Formation of intermetallic phase in Ni/Ti multilayer structure by ion implantation and thermal annealing

Ion implantation and thermal annealing effects on composition and structure of Ni/Ti multilayer have been studied and reported in this paper. The thin films composed of five (Ni/Ti) bilayers were deposited by d.c. ion sputtering on (100) Si wafers to a total thickness of ∼180 nm. Ion irradiations were performed by 180 keV Ar+ ions with fluence of 6 × 1016 ions cm−2. After deposition and implantation, the samples were annealed at 400 °C for 30 min in an inert ambient. Composition and structural characterizations were performed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Annealing of as-deposited samples at 400 °C induces a progressed interaction between Ni and Ti layers with the initial formation of NiTi alloy phase. Progressed alloying was achieved for the ion fluence of 6 × 1016 ions cm−2 and the formed structure is composed of NiTi compound, only at depth around the projected ion range. In the deeper layers, beyond the projected range of implanted ions, the diffusion of Ni atoms can lead to solid state amorphization. Subsequent annealing at 400 °C for 30 min enabled enhanced interaction between intermixed Ni and Ti layers, and in the layers close to the Si substrate the conditions for the formation of intermetallic compound are created.

► Ni/Ti multilayer system is modified by ion implantation and thermal annealing. ► Thermal annealing is induced initial formatiom of NiTi intermetallic compound. ► NiTi nanoalloy phase is formed at room temperature after Ar ion implantation. ► Subsequent annealing of implanted Ni/Ti multilayer is enhanced formation of NiTi nanoalloy.