Conductive nanomaterials for printed electronics

Screen-Printing of a Highly Conductive Graphene Ink for Flexible Printed Electronics

Conductive inks for the future printed electronics should have the following merits: high conductivity, flexibility, low cost, and compatibility with wide range of substrates. However, the state-of-the-art conductive inks based on metal nanoparticles are high in cost and poor in flexibility. Herein, we reported a highly conductive, low cost, and super flexible ink based on graphene nanoplatelets. The graphene ink has been screen-printed on plastic and paper substrates. Combined with postprinting treatments including thermal annealing and compression rolling, the printed graphene pattern shows a high conductivity of 8.81 × 10⁴ S m^-1 and good flexibility without significant conductivity loss after 1000 bending cycles. We further demonstrate that the printed highly conductive graphene patterns can act as current collectors for supercapacitors. The supercapacitor with the printed graphene pattern as the current collector and printed activated carbon as the active material shows a good rate capability of up to 200 mV s^-1. This work potentially provides a promising route toward the large-scale fabrication of low cost yet flexible printed electronic devices.

High-performance printable 2.4 GHz graphene-based antenna using water-transferring technology

Liquid-phase exfoliated graphene sheets are promising candidates for printing electronics. Here, a high-performance printed 2.4 GHz graphene-based antenna is reported. Graphene conductive ink prepared by using liquid-phase exfoliation process is printed onto a water-transferable paper by using blade printing technique, which is then patterned as dipole antenna and transferred onto a target substrate. The fabricated dipole antenna (43 × 3 mm), exhibiting typical radiation patterns of an ideal dipole antenna, achieves -10 dB bandwidth of 8.9% and a maximum gain of 0.7 dBi. The printed graphene-antennas satisfy the application requirements of the Internet of Things and suggest its feasibility of replacing conventional metallic antennas in those applications.

Temperature-Controlled Catalysis by Core-Shell-Satellite AuAg@pNIPAM@Ag Hybrid Microgels: A Highly Efficient Catalytic Thermoresponsive Nanoreactor

A novel wet-chemical protocol is reported for the synthesis of "temperature-programmable" catalytic colloids consisting of bimetallic core@shell AuAg nanoparticles encapsulated into poly(N-isopropylacrylamide) (pNIPAM) microgels with silver satellites (AgSTs) incorporated within the microgel structure. Spherical AuNPs of 50 nm in diameter are initially synthesized and used for growing a pNIPAM microgel shell with temperature stimulus response. A silver shell is subsequently grown on the Au core by diffusing Ag salt through the hydrophilic pNIPAM microgel (AuAg@pNIPAM microgel). The use of allylamine as a co-monomer during pNIPAM polymerization facilitates the coordination of Ag⁺ with the NH₂ nitrogen lone pair of electrons, which are reduced to Ag seeds (∼14 nm) using a strong reducing agent, obtaining thus AuAg@pNIPAM@Ag hybrid microgels. The two systems are tested as catalysts toward the reduction of 4-nitrophenol (4-Nip) to 4-aminophenol (4-Amp) by NaBH₄. Both exhibit extremely sensitive temperature-dependent reaction rate constants, with the highest K₁ value of the order of 0.6 L/m² s, which is one of the highest values ever reported. The presence of plasmonic entities is confirmed by UV-vis spectroscopy. Dynamic light scattering proves the temperature responsiveness in all cases. Transmission electron microscopy and energy-dispersive X-ray (EDX) elemental mapping highlight the monodispersity of the synthesized hybrid nanostructured microgels, as well as their size and metallic composition. The amount of gold and silver in both systems is obtained by thermogravimetric analysis and the EDX spectrum. The reduction reaction kinetics is monitored by UV-vis spectroscopy at different temperatures for both catalytic systems, with the AuAg@pNIPAM@Ag microgels showing superior catalytic performance at all temperatures because of the synergistic effect of the AuAg core and the AgSTs. The principal novelty of this study lies in the "hierarchical" design of the metal-polymer-metal core@shell@satellite nanostructured colloids exhibiting synergistic capabilities of the plasmonic NPs for, among others, temperature-controlled catalytic applications.

