Insights into NinTim clusters adsorption and diffusion on B2-NiTi phase from atomistic simulations

L El Atouani and K Sbiaai and A Hasnaoui, SURFACE SCIENCE, 701, 121655 (2020).

DOI: 10.1016/j.susc.2020.121655

In this work, we aim to study the adsorption and migration of NinTim (n,m = 1-4) clusters on low-index B2-NiTi surfaces (100), (110) and (111). Ni and Ti diffusion was investigated using molecular static simulations with the conjunction of the MEAM formalism to describe atomic interactions. Ni-rich clusters are found to be more mobile than Ti-rich ones on Ni- and Ti-terminated (100) surfaces. On the other hand, the activation energy of Ni diffusion on the mixed (110) is found to be 0.51 eV, while that on Ni- and Ti-terminated (111) surfaces corresponds to barriers of 0.61 eV and 0.71 eV, respectively. These results demonstrate that on the (110) surface, a high thermal activity of clusters is expected due to the lower migration barriers. In addition, the diffusion mechanisms of Ti and Ni adatoms are quite similar and are characterized by a hopping mechanism between adsorption sites. While for the small cluster diffusion such as dimers, trimers and tetramers a variety of mechanisms is noted. Using classical molecular dynamics, we found that at 800 K, the Ni-terminated (100) and Ti- terminated (111) surfaces show an important segregation effect of Ni atoms on the surface. We have also found that the homogenous Ti clusters are stable on most surfaces with slight changes of their forms. While Ni clusters are found to show less stability with a higher mobility of their dissociated atoms.

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