The effect of deposition rate and thermal annealing on morphology and microstructural evolution of Nickel-Bismuth thin film

Bismuth/Nickel thin films were deposited on borosilicate glass substrates using an electron beam evaporator equipped with thickness monitor. Thin film of Bi (10 nm) was deposited on top of pre-deposited Ni (10 nm) film at 0.6 and 1.8 Å/second deposition rates. The samples were then annealed at temperatures between 60 °C and 260 °C for 1 to 5 h under vacuum of ~ 1 × 10− 6 mbar. Scanning electron microscopy was used to investigate surface morphology. Scanning electron microscopy images depicted islands at all temperatures including the as-deposited sample. High resolution transmission electron microscopy reveals highly crystalline film and nanowires with energy dispersive x-ray spectroscopy showing that the film and nanowires were formed by Bi and Ni elements with oxygen as impurity. Rutherford backscattering spectrometry revealed intermixing of layers at the interface. Furthermore, spontaneous formation of NiBi3 and NiBi stoichiometry was observed attributed to reaction-diffusion mechanism during deposition. X-ray diffraction revealed structural transformation of the films from amorphous (as-deposited) to polycrystalline hexagonal β-NiBi crystal structure at 60 °C to 200 °C. X-ray diffraction pattern also revealed hexagonal crystal lattice with preferential growth orientation along the [1 0 1] plane with other supported planes [0 0 2], [1 0 2], [1 1 0] and [1 0 3]. The results pointed toward successful utilization of this approach to prepare templates for the synthesis of well controlled, vertically aligned and well distributed crystalline nanowires of Ni-Bi binary system more relevant to the industrial application.