Structural coloration via photonic crystals (PCs) offers a promising alternative to conventional pigment-based color generation. However, existing electrochromic technologies suffer from slow response and limited color tunability. Herein, we propose a low-voltage dielectric elastomer (DE) actuator integrated with two-dimensional (2D) SiO2 microsphere arrays to achieve rapid and reversible structural coloration. By introducing annular interdigital electrodes (A-IDT), the device generates in-plane Maxwell stress under sub-120V driving voltages, inducing uniform deformation of the DE film and dynamically tuning the lattice spacing of the SiO2 microsphere arrays. COMSOL simulations reveal that the optimized A-IDT configuration reduces the electric field distance, enabling a high strain energy density (906.49 J/m-3), significant uniform deformation (uplift deformation:1.38 mm, area stretching rate:7.81%), and ultrafast response (coloration time:1.2 ms, recovery time:2 ms). The structural coloration spans a broad wavelength range (473.3-567.1 nm), covering cyan to light blue. Mechanistic analysis demonstrates that the A-IDT design enhances electro-deformation efficiency by concentrating Maxwell stress parallel to the film surface, thereby avoiding localized breakdown and enabling low-voltage operation. This work pioneers a scalable strategy for voltage-tunable structural coloration, with transformative potential in flexible displays, adaptive camouflage, and multifunctional optical sensors.

AlN-based ternary nitride thin films are promising for radio-frequency (RF) devices, power electronics, and thermal barrier coatings due to their tunable properties, where thermal conductivity (k) critically impacts performance. Here, we establish rational design principles for achieving ultralow k by investigating epitaxial thin films of novel YbxAl1-xN alongside classic ScxAl1-xN alloys from RF sputtering, where dramatic Yb-Al ionic mismatch creates significant structural perturbation within the wurtzite lattice. Frequency-domain thermoreflectance measurements reveal unprecedented k reduction through Yb alloying (0.184 <= x <= 0.538): from 320 W/(m center dot K) in pristine AlN to 0.98 W/(m center dot K) at x = 0.491, merely 10% above the amorphous limit of AlN and 18% above measured glassy Yb0.538Al0.462N , while Sc-alloying reduces k to 3.03 W/(m center dot K) (x = 0.359), at room temperature. Both systems exhibit monotonic k increase with temperature (100-500 K), defying conventional Debye-Callaway predictions. To elucidate mechanisms, we combine machine-learning-based molecular dynamics with quasi-harmonic Green-Kubo analysis and achieve excellent agreement with experiments. We reveal that low-frequency thermal diffusivity remains anomalously constant with Yb concentration due to unusual invariance of generalized group velocities for heat-carrying vibrational modes below 5 THz, which opposes conventional alloying expectations. This work provides predictive insights for engineering crystalline materials with amorphous-like k, establishing YbxAl1-xN as a scalable platform for thermal-barrier applications while guiding thermal management in electronics.

The transient Pauli blocking effect offers a promising route for achieving ultrafast optical switching in semiconductors, enabling a rapid switching from an initially opaque state to a relatively transparent state upon photoexcitation. Herein, we demonstrate broadband ultrafast optical switching in degenerate InN thin films, spanning the visible to near-infrared spectral range, using pump-probe transient transmittance measurements. To elucidate the underlying physical mechanism, we perform probe-energy-resolved analysis for ultrafast dynamics, and we develop a theoretical model based on a quasiequilibrium Fermi-Dirac distribution. The model successfully captures the experimental transients and yields an electron-phonon coupling constant of 1.0 x 1017W/m3 K, along with an electronic specific-heat coefficient ranging from 1.52 to 2.02 mJ/mol K2, which allows direct prediction of the spectral switching window. Notably, we demonstrate that the Pauli blocking effect can be induced solely by a laser-excitation-driven rise in electronic temperature, without requiring significant carrier injection into the conduction band in degenerate semiconductors. These findings offer new insights for designing ultrafast optical modulators, shutters, and photonic devices for next-generation communication and computing technologies.

Traditional metal and n-type doped semiconductor materials serve as emerging epsilon-near-zero (ENZ) materials, showcasing great potential for nonlinear photonic applications. However, a significant limitation for such materials is the lack of versatile ENZ wavelength tuning, and thus dynamic tuning of the ENZ wavelength remains a technical challenge, thereby restricting their potential applications, such as multi-band communications. Here, dynamic tuning of the ENZ wavelength in p-type organic PEDOT: PSS films is achieved through a reversible change in hole concentrations originating from the polaron formation/decoupling following optical excitation, and a tunable ENZ wavelength shift up to 150 nm is observed. Experimental investigations about ultrafast dynamics of polaron excitation reveal a ∼80 fs time constant for polaron buildup and a ∼280 fs time constant for polaron decoupling, indicating the reversible ultrafast switching for the ENZ wavelength within subpicosecond time scale. These findings suggest that p-type organic semiconductors can serve as what is believed to be a novel platform for dynamically tuning the ENZ wavelength through polaron excitation, opening what we feel are new possibilities for ENZ-based nonlinear optical applications in flexible optoelectronics.

