Non-Equilibrium Phenomena in Graphene
Hornett, Samuel M.
Date: 12 April 2013
Thesis or dissertation
Publisher
University of Exeter
Degree Title
PhD in Physics
Abstract
Graphene has displayed much promise as an electrical conductor and as a optical
material. To date there is a large body of literature dedicated to the equilibrium
properties of graphene. In this thesis the properties of graphene out of equilibrium
are probed. Through combined optical and transport measurements the behaviour
of hot ...
Graphene has displayed much promise as an electrical conductor and as a optical
material. To date there is a large body of literature dedicated to the equilibrium
properties of graphene. In this thesis the properties of graphene out of equilibrium
are probed. Through combined optical and transport measurements the behaviour
of hot electrons are probed at temperatures over five orders of magnitude from
50mK to 2000K. This wide range of temperatures allows access to the behaviour
of quantum corrections at the lowest temperatures to the highest energy phonon
modes. From ultrafast femtosecond laser pulses to steady state heating from an
electric field the cooling of hot electron populations through coupling to various
phonon modes in the graphene and the substrate are explored. Additionally the
effect of an electric field on the weak localisation correction to the conductivity was
separated from heating effects using applied magnetic fields combined with careful
modelling of the heat transport properties of the graphene. Finally the desorption
dynamics of oxygen bound to the surface are shown using a combination of transport
and two pulse correlation technique using an ultrafast laser. Surprisingly the cooling
of hot carriers in graphene at low energies shows substrate surface phonons as an
important cooling mechanism, highlighting the importance of substrate choice in
future graphene devices. In contrast at the very highest energy scales accessed
only by photoexcitation the cooling is shown not to be influenced by the presence
of a substrate, but out-of-plane phonon modes increase cooling of the hot optical
phonons.
Doctoral Theses
Doctoral College
Item views 0
Full item downloads 0