In situ characterization of NiTi based shape memory thin films by optical measurement
Résumé
In this note, we present an alternative in situ approach to determine the phase transformation temperatures of sputter deposited NiTi based shape memory thin films atop a substrate. Reflection in three thin films upon thermal cycling was measured with a reflection spectrometer in a wavelength range from 360 nm to 2 μm. Subsequently, the relationship of the reflection change versus temperature was obtained, which shows obvious hysteresis, clear evidence of the phase transformation. Hence, the transformation temperatures were determined and then compared with the result of the differential scanning calorimeter test; good agreement was observed. Additionally, we started modeling the phenomenon by identifying and quantitatively estimating four potential contributors to the change of reflection during phase transformation in deposited shape memory thin films.