In-situ TEM investigation of toughening in Silicon at small scales

We report a length-scale-controlled Brittle-Ductile Transition giving rise to significant toughening of a commonly brittle material. Using quantitative in-situ Transmission Electron Microscopy (TEM) fracture experiments at room temperature on single crystal Silicon, we find that large samples fracture concordant with the brittle bulk behavior at a stress intensity KIC - 1 MPa:m1=2. Below characteristic dimensions of about 250 nm, however, the fracture toughness strikingly increases inversely with size to at least triple. As evidenced from advanced in-situ TEM nanoscale strain mapping the stresses at the crack tip approach the theoretical strength. At the same time, below this critical transition length nucleation and propagation of dislocations was observed, shielding the crack tip and enabling the unprecedented rise in fracture toughness. These first time in-situ TEM observations in nanoscale Silicon at room temperature open new strategies to simultaneously strengthen and toughen indispensable yet brittle functional materials solely by geometrical miniaturization.

Automated summary

The study reports a Brittle-Ductile Transition in silicon controlled by length scale, leading to a significant increase in fracture toughness. In situ Transmission Electron Microscopy experiments show that below 250 nm, fracture toughness inversely increases with size, accompanied by nucleation and propagation of dislocations at the crack tip. The findings offer new strategies for strengthening and toughening brittle materials through geometric miniaturization.