Silver Nanoparticles Based Ink with Moderate Sintering in Flexible and Printed Electronics

Chemically Driven Sintering of Colloidal Cu Nanocrystals for Multiscale Electronic and Optical Devices

Emerging applications of Internet of Things (IoT) technologies in smart health, home, and city, in agriculture and environmental monitoring, and in transportation and manufacturing require materials and devices with engineered physical properties that can be manufactured by low-cost and scalable methods, support flexible forms, and are biocompatible and biodegradable. Here, we report the fabrication and device integration of low-cost and biocompatible/biodegradable colloidal Cu nanocrystal (NC) films through room temperature, solution-based deposition, and sintering, achieved via chemical exchange of NC surface ligands. Treatment of organic-ligand capped Cu NC films with solutions of shorter, environmentally benign, and noncorrosive inorganic reagents, namely, SCN- and Cl-, effectively removes the organic ligands, drives NC grain growth, and limits film oxidation. We investigate the mechanism of this chemically driven sintering by systemically varying the Cu NC size, ligand reagent, and ligand treatment time and follow the evolution of their structure and electrical and optical properties. Cl--treated, 4.5 nm diameter Cu NC films yield the lowest DC resistivity, only 3.2 times that of bulk Cu, and metal-like dielectric functions at optical frequencies. We exploit the high conductivity of these chemically sintered Cu NC films and, in combination with photo- and nanoimprint-lithography, pattern multiscale structures to achieve high-Q radio frequency (RF) capacitive sensors and near-infrared (NIR) resonant optical metasurfaces.

Biodegradable polylactic acid emulsion ink based on carbon nanotubes and silver for printed pressure sensors

Investigating biodegradable and biocompatible materials for electronic applications can lead to tangible outcomes such as developing green-electronic devices and reducing the amount of e-waste. The proposed emulsion-based conducting ink formulation takes into consideration circular economy and green principles throughout the entire process, from the selection of materials to the production process. The ink is formulated using the biopolymer polylactic acid dissolved in a sustainable solvent mixed with water, along with conductive carbon nanotubes (CNTs) and silver flakes as fillers. Hybrid conductive fillers can lower the percolation threshold of the ink and the production costs, while maintaining excellent electrical properties. The coating formed after the deposition of the ink, undergoes isothermal treatment at different temperatures and durations to improve its adhesion and electrical properties. The coating's performance was evaluated by creating an eight-finger interdigitated sensor using a Voltera PCB printer. The sensor demonstrates exceptional performance when exposed to various loading and unloading pressures within the 0.2-500.0 kPa range. The results show a consistent correlation between the change in electrical resistance and the stress caused by the applied load. The ink is biodegradable in marine environments, which helps avoiding its accumulation in the ecosystem over time.

Systematic Investigation of Novel, Controlled Low-Temperature Sintering Processes for Inkjet Printed Silver Nanoparticle Ink

Functional inks enable manufacturing of flexible electronic devices by means of printing technology. Silver nanoparticle (Ag NP) ink is widely used for printing conductive components. A sintering process is required to obtain sufficient conductivity. Thermal sintering is the most commonly used method, but the heat must be carefully applied to avoid damaging low-temperature substrates such as polymer films. In this work, two alternative sintering methods, damp heat sintering and water sintering are systematically investigated for inkjet-printed Ag tracks on polymer substrates. Both methods allow sintering polyvinyl pyrrolidone (PVP) capped Ag NPs at 85°C. In this way, the resistance is significantly reduced to only 1.7 times that of the samples on polyimide sintered in an oven at 250°C. The microstructure of sintered Ag NPs is analyzed. Taking the states of the capping layer under different conditions into account, the explanation of the sintering mechanism of Ag NPs at low temperatures is presented. Overall, both damp heat sintering and water sintering are viable options for achieving high conductivity of printed Ag tracks. They can broaden the range of substrates available for flexible electronic device fabrication while mitigating substrate damage risks. The choice between them depends on the specific application and the substrate used.

