Journal of the Korean Physical Society最新文献

In this work, the Fermi level pinning phenomena in erbium-silicided metal–semiconductor Schottky contact is investigated for the understanding on the difficulties forming ohmic contacts between metal and semiconductor materials. The work function of erbium-silicide is extracted by using UPS (ultraviolet photoelectron spectroscopy) and I–V (current–voltage) method with metal–semiconductor diode pattern, respectively. In UPS analysis, the extracted workfunction gradually decreased with increase in the deposited erbium-silicide and saturated to 3.8 eV with 500 Å thick erbium-silicide. However, the extracted work function value of erbium-silicide by I–V method from erbium-silicide on p-type silicon substrate diode pattern is 4.4 eV which shows the strong Fermi level pinning phenomena in erbium-silicided Schottky contact. From the numerical model analysis, the main reason for Fermi level pinning in erbium-silicide is mainly attributed due to the metal induced gap state rather than chemical bonding at interface. Finally, this analysis method will be very effective for the analysis in Fermi level pinning phenomena in metal–semiconductor Schottky contacts.

Zinc oxide films doped with iron (Fe-doped ZnO) were fabricated via spray pyrolysis technique by utilizing zinc nitrate and ferric chloride as the source materials. The film manifests a hexagonal wurtzite crystalline structure. Variations in the atomic dimensions of ZnO matrix were observed with an escalation in dopant concentration ranging from 0 to 5 at.% (atomic percent). The incorporation of Fe into the lattice was found to influence the optical transmittance properties and resulted in a decrement of the optical bandgap from 3.28 eV to 2.90 eV. X-ray diffraction (XRD) analysis confirmed that the films are monophasic, retaining a wurtzite structure characteristic of pure ZnO. Comprehensive material characterization was conducted by utilizing a suite of analytical techniques, including scanning electron microscopy (SEM), ultraviolet–visible (UV–Vis) spectroscopy and X-ray photoelectron spectroscopy (XPS), to substantiate the successful synthesis of the nanocomposite and to evaluate various attributes such as surface area, structural and morphological features, chemical composition, and purity. The gas-sensing efficacy of the Fe-doped ZnO films towards nitrogen dioxide (NO₂) was assessed, revealing a significant gas response of 31.81% at an operational temperature of 400 degrees Celsius for a NO₂ concentration of 100 parts per million (ppm). This gas-sensing performance is characterized by prompt response and recovery times, recorded at 23 s and 61 s, respectively. In addition, it was determined that the sensor response is contingent upon the operating temperature.

Non-trivial sound speed may occur in various interesting scenarios in cosmology and affect the growth of primordial perturbation in the early Universe. This can lead to several observable signatures in the Baryon Acoustic Oscillations, CMB anisotropies, Dark Matter–Baryon Interactions, and the large-scale structure. On the other hand, the vacuum state of curvature perturbation could be expressed as a two-mode squeezed state. In this paper, we study the effects of the non-trivial speed of sound of the perturbations on the evolution of quantum discord for the primordial curvature perturbation using the squeezed formalism. Quantum discord, a measure of the non-classical correlations or quantum correlations between two subsystems of a quantum system, is closely related to the concept of entanglement in the field of quantum information science. We show that the effective speed of sound of primordial perturbations affects the final freeze-in amplitude of the quantum discord. This should provide us with a way to discern the effective speed of sound from quantum discord. We further argue that this may help us further understand the connection between the scrambling time and the effective speed of sounds of the perturbations. These connections can usher a direction when understanding the early Universe from a quantum information point of view.

We implemented a sensor to measure the concentration of solvents in water and evaluated the accuracy of the sensor. The sensor’s measurement results were compared using cyclic voltammetry, which measures the chemical potential of the solution. A film was produced using Indium-Tin-Oxide (ITO) nanoparticles. Structural and electrical properties of the film, which are closely related to sensor operating characteristics, were investigated. X-Ray Diffraction (XRD) measurements showed that the ITO nanoparticle size is ~ 35 nm. Hall effect measurements at 300 K showed that the carrier concentration n was 4.2–9.2 × 10¹⁸ cm⁻³ and the mobility μ was 0.13–0.68 cm²/Vs. Hall measurements show that grain boundary scattering is the main factor limiting the mobility of ITO film. The response of the sensor to three representative organic solvents methanol (MeOH), ethanol (EtOH), and isopropyl alcohol (IPA) was evaluated at various concentrations of each substance. The electrochemical potential of the analyte was determined using cyclic voltammetry (CV) measurements, and the sensor response was calculated using a simple model. The measurement results of the ITO sensor and the results obtained using CV measurement were consistent with each other within a maximum offset values of 4.9%.

Twisted trilayer graphene hosts two moiré superlattices originating from two interfaces between graphene layers. However, the system is generally unstable to lattice relaxation at small twist angles and is expected to show a significantly modified electronic band structure. In particular, a helical trilayer graphene—whose two twisted angles have the same sign—provides an attractive platform with a flat band isolated by large energy gaps near the magic angle, but the interplay between the lattice and the electronic degrees of freedom is not well understood. Here, we performed a large-scale molecular dynamics simulation to study the lattice relaxation of helical trilayer graphenes and evaluated their electronic spectra with a tight-binding model calculation. The comparison of the electronic spectra with and without the lattice relaxation reveals how the lattice relaxation significantly modifies the electronic spectra, particularly near the charge neutrality point. We also investigated the local density of states to visualize the spatially varying electronic spectra that accord with macroscopic domain patterns of moiré lattice stackings. We propose these characteristic spectral features in the electronic degrees of freedom of a relaxed helical trilayer graphene to be confirmed by scanning probe techniques, such as scanning single-electron transistors and scanning tunneling microscopes.

An X-band electron LINAC comprising 23 cells was fabricated and tuned for radiation therapy. The fabrication process used oxygen-free high-conductivity copper, which was divided into roughing and finishing stages to minimize machining errors. Resonance frequency measurements and tuning were performed for the half-cell, the unit cell with two half-cells combined, and all cells after assembly. Finally, the electric field inside the entire RF cavity was measured and tuned using a bead-pull test. The reason for the multi-step measurement and tuning was to minimize the number of tunings. Most of the tuning was done in the direction of increasing the frequency, and only a few were done in the direction of decreasing the frequency. All cells were tuned the same way. The finalized cavity had a resonance frequency of 9.306 GHz and a coupling coefficient of 1.277. Performance validation was performed through the percentage depth dose (PDD) test, confirming good agreement with the results for 6 MV X-rays.

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.