GROWTH MECHANISMS OF COEVAPORATED SMBA2CU3OY, THIN-FILMS

The growth mechanisms of coevaporated SmBa2Cu3Oy, (Sm123) films grown epitaxially on [100] SrTiO3 substrates were investigated using scanning probe microscopy, transmission electron microscopy, scanning electron microscopy, and x-ray diffraction. The Sm123 films were predominantly oriented with their crystallographic c axis perpendicular (c perpendicular to) to the substrate. Only small fractions of grains with their c axis parallel to the substrate (c parallel to) and some impurity phases were found. It was found that Sm123 growing with a c perpendicular to orientation displayed a frequent bending of its unit-cell thick layers, which could often be related to the presence of impurity phases. We present strong evidence that this impurity-related bending of the Sm123 lattice is responsible for the formation of screw dislocations. Furthermore, we find that the volume fraction of c parallel to to c perpendicular to material increases with increasing chamber pressure and decreasing substrate temperature, indicating that kinetic factors (i.e., reduced mobility of the adsorbed species during film growth) play an important role for the formation and growth of c parallel to grains. No evidence for a strain-driven crossover from c perpendicular to to c parallel to growth as a function of film thickness was found. It was also observed that the presence of c parallel to outgrowths depends on the amount of CuO droplets on the surface of the films. This suggests that impurity phases can play a role in the formation of c parallel to grains. Finally, many of the impurity phases observed in our films are unexpected from a thermodynamic point of view, suggesting that the kinetic barrier to their creation is low. Based on the results presented here, the smoothest and most homogeneous RBa(2)Cu(3)O(y) (R = Y or lanthanide) films are expected to grow under conditions which favor a high surface mobility during film growth.