Determination and gas-phase stability evaluation of metal complexes by nanoelectrospray ionization and collision-induced dissociation tandem mass spectrometry

RATIONALE

The structures of metal complexes determine their stable functioning in product performance. Electrospray ionization mass spectrometry (ESI-MS) is used in studying metal complexes despite exhibiting limitations in analyzing labile complexes. Therefore, identifying a method for detecting unstable complexes and evaluating their stabilities is necessary, providing a theoretical basis for material selection and performance evaluation.

METHODS

The standard complexes Zn(BTZ)2 , Fe(acac)3 , and Sn(Oct)2 were analyzed using nanoESI quadrupole orbitrap MS (nanoESI-MS) and compared with ESI-MS for two temperature modes. The three complexes and alkylamine-Ag+ complexes were analyzed using nanoESI and collision-induced dissociation MS/MS (CID-MS/MS). Breakdown plots of the survival yield against collision energies expressed in terms of the center-of-mass were constructed according to the obtained product ion spectra. Quantum chemical calculations based on density functional theory were performed to calculate the binding energies between the alkylamines and Ag+ .

RESULTS

The three standard complexes were detected in the native structures using nanoESI-MS, confirming the advantage of nanoESI over ESI for detecting unstable complexes. The gas-phase stabilities of the amine-Ag+ complexes, estimated using the breakdown plots constructed by plotting the data obtained via nanoESI and CID-MS/MS, were consistent with the established theories, previous studies, and binding energies calculated using computational methods.

CONCLUSIONS

NanoESI-MS is suitable for detecting labile complexes and enables the structural analyses of unknown complex additives. A novel approach based on nanoESI and CID-MS/MS was developed to determine the gas-phase stabilities of complexes, enabling their quantification and comparison and providing a technical basis for product improvement, which is essential in developing industrial materials.

Large-Area Inkjet-Printed Flexible Hybrid Electrodes with Photonic Sintered Silver Grids/High Conductive Polymer

The field of printed organic electronics has not only made flexible devices accessible but also allows the production process toward a high throughput industrial scale. The current research involves the inkjet-printing of an indium tin oxide-free large-area flexible hybrid electrode compose of a high conductivity organic layer (PEDOT: PSS) as a main electrode and inorganic silver nanoparticles-based grid/film for the auxiliary electrode. The current bottleneck in the roll-to-roll production of printed electronics is the time required for the conductive inks to dry and sinter. Flash sintering is used to dry nano-silver conductive ink to 77.6 m Ω □-1 sheet resistance in <20 ms, the quickest annealing procedure, without damaging flexible substrates. Flexible organic light-emitting diodes (OLEDs) are created with a large active area (500 mm2 ) to demonstrate the efficacy of the flexible hybrid electrodes and the excellent bending stability (4 mm bending radius) of OLEDs. Maximum current efficiency of 19.58 cd A-1 and a maximum luminescence of 8708 cd m-2 at a low turn-on voltage of 3.1 V for the small-area (16 mm2 ) OLEDs are achieved. This method is promising for reducing indium consumption and paving the way for creating new high throughout hybrid electrodes for large-area flexible printed electronics.

Polyaniline/poly (2-acrylamido-2-methyl-1-propanesulfonic acid) modified cellulose as promising material for sensors design

A material based on cellulose coated with polyaniline/poly (2-acrylamido-2-methyl-1-propanesulfonic acid) (Cell/PANI-PAMPSA) was synthesized in a simple way starting from cellulose fibres, aniline and using PAMPSA as dopant. The morphology, mechanical properties, thermal stability, and electrical conductivity were investigated by means of several complementary techniques. The obtained results highlight the excellent features of the Cell/PANI-PAMPSA composite with respect to the Cell/PANI one. Based on the promising performance of this material, novel device functions and wearable applications have been tested. We focused on its possible single use as: i) humidity sensors and ii) disposable biomedical sensors to provide immediate diagnostic services as close to the patient as possible for heart rate or respiration activity monitoring. To our knowledge, this is the first time that Cell/PANI-PAMPSA system has been used for such applications.

