NiAl (0 0 1) terminated surface effect on the growth of the Al thin film

Abstract

In this work, NiAl alloy material was adopted as a substrate surface to investigate the formation process of Al thin film using molecular dynamics simulation. The NiAl (001) substrate with both Al-terminated and Ni-terminated surface was considered to identify their effect on the growth behavior of Al thin film. The results show that Al atoms follow initially bilayer-like growth mode for both terminated surfaces. At this stage, the film seemed to adopt the fourfold geometry with (001)-orientation. However, upon further deposition, the Al adatoms behavior on the Al-terminated surface becomes different from that on the Ni-terminated surface. The stress analysis along the growth direction indicates that the Al film on the Al-terminated surface has a compressive stress in the bulk film, while on the Ni-terminated surface, the Al film has a tensile stress. These results have a significant effect on the lattice parameter when the Al film exceeds four layers. By using the radial distribution function, we demonstrate that when Al film is deposited on Al-terminated surface, its lattice parameter is changed until 2.85Å, which close to the Al-Al bulk, but on the Ni-terminated surface this value becomes 2.49Å, which is near to the Ni-Ni bulk. These behaviors indicate that Al atoms on (Al or Ni)-terminated are arranged differently. For this, the Al film structure was characterized by common neighbor analysis. It is found that the Al atoms are arranged within the fcc structure for Al-terminated, but for Ni-terminated, the result shows the appearance of the fcc and hcp structures. On the other hand, the surface roughness investigated at 0.1 eV showed that the Al film has a rough surface morphology when deposited on Al-terminated compared to that obtained on Ni-terminated. However, by increasing the incident energy from 0.1 to 2 eV, the surface roughness decreases significantly for both terminated surfaces.