Growth mode study of ultrathin HTSC YBCO films on YBaCuNbO buffer

Abstract

It is known that the critical temperature T c of ultrathin YBCO films is reduced to values far less than 77 K. To improve the superconducting properties of ultrathin YBCO films, we developed a new buffer layer which allowed an increase in the critical temperature of five-unit-cell-thick YBCO films to values above 77 K. Using atomic force microscopy (AFM) to study the growth modes of ultrathin YBCO films deposited on a SrTiO 3 substrate and on a YBaCuNbO buffer layer, we found that ultrathin YBCO films deposited on a SrTiO 3 substrate are formed due to 2D nucleation. The growth of ultrathin YBCO films deposited on YBaCuNbO buffer is governed by the step-flow mode. As a consequence of the different growth modes, the ultrathin films deposited on a SrTiO 3 substrate and a YBaCuNbO buffer layer have different surface morphologies and superconductive properties. We believe that the step-flow mode makes it possible to improve the ultrathin YBCO film structure and increase the critical temperature.