Water-Based Solution Processing and Wafer-Scale Integration of All-Graphene Humidity Sensors

One of the main advantages of 2D materials for various applications is that they can be prepared in form of water-based solutions. The high yield and cost-effectiveness of this method make them of great interest for printed electronics, composites, and bio- and healthcare technologies. However, once deposited on a substrate, etching away these solution-processed materials is a difficult task, yet crucial for pattern definition and thus device fabrication. In particular, the realization of micrometer-sized patterns requires mesh and paste optimization when screen-printed or solvent-engineered and surface functionalization when inkjet-printed, both usually involving additional postdeposition steps. These constraints are holding back the integration of these 2D materials in devices and applications. In this work, a method for the fabrication of micrometer-sized well-defined patterns in water-based 2D materials is presented, with an extensive characterization of the films and patterns obtained. The method is ultimately used to create humidity sensors with performance comparable to that of commercial ones. These sensor devices are fabricated onto a 4' silicon and polyethylene terephthalate (PET) wafers to create all-graphene humidity sensors that are flexible, transparent, and compatible with current complementary metal-oxide-semiconductor (CMOS) and roll-to-roll workflows.

Inkjet Printing of Functional Electronic Memory Cells: A Step Forward to Green Electronics

Nowadays, the environmental issues surrounding the production of electronics, from the perspectives of both the materials used and the manufacturing process, are of major concern. The usage, storage, disposal protocol and volume of waste material continue to increase the environmental footprint of our increasingly “throw away society”. Almost ironically, society is increasingly involved in pollution prevention, resource consumption issues and post-consumer waste management. Clearly, a dichotomy between environmentally aware usage and consumerism exists. The current technology used to manufacture functional materials and electronic devices requires high temperatures for material deposition processes, which results in the generation of harmful chemicals and radiation. With such issues in mind, it is imperative to explore new electronic functional materials and new manufacturing pathways. Here, we explore the potential of additive layer manufacturing, inkjet printing technology which provides an innovative manufacturing pathway for functional materials (metal nanoparticles and polymers), and explore a fully printed two terminal electronic memory cell. In this work, inkjetable materials (silver (Ag) and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS)) were first printed by a piezoelectric Epson Stylus P50 inkjet printer as stand-alone layers, and secondly as part of a metal (Ag)/active layer (PEDOT:PSS)/metal (Ag) crossbar architecture. The quality of the individual multi-layers of the printed Ag and PEDOT:PSS was first evaluated via optical microscopy and scanning electron microscopy (SEM). Furthermore, an electrical characterisation of the printed memory elements was performed using an HP4140B picoammeter.

Printable Thick Copper Conductors from Optically Modulated Multidimensional Particle Mixtures

Printing techniques that enable the formation of arbitrarily designed architectures have been implemented in various research fields owing to their characteristic advantages in processing over other techniques. In particular, low-cost, printable conductors are of paramount importance in the production of highly functioning printed electronics. Among various candidates, copper (Cu) particle-based printable fluid has been regarded as the most promising constituent material in conjunction with the use of the flash-light-sintering (FLS) process in air. In this study, we synthesized surface-oxidation-suppressed Cu nanoparticles, sub-micronparticles, and flakes to regulate the optical absorption characteristics in FLS-processed, Cu-based printed conductors. Our results revealed clearly that the critical issues in FLS-processed conductors, namely, undesirable crack formation and a limitation of thickness, are resolved by adjusting the optical behaviors of particulate layers by variation of the composition of multidimensional mixture particles. It is suggested that crack-free, 13.2 μm thick printed Cu conductors can be generated with a resistivity of 11.4 μΩ cm by printing and FLS processes in air. The proposed alternative approach is demonstrated with electrical circuits comprising electrodes and interconnections.

3D Bioprinting: from Benches to Translational Applications

Over the last decades, the fabrication of 3D tissues has become commonplace in tissue engineering and regenerative medicine. However, conventional 3D biofabrication techniques such as scaffolding, microengineering, and fiber and cell sheet engineering are limited in their capacity to fabricate complex tissue constructs with the required precision and controllability that is needed to replicate biologically relevant tissues. To this end, 3D bioprinting offers great versatility to fabricate biomimetic, volumetric tissues that are structurally and functionally relevant. It enables precise control of the composition, spatial distribution, and architecture of resulting constructs facilitating the recapitulation of the delicate shapes and structures of targeted organs and tissues. This Review systematically covers the history of bioprinting and the most recent advances in instrumentation and methods. It then focuses on the requirements for bioinks and cells to achieve optimal fabrication of biomimetic constructs. Next, emerging evolutions and future directions of bioprinting are discussed, such as freeform, high-resolution, multimaterial, and 4D bioprinting. Finally, the translational potential of bioprinting and bioprinted tissues of various categories are presented and the Review is concluded by exemplifying commercially available bioprinting platforms.

