Surface Roughness Using Rutherford Backscattering

Ion bombardment has often been used to investigate the submicroscopic or atomic structure of surfaces, but rarely to look at the macroscopic structure. The nature of the surface depends on the way in which it is formed and on its crystalline or amorphous character. The processes of grinding and polishing produce periodic correlations in the surface both of ordinate and gradient. Much nondestructive information about such features of the surfaces can be obtained by Rutherford backscattering. Roughness changes the shape of the energy spectrum as compared with a spectrum from a material with a perfectly flat surface. This change can be described in terms of the surface profile and the autocorrelation function. Such information is particularly valuable for all experiments in which scattered particles are used to analyze the surface region. Roughness, for example, puts an upper limit on the depth resolution in profiling experiments. We have investigated a number of prepared surfaces, measuring proton energy spectra as a function of angle at energies in the vicinity of 400 keV. The results have been compared with analytical and computer calculations and establish a unique and new method to judge surface roughness by ion scattering.