Substrate Material Research Articles

Abstract Global water scarcity, intensified by climate change and population growth, necessitates sustainable freshwater solutions. Solar thermal desalination offers promise due to its energy efficiency, yet optimizing system performance hinges critically on material selection, particularly for photothermal absorbers and their substrates. While extensive research addresses photothermal nanomaterials, substrate materials vital for structural integrity, thermal management, and interfacial stability remain underexplored. This review comprehensively examines current advances in solar evaporator components, evaluating photothermal materials and substrates against key selection criteria: thermal conductivity, stability under harsh conditions, scalability, and compatibility. We analyze diverse substrate materials (e.g., metals, ceramics, polymers, bio-based, and aerogels) and their synergistic roles in enhancing evaporation efficiency and durability. Critical gaps in large-scale feasibility, long-term stability under variable solar flux, and cost-performance trade-offs are identified. The review also highlights emerging trends such as 3D-printed substrates and bio-inspired designs to overcome salt accumulation and fouling. By addressing these challenges and outlining pathways for scalable implementation, this work aims to advance robust, economically viable solar thermal desalination technologies for global freshwater security.

A new and transformative era in semiconductor packaging is underway, wherein, there is a shift from transistor scaling to system scaling and integration through advanced packaging. For advanced packaging, interconnect scaling is a key driver, with interconnect density requirements for chip-to-substrate microbump pitch below 5 μm and half-line pitch below 1 μm for Cu redistribution layer (RDL). Here, we present a comprehensive theoretical comparison of thermal cycling behavior in accordance with JESD22-A104D standard, intermetallic thickness evolution, and steady-state thermal analysis of Cu-microbump assembly for different bonding materials and substrates. Bonding materials studied include solder caps such as SAC105 (Sn98.5Ag1.0Cu0.5), eutectic Sn-Pb (Sn63Pb37), eutectic Sn-Bi (Sn42Bi58), Pb95Sn5, Indium, and Cu-Cu TCB structure. Effect of substrates including Si, glass and FR-4 is evaluated for various microbump structures with varying pitches (85 µm, 40 µm, 10 µm, and 5 µm) on their fatigue life. Results indicate that for Cu-microbump assemblies at an 85 µm pitch. The Pb95Sn5 exhibits the longest predicted fatigue life (3267 cycles by Engelmaier and 452 cycles by Darveaux), while SAC105 shows the shortest (320 and 103 cycles). Additionally, the Cu-Cu TCB structure achieves an estimated lifetime of approximately 7800 cycles, which is significantly higher than all solder-based Cu-microbump assemblies. The findings contribute to advanced packaging applications by providing valuable theoretical references for optimizing solder materials and structural configurations.

Highly sensitive flexible pressure sensors are crucial for wearable health monitoring and human–machine interaction. While the emerging iontronic sensors inherently offer high sensitivity, this can be further improved by engineering microstructured interfaces. In this study, we employ four different types of common fiber materials as substrates for fabricating ionic dielectric layers by a simple impregnation of ionic liquid (IL). A comparative study reveals that the porosity and microstructural architecture (e.g., fiber diameter) of the substrate material directly influences the amount of adsorbed IL and consequent sensing performance. We achieved the highest sensitivity by using a thin electrospun TPU/IL nanofiber mat (33 μm), which exhibited high sensitivities of 3.10 kPa−1, 1.85 kPa−1, and 1.02 kPa−1 in the pressure ranges of 0–200 kPa, 200–400 kPa, and 400–700 kPa, respectively. Furthermore, the sensor exhibited an excellent fast response (2.71 ms) and recovery time (8.71 ms), along with outstanding cyclic stability. This work provides valuable guidance for selecting and utilizing common fiber materials to develop high-sensitivity iontronic pressure sensors, paving the way for their practical application in next-generation wearable electronics.

Oxygen evolution reaction driven co-reactant-free antifouling electrochemiluminescence sensor based on electrocatalytic macromolecular heterocyclic compounds/electrically neutral hydrogel.

TiO2/WO3 nanoarrays photodetector and liposomes equipped with electron donor-mediated signal amplification for immunoassay applications.

