Berlin 2024 – scientific programme
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O: Fachverband Oberflächenphysik
O 36: Poster: Ultrafast Electron Dynamics at Surfaces and Interfaces
O 36.3: Poster
Tuesday, March 19, 2024, 18:00–20:00, Poster C
Transient Absorption Spectroscopy of NiO — •Mahendra Kabbinahithlu1, Tobias Lojewski1, Sergey Kovalenko2, Nico Rothenbach1, Katharina Ollefs1, Heiko Wende1, Uwe Bovensiepen1, Julia Stähler2, and Andrea Eschenlohr1 — 1Universität Duisburg-Essen, Fakultät für Physik und Center for Nanointegration (CENIDE), Lotharstraße 1, 47057 Duisburg, Germany — 2Humboldt-Universität zu Berlin, Institut für Chemie, Brook-Taylor-Straße 2, 12489 Berlin, Germany
In nickel oxide (NiO), a correlated transition-metal oxide, the strong electron-electron repulsion splits the d-bands into an occupied lower Hubbard band (LHB) and an unoccupied upper Hubbard band (UHB). The presence of additional oxygen p-bands from adjacent sites, located between the Hubbard bands makes NiO a charge-transfer insulator. We present excited state dynamics in NiO thin films via time-resolved optical spectroscopy. NiO is pumped above the band gap with 3.98 eV photons and the transient absorption spectrum is probed using a time-delayed supercontinuum. The time-resolved absorption spectrum shows within the first 500 fs pump-induced changes at 2.2 eV, 3.2 eV and 4.3 eV. The negative change represents the reduced transitions from the bleached ground state and the positive changes represent the increased transitions from the photo-excited state. Around 2 ps, relaxation from the photo-excited state leads to emergence of a fluence dependent positive feature. We discuss this feature as transitions from polarons and shallow defect states lying below the UHB edge.
Keywords: NiO; time-resolved optical spectroscopy