Multi-nozzle electrohydrodynamic inkjet printing of silver colloidal solution for the fabrication of electrically functional microstructures

In this paper, multi-nozzle electrohydrodynamic (EHD) inkjet printing of a colloidal solution containing silver nanoparticles in a fully controlled fashion is reported. For minimizing interaction, i.e. cross-talk, between neighboring jets, the distance between the nozzles was optimized numerically by investigating the magnitude of the electric field strength around the tip of each nozzle. A multi-nozzle EHD inkjet printing head consisting of three nozzles was fabricated and successfully tested by simultaneously printing electrically conductive lines of a colloidal solution containing silver nanoparticles onto a glass substrate. The printed results show electrical resistivity of 5.05×10⁻⁸ Ω m, which is almost three times larger than that of bulk silver. These conductive microtracks demonstrate the feasibility of the multi-nozzle EHD inkjet printing process for industrial fabrication of microelectronic devices.     

Low temperature nanoparticle sintering with continuous wave and pulse lasers

New manufacturing methods are being sought for electronics production. Printable electronics is a promising method for producing low cost and large-scale electronics. In printable electronics nanoparticle inks printed on the surface of substrate contain additives, such as dispersing agent and carrier fluids that provide good printing properties by changing the viscosity and separating the nanoparticles of the ink. In the sintering process ink particles are heated to a certain, ink-specific temperature. During the sintering process the carrier fluid and dispersing agents are evaporated from the ink. Additional heating after evaporation causes the nanoparticles to start to agglomerate. A small particle size allows the use of a considerably lower sintering temperature than with bulk silver, for example 220 °C. The sintering process is usually utilized with a convection oven, with a long sintering time, and the thermal load on the surrounding material can become too great as components and patterns are formed from layers of different type inks. Hence, alternative sintering methods are sought. This paper describes tests done with two different types of laser; pulsed and continuous wave lasers. Laser sintering enables short sintering times and selective sintering, making it possible for printed structures to contain fragile active components produced with other technologies.     

High-performance electrically conductive silver paste prepared by silver-containing precursor

A high-performance electrically conductive silver paste with no solid particles before drying and/or sintering is developed, in which silver-containing precursor is employed as conductive functional phase. Thermogravimetry analysis, volume electrical resistivity tests and sintering experiments show that the paste with about 14 wt.% silver pristine content is able to achieve the volume electrical resistivity of (2–3) ×10⁻⁵ Ω cm after it is sintered at 220°C. A micro-pen direct-writing process indicates that it is very suitable for the fabrication of high-resolution (25 μm) and high-integration devices and apparatus.     

A promising approach to conductive patterns with high efficiency for flexible electronics

A promising approach for conductive patterns with high efficiency for flexible electronics was developed by direct-writing, silver(I) solution (silver nitrate, acetate silver, etc.) with no solid particles as a conductive ink, conductive pen as a writing implement, and polyimide (PI) film as a substrate. The physical properties of the conductive ink were investigated by a dynamic contact angle system, ubbelohde viscometer and surface tension instrument. Conductive properties of silver ink film were investigated by 4-point probe, scanning electron microscope (SEM) and surface profilometer. It is demonstrated how the design of solvent composition in conductive ink affects surface morphology, and conductivity of silver ink films. It can be obtained that conductive patterns drawn on PI substrate not only have good mechanical/electrical fatigue properties, but also have low resistivity. Especially, when the sintering condition is 200 °C for 60 min, the resistivity can be down to 6.6 μΩ cm, 4.25 times the silver bulk resistivity.     

Cerium oxide nanoparticles protect primary mouse bone marrow stromal cells from apoptosis induced by oxidative stress

The sintering of a silver (Ag) nanoparticle film by laser beam irradiation was studied using a CW DPSS laser. The laser sintering of the Ag nanoparticle thin film gave a transparent conductive film with a thickness of ca. 10 nm, whereas a thin film sintered by conventional heat treatment using an electronic furnace was an insulator because of the formation of isolated silver grains during the slow heating process. The laser sintering of the Ag nanoparticle thin film gave a unique conductive network structure due to the rapid heating and quenching process caused by laser beam scanning. The influences of the laser sintering conditions such as laser scan speed on the conductivity and the transparency were studied. With the increase of scan speed from 0.50 to 5.00 mm/s, the surface resistivity remarkably decreased from 4.45 × 10⁸ to 6.30 Ω/sq. The addition of copper (Cu) nanoparticles to silver thin film was also studied to improve the homogeneity of the film and the conductivity due to the interaction between the oxidized surface of Cu nanoparticle and a glass substrate. By adding 5 wt% Cu nanoparticles to the Ag thin film, the surface resistivity improved to 2.40 Ω/sq.     

