Journal of the Korean Physical Society最新文献

We investigate the photoluminescence (PL) characteristics of GaAs quantum dots (QDs) fabricated via droplet epitaxy as a function of temperature. With increasing temperature, the PL peak energy and integrated PL intensity decrease, while the full width at half maximum (FWHM) broadens. These variations are attributed to enhanced phonon interactions and carrier dynamics. Specifically, the reduction in transition energy and the FWHM broadening are attributed to electron–phonon interactions, whereas the decline in integrated PL intensity is associated with carrier transfer and exciton dissociation.

The enhanced electron heating by electron plasma wave assisted beat wave of Hermite cosh-Gaussian and cosh-Gaussian laser beams is theoretically investigated in magnetized collisional plasma with density rippled. The nonlinear interactions of two slightly difference frequencies of laser beams produce the generation of beat wave at frequency (omega ={omega }_{1}-{omega }_{2}) and wavenumber (k={k}_{1}-{k}_{2}). The beating of this wave with density ripple plasma causes the generation of a strong nonlinear ponderomotive force on the plasma electrons and couples the large amplitude electron plasma wave. An analytic formalism of anomalous electron heating rate is derived. The effect of external magnetic field and field optimization properties of two laser beams on electron heating rate is investigated. The Landau damping predominated for immense excitation of electron plasma waves and thus lead to anomalous electron heating rate. As the lasers beat wave frequency approaches near the electron plasma, the resonant electron heating rate is observed. By varying the various interacting medium parameters (amplitude of density ripple and collisional frequency) and laser parameters (Hermite polynomial mode index, beam decentered parameter, initial beam width of each laser, and lasers beat wave frequency), the heating rate can be tuned and optimized. This effective electron heating rate can have possible applications in plasma fusion devices and targets normal sheath acceleration.

The precise timing of synaptic transmission in auditory hair cells is important to hearing and speech recognition. Neurotransmitter release is an underlying step in translating sound. Thus, understanding the nature of synaptic fusion is key to understanding the hearing mechanism. Extraordinary large excitatory postsynaptic currents (EPSCs) have been observed in the auditory hair cell synapse, and their origin has been controversial. It is not known yet whether the size and shape of the EPSCs are the results of a single large vesicle or many small vesicles. We report our numerical simulation of the vesicular fusion process from calcium channel process to the generation of EPSCs. Our numerical experiments indicate that the origin of the large EPSC with its mysterious form is close to the scenario of the multivesicular release. The large EPSCs might be triggered by strong calcium channeling of the calcium channel clusters.

The Tinkham formula is commonly used to study the transmission characteristics of electromagnetic waves through thin conducting films. However, its applicabiltiy is constrained by certain film parameters, such as thickness and electrical conductivity. Herein, we systematically investigate the validity ranges of the Tinkham formula for metal films whose electrical and optical properties are described by the Drude model. Specifically, we compare analytical and numerical results for the terahertz transmission through various metal films with providing appropriate application conditions for the Tinkham formula.

This study presents the development and evaluation of AlGaN/GaN high-electron-mobility transistors (HEMTs) designed for high-power and high-frequency applications. The devices incorporate micro-gate field plates using a discrete field plate design, effectively reducing the peak electric field between the gate and drain. This results in a notable improvement in breakdown voltage, reaching up to 1330 V. The integration of copper interconnects significantly lowers parasitic capacitances, which enhances the cut-off frequency (f_T) from 45.5 GHz to 51.3 GHz. These HEMTs demonstrate strong DC performance, with a peak transconductance of 0.275 A/V. Under RF conditions, the devices deliver a high output power density of 6.8 W/mm and achieve an impressive power-added efficiency of 73% at 40 GHz. Furthermore, the transistors exhibit excellent high-frequency characteristics, achieving a maximum cut-off frequency of 51 GHz and a maximum oscillation frequency (f_max) of 163 GHz. These results underscore the effectiveness of copper interconnect technology in enabling high-performance AlGaN/GaN HEMTs for advanced power and microwave applications.

