Applied Physics A最新文献

The concept of valley pseudospin, which is associated with energy peaks at specific momentum locations, has garnered significant attention in recent research as an effective means of controlling classical waves. In this paper, we investigate composite acoustic topological metamaterials composed of hollow tubes (HTs) and opened-hole hollow tubes (OHTs) arranged in a honeycomb pattern with C_3v symmetry. By adjusting the rotation angle of the systems, we obtain a degenerate Dirac point for structure B and band inversions for structures A and C within two bands. We have engineered an A|B|C configuration to confine topological valley-locked waveguide states (TVWSs) within the B region composed of x layers, targeting two discrete frequency bands centered at 5820 Hz and 5280 Hz. In this configuration, the dual-band TVWSs can be tuned by geometry sizes of meta-atoms HTs and meta-molecules OHTs. These dual-band states incorporate both gapless dispersion, valley-locked unidirectional transport, and defect immunity, while demonstrating high-efficiency energy transmission. Our findings could facilitate the realization of broadband TVWSs and hold significant promise for acoustic wave manipulation applications, including wave splitting, reflection-free guiding, and acoustic wave focusing.

Selective Laser Sintering (SLS) of poly(ether ether ketone) (PEEK), a high-performance polymer, presents significant challenges due to its narrow processing window, high melting temperature, and low thermal conductivity in powder form. The successful fabrication of highly functional, dense components necessitates precise control over the intricate thermal and fluid dynamics governing the PEEK sintering process. However, experimental and single-physics modeling approaches are often insufficient to capture these transient multi-physics phenomena. This study introduces a novel two-dimensional (2D) multi-physics Finite Element Analysis (FEA) model to simulate the SLS processing of PEEK powder. This study realistically models the transient thermal and fluid behaviour during the SLS process and evaluates the effect of fundamental parameters such as laser power and scanning speed by incorporating combined multi-physical phenomena such as heat transfer, fluid dynamics, and phase transformations. Although optimum thermal profiles are obtained at an Energy Density (ED) of 0.03 J/mm², it has been determined that ED is not the single factor in understanding the thermal behavior. The results show that scan speed significantly regulates heat accumulation and thermal gradients. Slower scanning speeds promote high heat buildup and surface degradation at low powers, while higher speeds limit thermal penetration, increasing the temperature difference between the top and bottom surfaces. This computationally efficient 2D multi-physics approach improves understanding of PEEK laser sintering mechanisms, providing quantitative information for rapid and effective parameter identification in high-performance polymer additive manufacturing.

This study proposes a thorough examination of a label-free biosensor based on a drain-engineered pocket-doped and dielectrically modulated SOI Ferroelectric (Fe) gate Tunnel FET design. The n + pocket in the source TFET architecture enhances band-to-band tunnelling, enhancing the device's drain current sensitivity -a nanocavity forms between the SiO2 layer and the TiN gate on the device's source side. The device's sensing ability is evaluated using the dielectric constant as well as the positive and negative charge densities of biomolecules, specifically macromolecular polypeptides-proteins, blood glucose or glycemia, deoxyribonucleic acid (DNA), and bacteria. The device demonstrated drain current sensitivity in the order of 10⁹.

The Al_xCrNbTiV (x = 0.2-1.0) high-entropy alloy coatings were fabricated on Ti6Al4V by laser cladding to investigate their phase evolution and wear behaviour. X-ray diffraction revealed a body-centered cubic solid solution matrix with composition-dependent intermetallics simultaneously, scanning electron microscopy and energy dispersive spectroscopy results showed that the Ti-rich Cr₂Nb-type Laves phase decreases with Al addition, while a needle-like Ti₂AlNb phase increases; Vickers microhardness testing indicated that the average cladding-zone microhardness decreased slightly from 582 ± 25 HV_0.5 (at x = 0.2) to 550 ± 16 HV_0.5 (at x = 1.0); However, dry sliding tribological tests (10 N, 18 m) demonstrated that the wear resistance significantly improved with increasing Al content. The specific wear rate decreased from (1.61 ± 0.08) × 10^− 4 mm³/(N·m) at x = 0.2 to a minimum of (4.33 ± 0.22) × 10^− 5 mm³/(N·m) at x = 1.0. The steady-state coefficient of friction also decreased from 0.69 ± 0.03 to 0.58 ± 0.03. The curves evolved from fluctuating, adhesion-dominated traces at low Al to lower and more stable signals at intermediate Al, while worn morphologies transitioned from adhesive and oxidative wear to predominantly abrasive wear at high Al. The main mechanism is attributed to the Al-driven stabilization of Ti₂AlNb and the dilution-limited stability of the Cr₂Nb-type Laves phase. The results establish a phase-engineering route to design, wear-resistant laser cladding high-entropy alloy coatings for titanium alloys.

