Laser heating and melting of metals on the nanoscale: Breakup of metal filaments and thermal crowding

We apply our recently developed mathematical model to study the instability and breakup of metal filaments exposed to heating by laser pulses and placed on thermally conductive substrates. One notable aspect of this setup is that the heating is volumetric since the absorption length of the laser pulse is comparable to the typical filament thickness. In such a setup, the absorption of thermal energy and the filament's evolution are coupled and must be considered self-consistently. Our model enables significant simplification, which is crucial for understanding the main physical effects—including the relevance of the Marangoni effect and the temperature dependence of fluid viscosity and thermal conductivity — and for developing efficient simulations of filament evolution and subsequent nanoparticle formation. We focus particularly on the influence of thermal crowding, meaning that the evolution of the filaments depends on their size and number. This discovery opens the door to considerations of self- and directed-assembly of metal nanoparticles through a suitable choice of the initial metal geometry on the nanoscale. We illustrate some possibilities by arranging nanoscale structures to achieve controlled breakup of metal filaments at desired locations. More details can be found in recent research papers, including Phys. Rev. Lett. vol. 133 (214003), Phys. Rev. Fluids vol. 7 064001 (2002), and J. Fluid Mech. vol. 915, A133 (2021).