Size dependence on Young's modulus of sub-nanometer gold nanocontacts using microscopic nanomechanical measurement method

Nanomaterials, often exhibiting single-crystalline structures, show pronounced size- and orientation-dependent mechanical behaviors. However, there is still a lack of experimental measurements for metallic nanomaterials, particularly at sub-nanometer scales. Recently, we developed a Microscopic Nanomechanical Measurement Method (MNMM) that allows us to precisely obtain the equivalent spring constants (force gradients) of nanomaterials while observing their atomic structures [1]. As shown in Fig. 1, a gold nanocontact was fabricated in our home-built TEM specimen holder by bringing two gold wires into contact. The nanocontact was elongated along the [110] direction, both the length and the cross-sectional area varied through slip deformation. The length of the nanocontact was obtained from in situ TEM images, and its cross-sectional area was estimated from the measured electrical conductance. By correlating the measured spring constants with the geometric evolution, we established a relationship and fitted it to determine the Young’s modulus of the nanocontact. We summarized the Young’s moduli of gold nanocontacts with cross-sectional areas ranging from approximately 3 nm² to 0.5 nm². When the cross-sectional area was larger than about 2 nm², the Young’s modulus along the [110] direction was measured to be around 65 GPa, as the area decreased below 2 nm², the modulus began to increase markedly, exceeding 100 GPa at the smallest sizes. This clear stiffening trend indicates a size-dependent enhancement of the elastic modulus at the sub-nanometer scale, reflecting the influence of atomic confinement and surface effects.