Table of contents

We investigated the anisotropic selective-area HCl-gas etching behavior of SiO₂-masked (001) β-Ga₂O₃ and its dependence on the temperature T (548 °C–949 °C) and HCl partial pressure P₀(HCl) (25–250 Pa). The cross-sectional width-to-depth aspect ratio of the etched trenches formed under the striped window along [010] decreased with increasing T and decreasing P₀(HCl). Secondary-ion mass spectrometry revealed slight diffusion of Si into β-Ga₂O₃ at T = 949 °C, while no diffusion was detected at T = 750 °C. These results provide practical guidelines for the fabrication of desired three-dimensional structures, such as fins/trenches, for high-performance β-Ga₂O₃-based power devices.

All-dielectric metasurfaces can realize flexible full-vector manipulations of the complex optical field, without confronting the loss issues of plasmonic counterparts, and thus have been proposed for lots of nanophotonic functionalities. In this work, a silicon-bar metasurface is designed to generate multifunctional focusing characteristics, which act as duplexed metalens with unlocked topological charges of terahertz vortex for orthogonal linearly-polarized incident waves. It achieves full phase modulation by tuning lateral sizes of the bar without the anisotropic orientation requirement associated with the geometric phase, which is consequently of high efficiency since no polarization conversion is involved in this duplexed all-dielectric vortex metalens.

The coincidence time resolutions of thallium bromide chloride (TlBr_xCl_1−x) crystals used as Cherenkov radiators were characterized. A pair of TlBr_xCl_1−x crystals with the same composition was used to coincidentally detect positron annihilation gamma rays from a ²²Na source. The size of the crystals was approximately 3 mm × 3 mm × 3 mm. A polished surface of the crystals was coupled to a silicon photomultiplier. The time resolution improved with an increase in the Cl concentration in the crystals. TlBr_0.3Cl_0.7 crystals exhibited the best coincidence time resolutions of 378 ± 17 ps and 635 ± 31 ps with and without event selection based on the photoelectron level, respectively.

This paper describes an inverse analysis method using neural networks on optical spectroscopy, and its application to the quantitative optical constant evaluation. The present method consists of three subprocesses. First, measurable UV–visible spectroscopic quantities were calculated as functions of the optical constants of the solid based on the Tomlin equations [J. Phys. D 1 1667 (1968)] by carefully eliminating the unpractical combinations of optical constants. Second, the backpropagation neural network is trained using the calculated relationships between the measurable quantities and the optical constants. Finally, the trained network is utilized to determine the optical constants from measured responses. The conventional (Newton–Raphson) method tends to require the judgment of a well-experienced analyst, while machine learning shows automatically human-free performance in data conversion.

We report the fabrication of novel 0.1Cr₂O₃-25CaO-75GeO₂ glass and glass ceramics with wideband NIR luminescence and the annealing temperature dependence of the photoluminescence (PL) properties for applications as NIR phosphors. The anisotropic growth of Ca₂Ge₇O₁₆ nanocrystals in the annealing samples was confirmed. Annealing-induced variations in the body colors and diffuse reflectance spectra suggest that change in the valence of Cr ions and their coordination environments. Broadband luminescence of 700–1300 nm attributed to the ⁴T₂ → ⁴A₂ transition of Cr³⁺ was observed for the as-made glass. The peak wavelength is shifted from 860 to 780 nm, and line-shaped ²E → ⁴A₂ emission appears due to the crystallization of Ca₂Ge₇O₁₆ by heat treatment. The PL quantum yield reaches the maximum at 0.19 when the sample is annealed at 775 °C, and the dependence on annealing temperature can be understood by the change in the PL lifetimes and diffuse reflectance spectra.

Valley photonic crystal (VPhC) waveguides have attracted much attention because of their ability to enable robust light propagation against sharp bends. However, their demonstration using a CMOS-compatible process suitable for mass production has not yet been reported at the telecom wavelengths. Here, by tailoring the photomask to suppress the optical proximity effect, VPhC patterns comprising equilateral triangular holes were successfully fabricated using photolithography. We optically characterized the fabricated VPhC devices using microscopic optics with NIR imaging. For comparison, we also fabricated and characterized line-defect W1 PhC waveguides, in which the transmission intensities decreased at some regions within the operating bandwidth when sharp turns were introduced into the waveguide. In contrast, the developed VPhC waveguides can robustly propagate light around the C-band telecommunication wavelengths, even in the presence of sharp bends. Our results highlight the potential of VPhC waveguides as an interconnection technology in silicon topological photonic ICs.