Application of metallic inks based on nickel-silver core-shell nanoparticles for fabrication of conductive films

Conductive inks based on nickel nanoparticles (NPs) have attracted much attention as a low-cost replacement for the currently used silver and gold inks, for fabrication of printed electronic circuits and devices. Nickel NPs as a component of conductive inks should be stable against oxidation process at all stages of preparation of conductive patterns: ink formulation and storage, printing, and post-printing treatment. In the present study, the oxidation resistance of the Ag layer and the conductive properties of the Ni core allowed the use of nickel-silver core-shell (Ni@Ag) NPs as the component of conductive ink. Thick films composed of Ni-Ag core-shell NPs were deposited on a glass substrate and then sintered at temperatures ranging from 250 °C-370 °C. The conductivity of Ni@Ag coatings after sintering at 350 °C reached 11% of that for a bulk nickel.

All Inkjet-Printed Graphene-Silver Composite Ink on Textiles for Highly Conductive Wearable Electronics Applications

Inkjet-printed wearable electronic textiles (e-textiles) are considered to be very promising due to excellent processing and environmental benefits offered by digital fabrication technique. Inkjet-printing of conductive metallic inks such as silver (Ag) nanoparticles (NPs) are well-established and that of graphene-based inks is of great interest due to multi-functional properties of graphene. However, poor ink stability at higher graphene concentration and the cost associated with the higher Ag loading in metal inks have limited their wider use. Moreover, graphene-based e-textiles reported so far are mainly based on graphene derivatives such as graphene oxide (GO) or reduced graphene oxide (rGO), which suffers from poor electrical conductivity. Here we report inkjet printing of highly conductive and cost-effective graphene-Ag composite ink for wearable e-textiles applications. The composite inks were formulated, characterised and inkjet-printed onto PEL paper first and then sintered at 150 °C for 1 hr. The sheet resistance of the printed patterns is found to be in the range of ~0.08-4.74 Ω/sq depending on the number of print layers and the graphene-Ag ratio in the formulation. The optimised composite ink was then successfully printed onto surface pre-treated (by inkjet printing) cotton fabrics in order to produce all-inkjet-printed highly conductive and cost-effective electronic textiles.

Hybrid Machine Learning Method to Determine the Optimal Operating Process Window in Aerosol Jet 3D Printing

Aerosol jet printing (AJP) is a three-dimensional (3D) noncontact and direct printing technology for fabricating customized microelectronic devices on flexible substrates. Despite the capability of fine feature deposition, the complicated relationship between the main process parameters will affect the printing quality significantly in a design space. In this paper, a novel hybrid machine learning method is proposed to determine the optimal operating process window for the AJP process in various design spaces. The proposed method consists of classic machine learning methods, including experimental sampling, data clustering, classification, and knowledge transfer. In the proposed method, a two-dimensional design space is fully explored by a Latin hypercube sampling experimental design at a certain print speed. Then, the influence of the sheath gas flow rate (SHGFR) and the carrier gas flow rate (CGFR) on the printed line quality is analyzed by a K-means clustering approach, and an optimal operating process window is determined by a support vector machine. To efficiently identify more operating process windows at different print speeds, a transfer learning approach is applied to exploit relatedness between different operating process windows. Hence, at a new print speed, the number of line samples for identifying a new operating process window is greatly reduced. Finally, to balance the complex relationship among SHGFR, CGFR, and print speed, a 3D operating process window is determined by an incremental classification approach. Different from experiment-based approaches adopted in 3D printing technologies for quality optimization, the proposed method is developed based on the theory of knowledge discovery and data mining. Therefore, the knowledge in different design spaces can be fully explored and transferred for printed line quality optimization. Moreover, the data-driven-based characteristics can help the proposed method develop a guideline for quality optimization in other 3D printing technologies.

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

Printed electronics on flexible substrates has attracted tremendous research interest research thanks its low cost, large area production capability and environmentally friendly advantages. Optimal characteristics of silver nanoparticles (Ag NPs) based inks are crucial for ink rheology, printing, post-print treatment, and performance of the printed electronics devices. In this review, the methods and mechanisms for obtaining Ag NPs based inks that are highly conductive under moderate sintering conditions are summarized. These characteristics are particularly important when printed on temperature sensitive substrates that cannot withstand sintering of high temperature. Strategies to tailor the protective agents capping on the surface of Ag NPs, in order to optimize the sizes and shapes of Ag NPs as well as to modify the substrate surface, are presented. Different (emerging) sintering technologies are also discussed, including photonic sintering, electrical sintering, plasma sintering, microwave sintering, etc. Finally, applications of the Ag NPs based ink in transparent conductive film (TCF), thin film transistor (TFT), biosensor, radio frequency identification (RFID) antenna, stretchable electronics and their perspectives on flexible and printed electronics are presented.

