Effects of focused-ion-beam irradiation and prestraining on the mechanical properties of FCC Au microparticles on a sapp
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Dan Mordehai and Eugen Rabkin Department of Materials Engineering, Technion-Israel Institute of Technology, 32000 Haifa, Israel
William D. Nix Department of Materials Science and Engineering, Stanford University, Stanford, California 94305-4034 (Received 4 May 2011; accepted 23 June 2011)
We have studied the effects of focused-ion-beam (FIB) irradiation and prestraining on the mechanical properties of nearly defect-free Au microparticles on a sapphire substrate. The Au microparticles, which were produced by a solid-state diffusion dewetting technique, were FIBirradiated and/or prestrained, the latter using a nanoindenter with a flat ended punch operating under a nanohammering mode. Also, the prestrained Au microparticles were exposed to FIB to examine the effects of ion-beam damage on the properties of crystals containing mobile dislocations. We found that both FIB irradiation and prestraining reduced the yield strength of pristine Au microparticles significantly and made the stress–strain curves jerky. However, FIB irradiation does not affect the mechanical properties of prestrained Au microparticles very significantly. Once a microparticle contains mobile dislocations, its mechanical properties are not influenced much by the defects generated by FIB irradiation, even at the submicrometer scale.
I. INTRODUCTION
Nanotechnology has played a significant role in the development of useful engineering devices and in the synthesis of new classes of materials. For the reliable design of miniaturized devices and for the structural applications of nano- or microsized materials, nanotechnology has always called for an understanding of the mechanical properties of materials at small length scales.1 Recently, micropillars, which are commonly fabricated by focused-ion-beam (FIB) milling, have been used extensively to study size effects on the mechanical properties of materials without significant strain gradients.2–4 However, FIB irradiation generates various defects, such as dislocation loops, precipitates, Ga+ ion implantation, and amorphous layers near the free surfaces, which might be expected to alter the mechanical properties.5 When the sample dimensions are reduced to the submicrometer scale, the FIB-damage effects might be particularly significant because of the high volume fraction of the damaged material. For these reasons, specimen preparation techniques that do not involve FIB irradiation are desired, not only to avoid the effects of FIB damage on the a)
Address all correspondence to this author. e-mail address: [email protected] This paper has been selected as an Invited Feature Paper. DOI: 10.1557/jmr.2011.221 J. Mater. Res., Vol. 26, No. 14, Jul 28, 2011
mechanical properties being studied but also to provide a non-FIBed reference that can be used to study the effects of FIB irradiation systematically. Several synthesis techniques, which do not use FIB irradiation, have been developed for producing high-quality mechanical test samples; these include the directional solidification/matrix etching technique,6 the m
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