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

¹  Department of Physics, University of Helsinki - P.O. Box 43, FI-00014 Helsinki, Finland, EU
²  IFW Dresden, Institute for Metallic Materials - P.O. Box 270116, D-01171 Dresden, Germany, EU
³  Institut für Materialwissenschaft, Technische Universität Darmstadt - Petersenstr. 23, D-64287 Darmstadt, Germany, EU
⁴  Institute of Ion Beam Physics and Materials Research, Forschungszentrum Rossendorf - P.O. Box 510119, D-01314 Dresden, Germany, EU

Corresponding author: tommi.t.jarvi@helsinki.fi

Received: 14 August 2008
Accepted: 13 December 2008

Abstract

We present experimental evidence for structural transformation 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.