make the best use of nanowires' unique properties; however, satisfying both requirements is very challenging due to the mechanical instability of air-suspended nanowires. Here, a perfectly aligned air-suspended nanowire array called "nanolene" is demonstrated, which has a high mechanical stability owing to a C-channel-shaped cross-section of the nanowires. The excellent mechanical stability is provided through geometrical modeling and finite element method simulations. The C-channel cross-section can be realized by top-down fabrication procedures, resulting in reliable demonstrations of the nanolenes with various materials and geometric parameters. The fabrication process provides large-area uniformity; therefore, nanolene can be considered as a 2D planar platform for 1D nanowire arrays. Thanks to the high mechanical stability of the proposed nanolene, perfectly aligned air-suspended nanowire arrays with an unprecedented length of 1 mm (aspect ratio ≈5100) are demonstrated. Since the nanolene can be used in an energy-efficient nanoheater, two energy-stringent sensors, namely, an air-flow sensor and a carbon monoxide gas sensor, are demonstrated. In particular, the gas sensor achieves sub-10 mW operations, which is a requirement for application in mobile phones. The proposed nanolene will pave the way to accelerate nanowire research and industrialization by providing reliable, high-performance nanowire devices.
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Affiliation(s)
- Jae-Shin Lee
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea
| | - Kwang-Wook Choi
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea
| | - Jae-Young Yoo
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea
| | - Min-Seung Jo
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea
| | - Jun-Bo Yoon
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea
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Lee JS, Seo MH, Choi KW, Yoo JY, Jo MS, Yoon JB. Stress-engineered palladium nanowires for wide range (0.1%-3.9%) of H 2 detection with high durability. Nanoscale 2019; 11:16317-16326. [PMID: 31309962 DOI: 10.1039/c9nr01975h] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Pd nanowire-based H2 sensors have attracted significant attention because of their superior sensing performance. However, when exposed to H2 concentrations of more than 2%, Pd experiences volume expansion over 10%, resulting in a significant amount of mechanical stress. Thus, exposure to such high H2 concentrations causes physical destruction of Pd nanowires, such as breaks and peel-offs, leading to severe difficulty in the reliable detection of H2 over a wide concentration range. Here, we proposed a structural approach to resolve this issue by introducing a partially anchored Pd nanowire (PA-PdNW) structure. In this configuration, most of the structure was air-suspended, leaving a small portion anchored to the substrate. Air-suspension enabled PA-PdNW to expand freely, thus relieving the mechanical stress; therefore, the Pd nanowires could withstand numerous exposures to high H2 concentrations. To demonstrate the PA-PdNW structure, we developed a nano-fabrication method based on conventional semiconductor processes and successfully manufactured H2 sensor devices with uniform, perfectly aligned PA-PdNW arrays stably air-suspended with designed gaps from the substrate. The fabricated sensors achieved reliable detection of H2 in the 0.1%-3.9% concentration range with a significant resistance change. In addition, compared with fully anchored Pd nanowire (FA-PdNW) sensors, the PA-PdNW sensors showed superior durability, and the nanowires retained their initial structures even after 300 exposures to high H2 concentrations. Furthermore, it was confirmed that the PA-PdNW sensor can stably operate even in extremely humid environments at 85% relative humidity.
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Affiliation(s)
- Jae-Shin Lee
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea.
| | - Min-Ho Seo
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea. and Information & Electronics Research Institute Korea Advanced Institute of Science and Technology (KAIST), 291, Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - Kwang-Wook Choi
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea.
| | - Jae-Young Yoo
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea.
| | - Min-Seung Jo
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea.
| | - Jun-Bo Yoon
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea.
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Jo E, Seo MH, Pyo S, Ko SD, Kwon DS, Choi J, Yoon JB, Kim J. Integration of a Carbon Nanotube Network on a Microelectromechanical Switch for Ultralong Contact Lifetime. ACS Appl Mater Interfaces 2019; 11:18617-18625. [PMID: 31018637 DOI: 10.1021/acsami.9b02747] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Micro-/nanoelectromechanical (MEM/NEM) switches have been extensively studied to address the limitations of transistors, such as the increased standby power consumption and performance dependence on temperature and radiation. However, their lifetimes are limited owing to the degradation of the contact surfaces. Even though several materials and structural designs have been recently developed to improve the lifetime, the production of a microswitch that is compatible with a complementary metal-oxide semiconductor (CMOS) with a long lifetime remains a significant challenge. We demonstrate a vertically actuated MEM switch with extremely high reliability by integrating a carbon nanotube (CNT) network on a gold electrode as the contact material using a low-temperature, CMOS-compatible solution process. In addition to their outstanding mechanical and electrical properties of CNTs, their deformability dramatically increases the effective contact area of the switch, thus resulting in the extension of the lifetime. The CNT-coated MEM switch exhibits a lifetime that is more than 7 × 108 cycles when operated in hot-switching conditions, which is 1.9 × 104 times longer than that of a control device without CNTs. The switch also shows an excellent switching performance, including a low electrical resistance, high on/off ratio, and an extremely small off-state current.
