Surface Excess Elasticity: Influence on Nanowire Stiffness from First PrinciplesThursday (29.09.2016) 12:42 - 12:45 Part of:
The size-dependent elastic response of nanomaterials and nanostructures with a large surface-to-volume ratio has attracted increasing attention. For example, in the order of tenfold stiffening has been reported for nanoporous gold (NPG) as the ligament size is decreased [1,2]. The local elasticity of the surface, expressed in terms of the surface excess elastic constants has been proposed as a key factor regarding this considerable size effect – and in fact, for NPG the contribution of surface excess
elasticity to the effective elastic response has been experimentally verified . However, quantitative prediction of the influence of surface excess elasticity remains a challenging task, which is addressed in this contribution.
Density Functional Theory (DFT) simulations are employed to compute the surface excess elastic constants for selected low-index metallic surfaces, such as the (111) and (001) surfaces of gold. As a nanostructure is deformed, the effective stiffness arises from the interplay between bulk elasticity
and the contribution of the surface. Combination of the DFT parameters with a continuum description of a circular nanowire subjected to axial tension, bending, or torsion allows to assess the relative stiffness change as a function of the nanowire diameter.
Positive-valued surface excess elastic constants for gold indeed imply a stiffening effect of the surfaces. However, even for nanowire diameters as small as 10 nm, the relative change in stiffness only amounts to a few percent – implying that surface excess elasticity does not exclusively explain the experimentally observed size effect.
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