TEM CHARACTERIZATION OF HIGH T(C) SUPERCONDUCTIVE MULTILAYERED THIN-FILMS

Superconductive multilayered thin films have been deposited by excimer laser ablation and d.c. magnetron sputtering. The laser deposited films were grown on (100) SrTiO3 substrates and consisted of alternating layers of La2-xSrxCuO4 (LSCO) and YBa2Cu3O7-delta (YBCO) while the sputtered films, deposited on (100) MgO substrates, consist of a 3 nm MgO layer sandwiched in 100 nm YBCO layers. Cross-sectional transmission electron microscopy (TEM) specimen have been prepared so as to investigate the different interfaces and the local structure of the films. The results show that the laser deposited films are epitaxially grown with the c-axis normal to the surface. The interfaces are rather sharp but some roughness of the YBCO over LSCO interface, possibly related to the presence of shear defects in the LSCO layers is evidenced. The observations of the sputtered films reveal the presence of some a-axis oriented YBCO grains and th partial crystallization of the amorphous deposited MgO layer. Some a-axis oriented grains are also observed in the lase deposited films but only in the upper layers. The different types of structural defects as well as the different interfaces, characterized by high resolution electron micrsocopy (HREM), will be reported.