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利用高分辨透射电子显微镜对高T_c YBa_2Cu_3O_7/PrBa_2Cu_3O_7(以下简称为YBCO/PrBCO)超晶格的微结构进行了系统的观察分析,高分辨电子显微象(HREM)表明YBCO/PrBCO超晶格层与层之间具有清晰的衬度,没有界面互扩散,通过HREM象观察,发现衬底表面的原子台阶和缺陷使薄膜最初1—2个晶胞层中出现层错等缺陷,但这些缺陷并没有向薄膜内部扩展,当薄膜厚度超过几个晶胞层后,其结构趋于完整。另外,在HREM照片上还可看出YBCO/PrBCO超晶格的调制周期存在波动,波动范围相当于一个晶胞层厚度,实验结果表明,利用YBCO/PrBCO超晶格研究CuO_2面的二维超导电性时,临界温度T_c和临界电流密度J_c的变化不仅与二维CuO_2面的失耦程度有关,还会受到各种晶格缺陷的影响,对YBCO/PrBCO超晶格和超薄YBCO膜的输运特性进行理论解释时,必须考虑衬底和晶格缺陷造成的影响。
The microstructure of the superlattice with high T_c YBa_2Cu_3O_7 / PrBa_2Cu_3O_7 (hereinafter referred to as YBCO / PrBCO) was systematically observed by high resolution transmission electron microscopy. High resolution electron microscopy (HREM) showed that the YBCO / PrBCO superlattice layer There is a clear contrast between the layers and no interdiffusion of the interface. The observation of HREM shows that atomic steps and defects on the surface of the substrate lead to faults such as stacking faults in the first 1-2 cell layers. However, No internal expansion to the film, when the film thickness of more than a few cell layer, its structure tends to be complete. In addition, the modulation period of YBCO / PrBCO superlattices also shows fluctuation in the HREM photograph, and the fluctuation range corresponds to a unit cell layer thickness. The experimental results show that the YBCO / PrBCO superlattices have two- The changes of critical temperature T_c and critical current density J_c are not only related to the degree of decoupling of two-dimensional CuO_2 surface but also influenced by various lattice defects. For the YBCO / PrBCO superlattices and ultrathin YBCO films The theoretical explanation of transport properties must consider the effects of substrate and lattice defects.