Novel Process for Ceramic Epitaxy Using Laser MBE
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NOVEL PROCESS FOR CERAMIC EPITAXY USING LASER MBE MAMORU YOSHIMOTO, HIROTOSHI NAGATA*, SATOSHI GONDA AND HIDEOMI KOINUMA
TADASHII TSUKAHARA,
The Research Laboratory of Engineering Materials, Tokyo Institute of Technology, Nagatsuta-cho 4259, Midori-ku, Yokohama, Kanagawa 227, Japan
ABSTRACT An ArF excimer laser MBE system specially designed for the deposition of ceramic thin films was used to construct atomically defined epitaxial SrCuO 2 -x films. According to XPS analysis, Cu valence was evaluated to be 2+ in the film as-grown in the presence of 10-7Torr NO2 , but it was less than 2+ in the film prepared in the presence of 10- Torr 02' In situ XPS depth analysis of as-grown SrCuO2 -x film on SrTiO3 substrate revealed the band profile at the interface of the film and substarte. Ceramic superlattices composed of metallic SrCuO 2 _x (3%8nm thick) and insulative SrTiO3 (8nm thick) were prepared by sequential heteroepitaxial growth. INTRODUCTION Recently, epitaxial thin film growth of ceramics including high-Tc superconducting oxides attracts much interest and was achieved by various methods such as reactive evaporation (11 and molecular beam epitaxy (MBE).[2] We succeeded in the epitaxial growth of cerium oxide films on Si by pulsed-laser deposition and verified its two-dimensional growth mode by the observation of RHEED intensity oscillation.[3] The system we employed was specially designed for the preparation of high-melting ceramic thin films in ultra-high vacuum (UHV) so that the ablated species could be a molecular beam and the film thickness regulated on an atomic scale (laser MBE). In comparison with the conventional laser deposition under relatively high pressures (10.1 Torr),[41 this laser MBE was favorable to get smooth and particulate-free ceramic thin films.[51 However, UHV may provide large oxygen deficiency in the as-grown oxide films. There should be two ways for obtaining desired oxidation state in the films prepared in UHV; one is to select high-oxygen affinity materials such as CeO 2 (5], and the other is to use highly oxidative gases such as N0 2 .16] In this study, we have examined the
*on leave from Central Research Laboratory, Sumitomo Cement Co.Ltd., Toyotomi-cho 585, Funabashi, Chiba 274, Japan Mat. Res. Soc. Symp. Proc. Vol. 201. '1991
Materials Research Society
178
laser MBE synthesis and characterization of epitaxial SrCu02_x thin films. This compound attracts much attention in view of its (CuO2 ) 2 -- layered structure, which is essential for high-Tc superconductivity in cuprate superconductors. In situ RHEED and XPS were measured to analyze the crystal structure and valence state of growing films. Fabrication of superlattices composed of SrCuO2 _x and SrTiO 3 was also attepmted.
EXPERIMENTAL of our laser MBE system is The schematical illustration shown in Fig.1. The apparatus is composed of three main parts; an UHV deposition chamber (ULVAC Co. Ltd.) epuipped with sixteen targets for laser ablation, an ArF excimer laser (193nm, LABMDA PHYSIK model LPX-100), and in situ analyzers
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