Elastic instability in Ge_(1-x)S_x alloys under heavy-ion .irradiation

摘要

We report Brillouin scattering measurements of heavy-ion-irradiated Ge_(1-x)S_x alloys, from which we infer the existence of an instability in the elastic properties, in which the bulk modulus in the amorphized state decreases drastically under continued irradiation. This instability results in the formation of a low-density void-containing 'spongy' state upon further irradiation. Variations in the elastic wave velocity with alloy concentration in the spongy state can be explained by the balance between the enhancement of dynamic annealing caused by the presence of Si and the preferential formation of dangling bonds on Ge sites compared with Si sites. This preference for Ge rather than Si dangling bonds may also lead to a migration of the Si atoms away from surfaces, which results in an increase in the sound velocity.