Anisotropic elastic properties of nanocrystalline nickel thin films
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N.M. Jennett and A.S. Maxwell Materials Centre, National Physical Laboratory, Teddington, Middlesex TW11 0LW, United Kingdom (Received 5 October 2004; accepted 26 January 2005)
The elastic properties of a nickel film approximately 800 nm thick were measured with nanoindentation, microtensile testing, atomic force acoustic microscopy (AFAM), and surface acoustic wave (SAW) spectroscopy. Values for the indentation modulus (220–223 GPa) and Young’s modulus (177–204 GPa) were lower than predicted for randomly oriented polycrystalline nickel. The observed behavior was attributed to grain-boundary effects in the nanocrystalline film. In addition, the different measurement results were not self-consistent when interpreted assuming elastic isotropy. Agreement was improved by adopting a transversely isotropic model corresponding to the film’s 〈111〉 preferred orientation and reducing the elastic moduli by 10–15%. The SAW spectroscopy results indicated that the film density was 1–2% lower than expected for bulk nickel, consistent with models for nanocrystalline materials. Similar reductions in modulus and density were observed for two additional films approximately 200 and 50 nm thick using AFAM and SAW spectroscopy. These results illustrate how complementary methods can provide a more complete picture of film properties.
I. INTRODUCTION
As the usefulness and applicability of thin films continues to expand, increasingly more detailed information about them is needed. In particular, many applications require knowledge about a film’s mechanical behavior to predict or diagnose its performance in a product. Several techniques based on a variety of physical principles have accordingly been developed to evaluate the mechanical properties of thin films.1–4 Although all of these techniques provide useful information, the measured properties often differ from one another. The question of how well the disparate measurements agree to form a unified, consistent picture of a film’s properties has not yet been fully answered. In this paper, we compare measurements of the elastic properties of thin films obtained by four very different measurement methods. Methods included nanoindentation, microtensile testing, surface acoustic wave spectroscopy, and atomic force acoustic microscopy. The methods spanned several orders of magnitude in their
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0146 1186
http://journals.cambridge.org
J. Mater. Res., Vol. 20, No. 5, May 2005 Downloaded: 03 Jul 2014
spatial resolution, from the macroscale to the nanoscale. Some of the methods were nondestructive; others permanently damaged the sample. Some measurements were performed under quasistatic conditions; others involved acoustic vibrations at frequencies greater than 100 MHz. In spite of their differences, all four methods provide valuable information about a film’s properties. By combining and comparing measurement results,5 we can obtain a more complete picture of the film’s properties, including de
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