Transparent Electronics for Wearable Electronics Application

Recent advancements in wearable electronics offer seamless integration with the human body for extracting various biophysical and biochemical information for real-time health monitoring, clinical diagnostics, and augmented reality. Enormous efforts have been dedicated to imparting stretchability/flexibility and softness to electronic devices through materials science and structural modifications that enable stable and comfortable integration of these devices with the curvilinear and soft human body. However, the optical properties of these devices are still in the early stages of consideration. By incorporating transparency, visual information from interfacing biological systems can be preserved and utilized for comprehensive clinical diagnosis with image analysis techniques. Additionally, transparency provides optical imperceptibility, alleviating reluctance to wear the device on exposed skin. This review discusses the recent advancement of transparent wearable electronics in a comprehensive way that includes materials, processing, devices, and applications. Materials for transparent wearable electronics are discussed regarding their characteristics, synthesis, and engineering strategies for property enhancements. We also examine bridging techniques for stable integration with the soft human body. Building blocks for wearable electronic systems, including sensors, energy devices, actuators, and displays, are discussed with their mechanisms and performances. Lastly, we summarize the potential applications and conclude with the remaining challenges and prospects.

Facile Preparation of Monodisperse Cu@Ag Core-Shell Nanoparticles for Conductive Ink in Printing Electronics

Copper-based nanoinks are emerging as promising low-cost alternatives to widely used silver nanoinks in electronic printing. However, the spontaneous oxidation of copper under ambient conditions poses significant challenges to its broader application. To address this issue, this paper presents an economical, large-scale, and environmentally friendly method for fabricating Cu@Ag nanoparticles (Cu@Ag NPs). The as-prepared nanoparticles exhibit a narrow size distribution of approximately 100 nm and can withstand ambient exposure for at least 60 days without significant oxidation. The Cu@Ag-based ink, with a 60 wt% loading, was screen-printed onto a flexible polyimide substrate and subsequently heat-treated at 290 °C for 15 minutes under a nitrogen atmosphere. The sintered pattern displayed a low electrical resistivity of 25.5 μΩ·cm (approximately 15 times the resistivity of bulk copper) along with excellent reliability and mechanical fatigue strength. The innovative Cu@Ag NPs fabrication method holds considerable potential for advancing large-scale applications of copper-based inks in flexible electronics.

Screen-Printed Textile-Based Electrochemical Biosensor for Noninvasive Monitoring of Glucose in Sweat

Wearable sweat biosensors for noninvasive monitoring of health parameters have attracted significant attention. Having these biosensors embedded in textile substrates can provide a convenient experience due to their soft and flexible nature that conforms to the skin, creating good contact for long-term use. These biosensors can be easily integrated with everyday clothing by using textile fabrication processes to enhance affordable and scalable manufacturing. Herein, a flexible electrochemical glucose sensor that can be screen-printed onto a textile substrate has been demonstrated. The screen-printed textile-based glucose biosensor achieved a linear response in the range of 20-1000 µM of glucose concentration and high sensitivity (18.41 µA mM^-1 cm^-2, R² = 0.996). In addition, the biosensors show high selectivity toward glucose among other interfering analytes and excellent stability over 30 days of storage. The developed textile-based biosensor can serve as a platform for monitoring bio analytes in sweat, and it is expected to impact the next generation of wearable devices.

A hybrid multi-objective optimization of functional ink composition for aerosol jet 3D printing via mixture design and response surface methodology

The limited electrical performance of microelectronic devices caused by low inter-particle connectivity and inferior printing quality is still the greatest hurdle to overcome for Aerosol jet printing (AJP) technology. Despite the incorporation of carbon nanotubes (CNTs) and specified solvents into functional inks can improve inter-particle connectivity and ink printability respectively, it is still challenging to consider multiple conflicting properties in mixture design simultaneously. This research proposes a novel hybrid multi-objective optimization method to determine the optimal functional ink composition to achieve low electrical resistivity and high printed line quality. In the proposed approach, silver ink, CNTs ink and ethanol are blended according to mixture design, and two response surface models (ReSMs) are developed based on the Analysis of Variance. Then a desirability function method is employed to identify a 2D optimal operating material window to balance the conflicting responses. Following that, the conflicting objectives are optimized in a more robust manner in the 3D mixture design space through the integration of a non-dominated sorting genetic algorithm III (NSGA-III) with the developed ReSMs and the corresponding statistical uncertainty. Experiments are conducted to validate the effectiveness of the proposed approach, which extends the methodology of designing materials with multi-component and multi-property in AJP technology.

