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Binary and ternary NiTi-based shape memory films deposited by simultaneous sputter deposition from elemental targets

Sanjabi, S ; Sharif University of Technology | 2005

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  1. Type of Document: Article
  2. DOI: 10.1116/1.2011404
  3. Publisher: 2005
  4. Abstract:
  5. The most challenging requirement for depositing NiTi-based shape memory thin films is the control of film composition because a small deviation can strongly shift the transformation temperatures. This article presents a technique to control film composition via adjustment of the power supplied to the targets during simultaneous sputter deposition from separate Ni, Ti, and X (e.g., Hf) targets. After optimization of sputter parameters such as working gas pressure, target-substrate distance, and target power ratio, binary Ni100-x Tix thin films were fabricated and characterized 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). To explore the possibility of depositing ternary shape memory NiTi-based thin films with a high temperature transformation >100 °C, a Hf target was added to the NiTi deposition system. Annealing was carried out in a high vacuum furnace slightly above the films' crystallization temperatures (500 and 550 °C for NiTi and NiTiHf films, respectively). Differential scanning calorimetry (DSC) results of free-standing films illustrated the dependence of transformation temperatures on film composition: Ap and Mp (referring to the austenitic and martensitic peaks in the DSC curve) were above room temperature in near equiatomic NiTi and Ti-rich films, but below it in Ni-rich films. In NiTiHf films, the transformation temperatures were a function of Hf content, reaching as high as 414 °C (Ap) at a Hf content of 24.4 at. %. Atomic force microscopy revealed nanostructure surface morphology of both NiTi and NiTiHf films. Detailed characterization showed that the film properties were comparable with those of NiTi and NiTiHf bulk alloys. © 2005 American Vacuum Society
  6. Keywords:
  7. Composition ; Differential scanning calorimetry ; Mathematical transformations ; Morphology ; Scanning electron microscopy ; Shape memory effect ; Sputter deposition ; Thin films ; X ray diffraction ; X ray spectroscopy ; Film composition ; Gas pressure ; Shape memory films ; Ternary shape ; Nickel
  8. Source: Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films ; Volume 23, Issue 5 , 2005 , Pages 1425-1429 ; 07342101 (ISSN)
  9. URL: https://avs.scitation.org/doi/10.1116/1.2011404