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Stress-Strain Response of Free-Standing Nano-Crystalline Gold Thin-Films
Published online by Cambridge University Press: 21 March 2011
Abstract
Free-standing gold thin-film tension specimens of thicknesses in the range 500-700 nm were fabricated by e-beam deposition methods. The films have grains which have thicknesses essentially equal to the film thickness, and an in-plane grain-size distribution which is bi-modal, with a collection of small grains with an average size of 130 nm, and another collection of larger grains with an average size of 380 nm. The films possess a strong texture with the {111} crystallographic planes aligned with the plane of the film. The thin-film specimens have been tested in simple tension using a novel testing machine which enables measurement of the elastic-plastic stress-strain response of the films with high resolution. The experiments show that the gold thin-films have an initial yield strength of around 100 MPa, which is followed by rapid strain hardening to a stress level of 360 MPa at a strain of only ~1.2%, at which point the specimens fail abruptly. Transmission electron microscopy (TEM) investigations of the deformed films shows that the rapid strain hardening is attributable to extensive dislocation activity in the larger grains. The reason behind the low ductility in our gold specimens is still unclear, but it may be attributable to the observed lack of dislocation activity in the smaller grains, whose boundaries then serve as easier sites for alternative inelastic mechanisms such as grain boundary sliding and decohesion leading to low macroscopic strains to failure.
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- Copyright © Materials Research Society 2002
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