Journal of the Korean Physical Society最新文献

The three-nucleon transfer (α, p) reaction has been analyzed within the framework of the full finite-range (FFR) distorted-wave Born approximation (DWBA) method at an incident energy of 31 MeV. To investigate the bound states of the ⁴³Sc, ⁴⁷Sc, and ⁵¹Sc nuclei for 8, 4, and 5 transitions, respectively, the four forms of the optical model potentials, such as Woods–Saxon, Michel, shallow non-monotonic (molecular), and deep non-monotonic (DNM) potentials are used. The three-nucleon transfer spectroscopic factors have been extracted for the observed angular distributions of the ⁴⁰Ca(( alpha ), p)⁴³Sc, ⁴⁴Ca((alpha ), p)⁴⁷Sc, and ⁴⁸Ca((alpha ), p)⁵¹Sc reactions for all forms of the optical model potentials. The spectroscopic factors that have been obtained in different states of the ⁴³Sc, ⁴⁷Sc, and ⁵¹Sc nuclei are mostly consistent for all forms of the potentials. The (chi_{N}^{2}) values are computed for the α+ ^{40, 44, 48}Ca elastic scattering and the (α, p) reactions with targets ⁴⁰Ca, ⁴⁴Ca, and ⁴⁸Ca to evaluate the quality of the fits. The two forms of the non-monotonic potentials, namely the molecular and DNM potentials, give an overall satisfactory description of the elastic scattering and reaction data than the Woods–Saxon and Michel potentials. Moreover, in this study, the form factors of the (α, p) reaction on ⁴⁰Ca have also been calculated for L = 1, 3, and 5 transfers.

The density of graphite insulation largely affects a temperature gradient of the horizontal direction of the hot-zone in SiC crystal growth using the physical vapor transport (PVT) method. Three types of stacking configurations of graphite insulation with different densities were implemented to graphite hot-zone. The stacking configuration adoption with denser graphite insulation at the seed region gives rise positive effect on the achievement of a convex crystal shape, no polytype inclusion, improvement of crystal quality as well as lower defect density due to maintainance of constant temperature gradient during the SiC crystal growth. These results were investigated using ultraviolet fluorescence (UVF) images, map of Full width at half maximum (FWHM) and shift of an X-ray rocking curve (Omega scan), and surface morphology analysis after molten KOH etching. Optimization of hot-zone design adopting with stacking configuration of graphite insulation led to high-quality SiC crystal through the PVT method.

The main objective of this study is to fabricate a control (a standard single-junction solar cell grown straight on bare GaAs substrate) and flexible freestanding GaAs-based single-junction solar cells (grown on a graphene layer deposited on GaAs substrate). Besides, the research work aims to characterise and mathematically simulate the PV cell behaviour using COMSOL Multiphysics (version 6). The control PV cell, as a baseline for comparison, was epitaxially grown by metal–organic chemical vapour deposition (MOCVD). Whilst remote epitaxy technique in addition to the ‘MOCVD’ method was used to fabricate the flexible freestanding GaAs solar cells. Remote epitaxy technique was employed to reduce the cost of the expensive monocrystalline GaAs substrate and produce flexible solar cells. The electrical properties of the membranes, including the current–voltage (I–V) curve, dark current, and quantum efficiency, were measured experimentally to evaluate how new flexible membranes perform relative to the control (traditional PV cell). The results showed that the power conversion efficiency of the fabricated single-junction GaAs membranes was about 9% at air mass condition AM1.5 (1000 W/m² insolation and 25 °C). Therefore, a mathematical simulation by COMSOL and a design of experiment by Minitab were proposed to improve their efficiency. The efficiency of the fabricated GaAs solar cells was enhanced to 19.62% by optimising the layer thickness and doping. Furthermore, the (I–V) curve, dark current, and quantum efficiency of the control solar cell as a benchmark for the flexible membrane were analysed by COMSOL Multiphysics/Semiconductor physics to compare with the experimental measurements.

The stagnation flow in a ternary hybrid nanofluid towards a cylinder that stretches and shrinks with suction velocity is investigated in this work. Here, water serves as conventional fluid and the nanoparticles are titanium dioxide (TiO₂), copper (Cu), and alumina (Al₂O₃). This work aims to study the flow behaviour for velocity, concentration, and temperature including the novel effects of heat radiation in energy equation and energy activation in concentration equation. Using proper similarity variables, governing equations are transformed to dimension-free form. The bvp4c method is used to solve these nonlinear dimension-free equations numerically. The flow behaviour of various physical parameters is studied graphically for velocity, temperature, and concentration boundary layer. Moreover, considerable importance in this investigation are skin friction coefficient, mass transport rate, and heat transport rate. Observation reveals that Reynolds number and suction parameter enhance fluid velocity and skin friction. Also, fluid velocity in the case of ternary hybrid nanofluid, i.e., for Al₂O₃–Cu–TiO₂/H₂O enhances than hybrid nanofluid (Al₂O₃–Cu/H₂O) and nanofluid (Al₂O₃/H₂O). The temperature profile and heat transport rate are improved by heat sources. Increasing the radiation parameter reduces fluid temperature by 4.76% from ternary to hybrid nanofluid and 4.54% from hybrid to nanofluid. Chemical reaction and Schmidt number reduce concentration boundary layer. This mathematical modelling of nanofluid with stretching/shrinking cylinder can benefit society through applications in some processes such as polymer sheets, crystal mass production, metal extrusion, bath cooling, and plate cooling.