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Affiliation(s)
- Eunhwan Jo
- School of Mechanical Engineering , Yonsei University , 50 Yonsei-ro , Seodaemun-gu, Seoul 03722 , Republic of Korea
| | - Min-Ho Seo
- School of Electrical Engineering , Korea Advanced Institute of Science Technology (KAIST) , 291 Daehak-ro , Yuseong-gu, Daejeon 34141 , Republic of Korea
- Information & Electronics Research Institute , Korea Advanced Institute of Science and Technology (KAIST) , 291, Daehak-ro , Yuseong-gu, Daejeon 34141 , Republic of Korea
| | - Soonjae Pyo
- School of Mechanical Engineering , Yonsei University , 50 Yonsei-ro , Seodaemun-gu, Seoul 03722 , Republic of Korea
| | - Seung-Deok Ko
- Broadcom Limited , 1730 Fox Dr , San Jose , California 95131 , United States
| | - Dae-Sung Kwon
- School of Mechanical Engineering , Yonsei University , 50 Yonsei-ro , Seodaemun-gu, Seoul 03722 , Republic of Korea
| | - Jungwook Choi
- School of Mechanical Engineering , Yeungnam University , 280 Daehak-ro , Gyeongsan , Gyeongbuk 38541 , Republic of Korea
| | - Jun-Bo Yoon
- School of Electrical Engineering , Korea Advanced Institute of Science Technology (KAIST) , 291 Daehak-ro , Yuseong-gu, Daejeon 34141 , Republic of Korea
| | - Jongbaeg Kim
- School of Mechanical Engineering , Yonsei University , 50 Yonsei-ro , Seodaemun-gu, Seoul 03722 , Republic of Korea
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Yoon GW, Bae SW, Lee YB, Yoon JB. Edge-lit LCD backlight unit for 2D local dimming. Opt Express 2018; 26:20802-20812. [PMID: 30119385 DOI: 10.1364/oe.26.020802] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/21/2018] [Accepted: 07/22/2018] [Indexed: 06/08/2023]
Abstract
Local dimming technology has been highly desired for integration with liquid crystal displays (LCDs) in order to improve their contrast ratios (CRs) as well as to overcome power efficiency bottlenecks. In this paper, we propose and demonstrate a slim (~1 mm) edge-lit LCD backlight unit (BLU) capable of 2D local dimming. We designed a semi-partitioned light guide plate (LGP) patterned with inverse-trapezoidal microstructures, which allows the ultra-slim BLU to function without prism sheets. Since light emitting diodes (LEDs) are placed in the middle of the LGP, the BLU can freely define illuminated areas and the whole BLU can be modularly expanded like a tile canvas. The fabricated BLU achieves uniformity in both local and global luminance distributions, as well as in high local dimming performance. Experimentally, the BLU increases the CR of the display up to two orders of magnitude compared to conventional BLUs.
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Seo MH, Choi SJ, Park SH, Yoo JY, Lim SK, Lee JS, Choi KW, Jo MS, Kim ID, Yoon JB. Material-Independent Nanotransfer onto a Flexible Substrate Using Mechanical-Interlocking Structure. ACS Nano 2018; 12:4387-4397. [PMID: 29589909 DOI: 10.1021/acsnano.8b00159] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
Nanowire-transfer technology has received much attention thanks to its capability to fabricate high-performance flexible nanodevices with high simplicity and throughput. However, it is still challenging to extend the conventional nanowire-transfer method to the fabrication of a wide range of devices since a chemical-adhesion-based nanowire-transfer mechanism is complex and time-consuming, hindering successful transfer of diverse nanowires made of various materials. Here, we introduce a material-independent mechanical-interlocking-based nanowire-transfer (MINT) method, fabricating ultralong and fully aligned nanowires on a large flexible substrate (2.5 × 2 cm2) in a highly robust manner. For the material-independent nanotransfer, we developed a mechanics-based nanotransfer method, which employs a dry-removable amorphous carbon (a-C) sacrificial layer between a vacuum-deposited nanowire and the underlying master mold. The controlled etching of the sacrificial layer enables the formation of a mechanical-interlocking structure under the nanowire, facilitating peeling off of the nanowire from the master mold robustly and reliably. Using the developed MINT method, we successfully fabricated various metallic and semiconductor nanowire arrays on flexible substrates. We further demonstrated that the developed method is well suited to the reliable fabrication of highly flexible and high-performance nanoelectronic devices. As examples, a fully aligned gold (Au) microheater array exhibited high bending stability (106 cycling) and ultrafast (∼220 ms) heating operation up to ∼100 °C. An ultralong Au heater-embedded cuprous-oxide (Cu2O) nanowire chemical gas sensor showed significantly improved reversible reaction kinetics toward NO2 with 10-fold enhancement in sensitivity at 100 °C.
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Affiliation(s)
- Min-Ho Seo
- School of Electrical Engineering , Korea Advanced Institute of Science and Technology (KAIST) , 291 Daehak-ro , Yuseong-gu, Daejeon 34141 , Republic of Korea
| | - Seon-Jin Choi
- Department of Chemistry , Massachusetts Institute of Technology , Cambridge , Massachusetts 02139 , United States
| | - Sang Hyun Park
- National NanoFab Center (NNFC) , 291 Daehak-ro , Yuseong-gu, Daejeon 34141 , Republic of Korea
| | - Jae-Young Yoo
- School of Electrical Engineering , Korea Advanced Institute of Science and Technology (KAIST) , 291 Daehak-ro , Yuseong-gu, Daejeon 34141 , Republic of Korea
| | - Sung Kyu Lim
- National NanoFab Center (NNFC) , 291 Daehak-ro , Yuseong-gu, Daejeon 34141 , Republic of Korea
| | - Jae-Shin Lee
- School of Electrical Engineering , Korea Advanced Institute of Science and Technology (KAIST) , 291 Daehak-ro , Yuseong-gu, Daejeon 34141 , Republic of Korea
| | - Kwang-Wook Choi
- School of Electrical Engineering , Korea Advanced Institute of Science and Technology (KAIST) , 291 Daehak-ro , Yuseong-gu, Daejeon 34141 , Republic of Korea
| | - Min-Seung Jo
- School of Electrical Engineering , Korea Advanced Institute of Science and Technology (KAIST) , 291 Daehak-ro , Yuseong-gu, Daejeon 34141 , Republic of Korea
| | - Il-Doo Kim
- Department of Materials Science and Engineering , Korea Advanced Institute of Science and Technology (KAIST) , 291 Daehak-ro , Yuseong-gu, Daejeon 34141 , Republic of Korea
| | - Jun-Bo Yoon
- School of Electrical Engineering , Korea Advanced Institute of Science and Technology (KAIST) , 291 Daehak-ro , Yuseong-gu, Daejeon 34141 , Republic of Korea
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Seo MH, Ko JH, Lee JO, Ko SD, Mun JH, Cho BJ, Kim YH, Yoon JB. >1000-Fold Lifetime Extension of a Nickel Electromechanical Contact Device via Graphene. ACS Appl Mater Interfaces 2018; 10:9085-9093. [PMID: 29461033 DOI: 10.1021/acsami.7b15772] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Micro-/nano-electromechanical (M/NEM) switches have received significant attention as promising switching devices for a wide range of applications such as computing, radio frequency communication, and power gating devices. However, M/NEM switches still suffer from unacceptably low reliability because of irreversible degradation at the contacting interfaces, hindering adoption in practical applications and further development. Here, we evaluate and verify graphene as a contact material for reliability-enhanced M/NEM switching devices. Atomic force microscopy experiments and quantum mechanics calculations reveal that energy-efficient mechanical contact-separation characteristics are achieved when a few layers of graphene are used as a contact material on a nickel surface, reducing the energy dissipation by 96.6% relative to that of a bare nickel surface. Importantly, graphene displays almost elastic contact-separation, indicating that little atomic-scale wear, including plastic deformation, fracture, and atomic attrition, is generated. We also develop a feasible fabrication method to demonstrate a MEM switch, which has high-quality graphene as the contact material, and verify that the devices with graphene show mechanically stable and elastic-like contact properties, consistent with our nanoscale contact experiment. The graphene coating extends the switch lifetime >103 times under hot switching conditions.