We report effective control of the metal–to–insulator transition (MIT) temperature in polycrystalline VO2 thin films grown on flexible μ–sheet glass substrate by applying uniaxial compressive stress during deposition. The MIT temperature decreases from 334.5 K to 328.0 K, 324.5 K, and 321.5 K under applied compressive stresses of 0.11, 0.13 and 0.18 GPa, respectively, corresponding to an average stress sensitivity of approximately 0.07 K/MPa, which is attributed to weakened Peierls–type dimerization. This exceptionally high sensitivity demonstrates that even MPa-level stresses, achievable by bending the supporting substrate, are sufficient to tune the transition temperature. Our findings provide a practical route for engineering the MIT in VO2 through ultralow–strain engineering, thereby enabling industrial applications such as flexible thermochromic devices.

Thermochromic VO2 films were successfully deposited on alkali-free glass substrates with high reproducibility by reactive DC magnetron sputtering using a V-metal target in the "transition region" equipped with the specially designed impedance-feedback control system. Slightly off-stoichiometric VO2 films were individually fabricated within the transition region, and their transition temperatures varied systematically with film stoichiometry. The highest resistivity ratio across the metal-insulator transition exceeded 103. Residual stress in these off-stoichiometric VO2 films was evaluated using the X-ray diffraction sin2 psi method. The results show that the transition temperature increases with higher oxidation states of VO2, and that larger tensile residual stress also leads to an increase in the transition temperature.

The performance of a semiconductor device crucially depends on the carrier concentration of the semiconducting material. The hole concentration is governed by the density of states (DOS) and the Fermi–Dirac distribution, indicating the importance of the DOS in the top region of the valence band. Herein, the DOS of the valence band top region of nondoped and nitrogen‐doped Cu 2 O films using UV photoelectron spectroscopy and constant‐final‐state yield spectroscopy is measured. The obtained DOS varies over six orders of magnitude from the valence band to the Fermi level. Judging from the DOS and the hole density observed from the Hall effect measurements, the valence band maximum (VBM) in the DOS distribution is then determined. The traditional method of determining the VBM by linear extrapolation of the onset region cannot reproduce the hole density; instead, the calculation requires the weak DOS of the in‐gap states above the traditional VBM up to the Fermi level. The wave function difference between the valence states and in‐gap states, observed using constant‐initial‐state yield spectroscopy, suggests that the traditional VBM is close to the border at which the wave function switches from conducting valence states to trap‐like in‐gap states.

This study investigates the effects of nitrogen doping on the structural, optical, and electrical properties of Cu2O and N-doped Cu2O films deposited by RF magnetron sputtering using Cu or Cu2O targets under varying nitrogen flow conditions. X-ray diffraction and transmission electron microscopy analyses reveal that nitrogen doping alters the polycrystalline orientation, particularly the (111) planes. The stability of the Cu2O phase across all the doping is confirmed by Raman spectroscopy. Optical bandgap estimates using Tauc's plots that shows approximate to 2.5 eV, implying that the doping does not significantly affect the band structure of Cu2O. Electrical properties of Cu2O and N-doped Cu2O demonstrate that the nitrogen doping increases hole density while reducing Hall mobility, with the effect being more pronounced in the films deposited using the Cu target. Device properties indicate a correlation between polycrystalline orientation and leakage current, with better control of orientation and lower leakage current observed in films deposited using the Cu2O target. Reverse voltage of N-doped Cu2O Films (N-2 = 1%) using Cu2O target shows 1024 V, where the strong preferred orientation of <111> is clearly observed. These findings provide valuable insights into optimizing nitrogen-doped Cu2O films for improved performance in electronic applications.

Multicolored optical switching phenomena are crucial for a broad range of applications, such as telecommunications and optical computing. However, most materials typically exhibit single-colored optical nonlinearity under intense laser illumination. Herein, our femtosecond time-resolved transient transmission measurements reveal the coexistence of the transient Pauli blocking effect in both the P and L valleys following intense optical excitation in Ge films, demonstrating their feasibility as multicolored optical switching materials based on multivalley scattering. Additionally, a split-off energy of 240 meV at the L point, attributed to the spin-orbit coupling effect, is directly observed from time-resolved transient transmission spectra. Based on an accurately calculated band structure, a scheme has been developed to interpret pump-probe transient transmission traces, effectively avoiding overinterpretation of overlapping transient signals caused by multiple-transition pathways. Furthermore, analysis of transmission transients using a three-level model indicates that the intervalley scattering time between the P and L valleys is within 196 fs, and the intravalley scattering time is within 1.10 ps in the P valley, highlighting the potential for achieving an ultrafast multicolored optical switching device for key applications in multiband communications and optical computing.