This article presents a comprehensive theoretical analysis of device characteristics achievable through innovative channel engineering and buffer layer optimization using validated TCAD simulation models. The AlGaN/InGaN/GaN HEMT (L_G = 55 nm) demonstrates impressive performance metrics, including a sheet carrier density of 2.6 × 10¹³ cm⁻², on-resistance of 0.31 Ω.mm, and maximum drain current density of 3.14 A/mm. The device achieves a peak transconductance of 0.71 S/mm and exhibits robust breakdown characteristics with a three-terminal off-state breakdown voltage of 96.8 V. In addition, it maintains an excellent I_ON/I_OFF ratio of 10¹³ and demonstrates outstanding frequency performance with f_T/f_max values of 285/310 GHz. The InAlN/InGaN/GaN architecture shows enhanced performance parameters, featuring a higher sheet carrier density of 3.9 × 10¹³ cm⁻², reduced on-resistance of 0.25 Ω.mm, and increased drain current density of 5.22 A/mm. This configuration achieves a peak transconductance of 0.74 S/mm, while maintaining a breakdown voltage of 57.1 V and an I_ON/I_OFF ratio of 10¹³. Notably, it demonstrates superior frequency characteristics with f_T/f_max values reaching 311/364 GHz. These results highlight the potential of β-Ga₂O₃ buffer engineering in advancing GaN HEMT technology for next-generation millimeter-wave applications.

The correction of environmentally scattered radiation and rapid determination of the dose rate at test points are important issues in the in-situ calibration of fixed X- and γ-ray radiation dosimeters with open X-ray reference radiation fields. In this study, a Monte Carlo calculation model of the environmentally scattered radiation for in-situ calibration was established, the environmental parameters that may affect scattered radiation under two calibration scenarios were systematically analyzed, and datasets were constructed. Three machine learning algorithms, Support Vector Regression (SVR), Adaptive Boosting (AdaBoost) and Gradient Boosting Regression Tree (GBRT), were used to establish a scattering factor prediction model, evaluate the prediction performance of the model in test sets and experiments, and carry out the application of in-situ calibration of typical dosimeters. The GBRT was found to have better comprehensive performance than the SVR and AdaBoost prediction models did, the GBRT was able to predict the scattering factor on the test set without exceeding the Mean Square Error (MSE) of 1.16E−04, the Root Mean Square Error (RMSE) of 1.08E−02 and the Mean Absolute Error (MAE) of 8.53E−03, respectively, and with R² converging to 1. The maximum relative deviation of the scattering factor in the experiments was −6.9%. This study provides an intelligent method for dose determination in the in-situ calibration of fixed dosimeters, which can be extended to more complex calibration scenarios by expanding the database. At the same time, it provides a feasible idea for replacing isotope radiation sources with X-ray sources.

We investigated the consequences of discrete Fourier transformation in coherent diffraction imaging (CDI). The object density reconstructed from the discretely sampled diffraction data within a truncated range is inherently aliased, blurred, and further aggravated in phase retrieval process. We devised a preprocessing procedure to correct input Fourier constraints using a convolution kernel and to exclude erroneous Fourier constraints. By applying the proposed preprocessing to both simulated and experimental data, we demonstrated that image reconstruction was substantially improved, effectively suppressing physically unsound fluctuations in the retrieved images. This procedure could improve the fidelity of the quantitative object density retrieved by CDI.

The Rare Isotope Science Project (RISP) was launched to construct a new facility called RAON (Rare isotope Accelerator complex for ON-line experiments), dedicated to advancing nuclear physics and rare isotope science. The project is motivated for studying and utilizing rare isotopes for a wide range of applications, including fundamental nuclear physics, nuclear astrophysics, materials science, and biomedical research. RAON is uniquely designed to incorporate both isotope separation on-line (ISOL) and in-flight fragmentation (IF) methods, and combining the ISOL and IF methods to produce more exotic rare isotopes. With the first phase of the project completed, this paper documents the major milestones of the facility’s construction progress. The key technical achievements, including the commissioning of major components such as the cryogenic system, superconducting linear accelerator, and ISOL system, are highlighted. Recently, a major milestone was achieved with the first acceleration of an ISOL-produced rare isotope beam, successfully delivering a ²⁵Na beam at 16.4 MeV/u. This paper provides an overview of RISP’s technical progress and achievements made to date.

The design method of a metalens significantly impacts its actual performance. Conventional design approaches, such as the phase-matching approach, often fail to achieve the desired performance in metalenses with rapid phase changes due to mismatches between the actual and intended phase outputs of the meta-atoms. In this work, we employ an adjoint-based design method combined with level-set functions to partially address this issue. We present the design of a one-dimensional metalens with a quadratic-phase profile for wide-field-of-view applications. Our simulations show that the optimized design extends the FOV while maintaining focusing efficiency, compared to the conventional design with the same geometric numerical aperture of 0.9. This adjoint-based method provides an effective approach to improving the performance of wide-field-of-view metalenses and other metasurfaces with rapid phase changes, building upon the phase-matching framework.