Binary and ternary NiTi-based shape memory films deposited by simultaneous sputter deposition from elemental targets
- Department of Materials Science and Metallurgy, Device Materials Group, Cambridge University, Pembroke Street, Cambridge CB2 3QZ (United Kingdom)
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 Ni{sub 100-x}Ti{sub x} 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 deg. 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 deg. 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 deg. 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.
- OSTI ID:
- 20723055
- Journal Information:
- Journal of Vacuum Science and Technology. A, Vacuum, Surfaces and Films, Vol. 23, Issue 5; Other Information: DOI: 10.1116/1.2011404; (c) 2005 American Vacuum Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 0734-2101
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ANNEALING
ATOMIC FORCE MICROSCOPY
AUSTENITIC STEELS
CALORIMETRY
CHEMICAL ANALYSIS
CRYSTALLIZATION
DEPOSITION
HAFNIUM ALLOYS
MORPHOLOGY
NANOSTRUCTURES
NICKEL ALLOYS
SCANNING ELECTRON MICROSCOPY
SHAPE MEMORY EFFECT
SUBSTRATES
TEMPERATURE RANGE 0273-0400 K
TEMPERATURE RANGE 0400-1000 K
THIN FILMS
TITANIUM ALLOYS
X-RAY DIFFRACTION
X-RAY SPECTROSCOPY