This paper utilizes an improved intercalation exfoliation and liquid-phase coating approach to effectively fabricate two-dimensional molybdenum disulfide van der Waals thin films on silk fibroin/polyvinyl alcohol substrate (MoS2@SF/PVA), which are then integrated into highly flexible, sensitive, and biocompatible piezoresistive strain-gauge sensors. This methodology is conducive for large-scale production, characterized by low production costs and high flexibility in terms of substrate selection. Experimental findings reveal that the as-fabricated sensor achieves peak sensitivity with a MoS2 layer thickness of 80 nm, boasting a high gauge factor (GF) of up to 290 and a resistance reduction of only 6-7 % after enduring 3000 testing cycles. Ultimately, the remarkable compatibility of silk fibroin biomaterials with skin allows for this flexible piezoresistive strain-gauge sensor to seamlessly adhere to human skin, without requiring any additional measures or imposing any discomfort. It proficiently captures the subtle surface texture of the skin and accurately senses human pulse signals, underscoring its considerable potential for innovative applications within the field of flexible electronics.

First-principles calculations revealed that (Mg,Zn)O and (Sc,Al)N have a tunable transition pressure from the wurtzite to rocksalt phase, which can be adjusted by the composition concentration. The piezoelectric response and electromechanical coupling show a clear enhancement near such a pressure-driven phase boundary. This suggests a new approach to designing novel piezoelectric materials with tunable piezoelectric response, driven by the external pressure.

Gd-doped WO3 nano-stalagmites (GW-NSs) film has been successfully prepared on indium-doped tin oxide (ITO)-coated glass substrates by co-sputtering deposition. Gd dopants can facilitate the vertically-aligned growth of WO3 nano-stalagmites on the WO3-nanoparticle seed layer. The microstructure analysis shows that the GW-NSs film with optimized aspect ratio and array density is fabricated with Gd/W = 0.6 % in atomic ratio. Such GW-NSs electrode (active area: 1 x 1.5 cm(2)) exhibits large transmittance modulation (Delta T = 52.7 % at 633 nm), high coloration efficiency (87.3 cm(2) C-1 at 633 nm), fast switching speed (5.9/13.1 s for coloration/bleaching), large diffusion coefficient (9.52 x 10(-10) cm(2) s(-1)) and long-term cycling stability (>2000) under an applied voltage of +/- 1.0 V, which can be attributed to a shorten Li+ diffusion distance and a large-area contact with the electrolyte. Importantly, the GW-NSs film also shows superior capacitive performance (calculated areal capacitance of 8.44 mF cm(-2) at 0.4 mA cm(-2)) and long-term cyclic stability (capacitance retention rate is 87.4 % after 2000 cycles). Furthermore, we fabricated the bifunctional smart window device combined with NiO counterpart electrode, which has the ability to visually monitor the level of stored energy from rapid and reversible coloration, indicating the potential applications of GW-NSs in both electrochromic and energy-storage fields.

Growing technical demand for thermal management stems from the pursuit of high-efficient energy utilization and the reuse of wasted thermal energy, which necessitates the manipulation of heat flow with electronic analogs to improve device performance. Here, recent experimental progress is reviewed for thermal switching materials, aiming to achieve all-solid-state thermal switches, which are an enabling technology for solid-state thermal circuits. Moreover, the current understanding for discovering thermal switching materials is reshaped from the aspect of heat conduction mechanisms under external controls. Furthermore, current challenges and future perspectives are provided to highlight new and emerging directions for materials discovery in this continuously evolving field. Thermal switching materials can switch between low (OFF-state) and high (ON-state) thermal conductivity states driven by an external trigger. They are expected to enable switching functions essential for developing thermal logic circuits. This review classifies numerous reported thermal switching materials into four categories (individual tuning or combined tuning) based on the three main heat carriers: charge carriers, phonons, and magnetic excitations in solid materials.image

