Uniting Ultrahigh Plasticity with Near-Theoretical Strength in Submicron-Scale Si via Surface Healing

W Xu and JH Yu and J Ding and YN Guo and L Deng and LQ Zhang and XX Wan and SC Zheng and YC Wang and ZW Shan, ADVANCED FUNCTIONAL MATERIALS, 34 (2024).

DOI: 10.1002/adfm.202404694

As a typical hard but brittle material, Si tends to fracture abruptly at a stress well below its theoretical strength, even if the tested volume goes down to submicron scale, at which materials are usually nearly free of flaws or extended defects. Here, via the thermal-oxidation-mediated healing of the surface that is the preferred site for cracks or dislocations initiation, the premature fracture can be effectively inhibited and the over 50% homogeneous plastic strain with the near- theoretical strength (twice the value of the unhealed counterpart) are united in submicron-sized Si particles. In situ transmission electron microscope observations and atomistic simulations elucidate the confinement effect from the passivated and smoothened thermal oxide, which retards the dislocation nucleation and transforms the dominant deformation mechanism from partial dislocation to the more mobile full dislocation. This work demonstrates an effective and feasible surface engineering pathway to optimize the mechanical properties of Si at small scales. Uniting ultrahigh strength with excellent plastic deformability in Si is of fundamental and practical interest, but it remains a great challenge due to the strong covalent bonds induced intrinsic brittleness. Via the thermal-oxidation mediated surface healing, it is realized that a surface dominant brittle-to-ductile transition at ambient temperature and the combination of near-theoretical strength and ultrahigh plasticity in submicron-sized Si. image

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