ELFT HÍRADÓ

[Szeminárium koordinátor <szfi-seminar AT wigner.hun-ren.hu>]

SZFI Seminar
J. G. R. Hernández Arteaga
(ELI Beamlines Facility, The Extreme Light Infrastructure ERIC, Czech 
Republic, host: Miklós Veres)
Ultrafast Optical Dynamics across the Percolation Threshold in Spin-Coated 
Cerium–Cobalt Oxide Thin Films
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 
MaterialsThursday, 9 July 2026, 10:00
Wigner FK SZFI, Bldg. 1, 2nd floor auditorium
Language of the talk: English
All interested are welcome!
Attila Nagyszfi-seminar AT wigner.hun-ren.hu