AgNP Ink Research Articles

Ultrasound-assisted facile and green preparation of Ag nanoparticle conductive ink for printing electronics

The development of low-cost, high-efficiency, and environment-friendly methods for the preparation of Ag nanoparticle (NP) conductive inks is key to promoting the application of such inks for printing flexible electronic components. This article presents an effective method for preparing a AgNP ink by reducing silver compounds in a polyol solution with ultrasonication. When the silver solution was ultrasonicated at 640 W, 21-nm AgNPs were readily produced within 5 min, and the particles grew considerably to 53 nm as the reaction was continued for 15 min. Thereafter, the NP size increased marginally with further increase in reaction time. When the reaction was conducted for a fixed duration of 15 min and the ultrasonic power was increased from 480 to 760 W, the AgNP size decreased from 63 to 48 nm. During ultrasonication, the bubble eruption in the solution generates large temperature and pressure gradients, inducing the rapid reduction of the Ag(I) to Ag(0). Printing experiments revealed that the synthesized AgNP ink has good inkjet printability. During the sintering of the printed film, the bridge connections between large particles increased and the interparticle voids decreased gradually, resulting in a decrease in film resistivity. A relatively low resistivity of 40×10−5 Ωcm was obtained when the flexible AgNP pattern was heated at 250 °C for 80 min. The facile synthesis process and the favorable conductive properties of the obtained ink render this preparation method promising for the low-cost production of flexible electronics.

Improved stability and film formability of oil-based silver nanoparticle suspensions by addition of polystyrene

In this study, we focused on how to develop an oil-based stable suspension of conductive silver ink and improve its film formability on the substrate. Silver nanoparticles (Ag-NPs) were first prepared in water with addition of oleic acid (OA) and butyl amine (BA) as co-stabilizing agents. The water medium was then replaced by an organic solvent to prepare the organic silver conductive ink. The synthesized Ag-NPs with an average particle size of about 13.3 nm were stabilized by steric hindrance of the attached OA− as proved by FTIR analysis and surface zeta potential. The Ag-NPs had higher stability in cyclohexane than in hexane, owing to the increased interaction between the long alkyl chain in OA− and cyclohexane. The stability was more than one year in cyclohexane with little change in particle size. Conductive films were obtained by drop-coating the organic Ag-NP inks on glass slide and sintering up to 250 °C. Moreover, addition of polystyrene at 1 wt % into the cyclohexane increased the wettability of conductive ink on the substrate and improved the film formability and integrity while preventing oxidation during sintering. A uniform and hydrophobic Ag-NP film was obtained with a sheet resistance of 0.64 Ω/Sq.

Synthesis of a silver nanoparticle ink for fabrication of reference electrodes

The silver nanoparticle (AgNP) ink synthesized was simple, well-dispersed, did not need sintering, had excellent conductivity and can be used as a conductive ink in several areas, particularly in the fabrication of reference electrodes. The AgNP ink was fabricated by synthesizing AgNP using the polyol method and then dispersing in methanol to fabricate the conductive ink. The synthesis was explained step-by-step, the proposed mechanism was discussed and photos of the entire process were shown. The materials (AgNO3 and AgNP) were characterized by UV–Vis, SEM and XRD. The UV–Vis exhibit a strong broad peak at 417 nm due the surface plasmon resonance (SPR) absorption band of AgNP. The SEM images showed spherical nanoparticles, non-aggregates and with an average diameter of 50 - 140 nm. The XRD of AgNP presented four main characteristic peaks for silver corresponding to (111), (200), (220) and (311) planes, confirming the cubic (FCC) silver. The AgNP ink has an excellent conductivity, with an average ohmic resistance of 1.53 Ω. Finally, the AgNP ink was tested in the fabrication of reference electrodes and the analytical response was higher than the conventional Ag/AgCl reference electrode.

Ag nanoparticle ink coupled with graphene oxide cellulose paper: a flexible and tunable SERS sensing platform.

