Abstract
We report on a self-assembly process, where high-temperature O 2 annealing induced a surface reorganization in CeO 2 deposited on r-cut sapphire substrates. When the CeO 2 film was thin ( t < 2 nm), a highly ordered phase was formed as 3D isotropic islands of CeO 2 with bare sapphire surface exposed. With increase in t, some of the isolated 3D islands started to be coalesced into large rectangular islands and finally connected with each other forming an ordered network. When the CeO 2 film exceeded a critical thickness of 10 nm, an atomically-flat surface with a high density of nanodots was formed by the reorganization. YBa 2Cu 3O 7− δ (YBCO) films grown on the atomically-flat CeO 2 surface had a high critical current density ( J c > 3.0 × 10 6 A/cm 2 at 77.3 K and 0 T). A correlation between the “matching field” and the mean density of nanodots was also demonstrated. The results showed that the nanodots possibly induced effective vortex-pinning centers in YBCO films.
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