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Han CH, Yoon YH, Ko SD, Seo MH, Yoon JB. Linear frequency tuning in an LC-resonant system using a C–V response controllable MEMS varactor. Micro and Nano Syst Lett 2017. [DOI: 10.1186/s40486-017-0059-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Han HJ, Jeong JW, Yang SR, Kim C, Yoo HG, Yoon JB, Park JH, Lee KJ, Kim TS, Kim SW, Jung YS. Nanotransplantation Printing of Crystallographic-Orientation-Controlled Single-Crystalline Nanowire Arrays on Diverse Surfaces. ACS Nano 2017; 11:11642-11652. [PMID: 29131582 DOI: 10.1021/acsnano.7b06696] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The fabrication of a highly ordered array of single-crystalline nanostructures prepared from solution-phase or vapor-phase synthesis methods is extremely challenging due to multiple difficulties of spatial arrangement and control of crystallographic orientation. Herein, we introduce a nanotransplantation printing (NTPP) technique for the reliable fabrication, transfer, and arrangement of single-crystalline Si nanowires (NWs) on diverse substrates. NTPP entails (1) formation of nanoscale etch mask patterns on conventional low-cost Si via nanotransfer printing, (2) two-step combinatorial plasma etching for defining Si NWs, and (3) detachment and transfer of the NWs onto various receiver substrates using an infiltration-type polymeric transfer medium and a solvent-assisted adhesion switching mechanism. Using this approach, high-quality, highly ordered Si NWs can be formed on almost any type of surface including flexible plastic substrates, biological surfaces, and deep-trench structures. Moreover, NTPP provides controllability of the crystallographic orientation of NWs, which is confirmed by the successful generation of (100)- and (110)-oriented Si NWs with different properties. The outstanding electrical properties of the NWs were confirmed by fabricating and characterizing Schottky junction field-effect transistors. Furthermore, exploiting the highly flexible nature of the NWs, a high-performance piezoresistive strain sensor, with a high gauge factor over 200 was realized.
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Affiliation(s)
- Hyeuk Jin Han
- Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST) , 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - Jae Won Jeong
- Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST) , 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
- Powder Technology Department, Korea Institute of Materials Science (KIMS) , 797 Changwondaero, Changwon 51508, Republic of Korea
| | - Se Ryeun Yang
- Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST) , 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - Cheolgyu Kim
- Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST) , 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - Hyeon Gyun Yoo
- Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST) , 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - Jun-Bo Yoon
- Department of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST) , 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - Jae Hong Park
- Division of Nano-Convergence Technology, Korea National NanoFab Center (NNFC) , 291 Daehak-ro, Daejeon 34141, Republic of Korea
| | - Keon Jae Lee
- Department of Materials Science and 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
| | - Seong-Woong Kim
- Titanium Department, Korea Institute of Materials Science (KIMS) , 797 Changwondaero, Changwon 51508, Republic of Korea
| | - Yeon Sik Jung
- Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST) , 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
- Division of Nano-Convergence Technology, Korea National NanoFab Center (NNFC) , 291 Daehak-ro, Daejeon 34141, Republic of Korea
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Lee JO, Choi KW, Choi SJ, Kang MH, Seo MH, Kim ID, Yu K, Yoon JB. Nanomechanical Encoding Method Using Enhanced Thermal Concentration on a Metallic Nanobridge. ACS Nano 2017; 11:7781-7789. [PMID: 28708372 DOI: 10.1021/acsnano.7b01475] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
We present a fast, energy-efficient nano-thermomechanical encoding scheme for digital information storage and retrieval. Digital encoding processes are conducted by the bistable electrothermal actuation of a scalable nanobridge device. The electrothermal energy is highly concentrated by enhanced electron/phonon scattering and heat insulation in a sub-100 nm metallic layer. The efficient conversion of electrothermal energy into mechanical strain allows digital switching and programming processes within 60 ns at 0.75 V with a programming energy of only 54 pJ. Furthermore, this encoding scheme together with the thermally robust design enables data retention at temperatures up to 400 °C. These results suggest that the proposed nano-thermomechanical encoding method could contribute to low-power electronics and robust information storage/retrieval systems.
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Affiliation(s)
| | | | | | - Min-Ho Kang
- National NanoFab Center (NNFC) , 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
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Jo MS, Choi KW, Seo MH, Yoon JB. Realization of large-scale sub-10 nm nanogratings using a repetitive wet-chemical oxidation and etching technique. Micro and Nano Syst Lett 2017. [DOI: 10.1186/s40486-017-0053-y] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Seo MH, Yoo JY, Choi SY, Lee JS, Choi KW, Jeong CK, Lee KJ, Yoon JB. Versatile Transfer of an Ultralong and Seamless Nanowire Array Crystallized at High Temperature for Use in High-Performance Flexible Devices. ACS Nano 2017; 11:1520-1529. [PMID: 28135071 DOI: 10.1021/acsnano.6b06842] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Nanowire (NW) transfer technology has provided promising strategies to realize future flexible materials and electronics. Using this technology, geometrically controlled, high-quality NW arrays can now be obtained easily on various flexible substrates with high throughput. However, it is still challenging to extend this technology to a wide range of high-performance device applications because its limited temperature tolerance precludes the use of high-temperature annealing, which is essential for NW crystallization and functionalization. A pulsed laser technique has been developed to anneal NWs in the presence of a flexible substrate; however, the induced temperature is not high enough to improve the properties of materials such as ceramics and semiconductors. Here, we present a versatile nanotransfer method that is applicable to NWs that require high-temperature annealing. To successfully anneal NWs during their transfer, the developed fabrication method involves sequential removal of a nanoscale sacrificial layer. Using this method, we first produce an ultralong, perfectly aligned polycrystalline barium titanate (BaTiO3) NW array that is heat treated at 700 °C on a flexible polyethylene terephthalate (PET) substrate. This high-quality piezoelectric NW array on a flexible substrate is used as a flexible nanogenerator that generates current and voltage 37 and 10 times higher, respectively, than those of a nanogenerator made of noncrystallized BaTiO3 NWs.
