Stable aqueous based Cu nanoparticle ink for printing well-defined highly conductive features on a plastic substrate

Fabrication of Nano Copper Highly Conductive and Flexible Printed Electronics by Direct Ink Writing

Nanoscale metals have emerged as crucial materials for conductive inks in printed electronics due to their unique physical and chemical properties. However, the synthesis of high-precision and highly conductive copper ink remains a challenge. Herein, a high-precision, highly conductive, and oxidation-resistant nanocopper ink was synthesized to fabricate highly conductive and flexible printed electronic devices. Copper nanoparticles with a particle size of only 8.5 nm, a controllable structure, and excellent oxidation resistance were synthesized by the alcohol phase reduction method. The conductive ink was formulated with ethylene glycol, ethanol, and isopropanolamine (IPA) as the solvent, exhibiting excellent printability and sintering reducibility. Fluid dynamics simulations were employed to investigate the influence of printing parameters on the circuit forming performance, enabling precise control over the printing process. The sintering behavior of copper nanoparticles with varying particle sizes was investigated by combining experiments with molecular dynamics (MD) simulations. Highly conductive and flexible circuits were fabricated using direct ink writing (DIW) under low-temperature sintering, exhibiting a low resistance level as low as 1.9 μΩ·cm. Moreover, the circuit demonstrated an excellent adhesion performance and bending flexibility. The developed copper ink demonstrates outstanding printing potential for applications in flexible electronics, advancing the field of flexible printing and wearable electronic devices.

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.

Copper inks for printed electronics: a review

Conductive inks have attracted tremendous attention owing to their adaptability and the convenient large-scale fabrication. As a new type of conductive ink, copper-based ink is considered to be one of the best candidate materials for the conductive layer in flexible printed electronics owing to its high conductivity and low price, and suitability for large-scale manufacturing processes. Recently, tremendous progress has been made in the preparation of cooper-based inks for electronic applications, but the antioxidation ability of copper-based nanomaterials within inks or films, that is, long-term reliability upon exposure to water and oxygen, still needs more exploration. In this review, we present a comprehensive overview of copper inks for printed electronics from ink preparation, printing methods and sintering, to antioxidation strategies and electronic applications. The review begins with an overview of the development of copper inks, followed by a demonstration of various preparation methods for copper inks. Then, the diverse printing techniques and post-annealing strategies used to fabricate conductive copper patterns are discussed. In addition, antioxidation strategies utilized to stabilize the mechanical and electrical properties of copper nanomaterials are summarized. Then the diverse applications of copper inks for electronic devices, such as transparent conductive electrodes, sensors, optoelectronic devices, and thin-film transistors, are discussed. Finally, the future development of copper-based inks and the challenges of their application in printed electronics are discussed.

Microgravity Removes Reaction Limits from Nonpolar Nanoparticle Agglomeration

Gravity can affect the agglomeration of nanoparticles by changing convection and sedimentation. The temperature-induced agglomeration of hexadecanethiol-capped gold nanoparticles in microgravity (µ g) is studied at the ZARM (Center of Applied Space Technology and Microgravity) drop tower and compared to their agglomeration on the ground (1 g). Nonpolar nanoparticles with a hydrodynamic diameter of 13 nm are dispersed in tetradecane, rapidly cooled from 70 to 10 °C to induce agglomeration, and observed by dynamic light scattering at a time resolution of 1 s. The mean hydrodynamic diameters of the agglomerates formed after 8 s in microgravity are 3 times (for low initial concentrations) to 5 times (at high initial concentrations) larger than on the ground. The observations are consistent with an agglomeration process that is closer to the reaction limit on thground and closer to the diffusion limit in microgravity.

Non-oxidized bare copper nanoparticles with surface excess electrons in air

Copper (Cu) nanoparticles (NPs) have received extensive interest owing to their advantageous properties compared with their bulk counterparts. Although the natural oxidation of Cu NPs can be alleviated by passivating the surfaces with additional moieties, obtaining non-oxidized bare Cu NPs in air remains challenging. Here we report that bare Cu NPs with surface excess electrons retain their non-oxidized state over several months in ambient air. Cu NPs grown on an electride support with excellent electron transfer ability are encapsulated by the surface-accumulated excess electrons, exhibiting an ultralow work function of ~3.2 eV. Atomic-scale structural and chemical analyses confirm the absence of Cu oxide moiety at the outermost surface of air-exposed bare Cu NPs. Theoretical energetics clarify that the surface-accumulated excess electrons suppress the oxygen adsorption and consequently prohibit the infiltration of oxygen into the Cu lattice, provoking the endothermic reaction for oxidation process. Our results will further stimulate the practical use of metal NPs in versatile applications.

