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SUMMARY:Quasiparticle dynamics at oxide surfaces: Electrons\, Excitons and
  Polarons
DTSTART:20131212T163000
DTEND:20131212T173000
DTSTAMP:20260407T135803Z
UID:8ca3efa6c98a8f7795eedace96911daf945e39d9cb6a3145a5c238a4
CATEGORIES:Conferences - Seminars
DESCRIPTION:Dr A. Julia Staehler\nDepartment of Physical Chemistry\nFritz 
 Haber Institute of the Max Planck Society\nBerlin\nTransparent conducting 
 oxides are promising compounds for the application in optoelectronic devic
 es and increasingly used as transparent electrodes. Both\, ZnO and SrTiO3 
 (STO)\, exhibit a large band gap (> 3.2 eV) and high carrier mobilities an
 d are\, therefore\, suitable candidates. The carrier and excitons dynamics
  at the surface of these materials crucially determine the functionality o
 f any interface formed for optoelectronic application.\nWe study the ultra
 fast quasiparticle dynamics in and below the ZnO and STO conduction band u
 sing femtosecond time-resolved two-photon photoelectron (2PPE) spectroscop
 y. Above band gap excitation (hvpump = 4.19 eV) enables the investigation 
 of the hot electron relaxation by electron-phonon scattering with an exces
 s energy of 0.8 eV down to the Fermi level EF. We furthermore show for ZnO
  that surface exciton formation creates additional density of states below
  EF already a few hundred femtoseconds after excitation. These quasipartic
 le formation dynamics are almost independent of temperature and absent at 
 the STO surface\, which exhibits a dense charge accumulation layer (CAL) t
 hat screens the electron-hole Coulomb interaction. We furthermore tune the
  charge density of the CAL at the ZnO surface by hydrogen termination and 
 thereby adjust the number of surface excitons formed. The remarkable stabi
 lity of this surface species with lifetimes exceeding hundreds of picoseco
 nds is enabled by downward surface band bending\, shifting the exciton dee
 p into the bulk band gap (DEbdg = 250 meV).
LOCATION:CH G1 495 https://plan.epfl.ch/?room==CH%20G1%20495
STATUS:CONFIRMED
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