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Tailoring high-refractive-index nanocomposites for manufacturing of ultraviolet metasurfaces

Microsystems & Nanoengineering 2024年第2期10卷 303-310页

作者： Hyunjung Kang Dongkyo Oh Nara Jeon Joohoon Kim Hongyoon Kim Trevon Badloe Junsuk Rho Department of Mechanical Engineering Pohang University of Science and Technology(POSTECH)PohangRepublic of Korea Graduate School of Artificial Intelligence Pohang University of Science and Technology(POSTECH)PohangRepublic of Korea Department of Chemical Engineering Pohang University of Science and Technology(POSTECH)PohangRepublic of Korea Department of Electrical Engineering Pohang University of Science and Technology(POSTECH)PohangRepublic of Korea POSCO-POSTECH-RIST Convergence Research Center for Flat Optics and Metaphotonics PohangRepublic of Korea National Institute of Nanomaterials Technology(NINT) PohangRepublic of Korea

Nanoimprint lithography(NIL)has been utilized to address the manufacturing challenges of high cost and low throughput for optical *** overcome the limitations inherent in conventional imprint resins characterized by a low refractive index(n),high-n nanocomposites have been introduced to directly serve as ***,comprehensive research on these nanocomposites is notably *** this study,we focus on the composition of high-n zirconium dioxide(ZrO_(2))nanoparticle(NP)concentration and solvents used to produce ultraviolet(UV)metaholograms and quantify the transfer fidelity by the measured conversion *** utilization of 80 wt%ZrO_(2)NPs in MIBK,MEK,and acetone results in conversion efficiencies of 62.3%,51.4%,and 61.5%,respectively,at a wavelength of 325 *** analysis of the solvent composition and NP concentration can further enhance the manufacturing capabilities of high-n nanocomposites in NIL,enabling potential practical use of optical metasurfaces.

关键词： ultraviolet refractive nanocomposites

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Restructuring the cell network of non-equiatomic CoCrFeNiMoC medium-entropy alloy fabricated by laser powder bed fusion

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材料科学技术（英文版） 2025年第11期214卷 143-152页

作者： Hyeonseok Kwon Eun Seong Kim Yoon-Uk Heo Jungho Choe Rae Eon Kim Soung Yeoul Ahn Sang-Ho Oh Jeong Min Park Byeong-Joo Lee Hyoung Seop Kim Center for Advanced Aerospace Materials Pohang University of Science and Technology(POSTECH)Pohang37673Republic of Korea Department of Materials Science and Engineering Pohang University of Science and Technology(POSTECH)Pohang37673Republic of Korea Graduate Institute of Ferrous & Eco Materials Technology Pohang University of Science and Technology(POSTECH)Pohang37673Republic of Korea Department of 3D Printing Materials Korea Institute of Materials Science(KIMS)Changwon 51508Republic of Korea Department of 3D Printing Materials Korea Institute of Materials Science(KIMS)Changwon 51508Republic of Korea Department of Advanced Future Convergence Materials Korea UniversitySeoul 02841Republic of Korea Department of Materials Science and Engineering Pohang University of Science and Technology(POSTECH)Pohang37673Republic of Korea Graduate Institute of Ferrous & Eco Materials Technology Pohang University of Science and Technology(POSTECH)Pohang37673Republic of Korea Institute for Convergence Research and Education in Advanced Technology Yonsei UniversitySeoul03722Republic of Korea Advanced Institute for Materials Research(WPI-AIMR) Tohoku UniversitySendai980-8577Japan

Metal additive manufacturing(MAM)enables near-net shape production of components with minimized waste and excellent mechanical performance based on multi-scale microstructural ***-cially,the dislocation cell network that often bears elemental segregation or precipitation of a secondary phase contributes to enhancing the strength of additively manufactured *** cell boundaries can also act as active nucleation sites for the formation of precipitates under post-MAM heat treatment,as the chemical heterogeneity and profuse dislocations generate a driving force for *** this work,we subjected a Co18Cr15Fe50Ni10Mo6.5C0.5(at％)medium-entropy alloy fabricated by laser powder bed fusion(LPBF)to post-LPBF annealing at 900 ℃ for 10 *** investigation revealed that the cell boundaries of the as-built sample,which were decorated by Mo segregation,are replaced byμ phase and M6C type carbide precipitates during annealing while the grain structure and size remain unaffected,indicating that the post-LPBF annealing delivered the proper amount of heat input to alter only the cell *** yield strength slightly decreased with annealing due to a reduction in the strengthening effect by the cell boundaries despite an increased precipitation strengthening ***-ever,the post-LPBF annealing improved the strain hardenability and the ultimate tensile strength was enhanced from～1.02 to～1.15 GPa owing to reinforced back stress hardening by the increased disloca-tion pile-up at the *** results suggest that the cell structure with chemical heterogeneity can be successfully controlled by careful post-MAM heat treatment to tailor the mechanical performance,while also providing insight into alloy design for additive manufacturing.

