Controllable Synthesis Of Silver Nanomaterials And Its Application In Printed Electronics

With the development of modern technology, printed electronics has risen from the field of printed circuit. As the new technology can directly print electronic circuits or device on all sorts of substrates by conductive inks, it presents great advantages comparing with the traditional process, such as: more convenient operation, shorter production cycle, lower cost, lower resource consumption and lower environmental pollution. Although the technology is only in its infancy, it has been pursued by many people. It makes us believe that the technology will become a new force in printed circuit field.Since printed electronics is not developed, many problems need to be handled, such as: lack of technical printing equipment, too cumbersome for the preparation of conductive inks, high requirements of experimental conditions, low yield of nanomaterial, low efficiency, nonuniform of printed patterns, high sintering temperature leading to the oxidation of metal and damage of substrates, et al.. Under such a condition, our works and researches were started to resolve the primary problems that parasitized in the preparation process of conductive inks. The liquid synthesis of silver nanomaterial was focused by our research; and the experiments were carried out following in proper iterative sequence as: theory â†' experiment â†' results â†' summary â†' theory, to find simple, effective, low energy consumption, low cost ways to solve these problems. The detailed contents are as follows:(1) Monodispersed silver nanoparticles(Ag NPs) were successfully prepared in a polyol process using ethylene glycol(EG) as solvent, silver nitrate(AgNO3) as precursor, poly(vinylpyrrolidone)(PVP) as capping agent under 160 ℃. The particles were ca. 90 nm in size and spherical in shape. As PVP can be desorbed from the surface of Ag NPs by Cl-, it causes spontaneous coalescence and agglomeration between particles, which can greatly improve the conductivity of the patterns fabricated with Ag NPs. The final conductivity of printed samples in our research could reach about 16% of the bulk silver.(2) Small Ag NPs with average size ca. 37 nm were successfully synthesized in a polyol process by using polyethylene glycol(PEG) as inhibitor. The small Ag NPs could be easily dispersed in organic solvent to prepare steady conductive inks. It performs well in the room temperature sintering due to the small size, high surface energy and high space utilization, forming high compact and conductive patterns. The printed samples could reach about 40% of the conductivity of bulk silver after room temperature sintering, and have a well adhesion to substrate.(3) Silver nanoellipsoids(Ag NEs) with about 40 nm in diameter of minor axis and 100 nm in major axis were prepared by a typical polyol process in the presence of PVP, using Cl- as etching agent at early stage of synthesis and PEG at later stage to control the size. The suspension of these kinds of Ag NEs can resist coffee-ring effect and deposit uniform films after drying. By contrast, suspension of spherical silver nanoparticles have badly suffered coffee-ring effect, always leaving a ring on the edge of patterns after evaporation is complete. The reasons behind these phenomena mainly attribute to the long-ranged interparticle attraction between Ag NEs that has preserved them from being transported by Marangoni flows during drying process. The Ag NEs will be very useful in preparing conductive inks. They can perform well in the solidification process of printed patterns, forming uniform and smooth films, greatly enhancing the printing efficiency.(4) A fast, convenient, low cost, high yield way to prepare silver nanowires was present through a new approach of liquid synthesis. Monodispersed silver nanowires were successfully prepared with a diameter of 40 nm and length more than 10 μm. Due to the perfect 1D structure, silver nanowires own a good electrical conductivity. The patterns directly fabricated with the silver nanowires could reach ca. 13% of the conductivity of bulk silver. After room temperature sintering, its conductivity could even climb up to 41% of the conductivity of bulk silver. Because of its simple production process, high yield, low pollution, it can be well used for large-scale preparation of conductive silver paste, to satisfy the application requirements.(5) Experiments were carried out to investigate the influence of various factors, including temperature, reaction time, reducing agent, protective agent, et al., on the shape control of silver nanostructure. Finally, monodispersed silver nanocubes were synthesized through a polyol process. It was found that the silver nanocubes could self-assemble on the substrate forming a compact 2D super lattice structure when its suspension was printed on substrate. Hence the printed pattern presents high dense and high conductive after room temperature sintering, which has potential advantages in preparation of conductive ink. The controllable synthesis provides new approach to the morphology of silver nano materials and offers an alternative selection to prepare conductive inks.