Modeling structural metastability of irradiated thin films

The nucleation of crystalline or amorphous phases in irradiated binary metallic, as well as non-metallic compound thin films is interpreted using the atomistic interface migration-charge transfer (IMCT) model. The space and time evolution of dense collision cascades, which form upon ion bombardment of the target, lead to non-equilibrium compositional and electronic density profiles at the interface between each cascade and the surrounding crystalline matrix. This occurs because one of film constituents preferentially migrates to the interface, which becomes enriched in it. Cascade relaxation to metastable equilibrium is simulated by local charge transfer reactions (CTR), each involving a pair of dissimilar atoms of the initial compound, which constitute a dimer of an effective compound. The energy cost to introduce an effective compound dimer into the matrix, the difference of formation enthalpy between effective and initial compound and the local strain suffered by the film as a consequence of ion formation by a CTR are evaluated. Threshold values are found in the above structure stability parameters that allow for a qualitative separation of amorphised from crystalline compounds, both metallic and non-metallic.