本文采用原子力显微镜(AFM)和XRD研究了生长在蓝宝石(11-02)基片上的CeO_2缓冲层在不同的退火温度和退火时间下表面形貌和相结构的变化,以及对Tl-2212薄膜超导特性的影响.AFM和XRD研究表明,CeO_2薄膜在流动氧环境中退火,表面形貌发生显著的变化;CeO_2薄膜在最佳条件下退火后,可获得原子级光滑表面,结晶质量明显提高.实验结果表明,缓冲层的结晶质量和表面粗糙度与Tl-2212薄膜的超导特性密切相关.在经过最佳条件退火后的CeO_2缓冲层上制备了厚度为500 nm无裂纹的Tl-2212超导薄膜,其临界转变温度(T_c)达到107 K,液氮温度下临界电流密度(J_c)为3.9 MA/cm~2(77 K,0 T),微波表面电阻(R_s)约为281 μΩ(77 K,10 GHz).
The effect of high temperature treatment on the surface morphology,the phase structure of CeO_2 buffer layers grown on sapphire substrates was studied, and also the growth of CeO_2 on Tl-2212 films. The measurements of AFM and XRD showed that annealing of the CeO_2 films produced drastic change in surface morphology and crystalline quality. Annealing treatment at 950 ℃ for 1 h resulted in atomically flat CeO_2 surface and significant improvement of the crystalline quality of CeO_2 films. Experimental results revealed that the superconductivity of Tl-2212 films is closely interconnected with the crystal quality and morphology of buffer layers. The crack-free films with the thickness of 500 nm grown on such buffer layers had a high transition temperature (T_c =107 K), a high critical current density (J_c=3.9 MA/cm~2 at 77 K and zero applied magnetic field) and a low surface resistance (R_s=281 μΩ at 10 GHz and 77 K).
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