Using Thermal Crowding to Direct Pattern Formation on the Nanoscale.

Metal films and other metal geometries of nanoscale thickness deposited on an insulating substrate, when exposed to laser irradiation, melt and evolve as fluids as long as their temperature is sufficiently high. This evolution often leads to pattern formation, which may be influenced strongly by material parameters that are temperature dependent. In addition, the laser heat absorption itself depends on the time-dependent metal thickness. Self-consistent modeling of evolving metal films shows that, by controlling the amount and geometry of the deposited metal, one can control the instability development. In particular, we demonstrate the "thermal crowding" effect: additional metal leads to elevated temperatures, which strongly influence the metal evolution, even if the metal geometries are disjoint. We demonstrate that the communication of disjoint metal domains occurs via heat diffusion through the underlying substrate. Fully self-consistent modeling focusing on the dominant effects, as well as accurate time-dependent simulations, allow us to describe the main features of thermal crowding and provide a route to control fluid instabilities and pattern formation on the nanoscale.