Enhanced Performance Stability of Iridium Oxide-Based pH Sensors Fabricated on Rough Inkjet-Printed Platinum

Today, electrochemical sensors are used for a broad range of applications. A fundamental challenge is still the achievement of long-term sensor stability by ensuring good adhesion between the deposited sensing layer and the substrate material, e.g., a metal electrode. Until now, the most applied strategy to overcome this problem is to increase the surface roughness of the metal layer by mechanical etching or by electroplating of additional material layers, which both imply an increase in manufacturing steps and thus the final cost of the overall device. Alternatively, to overcome these adhesion problems, we propose the direct printing of a novel platinum nanoparticle ink, which is compatible with low-cost additive digital inkjet and with flexible low-cost substrates. This water-based platinum ink has two unique features: it leads to highly rough surfaces, which promotes the adhesion of deposited sensing material, and it is a highly low-temperature curing ink, compatible with polymeric substrates that cannot withstand high temperatures. Based on this concept, we report about a long-term stable and highly sensitive solid-state pH sensor functionalized by anodic electrodeposited iridium oxide on a rough nanostructured platinum printed layer. The sensors showed an excellent reproducibility with a linear super-Nernstian response (71.3 ± 0.3 mV/pH unit) in a wide pH range (pH 2-11). Long-term stability tests for over 1 year of application demonstrate an excellent mechanical sensor layer stability, which is correlated to the distinct roughness of the printed platinum layer. This novel approach is useful to simplify the fabrication process and with that the sensor costs.

Electrically conductive polymer/rGO nanocomposite films at ambient temperature via miniemulsion polymerization using GO as surfactant

We have developed a facile and industrially scalable method to synthesize colloidally stable polymer nanoparticles decorated with graphene oxide (GO) sheets via miniemulsion polymerization, which in turn enables the preparation of electrically conductive films using a simple dropcasting method at ambient temperature. The resulting nanocomposite films exhibited high electrical conductivity with a wide range of potential applications as conductive coatings.

Applications of 3D printing in small animal magnetic resonance imaging

Three-dimensional (3D) printing has significantly impacted the quality, efficiency, and reproducibility of preclinical magnetic resonance imaging. It has vastly expanded the ability to produce MR-compatible parts that readily permit customization of animal handling, achieve consistent positioning of anatomy and RF coils promptly, and accelerate throughput. It permits the rapid and cost-effective creation of parts customized to a specific imaging study, animal species, animal weight, or even one unique animal, not routinely used in preclinical research. We illustrate the power of this technology by describing five preclinical studies and specific solutions enabled by different 3D printing processes and materials. We describe fixtures, assemblies, and devices that were created to ensure the safety of anesthetized lemurs during an MR examination of their brain or to facilitate localized, contrast-enhanced measurements of white blood cell concentration in a mouse model of pancreatitis. We illustrate expansive use of 3D printing to build a customized birdcage coil and components of a ventilator to enable imaging of pulmonary gas exchange in rats using hyperpolarizedXe 129 . Finally, we present applications of 3D printing to create high-quality, dual RF coils to accelerate brain connectivity mapping in mouse brain specimens and to increase the throughput of brain tumor examinations in a mouse model of pituitary adenoma.

Printed Diodes: Materials Processing, Fabrication, and Applications

Printing techniques for the fabrication of diodes have received increasing attention over the last decade due to their great potential as alternatives for high-throughput and cost-effective manufacturing approaches compatible with both flexible and rigid substrates. Here, the progress achieved and the challenges faced in the fabrication of printed diodes are discussed and highlighted, with a focus on the materials of significance (silicon, metal oxides, nanomaterials, and organics), the techniques utilized for ink deposition (gravure printing, screen printing, inkjet printing, aerosol jet printing, etc.), and the process through which the printed layers of diode are sintered after printing. Special attention is also given to the device applications within which the printed diodes have been successfully incorporated, particularly in the fields of rectification, light emission, energy harvesting, and displays. Considering the unmatched production scalability of printed diodes and their intrinsic suitability for flexible and wearable applications, significant improvement in performance and intensive research in development and applications of the printed diodes will continuously progress in the future.

Conductive nanomaterials for 2D and 3D printed flexible electronics

This review describes recent developments in the field of conductive nanomaterials and their application in 2D and 3D printed flexible electronics, with particular emphasis on inks based on metal nanoparticles and nanowires, carbon nanotubes, and graphene sheets. We present the basic properties of these nanomaterials, their stabilization in dispersions, formulation of conductive inks and formation of conductive patterns on flexible substrates (polymers, paper, textile) by using various printing technologies and post-printing processes. Applications of conductive nanomaterials for fabrication of various 2D and 3D electronic devices are also briefly discussed.

