We propose a design of bilayer metasurfaces, imposing arbitrary and independent phase profiles on arbitrarily polarized beams at λ 1 = 505 nm and circularly polarized beams at λ 2 = 633 nm. The method cascades two layers that separately function as convertible waveplates and full-wave plates for modulation of polarization and phase. We investigate the performances of the asymmetric deflector and multi-foci metalenses. Specifically, polarization-independent deflector or single-focus metalens can be achieved at λ 1, while polarization-dependent deflector or dual-foci metalens are designed at λ 2. We demonstrate a simple yet effective approach interconnecting phase distributions and flexible polarization responses, which holds great promise in information multiplexing and security.

We report a microwave nonlinear transmission line (NLTL) based on AlGaN/GaN Schottky-barrier diodes. As a comb generator, the NLTL produces a frequency comb from 4 to 40 GHz at an input frequency of 4 GHz. The power of harmonics from 28 to 40 GHz exceeds that of commercial GaAs NLTL at an input power of 26 dBm. The power of harmonic starts to saturate as the input power increases to 33 dBm. Compared with the maximum input power of 26 dBm of commercial GaAs NLTLs, the comb generator based on AlGaN/GaN NLTL is more advantageous at a high input power.

A polarization wavelength filter was fabricated using two-beam interference and electroplating methods. The device consists of a Cu grating with a pitch of 400 nm on an ITO film. For normal incidence, the transverse magnetic (TM) transmission spectrum had a sharp spectrum at a wavelength of 648 nm and a significant dip at 735 nm. Furthermore, a sharp reflection spectrum in TM-light was obtained at a 685 nm wavelength and incident angle of 40°, and the peak wavelength shifted to a longer wavelength as the incident angle increased. This fabrication method is less complex and inexpensive than conventional methods.

A proof-of-concept experiment for sub-millisecond temporal and 10 μm order spatial resolution 4D X-ray tomography imaging using a multibeam X-ray imaging system is reported. The 3D structure of a tungsten wire during mechanical deformation was reconstructed using a super-compressed sensing-based algorithm from 28 projection images acquired simultaneously with a temporal resolution of 0.5 ms. The multibeam imaging system does not require rotation of the sample, X-ray source or detector. The experiment demonstrates the potential for improving the time resolution in observing non-repeatable dynamic phenomena, such as those occurring in fluids, living beings, or material fractures.

This study underlines the ceramic BaTiO3 dielectric layer adjacent to the electrode of long-term reliability-improved Ni–Sn alloy internal electrode BaTiO3-based multilayer ceramic capacitor to clarify the cause of electric barrier formation. Electron energy loss spectroscopy measurements of the Ti L3,2 near the edges and the O K near the edge structure changes to characterize the existence of an oxygen vacancy region, approximately 60 nm in width, and generated in BaTiO3 adjacent to the interface. Accordingly, the n-type semiconductor layer of BaTiO3 that originated from the oxygen vacancies, led to the formation of a rigid Schottky barrier at the interface.

A sidewall treatment process is proposed to recover the external quantum efficiency (EQE) loss in AlGaInP micro-LEDs (μLEDs). The proposed sidewall treatment consists of thermal annealing, ammonium sulfide chemical treatment, and sidewall passivation using atomic-layer deposition (ALD). The devices with sidewall treatment show improved optical power of more than 500% and 190% at 5 and 100 A cm−2, respectively, compared to devices with ALD sidewall passivation. The reduction in EQE was 20% when shrinking the device dimensions from 100 × 100 to 20 × 20 μm2. This work reveals that AlGaInP μLEDs can be energy efficient by employing proper sidewall treatments.

Ultrafast responses caused by ultrashort pulse excitation can be applied to ultrafast optical switches with high-speed information processing. In this paper, via the impulsive interference of excitons, we achieve an ultrafast optical response suited for ultrafast switches in all-optical networks. Due to the simultaneous excitation of two exciton states in the multiple quantum well on a strained buffer layer without the occurrence of adverse effects like stacking faults, impulsive interference is induced. The small compressive strain from the buffer layer modifies the orientation of the excitons inside the quantum well, and causes the ultrafast response.

We report a large modulation of spin pumping using temperature-induced magnetic phase transitions in c-axis oriented single crystalline dysprosium (Dy). From the temperature variation of the magnetic susceptibility, transitions from paramagnetic (PM) to ferromagnetic (FM) phases via antiferromagnetic (AFM) phase are clearly observed in the Dy. Unlike polycrystalline Dy, the spin pumping of both PM- and AFM-Dy are strongly suppressed owing to the increased non-dissipative backflow of spin current by the long-range spin transport, although two orders of magnitude difference exist between FM- and AFM-phases.

We demonstrate high-performance 10 × 10 μm2 InGaN amber micro-size LEDs (μLEDs). At 15 A cm−2, the InGaN μLEDs show a single emission peak located at 601 nm. The peak external quantum efficiency (EQE) and wall-plug efficiency are 5.5% and 3.2%, respectively. Compared to the 100 × 100 μm2 μLEDs, the 10 × 10 μm2 InGaN red μLEDs maintain a similar EQE value with the same efficiency droop. These results point out that InGaN materials are much more promising for higher efficiency than the common AlInGaP materials for the ultra-small size red μLEDs required by augmented reality and virtual reality displays.

We demonstrated the effectiveness of plasma-free HCl gas etching on a SiO2-masked (010) β-Ga2O3 substrate. The etching process proceeded anisotropically in the window areas, resulting in the fabrication of holes or trenches that were surrounded by etching-resistant (100)- and (01)-faceted sidewalls. When we etched in the striped windows along [001], we were able to create fins and trenches with flat (100)-faceted vertical sidewalls and slightly rough {310}-faceted inclined bottom corners. The vertical-to-horizontal etching ratio was as high as ∼11–14. Our findings indicate that HCl etching is a promising method for fabricating high-aspect-ratio fins/trenches on (010) substrates without causing plasma damage.

