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AIST TODAYNo.12 Spring 2004

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Improvements in Current-Density of YBa2Cu3O7-δ Films on Sapphire Buffered with Atomically-Flat CeO2 Having High Density of Nanodots
Jiacai NIE
Energy Electronics Institute
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YBa2Cu3O7-δ (YBCO) films was fabricated on CeO2-buffered R-cut sapphire substrate by pulsed laser deposition. Prior to the YBCO deposition, a self-assembly process was performed where high-temperature (1025°C) O2 annealing induces surface reconstruction of CeO2 on sapphire substrates. The results reveal an atomically flat surface of CeO2 film, superior crystalline quality, and the formation of a high density of nanodots on top of the CeO2 layer (Fig.1). YBCO films grown on such CeO2-buffered sapphire substrates had a high Tc ρ=0 (> 90 K) and a high Jc (> 3.0 &Atimes; 106 A/cm2 at 77.3 K and 0T, see Fig.2).


Figure Figure
AFM images and corresponding profiles of a 36.6-nm-thick CeO2 film grown on R-cut sapphire (a) before and (b) after high-temperature O2 annealing at 1025°C

Figure
Critical current density Jc as a function of temperature at 0 T for two typical 200-nm-thick YBCO films on R-cut sapphire (a) with a 33-nm-thick annealed CeO2 buffer layer and (b) with a 33-nm-thick as-grown CeO2 buffer layer

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