Investigating the oxidation behavior of a bimetallic thin film for a durable gate electrode in complementary metal–oxide semiconductor (CMOS) devices is challenging. Herein, Pt–Ru bimetallic thin films were synthesized using atomic layer deposition (ALD), followed by intentional oxidation at 600 °C. The as-deposited Pt–Ru thin films presented distorted lattices due to the solid solution, whereas the X-ray diffraction (XRD) peaks of the oxidized Pt–Ru thin films did not shift, except for the Pt-rich oxidized Pt–Ru thin films. Interestingly, due to the high resistance of Pt to oxidation, Ru atoms in the Pt-rich oxidized Pt–Ru thin films were not oxidized under an oxidation atmosphere. Upon increasing the Ru content, Ru atoms started to oxidize, followed by full oxidization into Ru oxide in the Ru-rich Pt–Ru thin films. Simultaneously, Ru atoms moved to the surface and were oxidized with surface oxygen, thereby separating the upper Ru oxide and Pt metal layer. The resistivity of the oxidized Pt–Ru thin films increased as the Ru content increased, whereas the as-deposited Pt–Ru thin films exhibited a volcano-shaped peak depending on the relative composition between Ru and Pt. The work functions of the oxidized Pt–Ru thin films were higher than those of the as-deposited films, due to the higher work function of RuO₂ than those of Ru metals; however, the Pt-dominant Pt–Ru thin films showed similar values both before and after oxidation, owing to the unoxidized Ru atoms.

Investigation of thermoelectric (TE) properties on two-dimensional (2D) materials attracts intensive research efforts due to its potential environment-friendly applications. We explore the TE properties of 2D bilayer GaTe. The GaTe bilayer has an indirect bandgap of 1.35 eV. The maximum Seebeck coefficient is 1550 µV/K regardless of the direction and doping type. The relaxation time has anisotropic behavior. In the n-type system, the armchair direction relaxation time is longer than the zig-zag direction. The p-type relaxation time has no directional dependency and shorter than that of n-type. Also, the n-type relaxation time is longer than that of the p-type. This anisotropic relaxation time in n-type system generates larger electrical conductivity and electronic thermal conductivity in the n-type armchair direction. The lattice thermal conductivity has no directional dependency and is larger than the electronic thermal conductivity. Overall, we obtain the maximum figure of merit (ZT) of ~ 0.82 in the n-type at 700 K.

Conductive-bridge random access memory (CBRAM) is gaining attention as a non-volatile memory device for next-generation storage-class applications. However, CBRAM cells exhibit stochastic natures during continuous bi-stable resistive switching, stemming from the randomness of high-mobility metal ions in the resistive switching layer. This randomness limits wafer-scale integration with complementary metal–oxide–semiconductor (CMOS) circuits. In this study, we fabricated a reliable forming-free CBRAM cell consisting of a Pt capping layer, a Cu active source layer, a nitrogen-doped GeSe resistive switching layer, and a W bottom electrode. We compared the continuous resistive switching loops with and without nitrogen contents in the GeSe layer, demonstrating that the nitrogen-doped GeSe CBRAM cell improved electrical variation for the forming and set voltages to below 10%. Using this nitrogen-doped GeSe-based CBRAM cell, we achieved outstanding synaptic plasticity characteristics compared to un-doped GeSe-based CBRAM cells. Finally, we designed a small-scale deep neural network trained with a hardware-based backpropagation learning rule, achieving recognition accuracy of up to 95.57% on handwritten image datasets. Our study demonstrates that the nitrogen-doped GeSe-based CBRAM cell can achieve high reliability and stable synaptic plasticity, thereby contributing to the advancement of next-generation memory technologies.

An Approximate bound state solutions of the Dirac equation under the spin and pseudospin symmetries for the generalized Mobius square plus generalized Yukawa potential (MSPGYP), including generalized tensor interaction was examined. With the help of the Nikiforov-Uvarov functional analysis (NUFA) method and an approximation scheme, the analytical and numerical energies and the corresponding wave functions of the combined potential were obtained for both symmetries, for different quantum numbers. Degeneracies were observed in the energy values in the absence of the generalized tensor interaction and these degeneracies were removed with the help of the generalized tensor interaction. The variations of the energies for spin and pseudospin symmetries were studied for various values of the quantum numbers. Our study shows that the relativistic energies obtained are very sensitive to the quantum numbers. Relativistic and nonrelativistic thermodynamic properties evaluation was carried out for pseudospin symmetry. The effect of the temperature dependent parameter was seen to be very strong on the thermodynamic properties considered.