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Affiliation(s)
- Min-Ho Seo
- School of Electrical Engineering, ‡KAIST Institute for NanoCentury, and §Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST) , 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - Jae-Young Yoo
- School of Electrical Engineering, ‡KAIST Institute for NanoCentury, and §Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST) , 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - So-Young Choi
- School of Electrical Engineering, ‡KAIST Institute for NanoCentury, and §Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST) , 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - Jae-Shin Lee
- School of Electrical Engineering, ‡KAIST Institute for NanoCentury, and §Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST) , 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - Kwang-Wook Choi
- School of Electrical Engineering, ‡KAIST Institute for NanoCentury, and §Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST) , 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - Chang Kyu Jeong
- School of Electrical Engineering, ‡KAIST Institute for NanoCentury, and §Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST) , 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - Keon Jae Lee
- School of Electrical Engineering, ‡KAIST Institute for NanoCentury, and §Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST) , 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - Jun-Bo Yoon
- School of Electrical Engineering, ‡KAIST Institute for NanoCentury, and §Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST) , 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
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22
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Affiliation(s)
- Seok-Won Bae
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
| | - Gun-Wook Yoon
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
| | - Jun-Bo Yoon
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
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23
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Song YH, Ahn SJK, Kim MW, Lee JO, Hwang CS, Pi JE, Ko SD, Choi KW, Park SHK, Yoon JB. High-performance hybrid complementary logic inverter through monolithic integration of a MEMS switch and an oxide TFT. Small 2015; 11:1390-1395. [PMID: 25418881 DOI: 10.1002/smll.201402841] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/23/2014] [Revised: 10/15/2014] [Indexed: 06/04/2023]
Abstract
A hybrid complementary logic inverter consisting of a microelectromechanical system switch as a promising alternative for the p-type oxide thin film transistor (TFT) and an n-type oxide TFT is presented for ultralow power integrated circuits. These heterogeneous microdevices are monolithically integrated. The resulting logic device shows a distinctive voltage transfer characteristic curve, very low static leakage, zero-short circuit current, and exceedingly high voltage gain.
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Affiliation(s)
- Yong-Ha Song
- Department of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon, 305-701, Republic of Korea
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24
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Yoon GW, Kim HD, Yeon J, Yoon JB. Novel buried inverse-trapezoidal micropattern for dual-sided light extracting backlight unit. Opt Express 2014; 22:32440-32449. [PMID: 25607206 DOI: 10.1364/oe.22.032440] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We devised a novel buried inverse-trapezoidal (BIT) micropattern that can enable light extracting to both front and back sides of the backlight unit (BLU). The proposed BLU comprised of only a single-sheet light-guide plate (LGP) having the BIT micropatterns only on the top surface of the LGP. The proposed BLU shows normal directional light emitting characteristics to both the front and back sides of the LGP and successfully acts as a planer light source for a dual-sided LCD. The proposed BLU has the potential to dramatically reduce the thickness, weight and cost of the dual-sided LCD thanks to its single-sheet nature.
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25
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Lee BH, Moon DI, Jang H, Kim CH, Seol ML, Choi JM, Lee DI, Kim MW, Yoon JB, Choi YK. A mechanical and electrical transistor structure (METS) with a sub-2 nm nanogap for effective voltage scaling. Nanoscale 2014; 6:7799-7804. [PMID: 24892839 DOI: 10.1039/c3nr06251a] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
A mechanical and electrical transistor structure (METS) is proposed for effective voltage scaling. The sub-2 nm nanogap by atomic layer deposition (ALD) without stiction and the application of a dielectric with high-permittivity allowed the pull-in voltage of sub-2 V, showing the strength of the mechanical actuation that is hard to realize in a typical complementary metal-oxide-semiconductor (CMOS) transistor. The results are verified by simulation and interpreted by the numerical equation. Therefore the METS can pave a new way to make a breakthrough to overcome the limits of CMOS technology.
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Affiliation(s)
- Byung-Hyun Lee
- The laboratory of Nano-Oriented Bio-Electronics Lab (NOBEL), Department of Electrical Engineering, Korea Advanced Institute of Science and Technology, Daejeon, 305-701, Korea.
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26
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Abstract
Abstract
An ultra-low voltage microelectromechanical system (MEMS) switch for low-power integrated circuit (IC) applications is proposed, fabricated and demonstrated. The folded hinge structure allows a large beam structure to be suspended with a designed air gap, effectively suppressing unwanted deflection. The actuation voltage of the switch was measured to be 1.7 V, the lowest among electrostatic switches. There was no variation in the actuation voltage until 106 cyclic actuations, showing the stability of a low actuation voltage in electrostatic actuation for the first time. The contact resistance was around 12 Ω, caused by a low contact force below 1 μN despite an Au–Au contact.
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27
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Yeon J, Lee YJ, Yoo DE, Yoo KJ, Kim JS, Lee J, Lee JO, Choi SJ, Yoon GW, Lee DW, Lee GS, Hwang HC, Yoon JB. High throughput ultralong (20 cm) nanowire fabrication using a wafer-scale nanograting template. Nano Lett 2013; 13:3978-3984. [PMID: 23899099 DOI: 10.1021/nl400209n] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Nanowires are being actively explored as promising nanostructured materials for high performance flexible electronics, biochemical sensors, photonic applications, solar cells, and secondary batteries. In particular, ultralong (centimeter-long) nanowires are highly attractive from the perspective of electronic performance, device throughput (or productivity), and the possibility of novel applications. However, most previous works on ultralong nanowires have issues related to limited length, productivity, difficult alignment, and deploying onto the planar substrate complying with well-matured device fabrication technologies. Here, we demonstrate a highly ordered ultralong (up to 20 cm) nanowire array, with a diameter of 50 nm (aspect ratio of up to 4,000,000:1), in an unprecedented large (8 in.) scale (2,000,000 strands on a wafer). We first devised a perfectly connected ultralong nanograting master template on the whole area of an 8 in. substrate using a top-down approach, with a density equivalent to that achieved with e-beam lithography (100 nm). Using this large-area, ultralong, high-density nanograting template, we developed a fast and effective method for fabricating up to 20 cm long nanowire arrays on a plastic substrate, composed of metal, dielectric, oxide, and ferroelectric materials. As a suggestion of practical application, a prototype of a large-area aluminum wire grid polarizer was demonstrated.
