Soft-lithographic patterning of room temperature-sintering Ag nanoparticles on foil

Room temperature-sintering, poly(acrylic acid)-capped silver nanoparticles (Ag-PAA NPs) were used in a wide range of nanofabrication methods to form metallic silver microstructures on flexible poly(ethylene terephthalate) (PET) substrates. Silver wires on top of PET foil were patterned by micromolding in capillaries (MIMIC), and silver wires embedded in SU8 on PET foil were fabricated by wetting-controlled deposition in open microchannels. One hundred mu m-wide Ag microwires with lengths of 5-15 mm, heights of 0.6-2.5 mu m, and a maximum conductivity of a factor 7.3 lower than bulk Ag were obtained. Methanol was studied as an alternative dispersing solvent. It sped up MIMIC drastically, but the low particle packing quality and pre-coalescence in solution resulted in a higher resistivity. The sintering depth was found to be limited to around 100 nm for HCl-vapor induced sintering. Aqueous NaCl, added in a concentration below 50 mM to the Ag-PAA NP ink, was investigated as self-sintering agent. It resulted mainly in strong particle clustering and formation of numerous non-connected grains upon the evaporation of water. A hydrogel reservoir stamping system was used as an alternative printing technique for the transfer of the Ag-PAA NP ink on a PDMS substrate to yield the repetitive printing of arrays of 144 three-micron-wide Ag dots.