High-Concentration Synthesis of Sub-10-nm Copper Nanoparticles for Application to Conductive Nanoinks

A simple, high-concentration (up to 0.6 M Cu salt) synthesis of sub-10-nm copper nanoparticles (Cu NPs) was developed in ethylene glycol at room temperature under ambient air conditions using 1-amino-2-propanol (AmIP) as the stabilizer. Monodispersed AmIP-Cu NPs of 3.5 ± 1.0 nm were synthesized in a high yield of ∼90%. Thus, nearly 1 g of sub-10-nm Cu NP powder was obtained using a one-step synthesis for the first time. It is proposed that metallacyclic coordination stability of a five-membered ring type between the Cu and AmIP causes the high binding force of Am IP onto the Cu surface, resulting in the superior stability of the AmIP-Cu NPs in a solution. The purified powder of AmIP-Cu NPs can be redispersed in alcohol-based solvents up to high Cu contents of 45 wt % for the preparation of Cu nanoink. The resistivity of the conductive Cu film obtained from the Cu nanoink was 30 μΩ cm after thermal heating at 150 °C for 15 min under a nitrogen flow. The long-term resistance stability of the Cu film under an air atmosphere was also demonstrated.

Hydrothermal-Assisted Cold Sintering Process: A New Guidance for Low-Temperature Ceramic Sintering

Sintering is a thermal treatment process that is generally applied to achieve dense bulk solids from particulate materials below the melting temperature. Conventional sintering of polycrystalline ceramics is prevalently performed at quite high temperatures, normally up to 1000 to 1200 °C for most ceramic materials, typically 50% to 75% of the melting temperatures. Here we present a new sintering route to achieve dense ceramics at extraordinarily low temperatures. This method is basically modified from the cold sintering process (CSP) we developed very recently by specifically incorporating the hydrothermal precursor solutions into the particles. BaTiO3 nano polycrystalline ceramics are exemplified for demonstration due to their technological importance and normally high processing temperature under conventional sintering routes. The presented technique could also be extended to a much broader range of material systems than previously demonstrated via a hydrothermal synthesis using water or volatile solutions. Such a methodology is of significant importance, because it provides a chemical roadmap for cost-effective inorganic processing that can enable broad practical applications.

Development of High-Performance Enamel Coating on Grey Iron by Low-Temperature Sintering

In this study, we report on a low-temperature sintered enamel coating with a high-strength bonding and wear-resistance that protected a grey cast iron substrate. The SiO₂–Al₂O₃–B₂O₃ composited prescription for the enamel coating was modified by the partial substitutions of SiO₂ for B₂O₃ and alkali metals for Li₂O. The optimized enamel coating was prepared by sintering at a relatively low temperature (730 °C) for seven minutes. Due to the composition of both the amorphous and crystalline phases, the enamel coating presented sufficient hardness and excellent wear resistance. The wear volume loss and the specific wear rate of the enamel coating were obviously lower than that of the metal substrate. The enamel coating can effectively improve the service life of the grey cast iron substrate in a complex frictional environment.

Design of a High-Efficiency and -Gain Antenna Using Novel Low-Loss, Temperature-Stable Li2Ti1-x(Cu1/3Nb2/3)xO3 Microwave Dielectric Ceramics

Microwave dielectric ceramics are vital for filters, dielectric resonators, and dielectric antennas in the 5G era. It was found that the (Cu_1/3Nb_2/3)⁴⁺ substitution can effectively adjust the TCF (temperature coefficient of resonant frequency) of Li₂TiO₃ and simultaneously increase its Q × f (Q and f denote the quality factor and the resonant frequency, respectively) value. Notably, excellent microwave dielectric properties (ε_r (permittivity) ≈ 18.3, Q × f ≈ 77,840 GHz, and TCF ≈ +9.8 ppm/°C) were achieved in the Li₂Ti_0.8(Cu_1/3Nb_2/3)_0.2O₃ (LTCN_0.2) ceramic sintered at 1140 °C. Additionally, the sintering temperature of LTCN_0.2 was reduced to 860 °C by the addition of 3 wt % H₃BO₃, exhibiting superior microwave dielectric properties (ε_r ≈ 21.0, Q × f ≈ 51,940 GHz, and TCF ≈ 1.4 ppm/°C) and being chemically compatible with silver. Moreover, LTCN_0.2 + 3 wt % H₃BO₃ ceramics were designed as a patch antenna and a dielectric resonator antenna, both of which showed high simulated radiation efficiencies (88.4 and 93%) and gains (4.1 and 4.03 dBi) at the center frequencies (2.49 and 10.19 GHz). The LTCN_0.2 + 3 wt % H₃BO₃ materials have promising future application for either 5G mobile communication devices and/or in low-temperature co-fired ceramic technology owing to their high Q, low sintering temperature, small density, and good temperature stability.