α-(Al x Ga1−x )2O3 alloys have attracted increasing interest as semiconductors with tunable wide band gaps. We report a systematic analysis of O vacancies in α-Al2O3, α-Ga2O3, and α-(Al x Ga1−x )2O3 alloys using first-principles calculations. The formation energies and electronic levels of the O vacancies are sensitive to not only the nearest-neighbor Al/Ga ratio but also the atomic relaxation around the vacancies. Consequently, the vacancy formation energies vary by up to ∼2 eV, reflecting diverse local atomic environments in the alloys. These results provide insight into further understanding and controlling the properties of α-(Al x Ga1−x )2O3 alloys.

It is a significant issue in controlling the polarization distribution in ferroelectric nematic liquid crystal cells. We investigated the polarization configuration of ferroelectric nematic liquid crystals on the surface and in the bulk of parallel/anti-parallel cells with rubbed substrates and proposed the polarization models in each cell. It is found that on the surface of rubbed polyimide films, the polarization direction is fixed and opposite to the rubbing direction. Splay and twist distribution of the polarization are formed in parallel and anti-parallel cells, respectively.

By controlling a metal-oxide-semiconductor interface of an AlSiO/GaN system, the electron inversion channel mobility was significantly improved to 229 cm2 V−1 s−1 in a field-effect transistor. A 3 nm thick AlN interlayer formed by atomic layer deposition effectively suppressed the oxidation of the GaN surface and reduced the border traps, resulting in high channel mobility. An additional nitrogen radical treatment before AlN deposition further improved the subthreshold slope and the channel mobility, which was consistent with the lower charged defects extracted from the mobility analysis in the low effective normal field region.

We investigated the effect of an ultrathin Fe interlayer on the growth of MnGa and spin–orbit torque (SOT) induced magnetization switching. MnGa was epitaxially grown on Fe at room temperature without thermal annealing. The MnGa/Fe bilayer was perpendicularly magnetized, and clear magnetization switching of the MnGa/Fe bilayer using the spin current, mainly from the adjacent Ta, was observed. The insertion of the Fe layer reduced the switching current density and increased a SOT-originated effective magnetic field. These results indicate that the MnGa/Fe bilayer is a promising spin source, capable of both perpendicular spin injection into GaAs and electrical manipulation of its spin direction.

We have proposed highly efficient microcavity second harmonic generation devices. In this work, we designed and fabricated an a-plane GaN vertical monolithic microcavity second harmonic generation device pumped with a femtosecond laser and obtained normalized wavelength conversion efficiency of 0.15% W−1. The efficiency was comparable to the theoretical estimations taking into account the time evolution of fundamental wave intensity in the microcavity, second harmonic generation and even sum frequency generation. This result indicates the possibility of realizing ultra-compact and ultra-efficient devices pumped with long-pulsed or continuous wave lasers, in which the effect of resonance enhancement is even more pronounced.

Hall effect measurements were conducted for MOSFETs with and without post-oxidation-annealing (POA) fabricated on the p-body doping in a wide doping range to vary the effective normal field (Eeff). The Hall mobility (μHall) in the high-Eeff region of the MOSFETs annealed in phosphoryl chloride (μHall = 41 cm2 V−1 s−1 at Eeff = 1.1 MV cm−1) is much higher than that of MOSFETs annealed in nitric oxide (NO) (μHall = 14 cm2 V−1 s−1 at Eeff = 1.1 MV cm−1), suggesting that the trapped electrons act as strong Coulomb scattering centers for the MOSFETs annealed in NO and without POA.

We demonstrate that the dislocation density in α-Ga2O3 epilayers is markedly reduced via rapid growth at low temperatures by halide vapor-phase epitaxy. An α-Ga2O3 epilayer grown on (0001) sapphire at a high growth rate of 34 μm h−1 and a low temperature of 463 °C exhibited a dislocation density of 4 × 108 cm−2, which was approximately 1/100 of that in a conventional film. It is likely that the three-dimensional surface morphology developed during the growth enhanced the bending of the dislocations to increase the probability of pair annihilation. The combination of this technique with thick film growth and epitaxial lateral overgrowth resulted in a further low dislocation density of 1.1 × 107 cm−2.

We demonstrate that fiber Bragg gratings in polymer optical fibers can lead to reflection peaks in any wavelength range when exciting high-order propagation modes, which can enhance the design of sensing systems for specific applications.

Accurate measurement of the net charge on nanoparticles is critical in research and practical applications. We proposed a method for accurately measuring charge through thermally and harmonically driven motion signals. Our direct-charge-calculation method achieves accuracies of better than 5% at thermal equilibrium pressures of more than 10 mbar and approximately 20% for pressures as low as 3 mbar. This method can improve the measurement accuracy for mass and density through iterations and provide a direction for non-contact characterization of atmosphere and space dust.

We present an effective protocol for extracting localization energy from WSe2 monolayers, based on temperature-dependent spectral variation of photoluminescence (PL), and observe time-sequential changes over a long period of time. We found that even freshly exfoliated WSe2 exhibits deviation from the Varshni formula upon exposure to air, while the temperature-dependent PL lineshapes of h-BN encapsulated WSe2 match well with delocalized features for as long as two years of the aging period. Our findings support the prospect of h-BN encapsulation for monoatomic transition metal dichalcogenides to meet the longevity condition, which is a prerequisite for practical components in the electronics industry.