Surface-enhanced Raman scattering (SERS) is highly promising for ultra-sensitive detection in a series of applications. Although extensive advances have been achieved in SERS technologies, the preparation of highly efficient SERS substrates still suffers from several limitations, including complex preparation procedures, high cost, and instability for long time storage. To address these problems, we report a novel, to the best of our knowledge, SERS platform that combines graphene oxide (GO) and cellulose composite paper with colloidal silver nanoparticle (Ag NP) ink. As an efficient substrate, the GO and cellulose composite paper that features hierarchical micro-nanostructures and improved interaction with target molecules can be fabricated on a large scale, and the Ag NP ink can be well stored, avoiding being oxidized in ambient conditions. In this way, our SERS platform not only reduces the cost, but also improved the stability. The sensitivity, reproducibility, and tunable SERS detection performance were evaluated using rhodamine 6G as probing molecules. To demonstrate the capability of our SERS platform in practical analysis, the SERS spectra of two monosodium salt solutions of different concentrations have been collected. The SERS platform has revealed great potential for practical application of SERS technologies.

Ultrasensitive Monitoring of Museum Airborne Pollutants Using a Silver Nanoparticle Sensor Array.

The preservation of cultural heritage materials requires extremely low concentration limits for indoor pollutants. This poses an unmet challenge for monitoring the artwork in museums and on exhibit, especially to do so in a cost-effective manner for a large number of locations. A novel type of colorimetric sensor array based on printed inks of 10 nm silver nanoparticles (AgNPs) with several different capping agents has been developed as an alternative to metal coupons or other passive sampling indicators traditionally used by conservators. The AgNP colorimetric sensor array, combined with digital imaging, offers ultrasensitive dosimetric identification of acidic and oxidizing gases and other air pollutants commonly found in a museum; the limits of detection are sub-ppb for 1 h exposures. For an array of AgNP inks with various capping agents, a unique and distinguishable color response pattern is observed for each specific analyte. Excellent discrimination among 11 gas pollutants over a wide range of concentrations was demonstrated using standard chemometric methods. The observed changes in color during pollutant exposure originate from the sintering of solid-state nanoparticles that leads to changes in the localized surface plasmon resonance. Such chemically induced sintering mechanism of nanoparticles paves the way for a new class of field-deployable solid-state optical sensor arrays. As an example, we have demonstrated the use of AgNP sensor arrays for the nondestructive analysis of acidic volatile emission from five types of printing paper, relevant for the conservation of cultural heritage objects, including ancient manuscripts and books.

Fabrication and Electrical Characterization of Printed Microresistors of Silver Nanoparticles Using Microcantilever-Based Printing Technology

In this article, we report the fabrication of printed microresistors (PMRs) of silver nanoparticles (AgNPs) based on microcantilever-based printing technology (MCPT). The PMRs have been fabricated using three different printing techniques based on MCPT, namely spot overwrite printing (SOP), dip-ink printing with SOP (DIPSOP), and surface-patterning tool drag printing (SDP). The fabrication process has been carried out over substrates such as glass, silicon, and polyethylene terephthalate (PET). A postprinting analysis has been carried out based on the electrical characterization of the PMRs, which shows SOP as the most preferred, DIPSOP as the most reliable, and SDP as the fastest printing technique having the highest uniformity of thickness. The electrical characterization of the PMRs shows that their average resistance varies from few ohms to kiloohms based on the print thickness. The printed resistors are single-material electronic devices (SMEDs) as we have used only AgNP ink for the complete fabrication of the device to avoid any interfacial mismatch and irregularities at the nanoscale. Moreover, the fabricated PMRs are smaller in size, have lower fabrication cost, and consume less power as compared to the standard surface-mount device (SMD) chip resistors and hence offer an effective alternative to be used as microchip resistors on printed circuit boards (PCBs).

