An ultra-wideband and wide-angle hexagonal electromagnetic stealth metamaterial is designed by optimally combining rhombus-carbon tiles on the top of and on the intermediate surface of a foam substrate by utilizing the genetic algorithm. For the first time, a stealth mechanism is unveiled that converts parts of absorptive surface plasmon polaritons induced in an ultra-wide bandwidth from three axial periodic edges and slots for both the transverse electric (TE) and the transverse magnetic (TM) polarizations into radiative ones that have undetectable polarized states for conventional antenna systems. From the measurement, the − 10 dB reflectance bandwidth (BW) is achieved from 1 to 11.66 GHz of which the fractional BW is 168.4% for the normal incidence. Besides, the − 10 dB fractional BW of 49.95% is confirmed for both the TE and the TM polarizations with the incident angle θ from 0° to 45°. Most importantly, the fractional BW is reached to 64.83% for the TE polarization with θ from 0° to 60° which has not been achieved based on square-shape metamaterial absorbers. The design strategy could pave the way to escape from long captivated stealth concepts, i.e., absorbing power, changing the angle of reflection, or shifting the frequency band.

Four-dimensional (4D) bioprinting holds significant promise in precision medicine, enabling the emulation of dynamic changes in the human body and tissues to provide personalized treatments. Smart materials for 4D printing (i.e., responsive to specific stimuli) should exhibit properties, such as biodegradability, biocompatibility, and ease of processing, while also enabling the prediction of time-dependent behavior in programmed geometry. This study focused on the development of a body temperature-responsive shape-memory polymer (SMP). The thermal properties of the SMP were analyzed, and its biodegradability and biocompatibility were assessed through structures fabricated by three-dimensional printing techniques. The simulation calculated with this finite element (FE) solution was in good agreement with those measured in experiments. The findings contribute to our understanding of the behavior of SMP under various conditions, validating the effectiveness of the developed material for potential applications in precision medicine and 4D bioprinting. It has the potential for use in medical devices, such as catheters, stents, and artificial scaffolds, prepared by 4D bioprinting.  

An ultra-wideband and wide-angle hexagonal electromagnetic stealth metamaterial is designed by optimally combining rhombus-carbon tiles on the top of and on the intermediate surface of a foam substrate by utilizing the genetic algorithm. For the first time, a stealth mechanism is unveiled that converts parts of absorptive surface plasmon polaritons induced in an ultra-wide bandwidth from three axial periodic edges and slots for both the transverse electric (TE) and the transverse magnetic (TM) polarizations into radiative ones that have undetectable polarized states for conventional antenna systems. From the measurement, the − 10 dB reflectance bandwidth (BW) is achieved from 1 to 11.66 GHz of which the fractional BW is 168.4% for the normal incidence. Besides, the − 10 dB fractional BW of 49.95% is confirmed for both the TE and the TM polarizations with the incident angle θ from 0° to 45°. Most importantly, the fractional BW is reached to 64.83% for the TE polarization with θ from 0° to 60° which has not been achieved based on square-shape metamaterial absorbers. The design strategy could pave the way to escape from long captivated stealth concepts, i.e., absorbing power, changing the angle of reflection, or shifting the frequency band.

Four-dimensional (4D) bioprinting holds significant promise in precision medicine, enabling the emulation of dynamic changes in the human body and tissues to provide personalized treatments. Smart materials for 4D printing (i.e., responsive to specific stimuli) should exhibit properties, such as biodegradability, biocompatibility, and ease of processing, while also enabling the prediction of time-dependent behavior in programmed geometry. This study focused on the development of a body temperature-responsive shape-memory polymer (SMP). The thermal properties of the SMP were analyzed, and its biodegradability and biocompatibility were assessed through structures fabricated by three-dimensional printing techniques. The simulation calculated with this finite element (FE) solution was in good agreement with those measured in experiments. The findings contribute to our understanding of the behavior of SMP under various conditions, validating the effectiveness of the developed material for potential applications in precision medicine and 4D bioprinting. It has the potential for use in medical devices, such as catheters, stents, and artificial scaffolds, prepared by 4D bioprinting.  

