Anisotropic mechanical properties of -MoO₃ nanosheets

The mechanical behaviors of 2D materials are fundamentally important for their potential applications in various fields. alpha-Molybdenum trioxide (alpha-MoO3) crystals with unique electronic, optical, and electrochemical properties, have attracted extensive attention for their use in optoelectronic and energy conversion devices. From a mechanical viewpoint, however, there is limited information available on the mechanical properties of alpha-MoO3. Here, we developed a capillary force-assisted peeling method to directly transfer alpha-MoO3 nanosheets onto arbitrary substrates. Comparatively, we could effectively avoid surface contamination arising from the polymer-assisted transfer method. Furthermore, with the help of an in situ push-to-pull (PTP) device during SEM, we systematically investigated the tensile properties of alpha-MoO3. The measured Young's modulus and fracture strengths along the c-axis (91.7 +/- 13.7 GPa and 2.1 +/- 0.9 GPa, respectively) are much higher than those along the a-axis (55.9 +/- 8.6 GPa and 0.8 +/- 0.3 GPa, respectively). The in-plane mechanical anisotropy ratio can reach similar to 1.64. Both Young's modulus and the fracture strength of MoO3 show apparent size dependence. Additionally, the multilayer alpha-MoO3 nanosheets exhibited brittle fracture with interplanar sliding due to poor van der Waals interaction. Our study provides some key points regarding the mechanical properties and fracture behavior of layered alpha-MoO3 nanosheets.