关键词： Laser powder bed fusion Medium-entropy alloy Cell structure Strain hardening Precipitation Back stress hardening

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The H∞ Robust Stability and Performance Conditions for Uncertain Robot Manipulators

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IEEE/CAA Journal of Automatica Sinica 2025年第1期12卷 270-272页

作者： Geun Il Song Hae Yeon Park Jung Hoon Kim the Department of Electrical Engineering Pohang University of Science and Technology (POSTECH) the Department of Electrical Engineering Pohang University of Science and Technology (POSTECH) the Institute for Convergence Research and Education in Advanced Technology Yonsei University

Dear Editor,H∞This letter develops a new framework for the robust stability and performance conditions as well as the relevant controller synthesis with respect to uncertain robot *** often exist model uncertainties between the nominal model and the real robot manipulator and disturbances. Hence, dealing with their effects plays a crucial role in leading to high tracking performances, as discussed in [1]–[5].

关键词： Robot applications

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Thermodynamic model for deoxidation of liquid steel considering strong metal-oxygen interaction in the quasichemical model framework

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International Journal of Minerals,Metallurgy and Materials 2024年第5期31卷 988-1002页

作者： Yong-Min Cho Youn-Bae Kang Graduate Institute of Ferrous and Eco Materials Technology Pohang University of Science and TechnologyPohangKyungbuk37673Rep.of Korea N.EX.T Hub POSCO HoldingsPohangKyungbuk37673Rep.of Korea Department of Materials Science and Engineering Pohang University of Science and TechnologyPohangKyungbuk37673Rep.of Korea

Herein,a thermodynamic model aimed at describing deoxidation equilibria in liquid steel was *** model provides explicit forms of the activity coefficient of solutes in liquid steel,eliminating the need for the minimization of internal Gibbs energy preliminarily when solving deoxidation *** elimination of internal Gibbs energy minimization is particularly advantageous during the coupling of deoxidation equilibrium calculations with computationally intensive approaches,such as computational fluid *** model enables efficient calculations through direct embedment of the explicit forms of activity coefficient in the computing *** proposed thermodynamic model was developed using a quasichemical approach with two key approximations:random mixing of metallic elements(Fe and oxidizing metal) and strong nonrandom pairing of metal and oxygen as nearest *** these approximations,the quasichemical approach yielded the activity coefficients of solutes as explicit functions of composition and temperature without requiring the minimization of internal Gibbs energy or the coupling of separate *** model was successfully applied in the calculation of deoxidation equilibria of various elements(Al,B,C,Ca,Ce,Cr,La,Mg,Mn,Nb,Si,Ti,V,and Zr).The limitations of the model arising from these assumptions were also discussed.

关键词： deoxidation equilibria thermodynamics quasichemical approach computational fluid dynamics

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Carbon-based materials for potassium-ion battery anodes: Storage mechanisms and engineering strategies

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Journal of Energy Chemistry 2025年第6期105卷 764-796页

作者： Hyun Chul Kim Hongjung Kim Sung Oh Moon Changshin Jo Ho Seok Park School of Chemical Engineering Sungkyunkwan University (SKKU) Department of Chemical Engineering Pohang University of Science and Technology (POSTECH) Department of Battery Engineering Pohang University of Science and Technology (POSTECH) SKKU Institute of Energy Science and Technology (SIEST) Sungkyunkwan University

Recently,potassium-ion batteries(PIBs) have received significant attention in the energy storage field owing to their high-power output,fast charging capability,natural abundance,and environmental ***,we comprehensively review recent advancements in the design and development of carbon-based anode materials for PIBs anodes,covering graphite,hard carbon,alloy and conversion materials with carbon,and carbon host for K metal *** strategies such as structural engineering,heteroatom-doping,and surface modifications are highlighted to improve electrochemical performances as well as to resolve technical challenges,such as electrode instability,low initial Coulombic efficiency,and electrolyte ***,we discuss the fundamental understanding of potassium-ion storage mechanisms of carbon-based materials and their correlation with electrochemical ***,we present the current challenges and future research directions for the practical implementation of carbon-based anodes to enhance their potential as next-generation energy storage materials for *** review aims to provide our own insights into innovative design strategies for advanced PIB's anode through the chemical and engineering strategies.

