Invited Paper SS+EN-TuA3
Ultrafast Time-resolved Photoelectron Spectroscopy of Photocatalytic Surfaces

Tuesday, October 20, 2015, 3:00 pm, Room 112

We investigate the ultrafast optical excitation and electron relaxation pathways for the clean and molecule covered rutile TiO₂(110) surface. Using high power, broadly tunable (2.9-4.6 eV), 20 fs noncollinear parametric amplifier excitation source, we perform multiphoton photoemission (mPP) spectroscopy of TiO₂ surface. The energy, momentum, and pump-probe delay time resolved mPP spectra provide information on the occupied and unoccupied density of states that participate in photoemission from the valence band or the Ti-3d defect states on reduced TiO₂ surfaces. We find a new bulk transition between the Ti-3d bands of t_2g and e_g symmetry, which dominates the photoemission process form the Ti-3d defect states below the conduction band minimum of TiO₂.¹ The 3D mPP spectra provide information on the phase and energy relaxation of photoexcited electrons and holes.² Adsorption of molecules introduces adsorbate-induced resonances,^3,4 which can be excited by charge transfer excitation from the Ti-3d defect states. Metal nanoparticles grown on TiO₂ also open new photoemission pathways. We map out the energy and momentum distributions of the adsorbate and nanoparticle resonances as well as their relaxation dynamics.

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2. Cui, X.; Wang, C.; Argondizzo, A.; Garrett-Roe, S.; Gumhalter, B.; Petek, H., Transient excitons at metal surfaces. Nat Phys10, 505 (2014).

3. Onda, K.; Li, B.; Zhao, J.; Jordan, K. D.; Yang, J.; Petek, H., Wet Electrons at the H₂O/TiO₂(110) Surface. Science308, 1154 (2005).

4. Li, B.; Zhao, J.; Onda, K.; Jordan, K. D.; Yang, J.; Petek, H., Ultrafast interfacial proton-coupled electron transfer. Science311, 1436 (2006).