The irradiation of solid materials with ion beams holds great promise for shape and surface control in materials processing at the nanoscale. When materials are irradiated by ions at sufficiently low energies that the ions don't penetrate into the bulk but rather stay near the surface, several interesting phenomena are observed. Certain irradiation conditions lead to ultra-smoothing, which has important potential applications in fields ranging from X-ray optics to light trapping devices to surgery tools. Under other conditions, one observes self-organized arrays of nanoscale surface ripples, mounds, or pits, with potential applications in fields such as optoelectronics. Although both phenomena are potentially rich sources of technological applications, currently the fundamental physical mechanisms determining ultra-smoothing or self-organized behavior are not well understood. The project is a tightly-integrated experimental (Harvard University) and theoretical (Southern Methodist University) study of the fundamental physical principles governing nanoscale morphology evolution during ion irradiation. The research activities are integrated with educational activities to train graduate students in nanoscience and nanotechnology.
This collaborative project explores the fundamental physical mechanisms of both the nanoscale topographic pattern formation by a high energy ion beam at a glancing incident angle, and the ultra-smoothing using low energy ion beam irradiation. The ultimate goal is to develop deep understanding and theory that could predict the outcome of arbitrary irradiation conditions. An important aspect of the project is the combined experimental approach and atomistic simulation to identify individual (nano-scale) ion impacts and correlate them with observed (macro-scale) morphological evolution. On one hand, a new multi-scale theoretical framework promises the ability to identify, via atomistic simulation, the atomistic origin of continuum effects such as stress. On the other hand, access to versatile experimental facilities allows measuring the continuum behavior and the critical material properties and testing theoretical predictions.