Temperature dependence of mechanical properties in ultrathin Au films with and without passivation
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Sven Olliges Laboratory for Nanometallurgy, Department of Materials, Eidgenössische Technische Hochschule (ETH) Zürich, 8093 Zurich, Switzerland
Eduard Arzt Universität Stuttgart, Institute of Physical Metallurgy, D-70569 Stuttgart, Germany; Max Planck Institute for Metals Research, D-70569 Stuttgart, Germany; and Leibniz Institute for New Materials (INM), D-66123 Saarbrücken, Germany
Ralph Spolenakb) Laboratory for Nanometallurgy, Department of Materials, ETH Zurich, 8093 Zurich, Switzerland (Received 10 February 2008; accepted 16 May 2008)
Temperature and film thickness are expected to have an influence on the mechanical properties of thin films. However, mechanical testing of ultrathin metallic films at elevated temperatures is difficult, and few experiments have been conducted to date. Here, we present a systematic study of the mechanical properties of 80–500-nm-thick polycrystalline Au films with and without SiNx passivation layers in the temperature range from 123 to 473 K. The films were tested by a novel synchrotron-based tensile testing technique. Pure Au films showed strong temperature dependence above 373 K, which may be explained by diffusional creep. In contrast, passivated samples appeared to deform by thermally activated dislocation glide. The observed activation energies for both mechanisms are considerably lower than those for the bulk material, indicating that concomitant stress relaxation mechanisms are more pronounced in the thin film geometry. I. INTRODUCTION
Microstructural and dimensional constraints in polycrystalline thin films strongly influence their mechanical properties.1,2 Small grain sizes and film thicknesses lead to high stresses at low temperatures due to the confinement of either dislocation motion3–5 or dislocation nucleation and interaction.6–9 However, at elevated temperatures increased stress relaxation by diffusional flow of matter between the free surface and the grain boundary is expected.10,11 Thus, the mechanical properties of thin films should depend significantly on temperature. The only technique routinely used to study deformation of thin films at elevated temperatures is the substrate curvature technique.3 Using this technique, several authors have shown that stress relaxation in unpassivated
a)
Present address: Universität Karlsruhe, Institut für Zuverlässigkeit von Bauteilen und Systemen, Kaiserstrasse 12, D-76131 Karlsruhe, Germany b) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0292 2406
http://journals.cambridge.org
J. Mater. Res., Vol. 23, No. 9, Sep 2008 Downloaded: 02 Apr 2015
thin films on substrates can occur by diffusional deformation.12–16 The presence of a passivation layer on the surface of the film can inhibit diffusional flow and results in the activation of dislocation processes within the grains.13–15,17,18 Although this technique has provided valuable insight into the deformation behavior of thin films on substrates over a wide range of temperatures and requires little sample preparatio
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