In this work, the motion of droplets on an inclined non-piezoelectric curved substrate is investigated to study the performance of the Lamb waves (LWs)-driven surface cleaning of the camera lens or other optical components. The droplets do not slide forward on the curved substrate with an inclination less than 5° is verified by experiments. And then, the shape changes of droplets are discussed from experiments and simulation. A two-phase flow simulation model is established using the level set method, which the deformation of gas-liquid interface can be clearly observed when the droplet moves. The observation results that the movement of droplets on the inclined curved glass driven by LW are propelled periodically in a stretching and spreading phases. To investigate the effect of LWs on droplets removal, the movement distance of droplets are measured in four main factors, namely, substrate inclination, input power, droplet volume and surface curvature.

A new strategy is demonstrated for confining graphene plasmons to resonantly enhance light–matter interactions for tunable mid-IR detection. Our devices consist of integrating monolayer graphene without patterning onto a nanoribbon-connected ring-shaped ferroelectric superdomain with alternately up- and down-polarization. The simulations show that our devices have a tunable spectral response from 11.7 to 19.5 μm by both reconfiguring the ferroelectric superdomain and varying the ferroelectric-gated graphene Fermi level. A highest photoresponsivity of 796–947 A W⁻¹ has been achieved in 10–20 μm. The proof-of-concept photodetector offers the possibility to simplify the fabrication of plasmonic devices and helps the development of applications of tunable mid-IR detection.

Plate-shaped hexagonal SrFe₁₂O₁₉ particles, synthesized using potassium bromide as the molten salt flux, were dispersed in the resin using a planetary ball mill. Oriented sheets were prepared by coating the dispersion onto the films under a magnetic field. The coercive force and squareness ratio of the oriented sheets were 412 kA m⁻¹ and 0.91, respectively. The magnetic anisotropy field was determined by measuring the rotational hysteresis losses of the oriented sheets with a magnetic torque meter. The anisotropy field was distributed in the range of approximately 200–1100 kA m⁻¹, and particles with an anisotropy field of 478 kA m⁻¹ comprised the majority. The magnetic anisotropy energy estimated from the magnetic anisotropy field was 104 KJ m⁻³. Assuming a reduction in the crystalline anisotropy field along the c-axis due to simply the shape anisotropy field resulting from the platelet shape of the particles, particles occupying the majority exhibited a maximum anisotropy field of 823 kA m⁻¹.

We investigated the dynamics of water molecules in the interfacial water around a carbon nanotube (CNT) by analyzing the rotational autocorrelation function (RACF) for water molecules using molecular dynamics simulations. We found that the function undergoes a gradual crossover with temperature for the interfacial water with double-molecular-layer structure around the CNT, in contrast to bulk water, which shows a discontinuous change in the RACF at 0 °C. This is consistent with recent experimental results showing that interfacial water does not exhibit a solid–liquid phase transition. In addition, the RACF results can be fitted by exponential functions with two different time constants, indicating that the proportion of disordered structures relative to ordered structures, in which water molecules have more restricted rotation, increases continuously with temperature. The continuous structural change yields the gradual solid–liquid crossover.

GaN films were grown on hydride vapor phase epitaxy (HVPE) AlN/SiC templates by metalorganic CVD (MOCVD) without annealing the reactor to eliminate the memory effect. A step-terrace structure and smooth surface were obtained for the GaN film, which had a thickness of ∼200 nm. Subsequently, AlGaN/GaN heterostructures for application in high electron mobility transistors (HEMTs) with thin GaN channels were fabricated without a C- or Fe-doped GaN buffer layer. The interface quality at the AlGaN/GaN heterostructure was good enough for a two-dimensional electron gas to exhibit Shubnikov–de Haas oscillation in a magnetic field at 1.8 K. The GaN HEMTs with a thin channel on the AlN/SiC templates exhibited both a pinch-off character and conventional properties. In view of both the shorter epitaxial growth time and higher thermal conduction, HVPE AlN/SiC templates are applicable to the fabrication of GaN HEMTs by MOCVD.

