Physics of the Solid State最新文献

Lead-free K_0.5Na_0.5NbO₃ (KNN) ceramics doped with varying concentrations of V₂O₅ (0, 1, 3, 5, and 9 mol %) were synthesized via a conventional solid-state method and sintered at 1100°C to evaluate the effects of vanadium modification on structural and electrical behavior. X-ray diffraction and Rietveld refinement confirmed the preservation of an orthorhombic perovskite structure for all compositions, with systematic lattice distortions and the emergence of minor secondary phases at higher V₂O₅ levels, indicating partial substitution and limited solubility. Dielectric, impedance, and modulus analyses conducted over 30 Hz–1 MHz and 30–400°C revealed thermally activated relaxation and non-Debye response characteristics. The AC conductivity exhibited dispersive behavior consistent with Jonscher’s universal power law, reaching a maximum value on the order of 10^–4 S cm^–1 at elevated temperatures. Electrical transport was governed predominantly by grain-boundary effects and small-polaron hopping facilitated by V-induced defect states and oxygen vacancies. Increasing V₂O₅ content resulted in reduced DC conductivity and higher activation energy, attributed to a decreased concentration of mobile oxygen-based charge carriers and the electronic influence of vanadium. Among the examined compositions, 5 mol % V₂O₅ provided the best balance between conductivity enhancement and dielectric stability. Overall, the results demonstrate that controlled V₂O₅ incorporation is an effective strategy to tailor defect chemistry, conduction mechanisms, and dielectric response in KNN-based lead-free functional ceramics for high-temperature applications.

Nanocomposites based on multilayer carbon nanotubes (MCNT) and gallium selenide (GaSe) are synthesized by laser ablation. The structure and morphology of the nanocomposites are studied by X-ray phase method and atomic force microscopy (AFM). The atomic-force microscopy shows that the nanotube morphology changes insignificantly after laser ablation, but the nanotube size slightly increases and is 20‒60 nm. The absorption and luminescence spectra of samples are studied experimentally under action of the second harmonic ((hbar omega ) = 234 eV) of Nd:YAG laser. The MCNT/GaSe nanocomposites are shown to demonstrate an increased luminescence intensity (by a factor of ~5 as compared to individual components) and have a wide wavelength range (576–887 nm).

Within the framework of density functional theory (DFT), the structural, electronic, magnetic, and elastic properties of Ir₂CrZ (Z = Ga,Ge) full-Heusler alloys are investigated. A comparison is made between the Cu₂MnAl and Hg₂CuTi type structures. It has been discovered that the Cu₂MnAl structure’s ferromagnetic state is energetically more stable than the Hg₂CuTi state. Spin-polarized computations reveal that the spin-up electrons of the Ir₂CrZ (Z = Ga,Ge) compounds exhibit metallic behavior in both the Cu₂MnAl and Hg₂CuTi structures. For the spin-down electrons, metallic behavior is observed in the Hg₂CuTi structure, whereas in the Cu₂MnAl structure, they exhibit semiconducting behavior. Ir₂CrZ, where Z is either Ga or Ge, is a half-metallic ferromagnet (HMF) with a magnetic moment of 3.0 and 4.0 µ_B/f.u, respectively. Theoretically, this research will result in experimental efforts in the subject of spintronics and its applications.

This study presents a comprehensive first-principles investigation of the structural, electronic, and thermoelectric properties of the YPt_xNi_1–xSb (x = 0, 0.25, 0.50, 0.75, 1) half-Heusler alloys, using density functional theory within the generalized gradient approximation (PBEsol). Our calculations of the lattice constant and bulk modulus for the parent compounds YNiSb and YPtSb show excellent agreement with available data. A key and unusual finding is the anomalous simultaneous increase in both the lattice parameter and the bulk modulus with rising Pt concentration, which deviates from the typical inverse correlation. Electronic band structure calculations reveal that all compositions are direct bandgap semiconductors. Furthermore, an analysis of the thermoelectric transport properties using the BoltzTraP code demonstrates high Seebeck coefficients and promising power factors for both p-type and n-type doping. The identified narrow direct bandgap in the YPt_xNi_1–xSb series suggests these materials are not only promising for efficient thermoelectric applications but also hold potential for infrared electronic and optoelectronic devices.