Two phosphors converted white light emitting diodes (WLEDs) were fabricated by coating a blend of red and green-emitting phosphors on a blue InGaN LED chip (CREE 460 nm). The required red and green-emitting phosphor samples were prepared by the modified wet chemical synthesis method. The synthesis method adopted here is Eco-friendly, Economical and Easy to handle. The powder XRD pattern and Rietveld refinement confirmed the crystal structures of phosphor samples. Photoluminescence (PL) emission and photoluminescence excitation spectra (PLE), and concentration quenching were noted for these phosphor samples. The red and green emitting phosphor samples showing optimal intensity were selected for WLED fabrication. SEM images were recorded to analyze particle size, and color coordinates were measured to assess color purity. Three types of WLED sources were fabricated by coating these two phosphors (red and green emitting) in different proportions on blue LED chips. The Commission Internationale de l’Éclairage (CIE) color coordinates, color rendering index (CRI), correlated color temperature (CCT), S/P ratio, Standard deviation of color matching (SDCM), and the hue bin comparison of R1-R16 values were noted for these WLEDs. Our fabricated LED, featuring this phosphor combination, achieves a record Ra value of 92.6 while also significantly enhancing other parameters.

Due to the strong structural design, light weight and high stability of carbon materials, carbon-based composite materials have attracted much attention in the field of absorbing waves. In this work, hollow carbon microspheres were constructed by the template method, and combined with TiO₂ particles, C@TiO₂ composite hollow microspheres were successfully prepared. This not only retains the excellent properties of carbon-based materials, but also optimizes the absorbing wave performance by constructing a rough surface and hollow structure. As a template, SiO₂ was obtained by hydrolysis of tetrapropoxy-silane (TPOS), the phenolic resin undergone in-situ polymerization on the surface of the template, and then the hollow carbon microspheres (HCMS) with a certain shell thickness were prepared by etching and sintering at high temperature. Particle coated core-shell HCMS@TiO₂ composites were prepared by subsequent hydrolysis of tetrabutyl titanate (TBT). The effect of the addition amount of TBT on its morphology and absorption performance was evaluated. When the filler ratio is 20wt% and the thickness is 2 mm, the lowest reflection loss (RL_min) and effective absorption bandwidth (EAB) were up to -48.93dB and 4.4 GHz respectively. TiO₂ has a low dielectric constant, which can effectively adjust the overall dielectric value of carbon materials, optimize impedance matching, and generate new heterogeneous interfaces, thus improving the wave absorption performance of the composites. In addition, the low density and hollow mesoporous characteristics of the hollow carbon microspheres are not damaged. The method has the advantages of low cost, controllable structure, uniform dispersion of coated particles, etc. It is a potential electromagnetic wave absorbing material that conforms to the characteristics of “wide, strong, light and thin”.

We investigated the subsurface plastic deformation accompanying laser-induced periodic surface structures (LIPSS) on a tensile-prestrained copper (Cu) single crystal irradiated by line‑scanned femtosecond (fs) laser pulses having a wavelength (λ) of 800 nm. Stable, sinusoidal LIPSS with a period of ~480 nm (≈0.6λ) and an amplitude of ~150 nm were reproducibly obtained at fluences between 0.49 and 0.65 J/cm². Cross‑sectional transmission electron microscopy (TEM) of a thinned sample revealed a high density of dislocations beneath the LIPSS crest within ~400 nm of the surface. Systematic two‑beam TEM analyses identified Burgers vectors consistent with slip on two {111} planes activated by uniaxial compression along the laser‑incident direction, while the LIPSS valley exhibited additional dislocations with Burgers vectors parallel to the laser-incident direction, indicating a locally more complex stress state. These results provide direct microstructural evidence that fs‑laser irradiation induces plasticity in Cu during LIPSS formation.

