Femtosecond carrier dynamics in bulk graphite and graphene paper

a b s t r a c t Femtosecond white-light continuum probe transient absorption and reflectivity measurements of bulk graphite and graphene paper are reported. In graphite, the relaxation of photoinduced electron-hole pairs happens through in-plane electron-electron and electron-phonon scattering in '200 fs, while the ps dynamics is due to the modulation of the electronic structure by out-of-plane structural motions. The ps dynamics of the optical signal is strongly reduced in graphene paper, where the out-of-plane bond is disrupted, while the short component of the dynamics is identical in both materials. These results show that in 2D-graphene, the carrier relaxation occurs in '200 fs. Ó 2011 Elsevier B.V. All rights reserved. In graphene, the first isolated 2D solid [1], two-dimensionality is responsible for its extraordinary high carrier mobility. Its transport properties promise to revolutionize future microelectronic and optical devices. For instance, it has been shown that the ultrafast carrier relaxation in graphene can be exploited in very efficient saturable absorbers for mode-locking fiber lasers A prerequisite for understanding the ultrafast properties of graphene, is a detailed description of those of bulk graphite. Surprisingly, despite years of research, a consensus on the microscopic interpretation of the observed ultrafast dynamics is still lacking. Transient absorption pump-probe studies revealed that the electronic excitation decays in a bi-exponential fashion with an ultrafast ('200 fs) component and a slower (1-2 ps) one A direct confirmation of this scenario would be to carry out pump-probe studies on isolated free-standing graphene, since the c-axis ps structural motions should be suppressed; however, this is not yet experimentally feasible. Recent interest has been triggered by the properties of turbostratic graphite Here, we present new pump-probe experiments with white light continuum on graphite and graphene paper. Our experiments extend previous studies both in spectral region and in fluence (up to those of permanent damage, 170 mJ/cm