National NanoFab Center

Introduction: Crowd crush is a type of disaster that continues to occur around the world, and some of these disasters have a devastating impact on society. Despite the high number of human casualties, there is no single solution, which is why a multidisciplinary approach is required rather than a single solution. Therefore, it is necessary to apply a scientific academic approach to understand crowd crush, but there is confusion on the terms and definitions underlying it. In this study, we aimed to derive appropriate conceptual definitions and terminology for crowd crush through a survey of experts. Methods: Experts were selected by discipline to conduct the expert survey. The experts were selected from the fields of safety and security management, engineering, medicine and health, sociology, and psychology, and a total of 25 experts were selected for in-depth interviews. The experts were selected based on their research, teaching, and consulting activities related to crowd crush, and only those with relevant interests and knowledge were included through preliminary interviews. Results: In some cases, experts expressed the same concept in different terms, and this was more pronounced when the experts came from different disciplines. This is likely due to applying the terminology used in their academic fields to crowd crush, which can be confusing if different terms are used. While most of the concepts and definitions were consistent, some terms needed to be reorganized to fit the context of crowd crush. Conclusion: There is some confusion about the concepts and terminology of crowd crush, even among experts. So a committee is needed to further clarify the concepts and terminology in order to develop standards of prevention, preparedness, and response in the crowd crush situation. This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korean government (MSIT) (No. NRF-2023R1A2C1002938).

We present a compact quantum gravimeter based on a grating magneto-optical trap using 87Rb atoms that achieves μGal-level long-term stability without passive vibration isolation. The sensor head integrates magnetic shielding, an ion pump, optical components, and a classical seismometer within a total volume of less than 75L. The gravimeter achieves a sensitivity of 270 μGal/Hz and a stability of 5 μGal at a 1-h average with the long-term gravity record in good agreement with the theoretical tidal model. These results demonstrate a field-deployable platform for portable and chip-integrable quantum gravimetry.

Von Neumann bottleneck in traditional computational architecture has spurred interest in neuromorphic computing, which integrates processing and memory in a single element for efficient data handling. Among neuromorphic hardware devices, oxide-based resistive random-access memory (RRAM) has gained attention due to its non-volatile nature, simple structure, low power consumption, and CMOS compatibility. Additionally, in RRAM, single-layer structures have limited control over conductive filament (CF) behavior, whereas bi-layer structures enhance switching characteristics through interfacial engineering, and tri-layer structures further improve reliability and analog synaptic performance by precisely controlling oxygen vacancy (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V_O</i>) distribution. In this study, we fabricated bi-layer (Pd/ZrO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>/HfO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>/Pd) and tri-layer (Pd/ZrO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>/ZnO/HfO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>/Pd) synaptic devices to investigate the impact of structural design on resistive switching (RS) and neuromorphic performance. Insertion of ZnO, known for its high <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V_O</i> concentration, into the tri-layer structure enhanced CF formation and rupture dynamics, resulting in improved RS behavior. The tri-layer device exhibited superior endurance, reduced variability, lower SET/RESET voltages, and more linear long-term potentiation (LTP) and long-term depression (LTD) characteristics compared to the bi-layer counterpart. These results demonstrate that tri-layer oxide structures incorporating vacancy-rich materials are promising for stable, low-power, and high-performance neuromorphic systems.

Abstract Ensuring secure and energy‐efficient authentication of resource‐constrained devices has become a critical challenge owing to the rapid expansion of the Internet of Things (IoT) ecosystem. Physically unclonable functions (PUFs) that exploit inherent manufacturing variations to generate device‐unique keys have emerged as a promising hardware‐based security primitive. In this study, a PUF architecture is proposed that utilizes multi‐level programming of flash memory capacitors. Reliable and reproducible binary responses are generated across multiple programmed states by extracting flat‐band voltage variations from capacitance–voltage measurements. Performance is evaluated using the uniformity, P ‐value, inter‐Hamming distance, and intra‐Hamming distance, which indicated strong randomness, uniqueness, and stability. To further enhance the entropy and cryptographic strength, a hash‐based message authentication code (HMAC)‐based key derivation function is integrated, which transformed the PUF outputs into high‐entropy pseudorandom keys. The final architecture supported key generation with zero standby power and is compatible with commercially available memory structures, thereby enabling low‐cost and scalable deployment in secure IoT systems. These results highlight the potential of multi‐level memory‐based PUFs as a lightweight and robust solution for next‐generation hardware security.

Abstract Practical optoelectronic application of 2D Pt dichalcogenides faces two crucial challenges: establishing a reliable synthetic route and developing a pertinent patterning technique. A streamlined strategy is proposed for site‐specific and size‐tunable synthesis of Pt dichalcogenides, achieved by pre‐defining of Pt templates via focused ion beam (FIB) combined with selenization or tellurization without requiring lithography processes. The synthetic conditions are optimized by altering reaction temperature, time, and thickness of Pt templates, as verified by comprehensive spectro‐microscopic analysis. The universal applicability of streamlined site‐specific synthesis for Pt dichalcogenides is ascertained, highlighting its potential for visible and NIR photodetection. The PtSe 2 ‐based photodetector exhibits maximized photocurrents of 134 µA at 532 nm and 178 µA at 980 nm, whereas the PtTe 2 ‐based device demonstrates enhanced values of 231 and 382 µA at the respective wavelengths. This approach corroborates an innovative route to resolve prerequisites associated with establishing a reliable synthetic route and developing a pertinent patterning technique.

