Quantitative Determination of Ion Impact-induced Smoothing on Sapphire Surfaces

Abstract

Format

This is a copy of the slides presented at the meeting but not formally written up for the volume.

Abstract

Surface morphology modification by low-energy ion bombardment is widely used in many thin film techniques such as sputter deposition, ion-beam-assisted growth and ion polishing, in order to obtain smooth surfaces desirable for device applications. Under certain circumstances, ion bombardment on surfaces is also known to produce 2-D (ripples or wires) and 1-D (dot) structures by a self-organization process that arises from a competition of a roughing instability mechanism and surface relaxation. Knowledge of the mechanisms which govern those surface processes is very crucial to engineer technologically significant surface morphologies at the submicron or nano-scale in a more controlled way. Recently, the fast-growing advances in synchrotron x-ray scattering and detector techniques have enabled detailed investigations into the surface kinetics during ion bombardment. In this work, a study of surface smoothing on nanocorrugated sapphire surfaces by low-energy ion bombardment at normal incidence will be presented. Real time characterization by synchrotron grazing incidence small angle x-ray scattering for the dependence of smoothing rate on ion energy and wavelength of sapphire ripples is performed. A ripple amplitude displays a classic behavior of profile-preserving exponential decay with time upon ion irradiation. The dependence of smoothing rate on ion energy and wavelength is discussed with existing surface smoothing mechanisms. The wavelength dependence exhibits a power law behavior with exponential close to 2 instead of 4, which suggests a dominant smoothing mechanism related to ion impact induced lateral mass redistribution for near normal incidence condition. The appearance of multiple smoothing rate constants at high temperature is thought to be relative with emerging atomic steps after surface recrystallization.