Journal of the Korean Physical Society最新文献

Surface acoustic waves (SAWs) have been utilized as a platform for single-electron transistors. When superposed with the split-gate potential, propagating SAWs create moving potential wells. We demonstrate the total potential landscape using the Laplace equation and apply the one-dimensional time-independent Schrödinger equation to determine the conditions necessary for single-electron transport. Our findings reveal that the ratio between the SAW amplitude and the split-gate voltage varies with the SAW wavelength and the absolute value of the gate voltage. We propose essential conditions for single-electron transport based on the ratios derived from our calculations, which can be applied to other material systems.

Raman spectroscopy is a powerful tool to investigate the properties of materials. In particular, the ability to analyze the crystallinity, the number of layers, defects, and electronic properties of two-dimensional materials (2DMs). 2DMs make it a valuable analytical tool in numerous fields. Among 2DMs, rhombohedral stacking graphite, which has ABC-stacked layers, has a different band structure that shows peculiar electronic properties compared to Bernal stacking graphite, which has ABA-stacked layers, and exhibits the characteristics of a topological insulator, making it a unique material. Using Raman spectroscopy, Bernal and rhombohedral stacking can be easily distinguished at room temperature. In multi-layer graphene (MLG), the stacking order can be distinguished by various bands generated from Raman scattering. Additionally, changes in the excitation energy of the laser result in shifts in the Raman peaks and changes in the line shape. In this study, 633 nm and 514 nm lasers were utilized to compare the Raman bands of MLG in Bernal and rhombohedral stacking order. The 2D band, which is a second-order overtone of different in-plane vibrations, was fitted with three Lorentzian peaks to investigate how each Lorentzian peak changes according to the stacking order. Subsequently, the D + Dʺ, N, and M bands, which are weak combination bands with double resonant Raman modes, were investigated to see how they change in Bernal and rhombohedral stacking MLG with increasing laser energy. Conclusively, we present an easy method to distinguish Bernal and rhombohedral stacking in MLG at room temperature using Raman spectroscopy.

An advanced hydride vapor-phase epitaxy (HVPE) method was used to improve the sublimation sandwich method for the formation of Si layers on SiC substrates. In this study, a graphite boat structure with a vertical source and growth zones was used, and the sublimation sandwich method was improved by directly attaching two substrates (without any spacing between them) differently from that of the existing sublimation sandwich method. After the deposition of the amorphous Si layer (using sputtering) on an SiC substrate, the recrystalline Si layer was formed at a temperature of 1250 °C using a SiCl_n source. Consequently, an Si layer with characteristics different from those of the sputtered Si layer was grown. The formed Si layer was characterized using field-emission scanning electron microscopy, energy-dispersive spectroscopy, high-resolution X-ray diffraction, X-ray photoelectron spectroscopy, secondary ion mass spectrometry, and atomic force microscopy. Overall, we propose an advanced HVPE sublimation sandwich method for forming Si layers on SiC substrates.

To prevent CaCO₃ scaling in oil and gas wells, scale inhibition are commonly used. This study utilized the molecular dynamics method to simulate the crystallization of a high concentration CaCO₃ solution, with particular attention given to the influence of the scale inhibitor sodium tripolyphosphate (Na₅P₃O₁₀). Examination of the distribution of CO₃²⁻ surrounding Ca²⁺ indicated that P₃O₁₀⁵⁻ effectively hinders the interaction between CO₃²⁻ and Ca²⁺, leading to a decrease in the root mean square displacement and diffusion coefficient of ions. Based on the analysis of intermolecular interaction energies, it is evident that the binding energy between Ca²⁺ and CO₃²⁻ is estimated at around 550 kcal/mol, whereas the binding energy between Ca²⁺ and P₃O₁₀⁵⁻ is approximately 1000 kcal/mol. These data support the conclusion that P₃O₁₀⁵⁻ exhibits a higher affinity for Ca²⁺ binding, thereby impeding the formation of CaCO₃.

A thorough performance analysis of sub-10 nm gate-length Tri-gate Fin-FETs with gates having single material (SMG) and triple material (TMG) has been conducted through technology computer-aided design (TCAD) simulations for low-power applications. The gate of the TMG device is formed of three metals with distinct work functions. To decrease the drain-induced barrier lowering (DIBL) and increase transconductance, the gate work function near the source is higher than near the drain. The DC and analog/RF are obtained, analyzed, and compared between SMG and TMG devices. It is engrossing that, the device’s OFF current (I_OFF) is drastically reduced and the ON current (I_ON) is improved in the TMG structure leading to a better switching ratio. Also, TMG Tri-gate FinFET device structures provide an excellent peak transconductance of 5.1756 µA/V at V_GS = 0.16 V and V_DS = 0.1 V, output conductance of 7.45 µA/V at V_GS = 1 V, a subthreshold slope of 120 mV/decade at V_DS = 0.1 V, an I_ON/I_OFF ratio of 557.12 at V_DS = 0.1 V, and DIBL of 33 mV/V. Whereas the SMG Tri-gate FinFET has a peak transconductance of 4.28 µA/V at V_GS = 0.4 V and V_DS = 0.1 V, output conductance of 5.88 µA/V at V_GS = 1 V, a subthreshold slope of 300 mV/decade at V_DS = 0.1 V, an I_ON/I_OFF ratio of 21.29 at V_DS = 0.1 V, and DIBL of 55 mV/V.

