Ultrafast multiphoton pump-probe photoemission excitation pathways in rutile TiO2(110)

Adam Argondizzo, Xuefeng Cui, Cong Wang, Huijuan Sun, Honghui Shang, Jin Zhao, and Hrvoje Petek
Phys. Rev. B 91, 155429 – Published 27 April 2015
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Abstract

We investigate the spectroscopy and photoinduced electron dynamics within the conduction band of reduced rutile TiO2(110) surface by multiphoton photoemission (mPP) spectroscopy with wavelength tunable ultrafast (20fs) laser pulse excitation. Tuning the mPP photon excitation energy between 2.9 and 4.6 eV reveals a nearly degenerate pair of new unoccupied states located at 2.73±0.05 and 2.85±0.05 eV above the Fermi level, which can be analyzed through the polarization and sample azimuthal orientation dependence of the mPP spectra. Based on the calculated electronic structure and optical transition moments, as well as related spectroscopic evidence, we assign these resonances to transitions between Ti3d bands of nominally t2g and eg symmetry, which are split by crystal field. The initial states for the optical transition are the reduced Ti3+ states of t2g symmetry populated by formation oxygen vacancy defects, which exist within the band gap of TiO2. Furthermore, we studied the electron dynamics within the conduction band of TiO2 by three-dimensional time-resolved pump-probe interferometric mPP measurements. The spectroscopic and time-resolved studies reveal competition between 2PP and 3PP processes where the t2geg transitions in the 2PP process saturate, and are overtaken by the 3PP process initiated by the band-gap excitation from the valence band of TiO2.

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  • Received 21 December 2014
  • Revised 4 April 2015

DOI:https://doi.org/10.1103/PhysRevB.91.155429

©2015 American Physical Society

Authors & Affiliations

Adam Argondizzo1, Xuefeng Cui1,2, Cong Wang1, Huijuan Sun2,3, Honghui Shang4, Jin Zhao1,2,3, and Hrvoje Petek1,*

  • 1Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
  • 2Department of Physics and ICQD/Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei, Anhui 230026, China
  • 3Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
  • 4Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany

  • *Corresponding author: petek@pitt.edu

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Issue

Vol. 91, Iss. 15 — 15 April 2015

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