Cyclo[18]carbon as an ultra-elastic molecular O-ring with unique mechanical properties

Recent atomic manipulation by an AFM tip created the first sp-hybridized carbon material – cyclo[18]carbon. Herein, we revealed the unique mechanical properties of cyclo[18]carbon by the first principle calculations. Under uniaxial tension, cyclo[18]carbon is ultra-elastic as demonstrated by a small Young's modulus of 0.11 TPa and a tiny specific tensile stiffness of 7.0 × 106 N m/kg, which are one and two orders of magnitude smaller than those of other carbon materials, respectively. The expansion and contraction of cyclo[18]carbon exhibit a relatively high specific stiffness of 9.95 × 108 N m/kg, and it would be broken with an energy requirement of 34.14 eV. While uniaxial tension enables the insulator-semiconductor transition of cyclo[18]carbon, expansion enlarges its energy gap. Furthermore, the strain energy was proposed as a function of bond angle and bond length for uniaxially-stretched and expanded/contracted cyclo[18]carbon respectively, which sheds light on predicting the mechanical properties of certain materials. The unique properties of cyclo[18]carbon are of great interest for its potential use as an ultra-elastic molecular O-ring in nanomechanical system and molecular electronics and devices.