Laser-induced forward transfer of silver nanoparticle ink: time-resolved imaging of the jetting dynamics and correlation with the printing quality

In this work, we used time-resolved imaging to study the dynamics of the laser-induced forward transfer (LIFT) process of a silver nanoparticle (NP) ink (NP size: 30-50 nm). LIFT is a versatile direct write technique in which a variety of functional materials can be transferred from a donor substrate to a receiving substrate with high spatial resolution. Two different LIFT configurations were employed: (a) dynamic release layer (DRL)-assisted LIFT, in which direct expose of the silver NP ink to laser irradiation is prevented, and (b) DRL-free LIFT, in which the silver NP ink is exposed to laser irradiation. Jetting dynamic behavior, initiated by a cavitation bubble generation and expansion, was observed in both LIFT configurations. However, jetting dynamics were significantly milder in the case of DRL-assisted LIFT, resulting in a wide laser fluence processing window (100-230 mJ/cm(2)) for high uniformity and reproducibility printing of silver NP ink droplets. On the contrary, DRL-free LIFT resulted in smooth jetting dynamics only for a narrow laser fluence window (30-40 mJ/cm(2)). The explanation of the different dynamics is based on the different mechanisms that govern the conversion of the laser pulse energy to a dynamic cavitation bubble for each LIFT configuration, i.e., (a) heat diffusion, mediated by the DRL layer, in DRL-assisted LIFT and (b) microcavitation around the silver NPs due to near field enhancement when no DRL is used. In addition, the mechanism of formation of undesirable satellite droplets around the main deposited droplets was studied by using a flexible polymeric receiving substrate. The importance of the smooth jetting behavior, achieved by DRL-assisted LIFT, was highlighted for high-resolution printing of silver NP ink as well as for ensuring enhanced LIFT processing stability.