Direct Laser Interference Ink Printing Using Copper Metal–Organic Decomposition Ink for Nanofabrication

In this study, we developed an effective and rapid process for nanoscale ink printing, direct laser interference ink printing (DLIIP), which involves the photothermal reaction of a copper-based metal–organic decomposition ink. A periodically lined copper pattern with a width of 500 nm was printed on a 240 μm-wide line at a fabrication speed of 17 mm/s under an ambient environment and without any pre- or post-processing steps. This pattern had a resistivity of 3.5 μΩ∙cm, and it was found to exhibit a low oxidation state that was twice as high as that of bulk copper. These results demonstrate the feasibility of DLIIP for nanoscale copper printing with fine electrical characteristics.

Metallic core-shell nanoparticles for conductive coatings and printing

The review is focused on bimetallic nanoparticles composed of a core formed by low-cost metal having high electrical conductivity, such as Cu and Ni, and a protective shell composed of stable to oxidation noble metal such as Ag or Au. We present the chemical and physical approaches for synthesis of such particles, as well as the combination of the two, the stability to oxidation of core-shell nanoparticles at various conditions, and the formulation of conductive compositions and their application in conductive coatings and printed electronics.

A flexible paper based electrochemical portable biosensor towards recognition of ractopamine as animal feed additive: Low cost diagnostic tool towards food analysis using aptasensor technology

Due to the costly and time-consuming traditional techniques, providing a low-cost, portability and flexibility diagnostic tool with the ability to monitor and detect various animal feed additive is highly demanded. Over the years, paper-based biosensors have emerged as point of care (POC) diagnostic, easy-to-use and miniaturized tools. However, they have been suffered from low sensitivity. Aptamer as appropriate bioreceptor can overcome the most common disadvantage of paper based sensor by increasing selectivity and sensitivity. In this study, a novel paper-based electrochemical aptasensor was successfully developed to detection of ractopamine (RAC). RAC concentration was evaluated using a designed three-electrode paper based biodevice system. Under the optimal experimental conditions, the engineered aptasensor provided good sensitivity and selectivity for the detection of RAC. Using proposed flexible sensor RAC was determined in the range of 0.001 µM to 100 mM which the lower limit of quantitation (LLOQ) was obtained as 0.01 µM. Finally, aptasensor was used to the monitoring of RAC in untreated human plasma specimens which LLOQ and linear range were 0.01 µM and 0.01 µM to 10 mM, respectively. We hope that the exploitation of aptamer in electrochemical paper based sensor will be able to broaden our understanding for developing the application of low-cost and portable biodevices for the sensitive and selective paper-based sensor to identify other chemical and biological compounds.

Stability of Cu-islands formed on Si substrate via 'dewetting' under subsequent thermal cycling

Very thin metallic films deposited on a substrate often dewet upon thermal exposure, forming discrete islands of micrometer and nanometer-sized metal particles. Herein, Cu islands on Si substrate, which were formed due to agglomeration (or 'dewetting') of Cu thin film at 600 °C, were exposed to thermal cycling, and the ensuing evolution in their morphology was monitored. Thermal cycling was performed between either -25 °C and 150 °C or 25 °C and 400 °C, using different heating and cooling rates. With faster heating-cooling rates, a change in the shape and size of the Cu islands was observed, whereas a slow heating-cooling rate did not induce noticeable effect on their morphology. Furthermore, the formation of new nano- and micro-sized particles, probably through the dewetting of the ultra-thin layer of Cu that was left intact during the initial agglomeration treatment, was observed during the thermal cycling performed at fast rates up to 400 °C. Finite element analysis, incorporating Anand's viscoplasticity model, revealed the existence of high strain energy density in the vicinity of the particle-Si interface when the thermal cycling is carried at a faster ramp rate, suggesting the pivotal role of thermal stresses, in addition to the maximum temperature, in controlling the morphology of the Cu particles and the dewetting of the residual ultra-thin layer of Cu on Si.

Development of dark-field dynamic light scattering microscopy and its application: Tracking dynamics of particles in condensed slurries spreading on planar/nonplanar substrates

HYPOTHESIS

While dynamics of particles in slurries is usually evaluated by dynamic light scattering measurements, this technique had only been applicable to particles in the bulk slurries. Because this limitation is mainly owing to strong reflection of light, the dynamics of particles in slurries spreading/drying on solid substrates is to be obtained by spatially separating the reflection light from scattering (signal) light. This may allow us to track the particles in practical samples such as cosmetics or inks spreading on solid surfaces.