Synthesis and characterization of copper ink and direct printing of copper patterns by inkjet printing for electronic devices

Among the conventional metallic inks used in the printing process, silver exhibits high conductivity and thermal stability. Nevertheless, due to the high cost of silver, it cannot be extensively used for the fabrication of inks. As a competitive alternative, copper can be considered as a substitute for silver; however, copper ink oxidizes under certain atmospheric conditions. To meet these shortcomings, a cost effective, highly conductive, and oxidation-free copper-based ink has been synthesized in this study, wherein, oxidation of the copper particles in the copper-based ink was prevented by using copper complexes. The copper ink thus fabricated was printed on chemically treated Si/SiO₂ substrates followed by the characterization of the printed copper films. The results of this study confirmed that the synthesized copper ink exhibited properties suitable for its use in the inkjet printing process for fabrication of various electronic devices.     

Electrohydrodynamic micropatterning of silver ink using near-field electrohydrodynamic jet printing with tilted-outlet nozzle

This paper introduces for the first time near-field electrohydrodynamic jet printing with tilted-outlet nozzle to obtain the fine and highly conductive patterns of silver (Ag) ink. Line widths produced by near-field electrohydrodynamic jet printing are less than 6 μm, which is approximately twenty times smaller than that of inkjet printing. Under optimized Ag ink annealing ranges 3–9 min for 30 wt% at 150°C, we observed Ag line pattern resistivities as low as 7×10⁻⁶ Ω⋅cm. Ag ink conduction mechanisms were brought to light from microstructure analysis and post-thermal-annealing examination of electrical characteristics.     

Novel materials for electronic device fabrication using ink-jet printing technology

Novel materials and a metallization technique for the printed electronics were studied. Insulator inks and conductive inks were investigated. For the conductive ink, the nano-sized copper particles were used as metallic sources. These particles were prepared from a copper complex by a laser irradiation process in the liquid phase. Nano-sized copper particles were consisted of a thin copper oxide layer and a metal copper core wrapped by the layer. The conductive ink showed good ink-jettability. In order to metallize the printed trace of the conductive ink on a substrate, the atomic hydrogen treatment was carried out. Atomic hydrogen was generated on a heated tungsten wire and carried on the substrate. The temperature of the substrate was up to 60 °C during the treatment. After the treatment, the conductivity of a copper trace was 3 μΩ cm. It was considered that printed wiring boards can be easily fabricated by employing the above materials.     

Synthesis and characterization of conductive silver ink for electrode printing on cellulose film

Silver nanoparticles with size less than 50 nm were synthesized from silver nitrate, polyvinylpyrrolidone (PVP) and ethylene glycol, where these chemicals acted as metal precursor, stabilizer and reducing agent, respectively. Then a conductive silver ink was prepared with a suitable solvent by adding a viscosifier, hydroxyethyl-cellulose (HEC), and a surfactant, diethylene glycol (DEG). The combined effect of both viscosifier and surfactant on the physical property of the silver ink was analyzed by measuring the contact angle of the silver ink on a cellulose film. Moreover, the influences of PVP molecular weight and reaction temperature on the size of the silver nanoparticles were analyzed. Then the silver ink was coated on the cellulose film by spin coating and the effects of different solvents, sintering temperatures and solid contents on its electrical resistivity were examined. It was found that, with 50 % co-solvent of deionized water and DEG and solid content of around 50 %, the silver ink exhibited the lowest resistivity. This ink can be used for inkjet printing of conductive patterns on cellulose films.     

Highly Stable Graphene Inks Based on Organic Binary Solvents

Formulating highly stable graphene-based conductive inks with consistency in electrical properties over the storage period has remained a significant challenge in the development of wearable electronics. Two highly stable graphene-based inks (Cyclohexanone:Ethylene glycol (CEG) ink and Cyclohexanone:Terpineol (CT) ink) are prepared by using two different organic binary solvents, for the first time, without using solvent exchange methods. Both the inks display remarkably high stability (stable even after two months) with negligible variability in electrical properties. Here, it is demonstrated how such inks can be utilized to coat flexible substrates to create wearable e-textiles. Both the inks coated e-textiles show significantly low sheet resistance (≈209.1 Ω □⁻¹ for CEG ink and ≈322.4 Ω □⁻¹ CT ink) that show less than a 15% increase in electrical resistance over two months. Therefore, these inks offer high productivity and reproducibility and can be one of the most effective methods for formulating graphene-based inks.     