In-Space Manufacturing of Carbon Nanotube Biosensor for Crew Health Diagnostics

The impact of space environment in human physiology is one of the biggest hurdles for the success of long duration manned missions.1 Traditionally, the impact of space environment is assessed by comparing different physiological parameters before and after deployment. For long duration missions (i.e Moon or Mars), sample return for a ground base analysis will be impractical and in-flight, portable analytical devices will be required. Additionally, the further crew travel from earth, the less feasible it is to rely on resupply of these portable analytical devices. One solution is to develop methodologies for manufacturing analytical devices on-demand and in an in-space environment. Electrochemical biosensors can serve as point-of-care (POC) analytical devices as they can be easily fabricated onto cheap, disposable substrates by printing nanomaterial-based electronic inks. Inkjet printing is a suitable deposition technique as it provides contactless deposition of material droplets (ink) in very precise coordinates (high spatial resolution), allowing the fabrication of complex features.2 This offers a highly tailorable manufacturing process as the printed features are based on a easily adjustable/editable digital file. Also, this manufacture approach is amenable for an in-space environment fabrication due to its low dependence on an operator, fast manufacturing time with low waste generation, easily scalable, highly/easily tunable, ability to print a variety of electronic inks (conductors and insulators) with minimal chance of cross contamination between materials and different types of sensors can be manufactured using the same printer.3,4 Inkjet printing has the added advantage of allowing POC devices to be manufacture on a demand basis, optimizing resource use. Here we present the first steps of the development of a print-on-demand 3-electrode electrochemical biosensor for the detection of cortisol, a stress biomarker.5 For these devices, 3 types of inks were use: multi walled carbon nanotubes (MWCNT), silver nanoparticles (AgNP) and SU-8. First, AgNP ink was printed onto a kapton substrate to define the reference electrode (RE), electrical contact pads and electrical connections. Second, MWCNT ink was printed to generate the working electrode (WE) and the counter electrode (CE). Third, the SU-8 ink is used to encapsulate and insulate the AgNP electrical connectors. Lastly, the surface of the WE was modified with an antibody anti-cortisol using EDC/NHS coupling chemistry. The surface modification and detection of cortisol is identified through a measurable electrical change such as current and impedance, etc.6 (1) Demontis, G. C.; Germani, M. M.; Caiani, E. G.; Barravecchia, I.; Passino, C.; Angeloni, D. Human Pathophysiological Adaptations to the Space Environment. Front. Physiol. 2017, 8, 1–17. (2) Raut, N. C.; Al-Shamery, K. Inkjet Printing Metals on Flexible Materials for Plastic and Paper Electronics. J. Mater. Chem. C 2018, 6 (7), 1618–1641. (3) Li, J.; Rossignol, F.; Macdonald, J. Inkjet Printing for Biosensor Fabrication: Combining Chemistry and Technology for Advanced Manufacturing. Lab Chip 2015, 15 (12), 2538–2558. (4) Khan, S.; Ali, S.; Bermak, A. Recent Developments in Printing Flexible and Wearable Sensing Electronics for Healthcare Applications. Sensors (Basel). 2019, 19 (5). (5) Hellhammer, D. H.; Wüst, S.; Kudielka, B. M. Salivary Cortisol as a Biomarker in Stress Research. Psychoneuroendocrinology 2009, 34 (2), 163–171. (6) Kimmel, D. W.; LeBlanc, G.; Meschievitz, M. E.; Cliffel, D. E. Electrochemical Sensors and Biosensors. Anal. Chem. 2012, 84, 685–707.

Chemically Induced Sintering of Nanoparticles

We have observed solid-state growth of pre-existing silver nanoparticles (AgNPs) upon exposure to trace (ppb) concentrations of reactive gases at room temperature. The consequent change in localized surface plasmon resonances alters the visible absorbance of dried, printed sensor spots made from inks of 10 nm-AgNPs and provides a novel mechanism for trace detection and dosimetry of reactive gases. Colorimetric sensor arrays based on these AgNP inks offer dosimetric identification of acidic and oxidizing gases and other reactive vapors with limits of detection below ppb levels for 1 h exposures. For an array of AgNP inks with various capping agents, a unique color response pattern is observed for each specific analyte. Excellent discrimination among 11 reactive gases was demonstrated using standard chemometric methods. The chemically induced sintering of NPs paves the way for novel solid-state sensors for the ultrasensitive detection of reactive gases and their application to the monitoring of trace airborne pollutants.

Programmable Contact Printing Using Ballpoint Pens with a Digital Plotter for Patterning Electrodes on Paper

A simple programmable contact printing method using ballpoint pens with silver nanoparticle (AgNP) and carbon nanotube (CNT) ink and a digital plotter were developed for quick patterning of electrodes on paper. This printing method enables sequential and programmable printing with two different inks and with ink consisting of high viscosity materials and is amenable to reproducibility of printed electrodes and customized designs. With this printing method, AgNP and CNT patterns with low electrical resistance and high density of the material can be printed. Using these AgNP and CNT inks, we fabricated disposable electrochemical sensors (ECSs) on paper. The ECSs were successfully used to detect glucose at various concentrations from 0 to 15 mM. The characteristics of the printed AgNP and CNT patterns, such as the printing resolution, surface morphology, and electrical properties, were also studied. The proposed contact printing method opens an avenue for printing paper-based electronics and devices.

