INFLUENCE OF THE GROWTH-MECHANISM ON THE GRAIN-BOUNDARY STRUCTURE IN YBA2CU3O7 THIN-FILM BICRYSTALS

The growth control of thin YBa2Cu3O7 (YBCO) film bicrystals determines the quality of Josephson junctions and weak links. Previous TEM exper iments on various thin him bicrystals showed grain boundary oscillatio ns that were not clearly explained. We combined AFM, SEM, conventional TEM and HRTEM in order to perform a complete characterization of both substrate and YBa2Cu3O7 thin film bicrystals. Our results clearly sho w that the grain boundary oscillations are due to the YBCO growth mech anisms leading to a conflictual crystallographic situation at the grai n boundary. The resulting crystallographic structure of the grain boun dary may affect the interpretation of several recant experiments purpo rting to determine the nature of the HTC superconductivity.