Fast and Low-Temperature (70 °C) Mineralization of Inkjet Printed Mesoporous TiO2 Photoanodes Using Ambient Air Plasma

Hybrid mesoporous titania/silica electron-generating and transporting layers were prepared using wet-coating with a dispersion consisting of prefabricated titania nanoparticles and a methyl-silica binder. Titania/methyl-silica wet layers were deposited by inkjet printing and further mineralized by low-temperature atmospheric-pressure air plasma using diffuse coplanar surface barrier discharge (DCSBD) to form a titania/silica hybrid nanocomposite coating. Morphological analysis performed by scanning electron microscopy revealed no damage to the titania nanoparticles and chemical analysis performed by X-ray photoelectron spectroscopy disclosed a rapid decrease in carbon and increase in oxygen, indicating the oxidation effect of the plasma. The coatings were further electrochemically investigated with linear sweep voltammetry and chronoamperometry. The magnitude of photocurrent and photocatalytic activity were found to increase significantly with the plasma exposure on the order of 10s of seconds. The results obtained demonstrate the potential of DCSBD ambient air plasma for fast and low-temperature mineralization of titania mesoporous coatings.

Inkjet Printing of Polyacrylic Acid-Coated Silver Nanoparticle Ink onto Paper with Sub-100 Micron Pixel Size

Printed electronics (PE) technology shows huge promise for the realisation of low-cost and flexible electronics, with the ability to pattern heat- or pressure-sensitive materials. In future developments of the PE market, the ability to produce highly conductive, high-resolution patterns using low-cost and roll-to-roll processes, such as inkjet printing, is a critical technology component for the fabrication of printed electronics and displays. Here, we demonstrate inkjet printing of polyacrylic acid (PAA) capped silver nanoparticle dispersions onto paper for high-conductivity electronic interconnects. We characterise the resulting print quality, feature geometry and electrical performance of inkjet patterned features and demonstrate the high-resolution printing, sub-100 micron feature size, of silver nanoparticle materials onto flexible paper substrate. Printed onto photo-paper, these materials then undergo chemically triggered sintering on exposure to chloride contained in the paper. We investigated the effect of substrate temperature on the properties of printed silver material from room temperature to 50 °C. At room temperature, the resistivity of single layer printed features, of average thickness of 500 nm and width 85 µm, was found to be 2.17 × 10^-7 Ω·m or 13 times resistivity of bulk silver (RBS). The resistivity initially decreased with an increase in material thickness, when achieved by overprinting successive layers or by decreasing print pitch, and a resistivity of around 10 times RBS was observed after overprinting two times at pitch 75 µm and with single pass print pitch of between 60 and 80 µm, resulting in line thickness up to 920 nm. On further increases in thickness the resistivity increased and reached 27 times RBS at print pitch of 15 µm. On moderate heating of the substrate to 50 °C, more compact silver nanoparticle films were formed, reducing thickness to 200 nm from a single pass print, and lower material resistivity approaching five times RBS was achieved.

