Journal of the Korean Physical Society最新文献

The K-4GSR project targets a 4.0 GeV 4th generation synchrotron radiation source with (sim )800 m circumference and 4 GeV beam energy. It features a 7 Multi-Bend Achromat (MBA) lattice structure with a beam emittance of less than 100 pm. It employs a 4 GeV full-energy injection using a booster installed in the same tunnel with the storage ring. The booster ramps the 200 MeV injection beam to 4 GeV beam energy for the storage ring injection and operates at 2 Hz. The booster consists of 60 combined-function dipoles, and 66 quadrupoles, with additional sextupoles and correctors. Combined-function dipoles are chosen as bending lattice elements to minimize the number of magnets and the total costs. In this study, the 2D pole face optimization, the 3D FEM analysis, and a detailed reference orbit, which is slightly different from a pure bending orbit are analyzed.

A novel technique has been developed to determine the three-dimensional position of a source emitting multiple cascade γ-rays with sub-millimeter accuracy using dual-layered GSO (Ce) scintillation detectors. This method reconstructs the source position by processing filtered energy and detector hit positions through a back-projection algorithm along the paths of incident γ-rays. The detector array and an ¹¹¹In-ion point source at five locations within the central detection volume were simulated using the GATE Monte Carlo framework. For a source at the detector center (0, 0, 0), the reconstructed coordinates are − 0.001 mm, − 0.001 mm, and − 0.001 mm along X, Y, and Z. This indicates that the reconstructed source centroid was centrally located and well within the spatial resolution limits of the detector system. For other simulated source positions, the reconstructed coordinates matched approximately 99.8% of the actual simulated positions, although some positions varied between 70.9% and 125% of the true values. Except for source at the center, other source positions were reported with uncertainty ranging from 0.006 × 10^–3 mm to ± 5.480 × 10^–3 mm. While reconstruction at the transaxial and axial edges is less precise due to limited valid coincidence events, the results demonstrate the method’s robustness. The achieved reconstruction precision indicates potential applications in nuclear medicine, nuclear security, radioactive waste assay, and proton beam therapy.

This study investigates the role of the projectile's charge state in the defect engineering of graphene using ion beams. A comparison was made between defects induced by He⁺ and He²⁺ ions at an identical kinetic energy of 120 keV. Raman spectroscopy analysis showed that He²⁺ ions generated a higher defect density, ranging from 40 to 65%, compared to He⁺ ions. To investigate how this defect difference impacts device performance, we fabricated and tested chemiresistive gas sensors, where devices irradiated with He²⁺ showed improved sensitivity to hydrogen. The observation of higher defect generation for He²⁺ can be explained by the absence of electron screening, which is present for the He⁺ ion. This condition could increase the Coulomb interaction with target carbon nuclei, consistent with a larger Rutherford scattering cross-section. The results indicate that, even within the same ion species, the ion charge state can serve as an additional parameter for modifying the properties of graphene-based devices.

A magnetocardiography (MCG) system is a medical device that diagnoses cardiac disease by measuring magnetic fields generated from electric currents flowing through the myocardium. However, the accuracy of measurement data can be degraded if strong magnetic materials are present or magnetic field changes occur near the MCG system. With the widespread use of implants, the number of patients with metallic implants is increasing, but there is a lack of in-depth research on the potential impact of implant materials on the results of the MCG examination. This study aims to analyze the effect of implant materials on MCG measurements and establish relevant criteria. In this study, a 96-channel MCG system employing Superconducting Quantum Interference Device (SQUID) sensors, specifically first-order gradiometers based on the Double Relaxation Oscillation SQUID method, and a magnetically shielded room were utilized. Titanium-6Aluminum-4Vanadium ELI was selected as the representative implant material sample. Experiments were conducted under extreme conditions, where a sample significantly larger than an actual implant was placed as close as possible to the sensors. As a result, when the implant material was at the minimum distance to the sensor, the noise increase was approximately 0.7 fT/√Hz, which satisfies the sensitivity criteria for MCG. Furthermore, since these results were obtained under severely adverse conditions designed to maximize the noise impact, it is anticipated that the effect would be even more negligible in actual clinical settings. In conclusion, it was confirmed that common implant materials have little to no effect on MCG measurements.

Vacuum degradation in the beam device is a critical concern in high-precision ion beam processing, as it perturbs beam optics and reduces energy efficiency. While pressure effects in the transport region are mitigated by space charge compensation and charge exchanges, the dynamics in the extraction region of low-energy sources under elevated vacuum conditions remain insufficiently understood. In this paper, we experimentally investigate the influence of background pressure on beam focusing and extraction efficiency in a small penning ion gauge (PIG) ion source, where the extraction section constitutes a dominant part of the beamline. Our results reveal that, under elevated pressure conditions, the current impinging on the suppression electrode increases with higher suppression voltages—a trend contrary to the low-pressure conditions. We demonstrate that this current loss increment is attributed to the trapping of low-energy ions generated via charge exchange and momentum transfer, rather than to the conventional electrostatic over-focusing mechanism. These findings indicate that elevated background pressures primarily accelerate device degradation through collision-induced beam loss, necessitating rigorous vacuum management for stable operation.

