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Epitaxial cerium oxide buffer layers and YBa_2Cu_3O7-δ thin films for microwave device applications

机译:外延氧化铈缓冲层和YBa_2Cu_3O7-δ薄膜在微波器件中的应用

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CeO_2 films with thicknesses ranging from 8.8 to l99 nm were grown on Al_2O_3 (l102) (R-cut) substrates by off-axis rf magnetron sputtering. X-ray diffraction showed an epitaxial relationship with the CeO_2 (00l) planes parallel to the Al_2O_3 (1l02) planes for all film thicknesses. Atomic force microscopy (AFM) revealed a rough surface morphology consisting of crystallites with lateral dimensions of 10-90 nm. In the thinnest film, these crystallites were regularly shaped and uniformly distributed on the substrate, while they were rectangularly shaped and oriented mainly in two directions, orthogonal to each other, in the thicker films. The surface roughness of the films increased with increasing layer thickness. Characterization of the microstructure was done by cross-sectional transmission electron microscopy (XTEM) and showed a polycrystalline, highly oriented, columnar structure with a top layer terminated by (l l l)-facets. High-quality YBa_2Cu_3O_7-δ(YBCO) thin films were deposited directly onto the CeO_2 layers. XTEM, rather surprisingly, showed a smooth interface between the YBCO and CeO_2 layer. Postdeposition ex situ annealing was carried out on two CeO_2 films and evaluated by AFM. Upon annealing samples at 930 deg. C, a relatively smooth morphology without facets was obtained. Annealing films at 800 deg. C caused no appreciable change in surface morphology, whereas igniting a YBCO plasma during a similar anneal clearly altered the sample surface, giving facets that were rounded.
机译:通过离轴射频磁控溅射在Al_2O_3(l102)(R形)衬底上生长了厚度为8.8至199 nm的CeO_2薄膜。对于所有厚度的膜,X射线衍射显示出与平行于Al_2O_3(1102)平面的CeO_2(00l)平面的外延关系。原子力显微镜(AFM)揭示了一个由表面尺寸为10-90 nm的微晶组成的粗糙表面形态。在最薄的薄膜中,这些微晶呈规则形状并均匀分布在基板上,而在较厚的薄膜中,它们呈矩形并主要沿彼此正交的两个方向取向。膜的表面粗糙度随着层厚度的增加而增加。通过横截面透射电子显微镜(XTEM)对微结构进行表征,并显示出多晶的,高度取向的柱状结构,其顶层由(111)小平面终止。高质量YBa_2Cu_3O_7-δ(YBCO)薄膜直接沉积在CeO_2层上。出乎意料的是,XTEM在YBCO和CeO_2层之间显示出光滑的界面。在两个CeO_2薄膜上进行沉积后异位退火,并通过AFM进行评估。在930度退火样品后。 C,获得没有小面的相对光滑的形态。在800度下退火薄膜。 C不会引起表面形态的明显变化,而在相似的退火过程中点燃YBCO等离子体会明显改变样品表面,使切面变圆。

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