Mechanical properties and deformation mechanisms of single-crystal 1D/2D MoO₂ nanostructures

The Young’s modulus is an intrinsic property of materials, which is irrelevant to its morphologies. However, in the studies of molybdenum dioxide (MoO₂) nanomaterials, the reported modulus varied a lot, strongly hindering its applications because the deformation usually affects its electronic structures. To make clear its mechanical properties, we successfully synthesized high-quality single-crystal MoO₂ nanosheets and nanowires with a rutile crystal structure. Based on the nanoindentation in an atomic force microscope and in-situ bending tests in a scanning electron microscope, we systematically measured the Young’s modulus, strength, and fracture strain of MoO₂. The results indicate that MoO₂ nanosheets and nanowires exhibit similar Young’s modulus and intrinsic strength, measured at 114–118 and 12.5–14 GPa, respectively. Additionally, MoO₂ nanowires demonstrated a maximum fracture strain of 11%, as validated by density functional theory (DFT) calculations. DFT further revealed that the fracture of Mo–O bonds within the MoO₂ unit cell induces mechanical instability, ultimately leading to the catastrophic failure of the crystal. These measured mechanical properties and the elucidated deformation mechanism not only provide valuable insights for designing strain-tunable optical, electronic, and catalytic applications of MoO₂ but also contribute to a deeper understanding of related electro-chemo-mechanical mechanisms.