| AVS 58th Annual International Symposium and Exhibition | |
| Thin Film Division | Tuesday Sessions |
| Session TF-TuP |
| Session: | Thin Films Poster Session |
| Presenter: | Suntharampillai Thevuthasan, Pacific Northwest National Laboratory |
| Authors: | M.I. Nandasiri, Western Michigan University P. Nachimuthu, Pacific Northwest National Laboratory T. Varga, Pacific Northwest National Laboratory V. Shutthanandan, Pacific Northwest National Laboratory W. Jiang, Pacific Northwest National Laboratory S.V.N.T. Kuchibhatla, Pacific Northwest National Laboratory S. Thevuthasan, Pacific Northwest National Laboratory S. Seal, University of Central Florida A. Kayani, Western Michigan University |
| Correspondent: | Click to Email |
Cerium oxide (CeO2) is one of the extensively studied rare earth oxides; however, it continues to attract attention because of its potential use in medical biology, catalysis, intermediate temperature solid oxide fuel cells (IT-SOFC), and resistive oxygen gas sensors. Driven by the need for fundamental understanding of its unique properties, CeO2 thin films grown on various substrates by different methods at different experimental conditions have been extensively studied. However, the influence of growth-rate on the orientation and the crystalline quality of the CeO2 thin films is relatively unexplored. While understanding the influence of growth-rate, we evaluated the ability to tailor the orientation and the epitaxial quality of CeO2 films on Al2O3(0001).
CeO2 thin films were grown on Al2O3 (0001) substrates at 650°C with different growth-rates (1-10 Å/min) by oxygen plasma assisted molecular beam epitaxy (OPA-MBE). The growth rate induced epitaxial orientations and crystalline quality of CeO2 thin films were studied by in-situ reflection high energy electron diffraction (RHEED), atomic force microscopy (AFM), and x-ray diffraction (XRD) techniques. CeO2 grows as three-dimensional (3-D) islands and two-dimensional (2-D) layers at growth-rates of 1-7 Å/min and ≥9 Å/min, respectively. AFM images show average surface roughness of 5-10 Å, indicating the high-quality surfaces of CeO2 thin films. The formation of epitaxial CeO2(100) and CeO2(111) thin films occurs at growth rates of 1 Å/min and ≥9 Å/min, respectively. Glancing incidence XRD measurements have indicated that the films grown at intermediate growth rates (2-7 Å/min) consist of some polycrystalline CeO2 along with CeO2(100). As indicated by x-ray pole figure measurements, the CeO2 thin film grown at 1 Å/min shows six in-plane domains, characteristic of well-aligned CeO2(100) crystallites. When increasing the growth rate from 1 Å/min to 2-7 Å/min, poorly-aligned CeO2(100) crystallites start to coexist along with well-aligned crystallites. The content of the poorly-aligned CeO2(100) crystallites increases with increasing growth rate from 2 Å/min to 7 Å/min, and three out of six in-plane domains gradually decrease and eventually disappear. At growth rates ≥9 Å/min, CeO2(111) film with single in-plane domain was identified. The formation of CeO2(100) 3D-islands at growth rates of 1-7 Å/min is a kinetically-driven process unlike at growth rates ≥9 Å/min, which result in an energetically and thermodynamically more stable CeO2(111) surface.