Low-Temperature Sintering of l-Alanine-Functionalized Metallic Copper Particles Affording Conductive Films with Excellent Oxidative Stability

Here, the alpha amino acid l-alanine is employed as both a capping and stabilizing agent in the aqueous synthesis of submicron-sized metallic copper particles under ambient atmospheric conditions. The reduction of the copper(II) precursor is achieved using l-ascorbic acid (vitamin C) as the reducing agent. The nature of the complex formed between l-alanine and the copper(II) precursor, pH of the medium, temperature, and the relative proportion of capping agent are found to play a significant role in determining the size, shape, and oxidative stability of the resulting particles. The adsorbed l-alanine is shown to act as a barrier imparting excellent thermal stability to capped copper particles, delaying the onset of temperature-induced aerial oxidation. The stability of the particles is complemented by highly favorable sintering conditions, rendering the formation of conductive copper films at significantly lower temperatures (T ≤ 120 °C) compared to alternative preparation methods. The resulting copper films are well-passivated by residual surface l-alanine molecules, promoting long-term stability without hindering the surface chemistry of the copper film as evidenced by the catalytic activity. Contrary to the popular belief that ligands with long carbon chains are best for providing stability, these findings demonstrate that very small ligands can provide highly effective stability to copper without significantly deteriorating its functionality while facilitating low-temperature sintering, which is a key requirement for emerging flexible electronic applications.

Color Tunable Composite Phosphor Ceramics Based on SrAlSiN3:Eu2+/Lu3Al5O12:Ce3+ for High-Power and High-Color-Rendering-Index White LEDs/LDs Lighting

Lu3Al5O12:Ce3+ phosphor ceramics were fabricated by vacuum sintering. On this basis, a bi-layer composite phosphor was prepared by low-temperature sintering to cover the phosphor ceramics with a layer of SrAlSiN3:Eu2+-phosphor-in-glass (PiG). The optical, thermal, and colorimetric properties of LuAG:Ce3+ phosphor ceramics, SrAlSiN3:Eu2+ phosphors and SrAlSiN3:Eu2+-PiG were studied individually. Combining the bi-layer composite phosphors with the blue LED chip, it is found that the spectrum can be adjusted by varying the doping concentration of SrAlSiN3:Eu2+-PiG and the thickness of Lu3Al5O12:Ce3+ phosphor ceramics. The maximal color rendering index value of the white LED is 86, and the R9 is 61. Under the excitation of a laser diode, the maximum phosphor conversion efficacy of the bi-layer composite phosphors is 120 lm/W, the Ra is 83, and the correlated color temperature is 4534 K. These results show that the bi-layer composite phosphor ceramic is a candidate material to achieve high color rendering index for high brightness lighting.

Piezoelectric Ceramics with High d33 Constants and Their Application to Film Speakers

A multilayer piezoelectric material was fabricated using piezoelectric materials with low-temperature sintering capabilities and high piezoelectric coefficients to develop a functionally superior piezoelectric speaker with a large-displacement deformation. A soft relaxor was utilized to prepare the component materials, with the optimized composition of the investigated piezoelectric ceramics represented by 0.2Pb((Zn0.8Ni0.2)13Nb23)O3−0.8Pb(Zr0.5Ti0.5)O3. Li2CO3 was added to assist the low-temperature sintering conducted at 875 °C, which yielded a multilayer piezoelectric material with superior properties (d33 = 500 pC N⁻¹, kp = 0.63, g33 = 44 mV N⁻¹). A multilayer piezoelectric actuator with a single-layer thickness of ~40 µm and dimensions of 12 × 16 mm² was fabricated by tape casting the prepared green sheets. Finite element analysis revealed that the use of a PEEK film and a smaller silicone–rubber film as a composite in the diaphragm realized optimal frequency-response characteristics; the vibrations generated by the piezoelectric element were amplified. The optimal structure obtained via simulations was applied to fabricate an actual piezoelectric speaker with dimensions of 20 × 24 × 1 mm³. The actual measurements exhibited a sound pressure level of ~75 dB and a total harmonic distortion ≤15% in the audible frequency range (250–20,000 Hz) at an applied voltage of 5 Vp.

