Transmission electron microscopy study of Ni–Si nanocomposite films

Nickel induced crystallization of amorphous Si (a-Si) films is investigated using transmission electron microscopy. Metal-induced crystallization was achieved on layered films deposited onto thermally oxidized Si(3 1 1) substrates by electron beam evaporation of a-Si (400 nm) over Ni (50 nm). The multi-layer stack was subjected to post-deposition annealing at 200 and 600 °C for 1 h after the deposition. Microstructural studies reveal the formation of nanosized grains separated by dendritic channels of 5 nm width and 400 nm length. Electron diffraction on selected points within these nanostructured regions shows the presence of face centered cubic NiSi2 and diamond cubic structured Si. Z-contrast scanning transmission electron microscopy images reveal that the crystallization of Si occurs at the interface between the grains of NiSi2 and a-Si. X-ray absorption fine structure spectroscopy analysis has been carried out to understand the nature of Ni in the Ni–Si nanocomposite film. The results of the present study indicate that the metal induced crystallization is due to the diffusion of Ni into the a-Si matrix, which then reacts to form nickel silicide at temperatures of the order of 600 °C leading to crystallization of a-Si at the silicide–silicon interface.

► Ni/Si films were deposited on a substrate by electron beam evaporation technique.
► SAED & HRTEM were performed to study the crystal structure of Ni/Si film.
► Z-contrast STEM was carried to distinguish the different regions of the Ni/Si film which posses same crystal structure.
► XAS was carried to understand the nature of Ni impurity when it is diffusing in a-Si matrix
► Mechanism behind metal induced crystallization and possibility of stabilizing the metastable phases of Si are discussed.