Alex Kitt - The Effects of Strain on the Phonons in Graphene

When: September 15, 2011 (Thu), 04:00PM to 05:00PM (add to my calendar)
Location: SCI 352

This event is part of the Preliminary Oral Exam.

Title: The Effects of Strain on the Phonons in Graphene

Examining Committee:  Bennett Goldberg, Anna Swan, Claudio Chamon, Linda Doerrer (Chemistry)

Abstract:
Studying the effects of strain on the phonon modes in graphene allows access to a rich variety of physics.  These include the downshift of the zone center E2G optical phonon, the origin of the high thermal conductivity of suspended graphene, and the observation of pseudo magnetic fields.  In all cases, strain is induced by applying pressure to a graphene sealed microchamber.  Upon the application of pressure, the graphene is pushed into the hole and variable strain develops in the sheet.  The zone center E2G optical phonon energy has been measured with Raman spectroscopy as a function of pressure.  The observed down shifts are fit to a continuum model to determine the phonon energies dependence on biaxial strain.  This geometry will also allow the thermal conductivity to be measured as a function of strain giving insight into the mechanism of heat conduction in graphene.  The damping of the out of plane acoustic phonon is believed to be the reason that graphene’s thermal conductivity decreases when it is supported [1].  With the application of strain, this phonon mode should change from quadratic to linear near the gamma point, lowering the density of states.  If it is the main channel for heat conduction, this should drastically lower the thermal conductivity.  Finally, it has been predicted that pressure applied to a triangular graphene sealed microchambers should give rise to a tunable pseudo magnetic field in graphene as high as 5 T for 14 MPa of pressure [2].  This exotic effect should manifest itself in anti-crossing behavior of the zone center E2G phonon as it goes into resonance with selected Landau level transitions.   The possibility of measuring this was Raman spectroscopy will be discussed.