Metallic core-shell nanoparticles for conductive coatings and printing

Surface Plasmonic Core-Shell Nanostructures in Surface Enhanced Raman Scattering and Photocatalysis

Core-shell nanostructures are a typical material design. Usually, it consists of a core wrapped in a shell. It has attracted much attention due to its tunable structure and composition, high surface area, and high programmability. The properties and resonance frequency of their surface plasmons can be adjusted by regulating the shape, size, and composition of metal core-shell nanostructures. This interaction makes core-shell nanostructures an excellent platform for plasmon-enhanced optical effects. This Perspective explores the categories of core-shell nanostructures, their exchanges with excitons in two-dimensional materials, their spectrum-enhanced aspects, and prospects for future applications of core-shell nanostructures.

Printable devices for neurotechnology

Printable electronics for neurotechnology is a rapidly emerging field that leverages various printing techniques to fabricate electronic devices, offering advantages in rapid prototyping, scalability, and cost-effectiveness. These devices have promising applications in neurobiology, enabling the recording of neuronal signals and controlled drug delivery. This review provides an overview of printing techniques, materials used in neural device fabrication, and their applications. The printing techniques discussed include inkjet, screen printing, flexographic printing, 3D printing, and more. Each method has its unique advantages and challenges, ranging from precise printing and high resolution to material compatibility and scalability. Selecting the right materials for printable devices is crucial, considering factors like biocompatibility, flexibility, electrical properties, and durability. Conductive materials such as metallic nanoparticles and conducting polymers are commonly used in neurotechnology. Dielectric materials, like polyimide and polycaprolactone, play a vital role in device fabrication. Applications of printable devices in neurotechnology encompass various neuroprobes, electrocorticography arrays, and microelectrode arrays. These devices offer flexibility, biocompatibility, and scalability, making them cost-effective and suitable for preclinical research. However, several challenges need to be addressed, including biocompatibility, precision, electrical performance, long-term stability, and regulatory hurdles. This review highlights the potential of printable electronics in advancing our understanding of the brain and treating neurological disorders while emphasizing the importance of overcoming these challenges.

Silver Shell Thickness-Dependent Conductivity of Coatings Based on Ni@Ag Core@shell Nanoparticles

Introductions

Ink based on metallic nanoparticles has been widely used so far for the fabrication of electronic circuits and devices using printing technology. This study aimed at the analysis of the effect of the silver shell thickness of nickel@silver core@shell (Ni@Ag) nanoparticles (NPs) on the fabrication and conductive properties of deposited coatings.

Methods

The process of the synthesis of Ni@Ag NPs with various silver shell thicknesses was developed. The physicochemical properties (size, stability against aggregation process) of synthesized Ni@Ag nanoparticles were analyzed. The films based on ink containing Ni@Ag NPs with different silver shell thicknesses were fabricated and sintered in a temperature range of 120-300 °C and at times from 15 to 90 min. The dependence of their conductive properties on the applied temperature and time as well as silver shell thickness was evaluated.

Results

Ni NPs were coated with 10, 20, 30, 35, 45, and 55 nm silver shell thickness. The resistivity of coatings based on obtained NPs depends on the thickness of the Ag shell and the sintering temperature. After sintering at 300 °C, the highest decrease in its value (at an optimal sintering time of 60 min) from about 100 µΩ·cm to 9 µΩ·cm was observed when the thickness of the shell increased from 10 to 55 nm. At the lowest sintering temperature (120 °C) the highest conductivity (about 50% of that for bulk nickel) was obtained for films based on Ni@Ag NPs with 45 and 55 nm of the silver shell thickness.

Discussions

The analysis of the resistivity of the sintered films showed that higher conductivity was obtained for the coatings formed from Ni@Ag NPs with the thicker Ag shell; moreover, thicker shells allowed a lowering of sintering temperature due to higher conductivity and a lower melting point of silver in comparison to nickel NPs.

Ti3 C2 TX MXene Ink Direct Writing Flexible Sensors for Disposable Paper Toys

Flexible electronics have gained great attention in recent years owing to their promising applications in biomedicine, sustainable energy, human-machine interaction, and toys for children. Paper mainly produced from cellulose fibers is attractive substrate for flexible electronics because it is biodegradable, foldable, tailorable, and light-weight. Inspired by daily handwriting, the rapid prototyping of sensing devices with arbitrary patterns can be achieved by directly drawing conductive inks on flat or curved paper surfaces; this provides huge freedom for children to design and integrate "do-it-yourself (DIY)" electronic toys. Herein, viscous and additive-free ink made from Ti3 C2 TX MXene sediment is employed to prepare disposable paper electronics through a simple ball pen drawing. The as-drawn paper sensors possess hierarchical microstructures with interweaving nanosheets, nanoflakes, and nanoparticles, therefore exhibiting superior mechanosensing performances to those based on single/fewer-layer MXene nanosheets. As proof-of-concept applications, several popular children's games are implemented by the MXene-based paper sensors, including "You say, I guess," "Emotional expression," "Rock-Paper-Scissors," "Arm wrestling," "Throwing game," "Carrot squat," and "Grab the cup," as well as a DIY smart whisker for a cartoon mouse. Moreover, MXene-based paper sensors are safe and disposable, free from producing any e-waste and hazard to the environment.

