Journal of the Korean Physical Society最新文献

We study the electric-field confinement of terahertz waves in an asterisk-shaped nano-slot antenna using finite-element-method-based simulations. The asterisk slot antenna, consisting of a single slot and an X-shaped slot antenna, exhibits near- and far-field characteristics depending on the coupling angle. In a regime of small coupling angles, three-dimensional confinement of terahertz waves is realized in X-shaped and coupled slot antennas. We analyze the coupling-angle-dependent confinement performance in terms of localized field strength and focusing degree, considering the gap size of the slot antennas. These findings provide valuable design insights for studying light-matter interactions in the terahertz frequency regime.

Topological chiral occurs when a crystal has an asymmetric structure that does not overlap with the mirror image. In this study, Si crystals with a topological chiral morphology were grown via mixed-source hydride vapor phase epitaxy (HVPE). AlN-based nanowires consisting of Al and Ga metal chlorides were changed to Si crystals, resulting in the formation of topological chiral Si crystals at the inflection point. The Si crystals grown from the AlN-based nanowires were single crystals exhibiting chirality based on an arbitrary point. In this study, we used 2H-Si lattice constants to predict the lattice structure at the inflection point of topological chiral Si crystals. As a result, a typical 2H-Si structure can be expected from the crystal structure at the top and bottom, and a topological chiral Si crystal with an inflection point rotated by 30° was confirmed. A high-resolution optical three-dimensional surface analyzer, field-emission scanning electron microscopy, X-ray photoelectron spectroscopy, high-resolution X-ray diffraction, and Raman spectroscopy were used to analyze the topological chiral Si crystals. The results indicated that topological chiral Si crystals can be used as a new quantum material that can be applied to high-power spintronic devices.

The use of SrTiO₃ substrates with either TiO₂- or SrO-terminated surfaces is essential for growing high-quality epitaxial perovskite oxide thin films. Adding niobium to SrTiO₃ introduces novel functionalities and imparts alterations to the metallic and structural characteristics. This study thoroughly investigates the physical and chemical processes involved in the chemical etching and annealing processes. This is to achieve an atomically flat, single-terminated surface of (001)-oriented Nb-doped SrTiO₃ (Nb:STO) surfaces and to optimize their performance. Atomic force microscopy (AFM) identified the most optimal treatment regimen, pinpointing annealing at 950 °C for a duration of 6 h, coupled with a 90-s etching procedure, which achieves a well-defined step terrace structure of the substrate. Additionally, angle-resolved X-ray photoelectron spectroscopy (AR-XPS) has revealed pronounced shifts in the predominant chemical component within the near-surface region due to changes in thermal parameters, even under consistent temperatures and durations. Reflection high-energy electron diffraction (RHEED) further confirms the creation of a single-terminated surface with the specified annealing conditions. This research provides valuable insights into the surface treatment processes for Nb:STO substrates and their influence on substrates’ structural and chemical properties.

This work presents a Segmented Gamma Scanning (SGS) efficiency calibration method based on Monte Carlo simulation and function model, to calculate the efficiency matrix and reconstruct the radioactivity of the radioactive waste drum. The middle- or low-energy gamma rays emitted by the transmission source ¹⁵²Eu, cannot transmit the high-density waste drum in the Segmented Gamma Scanning of the radioactive waste drum. Therefore, the accurate attenuation correction cannot be achieved through efficiency calibration, for the middle- or low-energy gamma rays emitted from the drum, which affects the accuracy of the reconstructed radioactivity. High-energy gamma rays have been employed to transmit the waste drum to determine the density of segment, and then the efficiency of segment is determined from the density of segment and the energy of gamma rays emitted from the waste drum. When the point source ¹³⁷Cs is distributed in segments with varying densities in the waste drum sample, the relative deviations of reconstructed radioactivity fall in − 90.69% ~ 22.33%. The method is convenient and effective for the SGS efficiency calibration while measuring the high-density waste drum, and the relative deviations of reconstructed activity are acceptable on this basis. Compared with alternative methods, the process outlined in this method is more simple, operational, and practical. Further, it provides the user with a practical method in SGS efficiency calibration and the activity reconstruction of the waste drum.

This study evaluated the dosimetric accuracy of SunCHECK, a calculation-based IMRT DQA program, when applied to VMAT DQA for the Halcyon LINAC. Virtual VMAT treatment plans were generated utilizing a Delta4 Phantom + diode detector array device to analyze the accuracy of the dose calculation algorithm in SunCHECK. The analysis revealed a strong correlation between the calculated dose in SunCHECK, the planned dose, and the measured delivery dose. The characteristics of dose distribution changes calculated by SunCHECK in the event of MLC errors during VMAT beam delivery were analyzed additionally. After delivering a beam with MLC position errors, the dosimetric error evaluated through log file-based calculations were compared with the error analysis findings obtained from measurements using the Delta4 Phantom + . The dosimetric error calculated based on the log file using SunCHECK showed a similar trend to the dose error calculated through the conventional measurement-based DQA method using a Delta4 Phantom + . The results of this study validate SunCHECK’s accuracy in dose calculation and analysis of dosimetric errors resulting from MLC position errors, thereby confirming its efficacy in VMAT DQA using the Halcyon LINAC.

