From multiply twinned to fcc nanoparticles via irradiation-induced transient amorphization

We present experimental evidence for structural trransformation of multiply twinned CuAu nanoparticles to single crystalline morphology by 0.5 keV helium irradiation. This finding is unexpected as the stability of twin boundaries should not be affected by ion-beam induced Frenkel pairs. Molecular dynamics simulations reveal, however, a new transformation mechanism based on transient amorphization of the particle. By comparing with irradiation simulations of elemental nanoparticles, as well as alloyed bulk samples and surface cascades, we show that this transformation route is only present in alloyed particles. Moreover, the observed amorphization is more efficient for twinned than single-crystalline particles. This, together with the fast recrystallization kinetics in CuAu, explains the experimentally observed untwinning process.