Highly conductive copper films prepared by multilayer sintering of nanoparticles synthesized via arc discharge

The major challenges in producing highly electrically conductive copper films are the oxide content and the porosity of the sintered films. This study developed a multilayer sintering method to remove the copper oxides and reduce copper film porosity. We used a self-built arc discharge reactor to produce copper nanoparticles. Copper nanoparticles produced by arc discharge synthesis have many advantages, such as low cost and a high production rate. Conductive inks were prepared from copper nanoparticles to obtain thin copper films on glass substrates. As demonstrated by scanning electron microscopy analyses and electrical resistivity measurements, the copper film porosity and electrical resistivity cannot be significantly reduced by prolonged sintering time or increasing single film thickness. Instead, by applying the multilayer sintering method, where the coating and sintering process was repeated up to four times in this study, the porosity of copper films could be effectively reduced from 33.6% after one-layer sintering to 3.7% after four-layer sintering. Copper films with an electrical resistivity of 3.49 ± 0.35μΩ·cm (two times of the bulk copper) have been achieved after four-layer sintering, while one-layer sintered copper films were measured to possess resistivity of 11.17 ± 2.17μΩ·cm.

Polycaprolactone-MXene Nanofibrous Scaffolds for Tissue Engineering

New conductive materials for tissue engineering are needed for the development of regenerative strategies for nervous, muscular, and heart tissues. Polycaprolactone (PCL) is used to obtain biocompatible and biodegradable nanofiber scaffolds by electrospinning. MXenes, a large class of biocompatible 2D nanomaterials, can make polymer scaffolds conductive and hydrophilic. However, an understanding of how their physical properties affect potential biomedical applications is still lacking. We immobilized Ti3C2Tx MXene in several layers on the electrospun PCL membranes and used positron annihilation analysis combined with other techniques to elucidate the defect structure and porosity of nanofiber scaffolds. The polymer base was characterized by the presence of nanopores. The MXene surface layers had abundant vacancies at temperatures of 305-355 K, and a voltage resonance at 8 × 104 Hz with the relaxation time of 6.5 × 106 s was found in the 20-355 K temperature interval. The appearance of a long-lived component of the positron lifetime was observed, which was dependent on the annealing temperature. The study of conductivity of the composite scaffolds in a wide temperature range, including its inductive and capacity components, showed the possibility of the use of MXene-coated PCL membranes as conductive biomaterials. The electronic structure of MXene and the defects formed in its layers were correlated with the biological properties of the scaffolds in vitro and in bacterial adhesion tests. Double and triple MXene coatings formed an appropriate environment for cell attachment and proliferation with mild antibacterial effects. A combination of structural, chemical, electrical, and biological properties of the PCL-MXene composite demonstrated its advantage over the existing conductive scaffolds for tissue engineering.

Sedimentation path theory for mass-polydisperse colloidal systems

Both polydispersity and the presence of a gravitational field are inherent to essentially any colloidal experiment. While several theoretical works have focused on the effect of polydispersity on the bulk phase behavior of a colloidal system, little is known about the effect of a gravitational field on a polydisperse colloidal suspension. We extend here the sedimentation path theory to study sedimentation-diffusion-equilibrium of a mass-polydisperse colloidal system: the particles possess different buoyant masses but they are otherwise identical. The model helps to understand the interplay between gravity and polydispersity on sedimentation experiments. Since the theory can be applied to any parent distribution of buoyant masses, it can also be used to study the sedimentation of monodisperse colloidal systems. We find that mass-polydispersity has a strong influence in colloidal systems near density matching for which the bare density of the colloidal particles equals the solvent density. To illustrate the theory, we study crystallization in sedimentation-diffusion-equilibrium of a suspension of mass-polydisperse hard spheres.

