Self-assembled CeO2 buffer layers on R-cut sapphire for high-current-density YBa2Cu3O7−δ films

Abstract

Experimental evidence of a cooperative self-assembly process was obtained where high-temperature O2 annealing (1000 °C) induced mass transport of CeO2 deposited on R-cut sapphire substrates to form a surface reconstruction on the substrate. When the CeO2 film exceeded a critical thickness (∼10 nm), an atomically flat surface with a high density of nanodots was preferred by the reconstruction (revealed by scanning atomic force microscopy) and the CeO2 layers had high lattice and surface perfection (revealed by x-ray diffraction). YBa2Cu3O7−δ films grown on such CeO2-buffered sapphire substrates had a high transition temperature (Tc ρ = 0 > 90 K) and a high critical current density (Jc > 3.0 × 106 A cm−2 at 77.3 K and a zero applied magnetic field).