Effect of SAM layer on bias-stability of inkjet printed TIPS pentacene thin-film transistor

We have studied the effect of self-assembled monolayer (SAM) on the performance and bias-induced changes in bottom contact, inkjet printed organic thin-film transistors (OTFTs) with 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene). The device was fabricated using the photo-definable photoacryl (PA) and silver (Ag) as gate insulator and source/drain metal electrodes, respectively. The SAM was formed by immersing the patterned Ag electrodes in pentafluorothiophenol (PFBT) solution or by spin coating of phenethyltrichlorosilane (PTS) on the substrate, and TIPS pentacene was inkjet printed at 90 °C. The OTFT with SAMs exhibited the field-effect mobility of 0.18 cm²/Vs and showed the stretched exponential decay with time constant of 1.13 × 10⁷ s and exponential exponent of 0.28.     

Direct fabrication of copper patterns by reactive inkjet printing

Reactive inkjet printing (RIP) was applied to fabricate arbitrary copper (Cu) patterns. RIP prints reactive inks which can provide desired materials after the reaction on a substrate. Here, Cu precursors and reducing agents were dissolved together in one solution as a printable ink instead of conventional Cu nanoparticle inks. The prepared reactive ink was applied to the RIP method to provide dot arrays, lines, and films of Cu. The synthesis of Cu was confirmed to occur successfully by thorough analysis. The RIP method can reduce the process cost and resolve critical drawbacks of the conventional inkjet printing such as a nozzle clogging problem. Furthermore, utilizing reactive precursor inks broadens the choice of materials that can be processed by inkjet printing.     

Sintering condition effect on the characteristics of ink-jet printed silver pattern on flexible cellulose paper

This paper reports sintering condition effect on an ink-jet printed conductive pattern of silver ink made on a cellulose paper. To fabricate the conductive pattern on the cellulose paper, silver ink is ink-jet printed and the influence of sintering temperature and time is investigated in terms of electrical resistivity and morphology by using scanning electron microscope and atomic force microscope. Two-level baking process composed of soft baking and hard baking is found to be effective for silver nanoparticle network. The sintering temperature and time are strongly associated with the conductivity of the ink-jet printed pattern.     

无颗粒型银导电墨水的制备及其印刷成膜研究

以柠檬酸银为导电金属前驱体化合物,仲丁胺为络合剂,并添加乙醇调节粘度和表面张力等物性参数,制备了无颗粒型银导电墨水。该导电墨水可以采用凹版印刷方式印刷在PET片基上,并且在较低的热处理温度下即可获得导电性较好的银导电膜。利用X射线光电子能谱仪、同步热分析仪、红外光谱仪、X射线衍射仪、扫描电子显微镜和四探针测试仪对柠檬酸银、导电墨水以及银导电膜进行表征。结果表明导电墨水在132 ℃时残留质量即达到恒重,远低于柠檬酸银的210 ℃;经150 ℃热处理之后,银导电膜由均匀致密、纯度高的纳米银颗粒组成;经150 ℃热处理50 min后得到的银导电膜的方块电阻值为1.83 Ω·□-1。     

A peculiarity of silver-based corona wire heating on ozone generation

The effect of corona wire temperature on the ozone generation in the positive dc corona electrostatic precipitator is studied experimentally. The external heating of the corona wire can suppress the ozone generation. In this study, nichrome and two kinds of silver-based wires 0.1 mm diameter were tested as discharges electrodes. The nichrome corona wire heating shows a well-known monotonic decreasing the rate of ozone production. In the case of the tested silver-based wires the rate of ozone production decreases nonlinearly and passes through a local minimum in the range from 35 to 55 °C with increasing the wire temperature. At the wire temperature about 46 °C ozone generation by positive dc corona discharge is decreased by 53% with Ag:Mn = 0.85:0.15 wire and by 25% with Ag:Ni = 0.7:0.3 wire as compared to the same wire at 26 °C. Under these conditions the corona wire heating increases slightly the corona current and speed of airflow.     