EXPERIMENT

We developed novel "dark-field dynamic light scattering microscopy". The system was evaluated with test samples of polystyrene beads dispersed in several viscosities of bulk glycerol aqueous solutions. This setup was then applied to slurries spreading/drying on planar and nonplanar substrates.

FINDINGS

The results for planar surface indicate that origin of coffee-ring are the particles flowing into the edge of the droplet just before complete drying. On a skin-modelled nonplanar substrate, the slurry on bumps was found to maintain semi-dry condition longer than that at dents. This suggests that the dispersive medium was supplied to bumps from dents. This unique flow was explained as effective drying from the bumps increased surface tension at the bumps to pull up the liquid around.

Ultrasonic-accelerated metallurgical reaction of Sn/Ni composite solder: Principle, kinetics, microstructure, and joint properties

The high-melting-point joints by transient-liquid-phase are increasingly playing a crucial role in the die bonding for the high temperature electronic components. In this study, three kinds of Sn/Ni composite solder pastes composed of different sizes of Ni particles were synthesized to accelerate metallurgical reaction among Sn/Ni interfaces under the ultrasonic-assisted transient liquid phase (U-TLP) soldering. The temperature evolution, microstructure and mechanical property in joints composed by these composite solder pastes with or without ultrasonic energy were systemically investigated. The intermetallic joint consisted of high-melting-point sole Ni₃Sn₄ intermetallic compound with a little residual Ni was obtained under the conditions of no pressure and lower power (200 W) in a high-temperature duration of only 10 s, its shear strength was up to 45.3 MPa. Ultrasonic effects significantly accelerated the reaction among the interfaces of liquid Sn and solid Ni, which attributed to the temperature rise caused by acoustic cavitation because of large number of liquid/solid interfaces during U-TLP, resulting in accelerated solid/liquid interfacial diffusion and growth of intermetallic compounds. This intermetallic joint formed by U-TLP soldering has a promising potential for applications in high-power device packaging.

Oxide rupture-induced conductivity in liquid metal nanoparticles by laser and thermal sintering

Metallic inks with superior conductivity and printability are necessary for high-throughput manufacturing of printed electronics. In particular, gallium-based liquid metal inks have shown great potential in creating soft, flexible and stretchable electronics. Despite their metallic composition, as-printed liquid metal nanoparticle films are non-conductive due to the surrounding metal oxide shells which are primarily Ga2O3, a wide-bandgap semiconductor. Hence, these films require a sintering process to recover their conductivity. For conventional solid metallic nanoparticles, thermal and laser processing are two commonly used sintering methods, and the sintering mechanism is well understood. Nevertheless, laser sintering of liquid metal nanoparticles was only recently demonstrated, and to date, the effect of thermal sintering has rarely been investigated. Here, eutectic gallium-indium nanoparticle films are processed separately by laser or thermal sintering in an ambient environment. Laser and thermally sintered films are compared with respect to electrical conductivity, surface morphology and elemental composition, crystallinity and surface composition. Both methods impart thermal energy to the films and generate thermal stress in the particles, resulting in rupture of the gallium oxide shells and achieving electrical conductivity across the film. For laser sintering, extensive oxide rupture allows liquid metal cores to flow out and coalesce into conductive pathways. For thermal sintering, due to less thermal stress and more oxidation, the oxide shells only rupture locally and extensive phase segregation occurs, leading to non-liquid particle films at room temperature. Electrical conductivity is instead attributed to segregated metal layers and gallium oxide which becomes crystalline and conductive at high temperatures. This comprehensive comparison confirms the necessity of oxidation suppression and significant thermal stress via instantaneous laser irradiation to achieve conductive patterns in liquid form.

Fabrication of a sensitive electrochemical sensor based on electrospun magnetic nanofibers for morphine analysis in biological samples

A sensitive electrochemical sensor for detection of morphine (MPH) at the surface of electrode modified with electrospun magnetic nanofibers (MNFs) was prepared. The features of constructed sensor were evaluated by scanning electron microscopy (SEM), X ray diffraction (XRD) and electrochemical impedance spectroscopy (EIS). The modified sensor was used for MPH analysis using of cyclic voltammetry (CV) and differential pulse voltammetry (DPV) method. The calibration curve has been composed of a linear portion in the concentration range of 0.0033-55 μM and 55-245 μM and the detection limit was 1.9 nM. The reproducibility of the peak current with a reliable relative standard deviation (RSD) value was acquired. Based on the results, the fabricated sensor has good stability and reproducibility, as well as the sensitive and selective analysis of MPH in human serum samples as real samples had effectively been feasible. The results of the actual sample were measured by HPLC procedure, and the results were compared with the results of the electrochemical method and corroborated them.