This work demonstrates a plasma-free, short-time potassium hydroxide (KOH) wet pretreatment for a hybrid bonding process, targeting high SiO₂–SiO₂ bonding strength while suppressing Cu surface oxidation. KOH treatment at 50 °C for 15 s significantly improved SiO₂ wettability, reducing the deionized water contact angle, and enabled a maximum shear strength of 29.6 MPa after 300 °C annealing. The oxide etching behavior was quantified using a TiO₂ cap structure, confirming time-dependent selective SiO₂ thinning in 5 M KOH at 50 °C. To evaluate the Cu surface stability, 400 nm Cu films were analyzed after exposure to citric acid and subsequent KOH treatment. While atomic force microscope (AFM) roughness showed no pronounced change, the mean conductive AFM current indicated progressively reduced conduction with longer KOH treatment. These results identify short-time KOH as a key process window that balances surface activation and Cu stability for plasma-free hybrid bonding.

We report on the crystal growth and superconducting properties of the transition-metal dichalcogenide 2H-NbSe₂. Millimeter-scale 2H-NbSe₂ single crystals with well-defined hexagonal platelets were grown by chemical vapor transport with iodine (I₂) as the transport agent. Rietveld analysis of X-ray powder diffraction confirms the single-phase P6₃/mmc space group with a = b = 3.443 Å and c = 12.542 Å. Electrical transport and magnetic measurements confirm bulk superconductivity (T_c = 7.06 K), coexistence of charge density wave order (T_CDW = 33 K), and nearly ideal diamagnetism (4πχ ~-0.98 at 2 K). Temperature-dependent specific heat shows a clear jump at T_c, which can be analyzed using a two-gap s + s-wave model with different weights. Approximately 97% of the total Sommerfeld coefficient is associated with the larger-gap ((Delta_{1} sim 1.68) meV), while the smaller-gap ((Delta_{2} sim 0.27) meV) accounts for the remaining 3%. This work provides useful quantitative information on multiband superconductivity in 2H-NbSe₂ single crystals.

In this work, ZnO thin films were deposited on c-plane Al₂O₃ substrates by atomic layer deposition (ALD) under various growth conditions. The Zn/O feeding time ratios were adjusted from 0.5 to 3.5 at growth temperatures between 120 °C and 300 °C. Films grown at a temperature (T_g) of 200 °C exhibited superior crystallinity and pronounced (200) orientation compared to those grown at lower temperatures, as increased thermal energy promoted more effective surface diffusion and improved atomic arrangement. Raman and photoluminescence analyses revealed well-defined phonon modes and enhanced near-band-edge ultraviolet emission for the film grown at 200 °C with a Zn/O feeding time ratio of 1.5:2, indicating a high degree of structural uniformity and efficient radiative recombination. These findings elucidate how growth temperature and precursor stoichiometry govern the structural and optical quality of ALD-grown ZnO thin films, underscoring the potential of low-temperature ALD for producing high-quality ZnO layers suitable for semiconductor and optoelectronic device applications.

In this work, we examine the electrical and dielectric characteristics of the SiO₂ oxide layer that was produced using the ECR-PECVD method on a p-Si substrate. The frequency range of 100 Hz–1 MHz has been used to record capacitance–voltage (C-Vg) and conductance-voltage (G/ω-Vg) properties. The interface states (N_ss) and series resistance (R_s) effects are associated with anomalous peaks in the C-Vg and G-Vg plots. It demonstrates how the capacitance at low frequencies is influenced by the interface state. Because the interface state capacitance decreases with increasing frequency, the effect of series resistance on capacitance becomes noticeable at higher frequencies. In addition, the frequency dependence of dielectric constants (ε’, ε”), dielectric loss tangent (tanδ), electric modulus (M', M''), and the electrical conductivity (σ_ac) is also studied for the Al/SiO₂/p-Si (MOS) structure. The double logarithmic σ_ac-w curve shows linear behavior, with its slope around 0.66 to 0.26, and this value of Al/SiO₂/p-Si (MOS) structure has a high AC conductivity.

We present a scanning tunneling microscopy (STM) study of nanometer-scale surface defects on the 2H-MoS₂(0001) surface of a natural single-crystal mineral. Two dominant types of nanometer-scale defects, denoted as B and D, were ubiquitously observed on freshly exfoliated surfaces in both ultra-high vacuum and ambient environments as well as on intentionally carbon-deposited surfaces. All these observations exclude an extrinsic adsorption-related origin and instead suggest a carbon-related bulk source. The B defects exhibit a pronounced bias-dependent contrast reversal, appearing as bright protrusions at negative sample biases and as dark depressions at positive biases. In contrast, the D defects appear consistently as dark depressions over the entire bias range. The defect population increases gradually over time, supporting an intrinsic bulk reservoir of carbon species. In addition, reversible interconversion between the B and D defects is observed during STM scanning, suggesting that they originate from the same defect species occupying closely related adsorption configurations with similar energies. These results identify carbon impurities as the origin of the most prevalent nanometer-scale surface defects on MoS₂ and establish a consistent framework for interpreting their STM contrast and evolution.