Abstract
Ultrathin and continuous epitaxial films with relaxed lattice strain can potentially maintain more of its bulk physical and chemical properties and are useful as buffer layers. We study surface, interface, and microstructural properties of ultrathin (∼10–12 unit cells thick) epitaxial ceria films grown on single crystal YSZ substrates. The out-of -plane and in-plane lattice parameters indicate relaxation in the continuous film due to misfit dislocations seen by high-resolution transmission electron microscopy (HRTEM) and substrate roughness of∼1-2 unit cells, confirmed by atomic force microscopy and HRTEM. A combination of secondary sputtering, lattice mismatch, substrate roughness, and surface reduction creating secondary phase was likely the cause of surface roughness which should be reduced to a minimum level for effective use of it as buffer layers.
Highlights
Cerium oxide is a widely studied material across several disciplines due to its use in oxygen storage, catalysis, and solid oxide fuel cells [1,2,3]
Epitaxial cerium oxide layers act as buffer layers for metal oxide semiconductors (MOS-s), silicon on insulator (SOI) for ferroelectrics, and superconducting thin films
Xray reflectivity (XRR) and atomic force microscopy (AFM) measurements on ceria thin film are shown in Figures 3(a) and 3(b), respectively
Summary
Cerium oxide is a widely studied material across several disciplines due to its use in oxygen storage, catalysis, and solid oxide fuel cells [1,2,3]. Doping ceria with +3 valence elements creates oxygen vacancy which can be an electrolyte for solid oxide fuel cells with oxygen ion conductivity in the intermediate temperature range [3]. It has been shown that growth of epitaxial ceria on silicon can create metal oxide emiconductor (MOS) layers useful in electronics [8]. Due to good lattice and thermal expansion coefficient matching with c-oriented epitaxial yttrium barium copper oxide (YBCO) superconductors, ceria had been consistently studied as a buffer layer to grow superconductors [9, 10]. Since the binding energies of most of the solids are on the order of few electron volts, for films with few unit cell in thickness, minor changes in incident ion energy can lead to variation in secondary sputtering rate from the film surfaces which can cause morphology changes resulting. A combination of secondary sputtering, lattice mismatch, substrate roughness, and secondary phase at the surface were most likely responsible for the film surface roughness
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