Laser-Induced Selective Metallization on Polymer Substrates Using Organocopper for Portable Electronics

Our work proposed a facile strategy for selective fabrication of the precise metalized patterns onto polymer substrates through the laser direct structuring (LDS) technology using organocopper compounds. Copper oxalate (CuC₂O₄) and copper acetylacetonate [Cu(acac)₂] which can be used as laser sensitizers were first introduced into an acrylonitrile-butadiene-styrene (ABS) matrix for preparing LDS materials. After the activation with 1064 nm pulsed near-infrared laser, the Cu⁰ (metal copper) was generated from CuC₂O₄ and Cu(acac)₂ and then served as catalyst species for the electroless copper plating (ECP). A series of characterizations were conducted to investigate the morphology and analyze the surface chemistry of ABS/CuC₂O₄ and ABS/Cu(acac)₂ composites. Specially, the X-ray photoelectron spectroscopy analysis indicated that 58.3% Cu²⁺ in ABS/CuC₂O₄ was reduced to Cu⁰, while this value was 63.9% for ABS/Cu(acac)₂. After 30 min ECP, the conductivities of copper circuit on ABS/CuC₂O₄ and ABS/Cu(acac)₂ composites were 1.22 × 10⁷ and 1.58 × 10⁷ Ω^-1·m^-1, respectively. Moreover, the decorated patterns and near-field communication circuit were demonstrated by this LDS technology. We believe that this study paves the way for developing organocopper-based LDS materials, which have the potential for industrial applications.

Elevated-Temperature 3D Printing of Hybrid Solid-State Electrolyte for Li-Ion Batteries

While 3D printing of rechargeable batteries has received immense interest in advancing the next generation of 3D energy storage devices, challenges with the 3D printing of electrolytes still remain. Additional processing steps such as solvent evaporation were required for earlier studies of electrolyte fabrication, which hindered the simultaneous production of electrode and electrolyte in an all-3D-printed battery. Here, a novel method is demonstrated to fabricate hybrid solid-state electrolytes using an elevated-temperature direct ink writing technique without any additional processing steps. The hybrid solid-state electrolyte consists of solid poly(vinylidene fluoride-hexafluoropropylene) matrices and a Li⁺ -conducting ionic-liquid electrolyte. The ink is modified by adding nanosized ceramic fillers to achieve the desired rheological properties. The ionic conductivity of the inks is 0.78  × 10 ^-3 S cm^-1 . Interestingly, a continuous, thin, and dense layer is discovered to form between the porous electrolyte layer and the electrode, which effectively reduces the interfacial resistance of the solid-state battery. Compared to the traditional methods of solid-state battery assembly, the directly printed electrolyte helps to achieve higher capacities and a better rate performance. The direct fabrication of electrolyte from printable inks at an elevated temperature will shed new light on the design of all-3D-printed batteries for next-generation electronic devices.

Roll-to-Roll Gravure Printed Electrochemical Sensors for Wearable and Medical Devices

As recent developments in noninvasive biosensors spearhead the thrust toward personalized health and fitness monitoring, there is a need for high throughput, cost-effective fabrication of flexible sensing components. Toward this goal, we present roll-to-roll (R2R) gravure printed electrodes that are robust under a range of electrochemical sensing applications. We use inks and electrode morphologies designed for electrochemical and mechanical stability, achieving devices with uniform redox kinetics printed on 150 m flexible substrate rolls. We show that these electrodes can be functionalized into consistently high performing sensors for detecting ions, metabolites, heavy metals, and other small molecules in noninvasively accessed biofluids, including sensors for real-time, in situ perspiration monitoring during exercise. This development of robust and versatile R2R gravure printed electrodes represents a key translational step in enabling large-scale, low-cost fabrication of disposable wearable sensors for personalized health monitoring applications.

