Abstract In this investigation, we enhance the performance of a flexible perovskite solar cell (FPSC) using SCAPS modeling software. The basic goal of this attempt was to build environmentally friendly and high-efficiency perovskite solar cells. The optimal structure of the device FTO/ZnSe/CH₃NH₃BiI₃/CNTS/Au consists of a CH₃NH₃BiI₃ absorber, ZnSe buffer, FTO electron transport layer (ETL), and CNTS hole transport layer (HTL). This research analyzes the effect of absorber layer thickness, buffer layer thickness, defect density of absorber layer, series resistance, and shunt resistance to get the optimized value. We optimized the device at a temperature of 300 K and an absorber layer thickness of 1.5 μm and a defect density of 1x10¹⁴ cm⁻³. The optimized cell demonstrated a power conversion efficiency of 23.34%, an open circuit voltage of 1.31 V, a fill factor of 80.63%, and a short circuit current density of 22.35 mA/cm².
Abstract The interaction of oxygen atoms with nanocavities (nanovoids) induced by hydrogen ion implantation in Si was investigated before and after annealing at 900 – 1100 °C using slow-positron and ion beams. Positron annihilation spectroscopy showed that the nanocavities remained even after annealing at 1100 °C. There was a clear difference between the Czochralski- and floating-zone-grown Si samples in terms of oxygen interaction. This difference can be ascribed to the oxygen concentrations and diffusion efficiencies to the nanocavities. Crystalline disorder owing to oxygen interactions around the nanocavities was confirmed by Rutherford backscattering channeling measurements. The accumulation of oxygen atoms near the hydrogen projected range was observed using secondary ion mass spectrometry, indicating the gettering effect of the nanocavities.
Abstract The phonon-limited electron mobility μ e of Si nanosheets, which are confined in the [001] direction with a thickness t less than 2 nm, is investigated in the presence of out-of-plane acoustic (ZA) phonons. Density functional theory, together with the Boltzmann transport theory within the relaxation-time approximation, is used to estimate the contribution of the ZA phonons. The results show that in the case of low temperature or thin thickness, μ e exhibits a distinctive decrease as the electron density n decreases even in the nondegenerate region. This low- n mobility reduction originates from the strong interaction with ZA phonons toward smaller n . At room temperature, the low- n mobility reduction remains for t < 1 nm but disappears for t > 1 nm.
Abstract We developed an eco-friendly gel plating method for Ni films. In this study, chloride- and sulfate-based gel electrolytes were compared to clarify the origin of the high cell voltage and low current efficiency. The chloride bath reduced the cell voltage from over 3.0 V to approximately 1.5 V and showed higher current efficiency. The potential difference between two positions in the gel was 0.07–0.08 V in the chloride bath and 0.25 V in the sulfate bath, much smaller than the total cell voltage. After 30 min, anode mass loss and deposit mass were 2.62 and 2.61 mg in the chloride bath, compared with 0.60 and 1.40 mg in the sulfate bath. These results suggest that the high cell voltage of the sulfate bath is related to inhibited Ni anode dissolution and electrode/gel interfacial phenomena, rather than the potential difference within the gel alone.
Lead-free dielectric ceramics are environmentally friendly candidates for energy-storage capacitors, while the recoverable energy density of ferroelectric perovskites is known to be enhanced in the vicinity of the Curie point. As such, (1–x)Ba 0.85 Ca 0.15 Zr 0.1 Ti 0.9 O 3 – x SrTiO 3 ceramics with x = 0–0.5 were prepared by a conventional solid-state reaction, and the effect of the ST solid-solution ratio on the energy-storage behavior was examined at a fixed field of 30 kV cm −1 . At room temperature, the recoverable energy density W rec reached approximately 133 mJ cm −3 at x = 0.3 and the efficiency η increased steadily from about 25% to 90%. The temperature-dependent measurements revealed that W rec peaked near the respective Curie point of each composition, with a comparable peak value of approximately 140 mJ cm −3 for all compositions. These results indicate that Sr does not intrinsically improve the achievable energy density, but instead shifts the temperature window over which the optimal performance is obtained.
