LOCAL STRESS-RELAXATION IN THERMAL SPIKES AS A POSSIBLE CAUSE FOR CREEP AND MACROSCOPIC STRESS-RELAXATION OF AMORPHOUS SOLIDS UNDER IRRADIATION

Under energetic particle bombardment, stress-free and substrate-bound amorphous films show substantial creep and stress relaxation. A visco- elastic model is described in which these phenomena are attributed to local shear stress relaxation in thermal spikes induced by the energy transfer from the projectile particle to the target, followed by freez ing-in of the associated strain increments during cooling down. For pr onounced thermal spikes, simple asymptotic expressions are derived and compared with experimental results.