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Affiliation(s)
- Jeongho Yeon
- Department of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST) , 291 Daehak-ro, Yuseong-gu, Daejeon, 305-701, Republic of Korea
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28
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Yeon J, Koh TW, Cho H, Chung J, Yoo S, Yoon JB. Actively transparent display with enhanced legibility based on an organic light-emitting diode and a cholesteric liquid crystal blind panel. Opt Express 2013; 21:10358-10366. [PMID: 23609746 DOI: 10.1364/oe.21.010358] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Transparent display is one of the most promising concepts among the next generation information display devices. Nevertheless, conventional transparent displays have two inherent problems: low forward light efficiency due to the light being emitted also in a backward direction; and low legibility due to the visual interruption caused by the light coming from the background. In this work, a cholesteric liquid crystal (Ch-LC) based, actively operational blind panel is combined with transparent organic light-emitting diodes (TR-OLEDs) to recycle the light wasted by backward propagation in transparent displays while blocking the light from behind the display, pursuing both improved forward light efficiency and enhanced image legibility. By tuning the reflectance spectrum of the Ch-LC panel to match the emission spectrum of TR-OLEDs, we achieved luminous efficiency increase by as large as 21% (85%) when the top metal cathode side (the bottom ITO side) of the OLEDs fa'transparent OLED' ces the blind panel. Maximum transmittance of the proposed device reached a high value of 60%, successfully demonstrating a new window-like transparent display concept.
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Affiliation(s)
- Jeongho Yeon
- Department of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, South Korea
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29
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Lee JO, Song YH, Kim MW, Kang MH, Oh JS, Yang HH, Yoon JB. A sub-1-volt nanoelectromechanical switching device. Nat Nanotechnol 2013; 8:36-40. [PMID: 23178336 DOI: 10.1038/nnano.2012.208] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/04/2012] [Accepted: 10/24/2012] [Indexed: 05/24/2023]
Abstract
Nanoelectromechanical (NEM) switches have received widespread attention as promising candidates in the drive to surmount the physical limitations currently faced by complementary metal oxide semiconductor technology. The NEM switch has demonstrated superior characteristics including quasi-zero leakage behaviour, excellent density capability and operation in harsh environments. However, an unacceptably high operating voltage (4-20 V) has posed a major obstacle in the practical use of the NEM switch in low-power integrated circuits. To utilize the NEM switch widely as a core device component in ultralow power applications, the operation voltage needs to be reduced to 1 V or below. However, sub-1 V actuation has not yet been demonstrated because of fabrication difficulties and irreversible switching failure caused by surface adhesion. Here, we report the sub-1 V operation of a NEM switch through the introduction of a novel pipe clip device structure and an effective air gap fabrication technique. This achievement is primarily attributed to the incorporation of a 4-nm-thick air gap, which is the smallest reported so far for a NEM switch generated using a 'top-down' approach. Our structure and process can potentially be utilized in various nanogap-related applications, including NEM switch-based ultralow-power integrated circuits, NEM resonators, nanogap electrodes for scientific research and sensors.
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Affiliation(s)
- Jeong Oen Lee
- Department of Electrical Engineering, Korea Advanced Institute of Science and Technology, Daejeon, Republic of Korea
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30
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Choi DH, Han YD, Lee BK, Choi SJ, Yoon HC, Lee DS, Yoon JB. Use of a columnar metal thin film as a nanosieve with sub-10 nm pores. Adv Mater 2012; 24:4408-13. [PMID: 22729900 DOI: 10.1002/adma.201200755] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/21/2012] [Revised: 04/18/2012] [Indexed: 05/15/2023]
Abstract
A columnar-structured nanosieve is unique in the sense that it is a general thin film formed by physical vapor deposition (PVD). Instead of additional processes to make nanopores, the numerous voids naturally formed among columnar grains during PVD are used as nanopores. Since the thin film formed by PVD has vertically grown columnar grains, the fabricated nanosieve has numerous straight-opened nanopores, which is an ideal structure for a nanosieve.
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Affiliation(s)
- Dong-Hoon Choi
- Department of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon, 305-701, Republic of Korea
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31
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Lee KH, Lee JO, Choi S, Yoon JB, Cho GH. A CMOS label-free DNA sensor using electrostatic induction of molecular charges. Biosens Bioelectron 2012; 31:343-8. [DOI: 10.1016/j.bios.2011.10.042] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2011] [Revised: 10/21/2011] [Accepted: 10/21/2011] [Indexed: 11/26/2022]
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32
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Lee B, Lee KH, Lee JO, Sohn MJ, Choi SH, Wang SW, Yoon JB, Cho GH. An electronic DNA sensor chip using integrated capacitive read-out circuit. Annu Int Conf IEEE Eng Med Biol Soc 2011; 2010:6547-50. [PMID: 21096503 DOI: 10.1109/iembs.2010.5627101] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
This paper presents fully integrated label-free DNA recognition circuit based on capacitance measurement. A CMOS-based DNA sensor is implemented for the electrical detection of DNA hybridization. The proposed architecture detects the difference of capacitance through the integration of current mismatch of capacitance between reference electrodes functionalized with only single-stranded DNA and sensing electrodes bound with complementary DNA strands specifically. In addition, to minimize the effects of parallel resistance between electrodes and DNA layers, the compensation technique of leakage current through the use of constant current charging and discharging is implemented in the proposed detection circuit. The chip was fabricated in 0.35um 4-metal 2-poly CMOS process, and 16 × 8 sensing electrode arrays were fabricated by post-processing steps.