关键词： Anode materials Carbon host Carbon materials Energy storage Graphite Hard carbon Potassium Potassium-ion batteries

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Electroplasticity in the Al_(0.6) CoCrFeNiMn high entropy alloy subjected to electrically-assisted uniaxial tension

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Journal of Materials science & technology 2023年第17期148卷 209-221页

作者： Zhiqin Yang Jianxing Bao Chaogang Ding Sujung Son Zhiliang Ning Jie Xu Debin Shan Bin Guo Hyoung Seop Kim State Key Laboratory of Precision Hot Processing Harbin Institute of TechnologyHarbin 150001China School of Materials Science and Engineering Harbin Institute of TechnologyHarbin 150001China Department of Materials Science and Engineering Pohang University of Science and TechnologyPohang 37673Republic of Korea Graduate Institute of Ferrous Technology Pohang University of Science and TechnologyPohang 37673Republic of Korea

Electrically assisted deformation(EAD)was adopted in this work to overcome the shortcomings such as poor formability and easy cracking in the processing of dual-phase the Al_(0.6) CoCrFeNiMn high entropy al-loy(HEA)at room *** of the Al_(0.6) CoCrFeNiMn HEA was studied systematically using electrically assisted uniaxial *** results showed that pulse current caused the temperature gradient along the tensile direction and the temperatures of the samples increased with the current *** flow stress decreased,and the elongation increased with increasing current density during the *** the current density was 30 A mm-2,the total elongation of the samples could be increased by 50%compared to that with no *** current can reduce local stress concentration and post-pone microcracks initiation in the body-centered cubic(BCC)phases,and hence can effectively inhibit cracks and *** dislocation tangles were opened by pulse current,and the dislocation recovery was enhanced at a high current *** with dilute solid solution alloys,the lattice distortion effect,the high fraction of the BCC phases,and the dislocations in HEAs can lead to the enhancement of the local Joule heating,which accelerated dislocation slip and dislocation *** study con-firms that EAD can effectively im prove the formability of HEAs and provides theoretical guidance and an experimental basis for forming HEAs components.

关键词： Electrically-assisted deformation Electroplasticity Microstructural evolution Tensile behavior High entropy alloys

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Fe-based high-entropy alloy with excellent mechanical properties enabled by nanosized precipitates and heterogeneous grain distribution

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Journal of Materials science & technology 2024年第14期181卷 71-81页

作者： Heechan Jung Sangwon Lee Taehyeok Kang Alireza Zargaran Pyuck-Pa Choi Seok Su Sohn Department of Materials Science and Engineering Korea UniversitySeoul 02841Republic of Korea Department of Materials Science and Engineering Korea Advanced Institute of Science and TechnologyDaejeon 34141Republic of Korea Graduate Institute of Ferrous and Energy Materials Technology Pohang University of Science and TechnologyPohang 37673Republic of Korea

High-entropy alloys(HEAs)consisting of CoCrFeNiAlTi systems,with a face-centered cubic(FCC)matrix reinforced by ordered L12 precipitates,have demonstrated exceptional strength-ductility ***,the current compositional design of HEAs heavily relies on high Ni and Co contents,compro-mising the balance between properties and ***,it is crucial to optimize the cost-performance trade-offby fine-tuning the range of Fe,Co,and Ni,while maintaining excellent strength-ductility *** this study,we propose a novel Fe-based HEA with nanosized precipitates and a heteroge-neous grain distribution,achieving a strength-ductility combination comparable to state-of-the-art Ni-or Co-based *** alloy benefits from both precipitation hardening and hetero-deformation-induced strengthening attributed to the heterogeneous grain distribution,resulting in excellent yield strength of 1433 MPa,tensile strength of 1599 MPa,and ductility of 22%.The microstructural evolution and its in-fluence on mechanical properties are unraveled with respect to the observation of precipitate-dislocation interaction and hetero-deformation-induced stress(HDI stress)*** study suggests that the challenge of balancing properties and cost can be addressed through optimized compositional and mi-crostructural design.

