Cheolmin Park

Magnetic actuation is a powerful strategy in robotics for tactile feedback, navigation, and biomedical applications and can be extended to interactive displays by coupling mechanical motion with optical emission. Here, we present a magnetically‐gated haptic locomotion display (MHLD) that integrates a flexible alternating‐current (AC)‐driven quantum‐dot light‐emitting diode (QLED) with a magnetoresponsive elastomeric soft actuator. Under external magnetic fields, the soft actuator deforms and modulates its contact with the AC display, triggering electroluminescence (EL) whose emission area and intensity are directly coupled to mechanical displacement. A maximum luminance of 396 cd m ^{– 2} was achieved, with emission area and intensity varying with deformation. The device maintains stable output under repeated actuation, with directional motion programmable via magnetization profiles. Demonstrations include a 3 × 3 haptic feedback array visualizing pixel displacement and a maze‐navigating locomotive display with path‐dependent emission. Finite element simulations support the contact‐mediated formation of the vertical electric field underlying motion‐coupled light emission.

To address interfacial friction losses associated with physical contact separation in triboelectric nanogenerators (TENGs), noncontact or liquid‐solid‐contact TENGs have recently been developed. However, the limited performance of noncontact TENGs has hindered their further advancement. This study proposed a large‐area deformable high‐entropy ceramic (HEC)‐enhanced noncontact TENG (HEC‐TENG) by integrating an HEC‐doped silicone triboelectric layer with a charge‐storage graphitic textile and a stretchable carbon black electrode. This strategy establishes a comprehensive tribo‐charge regulation mechanism, including charge generation, capture, transport, and retention, resulting in a noncontact output of 90 V and 450 µA m ⁻² at a separation distance of 1 mm, while maintaining a stretchability exceeding 230%. Notably, by leveraging the synergistic effects of HEC doping and the trilayer composite configuration, the HEC‐TENG achieved a maximum voltage of 466 V for droplet‐based energy harvesting. Furthermore, wearable power sources and large‐area rainwater‐harvesting systems enabled by HEC‐TENGs were demonstrated. Overall, this work validates the universal enhancement effect of HECs when employed as triboelectric layers in both noncontact and liquid‐solid contact TENGs, establishing a representative paradigm for the development of wearable HEC‐based TENGs. These findings provide new insights into future wearable self‐powered electronics and distributed energy‐harvesting systems.

Ambient humidity represents a ubiquitous and renewable energy source for next‐generation moisture‐driven energy harvesting, yet achieving stable and long‐term output remains a formidable challenge for practical use in wearable electronics and environmental sensing. Here, we report a high‐performance moisture‐driven energy generator (MEG) that exploits a gradient bilayer electrospun membrane to realize directional moisture transport, resulting in efficient and long‐term stable electricity generation. The device integrates two polyacrylonitrile/sulfonated polyaniline (PAN/S‑PANI) nanofiber layers with different porous structure, an electrostatic‐flocked carbon cloth electrode, and an aluminum electrode. Fixed anionic sites in S‑PANI facilitate cation (e.g., Li ⁺ , H ⁺ ) transport while suppressing anion (Cl ⁻ ) migration, whereas the flocked electrodes promote enhanced water evaporation and directional moisture transport. Benefiting from the rational design, the MEG delivers an output of up to 1.1 V and 3.3 mA ^. cm ⁻² under 45°C and >80% relative humidity, representing state‐of‐the‐art performance. Remarkably, after being stored for 180 days, the device still maintained an output voltage of ∼0.7 V and a current above 450 µA, which was sufficient to power calculators and smartwatches. This work offers a promising pathway toward durable, self‐powered, and flexible energy systems.

