Surface and film/substrate interface roughness of YBa2Cu3O7 films deposited on MgO(100) and SrTiO3(100) by rapid sequential pulse laser deposition has been determined from X-ray reflectivity data. The film on MgO had the average roughness of 26.2 Å at the film/substrate interface and roughness of one unit cell order at the surface. On the other hand, the film on SrTiO3 had approximately the average roughness of 40 Å at both the surface and film/substrate interface. Obviously, the surface of the film on MgO is smoother than that on STO. The rough surface of the film on SrTiO3 is considered to be partly due to the growth of the film along the steps of the substrate, while the film on MgO grows without the influence of the steps on the substrate.
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