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Typical stress-strain curves for different film thickness for (a) , showing no variation of the yield strength with film thickness, and (b) , showing a clear increase in film yield strength with a reduction in film thickness.
Variation of yield stress at 0.2% strain offset with on a Hall–Petch plot for different film thicknesses. The slope of the linear correlations increases with thickness reduction, implying additional thickness-dependent strengthening. The linear correlation for reaches that of bulk Cu (Ref. 2).
Variation of yield stress with the number of grains across the film thickness for different grain sizes. Thickness-dependent strengthening first emerges at and becomes increasingly prominent with reductions in grain size.
Variation of film electrical resistivity at 0.5% strain with film thickness. The sharp drop noted for and at small thicknesses is attributed to dislocation annihilation at the free surface.
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