Amphiphilic Silver Nanoparticles for Inkjet-Printable Conductive Inks

The large-scale manufacturing of flexible electronics is nowadays based on inkjet printing technology using specially formulated conductive inks, but achieving adequate wetting of different surfaces remains a challenge. In this work, the development of a silver nanoparticle-based functional ink for printing on flexible paper and plastic substrates is demonstrated. Amphiphilic silver nanoparticles with narrow particle size distribution and good dispersibility were prepared via a two-step wet chemical synthesis procedure. First, silver nanoparticles capped with poly(acrylic acid) were prepared, followed by an amidation reaction with 3-morpholynopropylamine (MPA) to increase their lipophilicity. Density functional theory (DFT) calculations were performed to study the interactions between the particles and the dispersion medium in detail. The amphiphilic nanoparticles were dispersed in solvents of different polarity and their physicochemical and rheological properties were determined. A stable ink containing 10 wt% amphiphilic silver nanoparticles was formulated and inkjet-printed on different surfaces, followed by intense pulsed light (IPL) sintering. Low sheet resistances of 3.85 Ω sq^-1, 0.57 Ω sq^-1 and 19.7 Ω sq^-1 were obtained for the paper, coated poly(ethylene terephthalate) (PET) and uncoated polyimide (PI) flexible substrates, respectively. Application of the nanoparticle ink for printed electronics was demonstrated via a simple flexible LED circuit.

Preparation of Low Volatile Organic Compounds Silver Paste Containing Ternary Conductive Fillers and Optimization of Their Performances

Conductive silver paste is a key material in the fields of printed circuits and printed electronic devices. However, the preparation of conductive silver paste with low-cost and volatile organic compounds (VOCs) is still a challenge. In this work, conductive silver pastes with excellent comprehensive performances were developed by using water-borne polyurethane (WPU) as the bonding phase and using the ternary mixture of Ag microflakes (Ag MFs), Ag nanowires (Ag NWs), and Ag nanoparticles (Ag NPs) as the conductive phase. WPU endowed conductive silver pastes with the adhesion along with releasing a few VOCs during the curing. Results showed that a small amount of Ag NPs or Ag NWs dramatically enhanced the electrical conductivity of silver paste paint film filled only with Ag MFs. The electrical resistivity for optimal ternary mixture conductive silver paste was 0.2 × 10^-3 Ω∙cm, and the conductive phase was composed of 20.0 wt% Ag MFs, 7.5 wt% Ag NWs, and 2.5 wt% Ag NPs. Meanwhile, the adhesive strength and hardness of silver paste paint film were effectively improved by increasing the curing temperature. The optimal overall performance of the conductive silver pastes was achieved at the curing temperature of 160 °C. Therefore, this work can provide a new route for preparing conductive silver pastes with high performances.

Cost-Driven Design of Printed Wideband Antennas with Reduced Silver Ink Consumption for the Internet of Things

The Internet of Things (IoT) accelerates the need for compact, lightweight and low-cost antennas combining wideband operation with a high integration potential. Although screen printing is excellently suited for manufacturing conformal antennas on a flexible substrate, its application is typically limited due to the expensive nature of conductive inks. This paper investigates how the production cost of a flexible coplanar waveguide (CPW)-fed planar monopole antenna can be reduced by exploiting a mesh-based method for limiting ink consumption. Prototypes with mesh grids of different line widths and densities were screen-printed on a polyethylene terephthalate (PET) foil using silver-based nanoparticle ink. Smaller line widths decrease antenna gain and efficiency, while denser mesh grids better approximate unmeshed antenna behavior, albeit at the expense of greater ink consumption. A meshed prototype of 34.76×58.03mm with almost 80% ink reduction compared to an unmeshed counterpart is presented. It is capable of providing wideband coverage in the IMT/LTE-1/n1 (1.92-2.17 GHz), LTE-40/n40 (2.3-2.4 GHz), 2.45 GHz ISM (2.4-2.4835 GHz), IMT-E/LTE-7/n7 (2.5-2.69 GHz), and n78 5G (3.3-3.8 GHz) frequency bands. It exhibits a peak radiation efficiency above 90% and a metallized surface area of 2.46 cm² (yielding an ink-to-total-surface ratio of 12.2%).

