Large elasticity and size-dependent fracture of micro-/nanoscale silicon carbide polytypes

With the rapid development of nanotechnologies, silicon carbide (SiC) nanostructures have been widely adopted in a broad range of cutting-edge applications as their basic building blocks. To ensure the service reliability of those intelligent devices, an in-depth understanding of their mechanical properties is crucial given that most of the dysfunction of those devices are directly caused by the mechanical failure of their basic units. Due to the ‘size effect’, materials’ properties undergo significant alterations when shrunk down to the micro-/nanoscale, which distinguishes them from their bulk counterparts. Thus, a comprehensive understanding of one-dimensional (1D) semiconductor nanocrystals’ mechanical properties is also crucial for the design, fabrication, and application of SiC-based devices. In this study, by employing a quantitative in situ measurement strategy, the mechanical properties of three classical types of SiC (3C-, 6H-, and 4H-) micro-/nanocrystals were investigated inside electron microscopes. Results demonstrated that all the three SiC polytypes exhibited ‘small is stronger’ size-dependent fracture strengths. Surprisingly, all these covalently-bonded SiC nanocrystals exhibited exceptionally large deformation behaviors with maximum strains exceeding 10% before rupturing in typical brittle fashions. Molecular dynamics simulations qualitatively indicated the elastic–brittle nature of SiC under tensile loading and further suggested a surface-dominated inverse size effect at ultrasmall scales, as well as a size- and condition-dependent change in the failure mode under compressive loading. Considering the potential breakthrough in intrinsic properties of covalent crystals brought about by their subtle strain tunability, we anticipate that the performance of covalent nanomaterials will usher in significant advancements under ultra-large strains.