Conferences
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Flexoelectricity-driven mechanical ferroelectric polarization switching in me
... Global Conference on Innovation Materials, jeju, Korea(2024)
Ji Hye Lee (초청강연)
Abstract
Flexoelectricity-based mechanical switching of ferroelectric polarization has recently emerged as a fascinating alternative to conventional polarization switching using electric fields. Here, we demonstrate hyperefficient mechanical switching of polarization exploiting metastable ferroelectricity that inherently holds a unique mechanical response. We theoretically predict that mechanical forces markedly reduce the coercivity of metastable ferroelectricity, thus greatly bolstering flexoelectricity-driven mechanical polarization switching. As predicted, we experimentally confirm the mechanical polarization switching via an unusually low mechanical force (100 nN) in metastable ferroelectric CaTiO3. Furthermore, the use of low mechanical forces narrows the width of mechanically writable nanodomains to sub-10 nm, suggesting an ultrahigh data storage density of ≥1 Tbit cm−2. This Letter sheds light on the mechanical switching of ferroelectric polarization as a viable key element for next-generation efficient nanoelectronics and nanoelectromechanics. -
Hygroscopic dough-type Zn-air battery capable of dry operation with high powe...
International Conference on Advadced Materials and Devices, Jeju, Korea(2023)
Ok Sung Jeon, Yunju La, Yong Bin Bang, Ji Hye Lee, Ye Rim Kim, Yong Yeol Park, Hyeon Seo Yang, Gyeong Hun Lee, So Yeon Han, Young Joon Yoo, Sang Yoon Park
Abstract
Zn-air battery (ZAB) is a promising next-generation energy storage device to be grafted onto the wearable electronics. Due to the half-open cathode configuration to use air as a fuel, drying out of water in an electrolyte is inevitable. Researchers focused on enhancing the water retention in the hydrogel. However, it is not practical solution to widen the scope of use in low relative humidity (RH) environment at 30% or less. To find a breakthrough in this issue, it is necessary to apply a new concept which can simultaneously obtain and retain water content. In addition, hydrophobic property of the cathode in contact with the aqueous electrolyte to avoid flooding phenomenon exerts significant influence on the number of active sites such as triple phase boundary (TPB). An immobilized solid-state electrolyte also suffers from poor contact at the interface between electrolyte and cathode.
Hence, our group has successfully fabricated novel type of electrolyte as dough-type which was able to absorb moisture at low RH as 30% or less by deliquescent property of KOH, and be tightly attached to the cathode with the porous structure retained. This dough-type electrolyte can be mass-manufactured on a large area as 10 cm × 10 cm due to the facile kneading preparation method, and crafted into desired shapes. The developed dough had high ionic conductivity of 248 mS cm-1 and superb water retention of 90.3% at RH 30% for 170 h. The dough-type ZABs showed a noticeable maximum power density of 160.1 mW cm-2, a specific capacity of 632 mAh gZn-1 and stability for 60 h at RH 30% and 120 h even at a low temperature of -20 oC, producing reasonable output though the pristine aqueous electrolyte-based ZAB shows only maximum power density of 45.84 mW cm-2 and stability of 14 h at RH 30%.
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Hierarchical Reduced Graphene Oxide Film as an Efficient Large-Area Solar The...
International Conference on Advadced Materials and Devices, Jeju, Korea(2023)
Dongpyo Hong, Ye Rim Kim, Seo Young Kang, Yong Joon Lee, Jae Yeon Won, Jun Yong Song, In-Sung Lee, In Gyun Jung, Ji-ni Kim, Young Joon Yoo, Sang Yoon Park
Abstract
As the demand for clean and sustainable energy sources continues to rise, solar energy conversion technology plays a pivotal role in meeting these needs. Solar absorbers serve as the foundational materials for diverse applications, ranging from solar-thermal power generation to household water heaters and water purification systems.
In this study, we introduce an innovative approach to create a highly efficient large-area solar absorber by employing an ultrafast self-expansion and reduction (USER) process on graphene oxide. The resulting material, termed Hierarchical Reduced Graphene Oxide Film (HrGOF), exhibits remarkable solar absorbance properties, reaching up to 99%. Under one sun irradiation, the HrGOF was observed to elevate temperatures to 70 degrees Celsius.
