Epitaxial Growth and Structural Characterization of Ceria Deposited by Atomic Layer Deposition on High-Surface Porous Yttria-Stabilized Zirconia Thin Films

Abstract

Yttria-stabilized zirconia (YSZ) is a well-known solid electrolyte material in high-temperature applications that involve the conduction of oxygen ions. One possible way of enhancing the performance of devices like solid oxide fuel cells at lower operation temperatures is the design of the electrolyte’s surface by increasing the surface area and modifying the surface properties by ceria coating to improve the oxygen incorporation reaction. However, the preparation of a conformal coating while maintaining a complex surface morphology on the nanoscale is challenging employing conventional evaporation methods. In this work we present thin ceria coatings (9–20 nm) that were deposited on porous 8 mol % YSZ thin films using atomic layer deposition (ALD). The YSZ films (with thicknesses between 90 and 130 nm) were prepared using pulsed laser deposition at various substrate temperatures, thus leading to different surface morphologies. The investigation of the sample cross section by high angle annular dark field transmission electron microscopy exhibits columnar growth of epitaxial grown ceria thin films with excellent coating conformity. This demonstrates the great potential of the ALD process for surface modification of porous materials, where controlled and conformal coating of high surface areas is desired.

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.…”

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

“…As shown recently, ceria grows epitaxially on ZrO 2 -based oxides with a grain size of a few nanometers when using ALD. 20 Thus, it is reasonable to assume that the coating layers exhibits a high grain boundary density, which can significantly affect the defect concentrations due to the formation of a space charge region at the boundary. As for ceria the formation of a space charge layer results in an accumulation of electrons and a depletion of oxygen vacancies at the grain boundary, 58−60 a high grain boundary density may be responsible for the high Ce 3+ concentration in the coating layer.…”

“…In order to cover the pore surfaces with the desired thickness, the layer growth using atomic layer deposition (ALD) has gained considerable scientific interest. − Due to its operation mode, including the separation of the gas–solid reactions with an inert gas purging step, the deposition of the desired metal oxide species is performed layer-by-layer. Hence, the ALD technique offers the possibility to coat even complex substrates such as porous and mesoporous thin films with atomic-level control of the formed layer and its thickness with significant reproducibility. − Thus, the ALD method classifies as superior in comparison with wet-chemical approaches such as wet impregnation, co-condensation, and grafting as well as physical attempts such as physical vapor or pulsed layer deposition.…”

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

“…Zscherp et al also examined the nanostructure of an ALD oxide coating, namely, 9-20 nm ceria deposited onto porous YSZ thin films. 312 TEM investigations revealed epitaxial growth of ceria with a columnar structure and excellent conformality (Fig. 29).…”