Applied Physics A最新文献

A series of zinc manganese lithium titanate nanoparticles doped with cerium (Ce) was successfully prepared using the sol-gel technique. The study employed X-ray diffraction (XRD), transmission electron microscopy (TEM), diffuse reflectance, and dielectric spectroscopies to identify nanoparticles and investigate the crystalline structure, dielectric properties, and electrochemical behavior of Zn₃Mn_0.5Li_0.2Ti_4−xCe_xO₁₂ with different cerium concentrations (x = 0.0, 0.2, 0.6, and 1 mol%). The spherical-nanoparticles were produced by the sol-gel technique and calcinated at 700 °C for 4 h. The optical properties of Z Zn₃Mn_0.5Li_0.2Ti₄O₁₂ co-doped with CeO₂ were analyzed using diffuse reflectance spectroscopy. The variation in the absorption edge with different CeO₂ content indicates changes in the material’s band gap and electronic structure. The impact of Ce³⁺ on the dielectric properties was also investigated. The improvement in electrochemical performance is attributed to internal rearrangements within the Zn₃Mn_0.5Li_0.2Ti₄O₁₂ nanostructure, driven by the presence of Ce³⁺ ions. The capacitance of Zn₃Mn_0.5Li_0.2Ti₄O₁₂ ranges from 41.58 to 38.28 F·g⁻¹ with varying the Ce³⁺ concentration from 0 to 1 mol% at a scan rate of 10 mV·s⁻¹. Additionally, EIS highlights the potential of these nanoceramics for energy storage applications. These findings supply priceless insights into how Ce co-doping affects the suitability of these nanostructures for electronic devices, solar cells, and energy storage implementations.

Dye-sensitised solar cell (DSSC) is a next-generation solar energy conversion device. The electrolyte, which is one of the key components of a DSSC, greatly affects its short-circuit current density (J_sc) and open-circuit voltage (V_oc) and hence, its overall performance. In this work, bis(trifluoromethane)sulfonimide (TFSI) cobalt complex was used for the first time as redox couple in DSSC, and an effort was carried out to study the effects of the varying concentration of cobalt complex redox ions on the characteristics of the prepared liquid electrolytes (LEs) and quasi-solid electrolytes (QEs), and on the photovoltaic parameters of DSSCs. Specifically, the electrolyte characteristics include the viscosity and electrical conductivity, while the photovoltaic parameters of DSSCs include J_sc, V_oc, fill factor (FF) and power conversion efficiency (PCE). The viscosity of electrolytes was found to increase with increasing molar concentrations and then further increased with the addition of polyethylene oxide (PEO); the highest viscosity of 2.49 cP was obtained at 44 rpm for QE-50. The highest conductivity measured by electrochemical impedance spectroscopy was 83 mS cm^− 1 for LE-50. Finally, zinc oxide-based DSSCs with platinum counter electrodes were fabricated for current-voltage measurements. Among the synthesised electrolytes, QE-35-based DSSC showed a better combination of J_sc and V_oc, resulting in a PCE of 0.48%.

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This study investigates the modulation of various characteristics of BaCeO₃ under hydrostatic stress using the ultrasoft pseudopotential method and the generalized gradient approximation approach. The structural, electronic, mechanical, optical, and thermodynamic properties were computed, alongside spectroscopic and structural characterization. The results revealed that, despite a 33% reduction in lattice volume and a 12% decrease in lattice parameters due to applied hydrostatic stress, the crystal lattice retained its cubic structure, with no phase transition observed. The electronic band gap varied from 2.641 eV to 2.711 eV under stresses of 0–50 GPa and decreased to 1.65 eV at 100 GPa. Hydrostatic stress influences not only the electronic structure but also optical properties such as reflectivity, refractive index, absorption, energy loss function, and dielectric function. The increased absorption peak intensity and the shift of these peaks to higher energies suggested a blueshift, indicating the material’s suitability for optoelectronic applications. Mechanical parameters, including bulk, shear, and Young’s moduli, confirmed the material’s stiffness, mechanical stability, and resistance to shear deformation. Under stress, the material was found to be less compressible, stiffer to shear stress, and less elastic. Thermodynamic analysis showed that, as stress increased, the total enthalpy, entropy, and heat capacity of the material decreased, while the average atomic vibrations and equilibrium state improved.