Integrating tactile sensing, neuromorphic processing, and visual emission within a single device is essential for next-generation intelligent interfaces. Although tactile neuromorphic displays have advanced significantly, further advances in brightness, stable continuous emission, and gate-tunable optical modulation would substantially broaden their applicability. Here, we present a tactile neuromorphic ion-gated vertical transistor display (TN-VTD) that integrates pressure sensing, ion-mediated synaptic plasticity, and electroluminescence within a compact vertical structure. Mechanical deformation of a hemispherical elastomeric gate modulates ion penetration through a permeable nanoporous Al electrode, inducing pressure-dependent n-type doping and band bending within the Super Yellow emissive layer. This ion-coupled design enables continuous and stable DC emission (∼46 cd m^–2 at V_DS = 3 V) for over 24 h and strong gate-enhanced brightness (∼427 cd m^–2 at V_G = 9 V), with the emissive area expanding proportionally with applied pressure. Pressure-dependent ionic accumulation further tunes synaptic relaxation time, generating nonlinear fading-memory electrical and optical responses that evolve along distinct temporal dynamics. From a single input, concurrent conductance and brightness outputs provide complementary state variables that expand the reservoir state dimensionality beyond single-observable operations. Leveraging this multidimensional state encoding, TN-VTD achieves 93.5% spoken-digit classification accuracy, substantially outperforming conductance-only operation (82.3%). These results establish TN-VTD as a unified platform capable of simultaneous sensing, neuromorphic processing, and visual output.

With the significant development of technologies based on dielectrophoretic or acoustophoretic forces, the dynamic visualization of these forces is important. Here, we present an electroluminescent display that enables comparative visualization of dielectrophoretic and acoustophoretic forces. Our display utilizes alternating current-driven electroluminescence in combination with conductive microparticle self-assembly controlled by dielectrophoretic and acoustophoretic forces. When an alternating current electric field is applied across the split-electrode configuration, the self-assembly of the conductive microparticles originating from the dielectrophoretic force generates a dielectrophoresis-dependent electroluminescence from the display. Alternatively, when an acoustic wave is transmitted to the display, the electroluminescence developed by dielectrophoresis is deactivated by acoustophoresis. The electroluminescent responses are modulated by the frequency and intensity of the dielectrophoretic and acoustophoretic forces, which enable force-sensitive visualization across both regimes and thereby a rewritable dual-mode sensing display. With this versatile display, visualization of temperature changes, noninvasive monitoring of microfluidic channels, and dynamic motion tracking are demonstrated. Our dual-mode electroluminescent display, responsive to forces across the piconewton to nanonewton range, holds significant potential for various applications in biomedical and physical sensing systems involving dielectrophoretic and acoustophoretic stimuli.

Hydrovoltaic energy generation (HEG) offers a sustainable route for converting water–solid interactions into electricity; however, guidance tailored to cellulose-based systems remains fragmented. This review provides a comprehensive overview of cellulose-based HEG across the four principal device classes—moisture, evaporation, osmotic, and droplet-induced electricity generators. Further, the review clarifies the role of the structural hierarchy of cellulose, its surface chemistry, and its hydration behavior in electrohydrodynamic transport and device-level performance. Beyond summarizing the prior work, we present system-level benchmarking through a consolidated performance table. The table explicitly links the material composition and device architecture with power output, robustness, and representative application scenarios such as power sources, self-powered sensors, and environmental monitoring, thereby offering actionable design guidelines. We further systematically discuss the chemical principles underlying cellulose-enabled HEG, including interfacial charge regulation, electric double-layer formation and overlap, and Donnan and ion-exchange effects, establishing a coherent theoretical basis for optimizing the voltage, current density, power density, and long-term stability. This mechanism-guided perspective connects the design of cellulose materials to the functional performances of moisture, evaporation, osmotic, and droplet systems. Additionally, it outlines practical directions for the sustainable sourcing, standardized testing, and scalable fabrication of efficient and environmentally friendly hydrovoltaic technologies.