Temperature and dosage-dependent reactions of NH₃ on the Si(111)-(7 × 7) surface have been studied by low-temperature scanning tunneling microscopy. It was found that the surface reaction exhibited three different dissociative adsorption channels as the temperature increases at low exposure. Under the condition of high exposure, the amorphous structure of silicon nitride film gradually transformed into an ordered phase, with the increase of substrate temperature, and finally presented an 8/3 × 8/3 structure. This means that both exposure and temperature are critical for forming an ordered surface structure. Furthermore, many adsorbates were observed on the nitride region during the growth process, which is believed to be the intermediate reactants in the nitridation reaction and consumed in the subsequent annealing process to form an orderly and clean surface morphology.

Graphene is grown directly on c-, a-, m-, and r-plane sapphire substrates by CVD, and their structures and electrical properties are compared. The obtained graphene is always polycrystalline, but the grain size is dependent on the sapphire surface orientation. The largest and smallest grains respectively appear on the m- and c-planes, and the graphene grown on the a- and r-planes has intermediate grain sizes. The carrier mobility is the largest for the graphene grown on the m-plane, indicating that the grain boundaries make a significant impact on the carrier transport as scattering centers. Nevertheless, the RT Hall effect mobility measured for the mm-sized m-plane samples reaches 7000 cm² V⁻¹ s⁻¹. m-plane sapphire is promising as an insulating substrate for direct graphene growth.

Fluidic self-assembly is a technique in which numerous semiconductor chips are integrated spontaneously. Here, we demonstrate that the integration efficiency is significantly improved by optimizing the separation conditions and appropriately controlling the external forces to which the microchips are subjected to the solution. In particular, an external drag force was found to prevent the Si microchips from forming aggregations and prompting transfer to the Si receiver pockets. This resulted in a significant improvement in the integration selectivity. Moreover, experiments with various microchip sizes statistically determined the effect of the Si receiver chip rinse on the evaluation functions: deposition selectivity, yield, and overall yield. While rinsing was effective for fluidic self-assembly of 10 μm scale Si microchips, rinsing of 800 nm scale chips is indicated to have different integration mechanisms. Our quantitative analysis indicated the potential applicability of the fluidic self-assembly technique to the integration technologies of Si micro semiconductor devices.

EUV technology has led to smaller device features, emphasizing the importance of minimizing defects in production. Research has focused on improving resist material uniformity to address variability in resulting patterns caused by stochastic factors, with attention paid to the underlying chemistry. In this study, we developed an automated method for analyzing resist patterns with defects using image recognition techniques. This method involves the analysis of line-and-space resist patterns using image processing technologies, comparison using established standards, and the identification of patterns with defects. A modified version of Hough transform technique was employed to automatically analyze approximately 2500 scanning electron microscopy images. Using our method, we can identify defective and deformed patterns by comparing the detected line-and-space resist patterns with the established standard. The indices that characterize the resist patterns with defects are proposed. Finally, simulated images were also used to uncover the chemical information underlying defective resist patterns.

We investigate the spatial resolution of direct-modulation Brillouin optical correlation-domain reflectometry (BOCDR) by exploring the impact of modulation amplitude and frequency. Our findings reveal that optimal resolution improvement is attained through an initial increase in modulation amplitude, followed by modulation frequency adjustment. These insights provide a basic guideline for enhancing the spatial resolution in direct-modulation BOCDR.

Electrochemical impedance spectroscopy (EIS) was used to examine the possibility of directly sensing plant stress under temperature environment changes. Changes in the extracellular and intracellular fluid resistances (Ro and Ri, respectively) were affected by changes in the cell phenomena under the temperature environment because Ro and Ri reflect the ionic fluctuations caused by the activation of cell membranes and change in solute viscosity, respectively, under the changing environment temperature. Examination of the effects of temperature environment change on plant cells via EIS measurements and theoretical calculations using the Okajima model can be used for in situ monitoring.

We compare the use of adaptive moment estimation (ADAM), simultaneous perturbation stochastic approximation (SPSA), Nakanishi–Fujii–Todo method (NFT), and CoolMomentum in a variational quantum eigensolver. Using a random weighted max-cut problem, we numerically analyze these methods and confirm that CoolMomentum performs better than the other methods. ADAM and SPSA tend to get trapped in local minima or exhibit infeasible optimization durations. Although NFT exhibits fast convergence, it tends to suffer from local minima similar to ADAM and SPSA. Contrarily, CoolMomentum shows a higher accuracy under noiseless and realistic hardware noise conditions.