Influence of thermal effects on stability of nanoscale films and filaments on thermally conductive substrates

TL;DR

This study uses coupled fluid and thermal simulations to analyze how temperature-dependent material properties affect the stability and evolution of nanoscale metal films and filaments on thermally conductive substrates under laser heating.

Contribution

It introduces a self-consistent Volume-of-Fluid simulation approach that accounts for thermal effects on surface tension and viscosity, revealing their impact on film stability and evolution.

Findings

Temperature variation of surface tension influences interface oscillations.

Viscosity changes affect the wavelength of instabilities.

Filament stability is less sensitive to temperature-dependent properties.

Abstract

We consider films and filaments of nanoscale thickness on thermally conductive substrates exposed to external heating. Particular focus is on metal films exposed to laser irradiation. Due to short length scales involved, the absorption of heat in the metal is directly coupled to the film evolution, since the absorption length and the film thickness are comparable. Such a setup requires self-consistent consideration of fluid mechanical and thermal effects. We approach the problem via Volume-of-Fluid based simulations that include destabilizing liquid metal-solid substrate interaction potentials. These simulations couple fluid dynamics directly with the spatio-temporal evolution of the temperature field both in the fluid and in the substrate. We focus on the influence of the temperature variation of material parameters, in particular of surface tension and viscosity. Regarding variation of surface tension with temperature, the main finding is that while Marangoni effect may not play a significant role in the considered setting, the temporal variation of surface tension (modifying normal stress balance) is significant and could lead to complex evolution including oscillatory evolution of the liquid metal-air interface. Temperature variation of film viscosity is also found to be relevant. Therefore, the variations of surface tensions and viscosity could both influence the emerging wavelengths in experiments. In contrast, the filament geometry is found to be much less sensitive to a variation of material parameters with temperature.