Ultrafast optical studies on graphene and graphene oxide

Abstract

In this thesis, ultrafast optical properties of graphene and graphene

oxide materials have been studied by use of steady-state and time-resolved

spectroscopic techniques. Carrier dynamics of monolayer graphene, stacked and

suspended few-layer graphene films were measured in the broad visible spectral range

by femtosecond pump/probe spectroscopy. The time scales of carrier-carrier scattering,

carrier-optical phonon scattering and optical phonon-acoustic phonon scattering have

been obtained and their roles in carrier relaxation process are distinguished.

Meanwhile, there are several unusual quasiparticle interactions in graphene samples,

including optical phonon emission and absorption, coherent phonon generation,

interband triple-resonance electron-phonon scattering and stimulated two-phonon

emission. On the other side, the broadband fluorescence from as-prepared graphene

oxide in water has been investigated in detail. Ultrafast fluorescence (~1 ps) of

graphene oxide was determined for the first time by femtosecond fluorescence

upconversion technique. The origin of the fluorescence is attributed to electron-hole

recombination from the bottom of the conduction band and nearby localized states to

the valance band. Structurally, the GO emission is from the non-oxidized sp2 regions

and the boundary of oxidized sp3 regions.