Interface Modified Flexible Printed Conductive Films via Ag2O Nanoparticle Decorated Ag Flake Inks

A new approach to stable, low resistance inexpensive printed flexible conductive inks is proposed. Silver inks have been extensively studied and commercialized for applications in printed electronics due to the inherent high conductivity and stability of silver, even in particulate-based percolation networks processed at temperatures compatible with low-cost polymer films such as poly(ethylene terephthalate) (PET). Recent interest in flexible and even stretchable circuits, however, has presented new challenges for particle-based inks as mechanical strains can result in the opening of critical particle-to-particle contacts. Here we report a facile, low-cost method for the single-step synthesis of stable, printable nanoscale Ag₂O decorated Ag flake inks which can be converted to highly conductive Ag films at 150 °C curing temperature without the use of limited shelf life organometallics or low metal loading nanoparticles to modify the interface between silver flakes. Analysis indicates that decoration of Ag flakes with Ag₂O nanoparticles (NPs) during ink synthesis improves the conductivity and flexibility of printed silver films by forming bridging interconnections between Ag flakes after low temperature reduction of the Ag₂O NPs. In this work, printed nanodecorated silver conductors with starting oxide to metal weight ratios of 5:95 exhibited lateral resistivities lower than 1.5 × 10^-5 Ω·cm, which was 35% less than films derived from undecorated Ag flake inks of the same total Ag loading and binder system. This resistivity difference increased to 45% after cyclic bend testing showing increased resilience to repeated flexing for the nanodecorated inks. Through detailed compositional and morphological characterizations, we demonstrate that such improved conductivity and flexibility are due to a more effective bridging afforded by the in situ synthesized Ag NPs on the surface of Ag flakes. These properties, combined with the simplified syntheses method of the nanoink, make the material a viable, advantageous alternative to the limited number of stretchable conductors currently available.

PVP-Mediated Galvanic Replacement Synthesis of Smart Elliptic Cu-Ag Nanoflakes for Electrically Conductive Pastes

Elliptic Cu-Ag nanoflakes were syntheszied via facile in situ galvanic replacement between prepared Cu particles and Ag ions. Alloy nanoflakes with high purity and uniformity present a size of 700 × 500 nm, with a thinness of 30 nm. Nontoxic and low-cost polyvinyl pyrrolidone was used as a dispersant and structure-directing agent, promoting the formation of the remarkable structure. Synthesized nanoflakes were utilized as a filler for conductive paste in an epoxy resin matrix. Conductive patterns on flexible substrates with a resistivity of 3.75 × 10^-5 Ω·cm could be achieved after curing at 150 °C for 2 h. Compared with traditional silver microflakes, smart alloy nanoflakes provide much improved conductive interconnection, whose advantage could be attributed to their nanoscale thicknesses. It is also noteworthy that the conductive patterns are able to tolerate multiple bendings at different angles, having good conductivity even after 200 repeated bendings. Therefore, alloy nanoflakes could be a promising candidate conductive filler for flexible printing electronics, electronic packaging, and other conductive applications.

Fully Printed Infrared Photodetectors from PbS Nanocrystals with Perovskite Ligands

Colloidal nanocrystals from PbS are successfully applied in highly sensitive infrared photodetectors with various device architectures. Here, we demonstrate all-printed devices with high detectivity (∼10¹² cm Hz^1/2/W) and a cut-off frequency of >3 kHz. The low material consumption (<0.3 mg per detector) and short processing time (14 s per detector) enabled by the automated printing promises extremely low device costs. To enable all-printed devices, an ink formulation was developed based on nanocrystals stabilized by perovskite-like methylammonium iodobismuthate ligands, which are dispersed in a ternary solvent. Fully inkjet printed devices based on this solvent were achieved with printed silver electrodes and a ZnO interlayer. Considerable improvements were obtained by the addition of small amounts of the polymer poly(vinylpyrrolidone) to the ink. The polymer improved the colloidal stability of the ink and its film-formation properties and thus enabled the scalable printing of single detectors and detector arrays. While photoconductors were shown here, the developed ink will certainly find application in a series of further electronic devices based on nanocrystals from a broad range of materials.