In situ microanalysis of organic colorants by inkjet colloid deposition surface‐enhanced Raman scattering

We present a new method for the minimally invasive in situ identification of inks and colorants on documents and other objects on the basis of the deposition of silver colloid nanodroplets on a region of interest in the objects to be tested using inkjet technology. By adapting commercially available thermal and piezoelectric inkjet heads, volumes of silver colloid in the 60–220 picoliters range (corresponding to impact diameters in the range of 50–150 µm) can be delivered onto substrates with great accuracy and precision. We demonstrate that the instantaneous superheating of the colloid in the thermal print head does not adversely affect the surface‐enhanced Raman spectroscopy efficiency of the Ag nanoparticles. Furthermore, by mounting a compact piezoelectric inkjet head within a large‐stage Raman microscope, we developed an instrument where all phases of surface‐enhanced Raman spectroscopy microanalysis are integrated, with great advantages in sample handling, spatial accuracy, and colloid delivery reproducibility. The approach can be considered functionally nondestructive as the amount of silver delivered, and the area affected are too small to be detected by visual observation, and in most conditions, even by optical microscopy. The method was successfully applied to the analysis of textile fibers, gel pen ink writing on paper, and a Japanese woodblock print dating to the end of the 19th century. Copyright © 2013 John Wiley & Sons, Ltd.     

Preparation of triethylamine stabilized silver nanoparticles for low-temperature sintering

In this article, silver nanoparticles were synthesized by chemical reduction from silver nitrate using triethylamine as the protecting and reducing agents simultaneously. The average size of the silver nanoparticles was about 2.10–4.65 nm, which allowed low-temperature sintering of the metal. X-ray diffraction (XRD), thermogravimetric analysis (TGA), and energy dispersive spectrometric (EDS) analysis results indicate that silver nitrate has been converted to silver nanoparticles completely. Using a 20 wt% silver nanoparticles suspension with thermal treatment at 150 °C, silver films with a resistivity of 8.09 × 10⁻⁵ Ω cm have been produced, which is close to the resistivity of bulk silver.     

Surface-enhanced Raman scattering active substrates by liquid flame spray deposited and inkjet printed silver nanoparticles

Surface-enhanced Raman scattering (SERS) active substrates were made via liquid flame spray deposition and inkjet printing of silver nanoparticles. Both processes are suitable for cost-effective fabrication of large-area SERS substrates. Crystal violet (CV) solutions were used as target molecules and in both samples the detection limit was approximately 10 nM. In addition, sintering temperature of the inkjet printed silver nanoparticles was found to have a large effect on the SERS activity with the higher curing temperature of 200 °C resulting in contamination layer on silver and cancelation of the SERS signal. This layer was characterized using an X-ray photoelectron spectroscopy (XPS).     

Densification and microstructure of lead zirconate titanate ceramics fabricated from a triol sol–gel powder

Lead zirconate titanate (PZT) nano-powder was prepared by a triol sol–gel process. X-ray diffraction and transmission electron microscopy results showed that as-synthesized amorphous powder started to crystallize at the calcination temperature above 500 °C. The crystalline powder was formed into pellets and sintered at temperatures between 900 and 1300 °C. Co-existence of tetragonal and rhombohedral phase was observed in all ceramics. Microstructural investigation of PZT ceramics showed that uniform grain size distribution with average grain size of ∼0.8–2.5 μm were received with sintering temperature up to 1200 °C. Further increasing the temperature caused abnormal grain growth with the grain as large as 13.5 μm. An attempt to optimize densification with uniform grain size distribution was also performed by varying heating rate and holding time during sintering. It was found that dense (∼97%) sol–gel derived PZT ceramic with uniform microstructure was achieved at 1100 °C with a heating rate of 5 °C min⁻¹ and 6 h dwell time.     

Evaluation of antibacterial activities of silver nanoparticles green-synthesized using pineapple leaf (Ananas comosus)

Pineapple leaf was used in this study for the synthesis of silver nanoparticles based on the search for sustainable synthetic means. Indeed, this offered an economical and sustainable synthetic route relative to expensive and toxic chemical methods. The leaf extract was used and the corresponding nanoparticles obtained were subjected to UV–vis analysis at different times. The UV–vis was used to monitor the silver nanoparticle formation through sampling at time intervals. The formation of silver nanoparticles was apparently displayed within 2 min with evidence of surface plasmon bands (SPB) between 440 and 460 nm. The crystals was equally characterized using FTIR, X-ray diffraction methods and TEM. The different results obtained suggested the appearance of silver nanoparticles (SNPs) as determined by the process parameters with a particle size of 12.4 nm. The sample was further screened against Staphylococcus aureus, Streptococcus pneumoniae, Proteus mirabilis and Escherichia coli using Gentamicin as control. From the results, there is evidence of inhibition towards bacteria growth. It can now be inferred from the studies that biosynthesis of nanoparticles could be a gateway to our numerous health issues.