Semigrand Canonical and Kinetic Monte Carlo simulations of binary B2-ordered nano-films with triple defects

Equilibrium atomic configurations and the kinetics of “order–order” and surface segregation processes in B2-ordering stoichiometric A-50 at.%B binary thin films are investigated by means of Semigrand Canonical Monte Carlo (SGCMC) and Kinetic Monte Carlo (KMC) simulations. The (100)-oriented films are modeled with an Ising-type Hamiltonian with previously evaluated pair-interaction energy parameters yielding the effect of “triple-defect disordering”. The SGCMC simulations provide equilibrium vacancy concentration and atomic configuration in the films with B-atom termination of both free surfaces achieved at high temperatures by the generation of an antiphase boundary. Despite strong vacancy surface segregation, the thermodynamic activation energy for their formation inside the films is the same as in the bulk material. KMC simulations implemented with the SGCMC-determined equilibrium vacancy concentration reveal very slow relaxation of the films towards equilibrium configuration. The B-termination of the (100) free surfaces is produced by A-atom diffusion inwards into the films mediated by vacancies segregating on surfaces. •“Triple-defect” (100) AB films were simulated by means of SGCMC and KMC algorithms.•B2 superstructure stability decreased with decreasing film thickness.•The activation energy for vacancy formation was equal to that in the bulk.•The B-termination of film surfaces resulted from A-atom diffusion into the films.•The model indicates structural metastability of the deposited NiAl layers.