关键词： High-entropy alloys Precipitation Heterogeneous microstructure Mechanical property HDI stress

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Regulation of cryogenic mechanical behaviors of C-added non-equiatomic CoCrFeNiMo ferrous medium-entropy alloy via control of initial microstructure

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材料科学技术（英文版） 2025年第5期208卷 141-151页

作者： Ji Yeong Lee Hyeonseok Kwon Jae Heung Lee Jihye Kwon Jaemin Wang Jae Wung Bae Jongun Moon Byeong-Joo Lee Yoon-Uk Heo Hyoung Seop Kim Department of Materials Science and Engineering Pohang University of Science and Technology(POSTECH)Pohang37673Republic of Korea Department of Metallurgical Engineering Pukyong National UniversityBusan 48513Republic of Korea Division of Advanced Materials Engineering Center for Advanced Powder Materials and PartsKongju National UniversityCheonanChungnam31080Republic of Korea Graduate Institute of Ferrous and Eco Materials Technology Pohang University of Science and Technology77 Cheongam-RoNam-GuPohang 37673Republic of Korea Department of Materials Science and Engineering Pohang University of Science and Technology(POSTECH)Pohang37673Republic of Korea Graduate Institute of Ferrous and Eco Materials Technology Pohang University of Science and Technology77 Cheongam-RoNam-GuPohang 37673Republic of Korea Advanced Institute for Materials Research(WPI-AIMR) Tohoku UniversitySendai980-8577Japan Institute for Convergence Research and Education in Advanced Technology Yonsei UniversitySeoul03722Republic of Korea

This study demonstrated the potential for customizing the desired properties of the Co18.5Cr12Fe55Ni9Mo3.5C2(at.％)ferrous medium-entropy alloy by manipulating the deformation-induced martensite transformation(DIMT)behavior at liquid nitrogen *** was achieved by modify-ing various initial microstructures through annealing at temperatures ranging from 900 to 1200 ℃.The variations in DIMT kinetics were analyzed based on two main factors.(1)Inducing carbide precipitation by annealing at 900 and 1000 ℃ results in changes in the composition within the matrix,which may affect the stability of the face-centered cubic *** with a higher volume fraction of the carbide precipitates exhibit lower ΔGFCC→BCC and faster DIMT kinetics.(2)The onset and kinetics of DIMT are also affected by the use of martensite nucleation sites,which may vary depending on the presence of non-recrystallized regions or the grain *** fine-grained structures,martensite primarily nucleated in the non-recrystallized regions and grain ***,in coarse-grained microstructures,martensite mainly nucleated along the in-grain shear bands and their *** precise control of the microstructure results in superior *** samples annealed at 900 and 1000 ℃ with carbide precipitates and fine grains exhibit ultrahigh ultimate tensile strength,which may reach elevated values up to～1.8 GPa,while those annealed at 1100 and 1200 ℃ with larger grains and no precipitates exhibit a uniform elongation that exceeds 100％.

关键词： Ferrous medium-entropy alloy Deformation-induced martensitic transformation Microstructures Phase stability Precipitation

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Direct high-resolution X-ray imaging exploiting pseudorandomness

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Light(science & Applications) 2023年第5期12卷 776-788页

作者： KyeoReh Lee Jun Lim Su Yong Lee YongKeun Park Department of Physics Korea Advanced Institute of Science and TechnologyDaejeon 34141Republic of Korea KAIST Institute for Health Science and Technology Korea Advanced Institute of Science and TechnologyDaejeon 34141Republic of Korea Pohang Accelerator Laboratory Pohang University of Science and TechnologyPohangKyungbuk 37637Republic of Korea Tomocube Inc Daejeon 34051Republic of Korea

Owing to its unique penetrating power and high-resolution capability,X-ray imaging has been an irreplaceable tool since its *** the significance,the resolution of X-ray imaging has largely been limited by the technical difficulties on X-ray lens *** lensless imaging methods have been proposed,but are yet relying on multiple measurements or additional constraints on measurements or *** we present coherent specklecorrelation imaging(CSI)using a designed X-ray *** has no prerequisites for samples or ***,from a single shot measurement,the complex sample field is retrieved based on the pseudorandomness of the speckle intensity pattern,ensured through a *** achieve a spatial resolution of 13.9 nm at 5.46 keV,beating the feature size of the diffuser used(300 nm).The high-resolution imaging capability is theoretically explained based on fundamental and practical *** expect the CSI to be a versatile tool for navigating the unexplored world of nanometer.

关键词： resolution speckle replace

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Discriminating circular polarization of light:Left or right?

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Light(science & Applications) 2025年第1期14卷 20-22页

作者： Wanhee Lee Changsoon Cho Department of Material Science and Engineering Pohang University of Science and Technology(POSTECH)PohangRepublic of Korea Institute for Convergence Research and Education in Advanced Technology Yonsei UniversitySeoulRepublic of Korea

Achiral dielectric nanostructures provide an efficient method for discriminating left-and right-circularly polarized photons,leveraging the photothermoelectric effect.

关键词： effect circular dielectric

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