Synthesis and Electrochemical Characterization of AgNP Ink Suitable for Inkjet Printing

Synthesis and Electrochemical Characterization of AgNP Ink Suitable for Inkjet Printing

Microscale Hybrid Flexible Circuit Printed With Aerosol Jet Technique

Today, a microprinted electronics circuits are gaining more and more importance, but still printed electronic devices such as transistors or OLEDs are unstable in air and shows a poor performance. Moreover, printed microelectronic elements do not meet quality and high-reliability requirements, essential in electronics applications. To fulfill these needs, hybrid electronic circuits, combining printed technology, and surface-mount technology, are recommended. This approach gets advantages from both methods:Surface-mount devices (SMD) elements provide a high device functionality whereas a printed pattern ensures the device flexibility and efficiency. In this work, silver nanoparticle-based aerosol jet ink (AgNP ink) is used to realize the approach of a hybrid circuit with aerosol jet printed pads and surface-mount devices. The ultrasonic atomization process ensures the high printing resolution and appropriate line formation. Electrical and mechanical characterization was performed to present the connection performance and quality. Cross section view and morphological inspection explain the joint high quality and good performance. Resistance characterization presents the high current conductance comparable with connections made by silver epoxy or ink-jet printing. Shear test results show an excellent connection strength complying with USA Military Standard. Finally, a flexible hybrid conductance touch sensor is manufactured, demonstrating the feasibility of the presented assembling solution.

Analysis of Superfine-Resolution Printing of Polyaniline and Silver Microstructures for Electronic Applications

Additive manufacturing (printing) of micrometer-scale patterns of metal and semiconductor particles is receiving significant attention due to its potential as an inexpensive alternative to the top-down fabrication of silicon microelectronic devices. However, printing of such devices needs an in-depth understanding of physico-chemical interactions between the liquid ink droplets and the substrate used for printing the devices. The paucity of detailed experimental studies in this area warrants a systematic investigation into the challenges involved in printing stable and reliable electronic devices. In this paper, we have analyzed the interactions between the liquid dispersions of polyaniline emeraldine salt (PANI-ES) and silver nanoparticles (Ag NPs) over various substrates such as silicon, glass, indium tin oxide, polyethylene terephthalate, and polyvinyl alcohol surfaces. The analysis has been carried out in terms of concentration of the dispersion, particle size, solvophilic or solvophobic nature of the substrate, evaporation rate of solvents, ambient humidity, and postprocessing. Furthermore, the resistors of various lengths and widths are printed on glass surface via a superfine resolution molecular printing system (MPS) that uses a piezoelectric response from a cantilever to deposit picoliters of Ag NP ink at precise locations. Substantially, low ratios of printed dot feature size to suspended particle size (1 for PANI-ES and 10 for Ag NP) have been obtained, indicating that the MPS can provide a much finer print resolution for flexible and printed electronic circuit components as compared to traditional inkjet, screen, or gravure printing.

Encapsulated silver nanoparticles in water/oil emulsion for conductive inks

Abstract Silver nanoparticle (AgNP) inks are the most commonly used conductive ink for printed conductive tracks. However, the ink stability against aggregation and sedimentation is poor and results in short shelf life, severe nozzle clogging, and bad printing qualities. Herein, a new method is developed to improve the stability of AgNP inks. In this work, a water-in-oil type emulsion is used as a carrier for water-based silver nanoparticles. Different water/surfactant ratio are examined for the complete AgNP uptake in water nano droplets. The morphology of AgNP after emulsification is carefully examined with electro-microscopy to elucidate the particle engulfment in water. The encapsulated AgNP show a much lower sedimentation rate due to the greatly reduced overall density of encapsulated AgNPs/water droplets. Moreover, the water/oil interfaces around AgNPs prevent aggregations, and thus leads to better long-term ink stability. The physical properties of AgNP emulsion meet the requirement of the printer and stable inkjet droplet can be produced. Conductive tracks with electrical resistance 4.92 μΩ-cm and line width 170 µm can be printed on photo papers, which demonstrates the potential of the emulsion for inkjet printing application.

