Atomic Layer Deposition of Nanometer-Sized CeO₂ Layers in Ordered Mesoporous ZrO₂ Films and Their Impact on the Ionic/Electronic Conductivity

Abstract

The physicochemical properties of thin metal oxide layers strongly depend on the layer thickness and thus differ significantly from their bulk counterpart. In this work, we present the growth of defined thin layers of CeO 2 within mesostructured ZrO 2 thin films using atomic layer deposition (ALD). The prepared films consist of a cubic ordered arrangement of 15 nm spherical mesopores induced by the used diblock copolymer poly(isobutylene)-block-poly(ethylene oxide) (PIB 50 -b-PEO 45 ), which allows studying the growth process and the successful coating of the interior pore surfaces via the combination of scanning electron microscopy (SEM), time-of-flight mass spectrometry (ToF-SIMS), and laser ellipsometry. These methods prove the CeO 2 layer growth and impregnation of the pores up to 100 ALD cycles, at which the interconnecting channels between the mesopore layers are filled completely impeding further transport of the gaseous CeO 2 precursors. X-ray photoelectron spectroscopy (XPS) and diffractometry (XRD) measurements point out the increased amount of Ce 3+ after a low number of ALD cycles and show the presence of cubic CeO 2 with increasing amount of ALD cycles, respectively. Impedance spectroscopic investigation further proves the formation of a continuous CeO 2 path through the entire porous network of the insulating ZrO 2 film and shows a strong influence of the layer thickness on the conductivity. All in all, our work presents the preparation of novel hybrid CeO 2 /ZrO 2 model systems, which enable us to tailor their physicochemical properties by changing the thickness of the active oxide layer, and promises improvements for their use as catalysts in oxidation reactions such as the HCl oxidation reaction or as a threeway catalytic converter in automotives.

Ordered mesoporous metal oxides for electrochemical applications: correlation between structure, electrical properties and device performance

“…Cop et al further probed the electrical properties of mesoporous ZrO 2 thin films coated with ceria using different numbers of ALD cycles. 318 Characterization via ellipsometry confirmed the homogeneity of coating in the pores up to 100 ALD cycles, after which pore plugging occurred. XPS measurements revealed a large Ce 3+ fraction in the coating because of the space-charge layer at the surface, which decreased with increasing thickness, as shown in Fig.…”

Thin Film NCM Cathodes as Model Systems to Assess the Influence of Coating Layers on the Electrochemical Performance of Lithium Ion Batteries

“…This is expected as ALD is well known as deposition technique, which allows the deposition of uniformal and homogeneous coatings with a precise control of the layer thickness even in case of porous thin films. [ 66–68 ] After cycling, the coated NCM thin film (Figure 6d) shows no significant difference compared to the pristine sample, while for the uncoated thin film (Figure 6c), changes of the surface morphology are clearly visible. Cracks formed at the surface and it appears as if the particles on the surface became porous.…”

“…To investigate the influence of an ultrathin surface coating with varying thickness on the electrochemical performance, NCM samples were coated with a thin Al 2 O 3 film using atomic layer deposition (ALD), which enables a homogeneous coating even of porous samples. [66,67,88] The ALD deposition was carried out in a PicoSun R200 ALD reactor using trimethylaluminium (TMA, STREM chemicals inc., min. 98%) as precursor and deionized water as reactant for TMA to form the oxide layer.…”

Development of Pore Morphology During Nitrate Group Removal by Calcination of Mesoporous CexZr1-x-y-zYyLazO2−δ Powders

“…2.3.18, Casa Software Ltd.). To determine the Ce 3+ content the spectra were subsequently fitted by considering six Ce 4+ 3d (v, v″, v‴ and u, u″, u‴) and four Ce 3+ 3d (v 0 , v′, and u 0 , u′) signals . A combination of two fits was employed to improve the fit quality of the u and v signals, based on Skála et al…”