Thermal treatment-induced ductile-to-brittle transition of submicron-sized Si pillars fabricated by focused ion beam

Si pillars fabricated by focused ion beam (FIB) had been reported to have a critical size of 310-400 nm, below which their deformation behavior would experience a brittle-to-ductile transition at room temperature. Here, we demonstrated that the size-dependent transition was actually stemmed from the amorphous Si (a-Si) shell introduced during the FIB fabrication process. Once the a-Si shell was crystallized, Si pillars would behave brittle again with their modulus comparable to their bulk counterpart. The analytical model we developed has been proved to be valid in deriving the moduli of crystalline Si core and a-Si shell.