A time-resolved shadowgraphic study of laser transfer of silver nanoparticle ink

The dynamics of liquid phase laser induced forward transfer (LIFT) of silver nanoparticle (NP) ink (particle size 30–50 nm) was investigated by time-resolved shadowgraphic imaging. LIFT was carried out by a KrF excimer laser (248 nm, 35 ns) using two donor substrate configurations: (a) a wet silver NP ink layer spread on a quartz substrate and (b) a wet silver NP ink layer spread on a quartz substrate covered by a 40 nm thick titanium layer. This comparative study revealed a completely different ejection mechanism for the two different donor configurations. The use of the titanium dynamic release layer (DRL) resulted in a highly directional and low velocity ejection of the material for a wide range of laser fluences. On the other hand, LIFT of silver NP ink without using the titanium DRL provoked supersonic velocity ejection and shock wave generation for laser fluences even slightly above the ejection threshold. The velocity of the ejected material (13–240 m/s) in the case of titanium DRL assisted LIFT was significantly lower than the one observed without using DRL (106–830 m/s). The use of the titanium DRL layer expanded, significantly, the processing window for directional and low velocity ejection of the silver NP ink.