C568: A new two-dimensional sp2-sp3 hybridized allotrope of carbon

Using first-principles calculations, we designed a new two-dimensional sp2−sp3 hybridized allotrope of carbon. This allotrope is made up of 5-6-8 carbon rings thus, known as C568. C568 is an indirect semiconductor with a band gap of 1.13 eV (HSE06) at Γ-M symmetric point in the Brillouin zone. The possibility of the existence of C568 is evident from its energetic, dynamical, mechanical, and thermal stabilities. C568 maintains its structural integrity up to 800 K, which we confirmed by employing ab-initio molecular dynamics (AIMD) simulations. C568 shows extraordinary room temperature in-plane electronic mobility of order ∼104 cm2V−1s−1, which is significantly higher than the black phosphorus (∼103 cm2V−1s−1) monolayer. Energetically, this sheet is more stable than the other sp2−sp3-hybridized carbon allotropes such as pentagraphene and tetrahexcarbon. Moreover, C568 can be stacked into three different configurations, which also exhibit interesting electronic as well as transport properties. These configurations are also dynamically stable and show in-plane mobilities of order ∼104 cm2V−1s−1.