Monolayer-protected silver nanoparticles were directly synthesized in a highly concentrated organic phase (>2 M) and then printed into conductive lines on polyimide by a drop-on-demand inkjet printer. The fully organic phase system contains silver nitrate as a silver precursor, n-butylamine as a media dissolving silver salt, dodecanoic acid as a capping molecule, toluene as a solvent, and sodium borohydride as a reducing reagent. Even using only generic chemicals, monodispersed silver nanocrystals with size of 7 nm were easily synthesized at the 100 g scale in a 1 litre reactor. Hydrocarbon monolayer-protected silver nanocrystal showed excellent dispersion stability even at metal content >70 wt%. The silver ink with metal content of 33 wt% had a viscosity of 5.4 cP and surface tension of 25 dyn cm −1 . The silver ink was successfully inkjetted on variable substrates and then metallized at 250 • C. The metallized silver patterns exhibited very low specific electrical resistance (6 µ cm)

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In this study, we attempted to synthesize organic-soluble silver nanoparticles in the concentrated organic phase with an environmentally friendly method. The fully organic phase system contains silver acetate as a silver precursor, oleic acid as both a medium and a capping molecule, and tin acetate as a reducing agent. Monodisperse silver nanoparticles with average diameters of ca. 5 nm can be easily synthesized at large scale. Only a small usage of tin acetate (<0.05 eq.mol) resulted in a high synthesis yield (>90%). Also, it was investigated that the residual tin atom does not exist in the synthesized silver nanoparticles. This implied that tin acetate acts as a reducing catalyst.

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The microstructure and electrical resistivity of inkjet-printed silver (Ag) films annealed under ambient air were characterized. Analyses of the impurity amounts in the films using secondary-ion mass spectrometry showed that the decomposition temperature of the capping molecules was just below 170 C. Both the characteristics of the microstructure and electrical resistivity when annealed at low temperatures (lower than the decomposition temperature) were significantly different from those when annealed at high temperatures. The results show that neither microstructural features, such as grain size, nor the amounts of impurities can explain both the magnitude and characteristic decrease in electrical resistivity. The changes in electrical resistivity can be described using exponential decay kinetics. The corresponding activation energy of 0.44 eV when annealed at the high temperatures is explained by the migration of point defects such as vacancy-oxygen pairs. On the other hand, negligible dependence on temperature was identified when annealed at low temperatures, which was attributed to decomposition of the capping molecules. The results indicate the importance of controlling the defects of nanoparticles and the properties of capping molecules from the viewpoint of electrical optimization of metallization fabricated using inkjet printing.