Efficient extracellular electron transfer (EET) is critical to harnessing bacteria like Shewanella oneidensis MR-1 in microbial electrochemical systems (MESs) aimed at sustainable energy production, environmental remediation, and resource recovery. This study investigates how palladium ions (Pd2+), which are of significant interest for catalysis and resource recovery, impact the bioelectrocatalysis of S. oneidensis MR-1 using electrochemical, transcriptomic, and microscopic methods. Pd2+ exposure significantly increased the observed current via EET, which correlated with substantially increased viable biofilm formation on the electrode. Transcriptomics revealed a coordinated cellular response, including upregulation of genes facilitating EET (the Mtr pathway), metabolism, motility, and biofilm processes, alongside downregulation of competing pathways. Cellular reduction of Pd2+ to palladium nanoparticles, mainly near the outer membrane, was confirmed via microscopy. Pd2+ boosts S. oneidensis MR-1 bioelectrocatalysis through the combined effects of promoting biofilm development and upregulating essential cellular pathways, informing fundamental strategies for enhanced MESs targeted for sustainable engineering, bioremediation, and resource and material recovery applications.

ABSTRACTMultiscale imaging and spectroscopy play a pivotal role in understanding the structural, chemical, and dynamic behavior of battery materials, providing critical insights that drive advancements in performance, longevity, and safety. This review provides a comprehensive analysis of various imaging techniques, from macroscopic tools like x‐ray tomography to nanoscale methods such as atomic force microscopy and transmission electron microscopy. By categorizing these techniques based on spatial resolution, the review highlights their applications in resolving key issues like electrode degradation, dendrite formation, and phase transitions during battery operation. Moreover, the integration of machine learning accelerates data processing, enabling multiscale correlations and predictive modeling. The review underscores the necessity of multiscale approaches to optimize battery performance, safety, and lifespan, showcasing how emerging methodologies contribute to next‐generation energy storage technologies. image

Abstract Wearable sensor technology has garnered significant attention due to its considerable potential in personal healthcare and medical care. Various biomarkers present in human sweat, tears, and saliva can provide insights into an individual’s physiological state. However, the small volume of these noninvasive fluids poses challenges for the reliability and stability of sensor measurements. Efficient collection of body fluids and the use of nanostructured sensor electrodes is crucial for accurate detection. In this study, a cross-linked polyaniline network was synthesized directly onto highly ordered Au nanopillars. A potentiometric Ca2+ sensor was then fabricated using an as-synthesized nanoscale electrode, which was integrated into a microfluidic channel. The sensor exhibited a theoretical Nernst response (∼28.32 mV log−1[Ca2+]), a rapid response time (approximately &lt;0.1 s), excellent repeatability, and high selectivity (all K POT values &lt; 10−3). The microfluidic-integrated sensor exhibited good sensitivity for small samples of &lt; 10 μl. Furthermore, an on-body wearable sensor test was performed to monitor real-time Ca2+ dynamics in human sweat during physical activity.

The collective behavior of colloids in microsystems is characterized by precise micro-object control, broadening the applications of cargo manipulation in drug delivery, microfluidics, and nanotechnology. To further investigate this potential, we introduce a cargo-manipulating platform that utilizes micromagnetic patterns and fluid flow rather than conventional fluidic components. This platform, called the flowless micropump, comprises an encapsulating fluid system within a chip, containing both actuation particles (2.8 μm in diameter) and control targets, thereby eliminating external interactions. This platform enables two distinct modes of cargo manipulation: direct control of nonmagnetic cargo (e.g., MCF-7 and THP-1 cells) and indirect manipulation of particles (e.g., polymer particles) through secondary localized fluid flow. Direct manipulation is achieved via coordinated particle collisions, facilitated by an optimized guiding wall with a height of 25 μm. Conversely, indirect manipulation allows for high-speed control and mode change of individual targets. These manipulation events are achieved using two patterned structures: railway-track and connected half-disk (conductor) patterns. By employing a conductor pattern in conjunction with a railway-track pattern, precise and agile control of microcargo (MCF-7 and THP-1 cells and polymer bead clusters) was achieved at frequencies of 1-3 Hz and a magnetic field strength of 10 mT. This study establishes a programmable platform for designing flowless micropumps with diverse functionalities for various experimental purposes. By using colloidal flow and localized fluid flow generated by the shape of magnetic patterns and semi-three-dimensional (3D) structures, this platform holds significant promise for applications in drug screening, cell-cell interaction studies, and organoid-on-chip research.