Dresden 2017 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 63: Poster: Quantum Dots and Optics

HL 63.15: Poster

Mittwoch, 22. März 2017, 15:00–19:00, P1A

CO2 activation on ZnO surface studied by ultrafast photoelectron spectroscopy — •Sesha Vempati, Lukas Gierster, and Julia Stähler — Fritz-Haber-Institute, Berlin, Germany

We investigate the electron injection dynamics from ZnO(10-10) into an adsorbed layer of CO₂ molecules via time-resolved two-photon photoelectron spectroscopy (TR-2PPE). ZnO is known to be a catalyst for the hydrogenation of the CO₂ producing methanol like fuels in heterogeneous catalysis. CO₂ adsorbs on ZnO in a bent geometry to form a tridentate configuration possibly due to partial reduction. Despite of various studies, the energies of the frontier molecular orbitals of CO₂ on ZnO are unknown. Using TR-2PPE we unveil the energies of the frontier molecular orbitals of CO₂ on ZnO. We find that CO₂ adsorption causes a significant increase in the work function (≈ 1.2 eV for 0.5 ML) consistent with a partial reduction (CO₂^−δ) and/or the dipole moment associated with the bent molecules. Furthermore, TR-2PPE measurements suggest that above gap excitation in fact injects electrons from ZnO into the lowest unoccupied molecular orbital (LUMO) of CO₂^−δ molecule. After this electron capture, the LUMO shifts below the Fermi energy within 2 ps and forms a metastable state. This down shift is presumably accompanied by the changes of the nuclear coordinates of CO₂ due to the additional charge. This is probably the stage where the CO₂ molecule is completely activated for hydrogenation.