With the widespread utilization of transparent conductive oxides (TCO) in various electronic devices, it is beneficial to revisit the fundamentals of heat conduction to formulate a comprehensive physical understanding for thermal properties of TCOs with the aim of improving the thermal design of electronic devices. For degenerate polycrystalline TCO films, both free electrons and phonons act as heat carriers, where free electron contribution can be calculated based on the Wiedemann-Franz law.Interestingly, the phonon thermal conductivity remains almost constant for degenerated polycrystalline TCO films with different dopant concentrations, suggesting the existence of dopant-induced minimum phonon thermal conductivity. For degenerate amorphous TCO film, free electrons act as heat carriers along the conduction path formed by the orbital overlap of cations, which also obey the Wiedemann-Franz law. Moreover, the atomic vibration contribution to thermal conductivity almost keeps unchanged for amorphous TCO films deposited under different conditions, indicating the existence of a minimum thermal conductivity caused by the scattering of vibrational mode due to structural randomness appeared in the bond angle. We anticipate that these fundamental understanding can provide a guide for the discovery of TCO materials with optimized thermal properties.

Because they can be easy to deposit on the non-planar structures by sputtering technology, ScAlN films are attractive for fabricating focus type transducers. They possess high electromechanical coupling coefficient k(t)(2) of 25%, which is comparable with the k(t)(2) of thin bulk plate PZT. In this study, we present three types of ScAlN thick film transducers deposited on a concave lens. The k(t)(2) values of two types of transducers were estimated to be 24% and 8.1%, respectively. We conducted experiments with longitudinal waves propagating in water medium and confirmed the excitation and reception of longitudinal waves in the bandwidth of 20-90 MHz and 10-80 MHz. Furthermore, we found that the lens-type free-standing structure transducer excites and receives longitudinal waves in a narrow bandwidth of 84 MHz.

Metastable rocksalt-type MgSnN2 (rs-MTN) films were fabricated on amorphous substrates via the high-pressure heat treatment (HPHT) of wurtzite-type MgSnN2 precursor layers. HPHT caused a wurtzite-to-rocksalt transition, and more importantly, the rocksalt structure was retained upon depressurization, even without epitaxial con-straints from the substrates. Single-phase rs-MTN films were obtained over a limited range of pressures and temperatures using HPHT. A pressure-temperature diagram for HPHT was also constructed, and the transition enthalpy barrier was estimated to be 0.21-0.23 eV. These results provide essential information on the kinetics of the wurtzite-to-rocksalt transition of MgSnN2.

Experimental measurements for the conversion loss between electric and mechanical energies of (Mg,Zn)Obased resonators show that Mg substitution can improve the electromechanical coupling of the wurtzite ZnO films up to the substitution concentration of 35%. Extended x-ray absorption fine structure (EXAFS) experiments indicate that both Mg and Zn exhibit tetrahedral local structures in (Mg,Zn)O films. With an increase in the Mg substitution concentration, the Zn-O bond length shows a slight tendency to increase and the Mg-O bond length practically remains the same. Further analysis of the EXAFS spectra reveals that a MgO4 tetrahedron cluster exists in the oxide alloy. First-principles calculations reproduce the experimental results, suggesting that the enhanced electromechanical coupling is mainly attributed to a decrease in the dielectric constant due to the Mg substitution. The enhancement in piezoelectricity caused by Mg substitution originates from an increase in the Zn-O bond length along the c axis, which enhances the c-axis-oriented electric dipole moment. Furthermore, the calculations show that the Mg substitution can reduce the critical transition pressure from the wurtzite phase to the rocksalt phase. This study shows that combining the EXAFS experiment and theoretical calculation is a reliable method for understanding the relationship between the electromechanical coupling and local cation structure in wurtzite alloy systems. This can guide the search for novel piezoelectric materials.

The ZnO–InN compound films were fabricated via both RF and DC sputtering by using indium and zinc metal target, where N2O and N2 gases were employed as the sputtering gas. The optical band gap was continuously tuned from 1.9 to 3.4 eV by precisely tailoring the chemical composition of the compound film. Both optical band gap and lattice spacing can be described by Vegard rule well. The carrier density can be adjusted up to 6.20 × 1020 cm−3 by varying the chemical composition of ZnO–InN compound. When the carrier density exceeds ∼1020 cm−3, the ZnO–InN compound films show the characteristics of degenerated semiconductor. Our experiments also reveal that the grain boundary scattering dominates carrier transport for ZnO–InN compound films with carrier density below 1020 cm−3.

To investigate the thermal-switching properties of Pd-catalyzed Ni–Mg alloy films, we conducted in situ analyses of the films’ electrical, optical, and thermal properties through hydrogen gasochromic reactions. These reactions allow the films to reversibly switch between metallic (dehydride) and semiconductor (hydride) phases. The thermal conductivities of the metallic and semiconductor states were found to be 14 and 1.0 W m −1 K −1 , respectively. By applying the Wiedemann–Franz law, we attributed the significant decrease in thermal conductivity during hydrogenation to the reduction in free electrons.