Lifetimes of optical phonons in graphene and graphite by time-resolved incoherent anti-Stokes Raman scattering

We report lifetimes of optical phonons (OPs) in graphene and graphite measured by time-resolved anti-Stokes Raman scattering. Lifetimes in graphite and monolayer graphene are 2.4 and 1.2 ps, respectively. For graphite and graphene with more than five layers, the lifetimes decrease with increasing temperature as similar to 1/T, indicating the dominance of anharmonic processes in the decay of the OP population. The decrease in lifetime with decreasing number of layers suggests an additional decay channel through which excitations in graphene interact directly with lattice vibrations of the a-SiO2 substrate.