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Affiliation(s)
- Byunghun Lee
- School of EECS, Korea Advanced Institution of Science and Technology (KAIST), Korea
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33
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Im M, Im H, Lee JH, Yoon JB, Choi YK. Analytical modeling and thermodynamic analysis of robust superhydrophobic surfaces with inverse-trapezoidal microstructures. Langmuir 2010; 26:17389-17397. [PMID: 20879754 DOI: 10.1021/la1031569] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
A polydimethylsiloxane (PDMS) elastomer surface with perfectly ordered microstructures having an inverse-trapezoidal cross-sectional profile (simply PDMS trapezoids) showed superhydrophobic and transparent characteristics under visible light as reported in our previous work. The addition of a fluoropolymer (Teflon) coating enhances both features and provides oleophobicity. This paper focuses on the analytical modeling of the fabricated PDMS trapezoids structure and thermodynamic analysis based on the Gibbs free energy analysis. Additionally, the wetting characteristics of the fabricated PDMS trapezoids surface before and after the application of the Teflon coating are analytically explained. The Gibbs free energy analysis reveals that, due to the Teflon coating, the Cassie-Baxter state becomes energetically more favorable than the Wenzel state and the contact angle difference between the Cassie-Baxter state and the Wenzel state decreases. These two findings support the robustness of the superhydrophobicity of the fabricated Teflon-coated PDMS trapezoids. This is then verified via the impinging test of a water droplet at a high speed. The dependencies of the design parameters in the PDMS trapezoids on the hydrophobicity are also comprehensively studied through a thermodynamic analysis. Geometrical dependency on the hydrophobicity shows that overhang microstructures do not have a significant influence on the hydrophobicity. In contrast, the intrinsic contact angle of the structural material is most important in determining the apparent contact angle. On the other hand, the experimental results showed that the side angles of the overhangs are critical not for the hydrophobic but for the oleophobic property with liquids of a low surface tension. Understanding of design parameters in the PDMS trapezoids surface gives more information for implementation of superhydrophobic surfaces.
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Affiliation(s)
- Maesoon Im
- Department of Electrical Engineering, KAIST, 335 Gwahangno, Yuseong-gu, Daejeon 305-701, Republic of Korea
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34
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Lee KH, Lee JO, Sohn MJ, Lee B, Choi SH, Kim SK, Yoon JB, Cho GH. One-chip electronic detection of DNA hybridization using precision impedance-based CMOS array sensor. Biosens Bioelectron 2010; 26:1373-9. [PMID: 20692155 DOI: 10.1016/j.bios.2010.07.055] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2010] [Revised: 07/07/2010] [Accepted: 07/15/2010] [Indexed: 11/30/2022]
Abstract
This paper describes a label-free and fully electronic detection method of DNA hybridization, which is achieved through the use of a 16×8 microarray sensor in conjunction with a new type of impedance spectroscopy constructed with standard complementary metal-oxide-semiconductor (CMOS) technology. The impedance-based method is based on changes in the reactive capacitance and the charge-transfer resistance after hybridization with complementary DNA targets. In previously published label-free techniques, the measured capacitance presented unstable capacitive properties due to the parallel resistance that is not infinite and can cause a leakage by discharging the charge on the capacitor. This paper presents an impedance extraction method that uses excitation by triangular wave voltage, which enables a reliable measurement of both C and R producing a highly sensitive sensor with a stable operation independent of external variables. The system was fabricated in an industrial 0.35-μm 4-metal 2-poly CMOS process, integrating working electrodes and readout electronics into one chip. The integrated readout, which uses a parasitic insensitive integrator, achieves an enlarged detection range and improved noise performance. The maximum average relative variations of C and R are 31.5% and 68.6%, respectively, after hybridization with a 1 μM target DNA. The proposed sensor allows quantitative evaluation of the molecule densities on the chip with distinguishable variation in the impedance. This fully electronic microsystem has great potential for use with bioanalytical tools and point-of-care diagnosis.
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Affiliation(s)
- Kang-Ho Lee
- School of EECS, Korea Advanced Institute of Science and Technology, 335, Gwahakro, Yuseong-gu, Daejeon 305-701, Republic of Korea
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Abstract
This paper reports on the electrowetting behavior of a flexible poly(dimethylsiloxane) (PDMS) microlens array. A Cr and Au double-layered electrode was formed on an array of microlenses with diameters of 10 microm and heights of 13 microm. A deposition of parylene and a coating of Teflon were followed for electrical insulation as well as for enhancement of the hydrophobicity. On the nearly superhydrophobic microlens array surface, the electrowetting of a deionized water droplet was observed over the contact angle range of approximately 140 degrees to approximately 58 degrees by applying 0-200 V, respectively. The electrowetting phenomenon was reversible even in air environment with applied voltages of less than 100 V. The electrowetting on the microlens array surface lost its reversibility after the microlens array surface was completely wetted when the water meniscus touched the bottom of the microlens array. Analysis of meniscus shapes and net force direction follows to elucidate the reversibility. The convex curvature of the microlens caused gradual rather than abrupt impalement of water into the gap among the microlenses.
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Affiliation(s)
- Maesoon Im
- Department of Electrical Engineering, KAIST, 335 Gwahangno, Yuseong-gu, Daejeon 305-701, Republic of Korea
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36
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Kim YH, Lee JO, Jeong HS, Kim JH, Yoon EK, Yoon DK, Yoon JB, Jung HT. Optically selective microlens photomasks using self-assembled smectic liquid crystal defect arrays. Adv Mater 2010; 22:2416-2420. [PMID: 20376850 DOI: 10.1002/adma.200903728] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Affiliation(s)
- Yun Ho Kim
- Department of Chemical and Biomolecular Eng., Korea Advanced Institute of Science and Technology, Daejeon, Korea
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37
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Affiliation(s)
- Jin-Woo Han
- Department of Electrical Engineering KAIST Guseong-dong, Yuseong-gu, Daejeon 305-701, Korea
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38
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Ren HX, Chen X, Huang XJ, Im M, Kim DH, Lee JH, Yoon JB, Gu N, Liu JH, Choi YK. A conventional route to scalable morphology-controlled regular structures and their superhydrophobic/hydrophilic properties for biochips application. Lab Chip 2009; 9:2140-2144. [PMID: 19606289 DOI: 10.1039/b905804d] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
We use a conventional and straightforward route to fabricate scalable morphology-controlled regular structures. This route is based on the etching of PDMS microlens array in CF4 and CF4/O2 plasma. PDMS microlens array can be changed to regularly isolated microdot structures array in CF4 plasma. Microbowl shaped structures array can be reached in CF4/O2 plasma. Moreover, a set of structures after CF4 plasma treatment display superhydrophobicity, while a set of structures after CF4/O2 plasma treatment present hydrophilicity. DNA molecules can be readily enriched on the hydrophilic surface. We believe that the regular structure array surfaces provide a useful inspiration towards biomolecular detection and transportation in biochips.
