Atomistic growth mechanisms of Ni<sub>55</sub>Ti<sub>45</sub> thin films on stepped Ni substrates: A molecular dynamics study.

Abstract

<h4>Context</h4>Surface defects, such as steps and ledges, significantly modify the local energy landscape of crystalline substrates, thereby affecting adsorption, diffusion, and mixing during alloy thin-film growth. However, the atomistic mechanisms of alloy deposition on stepped metallic surfaces, particularly for NiTi systems, remain poorly understood. In this work, molecular dynamics simulations are employed to investigate the growth behavior of Ni₅₅Ti₄₅ thin films deposited on Ni substrates with different step geometries. The effects of incident angle, step width, surface configuration, substrate temperature, and incident energy on surface morphology, interfacial mixing, and structural evolution were systematically analyzed. The results indicate that stepped substrates significantly enhance interfacial atomic mixing compared to flat surfaces, while step width has a limited effect on surface roughness but strongly influences intermixing at the upper terrace. Increasing the incident angle intensifies shadowing effects, leading to higher surface roughness. Radial distribution function and common neighbor analyses confirm that all deposited films remain predominantly amorphous. Elevated substrate temperature promotes surface relaxation, whereas higher incident energy enhances interfacial mixing. These findings provide atomistic insight into NiTi thin-film growth on defected substrates.<h4>Methods</h4>Classical molecular dynamics simulations were carried out using the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS). Structural evolution and atomistic mechanisms were analyzed with the Open Visualization Tool (OVITO). The surface mesh construction, radial distribution functions (RDF), common neighbor analysis (CNA), and atomic coordination analysis are used to elucidate interfacial mixing and structural evolution during thin-film growth.