The morphology and optical characteristics of the HrGOF are found to be intricately linked to the sheet size and chemical structure of the graphene oxide prior to reduction, particularly the presence of unexfoliated graphite oxide particles. The initial state of the graphene oxide film significantly influences the gas escape dynamics during the formation of HrGOF. The exceptional light absorption properties observed in the optimized HrGOF structure result from impedance matching and the interplay of multiple reflections within the material.
This research represents a significant advancement in the development of efficient solar thermal absorbers, with the potential to revolutionize various solar energy applications. The insights gained from this study provide a foundation for further optimizing solar absorber materials and advancing the field of solar energy conversion technology.
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Sustainable eco-friendly sub-micron NaCl crystal powder-assisted method to sy...
International Conference on Advadced Materials and Devices, Jeju, Korea(2023)
Young Pyo Jeon, Yeon Soo Kim, Tae Han Kim, Sang-hwa Lee, Se Hun Lee, Eun Jung Lee, Hak Ji Lee, Hae Ryeong Cho, Young Joon Yoo, Sang Yoon Park
Abstract
As environmental issues have recently emerged, research in a direction that can minimize environmental hazards in the process of material development as well as material development to solve only the energy density problem of graphite is urgently needed. Another challenge on graphite is that the Paris Agreement committed to reducing greenhouse gas emissions by at least 40% by 2030 compared to 1990 and the governance mainly focused to avoid dangerous climate change by limiting global warming to well below 2°C and pursuing efforts to limit it to 1.5°C. Unfortunately, purifying natural graphite requires a huge amount of hydrofluoric acid in the refinement process to remove containing mineral impurities while manufacturing synthetic graphite intensely demands a lot of electrical energy involved with carbonization and graphitization processes requiring high temperatures of over 3000°C. Isolation of the additive catalyst during the treatment process is also one of the practical problems. Therefore, it is required to develop an alternative solution that can solve multiple problems of a conventional graphite anode, regarding electrochemical performance, environmental pollution, hazardousness of synthesis, and methodological problems of material preparation.
In this study, we introduce SiOx/C produced through the NaCl sub-microm crystal-assisted synthesis method, which can complement environmental destruction, hazards, and complicated preparation processes while improving electrochemical performance using rice husk as a starting material. During the synthesis process, excess added NaCl plays three main roles: catalytic graphitization, activation of carbon, and formation of amorphous silica. In addition, the NaCl used in this process is not completely consumed and can be reused infinitely. As a result, the LIBs using a rice husk-derived SiOx/C through our NaCl sub-micron crystal powder-assisted method exhibited a high initial charge/discharge capacity of 422.05/915.93 mAh∙g-1 at 0.05 A∙g-1 and high cycle stability over 500 cycles. In addition, in the case of electrodes to which the NaCl micro-crystal method was not applied, the specific capacity of 333.96 mAh∙g-1 at a current density of 0.05 A∙g-1 was indicated, whereas the electrode adopting this method showed a high capacity of 479.77 mAh∙g-1 at a current density of 0.05 A∙g-1.
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Enhancing the Consistency of Porous Polymer Passive Daytime Radiative Cooling...
Materials Research Society, BOSTON, Massachusetts(2023)
Dongpyo Hong, Ok Sung Jeon, Se Hun Lee, Yong Joon Lee, Insung Lee, Ye Rim Kim, Yunju La, Yeong-pyo Jeon, Young Joon Yoo, and Sang Yoon Park
Abstract
Coating the building envelope with passive daytime radiative cooling (PDRC) paint has garnered enormous attention as an energy- and carbon-free alternative cooling technology. Achieving this goal requires the spontaneous formation of a suitable optical structure during the solvent drying process of the paint that effectively reflects sunlight and enables thermal emission through the atmospheric window (8-13 µm). In addition to their cooling abilities, PDRC coatings must also possess affordability, durability, and compatibility with diverse surfaces and climates for practical use.
Recently, porous polymer coating (PPC) has gained significant attention due to its numerous advantages, including cooling performance, cost-effectiveness, flexibility, and scalability. However, achieving consistent performance over a wide range of outdoor conditions is a challenge due to the morphology of PPC formed via the evaporation-induced phase separation method (EIPS), which is highly dependent on evaporation environment parameters such as temperature and humidity. Despite the advantages of PPC, there is a lack of systematic studies on the consistency of PDRC performance under varying environmental conditions of EIPS, and potential solutions to this issue have not been addressed.
