Hole stabilization and recombination in solid Ar investigated by low-energy electron stimulated desorption of neutral particles

Positive charge creation and annihilation induced by low-energy electron impact in thin Ar films (20--180 monolayers) is investigated within the 5--30-eV range by measuring the desorption of metastable particles, the emission of UV photons, and the threshold energies for these processes. The mechanisms of charge formation and electron-hole recombination are determined from measurements of the charge/discharge dependence on the duration and energy of electron irradiation. The accumulation of positive charge results from the trapping of holes in the lattice, principally at the film/vacuum interface. The localization of these holes is stable at 20 K and their migration within the Ar film after irradiation is practically absent. After electron bombardment with electrons of energy Eᵢᵣᵣ>~13eV, the positively charged films can be discharged if irradiated by electrons of lower energy. Film discharging is dominated by a single process, mainly the recombination of Ar₂⁺ centers with near thermal energy electrons.