Fast near infrared sintering of silver nanoparticle ink and applications for flexible hybrid circuits.

Near infrared(NIR) sintering technology is a photonic sintering approach for metal nanoparticle inks, which can selectively sinter metal nanoparticle inks more quickly and efficiently, and it is also compatible with high-throughput manufacturing processes. In this paper, silver nanoparticle (AgNP) ink sintered by near infrared light at a peak wavelength of 1100 nm was investigated. After only 8 seconds of exposure to NIR irradiation, resistivity of 2.78 μΩ cm was achieved for thin films printed with AgNP ink, which was only 1.7-fold higher than that of bulk silver (1.59 μΩ cm). The structure of the sintered silver film was examined by sintering printed silver nanoparticle ink samples having different thicknesses, and the results showed that AgNPs were homogeneously coalesced throughout the cross-sections of films, indicating the formation of dense silver layers. Furthermore, the morphology and electrical resistivity of the sintered AgNP film dried by NIR were compared with those of the film dried on a hot plate. It was found that drying conditions with a relatively long drying time rather than the drying temperature contributed to the reduction of voids in the film and to the improvement in its density and electrical performance. Finally, a flexible hybrid circuit integrated with a microcontroller chip on a poly(ethylene terephthalate)(PET) substrate was fabricated by screen printing with AgNP ink for interconnects, and its surface roughness and flexibility were investigated.

Sintering Inhibition of Silver Nanoparticle Films via AgCl Nanocrystal Formation.

Electrically conductive films are key components in most printed and flexible electronics applications. For the solution processing of conductive films, inks containing silver nanoparticles (AgNPs) remain important because of their relatively easy processing and generally low resistivity after a sintering procedure. Because the commonly used, moderate sintering temperatures of 150–300 °C are still too high for most low-cost flexible substrates, expanding the knowledge of surface-ink interactions that affect the sintering temperature is desirable. It is known that chloride ions can assist the sintering of AgNP films by displacing capping agents on the surfaces of AgNPs. However, very little is known about other possible Cl-AgNP interactions that affect the resistivity and no interaction having the opposite effect (sintering inhibition) has been identified before. Here we identify such a Cl-AgNP interaction giving sintering inhibition and find that the mechanism involves the formation of AgCl nanocrystals within the AgNP film. The AgCl formation was observed after inkjet-printing of AgNP inks with polyvinylpyrrolidone (PVP) as the capping agent onto papers with quick-absorbing coatings containing 0.3 wt % KCl. Our findings show that chloride can have opposite roles during sintering, either assisting or inhibiting the sintering depending on the prevalence of AgCl formation. The prevalence of AgCl formation depends on the absorption properties and the capping agent.

Three-dimensional Printing of Silver Microarchitectures Using Newtonian Nanoparticle Inks.

Although three-dimensional (3D) printing has recently emerged as a technology to potentially bring about the next industrial revolution, the limited selection of usable materials restricts its use to simple prototyping. In particular, metallic 3D printing with submicrometer spatial resolution is essential for the realization of 3D-printed electronics. Herein, a meniscus-guided 3D printing method that exploits a low-viscosity (∼7 mPa·s) silver nanoparticle (AgNP) ink meniscus with Newtonian fluid characteristics (which is compatible with conventional inkjet printers) to fabricate 3D silver microarchitectures is reported. Poly(acrylic acid)-capped AgNP ink that exhibits a continuous ink flow through a confined nozzle without aggregation is designed in this study. Guiding the ink meniscus with controlled direction and speed enables both vertical pulling and layer-by-layer processing, resulting in the creation of 3D microobjects with designed shapes other than those for simple wiring. Various highly conductive (>104 S·cm-1) 3D metallic patterns are demonstrated for applications in electronic devices. This research is expected to widen the range of materials that can be employed in 3D printing technology, with the aim of moving 3D printing beyond prototyping and into real manufacturing platforms for future electronics.

