Technical Description: Ion-based processes play a vital role in a wide range of thin-film growth, surface etching and surface modification processes. A major impediment to developing a robust understanding of surface evolution during ion bombardment has been the difficulty of quantitatively examining the kinetics of nanoscale morphology evolution. This project meets the challenge using a unique facility for in-situ x-ray surface studies developed at the National Synchrotron Light Source. In-situ grazing-incidence small-angle x-ray scattering (GISAXS) studies measure the wavenumber-dependent linear response governing the fundamental stability/instability of a surface to ion bombardment. The project pursues an integrated approach to resolve outstanding problems of ion-surface interaction along three directions. First, systematic studies of native semiconductor surface stability/instability to ion bombardment are carried out to test existing theory and provide insights for its further development. Stress development and its relationship to surface morphology evolution is an issue of particular focus. Second, nonlinear surface evolution and dynamics of the final steady-state surface morphology is examined using conventional real-time x-ray scattering and x-ray photon correlation spectroscopy, respectively. The latter technique uses a small x-ray beam, partially coherent across its width, to go beyond traditional kinetics studies. Finally, the effects of seeding are systematically examined to resolve the relative importance of stress and phase separation in driving nanostructure development.
Non-technical Description: A fundamental understanding of surface evolution during ion bombardment is an "enabling focus" because hyperthermal bombardment is so ubiquitous in surface and thin-film growth processes. Results from this research project could thus potentially impact a wide range of deposition and surface modification techniques. Moreover, the development of coherent GISAXS studies to investigate surface dynamics envisioned in this project would be a powerful tool with a broad range of potential applications in the surface growth/modification community. Graduate, undergraduate and high-school students participating in this research project have an opportunity to work in an area that bridges basic research and application. In addition to experiencing, and contributing to, an important topic in current materials research, they learn to use a wide range of characterization tools. Students interact with a growing materials research community at Boston University and the graduate student also have an excellent opportunity to participate in the multi-disciplinary synchrotron research environment.