Printing Reinforcing Structures onto Microsieves That Are Floating on a Water Surface

This article describes the preparation of hierarchically structured microsieves via a suitable combination of float-casting and inkjet-printing: A mixture of hydrophobized silica particles of 600 nm ± 20 nm diameter, a suitable non-water-soluble nonvolatile acrylic monomer, a nonvolatile photoinitiator, and volatile organic solvents is applied to a water surface. This mixture spontaneously spreads on the water surface; the volatile solvents evaporate and leave behind a layer of the monomer/initiator mixture comprising a monolayer of particles, each particle protruding out of the monomer layer at the top and bottom surface. Photopolymerization of the monomer converts this mixed layer into a solid composite membrane floating on the water surface. Onto this membrane, while still floating on the water surface, a hierarchical reinforcing structure based on a photocurable ink is inkjet-printed and solidified. In contrast to the nonreinforced membrane, the reinforced membrane can easily be lifted off the water surface without suffering damage. Subsequently, the silica particles are removed, and thus, the reinforced composite membrane is converted into a reinforced microsieve of 350 nm ± 50 nm thickness bearing uniform through pores of 465 nm ± 50 nm diameter. This reinforced microsieve is mounted into a filtration unit and used to filter model dispersions: its permeance for water at low Reynolds numbers is in accordance with established theories on the permeance of microsieves and significantly above the permeance of conventional filtration media; it retains particles exceeding the pore size, while letting particles smaller than the pore size pass.

Pseudo-ordered distribution of Ir nanocrystals on h-BN

A 2D material consisting of a pseudo-ordered distribution of Ir nanocrystals supported on a h-BN/Rh(111) surface is presented here. The particular spatial distribution of the Ir nanoparticles is achieved thanks to the existence of a large variety of adsorption positions within the pores of the h-BN/Rh(111) nanomesh template with hexagonal symmetry. The resulting deviations of nanoparticle positions with respect to a perfect hexagonal lattice, which make this material of special interest in the field of optics, can be tuned by the temperature and the amount of Ir. Upon annealing, this material undergoes slight structural changes in the temperature range of 370-570 K and much more drastic ones, due to cluster coalescence, between 670 and 770 K. This relatively high onset of coalescence is encouraging for using this 2D material as a catalyst for reactions such as the oxidation of carbon monoxide or of nitrogen monoxide, which are especially relevant in the field of environmental science. Finally, metal nanostructures exhibiting regular geometries have been created from this material using a scanning tunneling microscope tip. Because of the insulating character of h-BN, these nanostructures could be very promising to use in the design of conductive nanotracks.

Fully Printed Zinc Oxide Electrolyte-Gated Transistors on Paper

Fully printed and flexible inorganic electrolyte gated transistors (EGTs) on paper with a channel layer based on an interconnected zinc oxide (ZnO) nanoparticle matrix are reported in this work. The required rheological properties and good layer formation after printing are obtained using an eco-friendly binder such as ethyl cellulose (EC) to disperse the ZnO nanoparticles. Fully printed devices on glass substrates using a composite solid polymer electrolyte as gate dielectric exhibit saturation mobility above 5 cm² V⁻¹ s⁻¹ after annealing at 350 °C. Proper optimization of the nanoparticle content in the ink allows for the formation of a ZnO channel layer at a maximum annealing temperature of 150 °C, compatible with paper substrates. These devices show low operation voltages, with a subthreshold slope of 0.21 V dec⁻¹, a turn on voltage of 1.90 V, a saturation mobility of 0.07 cm² V⁻¹ s⁻¹ and an I_on/I_off ratio of more than three orders of magnitude.

Ambient Aqueous-Phase Synthesis of Copper Nanoparticles and Nanopastes with Low-Temperature Sintering and Ultra-High Bonding Abilities

Copper nanoparticles (NPs) with an average particle diameter of 50–60 nm were successfully obtained by reducing an aqueous solution of a copper(II)-nitrilotriacetic acid complex with an aqueous hydrazine solution at room temperature under an air atmosphere. Copper NP-based nanopastes were printed onto a glass substrate using a metal screen mask and pressureless sintered under a nitrogen atmosphere at 200 °C for 30 min. The electrical resistivity of the resulting copper electrode was 16 μΩ · cm. For a metal-to-metal bonding test, copper nanopaste was printed on an oxygen-free copper plate, another oxygen-free copper plate was placed on top, and the bonding strength between the copper plates when pressureless sintered under a nitrogen atmosphere at 200 °C for 30 min was 39 MPa. TEM observations confirmed that highly crystalline metal bonding occurred between the copper NPs and the copper plate to introduce the ultrahigh strength. The developed copper NPs could provide promising advances as nanopastes for sustainable fabrication of copper electrodes and die attachment materials for the production of next-generation power semiconductors.

