A molecular dynamics investigation of the growth and annealing mechanisms of TiNi thin films deposited on a Ni substrate

Thin films of TiNi have received considerable interest in industrial and medical fields due to their exceptional structural properties, including the shape memory effect and superelasticity. In this work, molecular dynamics simulations were selected as they have attracted significant attention in materials science and are widely used to investigate the properties of metals, alloys, semiconductors, and related materials at the atomic scale. The effects of incident energy of deposited atoms on the surface morphology, crystalline structure, density, and atomic stress of deposited TiNi films are investigated in detail. The results indicate that the film roughness decreases significantly with increasing incident energy from 0.1 to 15 eV. This behaviour can be attributed to the higher kinetic energy of the incoming atoms, which increases the frequency of surface atomic collisions. These collisions enhance atomic mobility at the surface, leading to an increase in surface energy and promoting atomic diffusion. In addition, enhanced surface collisions raise the film temperature, which stimulates atomic vibrations and facilitates atomic rearrangement. As a result, a smoother film morphology is obtained. Conversely, at low incident energies, atoms tend to agglomerate on the surface, resulting in a rougher morphology. In addition, intermixing is analysed, and the results reveal that both the penetration of Ti and Ni atoms into the substrate upper layers and the extraction of substrate atoms into the deposited film become more pronounced at an incident energy of 15 eV. The film density initially increases as the energy rises from 0.1 to 5 eV, but decreases when the energy exceeds 5 eV. This reduction in density can be attributed to the formation of internal voids within the film, resulting from intense atomic collisions that displace bombarded atoms from their equilibrium positions. This work contributes to a deeper atomic-level understanding of the deposition and growth mechanisms of TiNi thin films.