Several factors may be responsible for disorder and frustration in a magnetic nanoparticle, including atomic vacancies on the surface and inside, impurity atoms, long-range magnetic exchange coupling, etc. We use Monte-Carlo simulations within the Heisenberg model to examine the role of randomly distributed atomic vacancies and long-range magnetic-exchange coupling on the temperature-dependent magnetic properties of ferromagnetic nanoparticles. In particular, we study the role of the second-neighbor antiferromagnetic exchange coupling and missing atoms inside the particle, resulting in broken nearby bonds. We find that both factors may enhance the superparamagnetic behaviors of such particles.

The present study investigated the influence of deposition angle of sputtered atoms on the microstructure, morphology, mechanical and electrical properties of niobium (Nb) thin films by varying it from 0° to 50° in a step of 10°. It was found that the deposition rate follows cosine distribution with deposition angle. The root mean square (rms) surface roughness increases from 0.40 ± 0.05 to 1.5 ± 0.2 nm, and density decreases from 8.5 to 7.7 (± 0.2) g/c.c as the deposition angle increases while no significant change in crystallites size was observed. Room temperature electrical resistivity rises from 79 to 293 µΩ-cm with increasing deposition angle due to enhanced electron scattering. The residual stresses remain compressive but shift towards tensile as the deposition angle increases. Atomic force microscopy confirms the increase in surface roughness and showing columnar growth at higher deposition angle. This work provides some insights into the how the deposition angle of sputtered atoms affects the growth of Nb films and optimal deposition angular range of sputtered atoms to coat Nb films on irregular surfaces.

Exploiting the magnetocaloric effect for low-temperature magnetic refrigeration presents a compelling green technology for cryogenic applications in space science and hydrogen liquefaction. In this work, we investigate the structural and magnetic properties of RE(Fe_0.25Co_0.75)₂H₃ compounds, where RE represents Ho and Er. These compounds crystallize in the cubic MgCu₂ (C15) structure with a lattice parameter of 7.62 Å for RE = Ho and 7.60 Å for RE = Er. Magnetization measurements as a function of temperature, performed in a 0.05 T magnetic field, reveal that both hydrides exhibit ferrimagnetic behaviour. The Curie temperatures (T_C) for Ho and Er hydrides were determined to be 124 K and 75 K, respectively. We studied the magnetic entropy change (−∆S_M) and refrigerant capacity (RC) of both samples by measuring isothermal magnetizations under various field changes between 0 and 7 Tesla. With increasing applied field, both −∆S_M and RC increase, and the temperature span of the −∆S_M versus T plots widens. Furthermore, from the −∆S_M (T) curves under an external magnetic field change of 5 T, we observed a maximum -ΔS_M of ∼ 3.11 and 4.41 Jkg^-1K^-1 for RE = Ho and Er, respectively. The corresponding temperature-averaged entropy change over a 10 K temperature span was TEC_10K ∼2.9 and ∼3.8 Jkg^-1K^-1 for RE = Ho and Er, respectively. These results indicate that Er(Fe_0.25Co_0.75)₂H₃ exhibits superior thermomagnetic properties compared to Ho(Fe_0.25Co_0.75)₂H₃ particularly for low-temperature magnetic cooling applications.

SnO₂, Sn_1-xW_xO [2, 5, 10 at.%] thin films were synthesised using the ultrasonic spray pyrolysis. Structural analysis revealed that W doping significantly improved crystallinity and modified the morphology of SnO₂ thin films, with 5% W doping resulting in the most uniform grain growth and optimal structural properties. In contrast, excessive doping at 10% induced lattice distortions and particle agglomeration. Fourier transform infrared spectroscopy (FTIR) analysis highlighted intensified O–H and H–O–H vibrational modes with increasing W content, indicating enhanced surface hydroxylation, which is crucial for optical and catalytic applications. The optical bandgap widened from 3.63 eV for pristine SnO₂ to 3.84 eV for 2% W-SnO₂ and stabilized around 3.82–3.83 eV for 5% and 10% W-SnO₂. Thermoelectric studies revealed improved electrical conductivity at 5% W doping due to an increased carrier concentration of 2.49 × 10¹⁸ cm⁻³. Notably, the Seebeck coefficient (│S│) showed partial recovery at 10% doping, suggesting a nuanced balance between carrier density and scattering mechanisms. For photodetection, the 5%-W-doped SnO₂ demonstrated a markedly enhanced Ultraviolet response, with significantly higher peak currents during UV exposure. Photocatalytic experiments showed superior performance for the 5% W-SnO₂ film, achieving 98% methylene blue degradation under Ultraviolet light within 150 min. Furthermore, contact angle measurements revealed a transition from hydrophilicity to hydrophobicity. The water contact angle increased from hydrophilic behaviour in pure SnO₂ to highly hydrophobic surfaces at 10% W doping. This change underscores the tunable surface properties of W-doped SnO₂ thin films. These findings establish them as promising candidates for multifunctional applications in optoelectronics, photocatalysis, and surface engineering.