Shape-Tuned Junction Resistivity and Self-Damping Dynamics in Intense Pulsed Light Sintering of Silver Nanostructure Films

Concurrently reducing processing temperature, electrical resistance, and material cost with scalable fabrication capabilities is critical for conductive elements of flexible and planar electronics. Intense pulsed light sintering (IPL) of mixed dissimilar-shape conductive nanostructures may achieve this goal. However, this potential is hindered by knowledge gaps on how dissimilarity in nanostructure shape affects interparticle neck growth kinetics in general and the self-damping coupling between neck growth and optical absorption in IPL. We study these phenomena for IPL of mixed Ag nanowires (NWs, 40 nm diameter, 100-200 μm length) and nanospheres (NSs, 40 nm diameter), both experimentally and by linking molecular dynamics simulations with optical modeling. An optimal 50:50 mixing ratio lowers resistivity (5.59 μΩ·cm) and peak temperatures (250-150 °C) relative to pure NS films and reduces material costs relative to pure NW films with similar resistivity, in 2.5 s of IPL. The drop in peak temperatures in consecutive optical pulses reduces with greater NW content. Sintering-induced dislocation generation drives higher neck growth at NW-NS and NW-NW interfaces and anisotropic neck growth at NW-NS interfaces. This indicates that when NWs are introduced into NS films, along with lesser number of interfacial contact points, an inherent reduction in sintering-induced junction resistivity plays a major role in reducing film resistivity. The self-damping coupling and optical absorption, which drive temperature evolution in IPL, are tunable by nanostructure shape. The introduction of NWs into a NS ensemble reduces the dependence of optical absorption on neck growth. We discuss how these insights elucidate a set of physical phenomena that can guide the choice of dissimilar shaped nanostructures to concurrently reduce resistivity and temperatures in IPL and other sintering processes.

Contactless In Situ Electrical Characterization Method of Printed Electronic Devices with Terahertz Spectroscopy

Printed electronic devices are attracting significant interest due to their versatility and low cost; however, quality control during manufacturing is a significant challenge, preventing the widespread adoption of this promising technology. We show that terahertz (THz) radiation can be used for the in situ inspection of printed electronic devices, as confirmed through a comparison with conventional electrical conductivity methods. Our in situ method consists of printing a simple test pattern exhibiting a distinct signature in the THz range that enables the precise characterization of the static electrical conductivities of the printed ink. We demonstrate that contactless dual-wavelength THz spectroscopy analysis, which requires only a single THz measurement, is more precise and repeatable than the conventional four-point probe conductivity measurement method. Our results open the door to a simple strategy for performing contactless quality control in real time of printed electronic devices at any stage of its production line.

Electrophysiology Meets Printed Electronics: The Beginning of a Beautiful Friendship

Electroencephalography (EEG) and surface electromyography (sEMG) are notoriously cumbersome technologies. A typical setup may involve bulky electrodes, dangling wires, and a large amplifier unit. Adapting these technologies to numerous applications has been accordingly fairly limited. Thanks to the availability of printed electronics, it is now possible to effectively simplify these techniques. Elegant electrode arrays with unprecedented performances can be readily produced, eliminating the need to handle multiple electrodes and wires. Specifically, in this Perspective paper, we focus on the advantages of electrodes printed on soft films as manifested in signal transmission at the electrode-skin interface, electrode-skin stability, and user convenience during electrode placement while achieving prolonged use. Customizing electrode array designs and implementing blind source separation methods can also improve recording resolution, reduce variability between individuals and minimize signal cross-talk between nearby electrodes. Finally, we outline several important applications in the field of neuroscience and how each can benefit from the convergence of electrophysiology and printed electronics.

The optimization of methods of synthesis of nickel-silver core-shell nanoparticles for conductive materials

Nickel-silver core-shell (Ni@Ag) nanoparticles (NPs) were formed in a two-step process: (1) the formation of a dispersion of Ni NPs; and (2) the transmetalation (galvanic displacement) reaction, where the surface of the Ni NPs acted as the reducing agent of Ag ions. Ni NPs were synthesized by the 'wet' chemical method, i.e., by the reduction of metal ions by using NaBH₄ as the reducing agent. The influence of the concentration of polymeric stabilizer, reducing agent and Ag precursor on the properties of synthesized NPs was evaluated. In the optimal condition of synthesis, Ni@Ag NPs with about 50 and 210 nm-diameter Ni core coated with a thin (∼10-20 nm) Ag shell, were obtained. Finally, the stability of the synthesized spherical-shaped Ni@Ag NPs was tested and the results indicate long-term stability against aggregation and Ni oxidation. Thus, the resulting NPs are promising candidates for application in electronic devices, e.g., as components of conductive inks or pastes.

Printed electronics based on inorganic conductive nanomaterials and their applications in intelligent food packaging

The diverse demands of consumers for packaging functions and increasingly complex product circulation systems have spurred the development of intelligent food packaging (IFP).

Preparation of silver nanoparticles with hyperbranched polymers as a stabilizer for inkjet printing of flexible circuits

Carboxyl-terminated hyperbranched polymer-stabilized silver nanoparticles were synthesized in the aqueous phase and used to prepare a printable conductive ink.