Filtration-induced production of conductive/robust Cu films on cellulose paper by low-temperature sintering in air

Cellulose paper is an attractive substrate for paper electronics because of its advantages of flexibility, biodegradability, easy incorporation into composites, low cost and eco-friendliness. However, the micrometre-sized pores of cellulose paper make robust/conductive films difficult to deposit onto its surface from metal-nanoparticle-based inks. We developed a Cu-based composite ink to deposit conductive Cu films onto cellulose paper via low-temperature sintering in air. The Cu-based inks consisted of a metallo-organic decomposition ink and formic-acid-treated Cu flakes. The composite ink was heated in air at 100°C for only 15 s to give a conductive Cu film (7 × 10^-5 Ω cm) on the cellulose paper. Filtration of the Cu-based composite ink accumulated Cu flakes on the paper, which enabled formation of a sintered Cu film with few defects. A strategy was developed to enhance the bending stability of the sintered Cu films on paper substrates using polyvinylpyrrolidone-modified Cu flakes and amine-modified paper. The resistance of the Cu films increased only 1.3-fold and 1.1-fold after 1000 bending cycles at bending radii of 5 mm and 15 mm, respectively. The results of this study provide an approach to increasing the bending stability of Cu films on cellulose paper.

Current status and future developments in preparation and application of nonspherical polymer particles

Nonspherical polymer particles (NPPs) are nano/micro-particulates of macromolecules that are anisotropic in shape, and can be designed anisotropic in chemistry. Due to shape and surface anisotropies, NPPs bear many unique structures and fascinating properties which are distinctly different from those of spherical polymer particles (SPPs). In recent years, the research on NPPs has surprisingly blossomed in recent years, and many practical materials based on NPPs with potential applications in photonic device, material science and biomedical engineering have been generated. In this review, we give a systematic, balanced and comprehensive summary of the main aspects of NPPs related to their preparation and application, and propose perspectives for the future developments of NPPs.

Highly durable Cu-based electrodes from a printable nanoparticle mixture ink: flash-light-sintered, kinetically-controlled microstructure

Recently, printable nanomaterials have drawn tremendous attention for low-cost, large-area electronics applications. In particular, metallic nanoparticles that can facilitate the formation of highly functioning electrodes are indispensable constituent nanomaterials. In this paper, we propose printable mixed inks comprising multicomponent ingredients of Cu, Ni and Cu/Cu₁₀Sn₃ core/shell nanoparticles. It is clearly revealed that a characteristic morphology appropriate to highly conductive and durable Cu-based electrodes can be derived easily in a timescale of about 1 ms through an instantaneous flash-light-sintering process, resulting in a resistivity of 49 μΩ cm and normalized resistance variation of around 1 (after 28 days under a harsh environment of 85 °C temperature and 85% humidity). In addition, it is demonstrated that highly functioning electrodes can be formed on thermally vulnerable polyethylene terephthalate (PET) substrates by incorporating an ultrathin optical/thermal plasmonic barrier layer.

Transcriptional responses and mechanisms of copper nanoparticle toxicology on zebrafish embryos

Copper nanoparticles (CuNPs) are used widely due to their attractive antimicrobial properties. However, their biosafety and kinetics on vertebrate embryogenesis are still limited. In this study, CuNPs were revealed to induce eye hypoplasia and almost no digestive gut in zebrafish embryos in a dose-dependent manner. Then, transcriptional responses of zebrafish embryos to CuNPs were investigated, and it was revealed that the genes related to wound healing and stimulus responses were up-regulated, but the genes associated with phototransduction and metabolisms were down-regulated. Differentially expressed genes (DEGs) in CuNPs-exposed and Cu²⁺-exposed embryos were compared further. Increased VEGF signaling and expression of fli1 were observed in CuNPs rather than Cu²⁺ treated embryos, but increased reactive oxygen species (ROS) and the resulting enhanced hemoglobin were observed in both CuNPs and Cu²⁺ treated embryos. This study for the first time revealed that CuNPs and Cu²⁺ both down-regulated the genes related to phototransduction and metabolisms, but up-regulated the genes associated with hemoglobin. Additionally, compared with Cu²⁺, CuNPs might be more effective in elevating blood vessels in embryos. Our results suggest that the biological effects of CuNPs are organogenesis-specific during fish embryogenesis, and both particles and ions might mediate their biological effects on embryogenesis.