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Affiliation(s)
- Hong-Xuan Ren
- School of Biological Science and Medical Engineering, Southeast University, Nanjing, 210098, PR China
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Huang XJ, Kim DH, Im M, Lee JH, Yoon JB, Choi YK. "Lock-and-key" geometry effect of patterned surfaces: wettability and switching of adhesive force. Small 2009; 5:90-94. [PMID: 19040219 DOI: 10.1002/smll.200800649] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Affiliation(s)
- Xing-Jiu Huang
- Nano-Oriented Bio-Electronic Lab, School of Electrical Engineering and Computer Science, Korea Advanced Institute of Science and Technology, Daejeon, 305-701, South Korea.
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40
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Huang XJ, Lee JH, Lee JW, Yoon JB, Choi YK. A one-step route to a perfectly ordered wafer-scale microbowl array for size-dependent superhydrophobicity. Small 2008; 4:211-216. [PMID: 18200645 DOI: 10.1002/smll.200700881] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Affiliation(s)
- Xing-Jiu Huang
- Nano-Oriented Bio-Electronic Lab, School of Electrical Engineering and Computer Science, Korea Advanced Institute of Science and Technology, Daejeon, 305-701, South Korea
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41
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Lee JH, Lee HS, Lee BK, Choi WS, Choi HY, Yoon JB. Simple liquid crystal display backlight unit comprising only a single-sheet micropatterned polydimethylsiloxane (PDMS) light-guide plate. Opt Lett 2007; 32:2665-7. [PMID: 17873928 DOI: 10.1364/ol.32.002665] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
A simple liquid crystal display (LCD) backlight unit (BLU) comprising only a single-sheet polydimethylsiloxane (PDMS) light-guide plate (LGP) has been developed. The PDMS LGP, having micropatterns with an inverse-trapezoidal cross section, was fabricated by backside 3-D diffuser lithography followed by PDMS-to-PDMS replication. The fabricated BLU showed an average luminance of 2878 cd/m(2) with 73.3% uniformity when mounted in a 5.08 cm backlight module with four side view 0.85cd LEDs. The developed BLU can greatly reduce the cost and thickness of LCDs, and it can be applied to flexible displays as a flexible light source due to the flexible characteristic of the PDMS itself.
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Affiliation(s)
- Joo-Hyung Lee
- School of Electrical Engineering and Computer Science, Korea Advanced Institute of Science and Technology, 373-1 Guseong-Dong, Yuseong-Gu, Daejeon, Korea.
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Abstract
Microlens array (MLA) diffusers for light-emitting diode (LED) backlight systems have been developed. A high fill-factor photoresist mold for the MLA was fabricated using three-dimensional diffuser lithography, and the patterns were transferred to a nickel master mold for UV-curable polymer replication. The fabricated microlens had various paraboloidal profiles, and its aspect ratio was controlled from 1.0 to 2.1. The MLA diffuser showed a batwing radiation pattern with a radiation angle of 150 degrees. The fabricated MLA diffuser may greatly enhance the color-mixing characteristics of LED backlight systems and help reduce the number of LEDs required.
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Affiliation(s)
- Sung-Il Chang
- Department of electrical Engineering and computer Science, Korea Advanced Institute of Science and Technology, Yuseong-gu, Daejeon, Korea.
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Chang SI, Yoon JB. Shape-controlled, high fill-factor microlens arrays fabricated by a 3D diffuser lithography and plastic replication method. Opt Express 2004; 12:6366-6371. [PMID: 19488283 DOI: 10.1364/opex.12.006366] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
This paper describes a simple and effective method to fabricate a plastic microlens array with controllable shape and high fill-factor, which utilizes the conventional lithography and plastic replication. The only difference from conventional lithography is the insertion of a diffuser that randomizes paths of the incident ultraviolet (UV) light to form lens-like 3D latent image in a thick positive photoresist. After replication of the developed concave microlens mold onto the polydimethylsiloxane (PDMS), the focal length of the fabricated hemispherical microlens was observed to be 13-88 microm depending on the UV exposure dose. Two PDMS curing conditions were tested, where the elevated temperature of 85 masculineC resulted in smoother surface roughness of 2.6 nm in RMS value in the microlens mold. The proposed method can be extensively applied for microlens fabrication with other plastic materials due to its simplicity and versatility.
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Affiliation(s)
- J M Kim
- Department of Obstetrics and Gynecology, Samsung Cheil Hospital and Women's Healthcare Center, Sung-Kyunk wan University, School of Medicine, Seoul, Korea
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Ahn JH, Park SM, Cho HS, Lee MS, Yoon JB, Vilcek J, Lee TH. Non-apoptotic signaling pathways activated by soluble Fas ligand in serum-starved human fibroblasts. Mitogen-activated protein kinases and NF-kappaB-dependent gene expression. J Biol Chem 2001; 276:47100-6. [PMID: 11600497 DOI: 10.1074/jbc.m107385200] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Many Fas-expressing cells do not undergo cell death upon Fas stimulation. In the normal human diploid cell line GM6112, the addition of soluble Fas ligand (sFasL) leads to morphological signs of cell death in less than 1% of cells. Treatment of serum-starved GM6112 fibroblasts with sFasL resulted in a rapid and transient phosphorylation of ERK1/2 without a significant increase in JNK and p38 activities. Unless co-treated with the protein synthesis inhibitor anisomycin, sFasL did not show gene-inducing activity in cells maintained in complete medium. However, when cells were serum-starved for 4 days, treatment with sFasL alone induced interleukin-6 gene expression and, less strongly, interleukin-8 gene expression. Sensitization of the gene-inducing activity by serum starvation correlated with NF-kappaB activation by sFasL. Furthermore, we found that the expression of FADD and caspase-8 was significantly reduced in serum-starved cells, whereas the level of cFLIP remained unchanged. Transfection of GM6112 cells with the antisense caspase-8 expression construct sensitized cells toward sFasL-induced NF-kappaB-dependent reporter activation. Our results support the notion that a change in the ratio of cFLIP and caspase-8 may be responsible for turning on the Fas-activated NF-kappaB pathway, which otherwise is supplanted by the death-inducing pathway.