Crystallization Behavior of the Low-Temperature Mineralization Sintering Process for Glass Nanoparticles

Bioactive glasses are promising materials for various applications, such as bone grafts and implants. The development of sintering techniques for bioactive glasses is one of the most important ways to expand the application to biomaterials. In this paper, we demonstrate the low-temperature mineralization sintering process (LMSP) of glass nanoparticles and their crystallization behavior. LMSP is a novel process employed to densify glass nanoparticles at an extremely low temperature of 120 °C. For this new approach, the hydrothermal condition, mineralization, and the nanosize effect are integrated into LMSP. To induce mineralization in LMSP, bioactive glass nanoparticles (BGNPs, 55SiO2-40CaO-5P2O5, mol%), prepared by the sol-gel process, were mixed with a small amount of simulated body fluid (SBF) solution. As a result, 93% dense BGNPs were realized under a temperature of 120 °C and a uniaxial pressure of 300 MPa. Due to the effect of mineralization, crystalline hydroxyapatite (HAp) was clearly formed at the boundaries of BGNPs, filling particles and interstitials. As a result, the relative density was remarkably close to that of the BGNPs conventionally sintered at 1050 °C. Additionally, the Vickers hardness value of LMSP samples varied from 2.10 ± 0.12 GPa to 4.28 ± 0.11 GPa, and was higher than that of the BGNPs conventionally sintered at 850 °C (2.02 ± 0.11 GPa). These results suggest that, in addition to LMSP being an efficient densification method for obtaining bulk bioactive glasses at a significantly lower temperature level, this process has great potential for tissue engineering applications, such as scaffolds and implants.

Novel Conductive AgNP-Based Adhesive Based on Novel Poly (Ionic Liquid)-Based Waterborne Polyurethane Chloride Salts for E-Textiles

The emergence of novel e-textile materials that combine the inherent qualities of the textile substrate (lightweight, soft, breathable, durable, etc.) with the functionality of micro/nano-electronic materials (conductive, dielectric, sensing, etc.) has resulted in a trend toward miniaturization, integration, and intelligence in new electronic devices. However, the formation of a conductive network by micro/nano-conductive materials on textiles necessitates high-temperature sintering, which inevitably causes substrate aging and component damage. Herein, a bis-hydroxy-imidazolium chloride salt as a hard segment to synthesize a waterborne polyurethane (WPU) adhesive is designed and prepared. When used in nano-silver-based printing coatings, it offers strong adherence for coatings, reaching 16 N cm-1; on the other hand, the introduction of chloride ions enables low-temperature (60 °C) chemical sintering to address the challenge of secondary treatment and high-temperature sintering (>150 °C). Printed into flexible circuits, the resistivity can be controlled by the content of imidazolium salts anchored in the molecular chain of the WPU from a maximum resistivity of 3.1 × 107 down to 5.8 × 10-5 Ω m, and it can conduct a Bluetooth-type finger pulse detector with such low resistivity. As a flexible circuit, it also offers high stability against washing and adhesion, which the resistivity only reduces less than 20% after washing 10 times and adhesion. Owing to the adjustability of the resistivity, we fabricated an all-textile flexible pressure sensor that accurately differentiates different external pressures (min. 10 g, ~29 Pa), recognizes forms, and detects joint motions (finger bending and wrist flexion).

A Highly Sensitive NiO Flexible Temperature Sensor Prepared by Low-Temperature Sintering Electrohydrodynamic Direct Writing

Flexible temperature sensors have diverse applications and a great potential in the field of temperature monitoring, including healthcare, smart homes and the automotive industry. However, the current flexible temperature sensor preparation generally suffers from process complexity, which limits its development and application. In this paper, a nickel oxide (NiO) flexible temperature sensor based on a low-temperature sintering technology is introduced. The prepared NiO flexible temperature sensor has a high-resolution temperature measurement performance and good stability, including temperature detection over a wide temperature range of (25 to 70 °C) and a high sensitivity performance (of a maximum TCR of -5.194%°C-1 and a thermal constant of 3938 K). The rapid response time of this temperature sensor was measured to be 2 s at 27-50 °C, which ensures the accuracy and reliability of the measurement. The NiO flexible temperature sensor prepared by electrohydrodynamic direct writing has a stable performance and good flexibility in complex environments. The temperature sensor can be used to monitor the temperature status of the equipment and prevent failure or damage caused by overheating.