Abstract Electrochemical (EC) etching has been studied as a processing technique for GaN, and increased carrier concentrations are expected to improve its processing capabilities. We investigated the EC etching of n-type GaN with carrier concentrations in the 10 20 cm -3 range, a regime rarely reported, using heavily oxygen-doped, n-type GaN grown by oxide vapor phase epitaxy (OVPE). EC etching was performed in a KOH solution for GaN samples with carrier concentrations ranging from 10 16 to 10 20 cm -3 . The results showed that while porous etching dominates in the 10 18 cm -3 range, OVPE-grown GaN (OVPE-GaN) samples with carrier concentrations of 10 19 and 10 20 cm -3 undergo electropolishing. In addition, selective removal of OVPE-GaN via EC etching based on carrier concentration differences was demonstrated. These findings suggest that high-carrier-concentration OVPE-GaN is suitable as a sacrificial layer, opening up new possibilities for GaN substrate processing and advanced device fabrication.
In this paper, the effects of the Ar/N 2 gas flow rates and annealing ambient dependence on ferroelectric HfN (Fe-HfN) formed by electron cyclotron resonance-plasma sputtering were investigated. The remanent polarization (2P r ) of 1.3 µC cm −2 and 1.2 µC cm −2 were obtained with Ar/N 2 gas flow rates of 8/6 and 8/8 sccm, respectively. Fatigue endurance up to 10 10 cycles was achieved with Ar/N 2 gas flow rates of 8/8 and 8/10 sccm. Annealing in He ambient increased 2P r from 1.2 µC cm −2 –3.0 µC cm −2 compared with annealing in N 2 ambient. PtSi S/D Schottky-barrier Metal–ferroelectric–Si field-effect transistors were fabricated with Ar/N 2 gas flow rates of 8/8 sccm and annealing in He ambient. An I ON / I OFF ratio of 5.9 × 10 3 and a subthreshold swing of 186 mV dec −1 were obtained. The I D – V G characteristics shifted in the positive direction after applying −3.7 V/100 ns pulses 100 times, indicating ferroelectric polarization switching.
Electron paramagnetic resonance (EPR) spectroscopy was used to investigate paramagnetic impurity centers in commercially available MgO single crystals at room temperature. Three dominant signals with resolved hyperfine structures were assigned to Mn-, V-, and Si-related centers based on their hyperfine patterns, angular dependences, and spin-Hamiltonian analysis. Angular-dependent measurements showed negligible anisotropy in the dominant resonance fields and hyperfine interactions, whereas weak Mn-related fine-structure components were reproduced by a cubic spin-Hamiltonian model. Sequential line-shape fitting and double integration enabled evaluation of representative g values, hyperfine constants, semi-quantitative spin concentrations, and effective spin-density ratios. The Mn-related signal is consistent with substitutional Mn 2+ in a nearly cubic environment, while the V-related signal is consistent with a nearly isotropic V 2+ -like center. The Si-related defect shows a much smaller hyperfine interaction, suggesting a spatially extended electronic state. These results provide a systematic EPR characterization of residual impurity centers in MgO substrates.
To facilitate the development of CuCl-based optical devices, this study investigated strategies for enhancing the crystalline quality of CuCl thin films, the fabrication of multilayer structures, and methods for improving their long-term durability. Samples were fabricated on CaF 2 (111) substrates using molecular beam epitaxy and vacuum deposition. Our primary finding is that the combination of a CaF 2 homo-buffer layer and pre-deposition electron beam irradiation significantly enhances the crystalline quality. This was confirmed by AFM observations of oriented triangular structures and reflectance spectra yielding exciton coherence lengths that exceed the film thickness, signifying the achievement of high-quality growth. Additionally, the introduction of a Si capping layer maintained the film’s optical integrity for up to 384 h, outperforming capping in long-term stability. These results, including the observations of pseudo-continuous structures in multilayered samples, provide essential guidance for the structural and material optimizations required to achieve stable, high-performance CuCl-based excitonic devices.
Surface structure of trehalose dihydrate crystals in liquid was investigated by using high-resolution frequency modulation atomic force microscopy (AFM). While trehalose exhibits remarkable bioprotective properties, its molecular-scale surface structure under liquid conditions remains poorly understood. Crystals prepared from a supersaturated aqueous solution were observed in hexanol, a non-solvent that can suppress dissolution and enables stable imaging. Wide-area imaging revealed that flat terraces emerged through gradual dissolution of surface microcrystals. The measured step height of 0.6–0.7 nm corresponds to a single molecular layer, indicating that the observed surface is the (100) plane. Molecular-resolution images exhibited periodic structures with spacings are close to the crystallographic lattice parameters. Two distinct contrast patterns were identified, reflecting two types of trehalose molecule with different orientations in the unit cell. These findings demonstrate the feasibility of stable liquid-phase AFM imaging of trehalose crystals and provide direct insights into their molecular-scale surface structure, contributing to an understanding of their physicochemical functionality.
