AVS 63rd International Symposium & Exhibition
    2D Materials Focus Topic Tuesday Sessions
       Session 2D-TuA

Paper 2D-TuA8
Femtosecond Hot Electron-Phonon Interactions of Single Layer Graphene and the undelying Substrate

Tuesday, November 8, 2016, 4:40 pm, Room 103B

Session: Novel Quantum Phenomena in 2D Materials
Presenter: Zina Jarrahi, Vanderbilt University
Authors: Z. Jarrahi, Vanderbilt University
J.L. Davidson, Vanderbilt University
N.H. Tolk, Vanderbilt University
Correspondent: Click to Email
We study the effect of substrate on the femtosecond transient electron and phonon dynamics of single layer graphene transferred on finely polished diamond, sapphire and quartz. Through a comprehensive set of fluence and energy dependent ultrafast optical conductivity measurements, we show that the temporal evolution of the hot carriers in graphene, differ significantly depending on the underlying substrate. We observe much faster(slower) relaxation and less(more) pronounced band filling dynamics for graphene on diamond(quartz). We demonstrate that the differences in the temporal evolution of the carrier temperature and inter/intraband transition interplay, cannot be accounted for by invoking the different static Fermi-levels of graphene on each substrate. These substrate-dependent dynamics are explained, using a multi-channel cooling picture, involving surface phonons of the substrate, intrinsic optical phonons of graphene, their competing scattering rates, phonon frequencies and the varying Fröhlich coupling strength of the different substrates. In this regard, the sub nm roughness of our studied substrates, enable a strong coupling between the phototexcited carriers in graphene and the surface vibrational modes of the polar substrates. We observe an increase in the carrier relaxation times as photoexcited carrier density is increased. This further confirms the existence of an additional relaxation mechanism through the substrate that competes with the intrinsic phonons of graphene to not only reduce the electron temperature but also carrier and optical phonon lifetimes. These results offer significant potential to selectively activate the desired energy relaxation channels in graphene and tune the carrier and optical phonon lifetimes, by simply varying the substrate and fluence regime. This knowledge will pave the road towards designing graphene-based (opto)electronics with highly tailored functionalities suited for specific device requirements.