Surface effects on elastic properties of silver nanowires: Contact atomic-force microscopy

Silver nanowires with different diameters were synthesized by a hydrothermal chemical method. The elastic properties of the nanowires with outer diameters ranging from 20 to $140\mathrm{nm}$ were measured using contact atomic force microscopy. The apparent Young modulus of the nanowires is found to decrease with the increase of the diameter. When the diameter of the silver nanowires is larger than $100\mathrm{nm}$, the Young modulus approaches a constant value. The size dependence of the apparent Young modulus of the silver nanowires is attributed to the surface effect, which includes the effects of the surface stress, the oxidation layer, and the surface roughness. Thus, a theoretical analysis is presented to explain the size dependence. This analysis is different from the previous models in that both the surface stress and the surface moduli are included in it. We also show that the apparent surface modulus and the surface stress of the silver nanowires can be experimentally determined.

Figure 1

SEM image of a typical suspended nanowire (diameter $79\mathrm{nm}$). Schematic diagram of a nanowire with midpoint deflected by an AFM tip is shown in the inset.

Figure 2

Typical $F\text{−}\delta$ curves of the substrate and of a nanowire located on the substrate (diameter $79\mathrm{nm}$).

Figure 3

Variation of the Young modulus as a function of the diameters of silver nanowires.

Figure 4

Image of a silver nanowire (with core diameter $46.6\mathrm{nm}$). The surface of the wire is covered with an oxidation layer (about $3.8\mathrm{nm}$).