High-performance piezoelectric devices are widely used in advanced electronic applications. Screen printing is considered a cost-effective and environmentally friendly method for fabricating oriented thick-film patterns. However, the universal factors governing oriented thick-film formation have not been clarified yet. This study investigates the material dependence of preferential orientation by fabricating various Pb-based piezoelectric thick films such as lead zirconate titanate (PZT), lead magnesium niobate–lead titanate (PMN–PT), and related material systems, on (100) pc -oriented BaTiO 3 (BT) template layers. To clarify the origin of the orientation behavior, a novel first-principles computational approach was introduced to evaluate surface free energies while preventing artificial structural collapse on slab surfaces. High-temperature X-ray diffraction analysis revealed that lattice matching alone does not determine orientation behavior. Instead, first-principles calculations showed that the appearance of orientation is governed by the balance of surface free energies (wettability) between the BT template layer and the overlying thick film. Based on the calculated surface free energy, materials exhibiting the layer-by-layer growth mode are shown to form highly oriented thick films, which explains their orientation, whereas the island-like growth mode accounts for randomly oriented films. These findings provide a novel guideline for material selection not only in oriented thick-film fabrication but also in solid-state single crystal growth methods.
When a resist film is immersed in a developer, it permeates the film. Polymer dissolution and developer permeation occur in parallel. However, differentiating between the two types of kinetics is challenging. Herein, we propose a method for the inverse analysis of quartz crystal microbalance profiles to reconstruct the temporal changes in the flow rates of the polymer and developer at the dissolution front. The inverse analysis of the dissolution kinetics of poly(4-hydroxystyrene) films in a 2.38 wt% aqueous tetramethylammonium hydroxide developer is demonstrated. The proposed method is applicable to resist films with dissolution times exceeding 0.1 s.
This study demonstrates that minimizing the curve-fitting (CF) error of a parametric point spread function (PPSF) may not optimize pattern prediction (PP) performance for advanced curvilinear extreme ultraviolet masks. To address this, a PP-based PPSF calibration framework incorporating additional basis functions, an independent performance index, and PP-based examination was developed. This framework improved the PP examination pass rate from 67% to 100%, reduced the average edge placement error by 76.7%, and decreased the average fitting-parameter count by 13%. These results demonstrate greater robustness under electron-beam process variations and indicate that minimizing CF error alone is insufficient for reliable PPSF selection.
Spontaneous orientation polarization (SOP) in organic light-emitting diodes (OLEDs) often induces excess interfacial charge accumulation, causing efficiency loss through exciton–polaron quenching. Dipolar doping is a promising strategy to induce SOP in otherwise nearly nonpolar hole transport layers (HTLs) and thereby control interfacial charge accumulation. In this study, we systematically investigated the SOP and hole transport properties of several dipolar-doped HTLs. We found that 2,2′,2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-bensimidazole) (TPBi):N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) and 1,3-bis[2-(4-tert-butylphenyl)-1,3,4-oxadiazo-5-yl]benzene (OXD-7): 4,4′-cyclohexylidenebis[N,N-bis(4-methylphenyl)benzenamine] (TAPC) films exhibit significant SOP while maintaining charge transport properties, unlike most dipolar-doped HTLs. This preservation of charge transport properties is likely related to their microscopic film structures, such as phase-separated morphology, which may suppress dipolar-disorder effects. Furthermore, we demonstrate that interfacial polarization charges strongly influence hole injection at electrode/HTL interfaces. These findings provide further insights into the selection of host–dopant combinations for dipolar-doped HTLs to optimize both interfacial electrostatics and charge transport properties in OLEDs.
Highly 〈100〉 c -oriented 0.3BaTiO 3 –0.1Bi(Mg 0.5 Ti 0.5 )O 3 –0.6BiFeO 3 (0.3BT-0.1BMT-0.6BF) lead-free piezoelectric ceramics were fabricated via a reactive templated grain growth (TGG) method combined with additional hot-pressing during lamination. The previous issue of the decrease in the Curie temperature of ceramics fabricated by a TGG method due to undesired template—matrix reaction was thoroughly overcome by the use of the reactive TGG method. By optimizing experimental conditions such as the sintering temperature, doctor blade gap, and sintering time, a high relative density of >95% and a high degree of orientation F 100 of 90% were simultaneously achieved. The textured ceramics maintained a high Curie temperature T C of 450 °C, which was comparable to that of randomly oriented ceramics. Furthermore, the 90%-oriented ceramics exhibited an approximate 1.3-fold improvement in the large-signal piezoelectric coefficient (∼440 pm V −1 ) under unipolar electric fields compared to randomly oriented ceramics, offering a promising pathway for high-temperature, high-performance lead-free applications.