Multimodal photonic information systems are redefining the landscape of data storage and encryption by harnessing a diverse range of optical channels and stimuli-responsive materials. Within these interactive photonic platforms, information can be encoded not only through spatial patterns but also across wavelength (color), intensity, polarization, phase, and temporal domains, significantly enhancing storage density and security. This review provides a comprehensive overview of the current state of multimodal photonic encryption and data storage with particular emphasis on the chemistry of advanced luminescent and nanostructured materials and the device physics underlying their unique optical behaviors. We delve into fundamental photonic encoding strategies, ranging from structural color and metasurface holography to fluorescence/phosphorescence and electroluminescence, and discuss how multiple emission pathways can be coupled within single platforms. Various external stimuli (optical, electrical, magnetic, thermal, mechanical, and chemical) used to activate or unlock photonic signals are examined, highlighting designs in which specific stimuli act as secure cryptographic keys. We then review strategies for engineering multimodal photonic platforms, including the integration of orthogonal emission channels, spatial and temporal multiplexing, and device architectures (thin films, fibers, metasurfaces, and multilayers) that support complex hierarchical encoding. Mechanisms of photonic encryption are discussed, distinguishing static from dynamic approaches and detailing how stimuli-responsive modulation, time-gated luminescence lifetimes, and logical multistep unlocking schemes enhance security beyond conventional optical tags. Finally, application-oriented sections illustrate how these advances are being translated into real-world security architectures, ranging from anticounterfeiting labels, encrypted displays, and wearables to secure QR codes and optical memory elements for neuromorphic computing.

Hydrovoltaic electricity generators (HEGs) have emerged as a class of distinctive green energy harvesters that convert the energy of ubiquitous water, including moisture and liquid water, into electricity through water-induced interfacial processes at solid-gas and solid-liquid interfaces. While early studies primarily focused on empirical material screening, recent advances have increasingly demonstrated that HEG performance is governed by the coupled interplay between interfacial chemistry and architectural design. Chemically, proton dissociation, surface charge regulation, ion-solvation dynamics, and electric double layer formation govern charge separation and transport at molecular scale. Architecturally, hierarchical and deliberately engineered structures, including pore design, asymmetric configurations, and multilayer coupling, can be implemented across one- to three-dimensional device formats, thereby dictating water distribution, ion diffusion, and mechanical integrity. This review establishes a unified chemical-architectural framework that correlates interfacial molecular processes with device-level architectures and macroscopic electrical outputs. We categorize representative HEG systems according to their structural motifs while elucidating the governing physicochemical mechanisms that drive energy conversion. Building on this foundation, we identify key design principles and functional objectives toward high-output, durable, and multifunctional HEGs. Finally, we outline future directions emphasizing synergistic chemical control and architectural innovation to realizing intelligent, sustainable, and scalable hydrovoltaic energy systems.

We report geometry-controlled organic ferroelectric field-effect transistors (FeFETs) that combine patterned poly(vinylidene fluoride–trifluoroethylene) (PVDF–TrFE) ferroelectric lines with selectively grown single-crystalline 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-PEN) channels. The patterned PVDF–TrFE layers, fabricated via soft-lithography-assisted floating-transfer printing followed by melt-quenching and annealing, exhibit well-oriented β-phase crystallinity with stable polarization. Solvent-directed deposition of TIPS-PEN using a toluene/dodecane cosolvent enables anisotropic, ribbon-shaped single crystals precisely aligned along the ferroelectric geometry. The structural confinement of ferroelectric domains and the single-crystal semiconductor channel act synergistically to yield well-defined polarization hysteresis, higher ON current, and suppressed gate leakage. Surface-energy-guided growth studies on self-assembled monolayer-modified and topographic substrates reveal that selective nucleation occurs when the substrate surface energy matches or exceeds the solvent surface tension. These findings demonstrate a simple, low-temperature, and scalable approach for realizing geometry-controlled FeFETs with enhanced characteristics through the integration of ferroelectric domain alignment and single-crystal transport.