涂层导体中,作为多层织构模板中的最上层,帽子层的表面形貌、晶粒尺寸、表面粗糙度、平整度、致密度等表面特征将直接影响其上YBa2 Cu3O7-δ超导层的形核、织构形成和外延生长,表面特征的优化成为近期涂层导体缓冲层研究的重点.采用磁控溅射方法在LaMnO3/Epi-MgO/IBAD-MgO/Y2O3/Al2O3/Hastelloy C276上动态外延生长CeO2薄膜作为涂层导体帽子层,主要研究了沉积温度对CeO2薄膜表面特征的影响.利用x射线衍射仪、扫描电子显微镜、原子力显微镜以及拉曼光谱仪等对CeO2薄膜的织构、微结构及表面形貌、表面粗糙度、平整度等表面特性进行细致表征.研究结果表明:CeO2薄膜的表面特征对沉积温度依赖性强;在沉积温度800℃左右获得了最好的织构和表面,CeO2薄膜具有最好的(00l)取向,面内半高宽为7.1°,晶粒尺寸接近YBa2 Cu3O7-δ最高形核密度对应的CeO2最佳尺寸,薄膜表面连续平整均匀,光滑致密无裂纹,其均方根粗糙度约1.4 nm;而且,在此CeO2缓冲层上用三氟乙酸—金属有机沉积方法(TFA-MOD)外延生长的YBa2Cu3O7-δ超导层具有良好的织构及致密平整的表面.
As the top layer of multi-layer textured template for coated conductors,the surface features,such as surface morphology,grain size,surface roughness,flatness and density,of the cap layer will directly affect the subsequent nucleation,texture formation and epitaxial growth of YBa2 Cu3 O7 δ superconducting layer.Recently,much attention has been paid to the optimizations of surface features for the buffer layer of coated conductors.CeO2 thin films,as cap layer for coated conductors,were epitaxially deposited on the substrate of LaMnO3/Epi-MgO/ IBAD-MgO/Y2 O3/Al2 O3/Hastelloy C276 continuously by magnetron sputtering.The texture,micro structure,surface morphology,surface roughness and flatness of CeO2 thin films were characterized by X-ray diffraction (XRD),scanning electron microscope (SEM),atomic force microscope (AFM) and Raman spectrometer.The results show that:the surface characteristics of CeO2 thin film are strongly dependent on the deposition temperature,and at an optimized deposition temperature of about 800℃,the prepared CeO2 film achieves perfect (00l) orientation and the best degree of in-plane alignment with (111) phi-scan full width at half maximum around 7.1°,accompanied by a nearly optimum grain size for the highest nucleation density of YBa2 Cu3 O7-a In addition,a flat,uniform,smooth and dense surface with the root mean square (RMS) roughness of about 1.4nm is obtained.Moreover,the YBa2 Cu3 O7-δ superconducting layer epitaxially grown on this CeO2 film by trifluoroacetate metal organic deposition (TFA-MOD) exhibits a good biaxial texture and a dense,uniform surface.
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