We demonstrate deterministic control of acoustic transmission using a tunable resonator comprising a maze cylinder and an adjustable slit integrated into a waveguide. This compact metamaterial structure supports Mie resonances that interfere with the continuum waveguide mode, generating a Fano resonance. The transmission spectrum can be continuously reconfigured through two independently adjustable mechanical pathways: changing the slit width and changing the resonator–slit separation. Experimental and numerical results show deterministic control of the asymmetry parameter q and quality factor Q , enabling direct adjustment of the transmission line shape and resonance bandwidth for applications such as reconfigurable acoustic filters and sensors.
The frequency noise of an external-cavity diode laser locked to an ultralow-expansion cavity (cavity-stabilized laser) and a whispering-gallery-mode (WGM) cavity optical-feedback semiconductor laser (WGM laser) was evaluated. The frequency noise of the WGM laser was approximately two orders of magnitude smaller than that of the cavity-stabilized laser at high Fourier frequencies. Using the WGM laser, phase noise reduction of approximately two orders of magnitude was observed in the dual-band stabilization of an optical-fiber-based interferometer at high Fourier frequencies. This noise reduction should improve the measurement fidelity in quantum key and entanglement distributions in long-distance quantum communication.
We investigate the temperature-dependent electrical characteristics and bias-temperature-instability (BTI) of InGaOx gate-all-around (GAA) nanosheet FETs with different HfO 2 thicknesses. The 5 nm-HfO 2 GAA device shows higher transconductance (1550 μS μm −1 ) and effective mobility (52 cm 2 Vs −1 ) than the 7 nm-HfO 2 device. The performance improvement arises from increased gate-capacitance and mobility enhancement. At low temperatures, subthreshold swing saturates due to band-tail-states effects. The 5 nm-HfO 2 device shows more pronounced phonon-like temperature dependence than 7 nm-HfO 2 device, suggesting a lower Coulomb-scattering contribution. Positive-BTI shows comparable negative V th shifts, whereas negative-BTI shows negligible shifts, against bottom-gate devices.
We developed and characterized a technique for the controllable implantation of Mg into β-Ga 2 O 3 . Oxygen co-implanted with Mg reduced O vacancies and unintentional Mg diffusion. By employing Mg/O co-implantation, the Mg diffusion depth could be successfully modulated and suppressed. Characterization results revealed that the Mg:O ratio determines the diffusion depth of the implanted Mg after high-temperature activation annealing. Co-implantation with a Mg:O = 1:10 concentration ratio produced the best Mg diffusion suppression among all samples. Fabricated Ga 2 O 3 Schottky diodes with Mg/O co-implanted edge terminations clearly show improved breakdown characteristics, indicating that O co-implantation with Mg is effective for edge termination.
We developed and characterized a technique for the controllable implantation of Mg into β-Ga _2 O _3 . Oxygen co-implanted with Mg reduced O vacancies and unintentional Mg diffusion. By employing Mg/O co-implantation, the Mg diffusion depth could be successfully modulated and suppressed. Characterization results revealed that the Mg:O ratio determines the diffusion depth of the implanted Mg after high-temperature activation annealing. Co-implantation with a Mg:O = 1:10 concentration ratio produced the best Mg diffusion suppression among all samples. Fabricated Ga _2 O _3 Schottky diodes with Mg/O co-implanted edge terminations clearly show improved breakdown characteristics, indicating that O co-implantation with Mg is effective for edge termination.
This paper presents a low-local-oscillator (LO)-power terahertz heterodyne detector chip based on AlGaN/GaN high-electron-mobility transistor (HEMT) technology, monolithically integrating an antenna-coupled HEMT mixer, an on-chip capacitor, a common-source HEMT amplifier and a HEMT switch. Source/drain ohmic contacts protrude toward the antenna apex to reduce series resistance and improve heterodyne mixing efficiency. On-chip amplifier offers a noise figure of 1 dB and an intermediate-frequency bandwidth of 1.1 GHz. With a low LO power of $-$ 10.5 dBm, the detector exhibits an optical noise-equivalent power of $-$ 150.7 dBm Hz $ ^{-1}$ at 275 GHz. The detector is readily integrable into a coherent receiver array with quasi-optical coupling to an LO source
Self-doped PEDOT (S-PEDOT) is a promising mixed ionic–electronic conductor with high stability. However, the design strategy to enhance the mixed transport of ions and electrons was poorly understood. Here, we demonstrate that high-molecular-weight S-PEDOT combines high electronic conductivity and high electrochemical capacitance to enable high-transconductance organic electrochemical transistors (OECTs). Increasing the apparent molecular weight from 43 to 150 kDa significantly enhanced the μC ^* , figure of merit of OECTs, from 5.2 F cm ^−1 V ^−1 s ^−1 to 290 F cm ^−1 V ^−1 s ^−1 , outperforming the conventional PEDOT:PSS-based devices and giving the highest reported value for self-doped OMIECs.