The vapor-phase polymerization (VPP) of poly(3-hexylthiophene) (P3HT) was achieved successfully as an alternative method to conventional solution-based thin film fabrication. Using Fe(III)Cl(3).6H(2)O, a spontaneous reaction of 3-hexylthiophene monomers resulted in the rapid formation of conducting P3HT thin films directly on substrates, such as glass, indium-tin-oxide, and poly(ethylene terephthalate), at thicknesses ranging from 50 to 1000 nm. The VPP of P3HT was achieved using ferric chloride hexahydrate and a 1:1 ratio of a methanol/ethanol mixture as the solvent system. The developed VPP technique can provide good processing consistency with an electrical conductivity, a transmittance, and a surface roughness of approximately 10(-2) S/cm, >90%, and <10 nm, respectively.

ABSTRACT Sintering refers to a process in which powdered materials are heated at high temperatures to form a solid mass. The process involves heating below the melting point to enhance strength and density and create electrical connections through particle adhesion. As semiconductor packaging becomes increasingly important in the current industry, advancements in sintering are essential. However, the oxide layer that forms on the surface of Cu during sintering hinders electrical conductivity and reduces adhesion performance, which can cause significant issues when used as semiconductor components. Therefore, removing this oxide layer is crucial to improving component performance. Various chemical etching methods are commonly employed to suppress and remove the oxide layer on the Cu surface. In this study, we suppressed the formation of the oxide layer using acid and compared the sintering performance using poly(acrylic acid) (PAA) with different molecular weights. Experiments were conducted to assess the effectiveness of oxide layer removal and the impact on the electrical and adhesive properties of the sintered Cu chips. To evaluate thermal stability among Cu particles, oxide layer removal efficiency, interparticle connectivity, adhesion, and electrical conductivity, we utilized analytical techniques such as thermogravimetric analysis (TGA), X‐ray photoelectron spectroscopy (XPS), X‐ray diffraction (XRD), scanning electron microscopy (SEM), lap shear strength tests, and four‐point probe measurements. The electrical conductivity showed the following results: Cu chip without activator had a conductivity of 1.0 × 10 4 S/m, that with acrylic acid (AA) had 7.9 × 10 3 S/m, that with PAA2k had 1.8 × 1 4 S/m, and that with PAA250k achieved 4.0 × 10 4 S/m. These results indicate that the electrical conductivity of the sintered Cu chips increased with increasing molecular weight of PAA. Furthermore, adhesion properties improved, and surface oxygen content decreased. These findings demonstrate that higher molecular weights of PAA lead to more effective removal of the oxide layer in sintered Cu chips. This study contributes to the research and development of Cu sintering in the semiconductor packaging industry and offers guidelines for selecting appropriate sintering additives and polymer molecular weights, thereby advancing semiconductor packaging technology.

This study investigated the interaction between UV-triggered curing binders and photoinitiators, focusing on their thermal, mechanical, and morphological properties. Using epoxy acrylate as the matrix and three potential photoinitiators with varying phosphorus contents, UV curing systems were fabricated and analyzed. 2-hydroxy-2-methyl-1-phenyl-1-propanone (HMPP), 2,4,6-trimethyl benzoyl diphenyl phosphine oxide (TPO), and their mixture were utilized as photoinitiators. We observed that the curing process significantly reduced residual double bonds within the first 5 s of UV irradiation time. The glass transition temperature (T_g) increased with curing time due to enhanced network density. For instance, in the MyA-TPO formulation, T_g of the cured sample tended to increase to 67.3 °C for 3 s to 79.8 °C for 15 s. Mechanical analysis revealed that HMPP facilitated the formation of robust network structures. Notably, the MyA-HMPP formulation exhibited a tensile strength of 63 MPa and a Young's modulus of 21 MPa, indicating excellent mechanical strength. SEM imaging confirmed these findings, illustrating distinct fracture morphologies that correlated with mechanical performance. These results provide insights into optimizing UV-curable materials for applications requiring high precision and durability. In particular, the combination of high T_g, superior tensile strength, and uniform fracture morphology indicates excellent thermal stability, mechanical integrity, and crack resistance-critical requirements in semiconductor packaging. These properties, along with rapid UV curing, support the suitability of the proposed systems for advanced applications such as system-in-package (SiP) and 3D integration.