Surface-immobilized gold nanospheres (SIGNs) are widely used as electric-field-enhancement platforms for spectroscopic techniques such as surface-enhanced Raman scattering and nonlinear optics because of the strong localized surface plasmon resonances (LSPRs). However, optical absorption in metallic nanostructures inevitably generates heat, resulting in a temperature rise that may cause thermal damage to target molecules and nanostructures. In this study, the photothermal properties of SIGNs were investigated using multiphysics simulations based on the finite element method. The results show that illumination at the LSPR wavelengths with an intensity corresponding to approximately 1 mW focused into a 1 μ m-diameter spot can induce a temperature rise of 100 ∘ C–250 ∘ C, indicating that careful thermal management is required to prevent thermally induced damage. A strong correlation was found between the temperature rise and the electric-field enhancement factor in the nanogap. This relation enables the temperature rise to be estimated directly from electromagnetic simulations without performing additional thermal analyses.
Abstract Although the polarization doping technique has achieved success in some gallium nitride (GaN)-based ternary materials, its current form is not applicable to other compound semiconductors.This paper proposes the concept of realizing polarization doping in general compound semiconductors by using process-induced stress. Taking zinc oxide (ZnO) as an example, the doping effect of this technique is studied and evaluated by means of analytical calculation and numerical simulation. It is shown that, with this technique, a p-type region with a maximum concentration larger than 1×10¹⁸ cm-3 can be formed in ZnO without using any acceptor impurities. The numerical simulation indicates that the diode constructed by this method has obvious rectification characteristics, demonstrating its application potential in electronic and optoelectronic devices.
The temperature-dependent evolution of the structural components in bulk and ground 87.5%(Bi 0.5 Na 0.5 )TiO 3 –12.5%BaTiO 3 (BNT–BT) ceramics was investigated using synchrotron radiation X-ray diffraction. Both the bulk and ground samples exhibited the coexistence of cubic ( Pm 3 ¯ m ) and pseudocubic ferrielectric ( P 4 bm ) components over a temperature range of 300–600 K. In bulk ceramics, tetragonal components ( P 4 mm ) with a large lattice strain abruptly appeared at the ferroelectric phase transition during cooling. In contrast, the ground powders retained a tetragonal component ( P 4 mm ) with a small lattice strain even at elevated temperatures, and both its volume fraction and lattice strain gradually increased with decreasing temperature over a wide temperature range, obscuring a distinct phase transition temperature. These results demonstrate that mechanical grinding modifies the evolution of the structural components and enhances the structural heterogeneity of BNT–BT ceramics. The diffuse transformation behavior observed in the ground powders was likely associated with the strain-induced stabilization of the ferroelectric structural component.
This study optimizes the geometric parameters of a circular multi-pass cell (CMPC) to maximize optical absorption path-length using a Taguchi L 27 orthogonal array. Three control factors—inner cell radius ( R ), number of vertices ( p ), and star polygon density ( q )—were evaluated through Signal-to-Noise ratio and ANOVA. Results identify cell radius as the dominant factor, contributing 85.64% to the total variance, followed by p (7.06%) and q (4.49%). A significant interaction between R and p ( P = 0.045) indicates a synergistic effect on beam trajectory. A linear regression model was developed and validated through methane direct absorption spectroscopy at 1651 nm. The experimental path-length deviated by less than 0.5% from the 88.3 m theoretical prediction. These findings provide a robust framework for optimizing CMPC designs in high-sensitivity trace gas detection by precisely quantifying the complex relationships among geometric parameters.
Single-junction solar cells are widely installed but have low conversion efficiency limits. Multi-junction solar cells achieve high conversion efficiency but are expensive and require concentrator tracking systems. Liquid crystals (LCs) can be used as gradient refractive index (GRIN) lenses, allowing refractive index (RI) control via applied voltage. LC GRIN lenses that accept multiple oblique-incident light can realize high-efficiency flat-panel concentrator tracking photovoltaic systems. Previous research proposed prototyped oblique-incidence LC GRIN lenses. This study investigated the relationship between the optical path length (OPL) RI and director calculated (DC) RI. The DC RI is calculated from the LC director. The OPL RI is calculated using the OPL toward the focal point for required light concentration. We clarified the fundamental conditions for the optical efficiency achieved with the current design for a focal length of 1100 μm.
