Effective Use of Focused Ion Beam (FIB) in Investigating Fundamental Mechanical Properties of Metals at the Nano-Scale.
J.R. Greer and W.D. Nix
Palo Alto Research Center, US
focused ion beam, FIB, nanoscale, micromachining, TEM, plast
In this work, FIB is utilized in manufacturing of nano-pillars to investigate plasticity of metals at nano-scale. Gold nano-pillars were fabricated from bulk gold and epitaxial gold films on MgO substrates and subsequently compressed using Nanoindenter fitted with diamond flat punch. We show that fundamental mechanical properties like flow stress, yield strength, and stiffness strongly depend on sample size, as some of our smaller specimens were found to plastically deform in uniaxial compression at stresses as high as 800 MPa, ~50 times higher than bulk gold. We believe that these high strengths are hardened by dislocation starvation. In this mechanism, once the sample is small enough, the mobile dislocations have a higher probability of annihilating at a nearby free surface than of being pinned by other dislocations. Therefore, plasticity is accommodated by nucleation and motion of new dislocations rather than by interactions of existing dislocations, like for bulk crystals. To validate this mechanism, direct observation of dislocations was accomplished by utilizing the Omniprobe micromanipulator, coupled with FIB-milling and Pt deposition, for fabrication of site-specific TEM specimens. Preliminary TEM images show the lack of mobile dislocations in deformed pillars, which agrees with the proposed dislocation starvation mechanism, as discussed.
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Nanotech 2007 Conference Program Abstract