Journal of the Korean Physical Society最新文献

This study demonstrates the fabrication and optical characterization of lithium niobate photonic devices including waveguides, beam splitters, and microring resonators on a thin-film lithium niobate platform. Through precise fabrication techniques and KOH post-cleaning following Ar-based etching, we achieved effective optical performance across key parameters such as transmission loss, splitting ratios, and Q-factors. These results show the potential of lithium niobate in advanced photonic applications, paving the way for its use in integrated on-chip photonics.

The low cost and scalability of silicon substrates have led to increasing attention to AlGaN/GaN high-electron-mobility transistors (HEMTs) on silicon wafer. We developed and simulated the GaN-based HEMT on Si wafer using the Silvaco TCAD software. The performance of rectangular-gate AlGaN/GaN HEMT on Si wafer is examined in detail with respect to the effects of channel length variation, barrier thickness variation, and gate length variation. The performance of this HEMT structure with a gate length of 100 nm and optimized channel layer thickness (CT) of 200 nm has shown a significant I_DS of 1.11 A/mm, a substantial G_m of 329.79 mS/mm, an impressive f_T of 199.40 GHz, and a notable output current of 1.71 A/mm. When the barrier layer thickness (BT) was varied from 6 to 10 nm while maintaining a 200 nm channel layer thickness, the performance declined at higher barrier thicknesses, yielding an I_DS of 0.8 A/mm, a G_m of 206 mS/mm, an f_T of 193.2 GHz, and an output current of 1.26 A/mm. Finally, this HEMT structure demonstrated superior performance with a gate length (LG) of 40 nm, exhibiting a drain current of 1.92 A/mm, a transconductance (G_m) of 465.49 mS/mm, and a cut-off frequency (f_T) of 465 GHz, and output current (I_D) of 2.11 A/mm. The optimized device structure’s high-power performance without compromising RF performance, they are suitable for millimeter-wave radar applications.

In the last decades, biological applications of single-molecule methods have grown rapidly and researchers with expertise in microscopy and instrumentation have adopted these techniques and advanced them even further. However, practicing single-molecule methods is still challenging for most because of the need for expensive equipments and instrumentation demands as well as complicated data acquisition and analysis workflow consisting of multiple steps using different software in each of them. smCamera is an all-in-one software package which aims to alleviate steep learning curves of the data acquisition and analysis. From recording movies through extraction of time series of single-molecule fluorescence resonance energy transfer (smFRET), everything can be done in a single program without any additional software or programming languages. Although smCamera has not been published before, it has been distributed to facilitate adaption of smFRET experiments and there has been requests for support for this software. We hope that this work answers questions from researchers using smCamera and also provides an opportunity to introduce and distribute smCamera for new users.

We designed and demonstrated antireflection coatings that exhibit high transmittance regardless of the angle of light incidence. The suggested design is adapted from a universal impedance matching layer model and is optimized by a particle swarm optimization technique. The thin layers separated from a layer with low refractive index is known to exhibit minimal changes in dielectric constant even when incident angle changes. The simulation results obtained by finite difference time domain method showed that designed structure has transmission with more than 96% at the incidence angle of less than 71° in the range of 700–900 nm wavelength. We fabricated the designed structure and measured transmission at different incidence angles to certify simulation results. By measuring transmittance of fabricated sample while changing an incidence angle from 0° to 80° by 10°, we found out that transmittance is more than 90% within the incidence angle of 70°, and the average of transmission at the wavelength of 800 nm measured within the above incidence angle is calculated as 0.916.

The interest of noncollinear spin structures in magnetic multilayers has recently gained a lot of interest in spintronics due to the observation of unique phenomena in these systems. In magnetic multilayers coupled by the Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction the study of noncollinear interactions has gained interest. In this paper, we study the magnetization reversal of two magnetic layers with different magnetic anisotropy directions coupled by the RKKY interaction. We have chosen Pt/Co/Ru/Co₄₀Fe₄₀B₂₀ structures where the Pt/Co show perpendicular-magnetic anisotropy and CoFeB show an in-plane magnetic anisotropy.