A general strategy for printing colloidal nanomaterials into one-dimensional micro/nanolines

Though patterned one-dimensional (1D) micro/nanoline arrays are of great importance in the field of integrated circuits and optoelectronics, the fabrication of high-precision micro/nanolines with excellent optical and electrical performance remains a great challenge. Herein, a general strategy for printing 1D micro/nanolines is proposed by manipulating the self-assembly of functional nanoparticles as a multilayer or monolayer stack with a single-nanoparticle width. This method is universal for dispersible nanoparticles, and the silver nanoparticle was selected as a model nanoparticle due to its good conductivity, dispersibility and narrow-size distribution. The results indicate that the morphologies of printed micro/nanolines can be precisely regulated by the substrate wettability and the suspension concentration. Specifically, 1D nanoparticle-assembled architectures are printed as a monolayer stack on the substrate with a low contact angle (below 45°), while a multilayer stack is formed on the substrate with a high contact angle (above 50°) or a high concentration (more than 0.12%). The controllability of micro/nanoline morphologies can be interpreted through the influence of the three phase contact line slipping motion and the nanoparticle diffusion on diverse substrates at different concentrations. Alteration of the printing template structures enables the intervals of 1D micro/nanolines to span from 16 μm to 48 μm. These results provide an efficient methodology for fabricating micro/nano-circuits or optics and strengthening the understanding of the self-assembling process.

Sustainable production of highly conductive multilayer graphene ink for wireless connectivity and IoT applications

Printed electronics offer a breakthrough in the penetration of information technology into everyday life. The possibility of printing electronic circuits will further promote the spread of the Internet of Things applications. Inks based on graphene have a chance to dominate this technology, as they potentially can be low cost and applied directly on materials like textile and paper. Here we report the environmentally sustainable route of production of graphene ink suitable for screen-printing technology. The use of non-toxic solvent Dihydrolevoglucosenone (Cyrene) significantly speeds up and reduces the cost of the liquid phase exfoliation of graphite. Printing with our ink results in very high conductivity (7.13 × 10⁴ S m⁻¹) devices, which allows us to produce wireless connectivity antenna operational from MHz to tens of GHz, which can be used for wireless data communication and energy harvesting, which brings us very close to the ubiquitous use of printed graphene technology for such applications.

Printed conductive inks show promise for future electronic device applications. Here, the authors report synthesis of graphene inks with conductivity of 7.13 × 10^4 S/m by Cyrene assisted liquid phase exfoliation, and their applications in data communication and RF energy harvesting.

Bioinspired and bristled microparticles for ultrasensitive pressure and strain sensors

Biological sensory organelles are often structurally optimized for high sensitivity. Tactile hairs or bristles are ubiquitous mechanosensory organelles in insects. The bristle features a tapering spine that not only serves as a lever arm to promote signal transduction, but also a clever design to protect it from mechanical breaking. A hierarchical distribution over the body further improves the signal detection from all directions. We mimic these features by using synthetic zinc oxide microparticles, each having spherically-distributed, high-aspect-ratio, and high-density nanostructured spines resembling biological bristles. Sensors based on thin films assembled from these microparticles achieve static-pressure detection down to 0.015 Pa, sensitivity up to 121 kPa⁻¹, and a strain gauge factor >10⁴, showing supreme overall performance. Other properties including a robust cyclability >2000, fast response time ~7 ms, and low-temperature synthesis compatible to various integrations further indicate the potential of this sensor technology in applying to wearable technologies and human interfaces.

The potential of electromechanical sensors has been limited by low volumetric density in sensing sites. Here, the authors demonstrate ultrasensitive pressure and strain sensors using ZnO microparticles that have high-aspect ratio and high-density nanostructured spines mimicking bristles in insects.

Precursors for Atmospheric Plasma-Enhanced Sintering: Low-Temperature Inkjet Printing of Conductive Copper

Bidentate diamine and amino-alcohol ligands have been used to form solid, water-soluble, and air-stable monomeric copper complexes of the type [Cu(NH2CH2CH(R)Y)2(NO3)2] (1, R=H, Y=NH2; 2, R=H, Y=OH; 3, R=Me, Y=OH). The complexes were characterized by elemental analysis, mass spectrometry, infrared spectroscopy, thermal gravimetric analysis, and single-crystal X-ray diffraction. Irrespective of their decomposition temperature, precursors 1-3 yield highly conductive copper features [1.5×10-6 Ω m (±5×10-7 Ω m)] upon atmospheric-pressure plasma-enhanced sintering.