Alloy and metallic nanoparticle production for printed electronics

Nanotechnology is a rapid expanding and advancing field which its nano sized products are tremendously useful in many technological applications with a multi-disciplinary approach. Nanostructured materials with high electrical conductivity are preferred advanced materials in conductive inks and printed electronics technology for their superior properties compared to bulk materials. Metallic conductive ink compositions that can accommodate conventional printed circuit and layered methods, will further enable miniaturization in advanced technological applications such as RFID tags, small electronic devices, sensors, insulation, smart cards, organic solar cells and flexible electronic circuits with significant technological improvements. With its applications and materials, it is estimated to reach 48.2 billion dollars worth market value in 2017. However, high cost of raw materials and processing in order to obtain nanostructured materials with high electrical conductivity is defined as the most important restriction for widespread use in industry. Alternatively, advances in nanotechnology have increased research and studies on the use of metal nanoparticles in ink compositions. Production of nanoparticles consisting of atoms or molecules clusters with desired size range, energy states, geometric structures, chemical and physical properties is also important topic of interest in nanotechnology. Nano-sized powders/particles can be produced in many different forms. In "Top-Down" approach, production is made from bulk materials that are divided into smaller pieces by physical methods (Mechanical Milling, Electrodeposition, Lithography). In "Bottom-Up" approach, nanoparticles are produced from materials at atomic or moleculer size. Sol-Gel, CVD, Inert Gas Condensation and aerosol based methods are based on this approach. The ultrasonic spray pyrolysis method is a production method which is considered as a "Bottom-Up" approach, known for its versatility, low-cost, ability to produce spherical particle morphology in a single step and variety of materials able to be used. Ultrasonic spray pyrolysis is a process in which solid particles are produced by evaporation, drying and thermal decomposition/reduction processes in controlled atmosphere, starting from droplets obtained from ultrasonic frequency from metal salt precursors. Single-step and atmospheric pressure droplet-to-particle conversion and particle collection processes in ultrasonic spray pyrolysis results as spherical, needle-like, diagonal and so on nanostructured materials with narrow size distribution metal, oxide, ceramic, carbon nased or composite agglomerated micro scale or nano sized particles. Conductive inks are essential components of printed electronics technology and evaluated mainly in 2 groups, which are dispersed colloidal solutions and polymer based solutions. Dispersed colloidal solutions or inks contain metallic additives such as nano scale silver (Ag), copper (Cu), gold (Au), nickel (Ni) etc. single particles and/or alloys to provide electrical conductivity for desired applications. Surface treatment by curing and/or sintering, drying after printing is applied in order to enhance electrical conductivity and longevity of printed tracks. Current commerical conductive inks are based on Ag nanoparticle containing inks. After appling Ag ink onto sample, surface and electrical conductivity properties are improved by certain secondary processes as mentioned above. Ag conductive inks are used in key technological areas such as flexible printed circuit boards, integrated circuits and organic photovoltaic cells contact materials and RFID tags, where majority of inks are used for its high electrical conductivity. Furthermore, it is also used as sensors, catalysts, EMI/RFI shields, applications requiring thermal conductivity, optical filters, screens and sintering additives. However, due to high raw material costs, silver alternatives or reduced silver content ink designs are prominent and studies in this area have great interest both academically and industrially. Conductive inks containing Cu metallic filler, like Ag inks, are used as flexible electrodes, flexible printed electronics and integrated circuit contact material and RFID labeling materials due to their high electrical conductivity properties. Cu conductive inks are also preferred in areas requiring chemical sensor, catalyst, especially high thermal conductivity for electronics cooling, lubricant, coating and sinter additives. Conductive inks containing Ni metallic filler are not used frequently for high electrical conductivity in areas where Ag and Cu based inks used, such as flexible printed electronics and circuit boards. The fact that Ni has lower conductivity compared to Ag- and Cu-containing inks is a major influence. Other physical and chemical properties are preferred, especially for electromagnetic shielding, capacitor material, fuel cell catalyst material, high current surge protectors. In this study; unlike conventional production methods, ultrasonic spray pyrolysis-hydrogen reduction technique has been used to produce AgCuNi ternary alloy nanoparticles with reduced silver content in a single step from high purity metal salts, optimizing production parameters and investigating electrical conductivity values. For this purpose, first step of the research activities was to determine the production parameters of AgCuNi ternary alloy nanoparticles. Production of AgCuNi ternary alloy nanoparticles by ultrasonic spray pyrolysis-hydrogen reduction technique was carried out by preparing precursors (0.01-0.4 M) at different concentrations from high purity metal salts to be used as starting solution. In production of AgCuNi nanoparticles, solution concentration and reduction temperature were determined and optimal production conditions were determined. In characterization studies of the produced nanoparticles, particle size, morphology, crystal structure and crytallite size were investigated dependinbg on the production parameters. It has been determined that AgCuNi nanoparticles phase-analyzed by X-ray diffraction, are composed of a mixture of face centered cubic and body centered cubic structures ranging between 20-48.8 nm crystallite sizes. Morphology and size analysis were performed with a field emission gun scanning electron microscope and the mean size of the alloy particles decreased from 619 nm to 198 nm with a decrease in solution concentration from 0.4 M to 0.01 M. By electron dispersive spectrometry analysis it was determined that the composition of the ternary alloy was 50% Ag, 25% Ni and 25% Cu by weight. The second part of the experimental work within the scope of thesis is the production of Ag, Cu and Ni nanoparticles by organic solution reduction method. Ag nanoparticles production were carried out in polyethanol amine-based solvent and reducing medium. Glycol-based solvent and reducing medium is used in the production of Cu and Ni nanoparticles. In characterization studies of the produced nanoparticles; particle properties such as size, morphology, crystal structure and crystallite size were investigated. It was observed that Ag nanoparticles consisted of spherical agglomerate particles with and average size of 282 nm in the range of 50-683 nm and a 34.11 nm crystallite size with face centered cubic structure. It was obverved that Cu nanoparticles weere in face centered cubic structure with a crystallite size of 37.35 nm and spherical morphology and PVP coated Cu nanoparticles averaging 24 nm particle size in the range of 15-43 nm. It has been determined that Ni nanoparticles are in face centered cubic structure where the polycrystallite structure is formed from 2-3 nm nanocrystallites and spherical morphology due to PVP coating, which resulted as an average of 47 nm particle size in the range of 23-87 nm. The third part of experimental studies were consisting of conductive ink preparations and applications. Dispersed colloid conductive inks were perpared using AgCuNi ternary alloy nanoparticles and Ag, Cu and Ni metallic nanoparticles. Dispersions prepared in a composition of 50% carrier solution and 50% metal nanoparticles infill were coated on glass surfaces with an automatic film coating apparatus and the electrical conductivity values of the coatings were measured by using a 4 point probe electrical conductivity measurement device. Electrical conductivity of conductive ink prepared with Ag nanoparticles produced by chemical reduction method is measured as 4.85.105 S/cm, while electrical conductivity of ink containing AgCuNi particles produced by ultrasonic spray pyrolysis-hyrdrogen reduction tecnique is measued as 3,55.105 S/cm. In conclusion, AgCuNi nanoparticles produced in a single-step from high purity metal salts precursor by ultrasonic spray pyrolysis-hydrogen reduction technique, are alternative suitable reduced silver content metallic infill material for conductive inks and applications that require high electrical conductivity.