Enhanced Oxidation-Resistant Cu@Ni Core-Shell Nanoparticles for Printed Flexible Electrodes

In this work, the fabrication and application of highly conductive, robust, flexible, and oxidation-resistant Cu-Ni core-shell nanoparticle (NP)-based electrodes have been reported. Cu@Ni core-shell NPs with a tunable Ni shell thickness were synthesized by varying the Cu/Ni molar ratios in the precursor solution. Through continuous spray coating and flash photonic sintering without an inert atmosphere, large-area Cu@Ni NP-based conductors were fabricated on various polymer substrates. These NP-based electrodes demonstrate a low sheet resistance of 1.3 Ω sq^-1 under an optical energy dose of 1.5 J cm^-2. In addition, they exhibit highly stable sheet resistances (ΔR/R₀ < 1) even after 30 days of aging at 85 °C and 85% relative humidity. Further, a flexible heater fabricated from the Cu@Ni film is demonstrated, which shows uniform heat distribution and stable temperature compared to those of a pure Cu film.

The role of ligands in coinage-metal nanoparticles for electronics

Coinage-metal nanoparticles are key components of many printable electronic inks. They can be combined with polymers to form conductive composites and have been used as the basis of molecular electronic devices. This review summarizes the multidimensional role of surface ligands that cover their metal cores. Ligands not only passivate crystal facets and determine growth rates and shapes; they also affect size and colloidal stability. Particle shapes can be tuned via the ligand choice while ligand length, size, ω-functionalities, and chemical nature influence shelf-life and stability of nanoparticles in dispersions. When particles are deposited, ligands affect the electrical properties of the resulting film, the morphology of particle films, and the nature of the interfaces. The effects of the ligands on sintering, cross-linking, and self-assembly of particles in electronic materials are discussed.

Gallium-Based Liquid Metal Amalgams: Transitional-State Metallic Mixtures (TransM2ixes) with Enhanced and Tunable Electrical, Thermal, and Mechanical Properties

Metals are excellent choices for electrical- and thermal-current conducting. However, either the stiffness of solid metals or the fluidity of liquid metals could be troublesome when flexibility and formability are both desired. To address this problem, a reliable two-stage route to improve the functionalities of gallium-based liquid metals is proposed. A series of stable semiliquid/semisolid gallium-based liquid metal amalgams with well-controlled particle packing ratios, which we call TransM²ixes, are prepared and characterized. Through effectively packing the liquid metal with copper particles (which are found to turn into intermetallic compound, CuGa₂, after dispersing), remarkable enhancements in electrical conductivity (6 × 10⁶ S m^-1, ∼80% increase) and thermal conductivity (50 W m^-1 K^-1, ∼100% increase) are obtained, making the TransM²ixes stand out from current conductive soft materials. The TransM²ixes also exhibit appealing semiliquid/semisolid mechanical behaviors such as excellent adhesion, tunable formability, and self-healing ability. As a class of highly conductive yet editable metallic mixtures, the TransM²ixes demonstrate potential applications in fields like printed and/or flexible electronics and thermal interface materials, as well as other circumstances where the flexibility and conductivity of interfaces and connections are crucial.

3D polymer objects with electronic components interconnected via conformally printed electrodes

We report the fabrication of 3D polymer objects that contain electrical components interconnected by conductive silver/carbon nanotube inks printed conformally onto their surfaces and through vertical vias. Electrical components are placed within internal cavities and recessed surfaces of polymer objects produced by stereolithography. Conformally printed electrodes that interconnect each electrical component exhibit a conductivity of ∼2 × 10⁴ S cm^-1 upon annealing at temperatures below 100 °C. Multiple 3D objects were created to demonstrate this hybrid additive manufacturing approach, including those with an embedded circuit operated by an air-suspended switch and a 3D circuit board composed of microcontroller unit, resistor, battery, light-emitting diode and sensor.

Inkjet-printed gold nanorods using biocompatible polyelectrolyte layer-by-layer coating for patterned photothermal applications

Photothermal effect using biocompatible nanoparticles with near infrared wavelength light is a versatile tool in biomedical applications due to the temperature sensitivity of cells and good penetrability of the light through many biological systems. However, precise patterning of the nanoparticles on biochips to control the location and intensity of the photothermal effect requires suitable fabrication methods. In this report, we show that inkjet printing of aqueous nanoparticle solution on polyelectrolyte layer-by-layer coated substrates enables micron-scale patterning of gold nanorods, and thus application of photothermal effect with good control.