Time-resolved laser-induced luminescence spectroscopy is useful for real-time measurement of lanthanide ion concentrations in aqueous solution. Gadolinium ions (Gd(^{3+})), in particular, have a long ((sim)ms) emission lifetime, so that the ion emission can be easily distinguished from scattering of the excitation pulsed laser without the need for a monochromator. In this work, we have developed a real-time monitoring method for Gd concentration in water, aiming at application to the Super-Kamiokande (SK) water Cherenkov detector in which 0.03% Gd is currently dissolved in the form of sulfate for the observation of supernova relic neutrino events. The basic concept is to install a tube to run a portion of the water sample through a quartz cell (2 cm on each side), where a ns-pulsed laser at 266 nm is irradiated to excite Gd(^{3+}) ions. The generated Gd(^{3+}) ion emission at 312 nm is collimated by a lens, transmitted through a bandpass filter, and then detected by a photomultiplier tube placed about 10 cm away from the quartz cell. While lower Gd concentration and higher pulsed laser energy resulted in shorter Gd(^{3+}) emission lifetime, good linearity was confirmed between Gd concentration and normalized peak emission voltage in the wide range of 1–1000 ppm (0.1%) Gd in ultrapure water. The detection limit, defined as three times the standard deviation of the background level, was determined to be (sim)60 ppb for Gd sulfate in ultrapure water. This value is about two orders of magnitude better than the reported value using laser-induced breakdown spectroscopy, and is close to that using inductively coupled plasma optical emission spectrometry which requires sample introduction into the spectrometer. Sulfate ions in aqueous solution appear to have a smaller quenching effect than O–H vibrations of water molecules coordinated to the cation. By confirming a detection sensitivity below the ppm-level, this method could be effective for monitoring of drainage water from the SK detector tank as well. Our real-time monitoring method is expected to support the long-term operation of the SK-Gd project.

Infant fall detection is critical for the timely identification of fall events, assessment of the severity, and reduction of potential injuries. Traditional fall detection technologies typically rely on devices such as cameras, force sensors, accelerometers, and gyroscopes. While these devices provide accurate measurements, they are often expensive, require complex installation, and depend on external power sources, leading to higher system complexity and maintenance costs. This paper reports a self-powered, wearable sensor based on triboelectric nanogenerator (TENG) for infant fall detection, featuring a bridge-structured PDMS layer and a copper foil electrode. By attaching the TENG sensor to the skin or joints of an infant model or human body, we successfully detected fall status, frequency, impact intensity, and impact localization. The sensor achieves a minimum detectable acceleration of 0.4 g on human skin, with a sensitivity of 2.6 V/g. When integrated with artificial intelligence algorithms, the system achieves over 94% accuracy in predicting fall locations. Furthermore, the sensor maintains a stable output after tens of thousands of cycles, demonstrating exceptional stability and repeatability. Compared to traditional fall detection technologies, the proposed system offers several advantages, including low cost, simple manufacturing, easy installation, self-powered operation, and high portability.

We fabricated 4 × 4 pixel two-dimensional (2D) photodiode array (PDA) out of monolayer graphene and n-type silicon (n-Si) electrodes on a silicon-on-insulator (SOI) substrate. Our device design is based on passive matrix sensor array architecture consisting of individual graphene and silicon electrodes aligned perpendicular to each other. I-V measurements conducted at room temperature to reveal the electronic characteristics of graphene and Si junction in the device structure. The spectral responsivity, respond speed and the optical crosstalk of each G/Si pixels in the array have been determined by wavelength resolved and time dependent photocurrent spectroscopy measurements. Micro-Raman mapping measurements were conducted to examine the surface coverage of graphene electrode on each pixel. The results of Micro-Raman mapping measurements were correlated with the corresponding photocurrent data acquired under light illumination. We believe that this work constitutes a significant potential in integrating variety of 2D materials and SOI technology into next generation image sensing and multiple pixel light detection applications.