EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

In recent years, different techniques have been established for in situ testing of nanostructures, revealing a size-dependency of the properties commonly referred to as size effect. While for plastic deformation a general trend of “smaller is stronger” is well-established, such a general observation has not been made for elasticity. For metal 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 load settings and the nanowire cross-section has been assumed by the expected Wulff-shape. 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 a systematic SEM study of the elastic properties of gold nanowires, demonstrating the interplay and impact of size and shape based on precise TEM analysis of the nanowire cross-section. Using resonance measurements inside the SEM enables us to directly analyze the characteristic resonance frequencies, which are used to calculate the Young’s modulus. Additionally, a subsequent tensile test on the same nanowire with a calibrated spring table is performed and the Young’s modulus based on the corresponding stress-strain curve is calculated. In our study, the general trend of softening or stiffening of nanowires with decreasing size could not be confirmed. Rather, our precise evaluation reveals a softening followed by a stiffening regime and shows a clear impact of the nanowire shape which has not been considered so far. 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.