Achieving High Piezoelectricity and Excellent Temperature Stability in Pb(Zr,Ti)O3-Based Ceramics via Low-Temperature Sintering

Developing piezoelectric ceramics with high piezoelectric properties and broad temperature usage ranges via low-temperature sintering is one of decisive importance for flourishing developments for emerging electromechanical applications. However, these properties are usually mutually exclusive, such as low-temperature sintering and high piezoelectricity as well as high piezoelectricity and temperature stability. Here, we report high piezoelectricity (i.e., piezoelectric constant d₃₃ ≈ 744 pC/N, electromechanical coupling factor k_p ≈ 75%, and Curie temperature T_C ≈ 201 °C) and superior temperature stability (d₃₃ varies less than 10% within 25-160 °C) in Pb_0.905Ba_0.095(Zr_0.54Ti_0.46)O₃ + 1 mol % Nb₂O₅ + 1 wt % Bi₂O₃ + x wt % CdCO₃ (PBZTNB-xCd) ceramics that are fabricated at a sintering temperature of as low as 960 °C, superior to those of other reported random and textured ceramics. Good piezoelectricity is attributed to the remaining rhombohedral-tetragonal (R-T) phase coexistence and the high ceramic density. Excellent temperature stability is related to the stable crystal structure and domain structure. These properties confer to the produced materials attractive characteristics for further consideration in several advanced applications, especially for piezoelectric transducer applications requiring constant structures over a broad temperature range.

Study on Low-Temperature Conductive Silver Pastes Containing Bi-Based Glass for MgTiO3 Electronic Power Devices

Low-temperature lead-free silver pastes deserve thorough investigation for sustainable development and application of MgTiO3 ceramics in electronic devices. In this study, a series of Bi2O3-B2O3-ZnO-SiO2-Al2O3-CaO glasses with suitable softening temperatures were prepared via melt quenching using a type of micrometer silver powder formed by silver nanoparticle aggregates. The composite pastes containing silver powder, Bi2O3 glass powder and an organic vehicle were then screen-printed. The effects of glass powder concentration and sintering temperature on the microstructure of the surface interface were also investigated. The results showed that the silver paste for microwave dielectric ceramic filters (MgTiO3) possessed good electrical conductivity (2.28 mΩ/□) and high adhesion (43.46 N/mm2) after medium temperature (670 °C) sintering. Thus, this glass powder has great application potential in non-toxic lead-free silver pastes for metallization of MgTiO3 substrates.

Low-Temperature Sintering of Ag Composite Pastes with Different Metal Organic Decomposition Additions

Rapid developments in wide-bandgap semiconductors have led to the demand for interconnection materials that can withstand harsh conditions. In this study, novel Ag composite pastes were developed with the assistance of metal organic decomposition (MOD) to significantly reduce the sintering temperature of commercial Ag pastes. The effects of the decomposition characteristics of different MODs on the microstructure, morphology, and the shear strength of the Ag-sintered joints were systematically investigated. Additionally, the low-temperature sintering mechanisms of the MOD-assisted Ag composite pastes were studied and proposed. Among all the MODs studied, the one consisting of propylamine complexed with silver oxalate demonstrated the best performance due to its ability to form Ag nanoclusters with the smallest size (~25 nm) and highest purity (~99.07 wt.%). Notably, the bonding temperature of the MOD-modified Ag pastes decreased from 250 °C to 175 °C, while the shear strength increased from 20 MPa to 40.6 MPa when compared to the commercial Ag pastes.

Three-Tier Hierarchical Porous Structure with Ultrafast Capillary Transport for Flexible Electronics Cooling