Inorganic nanomaterials for printed electronics: a review

Owing to their capability of bypassing conventional high-priced and inflexible silicon based electronics to manufacture a variety of devices on flexible substrates by using large-scale and high-volume printing techniques, printed electronics (PE) have attracted increasing attention in the field of manufacturing industry for electronic devices. This simple and cost-effective approach could enhance current methods of constructing a patterned surface for nanomaterials and offer opportunities for developing fully-printed functional devices, especially offering the possibility of ubiquitous low-cost and flexible devices. This review presents a summary of work to date on the inorganic nanomaterials involved in PE applications, focused on the utilization of inorganic nanomaterials-based inks in the successful preparation of printed conductive patterns, electrodes, sensors, thin film transistors (TFTs) and other micro-/nanoscale devices. The printing techniques, sintering methods and printability of functional inks with their associated challenges are discussed, and we look forward so you can glimpse the future of PE applications.

Synergetic Effect of Blended Alkylamines for Copper Complex Ink To Form Conductive Copper Films

Cu(II) complex ink consisting of copper formate (Cuf) and a primary alkylamine could yield highly conductive copper films at low heating temperatures without a reducing atmosphere. A synergetic effect of the blended alkylamines on the formation of conductive films was observed. It was found that blending two types of amines with different alkyl chain lengths as ligands could improve the conductivity of copper films, compared with using one of these amines alone. The decomposition mechanism of the Cuf-amine complex and the role of amines with different alkyl chain lengths were investigated. It was found that the decrease in the decomposition temperature and the formation of copper films were attributed to the activating effect and capping effect of the amine, and these two effects were dependent on the alkyl chain length. The relative intensity of the dual effects determined the decomposition rate of the complex and the nucleation and growth of particles. The use of blended amines with different alkyl chain lengths as ligands could balance the two effects and lead to appropriate nucleation and growth rates, so that densely packed copper films with low resistivity could be obtained at low heating temperature in a short time. The Cuf-butylamine-octylamine (Cuf-butyl-octyl) ink with 1:1 molar ratio of the amines showed the best performance. The understanding of the synergetic effect could provide guidance to the design of copper complex inks to control the morphology of the films.

Physical and chemical properties of Cu(i) compounds with O and/or H

The electronic structure and chemical bonding of Cu(i) compounds with O and/or H are investigated using ab initio calculations based on density functional theory. A hybrid functional PBE0 is employed, which accurately reproduces an experimental band gap of cuprite Cu₂O. Cuprous hydroxide CuOH (cuprice) is found to be an indirect band gap semiconductor. Depending on the bond network configuration of CuOH, its band gap is found to vary between 2.73 eV and 3.03 eV. The presence of hydrogen in CuOH has little effect on the character of Cu-O bonds, as compared to Cu₂O, but lowers the energy levels of the occupied states upon O-H bond formation. The bonding charge density and electron localization function calculations reveal that a closed-shell Cu-Cu interaction takes place in Cu₂O and CuOH between the neighbouring Cu cations belonging to different bond networks. Besides, three structures of cuprous hydride CuH are investigated. We find that the halite structure of CuH can be stabilized at high pressure (above 32 GPa) while wurtzite is the most stable structure of CuH at ambient pressure. The H-H interaction contributes to the dynamical stabilization of the halite structure. The wurtzite and sphalerite structures of CuH are predicted to be semiconducting with small band gaps, while the halite structure is calculated to be metallic.

Stabilization of the thermal decomposition process of self-reducible copper ion ink for direct printed conductive patterns

An alkylamine is added to stabilize the thermal decomposition process and to improve the surface morphology of printed patterns. The adhesion and mechanical stability of the copper thin films are also investigated.

Assembly and Electronic Applications of Colloidal Nanomaterials

Artificial solids and thin films assembled from colloidal nanomaterials give rise to versatile properties that can be exploited in a range of technologies. In particular, solution-based processes allow for the large-scale and low-cost production of nanoelectronics on rigid or mechanically flexible substrates. To achieve this goal, several processing steps require careful consideration, including nanomaterial synthesis or exfoliation, purification, separation, assembly, hybrid integration, and device testing. Using a ubiquitous electronic device - the field-effect transistor - as a platform, colloidal nanomaterials in three electronic material categories are reviewed systematically: semiconductors, conductors, and dielectrics. The resulting comparative analysis reveals promising opportunities and remaining challenges for colloidal nanomaterials in electronic applications, thereby providing a roadmap for future research and development.

Inkjet printed nanomaterial based flexible radio frequency identification (RFID) tag sensors for the internet of nano things

The Internet of Things (IoT) has limitless possibilities for applications in the entire spectrum of our daily lives, from healthcare to automobiles to public safety.

