Dynamics of laser induced metal nanoparticle and pattern formation


C E Rodriguez

Discontinuous metal films are converted into either almost round, isolated, and randomly
distributed nanoparticles (NPs) or fringed patterns of alternate non transformed film and NPs by
exposure to single pulses (20 ns pulse duration and 193 nm wavelength) of homogeneous or
modulated laser beam intensity. The dynamics of NPs and pattern formation is studied by
measuring in real time the transmission and reflectivity of the sample upon homogeneous beam
exposure and the intensity of the diffraction orders 0 and 1 in transmission configuration upon
modulated beam exposure. The results show that laser irradiation induces melting of the metal
either completely or at regions around intensity maxima sites for homogeneous and modulated
beam exposure, respectively, within 10 ns. The aggregation and/or coalescence of the initially
irregular metal nanostructures is triggered upon melting and continues after solidification
(estimated to occur at 80 ns) for more than 1 ls. The present results demonstrate that real time
transmission rather than reflectivity measurements is a valuable and easy-to-use tool for following
the dynamics of NPs and pattern formation. They provide insights on the heat-driven processes
occurring both in liquid and solid phases and allow controlling in-situ the process through the fluence.
They also evidence that there is negligible lateral heat release in discontinuous films upon
laser irradiation.

Artículo-CERG 2 2015