We study analytically the topological phase diagram in finite-thickness semiconductor nanowire with proximity-induced chemical potential, Zeeman splitting and superconducting gap at its interface. Approximating the electrostatic potential formed inside the semiconductor by the negative gate voltage to a triangular potential, we analytically derive the condition for topological phase transition of the semiconductor nanowire and the gate voltage for which the system can be tuned into the topological nontrivial regime at the minimal Zeeman splitting. We also derive analytically the width of the topological nontrivial region and the interval between them in the topological phase diagram. Our results provide a qualitative and good description of the previous numerical studies and will provide a rationale and general understanding for realizing Majorana fermion in superconducting-ferromagnetic insulator-semiconductor nanowires.

Pentanedioic acid-thiourea (PAT), a new hydrogen-bonded organic co-crystal, was produced using a slow evaporation method and examined for its structural and solid-state properties. Single-crystal X‑ray diffraction confirmed an orthorhombic Pnma structure, stabilized by N–H···O and O–H···S hydrogen-bonding frameworks. The FTIR spectrum validated the functional groups and successful co-crystallization. Optical absorption analysis revealed a strong UV band at 232 nm, a sharp cutoff at 298 nm, and a wide bandgap of 4.165 eV, showing UV-filtering and semiconducting properties. The low Urbach energy (0.085 eV) indicated that the material was well-crystallized and had fewer defects. Dielectric tests revealed temperature and frequency-dependent behavior, with AC conductivity following a thermally activated hopping process. Thermal investigation revealed a multi-stage decomposition process, with stability up to 126°C. Thus, the remarkable solid-state properties of PAT co-crystal make it a suitable material for optoelectronic and UV-filtering uses.

This study systematically investigates the static and dynamic behaviors of p-GaN-gate high electron mobility transistors (HEMTs) incorporating two distinct back barrier compositions: the conventional Al_0.05Ga_0.95N and a In_0.1Ga_0.9N layer. Both devices are designed with identical geometries, featuring a gate length of 1.2 μm. The InGaN back barrier HEMT consistently delivers superior output current (({{I}_{{text{D}}}})) and transconductance (({{g}_{m}})) compared to its AlGaN counterpart, reaching peak values of approximately 0.82 A/mm and 0.50 mS/mm, respectively. In contrast, the AlGaN backbarrier exhibits lower maxima, with ({{I}_{{text{D}}}}) of 0.60 A/mm and ({{g}_{m}}) near 0.40 mS/mm. The InGaN-structured device also surpasses AlGaN in RF performance, achieving a maximum unity current gain cutoff frequency (({{f}_{T}})) of about 75 GHz, versus 61 GHz for AlGaN. This heightened ({{f}_{T}}) stems from improved channel carrier transport and reduced gate-drain capacitance (({{C}_{{{text{GD}}}}})), with InGaN backbarrier showing a lower ({{C}_{{{text{GD}}}}}) (0.8 × 10^–13 F/mm) compared to AlGaN (1.3 × 10^–13 F/mm) in the high-bias regime, which is critical for fast switching and minimizing power losses. The InGaN back barrier HEMT demonstrates a higher gate-source capacitance (({{C}_{{{text{GS}}}}})) of about 1.0 × 10^‒12 F/mm, which enables enhanced transconductance for efficient gate control. The InGaN back barrier HEMT sustains a substantial breakdown voltage of 436 V, underscoring its potential for high-power and high-frequency electronic applications, while the AlGaN back barrier offers an even higher breakdown of 543 V.