High Strength Die-Attach Joint Formation by Pressureless Sintering of Organic Amine Modified Ag Nanoparticle Paste

Sintered silver (Ag) die-attach has attracted much attention in power systems with high power density and high operating temperature. In this paper, we proposed a novel surface modification method for Ag nanoparticles with organic amines as a coating agent for enhancing the pressureless sintering performance. This work systematically introduced the Ag nanoparticle modification process, Ag paste preparation, and sintering process and compared the changes in the sintering performance of Ag nanoparticles after modification with four different alkyl chain lengths of amines. The study showed that the sintered films of Ag nanoparticle pastes modified with n-octylamine (NOA) can achieve the lowest resistivity of the sintered film and the highest shear strength of the bonded joints. The resistivity of the sintered Ag film is affected by the grain size and microscopic morphology, and the strength of the bonded joints is also related to the sintering density and the amount of organic residues. The thermal behavior of the Ag particles coated with different amines is measured by thermal analysis. Finally, the mechanism of NOA-modified Ag nanoparticles to improve the sintering performance is proposed. This study can provide effective data and theoretical support for the further promotion and application of nano-Ag pressureless sintering.

Advances in constructing silver nanowire-based conductive pathways for flexible and stretchable electronics

With their soaring technological demand, flexible and stretchable electronics have attracted many researchers' attention for a variety of applications. The challenge which was identified a decade ago and still remains, however, is that the conventional electrodes based on indium tin oxide (ITO) are not suitable for ultra-flexible electronic devices. The main reason is that ITO is brittle and expensive, limiting device performance and application. Thus, it is crucial to develop new materials and processes to construct flexible and stretchable electrodes with superior quality for next-generation soft devices. Herein, various types of conductive nanomaterials as candidates for flexible and stretchable electrodes are briefly reviewed. Among them, silver nanowire (AgNW) is selected as the focus of this review, on account of its excellent conductivity, superior flexibility, high technological maturity, and significant presence in the research community. To fabricate a reliable AgNW-based conductive network for electrodes, different processing technologies are introduced, and the corresponding characteristics are compared and discussed. Furthermore, this review summarizes strategies and the latest progress in enhancing the conductive pathway. Finally, we showcase some exemplary applications and provide some perspectives about the remaining technical challenges for future research.

Low-Temperature Soldering of Surface Mount Devices on Screen-Printed Silver Tracks on Fabrics for Flexible Textile Hybrid Electronics

The combination of flexible-printed substrates and conventional electronics leads to flexible hybrid electronics. When fabrics are used as flexible substrates, two kinds of problems arise. The first type is related to the printing of the tracks of the corresponding circuit. The second one concerns the incorporation of conventional electronic devices, such as integrated circuits, on the textile substrate. Regarding the printing of tracks, this work studies the optimal design parameters of screen-printed silver tracks on textiles focused on printing an electronic circuit on a textile substrate. Several patterns of different widths and gaps between tracks were tested in order to find the best design parameters for some footprint configurations. With respect to the incorporation of devices on textile substrates, the paper analyzes the soldering of surface mount devices on fabric substrates. Due to the substrate's nature, low soldering temperatures must be used to avoid deformations or damage to the substrate caused by the higher temperatures used in conventional soldering. Several solder pastes used for low-temperature soldering are analyzed in terms of joint resistance and shear force application. The results obtained are satisfactory, demonstrating the viability of using flexible hybrid electronics with fabrics. As a practical result, a simple single-layer circuit was implemented to check the results of the research.

