Abstract
We report here the influence of growth temperature of CeO 2 buffer layer T ( CeO 2 ) as well as the post-annealing of the buffer layer on the crystallinity and the microwave surface resistance R s of DyBa 2Cu 3O z (DBCO) films grown by pulsed laser deposition (PLD). It is found that (i) an increase in the T ( CeO 2 ) facilitates the epitaxial growth of the CeO 2 films, which is a prerequisite to obtain the high quality superconducting films and (ii) the post-annealing of buffer layer at 1050 °C in flowing O 2 for 1 h leads to a profound improvement in the morphology and in the crystallinity of CeO 2 films. Apparently, there exists a critical growth temperature ( T ( CeO 2 ) = 800 – 820 ∘ C , as found in this and previous study [J.C. Nie, H. Yamasaki, Y. Nakagawa, K.D. Bagarinao, M. Murugesan, H. Obara, Y. Mawatari, J. Crystal Growth 284 (2005) 417]) for CeO 2, below which the crystalline quality of CeO 2 films might not be improved merely by the post-annealing. It is explained that for T ( CeO 2 ) < 800 ∘ C , the as-grown CeO 2 grains are longitudinal in shape, and it forms corrugated structure upon annealing. This poor morphology yields a deteriorated crystallinity (i.e., a large value of Δ ω and Δ φ, and the formation of secondary phase) for the CeO 2 as well as the overlying DBCO films, and hence a poor microwave performance of DBCO films for T ( CeO 2 ) < 800 ∘ C . We also observed that the R s in DBCO films monotonously decreased with increase in the growth temperature of CeO 2. Further, the post-annealing of the CeO 2 buffer layer prior to DBCO deposition greatly helps to reduce the R s at the liquid N 2 temperature region, which is immensely required for the use of superconducting films in the passive microwave device components. Thus, the 800–820 °C of T ( CeO 2 ) and the post-annealing of CeO 2 at 1050 °C in flowing O 2 for 1 h may be readily exploited to grow RBCO (R=Y or rare-earth elements) films for microwave applications on the technologically viable r-Al 2O 3 substrates.
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