In this study, we demonstrate the humidity vulnerability of PPC during the drying process and propose a simple strategy to mitigate this issue. Specifically, we found that the solar reflectance of PPC rapidly decreases with increasing humidity from 30% RH, causing the PPC to completely lose its PDRC ability at 45% RH and even become a solar-heating material at higher humidity levels. However, by adding a trace amount of fumed silica into PPC, we were able to maintain its PDRC performance up to 60% RH, resulting in a 1050% enhancement of areal coverage in the United States. This study highlights a crucial consistency issue for PPC-based PDRC paint that has been previously overlooked and offers engineering guidance to address this fundamental challenge for the development of reliable PDRC paint for industrial applications. -
Synthesis of Conducting Polymer-Intercalated Vanadate Nanofiber Composites ut...
The Korean Electrochemical society, YEOSU EXPO, Korea(2023)
Se Hun Lee, Ok Sung Jeon, Dong Pyo Hong, Yong Yeol Park, Seo Young Kang, Yong Joon Lee, Jae Yeon Won, Heejoon Ahn, Young Joon Yoo, Sang Yoon Park
Abstract
This study revolves around the development and use of stretchable zinc-ion micro-batteries (SZIMBs), crucial for wearable device applications. Many researchers have proposed various designs for SZIMBs, but their mechanical performance often suffers due to the lack of flexibility in the active materials of the electrodes. This research introduces a poly(3,4-ethylene dioxythiophene) (PEDOT)-intercalated zinc vanadium oxide nanofiber composite (E-ZVONF) as a cathode material for SZIMBs, synthesized through a simple sonochemical method. This new E-ZVONF composite brings flexibility and elasticity to the ceramic material and stabilizes the charge/discharge process. In addition, a new method called "short nduced pre-zincation (SIPZ)" is also introduced to improve the electrode thickness-dependence issue in stretchable devices field. The SIPZ method simplifies pre-zincation by adding zinc metal powder to the cathode, providing a more efficient approach compared to existing techniques. This research also proposes a wave-type SZIMB assembly that shows excellent electrochemical performance even when the thickness of the zinc metal anode is significantly reduced. When combined with the E-ZVONF composite, SIPZ method, and wave-type assembly, the new SZIMB demonstrated superior capacity retention under stretching conditions. By integrating these strategies, the fabricated PEDOT-intercalated zinc vanadium oxide nanofiber zinc-ion micro-batteries (E-ZVONF-SZIMBs) exhibit a peak specific capacity of 0.16 mAh cm-2, a high energy density of 0.112 mWh cm-2, a substantial power density of 3.5 mW cm-2, and they retain 83.7% of the initial specific capacity after 500 cycles. Further, the E-ZVONF-SZIMBs preserve 78.9% of the initial specific capacity even post 7,000 mechanical stretching/bending cycles, thereby demonstrating exceptional operando dynamic stretchability. Notably, they display practical viability by sustaining 80% and 90% of the capacity at -20 °C and 60 °C under 200% strain, respectively. These outstanding accomplishments in the realm of stretchable zinc-ion micro-batteries are anticipated to be impactful for the progression of future device platforms. -
Green Synthesis of SiOx/C Anode Materials for Lithium-Ion Batteries Using Sustai...
