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在BiO--(Sr+Ca)O--CuO相图上的Bi₂Sr₂CaCu₂O_8+δ(Bi--2212) 相附近选择不同成分, 用分子束外延法制备成薄膜, 利用XRD, EDS,SEM和AFM研究了成分、衬底温度和臭氧分压对Bi--2212相薄膜成相的影响, 分析了生长速率和错配度对Bi--2212相薄膜质量的影响. 结果表明, Bi--2212相薄膜单相生成的成分范围 (原子分数) 分别为Bi 26.3%---32.4%, (Sr+Ca)37.4%---46.5%, Cu 24.8%---32.6%; 当衬底温度为720℃且臭氧分压为1.3×10^-3 Pa时, 在MgO(100) 衬底上生长出质量较高的c轴外延Bi--2212相薄膜; 通过调整生长速率、更换衬底和插入不同厚度的Bi₂Sr₂CuO_6+δ过渡层的方法, 可以改善Bi--2212相薄膜的结晶质量、表面形貌和导电特性.

In the research field of Bi--based superconductor, the wire, tape and single crystal have been extensively used, but the application of Bi--based thin films is limited due to the appearances of intergrowth and impurity phases. Therefore, various fabrication methods have been adopted to improve the quality of Bi--based thin films. In these methods, molecular beam epitaxy (MBE) is recognized as one of the most adept thin film growth techniques for obtaining single phase, good surface morphology and low concentration of defects. In order to find the optimal preparation conditions, XRD, EDS, SEM, AFM and BiO--(Sr+Ca)O--CuO phase diagram were used in studying the effects of composition, substrate temperature and ozone partial pressure on the formation of Bi₂Sr₂CaCu₂O_8+δ(Bi--2212) thin films in the present work. At the same time, the influences of growth rate, mismatch and buffer layer on the quality of thin films have been analyzed in details. Results indicate that the component range (atomic fraction) forming Bi--2212 single phase is 26.3%---32.4% for Bi--composition, 37.4%---46.5% for (Sr+Ca)--composition and 24.8%---32.6% for Cu--composition. Furthermore, the c--axis epitaxial Bi--2212 thin film with high quality can be obtained on MgO(100) substrate when the substrate temperature and ozone partial pressure are 720℃ and 1.3×10^-3 Pa, respectively. The crystalline quality, surface morphology and electrical property of Bi--2212 thin films have been improved by the alteration of substrates, the adjustment of growth rates and the insertion of Bi₂Sr₂CuO_6+δ buffer layers with different thickness.