In this work, the total-ionizing-dose (TID) effects on graphene field effect transistors (GFETs) were investigated using 10 keV X-ray irradiation under various gate biases in irradiation environment. For reliability applications, the Dirac voltage (V_Dirac) shifted negatively during irradiation as the hole mobility (μ_h) and electron mobility (μ_e) declined under the positive gate and zero bias. Under negative gate bias, the Dirac voltage (V_Dirac) moved in a positive direction, reducing hole mobility (μ_h) and electron mobility (μ_e). Thus, we can conclude that the positive gate bias is the worst bias of GFETs by contrasting the experimental outcomes under various biases. During the recovery time of 9 h and 24 h after irradiation, and it became clear that the Dirac voltage (V_Dirac) shifted in a positive direction. Notably, the emergence of trap charges caused by irradiation, and the accumulation of trap charges can be used to explain these phenomena. The recovery time outcome data indicate that radiation damage was caused by the trap charge created during irradiation. Therefore, this work assists in the implementation of GFETs in challenging environments.

Polyalkylene cyclo[12] carbon (abbreviated: Cy12 carbon) has a unique structure and its bonding properties, vibrational spectra and excitation properties have been explored by quantum chemical methods. The bond order analysis and molecular orbital analysis show that this sp hybridized all-carbon cyclo exhibits a C–C “alternating long bond-short bond” planar structure with C_6h symmetry and two sets of in-plane (in-πMOs) and out-of-plane (out-πMOs) orbitals; After MPI (molecular polarity index) index calculation, Cy12 carbon showed significant non-polar; the vibration analysis shows that most of the vibrations are symmetrically forbidden and doubly degenerate, with strong in-plane stretching vibrations and vibrations perpendicular to the plane appear in the low-frequency region. The excited state analysis reveals two detectable absorption bands of π-π* transitioned with the strongest absorption peak located at 164.5 nm from two degenerate excited states (S35 and S36), corresponding to the electronically excited processes of maximum absorption with πinMOs-πin*MOs, πinMOs-πout*MOs, πoutMOs-πin*MOs and πoutMOs- πout*MOs with mixed characteristics.

Statistical hypothesis testing assumes that the samples being analyzed are statistically independent, meaning that the occurrence of one sample does not affect the probability of the occurrence of another. In reality, however, this assumption may not always hold. When samples are not independent, it is important to consider their interdependence when interpreting the results of the hypothesis test. In this study, we address the issue of sample dependence in hypothesis testing by introducing the concept of adjusted sample size. This adjusted sample size provides additional information about the test results, which is particularly useful when samples exhibit dependence. To determine the adjusted sample size, we use the theory of networks to quantify sample dependence and model the variance of network density as a function of sample size. Our approach involves estimating the adjusted sample size by analyzing the variance of the network density, which reflects the degree of sample dependence. Through simulations, we demonstrate that dependent samples yield a higher variance in network density compared to independent samples, validating our method for estimating the adjusted sample size. Furthermore, we apply our proposed method to genomic datasets, estimating the adjusted sample size to effectively account for sample dependence in hypothesis testing. This guides interpreting test results and ensures more accurate data analysis.

In this study, we investigate the effectiveness of machine learning (ML) models in constructing empirical formulas for the superconducting transition temperature (T_c) by comparing ML-derived equations with McMillan’s equation. We utilized artificially generated data with a size of 10,000 from McMillan’s equation and employed the parametric brute force searching (BFS) algorithm to search for model equations varying model complexity and dataset size. The BFS models with features of the Debye temperature and electron–phonon coupling exhibit the RMSE of 0.830 K and R² of 0.976 even with a small dataset size of 100. The ML-derived formula is also close to McMillan’s equation showing a linear relationship between the Debye temperature and T_c, as well as a cubic relationship between electron–phonon coupling and T_c. Furthermore, we analyzed feature contributions using non-parametric random forest (RF) regression and found the strong relevance of electron–phonon coupling on T_c. Our results demonstrate the importance of feature selection and model complexity in effectively predicting T_c rather than simply adding more data.

This study investigated the influence of solution-processed indium oxide (In₂O₃) thin-film transistors (TFTs) with various iodine vapor (I₂) doping times. Prolonged iodine doping time is found to induce some important changes in the devices: (i) increase in In₂O₃ film thickness and nanoparticle size; (ii) decrease in the metal-hydroxyl bonding and increase in the metal–oxygen bonding; (iii) the positive moved threshold voltage, lower field-effect mobility, and higher on/off current ratio from 0 s (sec) to 10 s. Furthermore, vacuum thermal treatment, as a facial, novel method to recover the electrical performances of I₂-doped In₂O₃ TFTs was examined. I₂-doped In₂O₃ TFTs for 10 s with vacuum thermal treatment at 200 ℃ exhibited excellent recovery properties of electrical. The results indicate that iodine doping can change the electrical properties of In₂O₃ TFTs and could potentially be used for I₂ gas sensor.