Synthesis of sub-10-nm Sn nanoparticles from Sn(II) 2-ethylhexanoate by a modified polyol process and preparation of AgSn film by melting of the Sn nanoparticles

•Ultrafine Sn nanoparticles were synthesized by a modified polyol process.•The formation of an oxide–organic complex layer on the Sn nanoparticles was confirmed.•The Sn nanoparticles exhibited an extremely low melting point of 128 °C.•The Ag/Sn composite ink containing the synthesized Sn nanoparticles was sintered.•The composite showed excellent sheet resistance even under mild sintering conditions.

Ultrafine Sn nanoparticles (NPs) (diameter < 10 nm) exhibiting a remarkable depression in their melting point were synthesized at room temperature by a modified polyol process. For the synthesis, low-grade Sn(II) 2-ethylhexanoate and sodium borohydride were used as the precursor and reducing agent in a diethylene glycol medium. Further, polyvinyl pyrrolidone was used as a capping agent during the synthesis. The synthesized crystalline Sn NPs showed an average diameter of 7.98 nm and an extremely low melting point of 128 °C. To test the applicability of the synthesized ultrafine Sn NPs to practical systems, an Ag-based composite ink containing the Sn NPs was prepared. The ink was easily sintered through local liquid-phase sintering by melting of the ultrafine Sn NPs added as a metal binder. Therefore, despite the low-temperature (170 °C) sintering with a short duration (~ 15 min), the composite ink exhibited excellent sheet resistance.