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O: Fachverband Oberflächenphysik

O 60: Graphene: Electronic Properties (O jointly with DS, HL, MA, TT)

O 60.6: Vortrag

Mittwoch, 2. April 2014, 17:15–17:30, WIL C107

Excited electron dynamics in spatially aligned 7a-graphene nanoribbons on Au(788) — •Nils Fabian Kleimeier¹, Alexander Timmer¹, Harry Mönig¹, Xinliang Feng², Klaus Müllen², Harald Fuchs¹, and Helmut Zacharias¹ — ¹Physikalisches Institut, Universität Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany — ²Max-Planck-Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany

Photoelectron spectroscopy of spatially aligned straight 7-armchair graphene nanoribbons (7-aGNRs) on Au(788) was carried out under ultra high vacuum conditions utilizing a time-of-flight spectrometer and a multi-anode detector. We found two unoccupied states at energies of E₁=3.6 eV and E₂=3.9 eV above the Fermi energy by exciting the sample with different photon energies (3.94 eV to 4.35 eV) from a femtosecond OPA. When exciting the sample with ultrashort pules (20 fs) at λ=390 nm (hν=3.15 eV) by frequency- doubling the output of a femtosecond Ti:sapphire laser amplifier, these states can further be investigated by 3-photon photoemission using a third state at an energy of E₃-E_F=0.6 eV as intermediate. All three states are in agreement with IPE measurements we performed previously on this system [1]. Thus the electronic dynamics of the state can be measured by time-resolved 3-photon photoemission spectroscopy with cross-polarized laser pulses. Preliminary evaluation of these measurements indicates electronic lifetimes of the unoccupied states of τ∼110 fs and 85 fs for the states at E-E_F 3.9 eV and 3.6 eV, respectively.

References: [1] S. Linden et al., Phys. Rev. Lett. 108 (2012) 216801