Ultrafast, scalable laser photothermal synthesis and writing of uniformly dispersed metal nanoclusters in polymer films

This paper presents a fast CO₂ laser synthesis and writing technique - laser photothermal synthesis and writing (LPSW) - to generate and write a high concentration of unaggregated, spherical sub-10 nm metal nanoparticles (sMNPs). The method is generic, and we demonstrate the fabrication of Ni, Cu, and Ag directly in polymer thin films. A partly IR-absorbing thin polymer film can be heated by the laser to high temperatures in a short time, triggering metal-reduction, nucleation, and growth. Rapid quenching of polymer films suppresses particle diffusion and traps the generated sMNPs in the polymer film. As a result, these particles are immobilized in the laser illuminated spot ("written" by the laser) on quenching. Here, Ag-polymer films are used as a model to demonstrate how laser parameters - pulse duration, laser energy flux, and number of pulses (pulsed thermal load) - can be varied to tune particle size distributions of metal sMNPs. Using this approach, we have been able to generate 4-12 nm Ag sMNPs with thermal pulses as short as 35 ms. Fast heating timescales employed in this approach allow for the scalable manufacturing of high yields of metal sMNPs, which we estimate to be around 1 g min^-1. This rapid, general synthesis and writing technique may have potentially important applications in fast, large-scale additive manufacturing and patterning of metal-loaded polymer multilayers, flexible electronics, and sensors.