The Korean Physical Society, DCC DAEJEON, Korea (2023)
Hyun Seo Yang, Yong Yeol Park, Yong Joon Lee, Seo Young Kang, Ye Rim Kim, Dong Pyo Hong, Ok Sung Jeon, Se Hun Lee, and Young Joon Yoo, Sang Yoon Park
Abstract
In the past, research on replacing graphite, which is used as the anode material for lithium-ion batteries, has primarily focused on solving the low energy density problem. However, due to emerging environmental concerns, it is necessary to conduct research in a direction that minimizes environmental hazards during the material development process, rather than solely focusing on performance. In this study, we introduce SiOx/C produced through the NaCl salt-assisted synthesis method, which can address environmental destruction and hazards, as well as complicated preparation processes, while improving electrochemical performance. The starting material for this synthesis method is rice husk. During the synthesis process, excess NaCl is added to the rice husks, which serves three main purposes: catalytic graphitization, activation of carbon, and formation of amorphous silica. Additionally, the NaCl used in this process can be infinitely and repeatedly reused through dissolution in water after the reaction is complete. As a result, the lithium-ion batteries that use rice husk-derived SiOx/C produced through our salt-assisted method exhibit a high initial charge/discharge capacity of 422.05/915.93 mAh∙g-1 at 0.05 A∙g-1 and high cycle stability over 500 cycles. -
Analysis of thermal and electromagnetic shielding properties ba
sed on copper/... The Korean Physical Society, DCC DAEJEON, Korea (2023)
Tae-Han Kim, In-Sung Lee, Yong Bin Bang Young Pyo Jeon, Jun Yong Song, Young Joon Yoo, and Sang Yoon Park
Abstract
In this study, we investigated the thermal and electromagnetic interference shielding properties of copper/diamond composites by varying the size and volume fraction of the diamond particles and the thickness of the interlayer material using 3D finite-difference time-domain (FDTD) simulations.
Copper coated diamond particles have shown great promise for improving the thermal and mechanical properties in semiconductor packaging materials. In addition to these advantages, Cu-coated diamond particles may also have the potential to provide the function of electromagnetic shielding effectiveness due to their electrical conductive properties. These versatile functions of copper/diamond composites can be beneficial to reduce the cost of packaging process and increase the performance of recent advanced semiconductor chips -
Enhanced dielectric properties of Be-doped magnesium oxide nanopowder
The Korean Physical Society, DCC DAEJEON, Korea (2023)
Eun Jung Lee, Gyung Hyun Kim, So Yeon Kwon, Yun Ju La, Sang-hwa Lee, Sang Yoon Park, and Young Joon Yoo
Abstract
Among metal oxide, magnesium oxide (MgO) has been widely used in many fields as one of the most important ceramic materials, owing to its applicability in areas such as catalysis, adsorption, refractory ceramic synthesis, nanoelectronics, optoelectronic and sensing devices, and superconducting products. However, it has a relatively low dielectric constant compared to other metal oxide semiconductors which restricts the range of its bandgap and applicability. Here we report the Be-doped magnesium oxide nanopowder showing increased dielectric constant of 10.4 as the Be ion was substituted to 5% without breaking the cubic crystalline structure of MgO.
A sample of MgO powder doped with Be ions was prepared using the Pechini method. The X-ray diffraction showed that the crystal structure of the doped MgO was maintained with very small lattice constant differences. The bonding structure in the lattice of the sample was identified through X-ray photoelectron spectroscopy, and the change in the bonding structure according to the amount of substitution was identified. The dielectric properties of the samples were analyzed as a function of frequency at room temperature. The real and imaginary parts of the dielectric constant were studied as a function of frequency and composition. It was confirmed that the dielectric constant increased as the Be ions were substituted. We suggest that improving the low dielectric properties of pure MgO can enable the application of MgO to wide bandgap and high voltage applications simultaneously. -
Low leakage current me
tal-insulator-me tal structure ba sed on beryllium ... The Korean Physical Society, DCC DAEJEON, Korea (2023)
So Yeon Han, Min Ji Lee, Hak Ji Lee, Ju Sang Park, Young Pyo Jeon, Young Joon Yoo, and Sang Yoon Park
Abstract
Beryllium oxide (BeO) is believed to be an attractive material for use in upcoming industries such as semiconductors, spacecraft, aircraft, and rocket technologies due to its high bandgap energy, melting point, thermal conductivity, and dielectric constants. The most common method used to produce BeO is the Pechini method. Pechini synthesis has successfully been adapted to 100 different mixed oxide compounds, including perovskite powders and metal oxide films, since the method was introduced. However, limitations of conbentional Pechini techniques include a lack of morphology controls for the thin film process due to the viscosity of the gel precursor and the inhomogeneous nucleation that occurs during polyesterification and sintering, respectively. Our approach is a novel method to create BeO insulting layer based on a two-step spin-coating innovation of the conventional Pechinisynthesis method. The surface morphology and the crystal structure of BeO thin films were observed to be dependent on the citric acid/beryllium sulfate ratio and the sintering temperature, respectively. Finally, the leakage current of a plannal metal-insulator-metal device consistingof Au/Ti/BeO thin film/Ti/Au electrodes was determined to perform low leakage current
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