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Creators/Authors contains: "Ahn, Jong-Hyun"

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  1. Abstract Skin‐like robust materials with prominent sensing performance have potential applications in flexible bioelectronics. However, it remains challenging to achieve mutually exclusive properties simultaneously including low interfacial impedance, high stretchability, sensitivity, and electrical resilience. Herein, a material and structure design concept of mixed ion‐electron conduction and mechanical interlocking structure is adopted to fabricate high‐performance mechanical‐bioelectrical dual‐modal composites with large stretchability, excellent mechanoelectrical stability, low interfacial impedance, and good biocompatibility. Flower‐like conductive metal‐organic frameworks (cMOFs) with enhanced conductivity through the overlapped level of metal‐ligand orbital are assembled, which bridge carbon nanotubes (denoted as cMOFs‐b‐CNTs). Then, precursor of poly(styrene‐block‐butadiene‐block‐styrene)/ionic liquid penetrates the pores and cavities in cMOFs‐b‐CNTs‐based network fabricated via filtration process, creating a semi‐embedded structure via mechanical interlocking. Thus, the mixed ion‐electron conduction and semi‐embedded structure endow the as‐prepared composites with a low interfacial impedance (51.60/28.90 kΩ at 10/100 Hz), wide sensing range (473%), high sensitivity (2195.29), rapid response/recovery time (60/85 ms), low limit of detection (0.05%), and excellent durability (>5000 cycles to 50% strain). Demonstrations of multifunctional mechanical‐bioelectrical dual‐modal sensors for in vivo/vitro monitoring physiological motions, electrophysiological activities, and urinary bladder activities validate the possibility for practical uses in biomedical research areas. This concept creates opportunities for the construction of durable skin‐like sensing materials. 
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    Free, publicly-accessible full text available August 1, 2026
  2. Electrostatic capacitors are foundational components of advanced electronics and high-power electrical systems owing to their ultrafast charging-discharging capability. Ferroelectric materials offer high maximum polarization, but high remnant polarization has hindered their effective deployment in energy storage applications. Previous methodologies have encountered problems because of the deteriorated crystallinity of the ferroelectric materials. We introduce an approach to control the relaxation time using two-dimensional (2D) materials while minimizing energy loss by using 2D/3D/2D heterostructures and preserving the crystallinity of ferroelectric 3D materials. Using this approach, we were able to achieve an energy density of 191.7 joules per cubic centimeter with an efficiency greater than 90%. This precise control over relaxation time holds promise for a wide array of applications and has the potential to accelerate the development of highly efficient energy storage systems. 
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  3. Abstract Freestanding single‐crystalline nanomembranes have gained increasing attention as promising platforms for both fundamental research and advanced electronic applications. However, internal stress gradients arising from epitaxial strain within the oxide membranes often result in high crack density during fabrication, leading to unsatisfactory yield and limited reliability. Here, an elastically graded polymer (EGP) support that enables wafer‐scale crack‐free transfer of single‐crystalline oxide membranes are developed. The engineered elastic gradient within the EGP accommodates the internal strain of the oxide membrane, effectively minimizing crack formation during lift‐off. Notably, this ability to spatially control the interfacial stiffness between the polymer and the oxide film enables crack suppression under both tensile and compressive strain. This approach provides a robust and scalable route to producing high‐quality freestanding oxide membranes, paving the way not only for their integration into novel device architecture but also opening new avenues for scientific exploration of functional systems. 
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  4. Although flakes of two-dimensional (2D) heterostructures at the micrometer scale can be formed with adhesive-tape exfoliation methods, isolation of 2D flakes into monolayers is extremely time consuming because it is a trial-and-error process. Controlling the number of 2D layers through direct growth also presents difficulty because of the high nucleation barrier on 2D materials. We demonstrate a layer-resolved 2D material splitting technique that permits high-throughput production of multiple monolayers of wafer-scale (5-centimeter diameter) 2D materials by splitting single stacks of thick 2D materials grown on a single wafer. Wafer-scale uniformity of hexagonal boron nitride, tungsten disulfide, tungsten diselenide, molybdenum disulfide, and molybdenum diselenide monolayers was verified by photoluminescence response and by substantial retention of electronic conductivity. We fabricated wafer-scale van der Waals heterostructures, including field-effect transistors, with single-atom thickness resolution. 
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