Mechanism of remote vacancy emergence by a supersonic crowdion cluster in a 2D Morse lattice

Abstract

The supersonic M×N-crowdions are excited in a two-dimensional lattice by giving sufficiently large initial velocity v to the M×N block of atoms along a close-packed direction, where N is the number of neighboring atoms in one close-packed row and M is the number of neighboring rows. In this study, dynamics of a pair of quasi-1D supersonic 1×2-crowdions moving in parallel close- packed atomic rows separated by one non-excited atomic row (middle row) are investigated in 2D triangular Morse lattice by means of molecular dynamics simulations. It is shown that when a certain threshold excitation energy value is exceeded, the motion of these two 1×2-crowdions leads to creation of a remote vacancy in the middle row at a significantly long distance from the initiation point at the moment, when the supersonic stage of the crowdion propagation turns into subsonic one. This distance is directly proportional to the excitation energy of the 1×2-crowdion pair. The mechanism of vacancy formation is related to appearance of a Frenkel pair in the middle row, namely an immobile vacancy and an interstitial atom, which, together with the two interstitials in the outermost rows, forms the stable subsonic 3×1-crowdion cluster. It is concluded that the crowdion propagation can be accompanied by not only mass transfer but also plays a role in the formation of atomic vacancies inside crystal lattices.