Decorating of Ag and CuO on ZnO Nanowires by Plasma Electrolyte Oxidation Method for Enhanced Photocatalytic Efficiency

In this work, photocatalytic performance is divulged in the ternary CuO-Ag-ZnO nanowire synthesized via a two-step approach. The decoration of Ag and CuO nanostructures onto the surface of ZnO nanowires was simply carried out by using the plasma electrolytic oxidation method in a short time. The structure, size, morphology, and optical properties of as-prepared samples were characterized by X-ray diffraction, field-emission scanning electron microscopy, and spectrophotometry measurements. The diameters of Ag nanoparticles and ZnO nanoflowers are in the range of 5–20 nm and 20–60 nm, respectively. Within the first 15 min, methyl orange was decolorized 96.3 and 82.8% in the CuO-Ag-ZnO and Ag-ZnO, respectively, and there is only about 46.7% of that decomposed in pure ZnO. The CuO-Ag-ZnO shows a higher rate constant k = 0.2007 min−1 and a lower half-life time t = 6.1 min compared to Ag-ZnO and bare ZnO nanowires. The photo-reusability of the ternary nanostructures was estimated to be much outweighed compared to ZnO nanowires. Interestingly, the synergic incorporation between noble metal–semiconductor or semiconductor–semiconductor in the interfaces of Ag-CuO, Ag-ZnO, and CuO-ZnO expands the visible light absorption range and eliminates the photogenerated electron–hole recombination, resulting in a superior visible-light-driven photocatalyst.

Optical transparent metasurface for dual-band Wi-Fi shielding

An optical transparent metasurface for dual-band Wi-Fi shielding is presented in this paper. The unit cell of the proposed metasurface is composed of a hexagonal ring and a three-petal oval flower which resonate at 2.4 and 5.5 GHz, respectively. The corresponding equivalent circuit is modelled to better understand the physical phenomena of electromagnetic shielding. Based on transmission line theory and curve fitting technique, a convenient and efficient method for extracting permittivity of substrate is presented. Simulation results show that the proposed metasurface is insensitive to the polarization of incoming wave under normal incidence and offers excellent angular stability. For verifying the design, two prototypes are fabricated using different manufacturing technologies, flexible printed circuit and ink-jet printing of silver nano-particles. The measured results are in good agreement with the simulated ones. The proposed metasurface has potential applications of electromagnetic wave suppression and information security in indoor environments.

Effect of silver nanoparticles on gene transcription of land snail Helix aspersa

Silver nanoparticles (Ag-NPs) are extremely useful in a diverse range of consumer goods. However, their impact on the environment is still under research, especially regarding the mechanisms involved in their effect. Aiming to provide some insight, the present work analyzes the transcriptional activity of six genes (Hsp83, Hsp17.2, Hsp19.8, SOD Cu-Zn, Mn-SOD, and BPI) in the terrestrial snail Helix aspersa in the presence of different concentrations of Ag-NPs. The animals were exposed for seven days to Lactuca sativa soaked for one hour in different concentrations of Ag-NPs (20, 50, 100 mg/L). The results revealed that the highest concentration tested of Ag-NPs (100 mg/L) led to a statistically significant induction of the Hsp83 and BPI expression in the digestive gland compared to the control group. However, a trend to upregulation with no statistical significance was observed for all the genes in the digestive gland and the foot, while in the hemolymph, the trend was to downregulation. Ag-NPs affected the stress response and immunity under the tested conditions, although the impact was weak. It is necessary to explore longer exposure times to confirm that the effect can be maintained and impact on health. Our results highlight the usefulness of the terrestrial snail Helix aspersa as a bioindicator organism for silver nanoparticle pollution biomonitoring and, in particular, the use of molecular biomarkers of pollutant effect as candidates to be included in a multi-biomarker strategy.

Silver Nanoparticles for Conductive Inks: From Synthesis and Ink Formulation to Their Use in Printing Technologies

Currently, silver nanoparticles have attracted large interest in the photonics, electrics, analytical, and antimicrobial/biocidal fields due to their excellent optical, electrical, biological, and antibacterial properties. The versatility in generating different sizes, shapes, and surface morphologies results in a wide range of applications of silver nanoparticles in various industrial and health-related areas. In industrial applications, silver nanoparticles are used to produce conductive inks, which allows the construction of electronic devices on low-cost and flexible substrates by using various printing techniques. In order to achieve successful printed patterns, the necessary formulation and synthesis need to be engineered to fulfil the printing technique requirements. Additional sintering processes are typically further required to remove the added polymers, which are used to produce the desired adherence, viscosity, and reliable performance. This contribution presents a review of the synthesis of silver nanoparticles via different methods (chemical, physical and biological methods) and the application of silver nanoparticles under the electrical field. Formulation of silver inks and formation of conductive patterns by using different printing techniques (inkjet printing, screen printing and aerosol jet printing) are presented. Post-printing treatments are also discussed. A summary concerning outlooks and perspectives is presented at the end of this review.