The optical characteristics of light-reflecting surfaces, birefringence, and pleochroism effects in multilayer coatings of metal, glass, and plastic packaging made from biaxially oriented isotactic polypropylene (BOPP) were investigated. Birefringence induces bright coloration in transparent, colorless BOPP films under polarized light, leading to the manifestation of pleochroism. Polarized light arises from the reflection of natural or artificial illumination on mirrored surfaces, with the proportion of polarized radiation in the reflected light flux depending on the angle of incidence and the properties of the dielectric mirror surface. The study proposes utilizing the color effects observed in polymer films to enhance the visual appeal of packaging and to provide protective marking. The protection of product packaging against counterfeiting represents a significant social and economic challenge in modern society. Protective marking, when combined with information encoding, ensures consumer safety—particularly for pharmaceuticals and corrosive household chemicals. The reliable encoding and recognition of hidden security information on transparent polymer packaging depend on the contrast and color differentiation of structural elements, such as barcodes or trademarks, which become visible only under polarized light. This article presents the results of instrumental measurements and quantitative assessments of colored radiation reflected from colorless mirrored surfaces of metal, glass, and polymer containers. The optimal number of transparent polymer film layers required to achieve vivid coloration of labels or packaging visible in polarized light, as well as the contrast necessary for effective protective marking, has been determined.

This study introduces an innovative photodetector device that integrates an L-shaped top gate with a photosensitive back gate (LTG-PBG-TFET), specifically engineered to detect incident light within the near-infrared (NIR) wavelength range of 750–1050 nm. The LTG-PBG-TFET design leverages the advantages of both the L-shaped top gate and the photosensitive bottom gate to extend the edge tunneling zone at the channel/source (C/S) junction. This structural configuration enhances the photocurrent (I_light) response, subthreshold swing (SS_avg), and turn-ON voltage (V_th) under illumination. Furthermore, the slight elevation near the gate corner minimizes corner effects at the source/channel interface, which in turn improves I_light/I_dark performance as the illumination wavelength (λ) transitions from 1050 to 750 nm. Consequently, notable enhancements in I_light, SS_avg, and the I_light/I_dark ratio were observed, yielding a high spectral sensitivity (S_n) of approximately 54.4 and a signal-to-noise ratio (SNR) of about 82.2 for the proposed LTG-PBG-TFET device. Additionally, incorporating a light exposure window in the back gate region increases the active area for electron-hole pair (EHP) generation, thereby enhancing quantum efficiency (η) and responsivity (R), particularly at longer wavelengths around 1050 nm. Finally, the influence of acceptor–donor trap charges at the semiconductor/oxide interface on the S_n of the device was examined. Results indicate that S_n remains relatively stable as the wavelength (λ) is tuned between 750 and 1050 nm.

Zn_1–xMg_xO (x = 0, 0.05, 0.1, and 0.15) nanoparticles (NPs) were prepared via the sol–gel method. A comprehensive investigation of the structural, morphological, vibrational, and optical characteristics of the prepared NPs was carried out by using the X-ray diffraction method (XRD), scanning electron microscopy (SEM), Fourier-transformed infrared spectroscopy (FTIR), and Ultraviolet-visible (UV–Vis) spectroscopy. XRD analysis confirmed the hexagonal wurtzite structure of ZnO. The average crystallite size decreased with increasing Mg concentration. Surface morphology was revealed by the SEM. FTIR spectra exhibited peaks below 700 cm^–1 corresponding to the zinc oxide (ZnO) and doped ZnO NPs. The UV–Vis result shows a blue shift in the optical bandgap for all samples when the Mg concentration increases in the ZnO lattice. The Tauc equation and Urbach tail analysis were employed to determine the optical bandgap, assess interband transitions, and evaluate defect-related states. The increased bandgap and improved optical characteristics make Mg-doped ZnO NPs promising candidates for optoelectronic devices, particularly in UV detectors and photovoltaic applications.