The ultrasonic bone‐screening market is rapidly advancing, driven by an aging population and the increasing prevalence of osteoporosis. In Japan alone, more than 6000 ultrasonic bone densitometry systems are currently in operation. Leveraging the inherent advantages of quantitative ultrasound (QUS) methods—its safety, ease of use, absence of ionizing radiation, portability, and low cost—various techniques have been developed for in vivo bone screening. Yet, despite this widespread clinical use, the complex material properties and structural heterogeneity of bone tissue hinder precise ultrasonic evaluation of bone. This paper reviews applications of ultrasonic methods for assessing reduced bone mass (skeletal status) and deterioration in bone properties. Attention is given to a Japanese in vivo ultrasonic evaluation method that utilizes the characteristic propagation of two longitudinal wave propagation in cancellous bone. Finally, the paper briefly mentions the piezoelectric properties of bone, which may contribute to ultrasonic fracture healing.
Molecular doping has enabled control of electronic properties in semiconducting polymers for studies of charge transport and device applications. However, conventional dopant anions are mostly organic monovalent species whose roles are largely limited to stable charge compensation. Here, we introduce polyoxometalates as multivalent oxide-cluster dopant ions into semicrystalline polymer semiconductors. In particular, films doped with size-compatible divalent [W _6 O _19 ] $ ^{2-}$ retain lamellar order, exhibit conductivity above 200 S cm $ ^{-1}$ , and show a Hall response, indicating partially coherent carrier transport. Compared with inert-anion-doped films, [W _6 O _19 ] $ ^{2-}$ -doped films show enhanced anodic response in the oxygen-evolution region, demonstrating functional multivalent-ion doping for electronic and electrocatalytic polymer semiconductor films.
We conducted an experimental study on the nonlinear source resistance ( r _s ) with selective n + GaN regrown Al _x Ga _1 _−x N/GaN high-electron mobility transistors (HEMTs). Experimental results show that r _s increases with drain current, limiting current and transconductance. Using devices with different gate and access lengths, r _s was extracted through a gate-current injection technique with corrected channel resistance. The effects of gate-to-source access length ( L _acc-s ) and drain current on intrinsic transconductance ( g _mi ) were analyzed in terms of r _s . The results indicate that g _mi is independent of L _acc-s , confirming that the compression of g _m in GaN HEMTs for high I _D is primarily attributable to the nonlinear r _s .
Temporal ghost imaging (TGI) reconstructs temporal structures from correlations between illumination signals and bucket measurements. However, that conventional TGI requires full-waveform acquisition and numerical integration raises an issue. Here, we introduce one-time readout TGI (OTR-TGI) and compressed sensing to ultrasonic TGI to address this. OTR-TGI performs temporal integration in the receiver circuit, enabling reconstruction from a single readout, while CS helps reduce the number of illumination patterns. Experiments demonstrate faithful temporal reconstruction at a sizable reduction, approximately 30%, in the required illumination patterns with only acceptable quality degradation, which holds promise for efficient ultrasonic temporal imaging.
In contrast to conventional semiconductor materials, this review outlines a new strategy for metals to be high-performance thermoelectric materials. We have proposed “intrinsic energy filtering” as a strategy to overcome the inherently low Seebeck coefficients in metals. This strategy involves engineering electronic structures where a dispersive conduction band and a localized flat band coexist near the Fermi level, creating strong energy dependence in the carrier relaxation time, thereby generating a large Seebeck coefficient S . Effectiveness has manifested in distinct material systems; Ni–Au alloys, where disorder-mediated s – d interband scattering achieves exceptionally high power factors ∼34 mW m ^−1 K ^−2 . Ni _3 Ge exhibits a relatively large S ∼−80 μV K ^−1 through interband scattering. The strategy was further extended to the Kagome metal Ni _3 In, with topological flat bands, revealing that Zener tunneling can suppress S, and we outline strategies to circumvent this quantum transport phenomenon. These developments point to a new horizon for the development of next-generation thermoelectric materials, unlocked by the precise control of scattering mechanisms.