The development of flexible electronics needs efficient cooling devices. The porous wick, the key component in a heat pipe (HP) and vapor chamber (VC), is generally fabricated by sintering copper particles at high temperatures (>1000 °C), which makes it only formed on an inflexible substrate. In this work, one three-tier hierarchical porous structure (mesocrack, micropore, and nanopapillae) was fabricated via a low-temperature sintering method based on the utilization of self-reducing metal precursors (∼300 °C), which can be used as a flexible porous wick. The mesocrack, acting as the main water flow channel, efficiently decreases the flow resistance. The micropore, covered with densely distributed spore-like nanopapillae, creates a heterogeneous wetting surface. By harnessing the synergistic effect of hydrophobic drag reduction and hydrophilic driving force enhancement, the capillary performance is significantly improved. The obtained wick on the flexible substrate can overcome the dilemma between diminishing viscous resistance and strengthening capillary force at different length scales. It can achieve an ultimate wicking coefficient of 7.132 mm/s0.5, representing an enhancement of 9.1% compared to the best micro/nano wick structure in the previous works. Moreover, for the flexible light-emitting diode, the passive cooling approach utilizing the fluid transport and evaporation within the porous structure fabricated in this study, in comparison to the natural cooling, achieved a temperature decrease of 35.9 °C, resulting in a cooling effect of up to 35.1%. The proposed method resolves the challenge of fabricating a porous wick for flexible HP and VC, and it will open up a way for the cooling technique of flexible electronics.

Low-Temperature Bonding for Heterogeneous Integration of Silicon Chips with Nanocrystalline Diamond Films

Integrating nanocrystalline diamond (NCD) films on silicon chips has great practical significance and many potential applications, including high-power electronic devices, microelectromechanical systems, optoelectronic devices, and biosensors. In this study, we provide a solution for ensuring heterogeneous interface integration between silicon (Si) chips and NCD films using low-temperature bonding technology. This paper details the design and implementation of a magnetron sputtering layer on an NCD surface, as well as the materials and process for the connection layer of the integrated interface. The obtained NCD/Ti/Cu composite layer shows uniform island-like Cu nanostructures with 100~200 nm diameters, which could promote bonding between NCD and Si chips. Ultimately, a heterogeneous interface preparation of Si/Ag/Cu/Ti/NCD was achieved, with the integration temperature not exceeding 250 °C. The TEM analysis shows the closely packed atomic interface of the Cu NPs and deposited Ti/Cu layers, revealing the bonding mechanism.

Elucidating the Sintering Mechanisms and Synergistic Doping Effects in CuO/Fe2O3 Codoped Gd-Doped Ceria Electrolytes for Advanced Low-Temperature Solid Oxide Fuel Cells (LT-SOFCs)

This paper presents a study of the synergistic effects on sintering activity and the electrical performance of a CuO and Fe2O3 codoped gadolinium-doped ceria (GDC) electrolyte. The isothermal sintering behavior is investigated, and the viscous flow sintering mechanism is validated. The findings indicate that when the molar ratio of CuO to FeO1.5 is 3:1, the sintering temperature can be reduced to 980 °C, which is approximately 450 °C lower than that of GDC (>1450 °C). The lowest sintering activation energy is found to be 389 kJ/mol when the molar ratio of CuO to FeO1.5 is 3:1. Additionally, the concept named "macrodensification temperature" is proposed in this research to describe the connection of the densification process at the microstructure and macrostructure scale. The macrodensification temperature is further verified by quasi-in situ observation and isothermal testing, meanwhile, Cu-Fe-Gd-O and Cu-Ce-O phases, which are beneficial for low-temperature sintering are first found in this work. Moreover, when the molar ratio of CuO to FeO1.5 is 3:1, the ionic conductivity reaches 0.041 S/cm@700 °C, which is 10% higher than that of GDC. The highest performance of the anode-supported cell is found when the electrolyte doping ratio of CuO to FeO1.5 equals 3:1. The open-circuit voltage is observed to be 0.82 V@700 °C, accompanied by a high-power density of 1.2 W/cm2@700 °C. The cell performance with GDC as the electrolyte is found to be 0.8 W/cm2@700 °C. In conclusion, the combined effects of CuO and Fe2O3 doping in GDC may offer a promising avenue for enhancing electrolyte performance and extending its applications to low-temperature solid oxide fuel cells (LT-SOFCs).