This study reports the one-pot microwave synthesis of Cu-Ag powders with varying copper-to-silver molar ratios (10:1, 5:1, 2:1, and 1:1) via the reduction of copper and silver salts using ascorbic acid. The resulting products were systematically analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and electrical resistivity measurements. XRD results reveal the coexistence of Cu-rich Cu(Ag) and Ag-rich Ag(Cu) solid solutions, with the weight fraction of Cu(Ag) decreasing as Ag content increases. The crystallite size ranges from 82 to 231 nm. Increasing Ag content disrupts the Cu lattice, enhances electron scattering, and reduces charge carrier mobility, leading to a significant increase in electrical resistivity, with ρ = 3.14 Ω·cm for CuAg10/1 and 6.71 Ω·cm for CuAg 1/1. The solid solutions display an oxidizing property in aqueous medium, which diminishes as Ag content increases. The oxidation of Methylene Blue (MB), used as a test molecule, occurs via an indirect process where the powder generates hydroxyl radicals in the acidic medium. Complete degradation of MB with CuAg 10/1 occurs within 25 min using 30 mg of the powder at 60 °C and pH 3. The processing time is further reduced to 6 min when the degradation is conducted under microwave irradiation.

This study investigates the synthesis and optimization of FeSiAl@Mn_0.8Zn_0.2Fe₂O₄-MXenes composites via a one-step hydrothermal method followed by calcination annealing. The resultant composite demonstrated excellent low-frequency microwave absorption properties. X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) analyses confirmed the successful formation of a stable, uniform composite structure. Scanning electron microscopy (SEM) images revealed the role of FeSiAl as a template, maintaining a two-dimensional morphology, while MXenes nanosheets and MnZn ferrite formed a heterogeneous interface post-annealing. Magnetic measurements indicated that, while FeSiAl exhibited the highest saturation magnetization, the composites maintained strong magnetization after annealing, with improved magnetic properties due to the conversion of non-magnetic hydroxides to ferrites. Electromagnetic parameter analysis showed a significant increase in the dielectric constant, attributed to polarization mechanisms, while magnetic permeability remained high and slightly increased post-annealing. The composites demonstrated superior microwave absorption performance with an optimized matching thickness, as shown by the RL values of -30 dB at 5 mm for the AFM5 sample, and − 26 dB and − 24 dB for the AFM5-400 and AFM5-600 at 4 mm and 5 mm, respectively. These findings suggest that the combination of high dielectric constant and magnetic permeability is effective for optimizing low-frequency microwave absorption materials, although a trade-off exists between absorption performance and bandwidth.

Ultrafast laser nanostructuring of semiconductor substrates can markedly improve the sensitivity of Surface-Enhanced Raman Spectroscopy (SERS). In this work, we investigated the SERS response of rhodamine 6G (R6G) on regular laser-induced periodic surface structures (LIPSS) fabricated on silicon using femtosecond laser pulses and subsequently decorated with silver nanoparticles produced by femtosecond laser ablation in ethanol. The resulting hybrid substrates enabled uniform analyte adsorption and efficient formation of plasmonic hotspots, allowing reliable detection of R6G down to 10⁻⁷ M. Compared to planar silicon, the nanostructured surfaces exhibited an approximately 25-fold higher enhancement factor, arising from stronger light backscattering by the periodic architecture and the tighter packing of Ag nanoparticles within the LIPSS valleys, which reduces interparticle spacing and increases electromagnetic coupling. FDTD simulations further revealed that the electric field intensifies dramatically when nanoparticle separations approach 2 nm significantly stronger than at 10 nm corroborating the experimentally observed enhancement.