Analysis of the surface termination of Nd_1+xBa_2−xCu₃O_y thin films

High quality, very flat Nd_1+xBa_2−xCu₃O_y films have been grown by sputtering and analyzed by low energy electron diffraction, scanning tunneling microscopy (STM) and grazing incidence x-ray diffraction (GIXD) employing synchrotron radiation, in order to investigate the surface structure and morphology. The refinement of the GIXD data has been performed on the basis of structural models sensitive to the nature of the terminating layer. The interpretation of the results provides a picture of the surface structure that is in full agreement with STM results. The surface is composed by two terraces with different termination, one of which is an ordered and complete Cu(1)-O layer and the other an incomplete BaO layer that partially covers a disordered Cu(1)-O layer. Atomic vacancies and steps bounding terraces with a height of about 0.4 nm, are present on the surface.