Nanometer-scale droplet formation and motion under the effects of a focused ion beam is described using a continuum model that combines a thin-film fluid model for dynamics with a Cahn-Hilliard type model for chemical diffusion and phase separation. The focused ion beam (FIB) is represented as a time and space dependent mass and chemical species source. Drops form and move due to the combined effects of a concentration-dependent surface energy, a concentration gradient on the edges of the droplet, and a beam angle-dependent net FIB incoming mass flux. The velocity is comparable to observations, and it has a similar dependence on the beam angle of incidence. Likewise, the ion dose at which droplets reach a width of 60 nm is in good agreement with experiments. The model also explains the biased motion of droplets under a raster-scan pattern focused ion beam.
ASJC Scopus subject areas
- Physics and Astronomy(all)