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 $K_{\mathrm{I}\mathrm{C}}~1MPa.m^{1/2}$. 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.

我们报告了一种长度尺度控制的脆性-韧性转变，导致常见脆性材料的显着增韧。在室温下对单晶硅进行定量原位透射电子显微镜 (TEM) 断裂实验，我们发现大样品断裂与应力强度下的脆性体行为一致${钾}_{\mathrm{一世}\mathrm{C}}~1米磷\mathrm{一种}.{米}^{1/2}$. 然而，低于约 250 nm 的特征尺寸，断裂韧性与尺寸成反比地显着增加至至少三倍。正如先进的原位TEM 纳米级应变映射所证明的，裂纹尖端的应力接近理论强度。同时，在此临界过渡长度以下观察到位错的成核和传播，屏蔽裂纹尖端并使断裂韧性前所未有地提高。这些首次在室温下对纳米级硅进行原位TEM 观察开辟了新策略，仅通过几何微型化即可同时增强和增韧不可或缺但易碎的功能材料。