Discrete breathers in hydrogenated graphene

Discrete breathers (DBs) in graphane (fully hydrogenated graphene) are investigated using molecular dynamics simulations. It is found that the DB can be excited by applying an out-of-plane displacement on a single hydrogen atom of graphane. The vibration frequency of the DB lies either within the gap of the phonon spectrum of graphane or beyond its upper spectrum bound. Both soft and hard types of anharmonicity of the DB, which have not been found in the same system, are observed in graphane. The study shows that the DB is robust and its lifetime is affected by various factors including its anharmonicity type, its amplitude and frequency, and the force on the hydrogen atom that forms it, whose competition results in a complex mechanism for the lifetime determination. The investigation of the maximum kinetic energy of DBs reveals that they may function to activate or accelerate dehydrogenation of hydrogenated graphene at high temperatures.