The injector system of fourth-generation synchrotron radiation accelerators should be optimally designed to produce a good quality beam. In the previous study, we used Multi-Objective Genetic Algorithm (MOGA) to optimize the injector system parameters to meet the beam requirements. To ensure that the injector operation parameters optimized by MOGA fall within practical ranges, we conducted an error analysis. The injector, composed of RF cavities and magnets, includes an analysis of potential errors in RF cavity phase and gradient, as well as magnet strengths across three distinct steps. First, we considered errors that could occur during operation, such as the input phases of RF cavities and the strengths of cavities and magnets. Second, we considered installation errors, including rotation errors of devices. Finally, we simulated scenarios where all errors occurred simultaneously. The simulation results showed that even when errors occurred, the beam quality remained within our acceptable range. Through this error analysis, we confirmed that the linac operation parameters optimized by MOGA are indeed practical and usable.

When an unprecedented infectious disease with high mortality and transmissibility emerges, immediate access to vaccines or medicines is often unavailable. Therefore, many health authorities rely on non-pharmaceutical interventions, such as contact tracing combined with isolation, to mitigate the spread of the disease. However, contact tracing is generally effective only for well-known fixed contacts such as regular contacts of an individual. In contrast, random and anonymous infections, which are difficult to trace, may still occur, potentially leading to large-scale outbreaks especially when the disease is highly transmissible. In this study, we test the efficacy of isolation based on contact tracing among fixed regular contacts even when untraceable random contacts exist as well. We simulate this scenario using the susceptible-infected-recover model on double-layered multiplex networks, where one layer has a fixed structure, while the other layer is time-varying. Our numerical results indicate that tracing the secondary contacts significantly reduces both the final epidemic size and the number of isolations per unit time, even with imperfect traceability. Our findings suggest that the isolation protocol combined with secondary contact tracing can be an effective measure against unprecedented infectious diseases, applicable to a broad range of fixed contact structures.

The as-cast and annealed Fe₇₆Si_19.4Nb_2.7Cu_1.7P_0.2 ribbons with width of 2.5 cm prepared by a single-roller cooling method were investigated. The structural properties of ribbons were studied by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The XRD result shows the α-Fe crystal phase of annealed film. The average crystallite sizes of the as-cast and annealed ribbons are about 28 nm and 43 nm obtained from EF-SEM. The dielectric and magnetic properties of ribbons were tested over frequency ranges of 5 MHz to 300 MHz and 5 MHz to 3000 MHz using an Impedance Analyzer, respectively. The dielectric constant and dielectric loss of the as-cast ribbon decreases from 4.3 × 10⁵ to 180 and from 3.01 to 0.06, while that of annealed ribbon decreases from 2.5 × 10⁴ to 180 and from 3.01 to 1.31. The permeability decreased with increasing frequency at first of each ribbon and the value of annealed ribbon is bigger. It was observed that the permeability loss value of annealed ribbon is smaller at first and then bigger than that of as-cast ribbon. The smallest values of permeability of the as-cast and annealed ribbons are about 1.4 and 1.8. The minimum of the permeability loss of the as-cast ribbon is 0.008. The magnetic hysteresis loops were investigated using a vibrating sample magnetometer. The saturation magnetizations of the as-cast and annealed ribbons are 113 emu g⁻¹ and 123 emu g⁻¹. The coercive fields of the as-cast and annealed ribbons are 259 A m⁻¹ and 1130 A m⁻¹. The saturation magnetization and coercive field could become bigger due to the crystallize property.

In this study, we investigated the underlying mechanisms of friction in graphene, which have been far less studied compared to its electrical properties. We manipulated the surface energy of the substrate and compared the friction using lateral force microscopy techniques. Additionally, we observed frictional domains within monolayer graphene sheets, which exhibited multiple friction levels. Through a series of experiments, we directly identified these frictional domains along with their intrinsic ripple structures oriented in a uniaxial direction. We also discovered intriguing properties by varying the angle between the scan direction and the ripple direction.