Cost-effective graphite aerogel for high-temperature thermoelectrics: Synergizing ultra-high electrical conductivity and thermal insulation.

Modeling the partially detected backside reflectance of transparent substrates in reflectance microspectroscopy.

Deep learning-assisted surface-enhanced Raman spectroscopy detection of stimulants.

Surface-enhanced Raman scattering refers to the phenomenon where the Raman signals of molecules are significantly enhanced when they are adsorbed onto or located near the surface of substrates with specific nanostructures. By integrating with scanning probe microscopy techniques, SERS effectively overcomes the low sensitivity of conventional Raman spectroscopy and has been widely applied in surface science, biological sciences, and other fields. This review provides a comprehensive overview of recent theoretical advances in understanding the substrate-induced enhancement mechanisms of molecular Raman signals, as well as progress in the design and optimization of surface plasmonic configurations. The primary objective is to explore effective strategies for achieving high-resolution Raman signal enhancement. We elaborate in detail on the individual mechanisms of electromagnetic and chemical enhancement , as well as their synergistic interplay. Several key factors influencing surface plasmon-enhanced effects are systematically discussed, including charge transfer, external electric fields, and the role of different substrate materials in enhancing single-molecule Raman responses. In addition, we briefly highlight recent developments in first-principles studies using dispersion-corrected density functional theory, which incorporate long-range corrections to describe weak interactions between molecules and substrates within van der Waals radii. Finally, we offer perspectives on the future theoretical and experimental directions of surface plasmon and tip-enhanced techniques in the single-molecule regime. We also discuss the potential of integrating single-molecule junction sensors with machine learning and density functional theory for deeper spectroscopic insights, aiming to further advance the field of single-molecule spectroscopy.&#xD.

Laser direct energy deposition is a metal additive manufacturing process that produces three-dimensional components by scanning the laser layer by layer, with simultaneously injecting metal powder into a molten pool occurred by a high-energy laser directly. In this process, due to the localized heat input and rapid cooling of the deposit, complex residual stresses typically occurred within the deposited material. This study aimed to analyze the residual stress formation behavior during the laser direct energy deposition process of Inconel 625 alloy and to develop a finite element analysis model that can predict the residual stress. To experimentally investigate the residual stress formation behavior, a rectangular shaped substrate material was prepared, and Inconel 625 alloy with different thicknesses was deposited on top of the substrate material using two different deposition strategies of unidirectional and 90-degree tilted. The bending of the substrate material was measured to quantitatively analyze the residual stress. Based on the experimental results, a finite element model was designed to reproduce the residual stress of the Inconel 625 alloy produced by laser direct energy deposition process.

The field of use of sheepskin fabrics significantly expands nowadays due to their high aesthetic properties, the possibility of their manufacture from various types of fur, including semi-finished sheepskin, and the possibility of regulating quality indicators. The article discusses the influence of the parameters of the fur fabric on its properties, namely drapability. To assess drapery, the “angle technique” was used, where the drapery coefficient, Kdr, is used as a quantitative indicator. It is established that the drapability of fur fabrics made from sheepskin semi-finished products is largely influenced by the step of stitching the fur thread, and to a lesser extent, by the properties of the substrate material. Creating fur fabrics from sheepskin semi-finished products with a low drapability index allows improving this index and expanding its application.

This study presents the fabrication and chemical modification of titanium meshes produced by nanosecond laser drilling, tailored for advanced photocatalytic and surface-enhanced Raman scattering (SERS) applications. Titanium meshes were fabricated via pulsed laser ablation (TM_1) and subsequently modified either by deposition of silver nanoparticles through irradiation (TM_2) and sonication (TM_3) or by surface oxidation using hydrogen peroxide (TM_4). Morphological and compositional analyses revealed that these modifications lead to distinct Ag nanoparticle morphologies and significant increases in surface oxygen content, notably enhancing photocatalytic performance. Photocatalytic tests demonstrated that the TM_4 mesh achieved the highest degradation rate of methylene blue, underscoring the critical role of surface oxygen enrichment. In contrast, TM_2 and TM_3 exhibit strong potential as surface-enhanced Raman scattering (SERS) substrates due to the well-distributed plasmonic silver nanostructures that enhance local electromagnetic fields. Their three-dimensional porous architecture facilitates high surface area and efficient analyte adsorption (MB), further improving SERS sensitivity. These findings establish nanosecond laser-processed titanium meshes, particularly those that are chemically modified, as promising, scalable materials for efficient water purification and effective SERS substrates for molecular sensing.