Copper laser patterning on a flexible substrate using a cost-effective 3D printer

We studied the cost effective direct laser patterning of copper (Cu) on thin polyimide substrates (PI thickness: 12.5-50 µm) using a 405 nm laser module attached to an inexpensive 3D printer. The focal length of the laser was intentionally controlled to reduce defects on patterned Cu and surface damage of PI under predetermined process conditions. The appropriate focal length was examined at various focal distances. Focal distances of - 2.4 mm and 3 mm were found for the shorter focal length (SFL) and longer focal length (LFL), respectively, compared to the actual focal length. This resulted in clean Cu line patterns without line defects. Interestingly, the SFL case had a different Cu growth pattern to that of LFL, indicating that the small difference in the laser incident angle could affect Cu precursor sintering. Cu square patterns had a lower resistivity of 70 μΩ·cm for an LFL after three or four laser scans, while the SFL showed a resistivity below 48 μΩ·cm for a one-time laser scan. The residues of the Cu precursor on PI were easily removed with flowing water and normal surfactants. However, the resistivity of the patterns decreased after cleaning. Among the scan gaps, the Cu square pattern formed at a 70 μm scan gap had the lowest sheet resistance and the least change in resistance from around 4 to 4.4 Ω/ϒ after cleaning. This result implies that the adhesion of the patterned Cu could be improved if the coated Cu precursor was well sintered under the proper process conditions. For the application of this method to bioelectronics, including biosensors, LEDs were connected to the Cu patterns on PI attached to the arm skin and worked well, even when the substrate PI was bent during power connecting.

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.

Study of Phase Transformations and Hyperfine Interactions in Fe3O4 and Fe3O4@Au Nanoparticles

The paper presents the results of a study of iron oxide nanoparticles obtained by chemical coprecipitation, coated (Fe₃O₄@Au) and not coated (Fe₃O₄) with gold, which were subjected to thermal annealing. To characterize the nanoparticles under study, scanning and transmission electron microscopy, X-ray diffraction, and Mössbauer spectroscopy on ⁵⁷Fe nuclei were used, the combination of which made it possible to establish a sequence of phase transformations, changes in morphological and structural characteristics, as well as parameters of hyperfine interactions. During the studies, it was found that thermal annealing of nanoparticles leads to phase transformation processes in the following sequence: nonstoichiometric magnetite (Fe_3-γO₄) → maghemite (γ-Fe₂O₃) → hematite (α-Fe₂O₃), followed by structural ordering and coarsening of nanoparticles. It is shown that nanoparticles of nonstoichiometric magnetite with and without gold coating are in the superparamagnetic state with a slow relaxation rate. The magnetic anisotropy energy of nonstoichiometric magnetite is determined as a function of the annealing temperature. An estimate was made of the average size of the region of magnetic ordering of Fe atoms in nonstoichiometric magnetite, which is in good agreement with the data on the average sizes of nanoparticles determined by scanning electron microscopy.

Supramolecular assembly of pentamidine and polymeric cyclodextrin bimetallic core-shell nanoarchitectures

Advanced nanoscale antimicrobials, originated from the combination of noble metal nanoparticles (NPs) with conventional antimicrobial drugs, are considered the next generation of antimicrobial agents. Therefore, there is an increasing demand for rapid, eco-friendly, and relatively inexpensive synthetic approaches for the preparation of nontoxic metallic nanostructures endowed with unique physicochemical properties. Recently, we have proposed a straightforward synthetic strategy that exploits the properties of polymeric β-cyclodextrin (PolyCD) to act as both the reducing and stabilizing agent to produce monodispersed and stable gold-based NPs either as monometallic (nanoG) structures or core-shell bimetallic (nanoGS) architectures with an external silver layer. Here, we describe the preparation of a supramolecular assembly between nanoGS and pentamidine, an antileishmanial drug endowed with a wide range of therapeutic properties (i.e., antimicrobial, anti-inflammatory, and anticancer). The physicochemical characterization of the supramolecular assembly (nanoGSP) in terms of size and colloidal stability was investigated by complementary spectroscopic techniques, such as UV-vis, ζ-potential, and dynamic light scattering (DLS). Furthermore, the role of PolyCD during the reduction/stabilization of metal NPs was investigated for the first time by NMR spectroscopy.

Challenges and Opportunities for Printed Electrical Gas Sensors

Printed electrical gas sensors are a low-cost, lightweight, low-power, and potentially disposable alternative to gas sensors manufactured using conventional methods such as photolithography, etching, and chemical vapor deposition. The growing interest in Internet-of-Things, smart homes, wearable devices, and point-of-need sensors has been the main driver fueling the development of new classes of printed electrical gas sensors. In this Perspective, we provide an insight into the current research related to printed electrical gas sensors including materials, methods of fabrication, and applications in monitoring food quality, air quality, diagnosis of diseases, and detection of hazardous gases. We further describe the challenges and future opportunities for this emerging technology.

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.