Scattering of fast protons on densely stepped surfaces of ionic crystals

The surfaces of KCl crystals were sputtered by irradiation with 5 keV electrons (500 μA/m2), in order to create a high density of surface steps. Energy loss distributions of 550 keV protons at glancing angle incidence scattered from the (001) surface were then measured for random (100 mrad off 〈100〉 direction) and surface-channeling (〈100〉 direction) conditions. The surfaces were examined using atomic force microscope (AFM) in air. The measured energy spectra of protons were compared with those calculated by computer simulation. For random incidence, the fraction of the projectiles which penetrate through the surface increases with increasing dose of electron-irradiation. These protons pass through the steps both at the entrance and the exit. For the case of channeling incidence, this fraction decreases with increasing electron-irradiation dose in the dose range from 1019 m−2 to 1020 m−2, because the projectiles do not necessarily pass through the surface steps. AFM observations show that there are many steps of several to several tens of monolayers' height on the surface for samples irradiated with doses of more than 1 × 1020 m−2.