Correlating in situ resonance and tensile tests to unravel the size and shape dependent elasticity of metal nanowires
Nanowires are progressively integrated in technical application and thus accurate determination of their properties is key for working on next generation nanodevices. In recent years, different techniques  have been established for in situ mechanical testing, showing a size-dependency of the mechanical properties commonly referred to as size effect. While for plastic deformation a general trend of “smaller is stronger” is now well-established, such a general observation has not been made for elasticity.
Interestingly, for nanowires different results regarding the Young’s modulus have been experimentally obtained, with some studies claiming a softening and others a stiffening effect. However, these studies employed different techniques such as 3-point bending , tensile  and compression tests , which may explain some of the differences. So far a combination of load types by non-destructive resonance measurement with subsequent tensile testing of the same nanowire, allowing a direct comparison and verification of the in situ data has not been applied.
Here we present an systematic in situ study of the elastic properties of Gold Nanowires , demonstrating the interplay and impact of size and shape. Using resonance measurements via electrical excitation inside the SEM enables us to directly analyze the characteristic resonance frequencies, which can be used to calculate the Young’s modulus (figure 1a). Additionally, a subsequent tensile test (on the same wire) with a calibrated spring table is performed and the Young’s modulus based on the corresponding stress-strain curve is calculated (figure 1b). To complete our study, we use TEM on wire cross-sections for the precise determination of size, shape and microstructure (figure 1c).
In our detailed study, the general trend of softening or stiffening of nanowires with decreasing size could not be confirmed. Rather, our precise evaluation of Young’s moduli reveals a softening followed by a stiffening regime. Moreover, our measurements show a clear impact of the nanowire shape (cross section) on the elastic properties which so far has not been considered. Taking a closer look on nanowires with rectangular cross-section, this “shape effect” constitutes itself in two different Young’s moduli extracted from measurements of nanowire resonances. In accordance with that, corresponding tensile tests on the same nanowires reveal an average “mixed” Young’s modulus.