Ultrastrong π-bonded interface as ductile plastic flow channel in nanostructured diamond

A combinational effect of nanostructured crystallites and π-bonded interface is much attractive in solving the conflict between strength/hardness and toughness in order to design extrinsically superhard materials with enhanced fracture toughness and/or other properties such as tunable electronic property. In the present work, taking the experimentally observed π-bonded interfaces in nanostructured diamond as prototype, we theoretically investigated their stabilities, electronic structures and mechanical strengths with special consideration of the size effect of nanocrystallites or nanolayers. It is unprecedentedly found that the π-bonded interfaces exhibit tunable electronic semiconducting properties, superior fracture toughness as well as an anomalously large creep-like plasticity at the cost of minor losses in strength/hardness; such unique combination is uncovered to be attributed to the ductile bridging effect of the sp2 bonds across the π-bonded interface that dominates the localized plastic flow cha...