Antioxidation Properties and Surface Interactions of Polyvinylpyrrolidone-Capped Zerovalent Copper Nanoparticles Synthesized in Supercritical Water

Zerovalent copper nanoparticles (CuNPs) (diameter, 26.5 ± 9 nm) capped with polyvinylpyrrolidone (PVP) were synthesized in supercritical water at 400 °C and 30 MPa with a continuous flow reactor. The PVP-capped CuNPs were dispersed in distilled water, methanol, ethanol, 1-propanol, 2-propanol, butanol, and their mixed solvents to study their long-term stability. Temporal variation of UV-vis spectra and surface plasmon resonance were measured and showed that ethanol, the propanols, and butanol solvents provided varying degrees of oxidative protection for Cu(0). Fourier transform infrared spectroscopy showed that PVP adsorbed onto the surface of the CuNPs with a pyrrolidone ring of PVP even if the CuNPs were oxidized. Intrinsic viscosities of PVP were higher for solvents that provided antioxidation protection than those that give oxidized CuNPs. In solvents that provided Cu(0) with good oxidative protection (ethanol, the propanols, and butanol), PVP polymer chains formed large radii of gyration and coil-like conformations in the solvents so that they were arranged uniformly and orderly on the surface of the CuNPs and could provide protection of the Cu(0) surface against dissolved oxygen. In solvents that provided poor oxidative protection for Cu(0) (water, alcohol-water mixed solvents with 30% water), PVP polymer chains had globular-like conformations due to their relatively high hydrogen-bonding interactions and sparse adsorption onto the CuNP surface. Antioxidative properties of PVP-capped CuNPs in a solvent can be ascribed to the conformation of PVP polymer chains on the Cu(0) particle surface that originates from the interaction between polymer chains and its interaction with the solvent.

Photocatalytic decomposition behavior and reaction pathways of organic compounds using Cu nanoparticles synthesized via a green route

Green, facile and environmentally friendly biosynthetic methodology for the fabrication of Cu nanoparticles using an aqueous extract ofAnas platyrhynchosegg shells.

Sintering mechanism of the Cu–Ag core–shell nanoparticle paste at low temperature in ambient air

Cu–Ag core–shell nanoparticles owned good anti-oxidation ability, and as-fabricated joints using the Cu–Ag core–shell nanoparticles paste showed high shear strength.

Formation of Oxidation-Stable Copper Nanoparticles in Water

Oxidation-stable copper (Cu) nanoparticles have been successfully prepared by electroless deposition in water at 353 K. Cupric oxide (CuO) and hydrazine (N2H4) are employed as the Cu precursor and reducing agent, respectively. The Cu nanoparticles have uniform particle sizes with average values ranging from 37 to 43 nm. The addition of gelatin has played a vital in role in controlling the particle size, agglomeration, and oxidation of Cu nanoparticles. In the absence of gelatin, both metallic Cu and cuprous oxide (Cu2O) are present in the sample, indicating incomplete reduction of the CuO. Pure metallic Cu nanoparticles with excellent oxidation and dispersability in water can only be formed when gelatin is employed as protective agent. At higher amounts of gelatin, the particle size of the Cu nanoparticles is reduced.

Green synthesis of copper nanoparticles for the efficient removal (degradation) of dye from aqueous phase

The present work reports the utilization of a common household waste material (fish scales of Labeo rohita) for the synthesis of copper nanoparticles. The method so developed was found to be green, environment-friendly, and economic. The fish scale extracts were acting as a stabilizing and reducing agents. This method avoids the use of external reducing and stabilizing agents, templates, and solvents. The compositional abundance of gelatin may be envisaged for the effective reductive as well as stabilizing potency. The mechanisms for the formation of nanoparticles have also been presented. The synthesized copper nanoparticles formed were predominantly spherical in nature with an average size of nanoparticles in the range of 25-37 nm. The copper nanoparticles showed characteristic Bragg's reflection planes of fcc which was supported by both selected area electron diffraction and X-ray diffraction pattern and showed surface plasmon resonance at 580 nm. Moreover, the energy dispersive spectroscopy pattern also revealed the presence of only elemental copper in the copper nanoparticles. The prepared nanoparticles were used for the remediation of a carcinogenic and noxious textile dye, Methylene blue, from aqueous solution. Approximately, 96 % degradation of Methylene blue dye was observed within 135 min using copper nanoparticles. The probable mechanism for the degradation of the dye has been presented, and the degraded intermediates have been identified using the liquid chromatography-mass spectroscopy technique. The high efficiency of nanoparticles as photocatalysts has opened a promising application for the removal of hazardous dye from industrial effluents contributing indirectly to environmental cleanup process.