Depth Profiles of Crystallinity and Preferential Orientation and Surface Characteristics of Sputter‐Deposited CeO 2 Thin Film Buffer Layers on Sapphire Substrates Evaluated Through Two‐Dimensional Grazing‐Incidence X‐Ray Diffraction

• Published in: Surface and interface analysis 2025-02, Vol.57 (2), p.121-130
• Main Authors: Fukano, Tatsuo, Nozaki, Hiroshi, Funayama, Keita, Katsuno, Takashi, Koganezawa, Tomoyuki, Harada, Masashi, Kawaura, Hiroyuki
• Format: Article
• Language: English
• ISSN: 0142-2421; 1096-9918
• DOI: 10.1002/sia.7365

Two‐dimensional grazing‐incidence wide‐angle X‐ray diffraction data were acquired from CeO 2 thin films serving as buffer layers on r ‐cut sapphire substrates to investigate the depth profiles of crystallinity and preferential orientation as well as surface conditions. The thin film samples were sputter‐deposited under different conditions. Data were obtained at an X‐ray wavelength of 0.100 nm at 0.02° intervals from 0.06° to 0.30° at the grazing‐incidence angle. A 60‐nm‐thick CeO 2 thin film sputter‐deposited under Ar (Ar‐60) and a 100‐nm‐thick CeO 2 thin film sputter deposited using 10 vol.% O 2 in Ar (O+Ar‐100) were found to have partially oriented three‐dimensional bulk crystal structures with preferential orientation in the (100) direction near the surface. The lattice constant for the Ar‐60 film was found to be approximately 0.30% smaller than that for a CeO 2 standard, whereas the lattice constant for the O+Ar‐100 film was approximately 0.50% larger. Lattice mismatch between the CeO and CeO 2 on the substrate surface is evidently not an issue based on the lattice constants near the surface. Hence, both films could be considered to represent optimal buffer layers for YBa 2 Cu 3 O 6+ δ thin film growth. However, even in the case of a CeO 2 thin film suitable for use as a buffer layer, the difference in lattice constants between the interior and surface of an Ar‐60 film was found to be relatively small, whereas that for an O+Ar‐100 film was relatively large. These results show that it is important to analyze the film surface in detail by reducing the incidence angle to less than 0.1°.