High Entropy Alloys (HEA) are multi-principal element materials that have been intensively studied over the past decade. In this work, two Al–Fe–Cr–Ni–Cu HEAs were synthesized and processed into thin films by DC magnetron sputtering, and their structural, mechanical and electrochemical properties were systematically evaluated. The coatings exhibited dense, uniform structures with strong adhesion to 304 L stainless steel. Coatings hardness was higher than the substrate material. Electrochemical tests in 3.5 g/L NaCl solution revealed superior corrosion resistance for the I8-10-derived coating, which achieved the lowest corrosion rate (5.54E-05 mm/year) and the highest polarization resistance (5.470.008 Ω), outperforming both the bulk alloys and uncoated substrates.

This paper presents a novel compact elliptical monopole antenna (EMA) integrated with a defected ground structure (DGS) and a U-shaped slot for enhanced performance in dual-band sub-6[Formula: see text]GHz 5G applications. The antenna was designed with overall dimensions of 21[Formula: see text]mm [Formula: see text] 26[Formula: see text]mm using an FR-4 substrate material, which achieves resonant frequencies at 2.4[Formula: see text]GHz and 3.2[Formula: see text]GHz with return loss values of –28.65[Formula: see text]dB and –27.55[Formula: see text]dB. The incorporation of DGS significantly improves impedance matching, gain, and radiation efficiency by achieving 4.69 and 98%. Simulation and experimental validation using HFSS and a vector network analyzer (VNA) confirm strong agreement, which demonstrates the antenna’s effectiveness. The proposed design stands out due to its simple geometry, high efficiency, and superior dual-band performance, making it an ideal candidate for compact 5G devices operating in the sub-6[Formula: see text]GHz range.

The development of tunable optical filters in the mid-infrared (MIR) region is crucial for a variety of applications, including environmental monitoring, medical diagnostics, and communication systems. This paper presents the design, fabrication, and characterization of a novel Twisted Liquid Crystal (TLC) electro-tunable optical cavity filter for the MIR region 3–5 μm. The filter is based on a Fabry–Perot interferometer configuration, which includes a polarization-independent TLC to achieve electrical control over the filter’s transmission characteristics. Two distinct filters were fabricated, differing in their substrate materials: silicon and glass. The silicon-based filter demonstrated an impressive 80% transmission with a tuning range of ∼13.6 nm and ∼14.64 nm in two separate bands, achieved by varying the applied voltage from 0 to 20 V. In contrast, the glass substrate filter exhibited a slightly higher transmission of 82% with tuning ranges of ∼10.5 nm and ∼7.2 nm across the spectral band when the voltage was adjusted from 0 to 27 V. Experimental validation showed a strong alignment between the simulations and results, demonstrating the feasibility of integrating tunable liquid crystals into mid-infrared optical cavities. This advancement highlights their potential for applications that require precise and dynamic control of the mid-infrared spectrum.

Automated Background Noise Removal from Substrate Materials in Raman Spectra Using Dynamic Time Warping

Abstract Einstein Telescope (ET) is expected to achieve sensitivity improvements exceeding an order of magnitude compared to current gravitational-wave detectors. The rigorous characterization in optical birefringence of materials and coatings has become a critical task for next-generation detectors, especially since this birefringence is generally spatially non-uniform. A highly sensitive optical polarimeter has been developed at the Department of Physics and Earth Sciences of the University of Ferrara and INFN - Ferrara Section, Italy, aimed at performing two-dimensional birefringence mapping of substrates. In this paper we describe the design and working principle of the system and present results for crystalline silicon, a candidate material for substrates in the low-frequency interferometers of ET. We find that the birefringence is $$\lesssim 10^{-7}$$ ≲ 10 - 7 for commercially available samples and is position dependent in the silicon (100)-oriented samples, with variations in both magnitude and axis orientation. We also measure the intrinsic birefringence of the (110) surface: $$\Delta n^{(110)}=-(1.50\pm 0.15)\times 10^{-6}$$ Δ n ( 110 ) = - ( 1.50 ± 0.15 ) × 10 - 6 @ $$\lambda =1550$$ λ = 1550 nm. Implications for the performance of gravitational-wave interferometers are discussed.

