Growth and characterization of Ti_xNi_(1-x) shape memory thin films using simultaneous sputter deposition from separate elemental targets

摘要

The fabrication of Ti_xNi_(1-x) shape memory films using simultaneous magnetron sputtering from two separate, elemental targets was investigated. The films were deposited at room temperature and then annealed at 500℃ to achieve the shape memory effect. The influence of sputtering parameters such as power ratio to the targets (to control the composition) and Ar gas pressure (to control the film structure) were studied. It was found that the Ar gas pressure had a critical influence on the shape memory effect of the films. Characterization of the films was carried out by energy dispersive X-ray spectroscopy in a scanning electron microscope (to measure the film composition and uniformity), in situ X-ray diffraction (to identify the phase structures) and differential scanning calorimetry (to indicate the transformation and crystallization temperatures). The results showed that, by controlling the power ratio to the Ti and Ni targets and the deposition geometry, the required film compositions (Ni-rich, equiatomic NiTi and Ti-rich) could be obtained. The evolution of the transformation temperatures is found to be qualitatively comparable to bulk material. The advantage of this method is the ability to control the film composition via control of target power.