DIFFERENCES IN THE NUCLEATION RATE OF YBA2CU3O7-DELTA ON PATTERNED (001)LAALO3 SUBSTRATES

The microstructures of laser deposited c-axis oriented YBa2Cu3O7-delta (YBCO) thin films have been characterised by scanning and transmissio n electron microscopy. Grain boundaries were produced using substrates with wavy step edge profiles on cubic (001) LaAlO3. The wavy step edg e profiles simulated a meandering profile which may arise due to uneve n etching of mask and substrate during conventional pattering procedur es. The nucleation rate of the a-axis oriented film in the step region varied along the wave profile. The results indicate that a well defin ed grain boundary geometry and behaviour require a straight step profi le on a sub micron scale. In addition, the YBCO nucleation in the step region can be suppressed by choosing a step direction which deviates from the [100](LAO) and [010](LAO).