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Affiliation(s)
- J H Ahn
- Department of Biology, Yonsei University, 134 Shinchon-Dong, Sudaemoon-Gu, Seoul 120-749, Korea
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Abstract
Histones, nuclear proteins that interact with DNA to form nucleosomes, are essential for both the regulation of transcription and the packaging of DNA within chromosomes. The N-terminal domain of histone H4 contains four acetylation sites at lysine residues and may play a separate role in chromatin structure from the remainder of the H4 chain. We performed circular dichroism and NMR characterization of both native (H4NTP) and acetylated (Ace-H4NTP) peptides containing N-terminal acetylation domain of histone H4 for various pH environments. Data from CD and NMR suggested that H4NTP exhibited a pH-dependent conformational change, whereas the Ace-H4NTP is insensitive to pH change. However, both peptides showed a defined structural form at acidic pH environments. The solution structure for Ace-H4NTP shows two structurally independent regions comprising residues of Leu10-Gly13 and Arg19-Leu22, demonstrating relatively well-defined turn-type structures. Our results suggest that N-terminal acetylated region of H4 prefers an extended backbone conformation at neutral pH, however, upon acetylation, the regions containing lysine residues induce structural transition, having defined structural form for its optimum function.
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Affiliation(s)
- E Bang
- Department of Chemistry, Yonsei University, Seoul, Korea
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Abstract
BACKGROUND There are racial differences in the prevalence and types of androgenetic alopecia (AGA). There have been several reports on the prevalence and types of AGA in the general population of caucasians, but few studies on Koreans with samples of sufficient numbers have been reported. OBJECTIVES To obtain a more precise estimate of the prevalence and types of AGA in Korean men and women and to compare the results with those in caucasians. METHODS The prevalence and types of AGA were analysed in 10,132 Koreans (5531 men and 4601 women) who had visited the Health Examination Centre at Kyung Hee University Hospital for regular health examinations between December 1997 and July 1999. To classify the degree of hair loss for each subject, the Norwood classification was used in men and the Ludwig classification in women. For AGA in men, 'female pattern' was added to the Norwood classification. RESULTS In Korean men, the prevalence of AGA (Norwood III or above) at all ages was 14.1%. It increased steadily with advancing age, but was lower than that of caucasians: 2.3% in the third decade, 4.0% in the fourth decade, 10.8% in the fifth decade, 24.5% in the sixth decade, 34.3% in the seventh decade and 46.9% over 70 years. Type III vertex involvement was the most common type in the third decade to the seventh decade; over 70 years, type VI was most common. A 'female pattern' was observed in 11.1% of cases. In Korean women, the prevalence of AGA (Ludwig I or above) at all ages was 5.6%. It also increased steadily with advancing age: 0.2% in the third decade, 2.3% in the fourth decade, 3.8% in the fifth decade, 7.4% in the sixth decade, 11.7% in the seventh decade and 24.7% over 70 years. Grade I was the most common type up to the sixth decade; over 60 years, grade I and II were similar in prevalence. Grade III (total baldness) was not observed. A family history of baldness was present in 48.5% of men and 45.2% of women with AGA. CONCLUSIONS The prevalence of AGA in Korean men and women was lower than that in caucasians, as recorded in the literature. Korean men tend to have more frontal hairline preservation and show a more 'female pattern' of hair thinning than caucasians. Therefore, 'female pattern' should be added to the classification of AGA.
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Affiliation(s)
- J H Paik
- Department of Dermatology, College of Medicine, Kyung Hee University, 1 Hoeki-Dong, Dongdaemun-Ku, Seoul 130-702, Korea
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Choy JH, Jung H, Yoon JB. Co K-edge XAS study on a new cobalt-doped-SiO2 pillared clay. J Synchrotron Radiat 2001; 8:599-601. [PMID: 11512864 DOI: 10.1107/s090904950001548x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/31/2000] [Accepted: 10/26/2000] [Indexed: 05/23/2023]
Abstract
New Co-doped-SiO2-sol pillared montmorillonite has been synthesized by interlayer hydrolysis and condensation of tetraethylorthosilicate (TEOS) in the presence of Co2+ ion using an organic template. The Co K-edge XANES and EXAFS analyses for the CoO-SiO2-PILC (before and after calcination) and for the references such as CoO and Co(OH)2 were performed in order to obtain electronic and local structural information of cobalt species, which may act as a catalytic active site for the selective reduction of NO(x), hydrodesulfurization, and Fischer-Tropsch reaction. According to the XANES spectra, the divalent cobalt ion is stabilized in an octahedral symmetry. The EXAFS result shows a significant change in local symmetry around cobalt ion upon calcination. The EXAFS fitting result before calcination shows that the cobalt species is in the form of hydroxide, with a small number of (Co-Co) pairs compared to the bulk Co(OH)2. After calcining at 550 degrees C, the first nearest neighbours were fitted to six oxygen atoms with two different distances, and the second and the third neighbours were fitted to two Si and one Co atoms. It is, therefore, reasonable to suggest a structure model, where the cobalt species on the SiO2 sol exists as a nano cluster of Co(OH)2 before calcination but transforms to a nanosized cobalt oxide covalently bound to the surface of SiO2 pillar after calcination.
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Affiliation(s)
- J H Choy
- National Nanohybrid Materials Laboratory, School of Chemistry and Molecular Engineering, Seoul National University, Korea.
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Choy JH, Yoon JB, Park JH. In situ XAFS study at the Zr K-edge for SiO2/ZrO2 nano-sol. J Synchrotron Radiat 2001; 8:782-784. [PMID: 11512930 DOI: 10.1107/s090904950001606x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/31/2000] [Accepted: 11/03/2000] [Indexed: 05/23/2023]
Abstract
The structural characterisation of SiO2/ZrO2 nano-sol particles, prepared by mixing SiO2 sol and aqueous solution of ZrOCl2 8H2O, has been carried out by in-situ XAS measurement at the Zr K-edge during condensation reaction. The detailed XANES features at the Zr K-edge of the mixed sol of SiO2/ZrO2 are compared with those of other references such as ZrO2, ZrOCl2 8H2O. BaZrO3, and ZrSiO4, and it becomes obvious that the Zr4+ ions are stabilised in an octahedral symmetry. The EXAFS result also indicates that each Zr atom is coordinated with six oxygen ones as the first nearest neighbour, where two oxygen atoms are from the linkage of (Si-O-Zr) at short distance, and four ones are from water molecules at long distance. As the condensation reaction proceeds, it is found that the number of oxygen atoms due to the formation of (Si-O-Zr) bond at short distance and the second neighbour of silicon atoms increase simultaneously. From the above EXAFS and XANES results, the structural and gelating models could be proposed, which is based on the octahedrally coordinated but distorted zirconium species attaching on the SiO2 sol surface.
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Affiliation(s)
- J H Choy
- National Nanohybrid Materials Laboratory, School of Chemistry and Molecular Engineering, Seoul National University, Korea.
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