Self-driving laboratories (SDLs) bring a paradigm shift to materials science by accelerating material development through autonomous exploration. This review explores recent SDL advances, including the evolution of search algorithms, hardware improvements, and expanded autonomy via large language model-based artificial intelligence (AI) agents. Research process transformations are discussed based on a data-acquisition “small loop” and a hypothesis-generation “large loop.” As AI increasingly controls experimentation and optimization (the “small loop”), researchers need to collaborate with AI, focusing on generating overarching hypotheses and strategies (the “large loop”). Finally, from the perspective of the patent system, we argue that the conception of and responsibility for inventions ultimately remain with researchers.
An efficient gain-switched single-frequency Tm3+-doped fiber laser at 2097.48 nm using a short DBR cavity under hybrid pumping (1570 nm pulsed and 793 nm continuous wave) is experimentally demonstrated. The laser delivers stable single-longitudinal-mode output with pulse widths ranging from 97 to 26 ns and repetition rates of 30-100 kHz. Comparative studies confirm that this 793/1570 nm hybrid scheme effectively lowers the lasing threshold while maintaining pulse performance. A gain-switched single-frequency pulsed fiber laser operating in the 2.1 mu m wavelength region is demonstrated.
Mg 3 Sb 2 -based materials have emerged as highly promising n -type thermoelectric materials within the medium temperature range (300–800 K), offering a more cost-effective and environmentally benign alternative to conventional telluride-based thermoelectric materials. These materials complement Bi 2 Te 3 -based systems for near-room temperature applications (300–500 K) and PbTe/GeTe/SnTe for medium-temperature ranges (500–800 K). This paper presents a systematic review of recent significant advances in the thermoelectric performance of Mg 3 Sb 2 , achieved through optimized doping and fabrication strategies. It outlines key methodologies and underlying physical mechanisms that contribute to high-performance n -type Mg 3 Sb 2 , discusses challenges associated with device integration, and proposes future research directions.
Thermally activated delayed fluorescence materials have attracted attention for organic light-emitting diodes owing to their high efficiency and stability. Accurate evaluation of the singlet–triplet energy gap (Δ E ST ), particularly in near-zero-gap systems, remains a key challenge. Here, we investigate the photophysical properties of HzTFEX 2 , a proposed inverted singlet–triplet (InvE ST ) emitter, using temperature- and solvent-dependent analyses based on a dynamic exciton model. The results show that InvE ST explains the emission decay profiles of HzTFEX 2 in the Marcus normal region. We demonstrate that conventional kinetic analyses are insufficient in the near-zero Δ E ST regime, highlighting the necessity of the dynamic exciton model.
Electric-field control in multiferroic materials is attracting attention for next-generation memory devices with low power consumption, high recording density, and non-volatility. This review overviews magnetization reversal in cobalt-substituted BiFeO 3 (BiFe 1– x Co x O 3 ), a single-phase room-temperature multiferroic. Experimental results from microscopic direct observations of domains using scanning probe microscopy are summarized, highlighting how electric-field-induced reversal is influenced by domain structures, film orientations, and switching angles. Spatial control of domains in nanodot arrays and associated size effects are also discussed. These insights offer a clear perspective toward magnetoelectric memory applications.
Ferroelectric HfO 2 is an emerging pyroelectric material with promising energy-harvesting applications. Herein, via ab-initio molecular dynamics simulations, we investigate the role of dopants in tailoring the pyroelectricity in ferroelectric HfO 2 . We demonstrate that dopant perturbs the local bonding environment of host HfO 2 structure, giving rise to notable pyroelectricity. The pyroelectric response is further enhanced at the ferroelectric-to-paraelectric phase transition, characterized by a Curie temperature that reduces with increasing doping concentrations. The reduction is more pronounced for dopants with ionic radii smaller than the host. The present work highlights the efficient tuning of pyroelectric response in ferroelectric HfO 2 by doping.
Al-rich AlGaN is a strong candidate for high-voltage power electronics, yet high-performance [>500 MW cm(-2) Baliga figure of merit (BFOM)] passivated AlGaN channel transistors on cost-effective sapphire remain limited. We demonstrate passivated, field-plated Al0.6Ga0.4N HEMTs achieving 2.33 kV breakdown with >2.2 MV cm(-1) average breakdown field. The device demonstrates 8.32 m Omega & centerdot;cm(2) on-resistance and a record 654 MW cm(-2) BFOM (>1 kV). With similar to 5.5 mu m gate-drain spacing, devices reach >2.5 MV cm(-1) and 556 MW cm(-2) BFOM, highlighting excellent field management and strong potential for scalable, cost-effective sapphire-based platforms.