Stretchable anisotropic conductive film (S-ACF) for electrical interfacing in high-resolution stretchable circuits

In stretchable electronics, high-resolution stretchable interfacing at a mild temperature is considered as a great challenge and has not been achieved yet. This study presents a stretchable anisotropic conductive film (S-ACF) that can electrically connect high-resolution stretchable circuit lines to other electrodes whether they are rigid, flexible, or stretchable. The key concepts of this study are (i) high-resolution (~50 μm) but low-contact resistance (0.2 ohm in 0.25 mm²) interfacing by periodically embedding conductive microparticles in thermoplastic film, (ii) low-temperature interfacing through the formation of chemical bonds between the S-ACF and the substrates, (iii) economical interfacing by selectively patterning the S-ACF, and (iv) direct interfacing of chips by using the adhesion of the thermoplastic matrix. We integrate light-emitting diodes on the patterned S-ACF and demonstrate stable light operation at large biaxial areal stretching (ε_xy = 70%).

Highly Conductive, Flexible, and Oxidation-Resistant Cu-Ni Electrodes Produced from Hybrid Inks at Low Temperatures

Recently, Ni and Ni-Cu nanoparticle-based inks have gained considerable research interest because of their high corrosion resistance as conductors in electronic devices. However, reported inks based on Cu-Ni nanoparticles need to be sintered at high temperatures above 300 °C to obtain electrodes with high conductivity on the order of 10^-5 Ω·cm. This study proposes a new conductive Cu-Ni-based hybrid ink that could be sintered at only 150-180 °C for producing Cu-Ni electrodes with low electrical resistance, high oxidation resistance, and flexibility. The hybrid ink contains Cu flakes and a complex of nickel formate and 1-amino-2-propanol (NiF-AmIP complex). At 150-180 °C, the Cu flakes catalyze the self-reduction of the NiF-AmIP complex, and Cu-Ni electrodes with high conductivity (on the order of 10^-5 Ω·cm) are formed on flexible polymer substrates at temperatures exceeding 150 °C. Analysis indicates that metallic Ni was decorated on the Cu flakes (especially on the edge) to improve the electrode's conductivity, oxidation resistance, and flexibility by forming bridging interconnections between the Cu flakes. The Cu-Ni electrodes demonstrated high stability against oxidation up to approximately 400 °C in air, as well as at 80 °C and 80% RH after 7 days. In addition to the excellent oxidation stability, the Cu-Ni electrode showed high durability under mechanical bending stress. Such sintered Cu-Ni electrodes obtained from hybrid inks have great potentials in printed/flexible devices due to their oxidation resistance and cost-effectiveness.

A novel porous silica-zirconia coating for improving bond performance of dental zirconia

OBJECTIVES

To coat a zirconia surface with silica-zirconia using a dip-coating technique and evaluate its effect on resin-zirconia shear bond strength (SBS).

METHODS

A silica-zirconia suspension was prepared and used to coat a zirconia surface using a dip-coating technique. One hundred and eighty-nine zirconia disks were divided into three groups according to their different surface treatments (polishing, sandblasting, and silica-zirconia coating). Scanning electron microscopy (SEM), energy dispersive X-ray (EDX), and X-ray diffraction (XRD) were used to analyze the differently treated zirconia surfaces. Different primer treatments (Monobond N, Z-PRIME Plus, and no primer) were also applied to the zirconia surfaces. Subsequently, 180 composite resin cylinders (Filtek Z350) were cemented onto the zirconia disks with resin cement (RelyX Ultimate). The SBS was measured after water storage for 24 h or 6 months. The data were analyzed by two-way analysis of variance (ANOVA).

RESULTS

SEM and EDX showed that the silica-zirconia coating produced a porous layer with additional Si, and XRD showed that only tetragonal zirconia was on the silica-zirconia-coating surface. Compared with the control group, the resin-zirconia SBSs of the sandblasting group and silica-zirconia-coating group were significantly increased (P<0.05). The silica-zirconia coating followed by the application of Monobond N produced the highest SBS (P<0.05). Water aging significantly reduced the resin-zirconia SBS (P<0.05).

