Simulation of laser-induced nanopattern formation

Abstract

Over the last decade it has been shown theoretically and experimentally that a near-resonant standing wave light field can be used during deposition to deflect collimated neutral atoms, thereby constraining them to form periodic structures. Another effect studied in recent experiments is that a laser interference pattern in contact with a substrate can also result in patterns mimicking the interference fringes. This patterning has tentatively been attributed to thermal gradients resulting from non-uniform heating induced by the interference patterns. We developed a model and a computer program to investigate the possibility of making these two laser effects interact constructively to refine the resolution. The simulations proceed in two stages: first, atom trajectories in a laser field are simulated using classical-mechanical equations of motion in an effective potential to obtain the deposition profile; then, the obtained profile is used as an input in a kinetic Monte Carlo (KMC) simulation of atom diffusion on a substrate with spatially varying temperature. Our results show substantial improvement in quality of the patterns compared to that achieved by using either effect alone. We examine many growth conditions in addition to the different laser parameter settings for optimal constructive interference of the two effects. The computer code used in the simulations is designed to run efficiently on both simple PC platforms and supercomputers; its design, data structures used and other features are described in detail.