Speaker: J. G. R. Hernández Arteaga (ELI Beamlines Facility, The Extreme Light Infrastructure ERIC, Czech Republic, host: Miklós Veres)
Title: Ultrafast Optical Dynamics across the Percolation Threshold in Spin-Coated Cerium–Cobalt Oxide Thin Films
Date: Thursday, 9 July 2026, 10:00
Place: Building 1, Conference Room
Abstract:
Transient spectroscopy comprises a family of advanced techniques capable of probing ultrafast processes occurring on the femtosecond timescale. The advent of high-power ultrashort-pulse lasers has enabled the observation of a wide range of nonlinear optical phenomena in semiconductors, including two-photon absorption, band-filling effects, and the Burstein–Moss shift, providing fundamental insight into carrier dynamics and energy relaxation mechanisms [1–4].
Metal oxide semiconductors (MOS) exhibit considerably more complex electronic structures than conventional crystalline semiconductors. Their density of states is strongly influenced by structural disorder, oxygen vacancies, grain boundaries, and the deposition technique employed during film growth. Consequently, their optical and electronic properties deviate from those of ideal crystalline materials, offering unique opportunities to tailor their functional response for optoelectronic and photonic devices [4].
Among these materials, cerium oxide (CeO2) and cobalt oxide (Co3O4) have attracted significant attention due to their complementary electronic structures and versatile optical properties. CeO2 crystallizes in the fluorite face-centered cubic (FCC) structure and possesses a wide band gap of approximately 3.5 eV, whereas Co3O4 adopts a spinel crystal structure with characteristic optical transitions in the 1.7–2.0 eV range. Ultrafast optical studies on these oxides have revealed rich carrier dynamics; for example, transient absorption measurements on CeO2 have reported the formation of small polarons on a timescale of approximately 330 fs [5].
In this presentation, we show how imaging ellipsometry and ultrafast transient reflection spectroscopy can be combined to investigate spin-coated CeO2– Co3O4 thin films. Imaging ellipsometry provides the composition-dependent dielectric function, whereas broadband pump–probe measurements reveal the corresponding femtosecond optical dynamics. Together, these complementary techniques allow us to correlate the static optical response with ultrafast photoinduced processes across the CeO2 – Co3O4 compositional series.
References
[1] E. Baron, Rüdiger Goldhahn,S. Espinoza, M. Zahradník, M. Rebarz, et al., J. Appl. Phys. 138, 125702 (2025)
[2] L. Kratschmer, Y. Slimi, L. Trefflich, Shirly Espinoza, et al, Phys. Status Solidi B 2025, 262, 2400547
[3] Yael Gutierrez, Shirly Espinoza, MateuszRebarz, et al, Appl. Phys. Lett. (2025), 127, 141102
[4] E. Baron, Rüdiger Goldhahn,S. Espinoza, M. Zahradník, M. Rebarz, et al., J. J. Appl. Phys. 134, 075703 (2023)
[5] Jacopo Stefano Pelli Cresi, Lorenzo Di Mario , Daniele Catone et al., J. Phys. Chem. Lett. 2020, 11, 5686−5691
[6] J.G.R. Hernández-Arteaga, Rafael Hernández Grimaldo, Saul Vazquez Miranda Shirly Espinoza et al., Optical Materials
2026. július 9. csütörtök, 10.00
Wigner FK SZFI, 1. ép. 1. em. nagy előadóterem
