Influence of annealing temperature on the structural, morphological, mechanical and surface properties of near equiatomic NiTi thin films

In this work, we report our studies on near equiatomic NiTi thin films grown on silicon (1 0 0) substrates deposited without intentional heating of the substrate by DC magnetron sputtering technique with separate elemental targets Ni and Ti. The films were annealed for one hour at various temperatures, i.e. 350, 450, 550 and 650 °C. X-ray diffraction (XRD) studies revealed that the degree of crystallinity increases up to 550 °C but decreases at 650 °C. The surface roughness value Rq, Ra and Rmax have been obtained by Atomic Force Microscopy (AFM). The hardness and elastic modulus values increase up to 550 °C and decreases at 650 °C. High Resolution X-ray Photoelectron Spectroscopy (HR-XPS) studies revealed that the annealed near equiatomic NiTi thin films have a strong tendency to form TiO2 (metal oxide) layer onto the film surface. This is due to the higher thermodynamic reactivity of Ti by leaving Ni-rich matrix trapped behind, most likely in the sub layers of NiTi along with Titanium carbide (Ti-C) and Silicon carbide (Si-C) precipitates.