Flexible hybrid circuit fully inkjet-printed: Surface mount devices assembled by silver nanoparticles-based inkjet ink

Nowadays, inkjet-printed devices such as transistors are still unstable in air and have poor performances. Moreover, the present electronics applications require a high degree of reliability and quality of their properties. In order to accomplish these application requirements, hybrid electronics is fulfilled by combining the advantages of the printing technologies with the surface-mount technology. In this work, silver nanoparticle-based inkjet ink (AgNP ink) is used as a novel approach to connect surface-mount devices (SMDs) onto inkjet-printed pads, conducted by inkjet printing technology. Excellent quality AgNP ink-junctions are ensured with high resolution picoliter drop jetting at low temperature (∼150 °C). Electrical, mechanical, and morphological characterizations are carried out to assess the performance of the AgNP ink junction. Moreover, AgNP ink is compared with common benchmark materials (i.e., silver epoxy and solder). Electrical contact resistance characterization shows a similar performance between the AgNP ink and the usual ones. Mechanical characterization shows comparable shear strength for AgNP ink and silver epoxy, and both present higher adhesion than solder. Morphological inspections by field-emission scanning electron microscopy confirm a high quality interface of the silver nanoparticle interconnection. Finally, a flexible hybrid circuit on paper controlled by an Arduino board is manufactured, demonstrating the viability and scalability of the AgNP ink assembling technique.

Engineering Crack Formation in Carbon Nanotube-Silver Nanoparticle Composite Films for Sensitive and Durable Piezoresistive Sensors.

We report highly sensitive and reliable strain sensors based on silver nanoparticle (AgNP) and carbon nanotube (CNT) composite thin films. The CNT/AgNP was prepared by a screen printing process using a mixture of a CNT paste and an AgNP ink. It is discovered that the sensitivity of such sensors are highly dependent on the crack formation in the composites. By altering the substrate use and the relative ratios of AgNPs and CNTs, the formation and propagation of cracks can be properly engineered, leading to piezoresistive strain sensors with enhanced sensitivity and robustness.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-016-1626-z) contains supplementary material, which is available to authorized users.

Electrical Property and Surface Morphology of Silver Nanoparticles After Thermal Sintering

In this study, the sintering behavior of silver (Ag) nanoparticle inks was investigated when different particle sizes and sintering methods were employed. Ag nanoparticle inks with two different particle sizes were investigated with average particle diameters of 12 nm and 50 nm. The two kinds of Ag nanoparticle inks were inkjet-printed onto glass substrates. The printed inks were sintered by a furnace and a continuous wave (CW) laser at a wavelength of 532 nm. The specific resistance and surface morphology of the Ag nanoparticle (Ag NP) inks were investigated under various furnace temperatures, laser intensities, and time durations. The ex situ specific resistance of each Ag NP ink was measured by a multimeter to determine the effects of various sintering conditions such as the furnace temperature, laser intensity, and sintering duration. To investigate the correlation between the specific resistance and surface morphology of the Ag NP inks, field emission scanning electron microscopy images were obtained. In addition, the effect of the particle size on the specific resistances of the inks annealed by the furnace and CW laser was evaluated.

Microcontact patterning of conductive silver lines by contact inking and its layer-transfer mechanisms

We developed a contact inking technique for microcontact printing aiming at the fabrication of conductive silver-nanoparticle (Ag NP) lines with rectangular cross section and constant layer thickness, irrespective of pattern size and shape. In the proposed process, Ag NP ink was first coated on a blanket and then inking was carried out by a contact with a microcontact stamp. The ink transferred onto the top of the stamp was finally settled on a workpiece by pressing to complete the printing process. To achieve robust inking to the stamp, the peel strengths between the Ag NP layer and the blankets and between the Ag NP layer and the stamp were investigated using poly (dimethylsiloxane) (PDMS) materials with different surface energies. Interestingly, it was revealed that the transferability of Ag NP from the blanket toward the stamp was not solely determined by the surface energy difference but also by the extent of solvent uptake by the PDMS blanket during inking. The solvent-containing PDMS significantly lowered its adhesion strength against adjacent ink layers and, as a consequence, the ink transfer was successfully achieved even if the ink passed from a higher to a lower energy surface. Furthermore, by the solvent-vapour annealing of contact-inked semi-dried patterns, arbitrarily iterated transfers between PDMS surfaces became possible. With the contact-inking process developed here, we demonstrate a finely defined printed structure of Ag NP conductive lines with widths of up to 1 μm.