In Situ Diagnostics and Role of Light‐Induced Forces in Metal Laser Nanoprinting

Compared to 3D laser nanoprinting of polymers, the mechanisms in laser nanoprinting of metals are rather poorly understood. For the example of platinum investigated here, the printing process starts with the formation of metal nanoparticles by photo-reduction of metal salts in aqueous solution in a diffraction-limited laser focus. To investigate the printing process in situ, a weak continuous-wave probe laser is co-focused in addition to the focused femtosecond printing laser. The light of the probe laser is backscattered off the emerging metal structures, and recorded with a temporal resolution of 1 mu s. It is found that the formed metal nanoparticles are quickly ejected from the focus on a timescale of some 10 mu s. Once a nanoparticle randomly adheres to the substrate surface, it serves as a seed from which structures can be built-up. The following nanoparticles are sintered onto that seed to form a metallic voxel on a timescale of some 10 ms. By polarization-dependent experiments and full-wave optical simulations, it is shown that light-induced forces onto the nanoparticles play a significant role. The improved understanding of the microscopic processes in metal nanoprinting is a prerequisite for further process optimizations and applications, for example in terms of printed optoelectronics.