Atmosphere-Assisted FLASH Sintering of Nanometric Potassium Sodium Niobate

The request for extremely low-temperature and short-time sintering techniques has guided the development of alternative ceramic processing. Atmosphere-assisted FLASH sintering (AAFS) combines the direct use of electric power to packed powders with the engineering of operating atmosphere to allow low-temperature conduction. The AAFS of nanometric Potassium Sodium Niobate, K0.5Na0.5NbO3, a lead-free piezoelectric, is of great interest to electronics technology to produce efficient, low-thermal-budget sensors, actuators and piezo harvesters, among others. Not previously studied, the role of different atmospheres for the decrease in FLASH temperature (TF) of KNN is presented in this work. Additionally, the effect of the humidity presence on the operating atmosphere and the role of the compact morphology undergoing FLASH are investigated. While the low partial pressure of oxygen (reducing atmospheres) allows the decrease of TF, limited densification is observed. It is shown that AAFS is responsible for a dramatic decrease in the operating temperature (T < 320 °C), while water is essential to allow appreciable densification. In addition, the particles/pores morphology on the green compact impacts the uniformity of AAFS densification.

A Strategy for Fabricating Ultra-Flexible Thermoelectric Films Using Ag2Se-Based Ink

Flexible thermoelectric materials have drawn significant attention from researchers due to their potential applications in wearable electronics and the Internet of Things. Despite many reports on these materials, it remains a significant challenge to develop cost-effective methods for large-scale, patterned fabrication of materials that exhibit both excellent thermoelectric performance and remarkable flexibility. In this study, we have developed an Ag2Se-based ink with excellent printability that can be used to fabricate flexible thermoelectric films by screen printing and low-temperature sintering. The printed films exhibit a Seebeck coefficient of -161 μV/K and a power factor of 3250.9 μW/m·K2 at 400 K. Moreover, the films demonstrate remarkable flexibility, showing minimal changes in resistance after being bent 5000 times at a radius of 5 mm. Overall, this research offers a new opportunity for the large-scale patterned production of flexible thermoelectric films.

Control of Silver Micro-Flakes Sintering and Connection Properties of Epoxy-Based Conductive Adhesives by the Effectiveness of Binder Chemistry

Bonding materials with high thermal and electrical conductivity and reliable resistance to thermal stress are required. The authors have been conducting fundamental research on sintering-type bonding, in which metal micro-fillers are low-temperature sintered in the resin-bonded type electrically conductive adhesives (ECAs), as a new bonding technology, with the aim of easing thermal stress through the resin binder. This study investigated the influence of the kind of additive diluent in epoxy-based ECAs containing silver (Ag) micro-flakes on the microstructure development in the adhesives and the connection properties to metal electrodes. As a result, the sintering of Ag micro-flakes was observed to proceed in the adhesive once cured at 150 °C and by post-annealing at 250 °C. Furthermore, the sintering behavior varied greatly depending on the kind and composition of the binder additive diluent, with corresponding changes in electrical conductivity and connection characteristics with metal electrodes. Additionally, electrode surface conditions affected the connection performance. These findings are valuable for designing sintering-type bonding using resin-bonded ECAs, optimizing interfacial interactions between binder chemicals and metals.

Additive Manufacturing of Binary and Ternary Oxide Systems Using Two-Photon Polymerization and Low-Temperature Sintering

Multicomponent oxide systems have many applications in different fields such as optics and medicine. In this work, we developed new hybrid photoresists based on a combination of an organic acrylate resin and an inorganic sol, suitable for 3D printing via two-photon polymerization (2PP). The inorganic sol contained precursors of a binary SiO2-CaO or a ternary SiO2-CaO-P2O5 system. Complex microstructures were 3D printed using these hybrid photoresists and 2PP. The obtained materials were characterized using thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) techniques. Our results revealed that the produced microstructures were able to endure sintering at 700 °C without collapsing, leading to scaffolds with 235 and 355 nm resolution and pore size, respectively. According to the TGA analysis, there was no significant mass loss beyond 600 °C. After sintering at 500 °C, the FTIR spectra showed the disappearance of the characteristic bands associated with the organic phase, and the presence of bands characteristic of the binary and ternary oxide systems and carbonate groups. The SEM images showed different morphologies of agglomerated nanoparticles with mean sizes of about 20 and 60 nm for ternary and binary systems, respectively. Our findings open the way towards precise control of bioglass scaffold fabrication with tremendous design flexibility.