Time-Resolved Raman Scattering in Exfoliated and CVD Graphene Crystals

Phonon lifetimes are fundamental physical parameters playing a significant role in phonon transport and thermal conductivity of two-dimensional materials. We employed the time-resolved incoherent anti-Stokes Raman scattering (TRIARS) technique to capture the G phonon dynamics and to extract the G phonon lifetimes in supported exfoliated and polycrystalline chemical vapor deposited (CVD) graphene samples of various thickness. We have found that substrate reduces considerably the G phonon lifetime of exfoliated monolayer graphene while the corresponding lifetimes for bilayer and trilayer converge gradually close to that of graphite. The lifetimes of CVD monolayers are systematically lower than exfoliated ones mainly due to the presence of various types of structural defects. Besides, the electron–phonon coupling strength of graphite is determined to be 10.6 cm^–1, in excellent agreement with theoretical predictions for graphene, justifying that the lifetimes of suspended graphene and graphite are similar.