The distribution of fluorocarbon surfactants potassium perfluoro (2-ethoxyethane) sulfonate (PESK) in 3.4% NaCl solution was studied using molecular dynamics (MD) simulation method. During the MD simulation, it was observed that the PES⁻ in the bulk solution spontaneously move to the water/gas interface. According to the change in the number of water molecules within 0.35 nm of PES⁻, it can be inferred that the solution has basically reached equilibrium when the simulation reaches 40 ns. At this moment, the vast majority PES⁻ are distributed at the air/water surface, the fluorocarbon chain is facing toward the gas phase, while the sulfonic acid radical faces toward the water, and there are about 12 water molecules within 0.35 nm of each PES⁻, a very small quantity of PES⁻ still in the bulk solution. Compared with K⁺, Na⁺ is more likely bound to PES⁻, and this is confirmed by RDF and number density distribution analysis. The weak intermolecular interactions were analyzed by the IGMH method, and the interaction energy between PES⁻ and water mainly comes from the h-bonds formed by the oxygen atom in the sulfonic acid group and hydrogen atom in water molecules; there is only van der Waals interaction between fluorine atoms and water molecules.

Scanning proton therapy offers advantages over conventional photon therapy due to the Bragg-peak effect and superior dosimetric precision. Compared with passive methods, however, scanning proton therapy tends to exhibit a wider penumbra in the low-energy range. To address this issue, the present study evaluated the effectiveness of a patient-specific aperture collimator (AC) and multi-leaf collimator (MLC) for the line proton scanning treatment system at the Samsung Proton Therapy Center in Korea. The penumbra reduction efficiency of the collimation devices and the neutron dose was assessed through Monte Carlo (MC) simulations. The clinical effectiveness was evaluated dosimetrically and by assessing quality assurance. Through the MC calculation, the AC displayed the highest efficiency in penumbra reduction (43.75% of no collimator’s penumbra width at a depth of 10 cm with a 150 MeV proton beam), while the MLC also presented a comparable effect (56.25%). The neutron dose was compared at varying distances from the field edge. The neutron dose was higher in the order of AC(+ 11.96%p), MLC(+ 2.61%p), and no collimator at the 10 cm distance from field edge. For the dosimetric study, treatment plans for the nasal cavity, prostate, liver, lungs, and breasts were generated by the treatment planning system using the MC algorithm. Three treatment plans were developed for each of these five sites: line scanning without any collimation, line scanning with patient-specific ACs, and line scanning with MLCs. These plans were then compared dosimetrically, and gamma pass-rates were measured at various depths. These multifaceted comparisons showed that the use of an AC optimized the OAR sparing effect, with an MLC having similar effects, while maintaining the same target coverage and producing less neutron dose. All measurement results demonstrated a gamma pass-rate (2%, 2 mm) of over 90%, indicating the feasibility of implementing these techniques in actual clinical practice.

Group-III monochalcogenides, particularly gallium sulfide (GaS), have garnered attention for visible–UV range optoelectronic applications owing to their wide bandgap, which can reach approximately 3 eV. The interplay between group-III monochalcogenides and metal electrodes needs to be understood to optimize the device performance. In this study, we explored the Schottky barrier height between GaS deposited through atomic layer deposition and commonly employed Ti/Au electrodes through low-temperature current–voltage measurements. The GaS photodetector exhibited p-type transport characteristics with a mobility of 7.71 × 10^–1 cm² V⁻¹ s⁻¹ and a photoresponsivity of 547 A W⁻¹.

While spontaneous spin polarization is a desirable property in semiconductors, it has not been observed in pristine materials. A theoretical study suggested that the Au/Si(553) surface exhibits anti-ferromagnetic properties spontaneously. The Si(5 5 12) surface shares a similar atomic structure with the Au/Si(553) surface, particularly the presence of a stable honeycomb chain. The Si(5 5 12) surface exhibits four distinct surface structures: honeycomb chain, dimer, adatom, and tetramer. We find that while the pristine Si(5 5 12) shows no spin polarization, the doped Si(5 5 12) surface leads to spin splitting, primarily concentrated at the dangling bonds of the adatom and honeycomb chain. This spin splitting induces a transformation of the surface into a ferromagnetic state. Although the behaviors are rather different for the electron and hole doping, the surface magnetization roughly strengthens as the number of doped charges increases. These findings suggest that charge doping can be a viable approach to induce spin polarization in Si(5 5 12) surfaces, offering a potential route towards achieving this desired property in semiconductors.

The motivation of geometry engineering with proton, deuteron, and helium-3 projectiles at relativistic heavy-ion collider (RHIC) is to investigate the relation between initial geometry and final momentum anisotropy, which is thought to be strong evidence of quark–gluon plasma. PHENIX Collaboration shows a hierarchy of elliptic and triangular flow in p/d/(^{3})He+Au collisions that follow a hierarchy of eccentricity described by the Monte Carlo Glauber model, whereas STAR Collaboration shows a different trend in the triangular flow results. For a complete understanding of the results, a detailed microscopic description, such as sub-nucleon geometry and area of energy deposition, becomes more important. A multiphase transport model (AMPT) can qualitatively describe the collective behavior with scatterings at partonic and hadronic stages. We utilize the AMPT to simulate small systems and investigate the relation between initial geometry and final momentum anisotropy with different geometry descriptions.