Microstructure and mechanical properties of sub-micron zinc structures
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Sujing Xie CAMCOR High Resolution and Analytical Facility, Department of Chemistry, University of Oregon, Eugene, Oregon, 97403-1241
Michael J. Bureka) Waterloo Institute for Nanotechnology, University of Waterloo, Waterloo, Ontario, N2L 3G1, Canada
Zeinab Jahed Department of Mechanical Engineering, Waterloo Institute for Nanotechnology, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
Ting Y. Tsuib) Department of Chemical Engineering, Department of Mechanical Engineering, Waterloo Institute for Nanotechnology, University of Waterloo, Waterloo, Ontario, N2L 3G1, Canada (Received 2 February 2012; accepted 26 April 2012)
The mechanical properties of submicron scale columnar zinc structures, with average diameters between 130 and 1060 nm, were characterized by uniaxial microcompression tests. The zinc pillars were fabricated by electron beam lithography and electroplating and were found to be generally single crystalline, with a preferred out-of-plane orientation close to the [0001] directions. Post deformation microstructural analysis suggests that the zinc pillars maintain their single-crystalline structure, but without twin boundary formation. Interestingly, the engineering flow stress results indicate that small-scale zinc structures are insensitive to both strain rate and size.
Present address: School of Engineering and Applied Sciences, Harvard University, 29 Oxford Street, Cambridge, Massachusetts, 02138 b) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.146
crystalline systems, such as tetragonal,18 rhombohedral,19 and hexagonal close packed (HCP).20–26 Size-dependent mechanical behaviors in nanoscale metals are generally attributed to the competition between the rate of dislocations generated by applied stress and the rate of dislocation annihilation at free surfaces.27–29 With decreasing sample size, the rate of dislocation annihilation during applied stress exceeds that of dislocation generation, thus yielding a crystal, which has a much lower dislocation density or is even completely absent of dislocations.29 In this “dislocation starved” state, further loading will be accommodated by elastic deformation until the applied stress is sufficient to nucleate new dislocations.27,29 Therefore, decreasing sample dimensions will yield stronger specimens due to the reduced dislocation density. Among the crystalline structures studied at the nanoscale, HCP metals are particularly interesting since they deform not only by dislocation glide along active slip systems but also deform by twin boundary formation. Recently, Lilleodden20 reported size effects in the mechanical strength of micron scale single-crystalline HCP magnesium pillars through uniaxial microcompression techniques. These columnar structures, with diameters in
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Ó Materials Research Society 2012
I. INTRODUCTION
The functionality, lifetime, and future commercial success of novel nanoelectronic and nanoelectromechanical devices will ultimately depend on a fundamental understanding of the phy
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