Dual phase amorphous carbon ceramic achieves theoretical strength limit and large plasticity

Ceramics are widely used as engineering materials due to their high strength; however, their lack of plasticity is a major drawback. We report that dual-phase amorphous carbon (a-C) reveals high yield strength of ∼E/11 (E is elastic modulus, and E/10 is theoretical limit for ideal material) and large plasticity of ∼70% at room temperature in uniaxial compression tests. To the best of our knowledge, this report describes the first time since 2006 that the experimental yield strength has been determined to agree with the theoretical prediction. Pillars with diameters smaller than 427 nm deform homogeneously and show plasticity comparable to that of metals. The mechanism for such unusual properties of a-C is explored using high-resolution transmission electron microscopy (TEM) and Raman spectroscopy. The results indicate that the near-ideal strength is ascribed to the limitation of both the size and the number of defects with the smaller sample size. Large plasticity is accompanied by material densification and phase transformation at compressive stress. This finding widens the possible application of strong-and-plastic ceramic films for both biomedical and micro/nano-electromechanical systems (MEMS/NEMS).