In-situ epitaxial growth study of Bi2(Sr,Ca)3Cu2Ox films by ion beam sputtering on cleaved MgO substrates

In-situ epitaxial growth of Bi₂(Sr_0.6Ca_0.4)₃Cu₂ O_x films on cleaved MgO substrates was studied by ion beam sputtering. The crystallographic structures were analyzed by using in-situ reflection high-energy electron diffraction, a four-circle X-ray diffractometer, and a scanning electron microscope. While the epitaxial films on polished MgO substrates commonly showed the fourfold symmetry, the epitaxial films having the twofold symmetry were successfully grown on the cleaved MgO substrates, and the films contained two types of misoriented domains. The epitaxial relationship between these domains and then cleaved MgO substrates was such that the b-axis of each domain deviated approximately ±13° from [010]MgO where the cleavage steps ran along [100]MgO. The early stage of film growth corresponded to an anisotropic growth mode, and the step edges tended to be the nucleation site. The step edges seemed to play an important role in determining the twofold epitaxial relationship, where the incommensurate modulation tended to align its direction so as to avoid the step edges