On the surface characterization of an Al2O3 charge state conversion surface using ion scattering and atomic force microscope measurements

Thermal certification campaigns in the temperature ranges of −50 °C to +85 °C and −70 °C to +130 °C on charge state conversion surfaces (aluminum-oxide coatings on a silicon wafer substrate) were performed. Such surfaces are often used in neutral particle sensing instruments in space science where neutral atoms must be ionized prior to their analysis. Ion scattering and atomic force microscope (AFM) instruments were used to characterize the surface properties, e.g., surface roughness, angular scattering distribution and negative ionization efficiency of charge state conversion surfaces before and after thermal certification campaigns. No significant changes in surface roughness were found in AFM images whereas ion scattering measurements revealed a significant increase of the angular scattering distribution of up to 21% after thermal campaign in the expanded temperature range of −70 °C to +130 °C. The present study shows clearly that ion scattering measurements are sensitive enough to measure surface changes on atomic and sub atomic level whereas at this level the AFM instrument finds its limits.