This article presents a compact, simplified structured, bendable, and lightweight antenna for wearable electronic devices. A multiwalled carbon nanotube and polydimethylsiloxane composite material is utilized for the radiating patch and ground plane, while curved PDMS is used as a substrate material. The design consists of a rectangular‐shaped patch loaded with rectangular‐shaped stubs to improve the impedance bandwidth and matching of the proposed antenna. The comparative simulated and experimental results indicate that the obtained antenna design is flexible and has good dielectric properties. The proposed antenna offers dual bands at 5.19–5.6 and 6.68–6.92 GHz, which cover wireless local area network and Wi‐Fi 6E frequency bands. The conformal analysis of the proposed antenna is performed, which offers stable outcomes in terms of S‐parameter, gain (>4.5 dBi) and radiation efficiency (>87%). Moreover, the design is also placed on the human body phantom to study the specific absorption ratio analysis and gain of the antenna. The results obtained from the proposed antenna, along with comparisons to recent work, demonstrate its strong performance and suitability for integration into wearable electronic devices operating within the 5G and 6G frequency bands.

ABSTRACTGold nanoparticles (AuNPs) are widely recognized as ideal substrate materials for surface‐enhanced Raman spectroscopy (SERS) due to their outstanding plasmonic properties and excellent chemical stability. However, conventional synthesis methods often involve multistep procedures, substantial energy input, and poor control over nanoparticle aggregation. In this work, we report a facile and energy‐efficient synthesis of SERS‐active AuNPs via a microdroplet‐based reaction platform. By tuning the reactant ratio of NaBH4 to HAuCl4, well‐dispersed AuNPs with strong SERS activity were obtained, as confirmed by transmission electron microscopy. These substrates enabled in situ, real‐time monitoring of the photocatalytic coupling reaction of 4‐nitrothiophenol, revealing the critical influence of laser power on the reaction kinetics. This work highlights a green and scalable strategy for fabricating high‐performance SERS substrates, offering new opportunities for studying on‐surface catalytic reactions under ambient conditions.

Abstract To enhance the spectral signal intensity and stability of LIBS for detecting trace elements in soil, a GO adsorption conversion mechanism is proposed. The experiment compared the enhancement effects of three substrates—glass plate, graphite plate, and GO adsorption layer—on metal elements such as Ni, Sr, and Ba in soil. The surface enhancement mechanisms of different substrates were analyzed from three perspectives: ablation morphology, thermal conductivity, and adsorption energy. It was concluded that a smooth substrate surface facilitates uniform solute distribution, and an increase in the thermal conductivity of the substrate material enhances the signal and enlarges the plasma morphology. The optimal soil-to-nitric acid ratio in the solid-liquid-solid conversion mechanism was determined to be 1:1, with a nitric acid concentration of 1 mol/L. The GO adsorption layer substrate demonstrated the best enhancement effect, with spectral intensities of Ni, Sr, and Ba enhanced by 3.4, 1.8, and 8.4 times, respectively, compared to the glass glass. The limits of detection (LOD) reached 3.148 mg/L, 0.578 mg/L, and 0.342 mg/L, with relative standard deviations (RSD) of 5.4%, 6.8%, and 8.5%, respectively. This indicates that the solid-liquid-solid conversion mechanism using the GO adsorption layer can effectively enrich metal elements in soil, enhancing the spectral signal and stability of LIBS in detecting trace elements while significantly lowering the detection limits. This approach provides a new strategy for the accurate measurement of trace elements in soil samples using LIBS.