CONCLUSIONS

Dip-coating with silica-zirconia might be a feasible way to improve resin-zirconia bonding.

Inkjet Printing on a New Flexible Ceramic Substrate for Internet of Things (IoT) Applications

In this article, the optimization of printing properties on a new, flexible ceramic substrate is reported for sensing and antenna applications encompassing internet of things (IoT) devices. E-Strate^® is a commercially available, non-rigid, thin ceramic substrate for implementing in room temperature and high-temperature devices. In this substrate, the printing parameters like drop spacing, number of printed layers, sintering temperature, and sintering time were varied to ensure an electrically conductive and repeatable pattern. The test patterns were printed using silver nanoparticle ink and a Dimatix 2831 inkjet printer. Electrical conductivity, high-temperature tolerance, bending, and adhesion were investigated on the printed samples. The three-factor factorial design analysis showed that the number of printed layers, sintering temperature, sintering time, and their interactions were significant factors affecting electrical conductivity. The optimum printing parameters for the thin E-Strate^® substrate were found to be 20 μm drop spacing, three layers of printing, and 300 °C sintering temperature for 30 min. The high-temperature tolerance test indicated a stable pattern without any electrical degradation. Repetitive bending, adhesion test, and ASTM tape tests showed adequate mechanical stability of the pattern. These results will provide insight for investigators interested in fabricating new IoT devices.

Two-Step Approach for Conformal Chemical Vapor-Phase Deposition of Ultra-Thin Conductive Silver Films

Conductive ultra-thin silver films are commonly fabricated by physical vapor deposition methods such as evaporation or sputtering. The line-of-sight geometry of these techniques impedes the conformal growth on substrates with complex morphology. In order to overcome this issue, volume deposition technologies such as chemical vapor deposition or atomic layer deposition are usually preferred. However, the silver films fabricated using these methods are generally non-electrically conductive for thicknesses below 20-50 nm due to island formation. Here, we demonstrate a novel approach for producing ultra-thin conductive silver layers on complex substrates. Relying on chemical vapor-phase deposition and plasma post-treatment, this two-step technique allows the synthesis of highly conductive and uniform silver films with a critical thickness lower than 15 nm and a sheet resistance of 1.6 Ω/□ for a 40 nm-thin film, corresponding to a resistivity of 6.4 μΩ·cm. The high infrared reflectance further demonstrates the optical quality of the films, despite a still large root-mean-square roughness of 8.9 nm. We successfully demonstrate the highly conformal deposition in lateral structures with an aspect ratio of up to 100. This two-step deposition method could be extended to other metals and open new opportunities for depositing electrically conductive films in complex 3D structures.

Silver Nano/Microparticles: Modification and Applications 2.0

Currently, nano/microparticles are widely used in various fields [...].

Silver nanoparticle conductive inks: synthesis, characterization, and fabrication of inkjet-printed flexible electrodes

Flexible electronics can be developed with a low-cost and simple fabrication process while being environmentally friendly. Conductive silver inks have been the most applied material in flexible substrates. This study evaluated the performance of different conductive ink formulations using silver nanoparticles by studying the material properties, the inkjet printing process, and application based on electrical impedance spectroscopy using a buffer solution. Silver nanoparticles synthesis was carried out through chemical reduction of silver nitrate; then, seven conductive ink formulations were produced. Properties such as resistivity, viscosity, surface tension, adhesion, inkjet printability of the inks, and electrical impedance of the printed electrodes were investigated. Curing temperature directly influenced the electrical properties of the inks. The resistivity obtained varied from 3.3 × 10⁰ to 5.6 × 10^-06 Ω.cm. Viscosity ranged from 3.7 to 7.4 mPa.s, which is suitable for inkjet printing fabrication. By using a buffer solution as an analyte, the printed electrode pairs presented electrical impedance lower than 200 Ω for all the proposed designs, demonstrating the potential of the formulated inks for utilization in flexible electronic devices for biological sensing applications.