Epitaxial growth of CeO2 films on Al2O3 (11̄02) substrates and the effect of CeO2 buffer layers on the growth orientation and superconducting properties of EuBa2Cu3O7-δ (EBCO) were investigated. CeO2 and EBCO films were prepared by rf and dc magnetron sputtering, respectively, and were characterized by X-ray diffraction (θ-2θ scan and ϕ scan), atomic force microscopy (AFM) and high resolution scanning electron microscopy. Epitaxial (001) CeO2 films were obtained at an off-center distance (D on-off) of 3.5 cm and a substrate temperature of 660°C. The structural and superconducting properties of EBCO films deposited at 650°C depended on the thickness of the CeO2 buffer layer. The EBCO films deposited on CeO2 50-400-Å-thick buffer layers had T ce's of 90 K or above. The high-T c EBCO films had in-plane epitaxial orientation relationships of Al2O3 [112̄0]\varparallelCeO2 [100]\varparallelEBCO[110]. The EBCO films on the thin CeO2 buffer layers had rectangular grains similar to those on MgO(001) substrates. The critical current density of the EBCO films with T ce=90 K was about 6 ×105 A/cm2 in zero field at 77.3 K. The T ce varied largely and decreased with increasing CeO2 buffer layer thickness above 500 Å. AFM observation of a 1000-Å-thick CeO2 film showed growth of bamboo-like crystal grains 1700 Å long and 300 Å wide along the direction of CeO2 [110]. The ravine depths were about 100 Å. The EBCO films on the thick CeO2 buffer layer (>500 Å) exhibited poor superconducting behavior and gave (103) or (110) diffraction peaks.
EuBa 2 Cu 3 O 7−δ (EBCO) thin films with different growth orientations were prepared on Al 2 O 3 (1102) substrates with CeO 2 buffer layers by dc magnetron sputtering. The EBCO thin films were deposited immediately after off-axis rf magnetron sputtering of CeO 2 (001) films. The effects of substrate temperature and oxygen concent on epitaxial orientation of EBCO thin films were examined. With the increase in oxygen concentration, the surface roughness of an EBCO thin film increased. An appropriate oxygen concentration existed. It was clarified that the orientation of an EBCO thin film depended on CeO 2 film thickness. The (100)-and (110)-oriented EBCO thin films were obtained on CeO 2 buffer layers 30-90 Å thick and more than 700 Å thick, respectively. The (100)-and (110)-oriented EBCO films had in-plane epitaxial orientation relationships of Al 2 O 3 [1120] CeO 2 [100] EBCO[013] and Al 2 O 3 [1120] CeO 2 [100] EBCO[110], respectively. The (100)-oriented EBCO films deposited on 50-Å-thick CeO 2 (001) buffer layers had T ce 's of 72.0 K, and (110)-oriented EBCO films deposited on 750-Å-thick CeO 2 (001) buffer layers had T ce 's of 70.0 K. The T ce decreased with increasing CeO 2 buffer layer thickness above 800 Å. The a-axis-oriented EBCO thin films exhibited T ce 's of about 85.4 K on the 50-Å-thick CeO 2 buffer layers prepared by a self-template method.KEYWORDS: EuBa 2 Cu 3 O 7−δ thin film, CeO 2 buffer layer, sapphire substrate, magnetron sputtering, self-template method 5857
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