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The Effect of Film Thickness on Stress and Transformation Behavior in Cobalt Thin Films

Published online by Cambridge University Press:  10 February 2011

H. Th. Hesemann
Affiliation:
Max-Planck-Institut für Metallforschung, and Universität Stuttgart, Institüt für Metallkunde, Stuttgart, Germany
P. Müllner
Affiliation:
ETH Zürich, Institut für Angewandte Physik, Zürich, Switzerland
O. Kraft
Affiliation:
Max-Planck-Institut für Metallforschung, and Universität Stuttgart, Institüt für Metallkunde, Stuttgart, Germany
E. Arzt
Affiliation:
Max-Planck-Institut für Metallforschung, and Universität Stuttgart, Institüt für Metallkunde, Stuttgart, Germany
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Abstract

Pure cobalt shows a martensitic transformation from a face-centered-cubic to an hexagonal-close-packed phase. In this work it is chosen as a model-system to investigate the influence of film thickness, film stress and microstructure on the martensitic transformation in thin films.

Co films of 0.2 μm to 3.0 μm thickness were sputter-deposited on Si substrates. This paper presents wafer curvature measurements during temperature cycles of these films and results obtained by focused ion beam microscopy. Upon repeated thermocycling, the martensitic transformation was repeatedly observed in 3 μm thick films, whereas it was not found in 0.2 μm Co films. A stress drop on heating as well as on cooling accompanied the martensitic transformation. It was observed that the stress level at which the transformation occurs can be changed by varying the film thickness or maximum temperature of the temperature cycles. As a result, the martensitic start temperature decreases with increasing stress. It is concluded that the film stress is a critical parameter which strongly affects the martensitic transformation.

Type
Research Article
Copyright
Copyright © Materials Research Society 2000

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References

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